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%。     

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.%)。     

镁热还原法制取金属钛的实验研究

对镁热还原二氧化钛制备金属钛反应过程进行了热力学分析,在此基础上,探索了二氧化钛"真空镁热还原-酸浸除杂"制取钛粉的新工艺.结果表明:镁还原二氕化钛在热力学上是可行的,且反应为教热反应;镁的热还原在实验条件下是压力减小的气固反应:在环境压力为10Pa～30Pa、温度为900℃～1400℃的条件下,低温利于钛粉的生成;过程中氯化钙的添加对还原影响不明显;在反应温度为900℃,反应时间为4h的条件下可得科粉状金属钛.     

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。     

原位合成TiB和TiC增强钛基复合材料热力学

根据热力学理论编程计算了钛与Ｂ４Ｃ反应的反应生成焓ΔＨ与Ｇｉｂｂｓ自由能ΔＧ以及反应式（ｘ＋５）Ｔｉ＋Ｂ４Ｃ＝ｘＴｉ＋４ＴｉＢ＋ＴｉＣ的绝热温度。计算结果表明：钛与Ｂ４Ｃ反应释放出大量热,反应能自发维持,而过量钛与Ｂ４Ｃ反应更易生成ＴｉＢ和ＴｉＣ增强体。由于钛作为稀释剂吸收热量,随着过剩钛含量的增加,反应的绝热温度逐渐下降,过剩钛完全熔解的初始温度逐渐升高。     

涂层材料对钛合金机加工石墨型铸造工艺成形质量的影响

通过在石墨铸型内表面涂敷Y₂O₃、Al₂O₃、CaZrO₃耐火氧化物涂料,研究涂层成分对纯钛铸件界面反应和表面组织性能的影响规律。结果表明：涂敷涂料能有效克服石墨铸型对铸件的激冷作用。Y₂O₃涂料与钛液无化学反应发生,稳定性最佳,仅物理粘附于铸件表面。Al₂O₃和CaZrO₃涂料均与钛液发生了界面反应,分别生成Ti-Al-O和 Ca-Ti-O的化合物,Al₂O₃反应程度尤为剧烈。涂刷涂料后钛铸件表面晶粒尺寸、粗晶层厚度和显微硬度明显增大,变化趋势均为未涂刷< Y₂O₃< CaZrO₃< Al₂O₃。     

自蔓延高温反应过程中热化学的编程计算

研究了自蔓延高温反应过程中热化学的计算问题。在建立有关热力学数据阼的基础上用FOXBASE语言编程计算了自蔓延高温反应过程中的绝热温度以及加入稀释剂后自蔓延高温反应发生所必需的最低预热温度。计算了一些常见的自蔓延高温反应的绝热温度,并将所计算的值和资料所报道的绝热温度进行了比较分析,同时示例计算绘制厂预热温度和稀释剂含量对反应绝热温度影响的曲线。利用计算结果和差热分析示例绘制丁热爆-自蔓延-普通反应合成的模式状态图。     

电解TiO2中间相的形成与溢出气体间的关系

熔盐电解TiO₂制备金属钛的过程中,钙钛矿是不可避免的中间相,这已得到国内外研究者的公认。本研究借助间断性实验,主要研究了熔盐电解TiO₂制备金属钛过程中,钙钛矿的形成与TiO₂脱氧及阳极产生气体间的关系。研究结果表明,CaCl₂熔盐中电解TiO₂制备金属钛的过程,按其脱氧进程可分为三个主要阶段。第一阶段为 TiO₂脱氧生成钛的低价氧化物,同时O_2-、熔盐Ca₂₊和未脱氧的TiO₂形成CaTiO₃。第二阶段为CaTiO₃脱氧、脱钙及钛低价氧化物继续脱氧为Ti₂O。第三阶段为Ti₂O进一步脱氧为Ti(2% O)。TiO₂脱氧量、熔盐消耗量及形成CaTiO₃量之间的摩尔比为1:1:1, 且钙钛矿形成阶段阳极只有Cl₂放出,钙钛矿形成结束后阳极放出CO₂、CO气体,无Cl₂放出。若以电解TiO₂到含2%氧的Ti[O]所消耗的时间记为100%的话,那么钙钛矿脱氧、脱钙过程约占总时间的38.9%,而钙钛矿形成的时间只占5.6%,其余时间为钛低价氧化物的脱氧过程。因此钙钛矿的形成是该工艺电流效率低的主要原因之一,钛低价氧化物深脱氧速率低是该工艺的主要限制性环节。     

