The preparation method of B4C powder can refer to the preparation method of SiC powder. For the preparation method of carbo-reducing boron anhydride, the reaction formula is as follows.

2B2O3+ 7C⇋B4C + 6CO

This method is the indirect heating ingredients or directly in the resistance furnace and electric arc furnace let electricity pass through are ingredients, temperature of 2200 when the B4C is decomposed into carbon and boron, and boron at high temperature, and volatile, preparing of B4C in electric arc furnace, contains a lot of free graphite, its content was 20% ~ 30% preparation of B4C in electric resistance furnace, containing a small amount of free carbon, but contains free boron, content of 1% ~ 2%.

In the presence of carbon, the reduction of boron anhydride by magnesium thermatics produces a very fine powder of boron carbide 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, so the content of free boron is slightly more than that of boron carbide produced by the reduction of boron anhydride by carbon in a resistance furnace.