FR2648219A1 - Receptacle and method of manufacturing such a receptacle, for incineration in a microwave oven - Google Patents

Abstract

The invention comprises a receptacle 75 which is resistant to heat, comprises walls, is light and porous, transmits microwaves, and is constituted by quartz microfibres which are held in the desired shape of the receptacle 75 with walls, as well as a method of manufacturing such a receptacle.

Description

CONTAINER AND METHOD FOR MANUFACTURING SUCH A CONTAINER,
FOR INCINERATION IN A MICROWAVE OVEN
The present invention relates to microwave incineration and analysis apparatuses, the components of such apparatuses and their methods of operation. More particularly, the present invention relates to apparatuses of this type which include a radiation source. b microwave, a chamber with walls towards which the microwave radiation is directed, a chamber which maintains this radiation inside, and an incineration oven located in the room, the walls of this oven being resistant to heat, low thermal conductivity and transmitting b microwave radiation. The oven also includes microwave absorbent material which is capable of being heated to an incineration temperature, temperature sensing means, used to adjust the temperature in the oven cavity, gas passages passing through the oven cavity and walled chamber, and a removable door in the front wall of the oven.

Although other temperature resistant supports can be used in the oven for incineration samples, it is preferred that this support is a container according to the invention, which is heat resistant, light, porous and transmits the microwave, and among these containers, those in quartz microfibers are strongly preferred.

The invention also relates to various components of the apparatus described and the uses of the apparatus in incineration and analysis procedures.

In patent U5-A-4,565,669, there are described apparatuses and methods for bruising a material to be incinerated, by heating an incineration means, such as silicon carbide, using micro radiation. waves and by incineration, by means of the heat generated in the incineration means, a sample to be analyzed which can rest on a support made of fused quartz fibers. In such devices, the silicon carbide rests on a refractory material and the sample to be incinerated is placed on a relatively thin quartz pellet, which is in contact with the silicon carbide. Such a device is placed inside a computer-controlled analysis device, such as the microwave drying / digestion system MDS-81, manufactured by
Corporation, which is described in their bulletin titled CEM Corporation
Microwave Drying / Digestion System MDS-81 (laboratory microwave system), published in 1981.

 While the apparatus and the microwave incineration process of the patent mentioned are useful for accelerating incineration operations and the analytical determinations which depend thereon, the present invention constitutes a further significant improvement. In the apparatuses and methods of the present invention, the sample to be incinerated is found in an oven made of microwave-transmitting material (preferably essentially or completely transparent to microwaves), which is a ceramic foam with open cells, preferably a fused quartz foam with open cells. Such an oven material and the structure of the oven, help maintain the incineration temperature uniform, throughout the oven cavity and, moreover; this temperature is maintained at a desired level by a thermocouple control system, the probe of which is located in the oven cavity.

More uniform heating of the sample to be incinerated makes the incineration process more repetitive and more precise. In addition, possible losses of sample materials to the air leaving the microwave apparatus are minimized and it is generally found to be unnecessary to use a cover sheet of clipped quartz fiber pellets to hold in place ashes and to prevent them from being entrained in the exhaust air. Thus, the tare weight may be lower when using the invention and therefore the weighings may be more precise. Various other advantages accompany the present invention, including the easy use of the appliance, the possibility of removing and replacing the oven door directly, improved complete combustion of the solvents in the sample to be incinerated, solvents which all accompany magnesium acetate incineration aids, precise automatic control of incineration conditions, and faster incinerations.

 Although various incineration devices for analytical purposes have been described in detail in the technical documentation, most of them use muffle furnaces to generate heat and they use crucibles to retain the samples to be incinerated . To the knowledge of the applicants of the present invention, no other apparatus and method of microwave incineration has been described in the literature before the filing of their patent US-A-4,565,669.

US-A-4,307,277 described a microwave heating furnace for heating materials at elevated temperatures, such as in the production of sintered ceramic. However, the heating ovens of this patent are not thermostatically controlled, do not use ceramic material b applicants 'open cells for the walls and the oven door, and differ from the applicants' apparatus by various other structural features. important. The various modifications incorporated into the present invention are improvements over the structures and methods of US Patents 4,307,277 and 4,565,669 and help to provide improved analysis results and faster incinerations that can be achieved when the the present invention is used.

 Discs made of quartz fibers have been described, before the present invention, as supports for samples to be incinerated by heat generated by directing microwave energy onto materials absorbing these microwaves. In US-A-4,565,669, a quartz fiber support pellet and a cover of the material noeme, are used to confine an analytical sample to be incinerated for analysis during the incineration of this sample by the heat generated by directing microwaves radiation on silicon carbide absorbing microwaves below such a support pad. The patent US-A-4,565,669 represents the closest neighbor art known to applicants with regard to the containers invented to contain the material to be incinerated, but it does not describe or suggest the invented containers and does not render them obvious (and the process of incineration of the patent does not entail the perfectlonnee incineration which can be obtained with the invented containers).

 According to the present invention, an apparatus intended to incinerate samples which can be incinerated comprises a chamber with walls for maintaining the microwaves, a source of radiation from the microwave intended to radiate on the contents of said chamber and an incineration oven. located inside the chamber, comprising an oven wall made of heat resistant material, which surrounds an internal oven cavity and comprises an opening intended to insert or remove a sample to be incinerated, a door made of heat resistant material heat to close and open the opening of said oven wall, a microwave absorbing material which can be heated by microwave radiation at an incineration temperature and a passage through the oven, intended to introduce gas into the oven cavity and to extract gas from said cavity, said heat resistant material from the oven wall and the oven door being coo low thermal ductivity and being essentially transparent to microwave radiation, the microwave absorbing oven material having one of its surfaces exposed to the cavity of the oven, and said chamber wall, intended to maintain microwaves, having inlet and outlet openings for the passage of gas entering and leaving the chamber around the furnace. In preferred embodiments of the present invention, a thermocouple or other suitable temperature sensing means is used to control the temperature of the oven cavity; the air passing in an adjustable way through the oven and through the chamber of walls maintaining the micro-odas, one uses a door transmitting microwaves peddling a handle or a gripping means to close an opening by pa passage of door in the oven; the material used to absorb the microwaves is silicon carbide and 11 is present in the form of strips and / or plates in the interior of the oven wall; the furnace structure material is an open cell quartz material, transparent to microwaves, and the container which is used to keep the sample to be incinerated is a walled container, porous, light, temperature resistant, in quartz microfibers, essentially transparent to microwaves, which allows gases to pass through it but prevents the passage of ash.

The invention further comprises components of the apparatus described, such as the oven, comprising a removable and adjustable door, a method for incinerating and analyzing materials to be incinerated and a container for the material to be incinerated, this material possibly being incinerated by the heat generated by microwave absorbing elements subjected to microwave radiation in an incineration oven, this container being a wall container, temperature resistant, which is light, porous and transmits microwaves which consists of micro quartz fibers which are kept in the form of a wall container. The invention also comprises a method for manufacturing a porous, light sheet by giving it a geometry of such a container, made of quartz microfibers, transmitting microwaves, and by heating, preferably after humidification and drying, this sheet, which presents this geometry to thus constitute a container which retains
Its shape, being resistant to incineration temperatures and other incineration conditions.

 The invented containers are particularly useful in connection with microwave incineration devices such as that described in the present patent application, which is also described in application US-SN-07 / 2g8 554, one of the priority requests of the present request, the inventors of which are MM. Collins and Hargett, However, the invented vessels are also usable in other incineration applications, for example those carried out in conventional muffle furnaces, and in other heating operations, including fusions and incinerations dry (in which the ashes are produced for later analyzes, such as heavy metal analyzes).

The invention will be immediately understood by referring to the present description, which includes the accompanying drawings, in which:
FIG. 1 is a front perspective view of the microwave incineration apparatus of the present invention, the chamber door being open, the oven door being removed and no samples a. incinerate not found in this oven;
FIG. 2 is a front perspective view on a larger scale similar to that of FIG. 1, the oven door being in place in an almost closed position, arrows indicating the flow of air towards the interior of the chamber, towards the oven, out of the oven and out of the room;
FIG. 3 is a disassembled view on a larger scale of the entire incineration oven, comprising a base support and a protective screen above this support;
FIG. 4 is a front perspective view, corresponding to that of FIG. 1, but representing two containers of material to be incinerated, placed in the oven;
the FIC. 5 is a rear perspective view of the exterior of the microwave incineration apparatus, on which is mounted a temperature control unit;
FIG. 6 is a schematic diagram of the electrical circuits of various elements of the microwave incineration apparatus;
FIG. 7 is a front perspective view of a microwave incineration apparatus, the door of the chamber being open and the oven door being removed to represent, placed in the oven, two of the invented containers; it is similar to FIG. 4 but identifies additional features of the invention;
FIG. 8 is a top view, from the front, in perspective of a container with walls for incineration according to the present invention; and
FIG. 9 is a perspective front view from above of an incineration container according to the present invention, the side wall of which is being formed around a mandrel.

