Ravi Kumar N V

Powder particles of polymer derived SiHfCN(O) ceramics were pulsed electric current sintered at 1300 and 1500 °C to produce amorphous and partially crystalline ceramic pellets for corrosion studies in salt (NaCl or Na2SO4) and acid (HF) environments. While, sodium dramatically accelerated phase transformation and catalyzed the crystallization process, the open porosity acted as the main cause for sodium penetration in these materials. The samples, however, were completely disintegrated during fluoride acid tests. The cristobalite and HfO2 crystalline phases were severely corroded and it was found that the SiC grains were relatively stable in comparison with other phases in the system.

The influence of pulsed electric current sintering on the structural evolution and indentation response of hafnia incorporated silicon carbonitride polymer derived ceramics was studied. Despite the absence of any sintering additives, appreciable sintering at 1400 C with a density of ∼2.7 g/cc was observed. Sintering beyond 1300 C resulted in the phase separation and nano-crystallization of amorphous Si-Hf-C-N-O ceramic. The crystallite coarsening was insignificant and thereby the tetragonal phase of hafnia was retained in the ceramic nanocomposite. A relatively high indentation hardness and elastic modulus of ∼18 GPa and ∼313 GPa were determined by depth sensing nanoindentation technique. © 2013 Elsevier Ltd and Techna Group S.r.l.

The coefficient of thermal expansion (CTE) of ZrMo2O8 can be fine-tuned by controlling the amount of tin substitution in zirconium lattice sites. The sintering challenges associated with this material and the optimal sintering conditions were investigated in this study. Powders of tin substituted ZrMo2O8 were synthesised by co-precipitation technique. X-ray diffraction studies confirmed the formation of cubic SnMo2O8. Sintered pellets were produced from the powders and optimal sintering without decomposition of the phase was achieved at the expense of porosity. The material was found to be thermally stable up to 600 °C using thermogravimetric analysis. Dilatometric analysis of the sintered compacts shows that the CTE of the sample is in the order of 3.9 × 10−6/K, between 25 °C and 600 °C.