Synthesis of Tungsten Carbide
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Tungsten is a rare element and the supply is limited. It has some unique properties,such as very high density, very high melting point, high electrical conductivity, high tensilestrength and hardness, and it is a part of the tungsten carbide/cobalt composite, which iswidely used for mining and drilling equipment.In this study several different samples were prepared in attempt to achieve a tungstencarbide coating on alpha silicon carbide support. The Pechini method with a 50wt% loadingof W, with ammonium metatungstate as W precursor, was used to coat the α-SiC support, andsubsequent drying, calcination and carburization were performed. Various carburizationschedules in CH4/H2 gas mixtures were used to form tungsten carbides. Some of the sampleswere impregnated with nickel or copper at the different stages of the synthesis process.Analysis of XRD spectra after carburization showed formation of different tungsten carbidesand metallic tungsten, depending on carburization schedule. Nickel and copper were found inthe samples impregnated with either of those. SEM images after carburization showed thatonly partial tungsten carbide coating on the α-SiC was achieved. Instead, small tungstencarbide clusters that eventually broke off from the surface of α-SiC were formed, creatingsmall tungsten carbide particles.A wetting experiment was conducted on the some of the synthesized powder samples.The powders were placed in a small glass sample holder along with a metal alloy and thenplaced in a high temperature furnace for 8 hours at 950 °C. The addition of copper or nickelseemed to enhance the wettability of tungsten carbide powder by metal alloy, and coimpregnationseemed much more successful than impregnation at a later stage. The wetting ofsamples without nickel or copper was very poor.Some of the synthesized powder samples along with a nickel base alloy powder wereused in a thermal spraying test to make a coating on steel plates. The coating of thesynthesized samples had a lot more voids compared to the coating of a commercial WCpowder.