Preparation of mullite whiskers derived from topaz doped with rare earth oxides for applications in composite materials

Mullite whiskers were obtained by means of the thermal decomposition of natural colorless topaz powder, both pure and doped with 5% by weight of La2O3 and/or Y2O3, treated at 1400 degrees C for 1 h. The analyses by thermogravimetry (TG) and differential scanning calorimetry (DSC) showed that the mullitization temperature of the topaz is 1315 degrees C; this temperature was reduced to 1298 degrees C and 1111 degrees C as a result of doping with Y2O3 and La2O3, respectively. The x-ray diffraction (XRD) analysis only exhibited, as an end product from the thermal decomposition of the topaz, mullite when doping with La2O3; the final product was mullite and alumina and, when doping with Y2O3, it was mullite, alumina and Y2Si2O7. In the doped samples, an SEM micrograph proved there to be a reduction in the aspect ratio of the whiskers and the presence of a small residual glassy phase, when compared with the pure mullite. An investigation was conducted with the intention of obtaining whisker development and disaggregation from the ceramic body. The conclusion of this investigation was that the higher porosity in the ceramic body, the better the development and disaggregation of the whiskers is. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.