| Description |
Titanium (Ti) metal has long been considered highly useful because of its high specific strength, high-temperature operability, corrosion resistance, and biocompatibility. Although it is one of the most abundant elements in the earth's crust, and the fourth most abundant of the structural metals, its use has been limited because of the high cost associated with its refining. The Kroll process and the vacuum arc re-melt (VAR) and forging/rolling steps that make up the wrought-processing (WP) route for commercial titanium alloy metal has been the commercial method of choice for decades, and it has been an effective approach for obtaining high-quality titanium alloy metal. Although several alternative routes have been developed over the years in an effort to bring the cost of titanium down, each of these have failed, leaving this WP method as the dominant source for primary titanium alloy metal to this day. This failure to find a cheaper production route is the primary reason for titanium's exclusion from many industries. A promising approach has emerged in the past few years called the HAMR (hydrogen assisted magnesiothermic reduction) process, where TiO2 is directly reduced under a hydrogen atmosphere and in the presence of a Mg-bearing salt. This process has the potential to eventually replace the WP route, as it uses relatively simple, scalable, low-temperature steps to produce a high-quality Ti-powder. Some technical questions have remained, however, on some core topics in the HAMR process. The first was related to purification of the TiO2 feedstock, and involved the development of a desilication step. The second main topic was more extensive and was related to the mechanisms, phase pathways, and kinetics of the first oxygen removal step in the HAMR process. This topic involved in-depth analysis of the complex Ti-H-O-Mg system during direct reduction/deoxygenation of TiO2 by Mg under a hydrogen atmosphere. A literature review was not able to answer some important questions, so parametric experiments were designed and executed, followed by analysis and discussion. In additional to investigation of these two core topics, significant research and analysis was done on the periphery to provide context, including an energy and cost analysis of the process (pursuant to commercialization of HAMR technology), as well as analysis of the leaching steps, and other scaleup issues. The combination of the investigations in the laboratory with relevant background in the literature provide a useful picture that helps expand the current scientific understanding surrounding the HAMR method for production of primary titanium powder. |
