An Efficient Electrolytic Preparation of MAX-Phased Ti-Al-C
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TION
LAYERED ternary carbides/nitrides, represented as Mn+1AXn (where M is an early transition metal, A is a group element mostly from IIIA to VIA groups, and X is either C or N), have attracted intensive interest in the past decades because of their unusual properties.[1–8] Compared with other MAX phases, Ti3AlC2 possesses low density and excellent high-temperature resistance and is promising for applications as a structural material or coating on the surface of alloys under elevated temperatures.[9,10] Furthermore, it shows better room-temperature compressive strength than other layered compounds. Traditionally, Ti3AlC2 is regarded as a kind of mechanical material, and most studies focus on its oxidation resistance at high temperatures. Recent investigations demonstrate that Ti3AlC2 is an important JINHANG FAN, DINGDING TANG, XUHUI MAO, HUA ZHU, WEI XIAO, and DIHUA WANG are with the School of Resource and Environmental Science, Hubei International Scientific and Technological Cooperation Base of Sustainable Resource and Energy, Wuhan University, Wuhan 430072, China. Contact e-mails: [email protected], [email protected] Manuscript submitted October 15, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS B
feedstock to produce Ti3C2 and carbide-derived carbons. The derived binary carbide (Mxene) and carbon are active materials in supercapacitors and batteries.[11–19] Additionally, Ti3AlC2 shows improved activity and enhanced durability as a catalyst support for Pt in fuel cells.[20] Since Ti3AlC2 was first identified in the early 1990s, numerous synthesis techniques have been developed using various raw materials at different temperatures and pressures.[21] A brief summary of the previously reported preparation of Ti3AlC2 is shown in Table S1. As can be seen, the previously reported methods, including hot isostatic pressing (HIP), hot pressing (HP), spark plasma sintering (SPS) and combustion synthesis, generally require either high pressure (> 20 MPa) or elevated temperature (> 1473 K). Therefore, the above-mentioned techniques place a high demand on the facilities and energy. Pressureless methods, e.g., magnetron sputtering, were applied to obtain Ti3AlC2 at lower temperatures (1073 K to 1273 K).[22] However, application of the pressureless method is limited because only thin films can be deposited on substrates. Notably, almost all the previously reported methods commonly use pure metal, metal carbide, alloy or metal hydride as the starting materials. Such feedstock is generally costly. To fabricate Ti3AlC2 on a large
scale, alternative methods under less-regulated pressure and lower temperature and using cheaper precursors are of great significance and urgency. In recent years, many refractory metals and their alloys have been successfully prepared by direct electro-deoxidation of solid metal oxides in molten salts.[23–31] In addition, nano-sized binary carbides and nanostructured hollow semiconductors were also obtained without templates by this process.[32–35] Very recently, Cr2AlC with micron-size particles was
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