Phase transformation and reduction kinetics during the hydrogen reduction of ilmenite concentrate

The reduction of ilmenite concentrate by hydrogen gas was investigated in the temperature range of 500 to 1200℃. The microstructure and phase transition of the reduction products were studied by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, and optical microscopy （OM）. It was found that the weight loss and iron metallization rate increased with the increase of reduction temperature and reaction time. The iron metallization rate could reach 87.5% when the sample was reduced at 1150℃ for 80 min. The final phase constituents mainly consist of Fe, M305 solid solution phase （M=Mg, Ti, and Fe）, and few titanium oxide. Microstructure analysis shows that the surfaces of the reduction products have many holes and cracks and the reactions take place from the exterior of the grain to its interior. The kinetics of reduction indicates that the rate-controlling step is diffusion process control with the activation energy of 89 kJ.mo1-1.

钛铝合金废料钇还原法熔炼脱氧

以钇为脱氧剂,采用熔炼脱氧工艺对高氧钛铝合金废料进行脱氧处理。计算脱氧反应的吉布斯自由能和平衡常数,考察钇含量和体系压力对TiAl脱氧合金氧含量的影响。结果表明,钇可以有效去除TiAl合金中的氧,脱氧后TiAl合金中的氧含量仅为原始合金废料中氧含量的10%。此外,随着钇添加量的增加,TiAl合金中氧含量降低;反应体系压力越高,TiAl脱氧合金中的氧含量越高。这些结果与理论计算值一致。脱氧合金的显微组织与原始合金的相似,但在脱氧合金的基体相中观察到Y_(2)O_(3)夹杂物。

ZrO_(2)−CaO−TiO_(2)体系的热力学模拟

ZrO_(2)−CaO−TiO_(2)体系相图对光催化材料和耐火材料的发展至关重要。采用CALPHAD方法研究ZrO_(2)−CaO−TiO_(2)体系。亚正规溶体模型用于描述液相和固溶相,亚点阵模型用于描述三元化合物。然后,结合文献实验结果,利用最小二乘法得到热力学参数。应用本研究优化的热力学参数,计算1473和1673 K下ZrO_(2)−CaO−TiO_(2)的等温截面,实验和计算的相关系吻合很好,部分不匹配的实验点误差可归结于实验误差和氧化锆基材料的动力学缓慢特性。为了进一步证实该数据库的有效性,利用该数据库模拟CaZrTi_(2)O_(7)化合物的比热容、熵和焓等热力学性能,模拟得到的误差范围在5%以内。模拟结果表明,本次优化的数据库是自洽和可靠的。

Effect of controlled rolling/controlled cooling parameters on microstructure and mechanical properties of the novel pipeline steel

The study of controlled rolling/controlled cooling process parameters which affect the microstructure and mechanical properties of a novel pipeline steel has been optimized by the orthogonal experiment with four factors and three levels in this paper. However, the parameters of thermo-mechanical control process （TMCP） optimized by the Gleeble-3500 hot simulator could not satisfy performance requirements of the X100 pipeline steel. In order to improve the performance of this steel, the influence of finish cooling temperature （FCT） on the microstructure and property is studied in detail. It is found that, as this steel is thermo-mechanically treated by this set of parameters （the start heating temperature, finish rolling temperature （FRT）, FCT and cooling rate of 1,180 ℃, 810 ℃, 350 ℃ and 35 ℃/s, respectively）, the micro- structures are mainly composed of granular bainite （GB） and acicular ferrite （AF）. The effective grain sizes are below 20 μm; the steel reaches the optimal balance between the strength and the toughness; the yield strength is 695 MPa; the tensile strength is 768 MPa; the elongation is 16.6 %; the impact energy is 262 J at room temperature. All indexes could meet the requirements of X100 pipeline steel.

Calculation of phase equilibria in Al-Fe-Mn ternary system involving three new ternary intermetallic compounds

In this study, the Al-Fe-Mn ternary system is reassessed by the CALPHAD method. Three new ternary intermetallic compounds are initially described and a rea- sonable and self-consistent set of thermodynamic parameters are established to describe this system. The 973 K, 1 073K, 1 173K, 1 273K, 1 373K, and 1 473K isothermal sections and the 1 073 K, 1 013 K, 968 K and 913 K isothermal sections at the AI corner as well as the liquidus projection at the Al corner are calculated. It is shown that the calculated results are in good agreement with almost all of the experimental results previously reported.

Multiple gaseous reduction of ilmenite: thermodynamic and experimental study

In this paper, the thermodynamics of the reduction of ilmenite using multiple gases (H2/CO) was calculated. It is found that the metallization rate of 20.1%–98.8%, H2 consumption rate of 43.0%–99.1%, and carbon deposition amount of 5.7×10?7?0.49mol can be obtained based on the conditions of hydrogen volume fraction of 10%–90% and temperature of 450–1200°C. Experimental study was also carried out using synthetic ilmenite as initial materials and reduced in a static bed reactor at 1100°C. The metallization rate reaches 97% when the multiple gas (70% H2/10% CO/20% Ar) flow rate is 120ml·min?1. A thermogravimetric analyzer was used to measure the variation of sample weight caused by the deposition of solid carbon. The amount of carbon deposited during experiments reaches its maximum while the original hydrogen volume content is 20%. The experimental results are well consistent with the thermodynamic analysis.