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)”。     

zA62镁合金中AB_2型金属间化合物的结构稳定性与弹性性能的第一原理计算

采用基于密度泛函理论Castep和Dmol程序软件包, 计算了ZA62镁合金中AB₂型金属间化合物 MgZn₂, Mg₂Sn和MgCu₂的结构稳定性、弹性性能与电子结构. 合金形成热和结合能的计算结果显示:  Mg₂Sn具有最强的合金化形成能力, 而MgCu₂结构最稳定; 体模量(B)、弹性各向异性系数(A)、Young's模量(E)、剪切模量(G)和Poisson比(ν)的计算结果表明: MgZn₂和MgCu₂为延性相, 而Mg₂Sn为脆性相, MgZn₂的塑性最好; 采用弹性常数、体模量和结合能的经验公式计算金属间化合物的熔点, 实验值均在采用弹性常数(±300 K)和体模量(±500 K)计算熔点预测的范围内, 采用弹性常数比采用体模量和结合能预测熔点的平均相对误差小, 其中采用弹性常数计算Mg₂Sn的熔点与对应的实验值十分接近, 相对误差仅为0.31%. 不同温度下热力学性质的计算结果表明, 在298-573 K温度范围内, MgCu₂的Gibbs自由能始终最小, 其结构热稳定性最好, 结构稳定性的强弱顺序并不随温度的升高而消失; 而对MgZn₂和Mg₂Sn, 以475 K为临界, 结构稳定性的强弱顺序随温度的升高发生了变化; 态密度和Mulliken电子占据数的计算结果表明: MgCu₂ 结构最稳定的原因主要在于体系在Fermi能级以下区域成键电子存在强烈的离子键作用.     

Influence of heat treatment temperature on the electrochemical properties and corrosion behavior of RuO2-TiO2 coating in acidic chloride solution

MMO (mixed metal oxide) anodes were prepared by depositing 60RuO₂-40TiO₂ coating on titanium substrate by the thermal decomposition of Ru and Ti chloride solution. The thin oxide films were prepared at different calcination temperatures. The effect of heat treatment temperature on electrochemically active surface area was investigated by cyclic voltammetry. Stability of the mixed oxide coating during electrolysis was evaluated in 0.5 M NaCl solution using cyclic voltammetry (CV), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and potentiodynamic polarization. The changes in voltammetric charge, current density and Tafel slope of cholrine evolution reaction with time were monitored during the electrolysis. The morphology and surface composition of the oxide coated anodes before and after accelerated life test (ALT) were analyzed. Deactivation process of the oxide coated anodes was also studied. High temperature preparation of the coatings can change the deactivation mechanism and improve the anodes stability through the changes in electrochemical porosity. Based on the obtained results, different mechanisms for degradation in electro catalytic activity were discussed.     

Preparation of niobium nanoparticles by sodiothermic reduction of Nb2O5 in molten salts

Niobium nanoparticles with high purity were prepared by a sodiothermic reduction process using Nb2O5 as the raw material, LiCl, NaCl, KCl and CaCl2 as the diluents and sodium as the reducing reagent. The effects of the different molten salt systems, CaCl2 content, reaction time, excessive sodium and reaction temperature on the characteristics of the obtained niobium powder were discussed. The as-prepared niobium nanoparticles under the optimum experimental conditions were obtained by sodiothermic reduction ...     

