RU2460698C2 - Inorganic fibre composition - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: inorganic fibres have the composition: Al₂O₃ greater than or equal to 5 mol %; K₂O - 12-40 mol %; SiO₂ - 5-80 mol %; viscosity modifiers less than or equal to 20 mol %, wherein SiO₂+Al₂O₃+K₂O is greater than or equal to 80 mol % and less than 100 mol %, wherein the fibre has a composition having melting point higher than 1400°C.

EFFECT: low bioproofness and improved thermal characteristics of articles.

20 cl, 4 tbl

Description

This invention relates to inorganic fiber compositions.

Fibrous materials are well known for their use as thermal and / or acoustic insulating materials, and are also known for their use as reinforcing components in composite materials, such as, for example, fiber reinforced plastic fiber reinforced elements, and as a component of metal matrix composites . Such fibers can be used as support structures for catalyst masses in devices for controlling emissions into the environment, such as catalytic converters of automobile exhaust systems and particulate filters of diesel engines. Such fibers can be used as components of friction materials (for example, for automobile brakes). The fibers of the present invention have a range of properties and can be used in any or all of these applications, depending on the properties shown.

Until 1987, there were four main types of fibrous materials used for the manufacture of heat-insulating products (such as, for example, rolled material, vacuum-formed shaped products and mastics). They were made in two main technological ways, although the details of specific technologies varied depending on the manufacturer. The fibers and paths were (in order of increasing cost and temperature characteristics):

Melt Shaped Fibers

- Mineral wool

- Glass wool

- Aluminosilicate fibers

Fiber sol-gel process

- The so-called polycrystalline fibers

Fibers formed from the melt are formed by melt preparation and fiberization of the obtained melt by any of many known methods. These methods include:

- the formation of a melt flow and providing the flow with the possibility of contact with rotating discs, from which it is discarded, forming fibers;

- the formation of a melt stream and allowing the stream to hit a gas stream, which can be transverse, parallel or go at any angle to the direction of the stream and as a result break the stream into fibers.

- the formation of fiber from the melt by a rotation method in which the melt flows out through openings in the periphery of the rotating bowl and is blown away by hot gases to form fibers;

- extrusion of the melt through small openings for forming filaments, in which additional processing can be used (for example, drawing by a flame, in which the filament is passed through a flame);

- or any other method by which the melt is converted into fiber.

Because of the history of asbestos fibers, much attention has been paid to the relative ability of a wide range of fiber types to cause pulmonary disease. Toxicology studies of natural and artificial fibers have led to the idea that fiber resistance in the lungs is what causes problems. Accordingly, it was suggested that if the fibers can be quickly removed from the lungs, then the entire health risk can be minimized. The concept of “biostable fibers” and “biostability” appeared: fibers that are stored for a long time in the animal’s body are considered biostable, and the relative time that the fibers remain in the animal’s body is known as biostability. Although it was known that some glass systems are soluble in lung fluids, resulting in low biostability, the problem was that such glass systems were generally not used for high temperature applications. The market's need for fiber was obvious, which would have low biostability combined with high temperature characteristics. In 1987, John Manville developed such a system based on the chemistry of calcium-magnesium silicates. Such material not only had higher temperature characteristics than traditional glass wool, but also had a higher solubility in body fluids than aluminosilicate fibers commonly used for high temperature insulation. Such low bio-resistant fibers were later developed, and now on the market there are a number of alkaline-earth silicate (AES) fibers (AES - abbreviation from the English Alkaline Earth Silicate).

Patents relating to AES fibers include:

- international patent application WO87 / 05007 - the initial application of John Manville, which describes fibers including oxides of magnesium, silicon, calcium and less than 10 wt.% alumina, soluble in saline. The solubility of the fibers described was in parts per million silicon (recovered from the silica-containing fiber material) present in saline after 5 hours of exposure;

- international patent application WO89 / 12032, which describes additional fibers that are soluble in saline, and disclosed some components that may be present in such fibers;

- European patent application 0300320, which describes glass fibers having high physiological solubility and having 10-20 mol.% Na ₂ O and 0-5 mol.% K ₂ O. Although it has been shown that these fibers are physiologically soluble, the maximum the temperature of their use was not indicated.

