Low Temperature Preparation Technology And Morphology Control Of Boron Carbide

Boron carbide（B₄C）has wide application due to its olfactive physical and chemical properties.At present,the preparation temperature of boron carbide is on the high side,the energy consumption is huge,the production efficiency is on the low side and the environment pollution is serious.How to reduce the synthesis temperature and reduce energy consumption has become a hot spot in the preparation of B₄C powders.In this paper,boron acid and glycerol are used as boron source and carbon source,respectively.Boron carbide powder is synthesized by esterification reaction,low-temperature pyrolysis and moderate temperature reduction.A boron-containing organic precursor is synthesized by the reaction of boric acid and glycerol in esterfication method.To get an insight into the reaction,the effect of glycerol/boric acid molar ratio,the reaction temperature,the reaction time on the reaction were investigated.Chemical analysis of organic precursor showed that the best preparation process for organic precursors was that the molar ratio of glycerol to boric acid was 1:1,the reaction temperature was 150°C and the reaction time was2.5 h.The polymeric precursor was heated at 250 ^oC for 2 h,350 ^oC for 2 h,and then ground and pyrolyzed at 500-800 ^oC for 2 h in different atmosphere（still air,air flow,nitrogen flow,argon flow）.The pyrolyzed product was characterized by FT-IR,XRD,TGA,EDS and chemical analysis.The results showed that the product after pyrolysis is a mixture of boron oxide and amorphous carbon.With the change of pyrolysis atmosphere and pyrolysis temperature,the molar ratio of carbon to boron oxide changes.The suitable pyrolyzed conditions were in still air,with the pyrolysis temperature of 750 ^oC,in the air flow,the pyrolysis temperature was 550 ^oC,in the nitrogen flow and argon flow,the pyrolysis temperature was 650^oC.B₄C was prepared by carbothermal reduction of the pyrolysis product in a high temperature furnace.The effect of reduction temperature and time on product was investigated.The pyrolyzed product was characterized by FT-IR,XRD,SEM,EDS and LPSA.The results indicate that with the increase of carbothermal reduction temperature and the increase in carbothermal reduction time,the crystallinity of B₄C increases,but the agglomeration becomes stronger and the particle size increases gradually.The suitable carbothermal reduction temperature was 1450℃and the carbothermal reduction time was 2 h.The B₄C powder with a hexagonal prismatic shape,uniform particle size,a particle size of about 1.5μm and a purity of 98.9%was obtained.