Method for preparing boron carbide

Abstract

The invention discloses a method for preparing boron carbide. The method comprises the following steps: using low-cost coal as a carbon source, boric acid as a boron source and sodium carbonate as a sintering aid; recrystallizing boric acid on surfaces of coal powder particles in a way of in-situ growth to obtain boric acid-coated coal particle mixed fine powder with small particle size and uniform distribution; pre-compressing and molding to prepare pieces, thereby avoiding violent combustion of the coal at high temperature and improving reproducibility of an experiment; and finally, utilizing a discharge plasma sintering process to realize rapid, green and efficient preparation of boron carbide crystals by changing sintering temperature, heat preservation time and load pressure. The decomposition of the sintering aid sodium carbonate enhances a gas-solid reaction probability in a sintering process; CO2 gas is ionized to form a space hot spot for promoting interfacial reaction of B atoms and C atoms, so that the boron carbide with high densification and excellent mechanical properties is prepared under low temperature and rapid sintering conditions with lower cost and less environmental pollution.

Description

technical field [0001] The invention belongs to the field of ceramic materials, in particular to a method for preparing boron carbide. Background technique [0002] Boron carbide is an important superhard material in nature. Its hardness is second only to diamond and cubic boron nitride. It also has low density, high elastic modulus, wear resistance, corrosion resistance, neutron absorption and high temperature semiconductor properties. It is a A new type of ceramic material with excellent comprehensive performance is used as sealing material, neutron absorbing material, bulletproof material, engine nozzle, polishing and fine abrasive of hard material, bulletproof armor material, nuclear radiation protection, etc., in nuclear energy, national defense and Widely used in machinery and other fields. [0003] The structure of boron carbide ceramics has extremely strong covalent bonds, the covalent bond fraction is above 90%, and the self-diffusion coefficient is very low. The e...

AI Technical Summary

Problems solved by technology

[0003] The structure of boron carbide ceramics has extremely strong covalent bonds, the covalent bond fraction is above 90%, and the self-diffusion coefficient is very low. The elimination of internal pores, grain boundaries and volume diffusion all require very high temperatures. The sintering of pure boron carbide ceramics is extremely difficult. Difficult, generally difficult to achieve densification; At present, the methods for preparing high-performance boron carbide ceramics to achieve industrialization include hot-press sintering and pressureless sintering; A pressure of tens of megapascals is applied to promote the rapid densification of boron carbide sintered bodies, but the hot-press sintering process requires a high temperature higher than 2000°C for sintered boron carbide density of 98%, a holding time of at least 1 hour, and a single hot-press sintering process. The output of the furnace is limited, the shape is single, and the size is small, so the price of hot-pressed sintered boron carbide ceramics is expensive; one or more sintering aids are added to the sintered boron carbide by the pressureless sintering method, and the sintering aids are used at high temperatures. It achieves densification; pressureless sintering has high production capacity and is suitable for mass production, but the pressureless sintering temperature is high, the holding time is long and densification is difficult, so the overall cost is high; high sintering temperature will make pressureless sintering and hot pressing Sintering boron carbide ceramics consumes a lot of electric energy, and the preparation cycle is long and the production cost is high, making it difficult to apply boron carbide bullet-resistant ceramics in large quantities to weapons and equipment; in addition, sintering at such a high temperature will rapidly coarsen the grains and When it grows up, the pores are difficult to discharge, resulting in a large number of pores remaining in the material. After sintering, the grains are coarse (the particle size of pressureless sintering is about 50 μm, and the particle size of hot-pressing sintering is 3-5 μm), and the density is not high, which results in boron carbide ceramics. Low strength and toughness; although the price of pressureless sintered boron carbide ceramics is lower than that of hot-pressed products, it is still expensive compared to other carbide structure ceramics

Images