钛铁矿（FeTiO3）粉末的氧化过程中的物相转变、微观形貌及其氧化机制

探讨钛铁矿氧化过程中的物相转化、形貌改变及其氧化机理。在700~800°C时,钛铁矿(FeTiO3)转变为赤铁矿(Fe2O3)和金红石(TiO2),当温度高于900°C时,三价铁板钛矿开始形成。原始的钛铁矿粉末呈现顺磁性,但是经过中温(800~850°C)氧化后,氧化产物呈现弱铁磁性。同时,讨论钛铁矿的氧化机理。通过对微结构的观察,发现在中温氧化过程中颗粒表面出现大量微孔,其在氧化过程中能够强化氧的传质。     

High-temperature oxidation of titanium-hydride powders

The oxidation kinetics of titanium-hydride powders were studied in the temperature range of 298–1378 K in air at atmospheric pressure. DTA, DSC, X-ray analysis, and scanning electron microscopy were used. Oxidation was found to take place by TiH_xO_y oxyhydride phases formation. The oxidation reaction rate at temperatures above 870 K was limited by diffusion of oxygen atoms through a rutile scale formed on the surface. The activation energy and preexponential values of the Arrhenius equation for different interaction stages as well as transformation enthalpies were calculated.     

Reduction mechanism of natural ilmenite with graphite

Reduction of Bama ilmenite concentrate containing 49.78% TiO2 and 27.96% total Fe by graphite was studied using thermogravimetric analysis system under argon gas ambient from 850 to 1 400 ℃. The reduction degree of Bama ilmenite is enhanced with increasing temperature and the molar ratio of carbon to oxygen, and the reaction rate varies with temperature and reduction time simultaneously. The phase transformation, chemical composition, microstructure and morphology of reduced samples were investigated by using X-ray diffractometry, scanning electron microscopy, and energy disperse spectroscopy, respectively. The high content of impurities in Bama ilmenite evidently bates the reduction of ilmenite. Forming the enrichment zone of manganese prevents complete reduction of Fe^2＋. The reduction products are mostly reduced iron, rutile, reduced rutiles, Ti3O5 and pseudobrookite solid solution. The reduction kinetics was also discussed. The results show that the reduction temperature is a key factor to control reaction rate.     

Kinetics on oxidation process of MgAlON spinel

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添加剂Na2CO3对钛精矿碳热还原的影响

研究添加不同含量的Na2CO3对钛精矿强化还原机理和动力学的影响,以不同的升温速率进行还原过程,并采用Starink方法研究其动力学.结果表明:Na2CO3的加入强化还原效果,并通过以反应物的形式增加其活性来降低还原反应的初始温度和表观活化能;然而,Na2CO3的加入会形成熔融相恶化还原后期的动力学条件,从而降低还原后...     

钛精矿的微波干燥特性及动力学

研究微波功率及物料量对钛精矿微波干燥的含水率、脱水速率、水分比等干燥特性的影响.实验微波功率范围为119～700 W,物料量为5～25 g.不同的干燥条件下干燥过程均延续2～8 min.研究发现微波功率密度对含水率和干燥速率的影响较大,所有干燥过程都有一个明显的特征,即在初始阶段有加速干燥峰.固定物料量为25 g和微波...     

Kinetics of high-temperature oxidation of boron carbide in oxygen

Thermogravimetry and gas-adsorption chromatography were used to study the kinetics of formation of solid and gaseous products during the hightemperature oxidation of compact boron carbide in oxygen at 740 Torr. Oxidation resistance was observed at temperatures up to 1200°C. The main oxidation products were B₂O₃ and CO₂. Oxidation was paralinear; the carbon consumption exceeded the consumption of boron as compared to the ratio of these elements in the compound B₄C. This difference resulted in carbon depletion of the carbide layer in the substrate near the scale>.     

High-temperature oxidation of pure titanium in CO2 and Ar-10%CO2 atmospheres

The oxidation behavior of pure titanium has been investigated in the temperature range of 1000 K to 1300 K in CO₂ or Ar-10%CO₂. Optical microscopy, electron probe microanalyses, and X-ray measurements on the oxide scales formed during oxidation indicate that their structures are nearly independent of temperature and the corrosion atmosphere. The scales consisted of two layers, an external one and an internal one, having a rutile (TiO₂) structure. The parabolic rate law was confirmed for growth of the external scale and the permeation depth of oxygen in titanium with apparent activation energies of 266 and 226 kJ/mol, respectively. The rate-determining diffusion species in the oxidation processes are discussed.     