The following patent descriptions, revealing the choice of fibers for their solubility in saline solutions, include, for example, European patents 0412878 and 9459897, French 2662687 and 2662688, WO86 / 04807, WO90 / 02713, WO92 / 09536, WO93 / 22251, WO93 / 15028, WO94 / 15883, WO97 / 16386, WO2003 / 059835, WO2003 / 060016, EP1323687, WO2005 / 000754, WO2005 / 000971 and US 5250488.

The heat resistance of the fibers described in these various documents of the prior art varies greatly, and for these alkaline earth silicate materials, the properties critically depend on the composition.

It is generally relatively easy to manufacture alkaline earth silicate fibers that behave well at low temperatures, because when used at low temperatures, additives such as boron oxide can be used to ensure good fiber formation and the amounts of components can be varied to meet the requirements for the desired material . However, in an attempt to increase the heat resistance of alkaline earth silicate fibers, we are forced to reduce the use of additives, since in the general case (although with exceptions), the more components are present, the lower the heat resistance.

WO93 / 15028 describes fibers comprising CaO, MgO, SiO ₂ and, optionally, ZrO ₂ , as main constituents. Such AES fibers are also known as CMS (calcium-magnesium-silicate) or CMZS (calcium-magnesium-zirconium-silicate) fibers. WO93 / 15028 insisted that the compositions used should be substantially free of alkali metal oxides. It has been shown that amounts up to 0.65 wt.% Are acceptable for materials suitable for use as insulation at 1000 ° C.

WO93 / 15028 also describes methods for determining the solubility of glasses and indicates materials that have been tested as glasses for their solubility, but which have not been formed as fibers. Among these compounds were compounds designated KAS, KMAS, and KNAS, which were potassium aluminosilicate, potassium magnesium aluminosilicate, and potassium sodium aluminosilicate, respectively. These compositions were rated as having poor solubility based on measurements of solubility in saline. The type of saline used had a pH of about 7.4.

It was later discovered that solubility depends on the environment in which the fiber is located. Although the physiological saline solution present in the intercellular pulmonary fluid approximates that given in WO93 / 15028 and has a pH of about 7.4, the mechanism for cleansing the fibers involves their attack by macrophages. The pH of the physiological saline solution present where macrophages are in contact with the fiber is known to be significantly lower (about 4.5), and this affects the solubility of inorganic fibers (see "In-vitro dissolution rate of mineral fibers at pH 4.5 and 7.4 - A new mathematical tool to evaluate the dependency on composition " , Torben Knudsen and Marianne Guldberg, Glass Sci. Technol., 78 (205) No. 3).

WO94 / 15883 describes a number of such fibers used in heat-resistant insulation at temperatures up to 1260 ° C or more. Like WO93 / 15028, this patent requires that the alkali metal oxide content be kept low, but indicates that some alkaline earth silicate fibers can withstand higher levels of alkali metal oxides than others. However, it is suspected that concentrations of 0.3% and 0.4 wt.% Na ₂ O cause increased shrinkage of materials for use as insulation at 1260 ° C.

WO97 / 16386 describes fibers used as heat-resistant insulation at temperatures up to 1260 ° C or more. These fibers include MgO, SiO ₂ and, optionally, ZrO ₂ as the main constituents. It is stated that these fibers require the practical absence of alkali metal oxides except in the form of trace contaminants (presence at the level of at most hundredths of a percent calculated on alkali metal oxides). The fiber has a basic composition,%:

SiO ₂ 65-86 MgO 14-35

moreover, the components of MgO and SiO ₂ comprise at least 82.5% by weight of the fiber, and the rest are named components and viscosity modifiers.

WO2003 / 059835 describes some calcium silicate fibers that use additives of La ₂ O ₃ or other lanthanides in order to improve the strength of the fibers and the roll material made from the fibers. This patent application does not mention the concentration of alkali metal oxides, but amounts in the range of 0.5 wt.% Are indicated for fibers intended for use as insulation at temperatures up to 1260 ° C. or more.

WO2006 / 048610 states that for the mechanical and thermal properties of AES fibers, it is beneficial to include small amounts of alkali metal oxides.

The scope of such low bio-resistant fibers is limited in that they are prone to performance degradation above about 1300 ° C.

