Chemical inhomogeneity of silicates treated by plasma spraying

The properties of thermally sprayed deposits are directly influenced by the homogeneity of their chemical composition as well as by their microstructu re. The presented work deals with the evaluation and quantification of the chemical homogeneity of silicates, i. e., basalt, cordierite, garnets, mull ite, steatite and wollastonite. The deposits were manufactured by a water-s tabilized plasma spray system WSP(R) PAL160. A number of point chemical ana lyses were performed for each deposit on a polished cross-section by X-ray microanalysis and the results were statistically evaluated. For some of the selected materials, the homogeneity of deposits was compared with the homo geneity of appropriate feedstock powder used for spraying. The microstructu re of the cross-sections was observed by back-scattered electron imaging. E lectron probe X-ray microanalysis (EDS-SEM) results were combined with X-ra y diffraction measurements and showed the presence of various crystalline a nd amorphous phases in the deposits. The mean concentration, its standard deviation, the minimum and maximum com pound content as well as Weibull statistics were used to characterize the c hemical homogeneity of the deposits. Generally, the materials showed changes in homogeneity after deposition. Th is was most notable in steatite and wollastonite.