不同颗粒尺寸辉钼矿的氧化焙烧动力学

通过差热?热重实验和非等温分析法研究辉钼精矿的氧化焙烧动力学.结果表明:高温焙烧有利于辉钼矿的氧化,其初始氧化温度为450℃,500℃以上时迅速氧化.氧化过程符合未反应收缩核模型.氧化初期受化学反应控制,其表观活化能为123.180 kJ/mol;后期受内扩散控制,表观活化能为80.175 kJ/mol.整个氧化过程中...     

Kinetics of oxidation of ferrous alloys by super-heated steam

The kinetics of the oxidation of ferrous alloys in steam (10–60 kPa) at 450–550°C have been studied by measuring both the rate of hydrogen emission and the amount of metal oxidized. Excellent agreement has been found between the amount of metal oxidized calculated from both the total mass of hydrogen produced in the reaction and the thickness of the oxide layer formed; rate constants calculated from the rate of hydrogen emission, the mass of hydrogen produced as the reaction proceeds, and the oxide formed agree within experimental error. The rate of oxidation of a 9%Cr-1%Mo alloy at 501°C was found to be independent of the partial pressure of the steam. For this alloy, the activation energy agreed with literature values obtained at higher temperatures and pressures. The effect of the chromium and silicon content on the oxidation rates is compared. The rate constants are compared with theoretical calculations, assuming that the rate is determined by diffusion of iron in the magnetite lattice. For the 9%Cr-1%Mo alloy, the parabolic rate constant and activation energy are in excellent agreement with values calculated using Wagner's theory. The experimental rate constants are greater for the alloys containing smaller amounts of chromium; diffusion of iron along magnetite grain boundaries may be the dominant mechanism.     

熔融镍渣等温氧化动力学研究

研究了富铁熔融镍渣在空气气氛下的等温氧化动力学行为。利用高温激光共聚焦显微镜(HT-CLSM)确定三元碱度0.6调质镍渣的实际熔融温度(液相线温度)为1488℃。通过管式炉等温氧化试验,获取温度1500～1575℃下熔融镍渣氧化过程Fe²⁺浓度-时间曲线,采用微分法和Arrhenius方程计算出熔渣中Fe²⁺的氧化反应级数为1.45～1.26,表观活化能为286.83 k J/mol,明确熔融镍渣氧化动力学主要受扩散传质控速。基于双膜理论和渗透理论,估算出1500～1575℃熔渣中氧的扩散系数分别为2.02×10^-9～4.42×10^-9 m²/s和0.50×10^-9～2.19×10^-9 m²/s,双膜理论估算出的氧扩散系数更具参考意义。     

钛铁矿的微波辅助磨细试验研究

试验以攀枝花钛铁矿为原料,于微波高温箱式炉内,在1kW～3kW微波功率和不同加热时间内进行加热处理,然后水淬骤冷,利用SEM研究了微波加热对矿石内部产生裂纹的影响,并通过磨矿试验说明这些裂纹对矿石易磨性的影响.结果表明,该矿石在2分钟内可以被微波加热至400℃以上,能有效吸收微波能量.在1kW,2.45GHz微波下加热30s,然后进行水淬处理,通过SEM检测发现在矿石内部有用矿物和脉石晶拉边界上产生了裂隙.随后,不同粒度样品在微波处理后进行了磨矿试验,样品粒度为25mm的矿石在磨矿后其产品中-200目含量由原矿的66%提高至94%,证明微波加热产生的裂隙使得矿物更易于磨细.     

High-temperature oxidation of titanium diboride of different purity

Oxidation in air of TiB₂ powders of two different types in the temperature range from 100 to 900°C as well as of compact samples produced from them (at 600–1200°C) was studied by DTA, thermogravimetry, X-ray analysis, AES, EPMA, and SEM methods. The admixture elements in powders were found to prevent oxygen from enriching the diboride surface. In compact TiB₂ samples impurities form diffusion barriers during oxidation at the matrix/scale and scale/gas interfaces as well as facilitate sintering of the scale being formed.     

High-temperature oxidation under time-dependent gas pressure: An application to steel oxidation

A study on the high-temperature growth of thick wustite films on low-carbon steel under a time-dependent oxygen partial pressure law is reported. The experimental data were interpreted using a general formulation of oxidation under non-time-constant gas activity. Good agreement between the theory and the experimental data was obtained. The physical reasons that justify the change of the oxygen activity at the steel-atmosphere interface as observed during the oxidation process are discussed also.     

