Study Of Preparation And Reaction Mechanism Of High Quality Boron Carbide Prepared By New Electrothemal Metallurgy Process

Boron carbide with the excellent properties of high hardness(second only to diamond and cubic boron nitride),wear resistance,low density,great neutron absorbing performance,which is widely applied in grinding materials,engineering ceramics materials,nuclear control materials and refractory materials,etc.In recent years,with the progress of science and technology,boron carbide powder of high quality can replace expensive diamond powder as the sapphire grinding materials.Sapphire is mainly used as the bottom line of the LED and the window of the mobile phone,The rapid development of LED industry and the graduallypopularization of sapphire in the mobile phone industry makes the demand of sapphire rapid growth at a speed of more than 20%every year in recent years.The rapid development of the sapphire industry makes a surge demand for boron carbide of high quality at home and abroad.However,the production of boron carbide has some disadvantages,such as high energy consumption,low production rate and pollution,especially the productivity for boron carbideof high quality is very low.So the study of reaction process and mechanism of the preparation is of great significance for the application of new type electrothermal metallurgy preparation of boron carbide to improve the output of boron carbide of high quality and has a positive role for the development of the sapphire industry.In this paper,the research content mainly includes the following parts:(1)The dehydration process of mixtures of boric acid and carbon and its dynamics.The dehydration process and the calculation of kinetics of the dehydration process of mixtures of boric acid and carbon were studied under different conditions.(2)The study of new electrothermal metallurgical process for the preparation of boron carbide.The thermodynamics of the reaction process was calculated by FactSage software,and was validated by the experiments.The influences of reaction temperature and pressure conditions on boron carbide products were discussed.And the exploring experiments of preparation of boron carbide by new electrothermal metallurgy process were done in the laboratory.(3)The industrial experiment and practice of preparation of boron carbide were done by the new electrothermal metallurgy process.Laboratory findings were applied in the industrial test,the difference between smelting in the terms of powder and in the terms of pellets were compared in such aspects as energy consumption,yield and quality.(4)The quality of boron carbide powder prepared by new electrothermal metallurgy process was studied and evaluated.The boron carbide crystal block was processed into sapphire abrasive in a company in Yunnan Province.The purity,crystal structure,phase structure and the apparent morphology were compared with the powder prepared by the traditional methods.Through the research,the main conclusions of this paper were as follows:(1)The loss of weight,weight loss rate and the dehydration rate of mixtures of boric acid and carbon were studied at 100?,150? 200?,300?,350? and 400?.Results show that the weightlessness rate of mixtures and dehydration rate increased with the increase of temperature.The dehydration rate of the mixtures was not only fast but also the dehydration was more complete at the temperature of 350??400?,meeting the industrial dehydration requirements.Therefore,the temperature of the mixtures outside the furnace should be 350??400?.(2)The kinetics of the dehydration reaction of mixtures of boric acid and carbon was calculated by isothermal thermo-gravimetric analysis technology.The kinetic parameters of dehydration reaction were calculated using the experiment data at different temperatures.The parameters contained activation energy and pre-exponential factor,the activation energy is 30.89kJ·mol-1 the pre-exponential factor is 0.0138s-1.The results showed that mixtures of boric acid and carbon dehydrated outside the furnace were extremely easily feasible.(3)The reaction process of new electrothermal metallurgy process was calculated.The main reactions in the preparation process were calculated by the thermodynamic software of FactSage,including the dehydration of boric acid,the synthesis of boron carbide and other side reactions.The synthesis temperature of boron carbide was calculated at 1557.15?,when the temperature higher than 2469.85 ? the generated boron carbide will smelt again or decompose,the verified experiment was done.In addition,the influence of reaction temperature and pressure for reaction were studied,the results showed that:if the temperature is 1800??2200? the generation of boron carbide is fruitful,while lower the reaction pressure can reduce the synthesis temperature of boron carbide.(4)The preliminary experiment on the preparation of boron carbide by new electrothemal metallurgy process.Materials of no water as the raw material,the massive charging process for smelting,the products were mainly B13C2,the content of boron carbide was 94.36%,the quality had meet the requirement of sapphire grinding material.The superiority of new electrothermal metallurgy process had been verified.(5)The industrial experiment and practice of preparation of high quality boron carbide were done by the new electrothermal metallurgy process.Practice proved:the energy consumption of the smelting in the terms of pellets was 20500kw·h/t,the product rate of high quality boron carbide was 63%,and the content of boron carbide was 94.72%.Compared with the traditional technology,the energy consumption could reduce by 17%,productivity increased by 15%,the purity increased by 2%.The practice proved that the new electrothermal metallurgy process had the incomparable advantage compared with the traditional technology.(6)The quality of the boron carbide crystal block prepared by new electrothermal metallurgy process was researched and validated.The high quality boron carbide crystal block made of new electrothermal metallurgy process was processed into sapphire abrasive.And it was studied from the aspects of purity,crystal structure,phase structure and apparent morphology.Compared with the products prepared by the traditional smelting process,boron carbide powder prepared by new electrothermal metallurgy process had the advantages of high purity,good crystallization,good compactness.