镁还原高钛渣直接制备钛合金粉的工艺研究

Titanium and its alloys exhibit remarkable properties, such as high specific strength, low density, strong corrosion resistance and good biocompatibility. They have been used in aerospace, chemical industry, biology and other fields; however, their high manufacturing cost restricted wider range of applications. Currently, titanium alloy products are mainly produced by titanium sponge chlorinated and reduced from titanium dioxide which originate from upgraded titania slag (UGS), and then to be refined and machined. UGS is a kind of enrichment with high content of titanium dioxide after smelting process in electric furnace, the product also contains a small amount of oxides such as oxides of Fe, Si, Cr, Al, Mn. UGS is generally used to produce titanium dioxide through sulfuric acid method or chlorination method. Sulfuric acid method has long manufacturing time and a complex process, produces titanium dioxide with poor quality, and creates serious pollution of FeSO₄ and dilute H₂SO₄ waste liquid. Meanwhile, the chlorination process of producing titanium dioxide also generates toxic and corrosive substances. In recent years, producing titanium from titanium dioxide by metal thermal reduction has become a research hotspot. The oxygen content of titanium powder reduced from titanium dioxide by metal reduction cannot meet the industrial requirements due to the difficulty of removing oxygen from Ti-O solid solution. Whereas, as presented by a previous study, Ti powder produced by the reduction of titanium dioxide trough magnesium thermal reduction in the presence of hydrogen could readily achieve the ultimately lower level of oxygen content, compared to the process which without the presence of hydrogen. The oxygen content of titanium powder produced by such method could be readily lower than 0.15% (mass fraction).The metal thermal reduction method used oxide as the precursor with no need for lengthy chlorination process and had small levels of pollution, and thus would drive crucially future research interests. Based on the shortcomings of the traditional smelting methods of UGS, considering the characteristics of UGS and the advantages of metal thermal reduction method, a new thought that preparing titanium alloy powder directly by magnesium powder reduction of titanium and other element oxides in UGS without removing metal elements was presented in this paper. A three-step process including reduction, heat treatment, and deoxidation was used to prepare low oxygen content titanium alloy powder. The UGS as raw material which from RioTinto Group was ball milled with Mg powder and then reduced in Ar and H₂ atmosphere respectively at 750 ℃. The change of elements content, especially the difference in oxygen content and phase composition of powder under different atmospheres were investigated. The reduced products were subjected to heat treatment in Ar at 900~1200 ℃ to explore the influence of heat treatment temperature on the morphology of the reduced products under different atmospheres. The results exhibited that at same temperature, the morphology of the products after heat treatment in Ar was irregular with high level of porosity, while the morphology of the products in H₂ atmosphere was dense and regular, and was less porous. Mg was used to deoxidize the heat-treated products after hydrogen reduction. The deoxidization experiment was carried out in H₂ atmosphere at 750 ℃. The results showed that the oxygen content of the products reduced by Mg in the first step in Ar and H₂ was 4.32% and 0.96%, respectively. The reduced product in H₂ was more favorable for heat treatment due to its lower oxygen content. Titanium hydride powder with 0.047% oxygen content was obtained after deep deoxidation. The main phase of the product was TiH_1.924 with a small amount of HFe₂Ti, Ti₅Si₃H_0.9 and Cr_1.8TiH_5.3, and the contents of S and P were lower than 0.001%. The reduction, heat treatment and deoxidization experiments were carried out in a tubular atmosphere furnace. This study also provided a new thought for the comprehensive utilization of high titanium slag, and provided valuable technical parameters for the preparation of titanium products.