In FIG. 1, the incineration apparatus 11 comprises a chamber b wall maintaining the microwaves, like that of CEM Corporation KDS-81
Microwave Dryizg / Digestion Systev, which is defined by a bottom, two sides, a top, a rear part, a front part and a door, chamber wall which is designated by the reference 13, and which is shown applied to a wall side of the room. The door 15 is shown in the open position so that one can see the incineration oven 17. This incineration oven will be described in more detail later in the description of FIG. 3. The temperature adjustment device 19 is connected to a thermocouple probe 21, located in the oven cavity by means of an electrical connection, not shown. The flow of air into the interior of the chamber and the internal cavity and out of the cavity and the chamber will be described with reference to FIG. 2, as will be the control and display panels of the microwave system part 1 of the apparatus, panels which are similar to those of the apparatus CEX Corporation MDS-81, mentioned above.

 In FIG. 2, a stream of air (or gas) passing through the incineration apparatus is represented by the arrows in broken lines. Air enters the chamber with the walls supporting the microwaves, designated by the reference numeral 23, through the grid openings 25 and 27 in the side walls of the chambers 29 and 31, openings which are located near the bottom of the chambers, and it goes up and around the oven 17, cooling the outside thereof, then exits through the opening or suction duct 33 from which it is discharged out of the device through a exhaust duct, as shown in FIG. 5, preferably to a fume hood or in another acceptable manner. In FIG. 2, the door 35 of the oven, which is substantially trapezoidal in horizontal transverse section, comprising parts of grip or of gripping by the fingers, cut in the base of the trapezoid (the front of the door), is in place in the wall of the oven, but the door opening is not completely closed, which allows the passage of air towards the interior of the oven cavity (not shown in FIG. 2) according to arrows 37 and 39. Although the arrows indicate the air flow below the door, air also enters the oven cavity through the side gaps between the door and the oven wall. Likewise, air can leave the oven cavity b through the top thereof, as shown by arrows 41 and 43, and the upper parts of the side openings. The arrow 45 represents the passage of air and combustion products out of the oven cavity b through the vertical opening 47, between the thermocouple probe 21 and the wall of said opening in the upper part of the oven 17. The gases evacuated from the oven cavity through the exhaust duct 33 to an appropriate hood or other means of evacuation. In this way, passages are created for air or for other gases passing through the oven, the chamber and the oven cavity. It should be mentioned that the air inlet openings 25 and 27 and the opening of the exhaust duct 33 are shielded by a shielding material (which is not specifically shown), to pocket only microwave radiation. does not escape out of the room, maintaining the microwaves.

The walls and door of the chamber are made of fetal or metallic alloy, such as aluminum or stainless steel, and they can be coated with a radiation-transmitting polymer, such as polytetrafluoroethylene. Alternatively, but this is not as desirable, the door may be of coated glass and shielded to prevent radiation from escaping.

 The temperature control device 19 includes three control keys and a display. The keys are marked S, increase (that is to say increase) and decrease (that is to say decrease), (which is not indicated in FIG. 2), and their use will be explained later in conjunction with a description of how the adjuster is programmed. The "microwave system" part of the device includes controls, like those of the CE MDS-81 laboratory microwave system. These devices are an on-off switch 49, and control panels 51 and 53. The panel 51 includes the Program, Reset (ie reset t) buttons, Enter (ie introduction), Stop (i.e. stop) and Start (i.e. start) and panel 53 has numbers 1, 2, 3, X, 5, 6, 7, 8, 9 and O (none of which is specifically represented). The display 55 is of the alphanumeric type.

 The incineration oven 17, shown in FIG. 3, includes the upper and lower sections in one piece, which can be combined or separate. The upper part 57 is made of a material resistant to temperature and having microwave transmission properties; it is also of low thermal conductivity, preferably made of molten quartz foam, with open cells. A vertical orifice or hole 58 allows the passage t through this upper part of a thermocouple probe and of a connection (neither one nor the other are shown in this view). The incineration furnace 17 also includes a single, separable lower portion 59, made of the same temperature-resistant material, which contains a cavity which, with a corresponding cavity in the upper furnace portion, forms the cavity of the oven. The lower part 59 comprises several slots or grooves 61 in its bottom and other slots or grooves, such as those shown at 63 and 65. The grooves 61 are intended to install the bottom heating elements 62 and the grooves 63 and 65 are intended to place the heating elements 64 and 66, respectively. Similar grooves, which are not visible in FIG. 3, are intended to set up the front heating elements 67 and the rear heating elements 68. The ceiling heating elements (not shown) can also be arranged in the upper part 57 of the oven, in slots or grooves or channels or other suitable holding means provided therein. The various heating elements are made of a microwave absorbing material, which is capable of being heated to an incineration temperature by microwave radiation. A clearly preferred material of this type is silicon carbide and the heating elements are preferably separated, their surfaces flush with the interior walls of the oven cavity. The oven door 35, which is shown to be of horizontal trapezoSdale cross section (but which may have another suitable cross section) corresponds in shape to a corresponding wall opening, in the front of the upper part of the oven and, when 'it is in place, the interior of this door and the interiors of the upper and lower wall parts define the oven cavity.

The door comprises in its front face a pair of grooves 69 which function as part of a handle or gripping means which makes it possible to remove the door, to close it or to adjust its position easily by hand. The oven is supported by a refractory block 71, which is located under a small part of the surface of the bottom of the oven. Such a support allows the circulation of air or other gases under a large part of the bottom of the furnace, which facilitates the cooling thereof. Under the refractory support is shown a separator, for example a fabric or a screen, which may be made of temperature-resistant plastic, metal or another suitable material. The function of this fabric or screen is to prevent the refractory support, which often has rough surfaces, from forming scratches on the finish of the interior of the chamber.

 As in FIG. 4 is substantially the same as FIG. 1, except for the presence of a pair of containers of material to be incinerated (or ashes), in the oven cavity of FIG. 4, only this aspect of FIG will be described here. 4. In FIG. 4, the incineration oven 17 is made up of separable upper and lower parts 57 and 59, respectively, as well as heating elements represented in FIG. 3, among which the rear heating elements 69 are visible t FIG. 4, and these parts define the incineration cavity when the door 35 is in place. In such a cavity are placed two porous containers 75, t walls, made of a material made of quartz microfiber sheets. The containers contain suitable charges of material 77 for incineration (or they may contain the resulting ash). The details of the cremation procedure will be indicated later in this description.

 In FIG. 5, the incineration device It is shown equipped with the temperature adjustment device 19, a thermocouple (in the oven cavity) being connected to the adjustment device The reference numeral 79 designates the current supply cable from the incineration apparatus and shutters 81 and 83 are intended to allow the flow of air through an air envelope surrounding the chamber, to help cool the outside of this chamber. Between the outer wall 85 and the chamber is placed a magnetron, from which microwave radiation is directed towards the interior of the chamber, intended to maintain the radiation, the walls of which are made of material reflecting microwaves, such as stainless steel or other suitable metal or alloy, which may be coated with a protective polymeric paint or coating. The magnetron is a standard part in microwave appliances of this type and is hidden inside the walls of the latter. Therefore, it is not shown in the present drawing. There is also no cooling fan for the magnetron, although there is such a fan in the apparatus. The reference numeral 87 designates an opening in the apparatus, intended to evacuate the air which is blown through the magnetron to cool it. A fan (not shown) is arranged inside the appliance to exhaust air and combustion gases from the oven and to create a flow of air through the chamber and through the oven. fan is designated by the reference numeral 89 and the corresponding exhaust is designated by the reference numeral 91. The also relid (s) to a thernocouple (not shown in FIG. 5), which is preferably located in the upper central part of the oven cavity. Such a connector enters the incineration apparatus 11 at 110.

 In FIG. 6, the relationships between the operator keyboard (and the alphanumeric display), the microwave processor, the temperature control device, the thermocouple and the magnetron power control are shown. The operator keyboard controls the amount of power used and the heating time, which are displayed in the alphanumeric display after being entered using the keyboard.

The temperature control device regulates the incineration temperature and the admissible temperature variation (often {2 C or @ 3 C) compared to that which is introduced. The thermocouple 114 brings the temperature of the oven cavity to the adjustment device and the device implements the microwave power control to deactivate the magnetron when the temperature is above the set point and to reactivate the magnetron when the temperature falls below this set point. More precise details concerning the operation of the operator's keyboard of the apparatus and the temperature adjustment device are given later.

