Plasma sprayed titanium diboride (TiB2) coatings (50-200 μm thick) have been prepared on alumina substrates. X-ray diffraction, oxygen analysis and electrical conductivity measurements on the sprayed specimens indicate substantial oxygen pick-up during the spray process, resulting in the formation of titanium oxide and boron trioxide, which is subsequently converted to H3BO3by absorbing moisture. The above reactions adversely effect the electrical conductivity of the coatings as evidenced by conductivity values which are found to be 100-1000 times less than that of sintered TiB2. The use of argon as a shield gas during spraying has been found to minimise this oxidation problem. The effects of carbon addition have also been studied, as well as the use of hydrogen as a secondary plasma gas in controlling the oxidation problem. The addition of carbon did not have much influence on the oxygen pick up. Although an argon-hydrogen (Ar-H2) plasma substantially brought down the oxygen-content in coatings, the oxidation problem could not be avoided totally. In order to completely overcome this problem, the spray process will have to be carried out in a controlled environment chamber. © 1993.
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