Ti-6Al-4V alloy powder was prepared through a two-step reduction of a mixture of TiO 2 , V 2 O 5 and Al 2 O 3 in this study. The oxide mixture was first reduced by Mg in MgCl 2 at 750 °C in argon, where oxygen was reduced to 2.47 wt% from 40.02 wt%. The oxygen content in the final powder was eventually reduced to an extremely low level (0.055 wt%) using calcium at 900 °C in argon, and the final powder had the composition of 90.12 wt% Ti, 5.57 wt% Al, and 3.87 wt% V, which meets the standard specification of Ti-6Al-4V (ASTM F1108-09). Between the two reductions, a heat treatment step was designed to help controlling the specific surface area and particle size. The effect of the heat treatment temperature on the morphology, and composition uniformity of the powder was investigated in detail. Heat treatment above 1300 °C attributed to a dense powder with a controlled specific surface area. Thermodynamic modeling and experimental results indicated that only α -Ti enriched with Al and β-Ti enriched with V exist in the final powder, and other possible phases including Al-Mg and Al-V were excluded. This study also offers a triple-step thermochemical process for producing high-purity Ti-based alloy powder.
Ultra-high pure metallic zirconium powder was successfully obtained through a two-step gradient reduction of nano-ZrO 2 in Ar atmosphere. The first reduction by Mg was to remove ~ 85% oxygen, followed by a heat-treatment step to control the particle size and specific surface area of the powder, and the final reduction by calcium was to further purify the powder and decrease oxygen to an extremely low level (0.068 wt.%). The oxygen level in the final powder meets the standard specification of Zr sponge (ASTM B349/B349M-16). Processing parameters, including the reduction temperature, the amount of Mg and MgCl 2 and the heat treatment temperature, were investigated. Thermodynamic modeling with the assistance of HSC Chemistry software was carried out to understand the reduction reaction. This study offers a novel process for producing ultra-high pure metallic zirconium powder with the potential to replace the conventional Kroll process.
Leipeng Ji,Zhisong Liu,Zihao Li,Wenjun Huang,Haomiao Xu,Zan Qu,Naiqiang Yan
The gypsum from flue gas desulfurization or the neutralization (D/N gypsum) process of acid wastewater, is an industrial by-product in nonferrous metal smelters. The S and Ca sources of D/N gypsum have significant application prospects. However, the S(IV) reduction is difficult due to the electronic inactivity of CaSO 4 and the stability of the S-O band. Our experimental results indicated that the start-up temperature of CaSO 4 reduced by CH 4 is 900 ℃. However, adding H 2 S gas with a H 2 S/CaSO 4 (S/Ca) ratio of 0.2, the start-up temperature of CaSO 4 reacted with CH 4 decreases to 650 ℃. With the increase of the S/Ca ratio from 0.04 to 0.2, the yield of CaS increased to 94.97%, and the selectivity toward CO 2 formation increases to 71.67%. In-situ diffuse reflectance Fourier transformations spectroscopy (in-situ DRIFTs) results indicate that adding H 2 S generates the new sulfide groups on the surface of CaSO 4 , resulted from the S(-II) in H 2 S changing the distribution of valence electrons of O and activating O. Moreover, the density functional theory (DFT) calculation results exhibit that the activation energy for the first O dissociation decreases to 2.89 eV in the presence of H 2 S. Furthermore, H 2 S optimized the reaction path of CH 4 and improved the selectivity toward CO 2 formation. Comparing to 1000 ℃ without H 2 S, under 800 ℃ with H 2 S, the consumption of CH 4 reduces to 45%, and the CO 2 selectivity increases to 71.67%. Thus, we have developed a method of CaSO 4 low-temperature reduction and provide a theoretical basis for its application in engineering.
危险品化学品经营许可证（带存储）