The observation of strong absorption of the yttrium L-alpha line in sialonceramics

beta-sialon ceramics sintered with yttria additives have been studied with the use of an electron probe X-ray analysis (EPMA). Sialon ceramics were pr epared from a carbothermally derived beta-sialon powder and then sintered i n a nitrogen atmosphere with yttria admixture. The above process was follow ed by annealing in flowing nitrogen. Scanning electron microscope (SEM) obs ervations have shown that the sintered material contains a glassy phase (Y- Si-Al-O-N) on the grain boundaries. Xray diffraction (XRD) after annealing in nitrogen revealed the presence of a considerable amount of yttrium alumi nium garnet (YAG). The higher voltage of 30kV was used in order to excite t he yttrium K-alpha radiation (14.96 keV) at an appropriate overvoltage rati o because in some phases of the material, the disappearance of the yttrium L-alpha line has been observed during EPMA examination at an accelerating v oltage of 15 kV in energy dispersive spectra (EDS). The intensity of the yt trium K-alpha line was sufficiently high, while the Y L-alpha line was not seen in the ED spectrum. Because the position of the yttrium L-alpha line ( 1.922 keV) is very close to the Si (K) absorption edge (1.84keV), the stron g absorption at this edge is probably responsible for the effect. This resu lt should be considered as a serious warning in the case of EPMA (EDS) stud ies on compounds or mixtures suspected to contain both silicon and yttrium, because at electrons energies lower than 15keV, the presence of yttrium in materials can go unnoticed. In wavelength dispersive spectra (WDS) obtaine d at 15 keV the intensity of the yttrium L-alpha line was also very low but measurable.