 In FIG. 7, a microwave incineration device 111 comprises upper, lower, lateral and rear walls, all designated by the reference numeral 113 applied to a side wall, and a door 115 which defines a chamber 118 intended to maintain the iicro -waves.

Inside the chamber is an oven 117 which includes upper and lower parts 119 and 121 and an oven door 123.

These furnace parts are made of quartz with open cells, transmitting microwaves, with low thermal conductivity and which resists heat and can be used at very high temperatures, without deterioration. One such material is ECCOFOAM # Q, preferably ECCOFOAM QG, which is described in a bulletin called
ECCOFOAM Plastic and Ceramic Foams, from Emerson and Cumming, Canton, Messachusetts, from March 1980. Inside the oven is an oven cavity 125 and a microwave-absorbing material 127 located in grooves or slots (not shown) in the upper and lower parts 119 and 121, their surfaces flush with the internal surfaces which define the oven cavity. In the oven cavity are represented two containers of the present invention, which are designated by the reference numeral 129. FIG. 7 also shows inlets 131 allowing air to enter the chamber, part of this air passing through the oven cavity, but most of it bypassing the chamber 118 and serving to cool its walls. Get air out of chamber b through outlet 133. A thermocouple 115 is located in the oven cavity and it is in communication by means of a connector (not shown) with a temperature control device 137. Both the unit the main microwave generation of the apparatus as the temperature control device 137, include controls and visual displays, which are immediately visible and therefore are not designated by specific reference numerals.

 In FIG. 8, one of the containers of the present invention has been shown. This container is of a single-piece structure, the bottom 139 and the side wall 141 being made of the same sheet of nonwoven porous quartz microfibers. The container shown was made from a square portion of fibrous material and includes weld lines, like the one shown in 143.

 In FIG. 9 shows a step of manufacturing the container 129. As illustrated, the nonwoven sheet of microfibrous quartz is formed from the base of a cylindrical mandrel 145 and the excess material has been cut flush along the upper edge. 147. A 149 quartz monofilament or an elastic band or similar holding means, holds b porous microfibrous quartz sheet tightly around the mandrel during the forming operation, but it is then removed, according to normal procedures Manufacturing. After shaping the sheet, it is wet, shaped properly around the mandrel, then cut to the brim, removed from the mandrel and air dried, after which it is heated (cooked) to produce the container retaining its shape according to the invention. Although air drying is preferred, this can sometimes be omitted.

 Although the invented container is shown as a short cylinder, other container shapes can also be adopted, using mandrels of corresponding shapes. Thus, it is possible to produce containers with a rectangular or square borizontal cross section. Other forms of containers can also be produced, but it is preferred that these containers are relatively flat, generally presenting. a main horizontal aspect ratio less than t 1: 1 and preferably not more than 1: 2. Ratios such as the height / diameter ratio, can be in the range of 1:10 to 1: 2, preferably in the range of 1: 5 to 2: 5, for example 1: 5 or 3:10. While various dimensions of containers can be used, when these containers are flat and cylindrical, it is normally preferred that they are of a diameter of 2 d 10 cm, preferably 4 to 6 cm, and a height of 0, 5 t 4 cm, preferably 1 to 2 cm, and flat cylindrical containers are preferred.

 The apparatus for applying sufficient microwave energy for a sample of material to be incinerated must be any suitable microwave apparatus which can direct microwave radiation onto the heating elements located in the oven. As previously indicated, a KDS 81 system from CEM Corporation can be used, but similar systems can also be used, in combination with an indoor oven, a temperature control device and the container for the material to be incinerated. Preferably, the system incorporates a microprocessor, a digital computer and controls for controlling the application of microwave radiation to the elements to be heated. Thus, microwave radiation can be applied for desired periods or at various levels of radiation if desired, but the level of radiation is often constant at the nominal power determined for the device.

 The key elements of the microwave system used are an adequate flow of gas (air) which passes through it to cool the oven, and the absence of microwave load in the system except that of the oven.

In addition, the oven must be such that it allows the evacuation of combustion gases and the entry of fresh gas (air or suitable oxidant).

 It should be noted that in some of the devices mentioned, the microwave power range can range from I to 100% of the total power (500 to 1500 watts in some cases), in increments of 1%. Obviously, lower or higher powers can also be used, for example up to several kilowatts, for example 0.3 to 5 or 0.4 to 2 kw, but a power of 0.9 or 1 kv is usually sufficient. In the United States, the microwave radiation frequency used is normally 2.45 gigahertz, and it is usually 0.896 gigahertz in Great Britain. Such a frequency may be in the range of 0.3 to 50 gigahertz (or more) and is preferably in the range of 0.8 to 3 giganertz. The readings that can be taken in the described devices can peeeéoer up to 10 characters in their alphanumeric displays, and include in some cases, audible tones to inform the operator. The commands, available to the operator, cooperate with a keyboard of up to 20 keys for the inputs.

 One of the advantages of the present invention is that the microwave apparatus described can be used for incineration or for other operations. which such an apparatus may have been designed primarily, such as humidity determinations, volatile matter analyzes and to promote chemical reactions.

Usually, when the devices are used for the incineration of materials, they are used in their maximum power supply condition, which is often around 560 d 1000 watts. The incineration times can be adjusted as desired and the incineration times are generally from 2 to 20 minutes or from 5 to 15 minutes, but the oven can be preheated for periods varying from 5 minutes to 2 hours, usually from 20 to 60 minutes.

The main structural material of the oven, which is inserted into the microwave system described above and which is a part of the present apparatus, is a material which is heat resistant, of low thermal conductivity and which transmits microwave radiation. It has been found that such materials include ceramics, glass and quartz foams, quartz foams being much preferred because they allow operation at higher temperatures, are of low thermal conductivity and transmit radiation exceptionally well microwaves because they are essentially or completely transparent to such radiation. Thus, it is considered that more than 99% of the microwave radiation passes through the walls of the ovens of the present invention unless they are absorbed by the heating means absorbing the microwaves in the oven. For quartz foam, we prefer those with open cells, and molten quartz is particularly preferable. Such materials are available from Eaerson and Cuming, from
Canton, Massachusetts, and they are marketed under the registered trademark ECCOFOAM Q. Two forms of ECCOFOAM # are sold, the ECCOFOAM QG and the ECCOFOAM QR. The latter is heavier and more robust, but for the purposes of the present invention, it is preferred to use the former. The characteristics of these open cell molten quartz foams are described in Technical Bulletin 6-2-12A, published by this company. It is considered that molten foam materials of the type mentioned are useful for making the present ovens, particularly when they have a density in the range 0.3. at 0.8 g / cm3, have a rupture modulus in the range of 10 to 50 kg / cm2 and a thermal conductivity in the range of 96 to 288 kcal / m2 / h- C / m. Such materials should also be usable in incineration applications of the present invention at suitable incineration temperatures, which are preferably in the range of 800 to 1000 C. Foam quartz which is essentially silicon dioxide , or a foam ceramic should not decompose or deteriorate significantly when subjected to such temperatures. When incineration is required at higher temperatures, a suitable structural material is used at higher temperatures and the "Eccofoams" foams mentioned are preferred because they are stable at 1650 C for relatively short periods of time and that they are considered to be more stable at 1090 X, the temperature to which they can be exposed for prolonged periods without adverse effects. The mentioned Eccofoam products are available in the form of sheets measuring 30.5 x 45.7 x 7.6 cm for the Eccofoas QG and 30.5 x 45.7 x 11.4 cm for the Eccofoam QR. These sheets or plates are machined to the desired shape, using abrasive cutting and grinding techniques. Although "Eccofoam" foam can be case-hardened to itself and other materials, this case-hardening will almost always be avoided in the manufacture of present compact ovens as case-hardening products are generally ineffective at higher temperatures or degrade at these temperatures.

 The incineration medium is a microwave absorbing material, which does not have a Curie point temperature below these desired incineration temperatures, and which can be heated by microwave radiation to a temperature within the range between 400 to 500 C and 1650 or 1700'C. Sometimes the incineration range may even be higher, being limited by the melting, sublimation or decomposition points of the equipment materials used or the substance to be incinerated or its oxides, but the range of 600 å 1000 C is normally adequate, and the range between 800 and 950 ', 975 or 1000' C is often particularly preferred. The incineration means is a means which is stable at the temperatures for which it is intended to be used and which is essentially or completely stainless at such a temperature. It must also be of healthy structure at this operating temperature, being resistant to disintegration, cracking and spraying. Although various materials are capable of absorbing microwave radiation and being heated to temperatures within the ranges described, silicon carbide is the most useful and the material particularly preferred among this. Silicon carbide, powdered, granular or in another form of small particles (in which the effective particle diameters can usually be up to 0.5 1 cm), can be heated by microwave radiation but it does not 'is generally not, in this form, effective enough to be used as a means of incineration for b incineration materials very diverse that can be encountered, and whose analysis in this device should be considered. However, silicon carbide, which is in a continuous sintered form or in solid form without particles is very satisfactory and it has been successfully used for analyzes of ash content of various materials.

