Boron carbide ceramic manufacturing process

Preparation of B4C powder

The preparation method of B4C powder can refer to that of SiC powder. For the preparation method of reducing boron anhydride with carbon, the reaction equation is as follows:

2 b2o3 + 7 c ⇋ B4C + 6 co

This method is indirect heating of the batching or direct electric current through the resistance furnace and electric arc furnace. When the temperature reaches 2200℃, B4C is decomposed into rich carbon and boron, and boron will volatilize at high temperature. The B4C prepared in the electric arc furnace contains a large amount of free graphite, its content reaches 20%~30%. B4C prepared in a resistance furnace contains a small amount of free carbon, but free boron, up to 1%~ 2%.

Reduction of boron anhydride in the presence of carbon by magnesimetry produces a very fine boron carbide powder in which the magnesium oxide is removed by pickling. In this boron carbide, magnesium and free boron may be the main impurities. Due to the low temperature of the process, the free boron content is slightly higher than that obtained by reducing boron anhydride with carbon in a resistance furnace.

Molding and firing

Boron carbide ceramics can be molded in a variety of ways. In order to obtain dense B4C, it is generally prepared by hot pressing sintering. Hot pressing sintering of B4C can reach 98% of the theoretical density, preparation in vacuum hot pressing furnace or ordinary hot pressing furnace, hot pressing temperature of 2100℃, pressure of 80~100MPa, holding for several minutes, cooling need to maintain the pressure. Due to the poor thermal shock resistance of B4C, the cooling should be slow. The hot pressing temperature should not be too high, b4C-C eutectic liquid phase will appear at 2150℃, but the temperature is too low, the product density is low.