Vacuum Heat Treatment Purification Of Boron Carbide Powder
With excellent performance, such as high hardness
, high modulus, low density, high chemical stability and high neutron absorption cross section, boron carbide owns peoples great concern in the field of modern high-tech. It is often used in armored cover plates, fighter pilot's bullet-proof armor, flow nozzle of the high-speed cutting machine, machinery wear sealing surface, cutting grinding tools, nuclear reactor control rods and barrier materials and thermoelectric conversion element. These properties of boron carbide are not only related with its manufacturing process but also its composition.At present, industrial carbide boron powder uses boron anhydride and coke as raw materials. They are got by arc melting the legal system. Because of their reaction is less complete, the furnace temperature distribution is not uniform, resulting in very uneven in its composition. And contains a certain amount of B2O3, B, C, etc.. Free C and B, although at certain times can promote the sintering densification process, but too much free carbon content of B, the study of other additives on the sintering behavior of boron carbide powder inconvenience. Additionally, due to the heterogeneity of boron carbide powder composition with added by homogenization, and purification of boron carbide powder B, C, and other additives, sintering of boron carbide products, may cause its performance is uneven. Therefore, the homogenization and purification of industrial boron carbide powder is very important.
When the boron carbide powder processing temperature of 1400 C, the powder removal of free carbon C mainly chemical reaction in which the residual phase. 1400 after the character of the boron carbide powder constant compared to its original state, there are changes, but little change. After 1500 to a 1600 C treatment, as a result of free C, the chemical reaction between the free B B203, and free carbon and boron carbide powder between the diffusion and the solid state reaction role of the free carbon content in the powder dropped zero, the character of the boron carbide constant value also decreased substantially. 1500 a 1600 C vacuum treatment when boron carbide powder, which free carbon and boron diffusion and solid state reaction between the removal of free carbon plays a key role.
The vacuum heat treatment is effective way to eliminate the free C, free B and B2O3 of industrial boron carbide powder and reach its chemical composition homogenization. The optimum manganese powder processing temperature is from 1500 to 1600 . In vacuum heating process, the combination reaction of free B and free carbon, B2O3 and free carbon 's thermal reduction reaction, free carbon and boron carbide diffusion and solid state reaction become the main mechanism for boron carbide powder purification and composition uniformity. The average particle size of boron carbide powder in the vacuum heat treatment process increases with the heating temperature. In the processing of 1600 , the powder particle size is increased by 2-3 times.
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