镁热法生产海绵钛还原过程强制散热研究

针对镁热法生产海绵钛还原过程散热慢和还原周期长的问题,采用强制散热的方法,考察了海绵钛散热量对海绵钛质量、四氯化钛加料速度和还原生产周期的影响。结果表明,强制散热是海绵钛还原中期降低反应釜壁温度、提高海绵钛质量和四氯化钛加料速度、缩短还原周期的有效方法。     

Mechanism of titanium sponge formation in the kroll reduction reactor

The Kroll process of magnesium reduction of titanium tetrachloride is used the world over the production of titanium metal in the form of sponge. Although the process has been in practice for the last five decades, there is no clear understanding of the reaction mechanism and sponge formation. The present study involved reduction experiments in a 2000 kg titanium sponge-capacity prototype reactor to develop a better understanding of TiCl₄ reduction of magnesium with respect to the process parameters. Experiments were also conducted in two smaller experimental reactors to study the temperature evolution during the process as a function of the TiCl₄ feed rate. Based on the results of all these experiments, a model has been proposed for the mechanism of sponge formation in the Kroll process.     

Preparation and properties of high-purity vanadium and V-15Cr-5Ti

A process has been developed to prepare high-purity vanadium consisting of an aluminothermic reduction of vanadium pentoxide followed by electron beam purification. The purity of the vanadium product was greater than 99.9 pct with typical total interstitials of 350 ppm, silicon content of 300 ppm, and other metallic impurities being below the limit of detection. Coldrolled, unalloyed material recrystallized fully at 980°C, with a microhardness of 60 Dph in the recrystallized condition. V-15Cr-5Ti alloy ingots were produced by arc melting, and fabricated to sheet forms. Purity of the alloy was comparable to that of the base metal. This sheet material recrystallized fully at 1050°C with a microhardness of 200 Dph in the recrystallized condition. Formerly Research Metallurgist, Wah Chang Corp.     

Contactless electrochemical reduction of titanium (II) chloride by aluminum

Because of the strong affinity between aluminum and titanium, it has not been possible to produce pure titanium by direct aluminothermic reduction of titanium chlorides. Described in this article is a new process for contactless reduction of titanium dichloride by aluminum in which titanium dichloride and the reductant (aluminum or aluminum alloy) were physically separated, but electrochemically connected through molten NaCl and an external circuit. Titanium dichloride was spontaneously reduced to metal by a cathodic reaction with the simultaneous discharge of chlorine ions into the melt. At the anode, metal aluminum was oxidized to form aluminum chloride dissolved in the molten salt. The electrons were transferred between the electrodes through the external circuit. The concentration of aluminum in titanium produced at 1223 and 1273 K varied from values below the detection limit of the X-ray fluorescence analysis (0.01 mass pct) to 4.5 mass pct. The average contamination was 0.76 mass pct Al. When an aluminum-nickel alloy was used as the reductant, nickel was not detected in the titanium obtained by reduction. This observation suggests that aluminum scrap may be used as a cheap reductant in this contactless electrochemical process.     

Precipitation of carbides in deformed vanadium

Strain aging measurements on alloys of vanadium with 0.3 at. pct carbon have been carried out over the temperature range 200°C to 500°C. The multiplicity of hardening stages char-acteristic of quench aging in this alloy is not altered by deformation. This behavior is in-terpreted as evidence that carbides nucleate in such profusion through the bulk of the metal that dislocations do not contribute an appreciable fraction of additional nucleation sites (even after 40 pct deformation). Only in the final stages of hardening does deformation in-fluence the kinetics of the process.     