微波辅助磨碎钛铁矿

研究微波加热对攀枝花钛铁矿磨矿性能的影响。微波辐射时间、微波功率密度和样品质量是磨矿过程的重要参数。将40g样品在微波功率1kW下辐射30s,然后进行水淬处理。SEM分析结果表明：经过微波辐射处理的钛铁矿在有用矿物和脉石间产生了裂纹,能够有效地促进矿物与脉石的解离。在随后的磁选实验中,经过微波辐射处理的钛铁矿的回收率从44%提高到72%。     

水玻璃在钛铁矿浮选中的作用

研究水玻璃对微细粒钛铁矿、钛辉石的抑制与分散性能,并通过动电位测定和红外光谱分析探讨其作用机理。结果表明:在pH=5.5～7.0的弱酸性环境下,水玻璃对钛铁矿与钛辉石的抑制表现出良好的选择性,这是因为水玻璃与钛辉石间的强烈作用阻碍油酸钠在钛辉石表面的吸附,起到抑制作用。红外光谱分析表明:水玻璃与钛辉石发生化学吸附,而在钛铁矿表面吸附较弱;在弱酸性条件下,由于钛铁矿与钛辉石表面带异相电荷而容易发生异相凝聚,添加水玻璃使二者表面电位均显负电性,矿粒间静电斥力迅速增大,从而减弱矿粒间的异相凝聚。     

Oxidation of titanium nitride in oxygen: Behavior of TiN0.83 and TiN0.79 plates

The oxidation of 0.13 mm thick TiN_0.83 plates between 850 and 1005°C and 0.38 mm thick TiN_0.79 plates between 890 and 1220°C was studied at oxygen pressures in the range 15–600 Torr. The oxidation behavior of the first compound, TiN_0.83, was found to be very close to that recently described for the nitride TiN_0.91. There was formation of a rutile scale with a layered structure and the kinetics were quasilinear for conversion degrees 0.25<<0.9. By applying a pseudolinear oxidation model involving a diffusion regime through a scale of variable thickness, it was found that the activation energy of the limiting process, i.e., the diffusion of the reactants through the inner growing layer, was 43 kcal/mole. The second compound, TiN_0.79, showed a slightly better oxidation resistance. The irregular kinetic curves obtained (mainly above 1000°C) were associated with sintering and grain growth in the oxide starting at the outer surface of the scale and gave indirect information on the pressure dependence of the linear oxidation of nitrides TiN_0.83 and TiN_0.91.     

尼日利亚钛铁矿的矿物学特征和浸出行为

研究尼日利亚钛铁矿矿物学特征和经机械活化和碱性焙烧处理后的浸出行为。研究了 NaOH/矿石比、H2SO4浓度、浸出和焙烧温度对钛回收率的影响。结果表明,机械活化对钛铁矿石的浸出有明显的增强作用。钛铁矿经机械活化后,加入60%NaOH在850°C下焙烧,在温度为90°C,经60%H2SO4浸出4 h下的浸出率为72%。对焙烧矿、水处理后残渣和酸浸滤渣的XRD物相分析证实了反应机理和实验结果。     

High-temperature oxidation of titanium carbide in oxygen

The kinetics of titanium carbide oxidation in oxygen over the temperature range of 600–1200°C and oxygen pressure from 0.1 to 740 Torr have been studied with a vacuum microbalance. Layer-by-layer x-ray analysis, petrography, metallography, and gas chromatography have been used to analyze the oxidation products. A paralinear nature of the oxidation of material was established, and the rate constants of the process were calculated for the corresponding parabolic and linear portions of the kinetic curves. It was shown that a gaseous product, CO₂, formed, as well as a solid product, TiO₂ (rutile), both stoichiometric and nonstoichiometric. The lower oxides, Ti₃O₅, Ti₂O₃, TiO, were noted in the scale at temperatures from 700 to 800° and low oxygen pressures, their relative quantity rising with decreasing pressure. Based on x-ray analysis and microhardness measurements, it was concluded that titanium oxicarbides formed in the TiC, directly adjacent to the scale. A possible oxidation mechanism of titanium carbide is proposed.     

High-temperature oxidation of zirconium-hydride powders

The oxidation kinetics of zirconium-hydride powders were studied in the temperature range of 298–1378 in air at atmospheric pressure. TG, DTA, DSC, x-ray analysis, and scanning electron microscopy were used. The results obtained are in accordance with the proposed pseudo-parabolic model of zirconium-hydride oxidation. This model includes the initial linear mode of oxide growth with oxygen diffusion through a non-solid film of ZrO₂ of variable depth and a stationary diffusion process followed by oxide sintering. It has been established that the activation energy of the limiting stage of oxidation (238.3 kJ/mol) coincides with the activation energy of oxygen self-diffusion in monocline ZrO₂.