制钛过程中阴极钙钛矿的形成与阳极溢出气体间的关系

采用FFC剑桥工艺在熔融CaCl₂中电解二氧化钛时,钙钛矿是阴极上不可避免形成的相。本文研究了在制备钛的过程中,阴极钙钛矿的形成与阳极释放气体的关系。结果表明,阴极上相的形成主要有三个阶段,包括钙钛矿的形成、钙钛矿的脱氧及钛的低价氧化物脱氧为TiO、和TiO到Ti的脱氧。尽管分解电压低于CaCl₂,但阴极形成的钙钛矿与从阳极释放的气体密切相关。由于短时间内钙钛矿的形成造成过电压,因而阳极释放出氯气,氯气的量取决于TiO₂和电解过程中产生的不同低价钛的量。当钛的低价氧化物介于Ti₃O₅和TiO₂之间时,在第一脱氧阶段TiO₂和氯的质量比为9：2到46：2。在氯气释放的过程中阳极没有明显的消耗。钙钛矿的形成和Ti₂O的脱氧是在熔融CaCl₂中电解制备钛的主要限制性环节。从TiO₂到Ti的总电流效率是24.07％。目前第一阶段的电流效率在22.37％~44.74％之间,第二阶段在30.18％~37.72％之间。     

熔盐电解法制备金属钛的氧空位导电机制和阴极结构的研究

熔盐电解法制备金属钛是取代高污染,高能耗的传统金属钛冶炼方法的重要工艺。但是,熔盐电解法所需时间长,效率低,是阻碍该法发展的瓶颈问题。因此,本文以提升脱氧速度为目标,首先研究了试片厚度对反应速度的影响,再配合采用量子化学方法,研究了TiO₂的导电机制。基于实验和计算结果,设计了多层阴极。多层TiO₂阴极经6 h的电解后,得到了含氧量在3 500-4 000 ppm的金属钛,且各片产物没有明显差别。相比传统的阴极制备方法,电解速度得到有效提高。并且多层阴极解决了电解速度与产量的矛盾,为熔盐电解法的工业应用提供了有益的参考。     

多级深度还原法制备Ti6Al4V合金粉体的基础研究

目前Ti6Al4V合金粉体的生产方法主要有雾化法、机械合金法和氢化脱氢法,它们都以Kroll法生产海绵钛为基础。使用钛的氧化物作为原料的熔盐电解法和金属热还原法仍处于研究阶段。本文依据变价金属Ti和V的氧化物在还原过程中逐级还原的特性,提出使用金属氧化物(TiO₂, V₂O₅)作为原料的多级深度还原法制备Ti6Al4V合金粉体的新思路。首先计算了TiO₂-V₂O₅-Mg-Ca体系的吉布斯自由能变,结果表明先进行镁热自蔓延反应,后进行钙热深度还原反应制备Ti6Al4V合金粉体在热力学上具备可行性。然后通过实验进行了的验证。镁热自蔓延反应产物酸浸后除去MgO可得到氧含量为15.84%的多孔Ti-Al-V-O前驱体。配入金属Ca后进行深度脱氧可得到低氧Ti6Al4V合金粉体(Al: 6.2wt.%, V: 3.64wt.%, O: 0.24wt.%, Mg: 0.01wt.%, Ca: < 0.01wt.%)。     

粉末冶金制备TNZS基生物材料的组织与弹性模量

采用高能球磨48h制备Ti-24Nb-4Zr-7.9Sn(TNZS)、5wt.%TiO2/TNZS及5wt.%HA/ TNZS混合粉末并进行冷压烧结,研究了三种混合粉末的形貌、物相以及冷压烧结后三种TNZS基生物材料的组织、成分、相组成、孔隙特征及弹性模量。高能球磨48h的三种混合粉末都发生机械合金化;烧结后TNZS相组成为α-Ti和β-Ti,TiO₂/TNZS相组成为α-Ti、β-Ti、金红石TiO₂和锐钛矿TiO₂,HA/TNZS相组成除α-Ti、β-Ti、HA外,还有Ti₂O、CaTiO₃、CaO和Ti_xP_y新相生成;三者孔隙率分别为2.466%、5.030%和13.027%;三者弹性模量分别为64.00 GPa、103.93 GPa和119.43 GPa。     

