Synthesis On Boron-containing Polymer And Its Application In The Synthesis Of Boron Carbide

Boron carbide is a new type of specialty ceramic materials in industry.It has a lot of prominent properties such as small weight,high hardness,good neutron absorption capacity and good chemical stability.Owing to these intriguing properties,it is widely used in wear-resistant nozzles,nuclear reactor shielding materials,lightweight bullet-proof armor and many other fields.In industry,boron carbide powder is mainly produced by carbothermal reduction.This method has many problems,for example,high temperature(above 2000 ? generally),high energy consumption,low purity,serious environmental pollution.Therefore,synthesis of boron carbide at lower temperature has attracted many researchers recently.In this paper,boron carbide and glycerol were used as boron source and carbon source,respectively.Ethylene glycerol was added as a modifier.Boron carbide powder was synthesized by esterification reaction,low-temperature pyrolysis and high temperature reduction.The polymeric precursor,pyrolysis products and the final products were characterized by FT-IR(fourier transform infrared spectroscopy),XRD(X-ray diffraction),SEM(scanning electron microscopy),TGA(thermogravimetric analysis),EDS(energy spectrum analysis),particle size analysis and other characterization methods.The effects of the addition ethylene glycerol,pyrolysis temperature,reduction temperature and time on the purity and particle size of boron carbide were investigated.The results showed that ethylene glycerol can promote the formation of polymeric precursor during the esterification reaction.The yield of polymeric precursors was biggest about 56.3% after the equimolar amounts of H3BO3 and glycerol with the addition of 20% ethylene glycerol were reacted at 150 ? for3 h.The process of low-temperature pyrolysis for preparing boron carbide was studied.Polymeric precursor was used as a raw material,and the pyrolyszed products were obtained after the polymeric precursor was pyrolyzed twice and ground twice.The results showed that the pyrolysis products had a three-dimensional bicontinuous structure composed of carbon and B2O3 components.With the increasing of the second pyrolyzed temperature,the molar ratio of free carbon and B2O3 in the pyrolyzed products decreased.The appropriate second pyrolyzed temperature was 650 ?.The process of high temperature reduction for preparing boron carbide was studied and pyrolyzed products were used as high temperature reducing raw materials.The results indicated that with the increasing of the reduction temperature and holding time,more boron carbide could be formed.Boron carbide powders were synthesized when the pyrolyzed products were heated at 1475 ? for 2.5 h under the flow of high purityAr.The purity of the synthesized boron carbide powder was about 98.29%.It was homogeneous powder with a regular hexagonal prismatic structure and the average particle size of powder was 3.089 ?m.