Synthesis of boron carbide powders from mono- and polysaccharides

Abstract

Boron carbide powders are usually synthesized by carbothermal or magnesiothermic reduction of boron oxy-compounds, a carbon source is usually graphite or some organic phases. The aim of the work is using of mono- and polysaccharides for synthesis of boron carbide powders in which the final grains are separated from each other by an unreacted excess of carbon preventing both grain growth and formation of strong aggregates. Aqueous solutions of glucose, fructose, dextrin or hydroxyethyl starch and boric acid were dried, pyrolyzed at 850 °C for 1 h and then heat-treated at temperatures from 1300 to 1700 °C for 1 h. The amount of boron carbide in the powders depends both on the saccharide and on the temperature. The grains prepared from precursors containing monosaccharides had oval shapes whereas polysaccharides were applied they had rhombohedral shapes corresponding to the boron carbide structure. This effect can be attributed to presence of molten boron oxide.