The continuous solid silicon carbide incineration means can take various forms to suitably fit into a furnace wall cavity, but regular parallelepipeds, such as flat prisms, of rectangular cross section are preferred. Suitable materials may be beech "bars of commercial finishes, which may otherwise be used to center grindstones; among these, preferred are those sold by Norton Co. under the trademark
CRYSTOLON, in particular Grade 37 C 220, which is a combined, vitrified silicon carbide, but other silicon carbide products can also be used. Among these are the JKV finishing bars from Norton Co., and silicon carbides combined with silicon nitride, designated by CN 137 and CN 233. n even if such products can physically deteriorate after many uses, they are relatively inexpensive, so that scheduled periodic replacements can be carried out, for example every 1000 analyzes, but the applicants have not hitherto had to replace Crystolon silicon carbide. Other microwave absorbing heating elements which may be used include ferrites, garnets, and other materials known in the art.

 The thermocouple which is used to measure the temperature in the oven during microwave heating of the latter may be any suitable thermocouple, which is capable of withstanding the incineration temperature and is not affected by combustion products or by other gases which may be released by the material to be incinerated during its incineration. It has been found that a type K thermocouple (chromel-alumel> is satisfactory in the invented devices. In use, a thermocouple of this type comprises a massive sheath which is electrically connected to ground at the chamber wall. practical that the operation of the thermocouple and its accuracy are not adversely affected by microwave radiation. Instead of a thermocouple, other temperature sensing devices (with temperature settings) can be used to set turn the magnetron on or off, and therefore adjust the oven temperature. For example, infrared detectors, vapor pressure sensitive switches, bimetallic switches, and expansion sensitive gauges can all be used. be suitably arranged in the device and connected to a sensitive temperature control device, which can transform any signal re u pulse on / off or instructions to the magnetron switch.

 The temperature control device is an electronic instrument of a conventional structure which opens and closes the power supply line of the magnetron in response to electrical signals from the thermocouple. It will be described in more detail below, together with its programming. However, other forms of the control device can be used with other temperature detection devices.

 The sample to be incinerated should obviously not be placed directly on the heating elements or on the wall material of the microwave transmitting oven and a sample holder is therefore used. This support must preferably be of a low weight and it must withstand the high temperature of incineration. In addition, it must allow microwave transmission, preferably be transparent to microwaves or essentially transparent to microwaves (usually transmitting more than 95% and preferably more than 99% of this radiation), and it must not allow the sample to be incinerated, or the resulting ash, to pass through it. A suitable support or container material for the sample to be incinerated is a light filter material made of icro-fibers (aicronic dimensions) of quartz. The microfibrous quartz sheet is preferably of a thickness in the range of 0.2 to 0.7 mm, of a porosity such that the pressure drop during its passage is from 131 to 658 Pa approximately ( l 8 5 mm of mercury) at 5 cm / sec of normal air speed, resistant to high temperatures up to 500 C, without unfavorable effects, retaining particles of micron dimensions, transmitting microwave radiation and d '' a weight in the range of 50 to 200 g / m2. Preferably, the material is of a thickness situated in the range of 0.3 to 0.6 mm, of a porosity such that the pressure drop during its crossing is from 263 to 526 Pa approximately (2 to 4 mm of mercury) for a normal air speed of 5 cm / sec, resistant, although with certain cracks, at high temperatures up to 1000 C, retaining more than 90% of particles of micron dimensions, transparent to micro radiation -waves, and weighing in the range of 75 to 125 g / m2. The weight of such a container is normally between 0.2 and 0.6 g, preferably between 0.3 and 0.5 g.

A material of very suitable structure for the containers of the present invention is that which is sold by Whatsan Laboratory.
Products, Inc., Clifton, New Jersey, for use as air pollution filters under the trademark Whatman # Ultra-
Pure QM-A Quartz Filters, which are described in publication N # 860-QM-AA of this firm. According to this publication, the material described is an ultra-pure quartz micro-fiber filter sheet, which contains a small proportion (5%) of dassic borosilicate glass micro-fibers, which are included in the sheet in order to produce a paper. This publication does not describe or suggest the use of this material as a container and it does not refer to the incineration of analytical samples, it does not mention the use of microwave heating to incinerate such samples or to incinerate other materials. According to Whatman's publication, the weight of a QM-A quartz filter is 85 g / m2, its thickness is 0.45 im, it retains 99.999 Z of 0.6 micron particles for a normal speed of air 5 cm / sec, it has a dry tensile strength, for a strip of 1.5 cm wide, from 250 to 300 g, and it is capable of withstanding a maximum temperature of 500 vs.

 To make the containers of the present invention, a relatively simple process is employed in which a non-woven sheet of quartz microfibers described is formed, wetted, rolled, cut to the ground, removed from the mandrel, air dried and fired. If the holding material (s) and the mandrel are sufficiently temperature resistant, firing can be performed while the sheet material is held in place on the mandrel. Such heating is carried out at a temperature high enough to constitute a container which retains its shape, a temperature which is normally at least SOO C, but is preferably within the range of 500 to 1200 CC. The heating time at temperature The desired "treatment" is normally in the range of 1 to 20 minutes, with ranges of 1 to 15 minutes and 5 to 12 minutes being respectively preferred and particularly preferred. For example, a 10 minute heating period at around 800-900 C C is often used. It has been theorized that, during the processing operation, the borosilicate glass component of the microporous quartz filter material is removed, leaving a container formed of quartz fibers, which are still porous and which are even more temperature resistant than the starting material.

 The heating or cooking of the container, described above, can be carried out in various heating means, including ovens or muffle ovens, but it is preferably carried out in a microwave incineration oven, of the type where the container will be used mainly. Preferably, the heating is carried out at a temperature at least as high as that to which the container will be subjected during the incineration operations, but lower temperatures may also suffice. The wetting of the sheet material can be carried out before or after forming, and this wetting can be done by spraying, applying with a roller or stamping. It is generally preferred to limit, in the microporous quartz to be formed, the quantity of moisture of the material to the presence of metals, the mold is desirably made of a material transparent to microwaves, such as quartz, although various ceramics and glasses may also be used in appropriate circumstances. Whichever cooking procedure is followed, it is satisfactory insofar as the container wall does not collapse or deform in an unacceptable manner.

 The heating or cooking is preferably carried out in a microwave incineration apparatus such as that described in the present application, this operation being practical and subjecting the containers to a test which is almost the exact replica of the actual conditions of 'use. The heating in such an apparatus is normally carried out in the range of 800 to 10OO ° C, for example, at 850 or 900T, but it can be situated in the range mentioned above from 500 to 1200 C, and can even go down to 400 or go up to 1600 ° C in certain circumstances.

 It should be noted that in the previous description of cooking temperatures, many exceed the maximum temperature given by the manufacturer of quartz filters, which is SOOT. Surprisingly, the applicants have found that these containers can be made capable of retaining their shape by heating to temperatures close to the temperature indicated by the manufacturer as the maximum temperature at which the filters should be raised, or exceeding this. heating operation, the sheet of filter material, which was previously flat, is converted into a container which retains its shape and which is useful for containing samples to be incinerated, for microwave incineration operations.

 Such a permanent conformation of the sheet material takes place at temperatures below the melting point of the quartz and the porous sheet does not lose its porosity as a result of the melting. It seems that the presence of the small proportion of borosilicate glass microfibers in the quartz sheet is favorable for the manufacture of the present containers, but this is not considered essential to obtain the desired result. It is considered that other glasses can replace borosilicate glass and that these glasses can be omitted, and that it is also possible to manufacture a useful container, keeping its shape, intended for microwave incineration analyzes, but that it is preferable to use the starting material present, containing a small proportion, usually from 1 to 10 Z of borosilicate glass microfibers.

 When heating is complete, the container is removed from the heat source and cooled in air to room temperature.

Slow cooling is preferred to relieve stress and avoid excessive embrittlement. Cooling times (to ambient temperature) of 30 seconds to 10 minutes are considered useful for producing satisfactory containers for incineration using microwaves.

