Study On Preparation Of Boron Carbide Products By Boron Carbide Waste Derived From Water Separation Process

Boron carbide has been widely used in sapphire wafer grinding due to its high hardness,good wear resistance,corrosion resistance,etc.In recent years,boron carbide abrasives,with the rapid growth of sapphire wafer applications,appears an increasing demand.However,large amounts of boron carbide waste derived from water separation process are produced in the production of boron carbide abrasives,which cannot meet sapphire abrasives standard because of their extremely small grain size(D50≈1 μm)and low purity.Currently,the recovery and utilization of the boron carbide waste are rarely researched.Therefore,this paper is aimed at exploring a new process for recycling the boron carbide waste and reusing it as raw material to prepare boron carbide products.Samples with different amounts of sintering aids(Al powder)were initially pelleted and dehydrated followed by a sintering process at low temperatures and under atmospheric pressure.This new process can not only realize the recycle of the boron carbide waste,reduce the environmental pollution,but also can prepare boron carbide products with excellent performance including high hardness,high strength and low porosity.This paper has investigated the effects of the pelletizing factors on the performances of the pellets and the sintering conditions on performances of the products.The sintering mechanism was also researched.The results are as follows:First,the effects of the pelletizing conditions on the performances of the pellets and sintering conditions on the performances of boron carbide products were studied.The suitable pelletizing conditions are:the type of the binder hydroxypropyl methylcellulose,the amount of binder addition 0.4%,the amount of water addition 10%,the preform pressure 30 MPa,the holding time 120 s.Under these conditions,the apparent porosity,bulk density and compressive strength of the green pellets were 42.31%,1.43 g/cm3 and 10.28 MPa,respectively.The suitable sintering conditions are:the amount of Al addition 9%,the sintering temperature 1400℃,the holding time 90 min,the sintering atmosphere with the reducing atmosphere covered by activated carbon.Under these conditions,the apparent porosity,bulk density,compressive strength and flexural strength of the sintered product were 19.08%,1.84 g/cm3,246.88 MPa and 71.10 MPa,respectively.Second,the sintering mechanism of the green pellets was studied.The conclusions are as follows:(1)The densification of boron carbide products can be increased at a low temperature by adding suitable amounts of Al powder due to the formation of low temperature liquid phase;(2)The densification of boron carbide products can be improved through increasing the sintering temperature,because of the formation of more stable phases such as AlB12,AlB12C2 and Al3BC;(3)The densification of the boron carbide products can also be improved by properly extending the holding time,which is mainly attributed to a more fully dissolution of liquid Al phase into the pores and a better infiltration of the activated carbon;(4)The carburizing of activated carbon can form a higher densification layer,meanwhile reduce the oxidation degree of boron carbide products;(5)The relationship between the density of the sintered products and sintering temperature conforms to the theory of the combined action of powder sintering of Huang Peiyun;(6)The main migration mechanism of the materials during the sintering process of boron carbide waste is viscous flow,and the apparent activation energy is 36.58 kJ/mol.