EP0492098A1 - Process for fabricating compressible wax-bound granulate of explosive material - Google Patents

Abstract

Pure crystals of explosive substances are phlegmatised in aqueous wax soap dispersions for the application of wax particles to the surface of the crystals. To obtain mere uniform deposition of the wax particles on the crystals of explosive, a wax soap microdispersion with particle sizes of < 0.1 mu m is used. If aluminium powder is used in addition, the pH of the water phase is stabilised after the precipitation by buffering, in order to prevent an uncontrollable evolution of hydrogen.

Description

The invention relates to a method for producing compressible, wax-bound explosive granules according to the preamble of patent claim 1.

Solid crystalline explosives, also known as explosives, such as trimethylene trinitramine (hexogen, RDX), tetramethylene tetranitramine (octogen, HMX), pentaerythritol tetranitrate (nitropenta, PETN) in pure form, or, if appropriate, with additions of metal powders such as aluminum, tungsten, etc. for special purposes are customary desensitized by applying wax to the particle surface in concentrations of 2 to 20%. The wax has the property of a plastic binder that reduces the frictional forces. It therefore enables laboratory processing in the pressing process and also lowers the sensitivity to bombardment of compressed explosive charges. The desensitizing effect increases with the concentration of the wax; however, it also reduces the speed of detonation and thus the performance of the explosive. It is essential for an optimization in terms of performance and sensitivity that the wax layer and the metal powder embedded in it are evenly applied to the surface of the explosive crystals. Furthermore, the use of as pure as possible wax waxes with a melting point above 71 ° C, which is not prone to exudation, is desirable because an upper temperature limit of at least 71 ° C is required for ammunition. Exudation means the exudation of impurities at an elevated temperature.

A large number of methods are known from practice for producing wax-bound explosives. For example, in the simplest process, the explosive crystals and the wax are heated above the wax melting point in an aqueous slurry with vigorous stirring. When cooling, the wax is deposited on the explosive crystals. This procedure leads to a drop-shaped, uneven and incomplete covering of the explosive crystals. The quality of explosives produced in this way with regard to susceptibility to cracking and phlegmatization is therefore unsatisfactory. Improvements with regard to the uniform coating of the explosive crystals with a wax layer, carried out in the aqueous phase, are achieved with the aid of aqueous wax dispersions in which the wax particles, depending on the method used, are in particle sizes of 1 to 20 µm. The wax particles present in disperse form are deposited on the explosive by breaking the dispersions with precipitants. The aqueous wax dispersions are usually prepared separately and added to the stirred explosives slurry. To prepare the wax dispersions, the wax is stirred intensively together with salts of fatty acids with or without further surfactants in water at temperatures above the wax melting point. If temperatures above 100 ° C are required, an autoclave must be used. Natural or synthetic waxes with melting points in the range from 50 to 100 ° C., such as, for example, polyethylene, polypropylene, montan, Fischer-Tropsch, bees, amide waxes, etc. are preferably used. Alkali, ammonium, , Morpholine, triethanolamine and diethanolamine salts of fatty acids, such as myristic, palmitic, stearic, oleic acids, etc. are used. The precipitation is carried out with water-soluble organic acids or mineral acids such as acetic acid, sulfuric acid, hydrochloric acid, phosphoric acid etc. or with aqueous solutions of polyvalent metal salts, for example barium chloride. In such processes, the dispersions produced with the aid of the salts of fatty acids do not result in an even distribution when the wax is deposited on the explosive crystals by precipitation. Furthermore, the water-insoluble free fatty acids are formed from the water-soluble salts of the fatty acids when precipitating with acids. These are deposited together with the wax. They lower its melting point and can also exude at an elevated temperature (exudation). Furthermore, when water-soluble polyvalent metal salts are precipitated, the water-insoluble metal salts of the fatty acids are formed, which separate out together with the wax. If they are in a relatively high concentration, they are undesirable.