 A relatively minor disadvantage of the mentioned quartz filter material is that it apparently crystallizes and becomes brittle when subjected for relatively long periods to high temperatures, such as those above about 500 C. However, it can be used for contain the sample to be incinerated and can be used repeatedly if the operation is carried out with care. It is estimated that five to fifty analyzes can be performed before a new container of quartz filter material has to be put into service.

Such elements are relatively inexpensive and this "disadvantage" is therefore not considered to be significant. In FIG. 4 and 7 to 9, a preferred container is shown for the sample to be incinerated.

 Other containers made of non-porous materials can be used to retain the sample to be incinerated during this operation, for example crucibles made of quartz, borosilicate glass, ceramic, porcelain and platinum, but the uses of these the latter are normally limited to certain mergers and "dry incinerations". For reasons which will be mentioned later, such containers are not as useful in microwave incinerations as are the supports and containers made of the described quartz microfiber filter material.

 Almost any material that can be incinerated within the operating temperature range of this device can be satisfactorily incinerated in this material.

Among these materials, we can mention synthetic organic polymers, waste water sludge, activated sludge, industrial waste, sediments from the bottom of rivers, lakes and streams, coals, foodstuffs, construction papers and materials. The ash contents of these materials are often low, for example 1 Z or 0.1 Z, but they can be higher, or even 10 Z and more, and the apparatus according to the invention incinerates in a reproducible manner and specifies these various materials and retains all the sludge in the porous containers described.

To start the appliance illustrated and described and operate it, the following procedure must be followed
1. If the thermocouple is not in place, it must be inserted into the microwave maintenance chamber, as shown in FIGS.

1, 2, 4 and 5, and as indicated previously in the description. The massive thermocouple sheath must be appropriately grounded to the chamber wall or other grounding location to prevent possible damage to the temperature control device.

 2. Place the screen (73) and the refractory support block (71) on the bottom of the chamber.

 3. Remove the upper part (57) from the incineration oven and place it in the chamber under the thermocouple.

 4. Align the hole in the upper part of the oven with the thermocouple and lift the upper part so that the thermocouple is in the oven cavity (23), which is created by installing the bottom section of the oven (59 ).

 5. While keeping the upper part of the oven in the high position, slide the lower part into the chamber and align it with the upper part.

 6. Lower the upper part of the oven onto the lower part. The thermocouple should extend into the incineration oven cavity by about 1 cm, but this distance can be adjusted at will, according to analytical results, and can range from 0.8 to 5 cm from the top of the oven cavity, preferably 0.8 to 3 cm for the oven described.

 7. Place the door (35) in the closed position on the incineration oven.

 8. Install the temperature control device on the top of the microwave maintenance chamber and insert the thermocouple plug on the back of the control device, and connect the temperature control device cable to the microwave system, as shown in FIG. 5.

 9. Insert the microwave system and plugs of the adjuster power cable (not shown) into the appropriate electrical outlets and turn ON the adjuster switch.

 10. To minimize the time required to heat the samples to be incinerated, preheat the incineration oven from room temperature to the desired incineration temperature, which is set in the temperature control device, as described below. separately. Then program the system to m: microwave for microwave heating for 60 minutes and set the power to 100 Z. Press the START key and allow the oven to preheat. The oven generally reaches an operating temperature of around 950 C in 30 minutes or a temperature of around 1200 C in one hour. If you wish to maintain the oven temperature longer than 60 minutes, the microwave system adjusters can be programmed for this longer time.

In addition, the temperature of the incineration oven can be programmed again according to the programming procedure of the adjustment device which will be described later.

 11. Place the quantity of sample to be incinerated in the container, or, if several samples are to be incinerated simultaneously, place them in several containers.

 12. Press the STOP key, open the chamber door, remove the oven door and place, using tongs, the sample container (s) to be incinerated in the incineration oven cavity. Replace the oven door, closing it or leaving it slightly ajar if preferred, then close the bedroom door.

 13. Press the RESET button and press the START key, which turns on the magnetron and begins heating the sample (s).

 14. At the end of the incineration, which usually requires about 10 minutes at the desired temperature, press the STOP button, open the chamber door and remove the oven door, which is easy to do manually despite the high internal temperature of the oven. Use tongs to remove the container (s) of ash and allow them to cool to room temperature. Replace the oven door after removing the container (s) to prevent thermal damage to the bedroom door. Then close the chamber door and press the START button to keep the oven at the incineration temperature.

 We will now describe the procedure used to program the temperature control device.

 1. Insert the thermocouple plug into the adjuster.

Press the S key on the adjusting device O appears on the display of the adjusting device. Press and hold the Increase button until the number 28 is displayed. If you exceed the number 28, press the Decrease button until you reach 28.

2. Press the S key, it will appear t or F.
at. If C appears and you want a reading in T, go to step 3.
b. If C appears and 'F is the desired reading, press the Decrease button and' F appears, then go to step 3.
vs. If 'F appears and F is the desired reading, go to step 3;
d. If T appears and C is the desired reading, press the Increase button and C will appear, then go to step 3.

 3. Press the S key and it will momentarily appear SPIH.

Press the Increase button or the Decrease button until the desired operating temperature setpoint appears. This sets the upper temperature limit SP1H. The maximum operating temperature is introduced into the circuit of the adjustment device. For example, it can be 1200'C in some cases, or 1650 C in others, depending on the structure of the device
4. Press the S key and it momentarily appears SPlL. Then press the Increase or Decrease button until it appears 0.

This sets the lower temperature limit SPIL
5. Press the S key and it will momentarily appear SP2H. Then press the Increase key until the maximum value 2499 appears. This sets the upper limit value SP2H, which is not used in the program but which is necessary for the unit to function properly.

 6. Press the S key and it will temporarily appear SP2L. Then press the Increase key or the Decrease key until a value 0 appears. This sets the lower limit value SP2L, which is also not used in the program, but which is also necessary for the unit is operating properly.

 7. Press the S key and it momentarily appears HYS. Then press the Increase or Decrease button until it appears 1.

This adjusts the operating insensitivity range for maximum operating accuracy.

8. Finally, press the S key and it appears momentarily
RUN. The actual temperature of the incineration oven then appears. The programming of the adjuster is now complete. This programming must be completed in two minutes, because otherwise the controller leaves programming mode and steps 8 must be repeated.

 It should be noted that by following the immediately preceding instructions (steps I to 8) to program the adjustment device, upper and lower temperature limits are introduced into the program of the adjustment device. These set points can be identical, in which case, when the measured temperature falls below a previously determined hysteresis value (which is usually 2 or 3 degrees) the magnetron is restarted, and it is stopped when the measured temperature increases to approximately the same value, beyond the set point temperature.

 The incineration apparatus of the present invention is regulated by a combination of a temperature control device and a microprocessor of the single micro-wafer type. The microprocessor executes instructions from the permanent memory in an electrically programmable read-only memory, or EPROM, internal. In operation, the microprocessor receives commands and time data from an operator using the instrument's keyboard or the microwave system. The operator can see a response to most orders on the accompanying 20-digit alphanumeric display.

 When the operator enters the time data on the numeric keypad, this data is stored in the temporary random access memory.

When the time has been entered for step 1, the microprocessor allows you to enter a start command: Start. When Start is pressed the microprocessor moves one of its output lines from high to low and starts counting down the time. This lower threshold is sent by a set of normally closed contacts from the temperature control device, then to the solid state microwave relay (SSR). This threshold turns on the SSR, which controls the microwave power. Then the SSR itself switches the alternating current (AC) to the high voltage microwave section, and the magnetron generates the microwave energy.

 The microwave energy directed into the oven cavity heats the heating elements of the incineration oven, which heat the oven cavity and the sample to be incinerated. The thermocouple detects the temperature of the incineration oven, the output of the thermocouple is communicated to the temperature control device, which continuously compares the measured temperature and the set point temperature which was previously entered. When the measured temperature equals the set temperature, the temperature control device opens the normally closed contact, and it interrupts the digital signal which had previously activated the SSR. Without this signal, microwave energy ceases and the incineration oven is maintained at this set point temperature and begins to cool slowly. When the measured temperature falls below a previously determined hysteresis value (usually 2 to 3 degrees), the control device closes the open contact and the SSR is started. The microwave energy then raises the temperature of the incineration oven to the set point temperature. This process continues until the total heating time, set by the operator, has been counted down to 0. The microprocessor returns the digital signal to a high state and microwave heating and control cease. At any time during the countdown, the operator can press the Stop or Stop button to stop the countdown and stop the heating process, if desired.