Extraction of vanadium from direct acid leach solution of converter vanadium slag

Direct acid leaching of converter vanadium slag by titanium dioxide waste is eco-friendly and efficient, but with low selectivity. This novel technique can result in a vanadium solution which contains chromium(III), aluminium(III), magnesium(II), manganese(II) and high amount of iron(II) and iron(III). Bis (2-ethylhexyl) phosphoric acid (D2EHPA) and tri-butyl-phosphate (TBP) diluted with sulphonated kerosene were applied for vanadium extraction from the multi-element leach solution. The effects of the initial pH, concentration of D2EHPA, ratio of organic to aqueous phase, and the extraction time on the extraction efficiency of vanadium were investigated in saponification and unsaponifiable systems, respectively. The results showed that the vanadium extraction percentage can be up to 97% and the iron extraction percentage can be less than 10% in a thirteen-stage counter-current simulation test and the separation coefficient between vanadium and iron can reach to 109.8. Furthermore, vanadium(IV) can also be separated from other impurities such as aluminium(III), magnesium(II), manganese(II), chromium(III) efficiently. The loaded organic phase was stripped by 184?g?L^?1 sulphuric acid solution in a three-stage counter-current stripping process and with the total vanadium stripping percentage of greater than 99.5%. In the end, the vanadium pentoxide products with a purity of 99.14% were obtained.     

Synthesis of ultrafine particles of intermetallic compounds by the vapor-phase magnesium reduction of chloride mixtures: Part I. Titanium aluminides

A new chemical synthesis process for the preparation of intermetallic compounds has been developed. It involves the vapor-phase reduction of mixtures of constituent metal chlorides by magnesium vapor to produce intermetallic compounds in the form of fine powder. The advantages of the process include (a) the use of inexpensive raw materials, (b) low reaction temperatures, and (c) products in the form of fine particles. Part I describes the synthesis of titanium aluminide particles by this method, whereas Part II presents the synthesis of nickel aluminides particles. Although nickel aluminides can also be prepared by the hydrogen reduction of nickel chloride and aluminum chloride vapor mixtures, titanium aluminides cannot be produced by hydrogen reduction because of unfavorable thermodynamics. The effect of AlCl₃/TiCl₃ partial pressure ratio on the formation of different titanium aluminides was studied. A two-phase mixture containing 80 mol pct of TiAl+20 mol pct of TiAl₃ formed at an AlCl₃/TiCl₃ ratio of 10. The amount of TiAl₃ was maximized to 72 mol pct at an AlCl₃/TiCl₃ ratio of 16. The maximum conversion of the limiting chloride TiCl₃ was 94 pct. The product particles were very fine in the size range of 0.2 to 0.3 μm.     

海绵钛副产品氯化镁高温气相氧化反应器内流场的模拟研究

针对"原位热解-热法还原炼镁"海绵钛清洁生产新工艺中镁、氯循环的关键步骤——气态MgCl_2与O_2的气相热解反应的反应器进行研究。设计了2种反应器模型,并采用物理模拟和数值模拟的方法研究反应器模型内的浓度场和速度场。物理模拟中,在N_2与CO_2流量比为6∶1时,CO_2采用环向四口进气方式,此时气体混合不均匀度为0. 02,混合程度最佳;数值模拟结果和物理模拟结果相吻合。     

Electrowinning of zirconium from zirconium tetrachloride

The Bureau of Mines has produced ductile zirconium dendrites at 800°C in an electrolyte containing NaCl-NaF-ZrCl₄. Sublimed zirconium tetrachloride was fed into NaCl containing a slight excess of NaF above that required to complex 2 pct Zr as Na₂ZrF₆. The chlorine gas generated at the graphite anode during electrolysis was confined in and vented out of the cell through a high-density graphite tube into a scrubbing solution of NaOH. At a cathode current density of 300 amp per sq ft, the zirconium metal produced was 95 pct +200 mesh size. The average anode and cathode current efficiencies were 86 and 96 pct. The metal product in the form of arc-melted buttons has a hardness ranging from 130 to 170 Bhn and can be cold-rolled into 15-mil thick strips without intermediate annealing.     

