Increasing Synthesis Efficiency of Monometallic Carbides to Near Stoichmetric Ratios

Carbides are a combination of metal and carbon atoms that form a solid solution. Early transition metals form a specific type of carbide known as interstitials. They are of interest due to their unique physical properties; high melting points, resistant to acid, high potential degradation, and carbon monoxide poisoning, they are also catalytically active. There are many methods for synthesizing carbides, however most require high temperatures, long times, or high pressure to form, causing large particle sizes, not conducive for good catalytic activity. Catalysts are ideally small particle sizes giving high surface area for better catalytic activity. A salt flux synthesis method was employed to reduce the temperatures at which these carbides are synthesized providing a pathway for nano-sized particles. Some of these carbides such as chromium, molybdenum, and tungsten also require an excess of carbon which could potentially inhibit the activity as a catalyst. The procedure in making these carbides was adjusted to determine an optimal way to synthesize them in a stoichiometric ratio. Changing the parameters of temperature, annealing time, type of salt flux, and type of sample holder used during the reaction provided ways of bringing the ratios of metal to carbon down to stoichiometric. X-ray diffraction (XRD) was used for phase identification and structure determination of the carbides synthesized. Scanning electron microscopy (SEM) was used to see the morphology and composition of the carbides.