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Resource and production technologies for scandium
Published in Natalia Yakovleva, Edmund Nickless, Routledge Handbook of the Extractive Industries and Sustainable Development, 2022
Scandium (Sc, atomic number 21) is classified as a rare earth metal (REM), along with yttrium (Y, atomic number 39) and the lanthanides (lanthanum (La), atomic number 57 to lutetium (Lu), atomic number 71). The physical and chemical properties of scandium, its content of the Earth’s crust, and its approximate price, along with other major REMs (La, cerium (Ce), praseodymium (Pr), neodymium (Nd), and samarium (Sm)) and some selected elements (iron (Fe), aluminum (Al), and titanium (Ti)), are shown in Table 15.1 (Taylor, 1964; Barin, 1993; Japan Inst. Metals, 2004; Meija et al., 2016; Alumu Publishing, 2019; U.S. Geological Survey, 2020). Scandium metal has a low density and is chemically reactive. The scandium compounds possess unique chemical and magnetic characteristics (Daane, 1961; Iyatomi and Nanjo, 1989). Although the content of scandium in the Earth’s crust is at a similar level to other rare earth elements, the prices of scandium metal and scandium oxide are considerably higher than those of other rare earth metals and rare earth oxides.
Plasma Sprayed Ceramic Coatings
Published in Ken N. Strafford, Roger St. C. Smart, Ian Sare, Chinnia Subramanian, Surface Engineering, 2018
Similarly, the metallic substrate may oxidise at high temperatures under ceramic thermal barrier coatings because of the diffusion of oxygen through the interconnected pores, and the substrate must therefore have adequate oxidation resistance. This effect is a significant factor in the service failure of thermal barrier coatings in gas turbine applications [43]. Although oxide ceramics will withstand air and normal combustion products at high temperatures, they may suffer corrosion by impurities in the gas phase. Zirconia-yttria thermal barrier coatings, for example, may preferentially lose Y2O3 by reaction with vanadates, salt, and other contaminants, resulting in destabilisation of the structure and failure under thermal cycling conditions. The use of other stabilising oxides, such as scandium oxide, reduces this effect, but at a price [44].
Original Demonstration of Depletion-Mode and Enhancement-Mode AlGaN/GaN Heterojunction Field-Effect Transistors
Published in Hongyu Yu, Tianli Duan, Gallium Nitride Power Devices, 2017
In 2012, another E-mode HFET with a high-k dielectric scandium oxide (Sc2O3) was presented by the Massachusetts Institute of Technology and Cambridge collaboration [15]. A high-k gate dielectric layer is introduced in this HFET to reduce the invert leakage current so that the switch current ratio (ION/IOFF) can reach 108. Furthermore, the threshold voltage of the MIS-HFET can be enhanced by changing the fabricated condition of the gate dielectric by altering the ultraviolet light and surface NH4OH.
Efficient Selective Extraction of Scandium from Red Mud
Published in Mineral Processing and Extractive Metallurgy Review, 2023
Wei Ding, Shenxu Bao, Yimin Zhang, Junhui Xiao
This indicates that the decomposition order of different metal sulfates is titanium (IV) oxysulfate, aluminum sulfate, ferric sulfate, scandium sulfate, and sodium aluminum sulfate. From thermodynamic calculations, it can be known that the decomposition sequence of TiOSO4(s), Fe2(SO4)3(s), and Al2(SO4)3(s) are preferred to that of Sc2(SO4)3(s), and the decomposition reactions are all endothermic reactions. Therefore, when TiOSO4(s), Fe2(SO4)3(s), Al2(SO4)3(s), and so on, are preferentially decomposed, the decomposition of scandium sulfate will be delayed, and the initial decomposition temperature will increase. On the other hand, it is speculated that part of scandium sulfate is converted to Na3Sc(SO4)3(s) or NaSc(SO4)2(s) by reactions (6) and (7). Owing to the higher decomposition temperature of the complex sulfate, the scandium oxide is tougher to generate. Thus, the selective leaching of scandium can be achieved when the roasting temperature is within a proper range.