Carbonitride precipitation in niobium/vanadium microalloyed steels

A detailed study of carbonitride precipitation in niobium/vanadium microalloyed steels is presented. A thermodynamic model is developed to predict the austenite/carbonitride equilibrium in the Fe−Nb-V-C-N system, using published solubility data and the Hillert/Staffansson model for stoichiometric phases. The model can be used to estimate equilibrium austenite and carbonitride compositions, and the amounts of each phase, as a function of steel composition and temperature. The model also provides a method to estimate the carbonitride solution temperatures for different steel compositions. Actual carbonitride precipitation behavior in austenite is then examined in two experimental 0.03Nb steels containing 0.05V and 0.20V, respectively. Samples were solution treated, rolled at 954°C (20 pct or 50 pct), held isothermally for times up to 10,000 seconds at 843°C, 954°C, or 1066°C, and brine quenched. The process of carbonitride precipitation in deformed austenite is followed by analytical electron microscopy (AEM) of carbon extraction replicas. Precipitates are observed at prior-austenite grain boundaries, and also within the grains (presumably at substructure introduced by the rolling deformation). Analysis of the grain-boundary and matrix precipitate compositions by AEM indicates that the grain-boundary precipitates are consistently richer in vanadium than the matrix precipitates, although compositional trends with holding time and temperature are similar for the two types of precipitates. The compositions of both the grain-boundary and matrix precipitates are not significantly influenced by the rolling reduction or the holding time at temperature. As predicted by the thermodynamic model, the precipitates become more vanadium-rich as the vanadium level in the steel is increased and as the temperature is reduced. The agreement between the measured and predicted precipitate compositions is quite good for the grain-boundary precipitates, although the matrix precipitates are consistently more niobium-rich than predicted by the model.     

Formation of aluminum-silicon alloys from feldspars—Determination of silicon,light, and heavy elements in silumin by scanning electron microscopy

Silumin has directly been deposited from feldspars by thermal reduction with aluminum metal at 1000 °C. The six analyzed samples of silumin alloys contained 10.8 to 15.3 mass pct silicon in aluminum. The amount of iron deposited was 0.17 to 0.40 mass pct, magnesium was in the range of 0 to 1.8 mass pct, and sodium was 0.35 to 0.55 mass pct. The amounts of titanium, calcium, and potassium were quite close to the detection limit for these elements, which is proposed to be 0.0 to 0.1 mass pct. The sulfur and phosphorous concentrations were too low to be measured by scanning electron microscopy. Analyses were made by scan plot and spot tests of both the aluminum matrix and silicon crystals.     

Effects of vanadium and nitrogen on recovery and recrystallization during and after hot-working some HSLA steels

The effects of vanadium/nitrogen additions on dynamic and static recovery and recrystallization have been studied in a set of aluminum-killed HSLA steels containing 0.1 pct carbon, 0.01 to 0.02 pct nitrogen, and either vanadium (0.1 or 0.2 pct), niobium (Cb) (0.03 pct), or vanadium and niobium together. Most, but not all, of the tests were carried out at 1173 K (900°C), a temperature at which precipitation of VN might be expected under some conditions. The net effect of dynamic recovery, recrystallization, and precipitation was monitored by measuring the change in compressive flow stress with strain at a constant temperature. Static changes were followed by measuring the change in compressive flow stress on isothermally holding unloaded specimens after a hot precompression. These kinetic data were supplemented by metallographic and electron-microscopic examinations of quenched specimens and of carbon extraction replicas taken from them. Evidence is presented which indicates that, at a holding temperature of 1173 K (900°C), static recrystallization occurs in vanadium steels containing 0.1 pct vanadium before any precipitation is detected. The progress of this recrystallization is arrested by the precipitation of vanadium nitride. At a higher vanadium concentration, 0.2 pct, recrystallization does not start. The effects of V/N ratio, austenitizing temperature (between 1373 K (1100°C) and 1523 K (1250°C), and isothermal holding temperature (between 1173 K (900°C) and 1273 K (1000°C)) on the kinetics of static softening and hardening are compared in some vanadium steels and plain-carbon and niobium steels of similar base-composition.     