Fe2O3-CaO-TiO2 体系下铁酸钙的合成过程及TiO2 和CaTiO3 的影响

为了确定高钛型钒钛磁铁矿烧结过程中铁酸钙的生成是受TiO₂还是TiO₂和CaO形成的CaTiO₃影响,首先利用Fe₂O₃和CaO的纯试剂合成了铁酸钙,并研究了TiO₂和CaTiO₃对钛铁酸钙 （FCT） 形成的影响。在Factsage 7.0软件进行热力学计算的基础上,通过在空气气氛下进行烧结,获得了在1023~1423 K温度范围内、不同烧结时间的不同样品。通过X射线衍射和扫描电镜-能谱分析等表征手段,对烧结样品的物相转变和微观结构变化进行了表征。发现FCT的形成过程主要分为2个阶段：前一阶段为1023~1223 K温度范围内Fe₂O₃与CaO之间的反应,合成产物为Ca₂Fe₂O₅,反应方程式为“Fe₂O₃(s)+ 2CaO(s)= Ca₂Fe₂O₅(s)”;后一阶段为1223~1423 K温度范围内Ca₂Fe₂O₅和Fe₂O₃的反应,主要产物为CaFe₂O₄,反应为“Ca₂Fe₂O₅(s)+ Fe₂O₃(s)= 2CaFe₂O₄(s)”,该阶段尤其是温度为1423 K时,反应速率显著加快,随温度的升高CaTiO₃显著增加。然而,Ti元素在铁酸钙中的固溶很难实现,TiO₂与铁酸钙之间的反应不是形成FCT的有效途径。随着保温时间的延长,CaTiO₃和FCT相界中Fe元素含量增加。FCT主要是通过Fe组分在CaTiO₃中固溶形成的,主要反应是“Fe₂O₃+CaTiO₃(s)=FCT(s)”。     

熔盐电解制备低成本Ti12LC钛合金的研究

采用熔盐电解法由混合氧化物成功制备出了低成本Ti12LC合金,并对脱氧过程机理进行分析。结果显示:脱氧反应过程首先生成CaTiO3、低价氧化物Ti6O、Ti2O和Ca2Al2O5;其次随脱氧时间的进行钛的低价氧化物含量逐步增加,再其次出现金属钼,最后生成Ti12LC合金相。由于MoO2的理论电压低于TiO2、Al2O3,因此钼优先还原,且钼在-Ti中能固溶,所以最终钼是以固溶体形式存在于钛中,而Fe2O3虽然理论分解电位更低,但由于含量低,而没有检测到铁的单质还原。通过对电解产物表面的背散射电子像分析,发现电解制备出的产物其形貌和Ti12LC合金的组织相似。     

电化学还原TiO2制备金属钛及反应过程的研究

采用熔盐电解法,在900℃熔盐CaCl2中以烧结TiO2为阴极,石墨棒为阳极制备出了金属钛.研究了不同温度下烧结阴极的形貌及其对电解反应的影响.结果表明：600℃下烧结4 h的阴极具有良好电化学反应性能;电解过程中脱氧速度不均匀;TiO2电极的还原是由外向内,由高价向低价再到金属分步进行的;电解还原过程电流效率低约为15%.阴极的孔隙大小和颗粒尺寸会影响电极的反应速度.     