In the description above, the temperature control device is separated from a microwave instrument (CEM Microwave Dry.ing/
Digestion Systeo MDS-81) because the MDS-81 system is available "hardware", usable in conjunction with a new, less complex adjustment device. However, it is included in the invention to integrate the temperature control devices in the microwave instrument.

 Incinerating a sample in this device is a simple procedure. It is simply necessary to place the sample in an appropriate container, of the type described above and to insert it into the oven cavity, to close the oven door and the chamber door and to press the Start button. When the incineration temperature has been reached, most samples are completely incinerated in about ten minutes, but the completion of the incineration can be checked by weighing the incinerated sample (in the container, after cooling) and weighing again after additional exposure to the conditions of incineration. When the weight stops decreasing, the completion of the incineration is established, the same is true of the time necessary to carry out complete incinerations, although a certain additional time is usually used, for example an excess of 20S in a safety goal. In these weighings, the incinerated sample and the container must not be weighed hot, but must be conditioned for weighing, as is well known in the art, but such packaging is very rapid with the invented support.

 The apparatus and method of the present invention are normally used to analyze the ash contents of materials. In such procedures, the container is weighed without and with a sample content to be incinerated, before incineration, and the container, with the ashes, is weighed after complete incineration. The percentage of ash in the original sample can be calculated immediately by dividing the weight in ash by the weight of the sample and multiplying by 100. However, in some incineration operations, it is conventional to use a dispersing agent , pod of magnesium acetate, which acts to prevent the production of a glassy or glass-like residue in the incineration vessel, a residue which may contain a portion of the non-incinerated sample. Without using such a dispersing agent, high readings or bases of erroneous ash content could be obtained. When the dispersing agent is used, a blank operation is normally carried out to determine the amount of apparent weight of ash which is in fact the incinerated dispersing agent, and this weight is subtracted from the apparent weight of ash to give the actual weight of ashes.

 Although different sample weights and different numbers of reduction sample containers may be used in the incineration apparatus of the present invention, it is normally charged in such a typical apparatus where the oven cavity is approximately 14 cm x 14 cm, that is to say an area of about 200 ci2, some 4 or 5 porous containers, heat resistant, transmitting microwaves and loads of materials to be incinerated, these containers preferably being of short cylindrical shape, with a unit base surface of approximately 15 to 25 cm 2, for example approximately 20 cm 2, and the heights being between 0.8 and 2 cm, for example approximately 1 or 1.5 cm. The unit weight of these containers is desirably as low as possible, generally between 0.2 and 1 g, preferably 0.3 and 0, g, for example about 0.4 or 0.5 g. The weight of the sample to be incinerated is normally between 1 and 10 g, preferably between 1.5 g and 6 g, for example around 2 or 5 g. The ash content can be high or low, between a maximum of about 50% and a minimum of 0.001% or even less. For materials such as unsaturated synthetic polymer plastics and grain flours, this content is usually relatively low, normally less than 5% and often less than 1%, for example from 0.01 to 0.8%. materials mentioned to be incinerated, or the ash contents are in the indicated ranges, magnesium acetate is normally used as a dispersing agent, dissolved in ethanol (at 95 S) so that the ethanol solution is d '' a magnesium acetate concentration of 15 g / l. About 3 µl of the solution is poured onto the sample to be incinerated when it is in the container and, if the container used is porous, made of light quartz micro-fibers, heat resistant and microwave-transmissible, the solution wets the whole sample to be incinerated and also wets the fibers of the container due to the porosity of the container, the nature of the micro-fiber quartz and the structure of the container, and the alcohol is released during heating, so 'nonaggressive1 without entraining ash or sample out of the container, while the vaporization and combustion of alcohol is often violent when using waterproof or conventional containers, such as @r cre @ sets in platinum, and quantities of samples are sometimes entrained out of the container causing erroneous ash content determinations. The incineration temperature, as set for the oven cavity, is normally between 400 and 1600 C, but this temperature must be chosen in the light of the characteristics of the sample to be incinerated and of the apparatus d microwave incineration. Many reductions and analyzes can be carried out below 1200 C and a large number can be carried out in the range of 600 to 1000 C, for example at 950 T. Thus, incinerations of wheat and other grain flours can be carried out at around 870 or 950 C, and incineration of polyethylene and polypropylene can be carried out at around 550 t. The incineration times can be adjusted appropriately, but they are normally in the range of 5 to 20 minutes, preferably 8 to 15 minutes, for example about 10 minutes. In certain cases, the incineration apparatus can be programmable in such a way that the oven temperature is modified during the experiment. In such a situation, the first heating or ramp temperature must be relatively low, for example 100 ° C. to dry the sample, as a result of which the temperature may rise to the set temperature for incineration.

 The present invention has many significant advantages over the apparatuses and methods for incineration and ash content analysis of prior art materials. It is automatic and allows a single operator to carry out a multiplicity of incineration operations and analyzes in several incineration devices, each of which may contain several specimens to be incinerated.

The adjustable heating of the sample to be incinerated is very uniform, little heat being lost out of the oven cavity, because the walls of those are of very low thermal conductivity (and they are also resistant to chemical reactions with chemicals. combustion and decomposition products of the material reduced to ashes). As indicated above, when the sample container to be incinerated is made of a porous sheet of quartz micro-fibers, it removes ethanol (and the small amount of water which accompanies it) out of the sample which has been treated with a dispersing agent, can be carried out without requiring the ethanol to flame externally and without loss of sample in an "explosion", as can occur with conventional crucibles, as in conventional muffle furnaces. The analyzes are not only carried out under conditions that are easier to adjust, but they are more significantly faster than conventional analyzes in a muffle furnace, and the results are exactly as precise (in fact we consider them to be more precise). .

 The device is easy to adjust and easy to use. It is not necessary to wait long periods for the parts to cool down so that they can be handled by an operator. For example, the oven door can be removed from the oven by hand and immediately after the completion of an incineration operation because, despite the high internal temperature of the oven, the door and the outer walls of the oven are not not hot enough to burn the fingers of an operator touching them. This can be attributed to the low thermal conductivity of the material constituting this door and the oven walls, and to the continuous cooling of these surfaces by the air which circulates in the chamber intended to maintain the microwaves.

An air flow in the oven can also be controlled, and it contributes to a faster incineration than that which has been obtained.
So far. The part of the air which is sucked into the chamber passes through the oven, in part to be carried out, even during the heating of the oven at high temperature, by a manual operation which involves contact of the fingers with the door handle or the means of capture. The blower fan speed can also be changed to vary the flow rates through the oven, but this is not necessary because opening the oven door gives good control.

 It can be considered that in the present apparatus the "microwave system", including the chamber, the blower, the ducts and the associated parts, acts as a smoke hood for the microwave oven contained therein, and achieves this without the usual space requirements of such a fume hood, without the undesirable heating of the laboratory due to the use of a muffle furnace and without the dangers for service personnel of burns by contact with the workpiece heated.

In addition to the advantages of the main aspects of the apparatus and process, the incineration vessel also provides special advantages to promote ease of analysis, speed and accuracy. Although the incineration temperature in the microwave incinerator can exceed SOO%, the maximum temperature specified by the filter manufacturer, it is found that the container according to the invention can be used satisfactorily in high temperature incineration without deterioration such as to adversely affect the accuracy of the determination of ash content. In fact, the same container can be used for several microwave incineration analyzes, often more than 5 and sometimes
Up to 50, for example, 10 scans. By continuously using the container, it can become more fragile but, if handled with care, it can be used for the number of analyzes mentioned above without losing the desired porosity for this incineration, without breaking and without giving sample or ash leaks.

 In addition to the unexpected advantage of usefulness at elevated temperatures, the containers of the present invention have other unexpected advantages and characteristics which make them ideal for microwave incineration and for ash content analyzes. by microwave. The micro-fibrous quartz material used is porous and allows air to pass through it without causing loss of sample or ash. This is important because the ignition and oxidation of the sample are favored (most of the ashes being in the form of oxides). When a dispersing agent, such as magnesium acetate in ethanol, is used to treat the sample to be incinerated before incineration, the porosity of the container material (which is maintained despite the high temperature of the latter during the forming operation) is believed to contribute to a gentle combustion of the solvent rather than what looks like an explosive combustion of the solvent, which could result in part of the sample.

Such a gentle ignition is believed to occur because the ethanol in the magnesium acetate solution disperses on the container due to the absorption properties of the container. Smooth ignition or combustion can also be attributed in part to the relatively low height of the container wall, which facilitates access of air to the sample and to the ethanol present. With the containers of the present invention, this ignition can be carried out in the oven of the microwave appliance during the automatic incineration operations whereas, when using the usual non-porous crucibles made of quartz, porcelain or in platinum, in muffle ovens or in microwave incineration ovens, where appropriate, it is usually desirable to remove alcohol from the sample by igniting it outside the oven before starting the incineration operation.

