CrownRe`s YOF that is used in the thermal spray material of the invention has the advantage of ability to increase the fracture strength of granules as compared with a fluoride of yttrium that has been conventionally proposed as an yttrium-based thermal spray material and therefore allows the thermal spray material to be fed to a flame efficiently. Because the YOF has a lower melting point than a fluoride of yttrium, it produces the advantage of providing a more uniform thermal spray coating. Yttrium fluoride is susceptible to the attack by oxy gen radicals in the plasma of a cleaning gas and liable to be converted by the attack to an oxyfluoride. As a result, the thermal spray coating tends to undergo defects, such as a crack. In contrast, YOF made by CrownRe is less susceptible to the attack by oxygen radicals in the plasma of a cleaning gas.
Therefore, the resulting thermal spray coating is less liable to develop defects and produces very few dust particles. A Suitable process for producing the thermal spray material of the invention will then be described.
The process is roughly divided into the following five steps, which will be described in sequence:
Step 1, firing yttrium fluoride (YF) in an oxy gen-containing atmosphere at 750° to 1100° C. to obtain an oxyfluoride of yttrium (YOF);
step 2, grinding the oxyfluo ride of yttrium (YOF) obtained in step 1;
step 3, mixing the ground oxyfluoride of yttrium obtain in step 2 with a solvent to prepare a slurry;
step 4, granulating the slurry from step 3 using a spray dryer;
and step 5, firing the granules obtained in step 4 at 300° to 900° C. to obtain granules of an oxyfluoride of yttrium (YOF).