CoCrFeNi高熵合金在金属氧化物熔盐电脱氧中的形成过程

在1173 K下将金属氧化物在CaCl₂熔盐中进行电脱氧,制备了CoCrFeNi高熵合金。通过X射线衍射（XRD）、扫描电子显微镜（SEM）和能量色散X射线能谱（EDS）研究了不同电解时间下金属氧化物转化为高熵合金的相变过程。结果表明,CoCrFeNi高熵合金的形成过程包括快速脱氧和深度脱氧2个阶段。在快速脱氧阶段,在1 h内去除了烧结氧化物球团中93.93%（质量分数）的氧,电流效率达到89.95%。电解结束后,产物的氧含量可达0.26%（质量分数）,电流效率为17.93%。该高熵合金的形成过程可用于指导建立低成本、高效率的电化学路线。     

多级还原制备钛粉的初级还原机制与配镁量作用规律

目前,Kroll法仍是金属钛生产的唯一工业化方法,新开发的电解法和金属热还原法均处于研究阶段。本文针对多级还原制备钛粉进行了初级还原阶段还原机制与配镁量作用规律的研究。通过分析及结果验证,提高配镁量可促进反应进行的动力学,有利于TiO₂还原程度的提升并抑制镁杂质残留,镁在初级还原过程中多以流体形式包裹在二氧化钛颗粒表面进行传质形成多相微球,钛氧化物则受高温作用发生烧结形成孔隙网络结构的产物形貌。在考虑镁的利用率及实际深度还原产物品质的基础上,实验确定化学计量比为最佳配料比。该配比的初级还原产物氧含量可达16.04wt%,比表面积和中位粒度分别为1.76m^₂/g和 34.39μm,制备的钛粉O、Mg含量分别为0.274wt%和0.010wt%。     

空气气氛下碳热还原筛分法制备Magnéli相Ti n O2 n -1

介绍了一种在空气气氛中通过碳热还原筛分法制备Magnéli相（Ti_nO_2n-1，4＜n＜10）低价钛氧化物的方法，研究了还原温度和还原时间对还原产物的物相、电阻率的影响。结果表明，提高还原温度和延长还原时间有利于将TiO₂还原为Magnéli相Ti_nO_2n-1。将Magnéli相Ti_nO_2n-1 (n=4，5) 粉末在1350 ℃下干燥20 min，通过扫描电子显微镜观察，其粒径为0.5~8 μm。在还原温度为1350 ℃时，还原产物的电阻率随还原时间的延长而显著降低。在1350 ℃下还原50 min的产物的电阻率最小，为79.3 Ω?cm，其物相组成几乎全部为Ti₃O₅。     

Electrolytic Production of Ti<Subscript>5</Subscript>Si<Subscript>3</Subscript>/TiC Composites by Solid Oxide Membrane Technology

This paper investigated the electrolytic production of Ti₅Si₃/TiC composites from TiO₂/SiO₂/C in molten CaCl₂. The solid-oxide oxygen-ion-conducting membrane tube filled with carbon-saturated liquid tin was served as the anode, and the pressed spherical TiO₂/SiO₂/C pellet was used as the cathode. The electrochemical reduction process was carried out at 1273 K and 3.8 V. The characteristics of the obtained cathode products and the reaction mechanism of the electroreduction process were studied by a series of time-dependent electroreduction experiments. It was found that the electroreduction process generally proceeds through the following steps: TiO₂/SiO₂/C → Ti₂O₃, CaTiO₃, Ca₂SiO₄, SiC → Ti₅Si₃, TiC. The morphology observation and the elemental distribution analysis indicate that the reaction routes for Ti₅Si₃ and TiC products are independent during the electroreduction process.     

Effect of reacted compounds in Al2O3+Ti investment mold on alpha-case formation for Ti casting

This paper proposes a newly developed alpha-case controlled mold material for Ti castings. An Al₂O₃ mold containing alpha-case reaction compounds, titanium oxide (TiO₂, Ti₂O and Ti₆O) and titanium silicide (Ti₅Si₃) was manufactured via a reaction between Al₂O₃ and Ti powder under different firing conditions in air and a vacuum. In comparison with the Al₂O₃ and Al₂O₃+Ti mold fired in a vacuum, the micro-Vickers hardness and nano indentation profiles of Al₂O₃+Ti indicated that the alpha-case thickness was significantly reduced from 350 μm to ～45 μm. The alpha-case formation in the Al₂O₃+Ti mold was reduced due to the presence of TiO₂, which formed the TiO intermediate phase that acted as a diffusion barrier. In addition, Ti₅Si₃ was effective in minimizing Si contamination at the casting surface due to the reaction between Ti and the colloidal SiO₂ binder. Therefore, alpha-case reaction compounds, such as TiO₂ and Ti₅Si₃ in Al₂O₃, can effectively reduce alpha-case formation at the casting surface.     