 The containers of the present invention not only are porous, but they are lighter and of low thermal conductivity.

As they are light, their weight is often significantly less than the sample weights and may be even less than the ash weights, in some cases, allowing more precise weighing of the sample and the ashes. In addition, despite the low thermal conductivity, the light and porous container cools more quickly when it is removed from the incineration furnace, which saves cooling time of the container and the ash before weighing, compared with the use of an ordinary crucible. The containers according to the invention, which are thinner than crucibles and other ordinary containers, transfer heat from external sources of heat more directly to the samples to be incinerated, such as microwave absorbing heating elements and oven refractory walls. to muffle.

 As the containers conforming to the invention have side walls, they are superior to the support pads of the flat sheet type described in patent US-A-4,565,669, and they do not require cover pads to prevent loss of ash, a feather lightness, in the exhaust air passing through the oven and the chamber of the incineration apparatus intended to maintain the microwaves. The wall achieves the desired effect of allowing the oxidation air to enter the sample, while at the same time reducing its speed, so as to avoid any loss of ash from the container.

However, as a safety measure, it is possible, if desired, to use a cover on current containers, which can be made of the same material, freely formed, or which can have more open pores or be a sieve, preferably in filament or quartz fibers.

 The examples which follow are representative of the invention but do not limit it. Unless otherwise indicated, all proportions are by weight and all temperatures are in C.

EXAMPLE 1
An official sample of wheat flour is analyzed for its ash content, using the microwave incineration apparatus of the present invention as described above, and the results obtained are compared to those obtained at From standard analyzes for which muffle furnace heating was used Ten "experimental" tests are carried out using, in the incineration apparatus, single containers of test samples or more of these containers at the time. The wheat flour to be used is the standard, which was a verification sample obtained from the American
Association of Cereal Chemists. The incineration device used is a
CEM Corporation MDS-81 Microwave Drying / Digestion System of 1000 watts, modified as indicated in the description and used in conjunction with a thermocouple, a temperature control device and an oven of the type previously described here. The furnace structure materials are ECCOFOAM HQ for the furnace body and door, and Norton Co. Crystallon grade 37C220 silicon carbide for the heating elements. The base surface of the oven is approximately 200 CD2, the oven cavity measuring approximately 14 cm x 14 cm in horizontal cross section and being approximately 5 cm high. The thermocouple is of the chromel-alumel type and the circuit is that of FIG. 6.

 The microwave incinerator is set at a temperature of 950 C and it is preheated to this temperature for about 1/2 hour. Then the chamber door and the oven door are opened and a wall container containing the sample is inserted into the oven, using tongs. The container is made of a quartz microfiber filter sheet called QM-A by the manufacturer, Whatman Laboratory Products Inc., and it is in the form of a flat cylinder 5 cm in diameter and approximately 1.5 cm in height. of wall. It contains 2.1241 g of wheat flour sample and approximately 3 cm3 of a 15 g / l solution of magnesium acetate in methanol (å 95 2), a few drops of which are dropped onto l sample so as to wet it completely, as well as the adjoining bottom and wall of the container. After inserting the sample container, the oven door is returned to a position such that there is a passage approximately 0.3 cm wide between the door and the oven wall. Shortly after adding the container and the test sample to the oven, the alcohol burns without incident. Ten minutes after loading the oven using the sample, the doors are opened and the container is removed, using tongs, and allowed to cool in a desiccator, which takes approximately 60 seconds. The container, including the ash and magnesium oxide residue (from magnesium acetate) is then weighed. Previously, the container was weighed empty and the equivalent magnesium oxide residue was determined for the magnesium acetate solution used. The amount of ash of 0.0112 g and the weight of the sample is 2.1241 g, so that the percentage of ash in the sample is 0.527%.

 The above ash content determination is repeated nine times to obtain a total of ten similar determinations. The results of these tests are given in Table 1, below.

As seen from Table 1, the high determination is 0.539 Z and the low determination is 0.513 X. The average is 0.524 S. According to the American Association of Cereal Chemists, fifty-one analysis by techniques cremation in a muffle furnace, in TABLE I
Test code ABCDEFGHIJ
Container weight + 0.5015 0.5014 0.5228 0.5890 0.4878 0.4940 0.5173 0.5060 0.5790 0.4753
Ash + MgO (g)
Container weight (g) @ 0.4893 0.4808 0.5024 0.5668 0.5656 0.4732 0.4967 0.4856 0.5567 0.4528
Center weight + MgO (g) 0.0212 0.0206 0.0204 0.0222 0.0222 0.0208 0.0206 0.0204 0.0223 0.0225
Weight of MgO (g) 0.0100 0.0100 0.0100 0.0115 0.0115 0.0100 0.0100 0.0100 0.0115 0.0115
Condon weight (g) 0.0112 0.0106 0.0104 0.0107 0.0107 0.0108 0.0106 0.0104 0.0108 0.0110
Sample weight (g) 2.1241 2.0392 2.0142 2.0144 2.0305 2.0659 2.0378 2.0276 2.0529 2.0426
Ash content 0.527 0.520 0.516 0.531 0.527 0.523 0.520 0.513 0.526 0.539 (% by weight) using an oven temperature of 871 C for one hour, indicate a maximum of 0.550 Z and a minimum of 0.504 Z with an average of 0.530 Z. It It therefore seems that the microwave incineration device gives more consistent results and is sufficiently precise to be used to replace the incineration procedure with a muffle furnace.

EXAMPLE 2
Two additional wheat flour samples, designated by B and C, are subjected to microwave incineration, and the ash contents of these samples are determined and compared with results obtained by standard oven analyzes. to muffle. The procedures followed are the same as in Example 1. For sample B, three tests are carried out and the ash content results are 0.508 t, 0.512% and 0.520%, which gives an average of 0.513 Z The ash content by standard muffle furnace analysis is 0.512 S.

In three ash analyzes of sample C, carried out using microwaves, the results are 0.724 S, 0.724% and 0.739%, giving an average of 0.729 Z. The standard analysis of the same sample gave a ash content of 0.730%,
EXAMPLE 3
A polyethylene sample is analyzed for its ash content, using the apparatus and method described in Example 1, but omitting magnesium acetate. Three samples of the same polyethylene are tested, the incineration temperature being maintained at 550 C + 3 C for periods of ten minutes. The ash contents of 0.008%, 0.008 Z and 0.006 Z are obtained, the average being 0.007 S. The various weights of the three tests are given in Table 2, as well as the ash contents.

TABLE 2
Test code 2 RS
Weight of container + ash (g) 0.6032 0.5972 0.5874
Container weight (g) 0.6028 0.5968 0.5869
Weight of ash (g) 0,0004 0,0004 0,0005
Sample weight (g) 5.0187 5.0082 8.0695
Ash content (%, by weight) 0.008 0.008 0.006
Three samples of a polypropylene material were analyzed for ash content in the same manner as that described for the analysis of polyethylene ash using the apparatus and process of the invention. . The ash contents determined are 0.024 Z, 0.025 Z and 0.024 S, the average being 0.024 S. The various weights are shown in Table 3, as well as the ash contents.

TABLE 3
IUY test code
Weight of container + ash (g) 0.5984 0.5939 0.5903
Container weight (g) 0.5972 0.5926 0.5884
Weight of ash (g) 0.0012 0.0013 0.0019
Sample weight (g) 5.0103 5.1606 8.0431
Ash content, by weight) 0.024 0.025 0.024 EXAMPLE 4
Microwave incineration devices are used to carry out, using microwaves, ash analyzes of various other materials, including other food products and other synthetic organic polymers, various sludge and sediment from waterways, paper, coals and building materials. The ash contents found in analyzes of these materials are often between 0.1 and 10% or more, and these analyzes are performed quickly and give accurate results compared to standard muffle furnace analyzes. Obviously, the incineration times are significantly reduced compared to the muffle furnace incineration times. Other incineration temperatures can be used, which range from 400 to 1200 ° C., and temperatures up to 1600 ° C. can be envisaged, the incineration times being between 5 and 20 minutes. To incinerate materials at these very high temperatures, some modifications to the microwave device and instrument may be desirable.

