Chemical inhomogeneity of silicates treated by plasma spraying

Abstract

The properties of thermally sprayed deposits are directly influenced by the homogeneity of their chemical composition as well as by their microstructure. The presented work deals with the evaluation and quantification of the chemical homogeneity of silicates, i.e., basalt, cordierite, garnets, mullite, steatite and wollastonite. The deposits were manufactured by a water-stabilized plasma spray system WSP ^® PAL160. A number of point chemical analyses 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 homogeneity of appropriate feedstock powder used for spraying. The microstructure of the cross-sections was observed by back-scattered electron imaging. Electron probe X-ray microanalysis (EDS-SEM) results were combined with X-ray diffraction measurements and showed the presence of various crystalline and amorphous phases in the deposits. The mean concentration, its standard deviation, the minimum and maximum compound content as well as Weibull statistics were used to characterize the chemical homogeneity of the deposits. Generally, the materials showed changes in homogeneity after deposition. This was most notable in steatite and wollastonite.