Formation behavior of CaTiO<Subscript>3</Subscript> during electrochemical deoxidation of ilmenite concentrate to prepare Fe–Ti alloy

The formation behavior of CaTiO₃ during electro-deoxidization of ilmenite concentrate to prepare Fe–Ti alloy was investigated by experiments and simulation. The results indicate that the formation and decomposition of intermediate products, CaTiO₃, are inevitable steps during electro-deoxidization of ilmenite concentrate. CaTiO₃ can be generated through the hydrolyzation of molten salt and electrochemistry reaction during electrochemical process. The main reason for the generation of CaTiO₃ is the electrochemistry reaction between Ca²⁺ from molten salt and TiO₂ in the cathode. With the proceeding of the electro-deoxidization, CaTiO₃ is further electrolyzed to form titanium sub-oxide. The current efficiency can be improved when CaTiO₃ forms in the cathode by adding CaCO₃ during sintering process.     

Impact of supporting electrolytes on the stability of TiO<Subscript>2</Subscript>–Ti counter electrode during H<Subscript>2</Subscript>O<Subscript>2</Subscript> electrogeneration

This work focuses on the role of common supporting electrolytes (SEs) in the electro-chemical inertness of Ti-based materials employed for the anodic (direct) oxidation coupled with H₂O₂ electro-generation at the graphite cathode for the concurrent decomposition of organic contaminants. SEs are added to boost up the ionic conductivity of solution but a question always remains on the effect of SEs on the stability of anode materials. The use of ClO ₄ ^? is encouraged in the electro-Fenton process as it does not form complexes with Fe²⁺/Fe³⁺; however, it is found that ClO ₄ ^? corroded the TiO₂ coated Ti (TiO₂–Ti) anode very fast (>60 min) and, Ti⁴⁺ ions formed a yellow color complex (λ_max = 380 nm) with H₂O₂. The influence of Cl^–, NO ₃ ^? and SO ₄ ^2? was insignificant on the stability of TiO₂–Ti. The cell current efficiency of H₂O₂ formation dropped sharply with in the case of TiO₂–Ti anode. The TiO₂–Ti corrosion also reduced the mass transfer co-efficient of DO transport from bulk to the cathode surface because of Ti⁴⁺ adsorption on graphite.     

Thermodynamics of titanium,nitrogen, and oxygen in liquid alloy steels

The thermodynamics of Ti, N, and O in liquid iron was studied in order to establish a database to predict the TiN and TiO_x formation in liquid steels as a function of temperature. The interaction parameters between Ti, N, and O in liquid iron and the equilibrium constants for the formation of TiN, Ti₂O₃, and Ti₃O₅ in liquid iron were determined as a function of temperature. Formerly Graduate Student, Department of Metallurgical and Materials Engineering, Hanyang University, Gyeonggi, 426–791, Korea.     

Reaction behavior and mechanism of anatase in digestion process of diasporic bauxite

Based on the study of influence of temperature, digestion time, amount of CaO added and composition of aluminate solution on reaction behavior of pure anatase in high-pressure digestion process of bauxite, reaction mechanism of anatase was preliminarily determined. Anatase first reacts with caustic soda to produce Na2TiO3, then the resultant Na2TiO3 reacts with 3CaO·Al2O3·6H2O resulting from the reaction of CaO with sodium aluminate solution to produce CaO·2TiO2·H2O which eventually converts into CaTiO3. Higher temperature, concentration of free Na2Ok (the caustic soda uncombined with aluminate anions in the form of Na2O) and molar ratio of CaO to TiO2 are favorable to the conversion of CaO·2TiO2·H2O to CaTiO3. And Al(OH)4- shows the function of a catalyzer in the reaction of anatase with caustic soda with or without CaO added during the digestion process of diasporic bauxite.     