The low bio-resistance alternative fibers that have been proposed are alkaline earth aluminates. Such materials have been proposed as calcium aluminate (EP0586797) and strontium aluminate (WO96 / 04214). Such fibers are not manufactured as a commercial product.

Sol-gel fibers have been developed, including aluminosilicates having significant additives of alkaline earth metal oxides or alkali metal oxides, and these fibers have been the subject of international patent application PCT / GB2006 / 004182.

Another chemical composition of the fiber has been developed in the present invention that provides fibers with low biostability and due to which some fibers are capable of at least fibers with thermal characteristics comparable to those of aluminosilicate fibers.

Accordingly, the present invention provides melt-formed inorganic fibers having a composition, mol%

Al ₂ O ₃ 5-90 K ₂ O 5-90 SiO ₂ 5-90

in which the sum of SiO ₂ + Al ₂ O ₃ + K ₂ O is 50 mol%, preferably more than 60 mol%, more preferably ≥70 mol%, even more preferably ≥80 mol% or even ≥90 mol% .

In specific implementations, such fibers include, mol.%:

Al ₂ O ₃ 5-34 K ₂ O 5-34 SiO ₂ 61-90

or

Al ₂ O ₃ 5-78 K ₂ O 17-90 SiO ₂ 5-61%

or

Al ₂ O ₃ 24-90 K ₂ O 5-17 SiO ₂ 5-61

The amount of K ₂ O may be less than 50 mol.%, Less than 40 mol.%, Less than 35 mol.% Or less than 30 mol.%. The amount of K ₂ O may be more than 10 mol.% Or more than 20 mol.%. The amount of Al ₂ O ₃ may be greater than 10 mol% and may be greater than 20 mol%.

The amount of SiO ₂ may be greater than 20 mol%, ≥30 mol%, or ≥35 mol%. The amount of SiO ₂ may be below 80 mol% or below 70 mol%.

Additional features of the invention are apparent from the claims and in light of the following description.

A series of potassium aluminosilicate fibers was made using an experimental setup in which a melt of the corresponding composition was formed, was released through an 8-16 mm hole and blown off in order to obtain fiber in a known manner. The size of the outlet opening was varied to take into account the viscosity of the melt (this is a setting that must be determined experimentally in accordance with the equipment and composition used).

The attached results differ from those shown in previous applications, since it was found that the insufficient melting point of some melts was the result of the presence of carbonate (potassium was introduced as potassium carbonate). Accordingly, the results shown in the following tables represent new material tests, examples of which are given in the prototype and in previous applications and in additional examples.

The attached table 1 shows the manufactured fibers and their composition in mass percent, determined by analysis by fluorescence in x-rays.

The attached table 2 shows the manufactured fibers and their calculated composition in molar percent.

The attached table 3 shows the shrinkage of the manufactured fibers. Shrinkage was measured by vacuum blank casting using 75 g of fiber in 500 cm ^{3 of a} 0.2% starch solution in a snap of 120 × 65 mm. Platinum needles (with a diameter of approximately 0.3-0.5 mm) were placed separately at a distance of 100 × 45 mm at 4 angles. Longer distances (L1 and L2) and diagonals (L3 and L4) were measured with an accuracy of ± 5 μm using a mobile microscope. Samples were placed in an oven and gradually heated to a temperature 50 ° C below the test temperature at a speed of 300 ° C / h and gradually heated at a speed of 120 ° C / h for the last 50 ° C to a test temperature and left for 24 hours. After removal from the oven, the samples were allowed to cool naturally. Shrinkage values are given as the average of 4 measurements.

The attached table 4 shows the solubility of the manufactured fibers in ppm of the main components of the glass after 5 hours of static testing in physiological saline with a pH of 4.5.

A detailed solubility measurement technique involves weighing 0.500 g ± 0.003 g of fiber in a centrifuge tube using plastic tweezers. The fiber was usually chopped (wire mesh No. 6) and degranulated (manually sieved with mesh No. 10), but it could be a solid body or roll material if only small amounts of fiber are available. Each sample was weighed twice. 25 cm ^{3 of} model body fluid was poured into each centrifuge tube using a graduated dispenser, and the tubes were sealed. The model body fluid was added to the fiber only at the beginning of the test and included the following ingredients in 10 l of water:

