Experimental Investigation of Strong Shock-Heated Gases Interacting with Materials in Powder Form
A novel method is developed in our laboratory to use shock tube for heating the test gases to extremely high temperature and to interact with the materials in the form of fine powder for millisecond time scale. As a case study, we present the results obtained on nitridation of TiO2 compound. Material shock tube (MST) is used to heat Ar and N2 gas mixture to 3750 K–6725 K with reflected shock pressure of about 25–50 bar for about 1–2 ms duration; at these shock conditions, nitrogen gas experiences real gas effect. This nitrogen gas interacts with the rutile TiO2 at the reaction chamber of the MST. The surface morphology, crystal structure, surface composition and electronic structure of the rutile TiO2 sample were examined before and after exposure to shock waves using scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS).
The results obtained from the experimental investigations show the formation of new titanium oxides and oxynitride compounds when exposed to multiple shocks. Formation of new compounds like Ti2O5 and TiN0.74O0.34 is due to noncatalytic reaction occurred during the shock treatment. The result shows that the nitridation of TiO2 is possible in millisecond time scale. MST is an important tool to study catalytic/noncatalytic surface reaction on high-temperature materials near the surface of the re-entry space vehicles.
Financial supports for this study from the DRDO, ISRO-IISc Space Technology Cell and DST, Government of India, are gratefully acknowledged. Thanks to Professors K P J Reddy and G Jagadeesh of Aerospace Engineering Department, IISc, Bangalore, for their fruitful discussion and encouragements.
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