Oxidation resistance and corrosion behavior of hot-dip aluminized coatings on commercial-purity titanium

Aluminizing is an effective method to protect alloys from oxidation and corrosion. In this article, the microstructure, morphology, phase composition of the aluminized layers and the oxide films were investigated by SEM, EDS and X-ray diffraction. The high temperature oxidation resistance and electrochemical behavior of hot dip aluminizing coatings on commercial-purity titanium had been studied by cyclic oxidation test and potentiodynamic polarization technique. The results show that the reaction between the titanium and the molten aluminum leads to form an aluminum coating which almost has the composition of the aluminum bath. After diffusion annealing at 950 °C for 6 h, the aluminum coating transformed into a composite layer, which was composed of an inner layer and an outer layer. The inner layer was identified as Ti₃Al or Ti₂Al phase, and the outer layer was TiAl₃ and Al₂O₃ phase. The cyclic oxidation treatment at 1000 °C for 51 h shows that the oxidation resistance of the diffused titanium is 13 times more than the bare titanium. And the formation of TiAl₃, θ-Al₂O₃ and compact α-Al₂O₃ at the outer layer was thought to account for the improvement of the oxidation resistance at high temperature. However, the corrosion resistance of the aluminized titanium and the diffused titanium were reduced in 3.5 wt.% NaCl solution. The corrosion resistance of the aluminized titanium was only one third of bare titanium. Moreover, the corrosion resistance of the diffused titanium was far less than bare titanium.     

废弃SCR脱硝催化剂与废NaCl盐焙烧回收催化剂中的钛、钒、钨（英文）

通过废弃选择性催化还原(SCR)脱硝催化剂与废NaCl盐焙烧,可以将催化剂中的钨和钒与钛分离。在最佳浸出条件下(焙烧温度900℃,焙烧时间3 h,废盐与废催化剂的质量比为0.5,浸出温度80℃,反应时间60 min),钨和钒的浸出率分别达到84.63%和66.42%,同时钛的损失率仅为1.3%。废NaCl盐和焙烧温度可以促进锐钛矿型TiO₂转化为金红石型TiO₂,反应后得到了金红石型TiO₂。金红石型TiO₂中的钛的价态为四价,晶格氧和化学吸附氧分别占57.26%和42.74%。该方法可以同时解决2种废弃物的处置问题。     

High temperature cyclic oxidation of aluminide layers on titanium

Aluminide layers containing TiAl₃ or TiAl on the surface were formed on titanium samples using the pack-cementation process. Cyclic oxidation (1 hr at the desired temperature and 20 min at room temperature) was carried out over the temperature range 850–1000°C. TiAl surfaces showed poor oxidation resistance compared to TiAl₃. The oxide morphology showed a peculiar protrusion formation on TiAl₃ surfaces at lower temperatures. A cross-section of the oxidized sample showed discrete Al₂O₃ and TiO₂ layers.     

Surface properties of a γ-based titanium aluminide at elevated temperatures

Nano indentation tests have been performed to investigate the mechanical properties of a gamma based titanium aluminides (Ti–48Al–2Nb–2Cr–B) at temperatures ranging from 25 to 400 °C. Indention and nano-scratch test have also been carried out after the samples were cooled down to room temperature to evaluate the effect of higher temperature exposure on the surface properties of the aluminide. The results show that the surface hardness and elastic modulus of the investigated intermetallics are higher at elevated temperatures as compared to those measured at room temperature. XPS analysis reveals that mixed oxides of TiO₂, Al₂O₃ and Nb₂O₅ have formed on the sample surface during the high temperature indentation tests. The Ti:Al ratio obtained from the integrated peak area of Ti 2p and Al 2p spectra decreases with increasing temperature and reaches a minimum value at 400 °C, indicating surface enrichment of aluminium oxide. The oxide layer formed at the higher temperature improves room temperature abrasive wear resistance of the titanium aluminide, as proved by the nano scratch test.     