If a mixed explosive is produced which contains very fine aluminum powder in addition to the pure explosive, a rapid reaction between the metal and the water occurs after the dispersion has been precipitated by adding acids or polyvalent metal salts, with the formation of hydrogen. The increasing reaction speed can assume an uncontrollable level and can become a risk in large-scale projects. Furthermore, the hydrogen produced interferes with the deposition of the wax-aluminum mixture on the explosive crystals. To brake this undesirable and dangerous effect to a tolerable level, relatively coarse-grained aluminum powders with a grain size of at least 50 µm must be used, which results in insufficient adhesion to the explosive surface and an increased tendency to separate. Finally, the explosive crystals coated with wax tend to become electrostatically charged, which is noticeable in filling, sieving or dosing operations through unpleasant gluing or spraying.

The invention has for its object the known methods for producing compressible, wax-bound To improve explosive granules in such a way that an optimally effective desensitization is guaranteed and when using aluminum powder an uncontrollable evolution of hydrogen is avoided.

This object is achieved by the method steps listed in the characterizing part of the claims.

The advantages achieved by the invention are essentially to be seen in the fact that an exudate-free wax is deposited on the explosive crystals evenly or evenly with the metal powder. Further, the hydrogen-forming reaction between the aluminum powder and the water is suppressed. In addition, segregation of the explosive granules is prevented and the ability to work is improved.

The invention is described below on the basis of further explanations and examples.

Optimally effective desensitization of an explosive with a fixed binder concentration requires the wax to be deposited evenly on the explosive crystals. Uniform deposition is understood to mean a complete covering of constant crystal thickness of the crystal surfaces free of bare spots. This aim is achieved according to the invention by precipitating a wax soap microdispersion in which particle sizes <0.1 μm are used. It looks clear, but shows the Tyndal effect and is therefore not a real solution in the physical sense. The Tyndal effect refers to the scattering of light on the smallest dispersed particles.

The wax soap microdispersion is preferably produced by pouring a hot wax soap solution into an intensely stirred, hot aqueous slurry of the explosive crystals, preferably one Wax soap solution is used from at least 40% by weight of 1-propanol, a nonionic surfactant and an acid wax, the carboxyl groups of which are partially or completely reacted with an amine. The carboxyl groups of the acid wax are converted by adding the amine with stirring to the propanolic wax solution just below their boiling point. The amines well suited for this purpose are morpholine, triethanolamine or others.

If, in addition to the pure explosive crystals as metal powder, an aluminum powder with an average grain size of less than 10 µm is added to the slurry of the explosive crystals in the aqueous microdispersion of the wax soap, the wax is mixed with an amount of a strong mineral acid equivalent to the amine used, e.g. Sulfuric acid, quantitatively precipitated. The pH of the water phase is then adjusted by adding a buffer solution, e.g. to a value of 3.8 ± 1.0, preferably 3.8 ± 0.2. The wax released from the amine derivative initially forms a very fine gel, which, when the slurry is heated, envelops the metal particles and is deposited on the explosive crystals as a uniform, increasingly denser wax-metal powder layer. The deposition is reached just below the wax melting point. Above the melting point of the wax, the coated explosive crystals unite to form aggregates that increase with increasing temperature. The grain size can therefore be controlled with the temperature. When the desired grain size is reached, graphite powder is added and cooled.

If working without the addition of metal powder, buffering can be dispensed with. The separation process of the wax gel particles on the explosive crystals remains unchanged.

A non-ionic, water-soluble surfactant is used for the uniform deposition of the wax alone or together with metal powder on the explosive crystals. The surfactant also facilitates the formation of the microdispersion. It is therefore preferably added to the wax solution.

The water phase can consist of both deionized and process water. If water for use is used, a slight cloudiness arises after the addition of the wax soap solution due to the formation of the poorly soluble Ca and Mg salts of the acid wax. This effect is still not disturbing.