Powder metallurgical processing of Ni–Ti–Zr alloys undergoing martensitic transformation: part I

Ni–Ti–Zr materials with Zr 12–25 at.% and Ni 42–50 at.% have been produced by powder metallurgy. Suitable temperatures for sintering in Ar-atmosphere Ni–Ti–Zr compacts are within the range 900–1000 °C. Sintering at temperatures above 1000 °C causes melting of the compacts with high Zr content. The presence of ZrC, ZrO₂, Zr₃O, TiO₂ and TiO of different modifications, complex oxides such as Ni₅TiO₇, Ti_0.5Zr_0.5O_0.2 and equilibrium phases after sintering at temperatures above 1000 °C in alloys with low Zr-content was derived from X-ray diffractometry. During sintering at temperatures below 1000 °C the phases belonging to the binary Ti–Ni and Ti–Zr systems were formed. Long-term sintering and slow furnace cooling allowed the precipitation of Ni₄Ti₃ and Ni₂Ti. The process of sintering is controlled by the diffusion of Ni in Ti and Zr particles during the early stages of sintering. Slow diffusion of Zr atoms in Ti₂Ni, Ti–Ni and diffusion of Ti atoms in Zr₂Ni, Ni–Zr controls the later stages of sintering.     

The properties of electroactive ruthenium oxide coatings supported by titanium-based ternary carbides

Electroactive oxide coatings on titanium, known in industrial chlorine production as dimensionally stable anodes (DSA), are of limited service life owing to the dissolution of active oxide, but also due to low corrosion stability of titanium, at high anodic potentials and elevated temperatures. In order to improve the anode stability, ternary carbide, Ti₃SiC₂, could be a promising material for the coating support, since chemical corrosion stability of Ti₃SiC₂ is significantly higher if compared to Ti. In this work, the possibility of the sol-gel preparation of RuO₂-TiO₂ coating on Ti₃SiC₂ is investigated and comparison of the basic characteristics of sol-gel processed oxide coating, Ru_0.5Ti_0.5O₂, applied onto Ti₃SiC₂ and Ti, is reported. Microscopic investigation of the coating surface showed that considerably less cracked coating is formed onto the Ti₃SiC₂ support. Slightly higher voltammetric currents are registered for Ti₃SiC₂-supported coating in H₂SO₄ and NaCl solution. The activity for chlorine evolution is higher, while the currents of oxygen evolution reaction are lower for Ru_0.5Ti_0.5O₂/Ti₃SiC₂ anode in comparison to Ru_0.5Ti_0.5O₂/Ti anode. Even though these preliminary results on the basic electrochemical properties of Ru_0.5Ti_0.5O₂/Ti₃SiC₂ anode and chemical stability of Ti₃SiC₂ are promising, the accelerated stability test in NaCl solution showed that coated Ti₃SiC₂ is not anodically stable and lasts considerably shorter than Ru_0.5Ti_0.5O₂/Ti anode prepared and tested under the same conditions.     

Über die Oxidschichtbildung einer Titanlegierung während einer Li2O-haltigen Schutzgasbehandlung bei hohen Temperaturen

Oxide layer formation on a titanium alloy during a high temperature treatment in protective gas containing Li₂O The adhesion of an oxide scale can be improved considerably by the incorporation of Li₂O in the lattice of the growing scale. The oxide layer on Ti alloys generally consists of three zones, an external TiO₂, an intermediate Ti₂O₃ and an internal TiO zone. When, however, the oxidizing gas contains Li₂O, only two layers can be identified, viz. an internal TiO₂ layer (1/8 of the total oxide thickness) and an external Li₂TiO₃ layer. The latter is responsible for the good adhesion; it is obtained primarily in combustion gases obtained by near stoichiometric combustion of natural gas. In gases obtained by sub-stoichiometric combustion TiO₂ is formed perferentially and the adhesion of the oxide layer is low