Study of the Effects of Key Processing Parameters on the Cost and Quality of Ti-Al Powders Produced Using the TiPro Process
Sichone, K. (2015). Study of the Effects of Key Processing Parameters on the Cost and Quality of Ti-Al Powders Produced Using the TiPro Process (Thesis, Doctor of Philosophy (PhD)). University of Waikato, Hamilton, New Zealand. Retrieved from http://hdl.handle.net/10289/9476
Permanent Research Commons link: http://hdl.handle.net/10289/9476
The high cost of titanium has motivated a global drive to research and develop low-cost titanium production technologies. In New Zealand, the TiPro process has been invented at the University of Waikato. The process starts with a combustion reaction between TiO₂ and Al powders, followed by: solid/liquid separation by extrusion which separates the metal rich liquid from the Al₂O₃ solid. The metal-rich phase is subsequently purified to reduce its oxygen content to acceptable level (e.g. <0.3 wt%). The aim of this study was to establish such key relationships required to maximise the yield of Ti-Al and quality of the Ti-Al powder product. An in-depth understanding of the effects of key process parameters (e.g. heating rate, temperature, time and pressure) and starting TiO₂/Al composite powder characteristics (e.g. microstructure and compressibility) on the quality, production rate and cost of Ti-Al based powders was achieved. The solid/liquid separation step was identified to be most critical in determining the quality and cost of Ti-Al powders produced using the TiPro process. The results indicated that the microstructure of reactant powders, wetting properties of TiAl alloy on the Al₂O₃ particles, the viscosity of the liquid TiAl and the degree of saturation of the combustion product with liquid TiAl are some of the major factors in the extraction of TiAl from the combustion product using extrusion as the solid/liquid separation technique. In the current state of the invention, where the alloy is extracted by extruding the combustion product, the TiPro process is not viable due to poor yields. The throughput, alloy product purity and yield of the TiPro process are constrained by the solid/ liquid separation unit operation. When extrusion is the sole separation technique, the alloy yields are limited to only 10% of total input. This falls far below the minimum yield, (60%) that is required to make the process economically viable. Therefore, unless the solid/ liquid separation is supplemented by other separation techniques, such as froth flotation and leaching, the cost of producing titanium alloy powders by the TiPro process will be high and the quality of the alloy poor, consequently making the process uneconomical. This study has demonstrated that froth flotation can recover 65.7 wt% of TiAl content of the extrusion by-product into a 71.0 wt% TiAl grade product. This corresponds to removing 20 wt% of the total Al₂O₃ contained in the extrusion by-product (flotation feed). The potential exists to increase the TiAl grade further by multiple flotation stages. However, further work is required to investigate more suitable reagents than the HF acid that was used to activate Al₂O₃ in this study.
University of Waikato
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