Carbonitride precipitation in niobium/vanadium microalloyed steels

A detailed study of carbonitride precipitation in niobium/vanadium microalloyed steels is presented. A thermodynamic model is developed to predict the austenite/carbonitride equilibrium in the Fe-Nb-V-C-N system, using published solubility data and the Hillert/Staffansson model for stoichiometric phases. The model can be used to estimate equilibrium austenite and carbonitride compositions, and the amounts of each phase, as a function of steel composition and temperature. The model also provides a method to estimate the carbonitride solution temperatures for different steel compositions. Actual carbonitride precipitation behavior in austenite is then examined in two experimental 0.03Nb steels containing 0.05V and 0.20V, respectively. Samples were solution treated, rolled at 954 °C (20 pct or 50 pct), held isothermally for times up to 10,000 seconds at 843 °C, 954 °C, or 1066 °C, and brine quenched. The process of carbonitride precipitation in deformed austenite is followed by analytical electron microscopy (AEM) of carbon extraction replicas. Precipitates are. observed at prior-austenite grain boundaries, and also within the grains (presumably at substructure introduced by the rolling deformation). Analysis of the grain-boundary and matrix precipitate compositions by AEM indicates that the grain-boundary precipitates are consistently richer in vanadium than the matrix precipitates, although compositional trends with holding time and temperature are similar for the two types of precipitates. The compositions of both the grain-boundary and matrix precipitates are not significantly influenced by the rolling reduction or the holding time at temperature. As predicted by the thermodynamic model, the precipitates become more vanadium-rich as the vanadium level in the steel is increased and as the temperature is reduced. The agreement between the measured and predicted precipitate compositions is quite good for the grain-boundary precipitates, although the matrix precipitates are consistently more niobium-rich than predicted by the model.     

钛生产过程腐蚀情况及防腐蚀技术的改进措施

对钛生产过程中粗四氯化钛生产、粗四氯化钛精制、镁还原蒸馏制取海绵钛、海绵钛的后续处理、镁电解、镁精制几道工序中设备、管道存在的腐蚀情况进行了论述。针对存在的问题提出相应技术改进措施,从而提高了防腐蚀的工艺水平,延长设备使用年限,收到较好经济效果。     

Precipitation and fine structure in medium-carbon vanadium and vanadium/niobium microalloyed steels

Hot-rolled and continuously cooled, medium-carbon microalloyed steels containing 0.2 or 0.4 pct C with vanadium (0.15 pct) or vanadium (0.15 pct) plus niobium (0.04 pct) additions were investigated with light and transmission electron microscopy. Energy dispersive spectroscopy in a scanning transmission electron microscope was conducted on precipitates of the 0.4 pct C steel with vanadium and niobium additions. The vanadium steels contained fine interphase precipitates within ferrite, pearlite nodules devoid of interphase precipitates, and fine ferritic transformation twins. The vanadium plus niobium steels contained large Nb-rich precipitates, precipitates which formed in cellular arrays on deformed austenite substructure and contained about equal amounts of niobium and vanadium, and V-rich interphase precipitates. Transformation twins in the ferrite and interphase precipitates in the pearlitic ferrite were not observed in either of the steels containing both microalloying elements. Consistent with the effect of higher C concentrations on driving the microalloying precipitation reactions, substructure precipitation was much more frequently observed in the 0.4C-V-Nb steel than in the 0.2C-V-Nb steel, both in the ferritic and pearlitic regions of the microstructure. Also, superposition of interphase and substructure precipitation was more frequently observed in the high-C-V-Nb steel than in the similar low-C steel.     

Nitride inclusions in titanium ingots: A study of possible sources in the production of magnesium-reduced sponge

An experimental program is being conducted to investigate possible sources of nitride defects in the production of magnesium-reduced titanium sponge, and to determine if such defects are capable of surviving consumable-electrode arc melting. Pilot plant experiments have shown that both air-burned and nitrided sponge pieces lose their color and texture when seeded into the process during both the reduction cycle and the distillation cycle. Such defect pieces act as nuclei for sponge growth during the reduction and are often found partially or completely clad by newly-formed sponge. Simulated air leaks during both reduction and distillation cycles and the incorporation of air-contaminated magnesium have been studied. The resulting sponge has a very uneven distribution of nitrogen. Some regions show nitrogen concentration as high as 12 pct and contain є Ti₂N, or Δ TiN, or both. Alpha-stabilized inclusions have been found in ingots produced from sponge made from dross-contaminated magnesium and from sponge contaminated by air during vacuum distillation. Although the nitride in the sponge is in the form of a fine powder, powder pockets, or soft friable lumps, it is capable of surviving single and in some cases, double arc melting. A theory of the mechanism of survival of these defects is proposed.     