Mechanism of Degradation of Titanium Alloy IMI 834 and Its Protection Under Hot Corrosion Conditions

The excellent combination of high-temperature strength and lightweight properties makes titanium-base alloys attractive for high-temperature applications in aircraft engines. However, more hot corrosion of titanium alloys is a life-limiting factor, particularly when aircraft fly at low altitudes across the sea. In the present paper, an attempt has been made to understand the degradation mechanism of titanium alloy, IMI 834 under hot corrosion conditions at elevated temperatures. The hot corrosion studies were carried out by determining weight loss at different temperatures and in salts of pure Na₂SO₄, 90% Na₂SO₄+10% NaCl and 90% Na₂SO₄+5% NaCl+5% V₂O₅. Subsequently, the rate constants were evaluated. The depth of attack due to hot corrosion was compared with oxidation data. Finally, the degradation mechanism of the titanium alloy that leads to degradation of mechanical properties in aggressive environments has been discussed and suitable coatings suggested to enhance the operational life of engines by effectively preventing both oxidation and hot corrosion.     

铝热自蔓延法制备低氧高钛铁合金及表征

以金红石、钛精矿、Al为原料采用铝热自蔓延法制备出低氧高钛铁。研究相关反应体系的热力学及动力学问题,考察配料比、熔渣类型、发热剂等对铝热自蔓延过程的影响,采用XRD,SEM以及化学分析等技术对高钛铁合金进行表征。结果表明:反应体系的绝热温度大于1800K,反应能自我维持进行;Al还原TiO2反应的表观活化能为93.676kJ.mol-1,反应级数为0.01,Al还原TiO2和Fe2O3的表观活化能为300.740kJ.mol-1,反应级数为1.20;合金主要由TiFe2、TiFe以及Fe2TiO0.13等钛铁低氧固溶体相组成,夹杂相存在是导致合金中氧含量高及微观缺陷存在的直接原因;合金中钛、铝、铁、硅含量分别为:60.0%～62%、7.0%～11.0%、21.0%～25.0%以及3.0%左右;合金中的氧被有效去除,最低为1.85%。     

Preparation of ultrafine/nano Mo particles via NaCl-assisted hydrogen reduction of different-sized MoO2 powders

The current study investigated the effects of the amount of NaCl addition, particle size of MoO₂, temperature (under isothermal condition) and heating rate (under non-isothermal condition) on the morphology, particle size and dispersivity of prepared Mo by hydrogen reduction of MoO₂. The formation of sufficient dispersed Mo nuclei and their controllable growth were crucial for transforming the large MoO₂ particles to dispersed ultrafine/nano Mo particles. It was found that in the absence of NaCl, it was hard to control the nucleation and growth of Mo grains, and the morphology and particle size of products still retain those of the raw MoO₂ in the temperature range of 840–1000 °C. However, as the amount of NaCl addition was above 0.05%, it was successful to control the nucleation and growth of Mo. Ultrafine/nano Mo powders with the average particle size from 100 nm to 800 nm were successfully prepared via adjusting the particle size of MoO₂ and temperature under isothermal condition. The use of MoO₂ with small particle sizes can increase the reaction rate and the number of Mo nuclei number, thus improve the particle dispersivity and decrease the particle size. Additionally, after reaction at 900 °C and 1000 °C, the residual Na was reduced to 140 ppm and 33 ppm from the initial value of 380 ppm, respectively. Under non-isothermal condition, the temperatures for the nucleation and growth could be adjusted by changing heating rate and particle size of raw MoO₂ particles. Mo nanoparticles with smaller particle size and better dispersivity were successfully prepared, and the average particle size can decrease to about 80 nm.     

Corrosion behavior of hydrophobic titanium oxide film pre‐treated in hydrogen peroxide solution

Hydrophobic titanium oxide (TiO₂) film formed on metallic titanium substrate in hydrogen peroxide solution with a subsequent oxidation under air atmosphere. Component, microstructure, and hydrophobicity of the oxide film were characterized by X‐ray diffraction, scanning electron microscope, and water contact angle methods. Corrosion resistance tests were carried out in seawater solution at different heating temperature conditions. Electrochemical impedance spectroscopy techniques and polarization curves were used to study the changes and the corrosion resistance of the TiO₂ film. The results demonstrate that the pre‐treated TiO₂ film heated at 400 °C environment owns small special groove‐shaped structure on its surface, which induce higher hydrophobic capability, larger impedance, and better electrochemical stability than the film that was prepared at other temperatures or the Ti with nature formed oxidation film. It would be an ideal candidate as engineering material in deep seawater environment.