The formation of the wax soap microdispersion depends on the degree of saponification of the acid wax, the amine used, the proportion of 1-propanol in the wax soap solution, the temperature of the water phase and the wax soap solution. A complete microdispersion preferably occurs when the temperature of the wax soap solution is at least 85 ° C, the temperature of the water phase is at least 65 ° C and the degree of saponification of the wax with amine is at least 30 mg KOH / g.

The wax soap microdispersion has the further advantage that no salts of fatty acids have to be used as dispersants, which form the free, low-melting fatty acids contaminating the wax after precipitation with acid. The hydrophilic amine groups required to produce the microdispersion are reversibly incorporated into the wax molecule. In addition to the free wax, acidification produces the completely water-soluble amine salts of the acid used for the precipitation. The deposition of a wax layer free of impurities and therefore not exuding is achieved.

The desensitized mixed explosive made of explosive crystals, which are coated with wax and metal powder, is still required to be mechanically sufficiently stable, i.e. that there is no separation between the metal powder and the explosive crystals due to mechanical stresses such as Transport vibrations. Demixed explosives of the type described lead to inhomogeneous compacts with different compositions. The tendency to segregate is reinforced above all by the use of coarse metal powders, which, embedded in the relatively thin wax layer, do not adhere sufficiently to the explosive crystals. This is remedied by the use of fine metal powders with a grain size of less than 10 µm. So that such fine metal powders can be applied evenly to the explosive crystals, they must be completely covered by the wax layer. This is made possible with the wax soap microdispersion according to the invention, whose particle size and the gel particles resulting therefrom after breaking the dispersion are smaller than the metal particles to be coated.

Wax or plastic-bound mixed explosives often show an unpleasant spraying of fine particles when pouring or dosing, sticking to the container wall can also occur. These unpleasant effects are due to the electrostatic charge. To eliminate this disturbing phenomenon, graphite powder is subsequently added to the dry explosives. Dry incorporated graphite has the disadvantage of poor adhesion to the surface of the explosive granules and an uneven distribution as a result. To apply a uniform layer of graphite, the graphite is preferably added to the explosive slurry in the aqueous phase after the wax has been deposited at the maximum temperature. This procedure In addition to simplifying the process, the adhesion and the distribution are improved because the graphite particles can be adhered well to the wax layer, which is still soft at elevated temperature.

If aluminum powder is used in the manufacture of wax-bound, metal-containing explosives in the aqueous phase, the problems mentioned in the introduction arise due to the high reactivity of this metal with water. According to the invention, however, the use of fine aluminum powder with a grain size of less than 10 μm is necessary for the desired goal of low demixability and good homogeneity of the explosive. Another object of the invention is therefore to make the fine aluminum powder accessible to the process by means of suitable measures to suppress the formation of hydrogen, which is achieved according to the invention by stabilizing the pH of the aqueous phase after the microdispersion has precipitated to a value of 3.8 ± 1.0 with a buffer system, preferably with a formate buffer to the value of 3.8 ± 0.2.

Table I below shows the influence of the pH of aqueous solutions on fine-grained aluminum powder. The test series clearly shows the high reactivity of calcareous service water and distilled water in the pH range of 6-7. In these cases, the aluminum reacts violently with foaming at 80 ° C. Dilute sulfuric acids have a minimum reactivity at pH 4 at a drastically slowed rate. From this it can be deduced that stabilization of the proton concentration by buffers in the minimum range must lead to a sufficient reduction in the reaction rate. The aqueous wax soap dispersion in the critical pH range of 7, consisting of an acid wax partially saponified with morpholine with a pH value of approx. 7, shows an extremely stabilizing effect compared to the slurried aluminum. The reason for this surprising effect is obviously the formation of poorly soluble aluminum salts of the wax, which form on the surface of the aluminum particles and thus provide protection against further attack by protons or hydroxyl ions. An indication of this mechanism is the clouding of the supernatant solution after a long storage period, caused by the poorly soluble aluminum salt of the wax.

Table II below shows the effect of buffer systems in the favorable pH range of 3-5. The data confirm the hypothesis derived from the preliminary tests (Table I).