Preparation of Titanium Deposit in Chloride Melts

The quality of titanium depends largely on the morphology of titanium deposit, which can be affected by electrokinetic parameters during the electrolysis. To obtain titanium deposit, titanium dichloride was prepared successfully by using a titanium sponge to reduce titanium tetrachloride in NaCl-KCl. Electroanalytical methods including cyclic voltammetry, chronopotentiometry, and square wave voltammetry were employed to investigate the cathodic behavior of Ti^2 + . The results proved that the reduction of Ti(II) proceeds in a one-step, diffusion-controlled process. A series of the tests were carried out to investigate the influence of electrokinetic parameters on the titanium deposit morphology. It was concluded that the deposit titanium grain size increases with increasing titanium ion concentration. In the system with a high titanium ion concentration, the grain size also increases with increasing the current density until a certain value. However, a subsequent increase of current density results in the formation of dendrites. It was found that stirring was an effective way to avoid dendrite. A compact deposit with large grains was obtained by the electrolysis with the stirring of argon injection.     

重铬酸钾滴定法结合X射线荧光光谱法测定钒钛磁铁矿中全铁

采用重铬酸钾滴定法与X射线荧光光谱法(XRF)相结合的方法,测定了钒钛磁铁矿中的全铁,消除了重铬酸钾滴定法测定铁矿石中全铁时常受到的钒和钛的干扰。实验表明:通过溶样时加 25 mL硫磷混酸溶解样品来有效避免钛盐的水解可消除钛的干扰;除钒、钛外,其他干扰元素如铜、砷、钼等含量都非常低,在0.01 %以下,对全铁的测定无干扰;在滴加三氯化钛溶液还原二价铁时,滴加至溶液呈蓝色,即三氯化钛溶液过量1～2滴时,全铁和全部的钒一起被滴定;通过采用XRF测定钒,再将滴定法测得全铁值减去由钒转化的干扰量可计算得到钒钛磁铁矿样品中全铁的含量。采用方法对钒钛磁铁矿实际样品和由钒钛磁铁矿与分析纯五氧化二钒合成的样品进行全铁量的分析,结果与国家标准方法测定值一致,相对标准偏差(RSD,n=9)为0.13%～0.30%。     

并联式镁法海绵钛生产中降低N、O含量的有效途径

随着海绵钛市场竞争的日益激烈以及应用领域的拓展,尽最大可能提高海绵钛质量成为海绵钛生产企业当前的首要技术任务.在海绵钛质量标准中,氮,氧杂质元素较大程度地影响着海绵钛质量.根据并联式镁法海绵钛生产过程中氮、氧杂质元素的来源及其影响因素,海绵钛生产可利用真空台包出镁、氩气保护四氯化钛贮槽、适当提高还原过程中反应液面、开始...     

Electromigration of hydrogen and deuterium in vanadium and niobium by a resistance method

The electric mobility of hydrogen and deuterium has been measured at 30°C in niobium (Cb) and vanadium by a resistance method. The electric mobility was found to be 5.7 × 10⁻⁴ cm²/V-s for hydrogen and 2.8 × 10⁻⁴ for deuterium in niobium. In vanadium the electric mobilities were 2.3 × 10⁻³ and 1.3 × 10⁻³ cm²/V-s for hydrogen and deuterium respectively. The effective charges calculated using reported diffusion coefficients are positive and are slightly greater for deuterium than for hydrogen in both vanadium and niobium. The resistivity increase due to the hydrogen isotopes in vanadium and niobium was also measured. Hydrogen was found to contribute 0.65 μ ohm-cm/at, pct and deuter-ium 0.58 μ ohm−cm/at, pct to the resistivity of niobium. In vanadium, the solute resistivi-ties were found to be 0.98 μ. ohm-cm/at, pct and 0.90 μ ohm−cm/at, pct for hydrogen and deuterium respectively. C. L. JENSEN, formerly a Graduate Student, Department of Materials Science and Engineering, Iowa State University