Reagent Weight NaHCO ₃ 19.5 g CaCl ₂ · 2H ₂ O 0.29 g Na ₂ HPO ₄ 1.48 g Na ₂ SO ₄ 0.79 g MgCl ₂ · 6H ₂ O 2.12 g Glycine (H ₂ NCH ₂ CO ₂ H) 1.18 g Na ₃ citrate · 2H ₂ O 1.52 g Na ₃ tartrate · 2H ₂ O 1.8 g Pyruvate Na 1.72 g 90 mol.% Total acid 1.56 g Formaldehyde 15 ml Hcl ~ 7.5 ml

with HCl added slowly, since this value is approximate for adjusting the pH to a final pH of ~ 4.5. The model body fluid was given a minimum of 24 hours in order to balance, and after this period, the pH was adjusted accordingly.

All reagents used were of the quality “for analysis” or equivalent, and the procedure was carried out using plastic equipment, since leaching of silicon oxide from glassware could occur.

Then the centrifuge tubes were placed in a shaken water bath, which was maintained at 37 ° C ± 1 ° C (body temperature) and shaken for 5 hours. A short time of 5 hours was chosen because the solubility of some of these materials is so high that the amount of leached K ₂ O can cause a pH shift to higher values, which will distort the results if a longer time is used.

After shaking, two solutions for each fiber were decanted and filtered through Whatman No. 40 ashless paper filters with a diameter of 110 mm into one 50 ml flask. The solution was then transferred for analysis by induced conjugated plasma atomic emission spectroscopy (IPC). The oxides to be determined depend on the composition of the test fiber. The results are given in ppm for the relevant oxides.

Turning first to the properties of the fibers, it was first found that when the molar ratio of K ₂ O: SiO _{2 is} less than 30:70, there is a tendency to form coarse fibers with a fiber diameter much larger than 10 μm (e.g., 50-250 μm). However, it was subsequently found that this was too hasty a generalization and it was found that fibers with more than 40 wt.% SiO ₂ (usually more than 52 wt.%) Were coarse. Such fibers having more than 40 wt.% SiO ₂ , and those made as thin fibers, tend to have relatively high shrinkage, since they tend to be subject to viscous flow. However, such fibers may be of interest for some applications. If thin fibers (<10 μm diameter) are required, viscosity modifiers can be added. Suitable viscosity modifiers may include alkali metal oxides, alkaline earth metal oxides, lanthanide elements, boron oxide, fluoride and, in fact, any element or compound known in practice as affecting the viscosity of silicate glasses. The amounts and type of such viscosity modifiers should be selected so as to be consistent with the intended use of the fibers. Boron oxide, for example, probably lowers the maximum usage temperature, although this can be tolerated (see KAS80 fiber). A viscosity modifier that has been found to be particularly useful is magnesium, which can be added in the form of oxide or in another form (see, for example, KMAS1 fiber). Calcium oxide may be acceptable, as is strontium oxide. Zirconia and iron oxide may be tolerated in small quantities. In general, the compositions of the present invention appear to be tolerant to additives, although an amount acceptable to achieve the desired properties should vary from additive to additive.

Table 3 shows that most fibers have relatively low shrinkage at temperatures from 1000 ° C to 1300 ° C, and many have low shrinkage even at such high temperatures as 1500 ° C. Apparently, fibers with too much excess of K ₂ O over Al ₂ O ₃ or with too little K ₂ O with respect to Al ₂ O ₃ show high shrinkage and, although they are used in such applications as reinforcement or as a filling material in composite products, are not recommended for use as high-temperature insulating materials.

A molar ratio of K ₂ O: Al ₂ O ₃ close to 1: 1, apparently, provides good results, and for the best temperature properties (low shrinkage after exposure to temperatures up to 1300 ° C for 24 hours), the molar ratio of K ₂ O : Al ₂ O ₃ may be less than 1.6, preferably less than 1.5, more preferably less than 1.45 and may be more than 0.4, preferably more than 0.8.

Preferably, the fibers of the above compositions have a melting point of greater than 1400 ° C. Even more preferably, the fibers have a melting point greater than 1600 ° C., more preferably more than 1650 ° C. and even more preferably more than 1700 ° C. (for glasses, the melting temperature is defined as the temperature at which the composition has a viscosity of 19 Pa · s). You can see that the composition KMAS1 melts at 1450 ° C, even though it has a relatively low shrinkage at 1400 ° C. Such a fiber can be reasonably used in insulating applications at temperatures of, say, up to 1350 ° C, while still leaving a margin for temporary deviations to higher temperatures. In contrast, many of the fibers still exhibit low shrinkage at 1500 ° C and should be suitable for use at higher temperatures.

