MAX Phase Synthesis via Sol-Gel Free Radical Polymerization — 58a — Lin-Lin Elliott, Jordan Sinclair

MAX phases are an important class of materials due to their hybridization of ceramic and metallic properties. This diverse range of functionality stems from the many possible combinations of early-to-mid transition metals (M), main group elements (A), and carbon and/or nitrogen (X). MAX phases adopt a layered structure consisting of edge-shared M6X octahedra alternated with layers of the A element. The general chemical formula is Mn+1AXn. They are traditionally prepared by high-temperature solid-state methods with limited flexibility of the starting materials. Therefore, exploring other synthesis routes can allow for more sustainable formation methods of MAX phases. One such method is the sol-gel-assisted approach, which has been widely used to form metal oxides but can also be applied to metal carbides and nitrides. This wet-chemical method can also be used to access MAX phases. Since the metal ions are now in solution instead of a mixture of elemental powders, it allows for atomic-level mixing resulting in a homogeneously mixed product. Additionally, due to the carbothermal reduction when heating, the temperature and holding times are decreased. Various known MAX phases, for example Cr2GaC and V2PC , were synthesized via the sol-gel-based method. Typically, these phases were synthesized using the Amorphous Metal Complex and Polymer Type II Complex method. However, another extension to the previous techniques was found to be viable, which utilizes an ammonia-assisted free radical polymerization approach. Using this method allows for greater tunability in terms of polymer chain lengths, metal ion entrapment, concentration, and scalability. The MAX phases were characterized using analytical techniques like X-ray diffraction (XRD), scanning electronic microscopy (SEM), and thermogravimetric analysis (TG/DTA).

Arizona State University
Christina Birkel