Vacuum plasma spraying of tantalum and niobium

Vacuum plasma spraying is a suitable process for producing high quality coatings of reactive metals such as tantalum and niobium. Ta and Nb coatings used for corrosion protection must be extremely dense, homogeneous, and of high purity and adhesion. Hence, the process parameters have to be carefully optimized even with regard to the spraying powder, its grain size and morphology. Spraying equipment with vacuum systems which allow for a final pressure of 10-3 mbar, which have heated and evacuated powder feeder units, and heated substrates, as well as the use of powders with high purity and low gas content, are required for producing high quality Ta and Nb coatings. Corrosion tests in sulfuric acid and aqua regia at different concentrations show that Ta and Nb coatings sprayed under optimized conditions have high resistance to both general and localized corrosion