Anish Paul

Heat flux mapping of oxyacetylene flames and their use to characterise Cf-HfB2 composites

Cost effective and fast ultra-high-temperature testing methods such as oxyacetylene torch testing are extremely useful for the rapid screening of ultra-high-temperature ceramic (UHTC) materials for hypersonic applications. There is no report in the literature, however, of an organised study to measure the heat flux and how it varies with gas flow rate, gas flow ratio and distance from the nozzle tip for an oxyacetylene flame. In this paper, the authors report for the first time the heat flux mapping of an oxidising, neutral and reducing flame. The measured heat flux was as high as ∼17 MW m−2 at a distance of 10 mm from the nozzle, which is much higher than that previously reported in the literature. Torch testing was carried out for Cf-HfB2 UHTC composites at this heat flux and the results are presented along with detailed microstructural characterisation.

Oxyacetylene torch testing and microstructural characterization of tantalum carbide

Tantalum carbide samples have been subjected to high‐temperature testing at ∼2300°C using an oxyacetylene torch to evaluate their potential for ultra‐high temperature applications. While large samples cracked during the rapid heating, indicating their inability to withstand thermal shock, small samples survived the severe test conditions. The oxidation products formed were characterized and found to comprise different phases of Ta2O5. The ultra‐high temperature experienced by the samples resulted in the formation of many interesting microstructures, including the formation of submicron sized grains, which has not been reported previously in the literature, as well as the expected evidence of melting.

Micro‐Raman spectroscopy of indentation induced phase transformation in nanozirconia ceramics

Abstract Abstract Micro‐Raman spectroscopy has been employed as an effective technique to determine the phase transformations in nanostructured yttria stabilised zirconia (YSZ) ceramics with different yttria contents. Samples have been prepared with varying mean grain sizes by a slip casting route followed by a microwave assisted two‐step sintering cycle starting with aqueous nanozirconia suspensions. Indents were generated using a Vickers pyramidal indenter at different loads, and the resulting phase transformations were mapped using micro‐Raman spectroscopy. The results were compared to those of a commercial submicrometre 3 mol.% YSZ. The amount of transformation was found to be much lower for nanozirconia compared to the submicrometre zirconia with similar yttria content.