【作者】 白羽；

【导师】 孙树臣；

【作者基本信息】 东北大学 ， 冶金工程（专业学位）， 2021， 硕士

【摘要】 碳化硼的高硬度、低密度、高熔点、高弹性模量、热中子吸收截面高、耐酸碱、热稳定性好等优点已使其成为一种性能优异的陶瓷材料,近年来已被广泛应用于国防军工、核工业以及工业陶瓷等领域。目前,碳化硼工业上主要的制备方法是电弧炉碳热还原法,受制备方法的影响,生产的碳化硼粉末含有大量的游离碳。游离碳的存在会导致碳化硼多孔,致密性不好,还会降低碳化硼硬度和弹性极限,提高断裂几率。此外,游离碳对碳化硼的致密化动力学以及烧结产物的机械和电物理性能有着显著影响。降低碳化硼粉末中游离碳的含量,可以极大地提高碳化硼的纯度,使其在尖端领域有更广泛的运用。目前国内外关于碳化硼的除杂主要是针对铁、硅等杂质,对碳化硼中游离碳的分离还没有一个成熟的方法。本文采用电弧炉碳热还原法制备的碳化硼粉末为原料,利用激光粒度仪、X射线衍射仪(XRD)、扫描电子显微镜(SEM)、差热分析仪以及化学滴定等分析检测设备和方法,对原料碳化硼中杂质碳的物相、形貌、氧化特性以及含量进行分析,发现碳化硼中的杂质碳主要以游离的形式存在,进而确定使用反浮选和静态焙烧的方法将杂质碳与碳化硼粉体分离。采用单因素实验,研究了浮选参数(料浆浓度、捕收剂用量、起泡剂用量、浆液pH值)对反浮选去除碳化硼粉末中游离碳去除率的影响。单因素实验结果表明,最佳料浆浓度的范围为20%～30%,最佳捕收剂用量范围为400～600g/t,最佳起泡剂用量范围为150～250g/t,最佳浆液pH值范围为8～9。进一步采用正交实验,正交实验结果表明,反浮选法去除碳化硼中游离碳的最佳工艺条件为料浆浓度25%,捕收剂用量600g/t,起泡剂用量200 g/t,浆液pH值8.5。在最佳条件下重复三次实验,游离碳的百分含量从2.98%被降低至0.6%以下,碳化硼粉中游离碳的去除率最高可达80%左右,且除碳前后碳化硼粉末粒度没有显著变化,反浮选过程极大地提高了碳化硼粉体的纯度,且不引入新的杂质。研究了焙烧温度和焙烧时间对碳化硼粉末除碳率及结构特征的影响。结果表明,除碳率随着焙烧温度的升高和焙烧时间的延长而升高。碳化硼不被氧化的前提下,焙烧法去除游离碳的最佳工艺条件为焙烧温度400℃,焙烧时间3h。在该工艺条件下,碳化硼中游离碳的去除率达到32%左右。焙烧过程中碳化硼的粉末的性质没有发生明显的变化,碳化硼粉末平均粒径变化率仅为1.551%。更多还原

【Abstract】 The advantages of high hardness,low density,high melting point,high elastic modulus,high thermal neutron absorption cross section,acid and alkali resistance,and good thermal stability of boron carbide have made it a ceramic material with excellent performance.It is widely used in the fields of national defense industry,nuclear industry and industrial ceramics.At present,the main preparation method of boron carbide in the industry is the electric arc furnace carbothermal reduction method.Affected by the preparation method,the produced boron carbide powder contains a large amount of free carbon.The presence of free carbon will cause the boron carbide to be porous and poorly compact,and it will also reduce the hardness and elastic limit of the boron carbide and increase the probability of fracture.In addition,free carbon has a significant impact on the densification kinetics of boron carbide and the mechanical and electrophysical properties of the sintered product.Reducing the content of free carbon in boron carbide powder can greatly improve the purity of boron carbide,making it more widely used in cutting-edge fields.At present,the impurity removal of boron carbide at home and abroad is mainly aimed at impurities such as iron and silicon,there is no mature method for the separation of free carbon in boron carbide.In this paper,boron carbide powder prepared by electric arc furnace carbothermal reduction method is used as raw material,and analysis and detection equipment and methods such as laser particle size analyzer,X-ray diffractometer(XRD),scanning electron microscope(SEM),differential thermal analyzer,and chemical titration are used.The phase,morphology,oxidation characteristics and content of the impurity carbon in the raw material boron carbide were analyzed,and it was found that the impurity carbon in the boron carbide mainly existed in free form.Therefore,it is determined to use reverse flotation and static roasting methods to separate impurity carbon from boron carbide.Single factor experiments were used to study the influence of flotation parameters(slurry concentration,collector dosage,foaming agent dosage,slurry pH value)on the removal rate of free carbon in boron carbide powder by reverse flotation.The single factor experiment results show that the optimal slurry concentration range is 20%～30%,the optimal collector dosage range is 400～600g/t,the optimal foaming agent dosage range is 150～250g/t,the best pH value range of the slurry is 8-9.Orthogonal experiments are further used.The results indicate the slurry concentration of 25%,collector dosage of 600g/t,foaming agent dosage of 200 g/t,and slurry pH value of 8.5 were found to be the best process conditions for removing free carbon in boron carbide by reverse flotation.The experiment was repeated three times under optimal conditions.The percentage of free carbon was reduced from 2.98%to less than 0.6%.The removal rate of free carbon in boron carbide powder was up to about 80%,and the particle size of boron carbide powder before and after carbon removal was not significant changes,the reverse flotation process greatly improves the purity of boron carbide powder,and does not introduce new impurities.The effects of roasting temperature and roasting time on the carbon removal rate and structural characteristics of boron carbide powder were studied.The results show that the carbon removal rate increases with the increase of the roasting temperature and the extension of the roasting time.On the premise that the boron carbide is not oxidized,the best process conditions for the roasting method to remove free carbon in boron carbide are the roasting temperature of 400℃ and the roasting time of 3h.Under this technological condition,the removal rate of free carbon in boron carbide reaches about 32%.The properties of the boron carbide powder did not change significantly during the roasting process,and the average particle size change rate of the boron carbide powder was only 1.551%.更多还原