【作者】 李健；

【导师】 袁铁锤；

【作者基本信息】 中南大学 ， 材料科学与工程， 2012， 硕士

【摘要】 由于高纯钛粉具有优异的抗腐蚀、吸气性、无磁性及生物相容性,使其在各行业得到广泛应用。然而,目前高纯钛粉行业发展所面临的两个瓶颈问题是：第一,如何有效降低杂质元素含量；第二,如何控制粉末粒径与形貌。本文采用熔盐电解法制备高纯钛粉,以海绵钛为阳极原料,纯钛板为阴极,NaCl-KCl为电解质,制备过程如下：升温后加入TiCl4使之与阳极海绵钛反应,在550℃形成NaCl-KCl-TiClx混合熔盐；再在700～950℃、氩气气氛下进行直流电解,在阴极获得钛粉。本文着重从钛离子价态演变、杂质含量、钛粉粒度及形貌等因素出发,进行电解机理和工艺优化研究,最终获得了氧含量低于200ppm、平均粒径60.70μm的高纯钛粉,并得出以下主要结论：1、钛离子价态变化：(1)气相室加料使熔体中钛离子价态在垂直方向上存在差异,越靠近电解槽底部钛离子的价态越低；(2)随电解时间延长,钛离子价态逐渐降低,电解前期主要以四价钛为主,后期主要以二价钛为主。2、杂质元素变化：(1)随着电解的进行,与钛电极电位相近的杂质元素Mn. V、Cr、Al的含量在电解前后变化不大,0、N、C等元素在熔盐中含量逐渐增加；(2)以Fe为代表的杂质会在预电解过程中在阴极沉积,可通过预电解脱除Fe等杂质；(3)电解钛的杂质主要存在于枝晶相交处以及晶体内部“坑道”结构中,随着离边界或者内部“坑道”距离越远,杂质含量逐渐降低。其中枝晶边界相交处的杂质元素主要为0、Fe、V、Cl。晶体内部的杂质除O、Fe、V外还夹有熔盐KC1、NaCl。3、粉末形貌与粒度：(1)靠近阴极内层的钛粉形貌为致密块状,存在一定的烧结现象,杂质含量相对较高。外层则是枝晶状,纯度高,具有明显的金属光泽。这种结构影响了单炉产量及质量；(2)电流密度和可溶钛浓度降低,可获得细颗粒钛粉。可溶钛浓度对粉末粒度的影响大于电流密度及温度影响。更多还原

【Abstract】 High purity titanium powder is widely used in various walks of life because of its excellent properties such as excellent anticorrosion, gas absorption, non-magnetism, and biocompatibility, etc. However, the high purity titanium powder industry is facing with two neck bottles:the first is how to reduce the impurity concentration effectively; the second is how to manipulate the particle shape and size.In this paper, high purity titanium powder is prepared by molten salt electrorefining with sponge titanium as the anode, pure titanium slab as the cathode, and NaCl-KCl as the electrolyte. The preparation process was conducted as follows. First, the mixed molten salt(NaCl-KCl-TiClx) was obtained at550癈by the reaction of the added TiCl4and the sponge titanium at anode without electrolysis; then titanium powder was produced on cathode by direct current electrolysis with protection of argon and temperature ranging from700～950℃. This paper optimized the process, and studied the electrolysis mechanism based on the valence transition of titanium ions, impurity concentration and particle shape and size of titanium powder. High purity titanium powder with oxygen concentration lower than200ppm, and mean particle size of60.70μm was obtained. The main conclusions are as follows:1. Valence transition of titanium ions:(1) The valence of titanium ions varies along the vertical direction of the melt because of loading in the vapor phase chamber. The titanium ions valence decreases from top to bottom in the electrolyzer.(2) The valence of titanium ion decreases as the electrolysis conducting. Ti4+dominates during the prophase while Ti2+dominates during the later stage.2. Transition of impurities:(1) The contents of impurities in the melt which have similar electrode potential with titanium, such as Mn, V, Cr, Al, will not change significantly before and after the electrolysis; with the electrolysis conducting, the elements content such as O, N, and C,etc. will increase;(2) The impurities, as represented by Fe, will precipitate previously, which can be eliminated by pre-electrolysis;(3) The impurities of electrolyzed titanium mainly exist in a "tunnel" structure of the dendrite boundary or the interior crystal. The impurity concentration decreases when it is farther away from the boundary or the internal "tunnel". The main impurities appear on the dendrite boundaries are O, Fe, V, and Cl. The impurities in the internal crystal include not only O, Fe, and V, but also molten salt such as KCl and NaCl.3. Particle shape and size:(1) the titanium powder near the inner layer of cathode has lump and dense morphology, accompanied with sintering phenomenon, and the impurity concentration is relatively high, while the titanium of outer layer is dendrite with higher purity and obvious metallic luster. This structure will affect the yield and quality of every single batch;(2) fine particle can be obtained by increasing the current density and reducing the concentration of soluble titanium. The soluble titanium concentration has a more significant effect on particle size than the current density.更多还原