The aqueous phase adjusted to pH 3.8 with the formate buffer system shows the assumed reactivity minimum compared to aluminum, characterized by an extraordinarily high inertia at a temperature of 80 ° C.

In the pH range below and above 4, adjusted with citrate buffer (pH 3.1) and acetate buffer (pH 4.8), an increased reactivity can be observed again. However, both buffer systems are still so effective that they can also be used for the intended purpose.

Further investigations showed that the 3 usable buffer systems are effective in the range from 0.02 to 0.2 mol / l. At lower concentrations, the effectiveness deteriorates due to the decreasing capacity, ie the pH increases too quickly as a result of the inevitable weak reaction with proton consumption. At higher concentrations, the worsened effectiveness is likely due to a change in activity coefficient attributed. In this series, too, the formate buffer system shows the greatest effectiveness in the pH range of 4.

K_s

[mol/l] Dissoziationskonstante der Säure

C_s

[mol/l] Konzentration der Säure

C_b

[mol/l] Konzentration der korrespondierenden Anionbase

The concentrations given for the buffer solutions are to be understood as the sum of the acid and anion base concentration in mol / l with an unchanged molar acid-base ratio of 1: 1. The pH value 3.8, which was preferably determined as optimal, and which was set with the formate buffer system with the molar acid-anion base ratio of 1: 1, can naturally also be used with other buffer systems by changing the acid-anion base ratio according to the following general relationship to adjust:

K _s

[mol / l] Dissociation constant of the acid

C _s

[mol / l] concentration of acid

C _b

[mol / l] Concentration of the corresponding anion base

The use of other buffer systems for the desired pH value leads to a loss of buffer capacity.

The following examples serve to further explain the invention:

example 1

360 g of maximum wax S, 360 g of 1-propanol and 9.0 g of Arkopal N-300 were heated to low boiling (94 ° C.) with stirring. After the solids had completely dissolved and the temperature had dropped by about 2 ° C., 39.6 g of morpholine were poured into the clear wax solution. The unchanged, clear solution with the partially saponified wax is used to produce the wax soap microdispersion.

Under the conditions listed, 50% of the carboxyl groups used in the acid wax are saponified.

Höchstwachs S

Säurewachs der Fa. Höchst/BRD mit einer Säurezahl von 145 mg/KOHg und einem Tropfpunkt von 81-87°C

Arkopal N 300

Tensid aus der Klasse der Nonylphenolpolyglykolether der Fa. Höchst/BRD

1-Propanol

Qualität purum, Kochpunkt ca. 96-98°C

Morpholin

Qualität purum, Reinheit > 98%, Kochpunkt 124-128°C

Raw materials used:

Maximum wax S

Acid wax from Höchst / FRG with an acid number of 145 mg / KOHg and a dropping point of 81-87 ° C

Arkopal N 300

Surfactant from the class of nonylphenol polyglycol ethers from Höchst / FRG

1-propanol

Pure quality, boiling point approx. 96-98 ° C

Morpholine

Pure quality, purity> 98%, boiling point 124-128 ° C

Example 2

1710 g of hexogen are heated in 9 l of deionized water with vigorous stirring. At a temperature of 70 ° C, the entire 90 ° C warm wax soap solution (Example 1) is poured into the explosive slurry. After cooling to 65 ° C, 900 g of aluminum powder are added. After 5 minutes, the wax soap microdispersion is added by adding 231 g of sulfuric acid [approx. 10%] and then the pH is stabilized to 3.8 by adding 50 cm³ of 4 molar formate buffer solution. After warming up to 77 ° C, 30.0 g of graphite powder are added quickly and immediately Cool to a temperature of 50 ° C. The explosive granules are filtered off in the usual way, washed acid-free with service water and dried at 50 ° C. under vacuum to constant weight.

