Experimental Study On Preparation Of Spherical Aluminum Powder By Vacuum Method

Aluminum powder is an important functional material that second only to iron powder. It has good corrosion resistance, electrical conductivity, thermal conductivity and ductility for the smooth development of the national defense industry, rocket plane manufacturing, nuclear, chemical, construction, powder metallurgy has important significance. In this paper, the properties, preparation methods, applications of spherical aluminum powder, to carry on the comprehensive review. For the evaporation of pure aluminum vacuum conditions-condensation process and AlN chloride-disproportionation of condensing process thermodynamics, kinetics, mechanism and process of system research.Through the theoretical analysis:in the experimental condition can be achieved within the scope of the evaporation temperature should be chosen for the 1623K to 1823K, at this time of aluminum vapor pressure p*>Pc. Crystal solidification process, the condensing temperature above 1642.2 K, because of the aluminum of saturated vapor pressure p*>15Pa, at this time there is no nucleation radius fairly rk, which could not form liquid core, aluminum vapor is not saturated, is conducive to form steam, so the condensation temperature should be lower than 1642.2 K can produce aluminum.Aluminum evaporation-condensation experiment study:the evaporation temperature higher than 1723K, the evaporation rate of growth has quickened significantly. Evaporation temperature is lower or the cooling plate surface temperature is lower, the growth of the condensed small aluminum particles are more; and continue to increase evaporation temperature, condensation on the surface of the disc temperature increase obviously, purpose-100 mesh aluminum began to decrease. Evaporation temperature T, remove any aluminum its mostly spherical or spherical, and aluminum powder particle surface is smooth, good dispersion. Influenced by gravity, aluminum powder particles in the process of solidification part deformation occurs, there is no perfect spherical morphology. And the evaporation temperature is higher, higher than 1823K, the graphite heater temperature, larger graphite particles fall off to evaporate into the cooling plate and condensed aluminum particles before and after the last reunion, finally to form honeycomb particles. In the pure aluminum evaporation process, the condenser temperature at about 692-933K, temperature gradient condensation area is about 6.0 K/mm when condensing pipe is 80 mm; the condenser temperature at about 600～812.5K, the temperature gradient condensation area is about 5.3 K/mm when condensing pipe is 120 mm.AlN chloride-disproportionation of spherical aluminum powder in vacuum prepared by the process of experiment that is concluded that:by thermodynamic calculation shows that the system pressure between 10 to 100Pa, when the reaction temperature higher than 1428K, AlN(s) and AlCl3(g) generated AlCl(g) and N2(g), when the condensation temperature is lower than 1064K, AlCl(g) will happen to the decomposed Al(1) and AlCl3(g). Under different reaction temperature, the aluminum purity is very high, all above 99.28%. In the process of experiments, when the distance condenser heat source is relatively close, condensation plate temperature is higher than the melting point of copper 1356 K, low prices failed to form aluminum vapor disproportionation, aluminum chloride in the cooling tray can’t pick up the aluminum powder, until the temperature below the melting point of aluminum cooling tower of 933K disproportionation generated aluminum vapor crystallization nucleation and growth. Such a case, through the calculation of weighing, the formation of condensation on the top cover aluminum is not entirely, because of the bleeding point is very closed, part of the metal aluminum was siphoned off, cause damage.Highly elevated after condensation, the level 4 condensation plate layers of collection, thereby reducing the loss of metal aluminum. In the chloride-disproportionation process, condenser temperature about933～1373K, temperature gradient condensation area is about 14.7 K/mm when condensing catheter to 0 mm. The condenser temperature at about 600-812.5K, the temperature gradient condensation area is about 5.3 K/mm when condensing pipe is 150 mm.