Determination of oxygen in chromium-aluminum and molybdenum-aluminum master alloy powder by inert gas fusion-infrared absorption method
LIU Pan1, ZHANG Xin-yao1, 2, ZHANG Yi1
1. Luoyang Ship Material Research Institute, Luoyang 471023, China; 2. Henan Key Laboratory of Technology and Application of Structural Materials for Ship and Marine Equipment, Luoyang 471023, China
Abstract：Chromium-aluminum and molybdenum-aluminum master alloys are important novel alloying agents for titanium alloy. The accurate determination of oxygen content is advantageous to the quality control of titanium alloy from the origin. (100±50)mg of sample was weighed and wrapped with a tin capsule. The analytical power was set at 5.0-5.5kW. It was determined in graphite double-crucible using standard steel sample to calibrate the instrument (the analytical power was 4.0kW). The determination method of oxygen content in chromium-aluminum and molybdenum-aluminum master alloy powder by pulse heating-inert gas fusion-infrared absorption was established. The sample mass and analytical power were optimized. The effect of flux type including tin capsule, nickel foil and nickel basket on the determination of oxygen was discussed. The results showed that the release of oxygen was greatly affected by the flux. To some extent, the nickel foil or nickel basket as a flux maybe hinder the release of oxygen in aluminum oxide, resulting in the quality risk of significantly lower and instable release rate and measurement results of oxygen in chromium-aluminum and molybdenum-aluminum master alloys. Under the selected experimental conditions, the limit of detection and limit of quantification was 0.004% and 0.012%, respectively. The quantitation scope was 0.012%-0.58%. The chromium-aluminum and molybdenum-aluminum alloy powder samples were analyzed according to the experimental method. The relative standard deviations (RSD, n=6) were less than 6%. The range was much lower than the critical tolerance calculated by 1.4 times repeatability limit, which was defined in YS/T 1075.7-2015 <Methods for chemical analysis of vanadium-aluminum and molybdenum-aluminum master alloys—Part 7: Determination of oxygen content—Inert gas fusion-infrared method>. The spiked sample was synthesized by adding aluminum oxide (Al2O3) powder, and the recoveries of oxygen in aluminum oxide were between 90% and 109%. The proposed method was appliable for the determination of oxygen content in chromium-aluminum and molybdenum-aluminum master alloy powder. It was expected to be popularized in the analysis of new aluminum-based master alloys using chromium and molybdenum as alloying element, for titanium alloy, such as aluminum-molybdenum-chromium, aluminum-molybdenum-vanadium and vanadium-aluminum-tin-chromium.
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