Method of producing aluminium powder

FIELD: metallurgy.

SUBSTANCE: invention relates to powder metallurgy, in particular, to production of powder materials with particle sizes below 0.2 mcm used in manufacturing cermet and composite materials, as well as those intended for use as fuel for thermite and pyro compositions. An aluminum wire is exploded in a gaseous chemically inert atmosphere. The aluminum powder thus produced is wetted with a solution of boric acid in ethanol with a 0,5 mole/l concentration, the powder being separated from solution in no less than an hour after wetting.

EFFECT: increase in thermal stability of aluminum powder to 580 °C.

2 tbl, 1 ex

 

The invention relates to the field of powder metallurgy, in particular the production of powder materials with particle size less than 0.2 microns, used for the production of metal-ceramic, composite materials, as well as fuel and pyrotechnic thermite compositions and other

A method of obtaining aluminum powder with an organic coating (Akashi L.A., Kononenko I., Kochegarov VI, Lundin VG Study of the oxidation process of the surface of the aluminum with an organic coating // Journal of physical chemistry. - 1985. - So - 59. No. 11. - S-2857). The essence of this method of producing aluminum powder is that for applying a protective coating polished plates of aluminum was immersed in a 1%solution in ethyl acetate of fluoropolymers or perkiset. Then the plate was removed from the solution and placed on a horizontal plane, the ethyl acetate was evaporated, and the fluorine-containing component to form a coating. Final drying of the film was carried out at 100°With vacuum (1-3 mm Hg). For thermal oxidation, the samples were placed in a tube furnace, kept at a certain temperature for a specified period of time, then the samples were removed from the furnace, cooled to room temperature. When heated was the decomposition of organic fluorine-containing substances with the formation of fluoride al the MINIA, that gives the increased thermal stability of aluminium up to 550°directly after coating.

The disadvantage of this method of protecting aluminum is the release of toxic products of decomposition of fluorinated organic compounds (HF, CF4and others). In addition, the coating of AlF3interacts with water vapor (hydrolysis) during storage in air with the formation of toxic HF and amorphous Al(OH)3that reduces the resistance of aluminum.

The closest in technical essence and the achieved result to the described invention is a method of obtaining aluminum powder by electric explosion of aluminum wire in a gas chemically inert environment, subsequent wetting obtained in the explosion of a powder of aluminum with a solution of stearic acid in toluene with a concentration of 3.5-20 mmol/l in an atmosphere inert with respect to aluminum gas under stirring to the formation of the suspension, and then the powder is separated from the solution (Applesto, Apelin, Gal. The surface modification of submicron powders of aluminum. Journal of applied chemistry. Volume 66, 1993, issue 6, s-1233). This method allows to increase the content of aluminum metal powder to 95.2 wt.%.

The disadvantage of this method is the low thermal stability of the coating of stearic acid, to ora when heated to 400° With in the air dissolves in CO2N2On and on organic matter, resulting in its protective properties are lost.

The technical result of the proposed method is the improvement of thermal stability of aluminum nanopowder to 580°With (45%).

The technical result is achieved in that in a method of producing aluminum powder by electric explosion of aluminum wire in a gas chemically inert environment, subsequent wetting obtained in the explosion of a powder of aluminum by acid solution and separating the powder from the solution, according to the proposed solution wetting of the powder aluminum carry the boric acid solution in ethyl alcohol with a concentration of 0.5 mol/l, and the separation of the powder from the solution performed not earlier than 1 hour after wetting.

Specific example

Aluminum billet with a diameter of 0.30 μm and a length of 80 mm is placed in a sealed chamber. The chamber vacuum and filled with argon to a pressure of 1.5·105PA. The explosion of the workpiece is carried out in an LC circuit with the following parameters: inductance of a loop L=0.4 mH battery capacity of the capacitor C=2,4 μf, the resistance of the circuit R=0,085 Ohm charging voltage Uo=26 kV, and the density of the energy transferred to the workpiece, 1.5 energy sublimation of aluminum (Ewith=302 kJ/mol). Under these conditions a t the d ' specific surface area obtained after the explosion of the aluminum powder is 9.9 m 2/g and credneformatny particle diameter of 0.25 μm.

The resulting powder was moistened (without prior contact with air) 2 l of boric acid solution in dehydrated ethanol with a concentration of 0.5 mol/l per 1 kg of the powder is required to 2.5 l of solution. The powder mix before formation of the suspension, after which the inert atmosphere is replaced by air. After 1 hour, the powder is separated from the solution by decantation and dried under traction to air-dry state. The resulting powder is pyrophoric and stable in the air.

Table 1
№ p/pThe concentration of H3IN3, mol/lThe aluminum sampleThe onset temperature of oxidation, °The content of aluminum metal, wt.%Note
1-without coating40090,6
20,2coated43090,3
30,4coated48090,0
40,5coated57589,8For the implemented method
50,7coated58089,4
60,9coated58089,2
71,1coated580and 88.8
81,3coated58088,2

Thus, with increasing concentration of boric acid (table 1) in the solution increases the onset temperature of oxidation obtained of aluminum nanopowder, reaching its optimal value (575-580° (C) at a concentration of 0.5-0.9 mol/L. Further increase in the concentration of boric acid in the solution is not advisable, because a considerable rise in the temperature of the beginning of oxidation is not observed, and the weight percent of aluminum in the nanopowder is reduced (table 1).

Table 2
No.The concentration of acidsE/EcThe onset temperatureNote
p/poxidation °
1Stearic acidprototip
(3.5 mmol/l)1,5410
2Boric acid (0,5Declared
mol/l)1,5520method

According to table 2 when using boric acid solution, the temperature at which oxidation of aluminum nanopowder increased by 170°that is 45% in comparison with the prototype.

Thus, the invention improves thermal stability of aluminum nanopowder, which is important for the processing of aluminum nanopowder, fire and explosion safety during transportation and storage, as well as to improve the compatibility of aluminum nanopowder with different chemical substances.

The method of obtaining aluminum powder by electric explosion of aluminum wire in a gas chemically inert environment, including subsequent wetting obtained in the explosion of a powder of aluminum by acid solution and separating the powder from the solution, characterized in that the wetting of the powder aluminum carry the boric acid solution in ethyl alcohol with a concentration of 0.5 mol/l, and the separation of the powder from the solution performed not earlier than 1 h after MacEwan who I am.



 

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