It should be noted that at elevated temperatures, fibers can tend to lose potassium. Although this may limit the applications to which the fibers could be directed, there are many applications for which this is not a problem.

The K ₂ O-Al ₂ O ₃ -SiO _{2 system} has a wide range of high melting points. For example, only as an indication:

- the mineral composition K ₂ O · Al ₂ O ₃ · 2 SiO ₂ (kaliophyllite) has a melting point of ~ 1800 ° C;

- the mineral composition K ₂ O · Al ₂ O ₃ · 4 SiO ₂ (levsite) has a melting point of ~ 1690 ° C.

On the contrary, there are areas where melting points are lower and where some eutectics form.

For ease of manufacture, a composition having a low melting point (e.g., close to a eutectic or eutectic) should be preferred, while for a higher temperature characteristic, a composition having a higher melting point should be preferred. It was found that compositions with about 35-40 wt.% Silicon oxide (usually 47-52 mol.%.) Easily converted to fibers and form fibers that show low shrinkage at elevated temperatures. Such fibers with about 23-25 wt.% K ₂ O (usually 18-22 mol.%) Are especially easily formed.

The solubility shown in table 4 indicates that extremely high solubility can be achieved. Fibers with K ₂ O + Al ₂ O ₃ + SiO ₂ > 80% and with less than 20 mol% K ₂ O, although they show significantly higher solubility than aluminosilicate fiber (RCF), are not inclined to show such high solubility as calcium magnesium silicate fibers. Good solubility for such fibers was found for K ₂ O in the range from 25 to 30 mol.%. For fibers having significant additives of certain viscosity modifiers (e.g. Mg), high solubility can be detected (see KMAS1).

For comparison, the total solubility of industrial calcium-magnesium-silicate fiber (which is considered bio-soluble in a model physiological saline with a pH of 7.4) and industrial aluminosilicate fiber (which is not considered bio-soluble in a model physiological saline with a pH of 7.4), measured at one and under the same conditions, there was ~ 13 ppm in both cases.

Although static solubilities are only indications of biostability, these results strongly support the assumption that inhaled fibers of the invention will not survive as long as industrial aluminosilicate fibers.

For applications where the mechanical resilience of the fibers is important, the fibers can be heat treated. One such application is in atmospheric abatement devices such as catalytic converters, filters or diesel particle traps, exhaust pipes, and the like. The requirements for such equipment are high and, in particular, the mats and end cones used must have sufficient resilience to remain in place after they are exposed to temperatures of 800 ° C or more (usually 900 ° C may occur). Amorphous fibers were used to make such end cones, but they tended to lose elasticity and, therefore, retaining pressure on the walls of the casing if they were exposed to temperatures above about 900 ° C.

By elasticity in this context is meant the ability of the product to restore its original shape after deformation. This can be measured by simply inspecting the size and shape of the product after deformation to see the extent to which it has returned from the deformed shape to the undeformed shape. However, this condition is most often measured by observing the strength of the deformation resistance, since this is an indicator of how well the end cones are able to remain in place.

WO2004 / 064996 proposes the use of fibers that are at least partially crystalline or microcrystalline, as they are considered more resistant to shrinkage and more elastic than amorphous fibers, although WO2004 / 064996 states that such crystalline or microcrystalline fibers are more fragile than amorphous fibers. The elastic nature of crystalline or heat-treated microcrystalline fibers is well known in the thermal insulation technique — see, for example, WO00 / 75496 and WO99 / 46028.

Glass fibers, such as melt-formed silicate fibers, are regulated in Europe, and different classes of fibers have different hazard classifications and different labeling requirements. Conventional glass aluminosilicate fibers require stricter labeling regarding health hazards (as the so-called carcinogens of category 2) than alkaline earth silicate fibers that do not fall into the classification of carcinogens.