 To carry out these additional analyzes, the size of the device can be modified, the power can be modified and the incineration procedure can be changed. Thus, in certain cases, a basic unit of 600 watt or 900 watt (CEM MDS-81) is used, or else this basic unit is replaced by other suitable microwave instruments of this general type, modified according to needs. Instead of using the quartz microfiber containers to maintain the sample during incineration, a porcelain or quartz container or a container made of another suitable material may be used. In these cases, the incineration procedure can be modified by igniting the alcohol accompanying the magnesium acetate (when it is used) outside the oven (to avoid loss of samples due to ignitions sometimes violent in the oven).

Sometimes, even when using the porous quartz microfiber container, if an alcohol present is not removed in the first place by evaporation by heating at low temperature, it may be considered desirable to remove the door. from the oven during the initial heating of the samples so that the ignition of the alcohol can be more easily controlled and that any loss of sample is therefore avoided.

 As mentioned above, the air flow rates in the oven can be adjusted by opening or closing the oven door. These flows depend on the degree of this opening, and they also depend on the total air flow through the chamber, which is usually in the range of I to 5 m3 / min. The total air flow and the various air inlet and outlet openings of the furnace, in combination, continue to admit air in the vicinity of the material being incinerated so that the products of combustion are, as they are evacuated, replaced by fresh air. Despite the relatively large air flow through the chamber, the incineration temperature can be maintained inside the oven due to the good insulating properties of the oven wall and door and due to the relatively low proportion gas entering and leaving the oven during incineration, with most of the air bypassing the oven.

 Other variants of the apparatus and method include the use of other radiation absorbing materials, instead of silicon carbide, for example ferrites, the installation of a quartz fiber safety screen above above the incineration vessel, the use of a rotary table transparent to radiation to provide even more uniform heating of the sample to be incinerated and the variation of the size and shape of the oven to further improve the heating and regulation of the air passing through it.

 Although a rotary table still promotes heating of the microwave absorbing heating elements, it is found that oven temperatures are essentially uniform throughout, and that multiple samples to be incinerated are uniformly so. This can be attributed to the excellent insulating properties of the quartz foam furnace material (Eccofoam). Therefore, turntables and special radiation mixers are not necessary but are sometimes used.

EXAMPLE 5
This example and examples 6 to 8 relate to the manufacture and the analytical uses of the incineration vessels according to the invention.

A 9 cm x 9 cm square of an Ultra-Pure QM-A quartz filter
Whatman, which is a nonwoven sheet of quartz microfibers, is formed on a substantially cylindrical glass mold into a flat cylinder about 6 cm in base diameter, and the cylinder is then moistened with about 3.0 g of water which is applied by substantially uniform spraying on the surfaces of the filter material. An elastic band is then applied to the wall of the cylinder, as shown in FIG. 9, to maintain this wall in position.

Applying water to the filter helps it keep its cylindrical shape.

Subsequently, the filter is cut flush and the elastic band is removed. Then the cylinder is removed, and it is air dried and then heated or baked) in a muffle furnace for about ten minutes at around 870 C to be treated; after which it is removed from the muffle furnace and cools in air to room temperature. The result is a short, hot-formed, cylindrical container that keeps its shape, useful for microwave incineration of suitable materials, such as analytical specimens.

 The container resembles that of FIG. 8 and those of FIG. 7.

Although the container retains its shape, even when used at elevated temperatures as a container of material to be incinerated during incineration using microwaves, it retains the desired porosity.

 Alternatively, the container can be cooked in a microwave incineration oven similar to that shown in FIG. 7, at a higher temperature, 9501C, and the result is the same.

EXAMPLE 6
An incineration vessel of flat cylindrical shape, substantially the same as that of Example 5 and of FIG. 8, is produced by wetting a 9 cm x 9 cm square of the same QM-A filter material with the same amount of water, forming it by means of a quartz mandrel, as shown in FIG. 9, in a flat cylinder, cutting flush with this cylinder to the desired height of 1.5 cm and maintaining one of its side walls on the mandrel by means of a quartz thread, also as shown in FIG. 9. The cylinder formed on the quartz mandrel, is then subjected to baking heating at a temperature of 950 C for ten minutes in a microwave oven like that of the
FIG. 7, whereupon the heating is interrupted and the mandrel and the flat cylindrical container are removed from the microwave oven and cooled in air to room temperature. After cooling, the container is removed from the mandrel and is ready to be used with the thread in place or after removal of the latter.

EXAMPLE 7
The container described in Example 5, which weighs 0.50 g, receives a wheat flour verification sample (from the American Association of Cereal Chemists) and approximately 3 ml of a container is applied to the container sample. ethanol solution (95%) with 15 g / l of magnesium acetate so as to wet the entire sample (and also to wet part of the container). The container of the test sample, wetted with the magnesium acetate solution, is placed in the FIG microwave oven. 7, as a result of which, the appliance oven is brought to a temperature of 935 ° C. and heated to this temperature continuously for ten minutes. Heating is stopped and the ash container is removed. The weight of flour ash and magnesium oxide is 0.02 g, and the weight of magnesium oryde (obtained experimentally before for the volume of solution added) is 0.01 g. Thus, the cereal ash weighs 0.01 g, which corresponds to 0.05 Z of ash, which overlaps the results obtained by standard incinerations of the same sample in muffle furnaces (for a period of 90 minutes).

 In variants of this experiment, containers produced by the procedure described in Example 5 as an alternative, and by the procedure shown in Example 6, are substituted and the results are the same. Furthermore, when several samples are incinerated at the same time, in several containers in a microwave incineration apparatus, such as that shown in FIG. 7, precise results can be obtained for each of them.

EXAMPLE 8
Containers corresponding to the invention, made of microfibrous filter paper not containing borosilicate glass (which is present in the filter material QM-A) can also be produced by the process described above, with temperatures heating systems in the range of 500 to 1000 C, for example 950 C, and this process is satisfactory even if only half of the water is applied and even if there is apply no water at all (other suitable liquids, such as ethanol, may be substituted). These containers may be used in microwave incineration devices such as those shown in FIG. 7 and precise analytical results can be obtained, as can be verified by comparing with standard muffle furnace analyzes, the same test samples.

 In addition, ash burners made of other materials, including other grain flours, synthetic organic polymer plastics, such as polyethylene and polypropylene, waterway sediments, sewage sludge , charcoal, milk powder and a large number of other products to be incinerated can be treated satisfactorily, using the procedures and apparatus described.

In these incinerations, the incineration temperature varies within a range of 500 to 1000 C and the incineration times also vary, usually from 8 to 20 minutes, depending on the type of material being incinerated and its temperature d 'incineration. In all these examples, the incinerations and the satisfactory analyzes have results which correspond to the determinations carried out by following the standard procedures in a muffle furnace, for the same test specimens.

Good results are also obtained when the cylinder is covered with a flat cylindrical cover of QA filter material, but the use of this cover is not necessary (although it can be considered as a safety measure, for s '' ensure that no ash is lost in the exhaust air).

The invention has been described with reference to illustrations, operational embodiments and descriptions thereof, but it is not limited to the latter since it is obvious that the person skilled in the art
art, which is informed of this specification, may use
substitutions and equivalents, without departing from the invention.

Claims (5)

 1. Container (75; 129) for a material (77) to be thermally incinerated in an incineration oven (17; 1170, container which is suitable for use in an incineration oven (17; 117) which is heated by subjecting elements (62, 6X, 66, 67, 68; 127) of this microwave absorbing oven to microwave radiation, which is temperature resistant, has walls, is light, porous, transparent to microwave, and which consists of quartz microfibers which are maintained in the form of a container (75; 129) with a wall.  2. Container (75; 129) according to claim 1 wherein the structural material of this container is a thin non-woven sheet of quartz microfibers, which sheet has been heat treated to create a container geometry (75; 129) wall.  3. Container (75; 129) according to claim 2 wherein the structural material is of a thickness in the range of 0.2 to 0.7 mm, of a porosity such that the pressure drop between its faces is about 131 to 658 Pa (1 to 5 mm of mercury) for a normal air speed on the face of 5 cm / sec, is resistant to high temperatures, up to 500 C, retains particles with micron dimensions, is transparent to microwave radiation and has a density in the range of 50 to 200 g / m2.  4. Container (75; 129) according to claim 3 whose shape is a substantially flat cylinder, the height / diameter ratio thereof being in the range of 1: 5 to 2: 5 and the weight of the container being in the range range from 0.2 to 0.6 g.  5 A method for manufacturing a container (75; 129) which is suitable for use as a container for materials (77) to be incinerated by subjecting elements (62, 6X, 66, 67, 68; 127) to microwave radiation absorbing microwaves in an incineration oven (17; 117), which comprises the steps of forming, to give it a container geometry, a light sheet, porous and transparent to microwaves, made of quartz microfibers, and of heating this sheet, which has this geometry, thus constituting a container (75; 129) keeping its shape.