A

[cm³/g] Spezifischer Säureverbrauch für Morpholin

D

[g/cm³] Dichte der Schwefelsäure ca. 10%ig

M

[g] Eingesetzte Morpholinmenge

Säuremenge [g]

= A . D . M

The amount of sulfuric acid used is equivalent to the amount of morpholine contained in the wax solution (Example 1). The exact demand is calculated using the titrimetric specific amount of acid according to the following procedure:

A

[cm³ / g] Specific acid consumption for morpholine

D

[g / cm³] density of sulfuric acid approx. 10%

M

[g] Amount of morpholine used

Amount of acid [g]

= A. D. M

A =

5,50 cm³/g

D =

1,061 cm³/g

M =

39,6 g

The following data apply to example 2:

A =

5.50 cc / g

D =

1.061 cc / g

M =

39.6 g

Hexogen

Produkt mit einer mittleren Korngrösse von 400 µm

Aluminiumpulver

Sphärisches Produkt mit einer mittleren Korngrösse von 7 µm und einem Reinmetallgehalt von > 95%

Formiat-Pufferlösung

Wässerige Lösung mit einer Konzentration von je

(4 molar)

2 mol/l Ameisensäure und Natriumformiat

Graphit-Pulver

Produkt mit einer mittleren Korngrösse von weniger als 40 µm

Raw materials used:

Hexogen

Product with an average grain size of 400 µm

Aluminum powder

Spherical product with an average grain size of 7 µm and a pure metal content of> 95%

Formate buffer solution

Aqueous solution with a concentration of each

(4 molar)

2 mol / l formic acid and sodium formate

Graphite powder

Product with an average grain size of less than 40 µm

The product produced according to Example 2 has the following composition: Hexogen 57.0% by weight Aluminum powder 30.0% by weight wax 12.0% by weight graphite 1.0% by weight

Claims (12)

A process for the production of compressible, wax-bound explosive granules by slurrying pure explosive crystals with stirring in an aqueous wax soap dispersion, breaking the dispersion and depositing the wax gel particles formed on the surface of the explosive crystals, characterized in that a wax soap microdispersion with particle granules is used as the aqueous wax soap dispersion 0.1 µm is used. A method according to claim 1, characterized in that in addition to the explosive crystals, metal powder with an average grain size of less than 10 µm is used. Method according to claim 1 or 2, characterized in that a wax soap solution with a minimum temperature of 85 ° C is poured into an intensely stirred water phase with a minimum temperature of 65 ° C as the wax soap microdispersion. A method according to claim 3, characterized in that a wax soap solution is used from at least 40% by weight of 1-propanol, an acid wax with an acid number of at least 30 mg KOH / g and a dropping point of at least 77 ° C, an amine and a nonionic surfactant. A method according to claim 4, characterized in that the amount of amine used corresponds at least to an acid number of 30 mg KOH / g equivalent amount of carboxyl groups of the acid wax used. A method according to claim 4, characterized in that a surfactant from the class of nonylphenol polyglycol ethers of the general formula C₉H₁₉ (C₆H₄) -0- (CH₂CH₂0) _x H with at least 23 (x) ethylene oxide groups in the polyglycol ether chain is used in the wax soap solution. A method according to claim 4, characterized in that the amount of surfactant in the wax soap solution is measured so that its concentration in the water phase after the wax soap solution has been added is at most 0.30% by weight. Method according to one of claims 3 to 7, characterized in that the wax soap microdispersion is broken at a maximum temperature of 70 ° C by adding a quantity of dilute sulfuric acid equivalent to the amine. A method according to claim 8, characterized in that aluminum powder is used as the metal powder and that immediately after breaking the wax soap microdispersion, a formate buffer is added to adjust the pH of the water phase. A method according to claim 9, characterized in that the pH is adjusted to 3.8 ± 1.0, preferably 3.8 ± 0.2. A method according to claim 9 or 10, characterized in that the temperature of the broken wax soap microdispersion is increased after addition of the buffer until the wax is deposited on the explosive crystals together with the metal powder. A method according to claim 11, characterized in that after reaching the maximum temperature, graphite powder is added and then cooled.