Directive 97 / (69) / EC, which replaces Appendix 1 to Directive 67/548 / EEC and classifies materials according to their potential carcinogenicity (Hazardous Substances Directive), has two broad chemical categories for silicate fibers with a diameter of less than 6 microns. These categories and their conclusions are as follows:

> 18 wt.% (CaO, MgO, Na ₂ O, K ₂ O, BaO) Category 3 - requires a warning label on the product, showing the cross of St. Andrew and indicating: "potentially harmful by inhalation" - such fibers can be exempted from labeling if they meet one or more specific tests for low biostability <18 wt.% (CaO, MgO, Na ₂ O, K ₂ O, BaO) Category 2 - requires a warning label on the product, showing a skull and crossbones symbol and indicating “potentially carcinogenic by inhalation” - the product cannot be exempted from the label

It should be clear that the fiber class claimed herein encompasses compositions that may fall into category 3 or category 2, it is beneficial that CaO + MgO + K ₂ O + BaO be greater than 18% by weight.

The appended claims limit the fibers to fibers formed from the melt. It should be clear that such fibers can be made using alternative methods, such as sol-gel methods. The present invention also covers such sol-gel fibers, provided that they comprise 12 mol% or more of K ₂ O.

Claims (20)

1. Inorganic fibers having the composition:
Al ₂ About ₃ greater than or equal to 5 mol.%;
K ₂ O - 12-40 mol.%;
SiO ₂ - 5-80 mol.%;
viscosity modifiers less than or equal to 20 mol.%,
in which SiO ₂ + Al ₂ O ₃ + K ₂ O is greater than or equal to 80 mol.% and less than 100 mol.%,
moreover, the fiber has a composition having a melting point above 1400 ° C. 2. Inorganic fibers according to claim 1, in which the amount of K ₂ O is less than 30 mol%. 3. Inorganic fibers according to claim 1, in which the amount of SiO _{2 is} greater than or equal to 35 mol.%. 4. Inorganic fibers according to claim 1, in which the amount of SiO ₂ below 70 mol.%. 5. Inorganic fibers according to claim 3, in which the amount of SiO ₂ below 70 mol.%. 6. Inorganic fibers according to claim 3, in which the amount of SiO ₂ more than 52 mol.%, And the fibers include viscosity modifiers in quantities sufficient to form fibers less than 10 microns in size. 7. Inorganic fibers according to claim 6, in which the viscosity modifier is selected from the group of alkali metal oxides, alkaline earth metal oxides, lanthanide oxides, boron oxide, fluorides and mixtures thereof. 8. Inorganic fibers according to claim 6, in which the viscosity modifier includes magnesium in the form of an oxide or in another form. 9. Inorganic fibers according to claim 1, in which the molar ratio of K ₂ About: Al ₂ About ₃ less than 1.5 and more than 0.4. 10. Inorganic fibers according to any one of claims 1 to 9, in which the amount of CaO + MgO + Na ₂ O + K ₂ O + BaO is more than 18 wt.%. 11. Inorganic fibers according to any one of claims 1 to 9, having the composition:
Al ₂ O ₃ - 10-50 mol.%;
K ₂ O - 12-40 mol.%;
SiO ₂ - 30-80 mol.%,
in which SiO ₂ + Al ₂ O ₃ + K ₂ O is greater than or equal to 80 mol.%. 12. Inorganic fibers according to claim 11, having the composition:
Al ₂ O ₃ - 15-40 mol.%;
K ₂ O - 15-30 mol.%;
SiO ₂ - 40-60 mol.%, In which SiO ₂ + Al ₂ O ₃ + K ₂ O is greater than or equal to 90 mol.%. 13. Inorganic fibers according to item 12, in which the amount of Al ₂ About ₃ is in the range of 25-35 mol.%. 14. Inorganic fibers according to any one of claims 1 to 3, in which the amount of SiO ₂ less than 52 mol.%. 15. Thermal insulation, including inorganic fibers in accordance with any one of claims 1 to 14. 16. Thermal insulation according to clause 15, in which the insulation is in the form of a rolled material. 17. Mastics, including inorganic fibers, in accordance with any one of claims 1 to 14. 18. Composite materials, including inorganic fibers, in accordance with any one of claims 1 to 14. 19. Support structures for catalyst masses, including inorganic fibers, in accordance with any one of claims 1 to 14. 20. Friction materials, including inorganic fibers, in accordance with any one of claims 1 to 14.