Jayaram Vishakantaiah; Gowtham Balasubramaniam
Abstract
A novel method of studying oxidation resistance and phase transformation of SiC fine powder was performed using multiple shock treatments in millisecond timescale using indigenously developed material shock tube (MST1). MST1 was used to produce shock waves which heat the ultra high pure oxygen test gas ...
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A novel method of studying oxidation resistance and phase transformation of SiC fine powder was performed using multiple shock treatments in millisecond timescale using indigenously developed material shock tube (MST1). MST1 was used to produce shock waves which heat the ultra high pure oxygen test gas to a reflected shock temperature and pressure of about 5300 K (estimated) and 25 bar, respectively for 1-2 milliseconds. Different characterization techniques like X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) show the formation of oxides and sub-oxide species after shock treatment. XRD studies shows the phase transformation of hexagonal SiC to amorphous SiO2. SEM and TEM micrographs show change in surface morphology of SiC from irregular shape to micro/nano spheres due to superheating and cooling at the rate of about 106 K/s. This novel method is used for the first time to demonstrate the behavior of material in presence of extreme aero-thermodynamic conditions for a short duration. These conditions generated using shock tubes are not achievable by conventional furnaces for oxidation studies of SiC in a short duration.
V. Jayaram; K. P. J. Reddy
Abstract
This paper presents a novel method of interaction of zirconia with strong shock wave in presence of dissociated/non-dissociated gas species for short duration using shock tube. Cubic zirconia (c-ZrO2) was synthesized by solution combustion method and exposed to strong shock heated N2 and O2 test gases ...
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This paper presents a novel method of interaction of zirconia with strong shock wave in presence of dissociated/non-dissociated gas species for short duration using shock tube. Cubic zirconia (c-ZrO2) was synthesized by solution combustion method and exposed to strong shock heated N2 and O2 test gases in a free piston driven shock tube (FPST). FPST is used to heat the test gases to very high temperature of about 7540-9530 K (estimated) and reflected shock pressure of about 65-70 bar for short duration (2-3 ms). X-ray diffraction (XRD) study shows the phase transformation of c-ZrO2 to m-ZrO2. Scanning electron microscopy (SEM) images shows the formation of sharp nano/micro zirconia needles due to melting and nucleation during super heating and cooling at the rate of about 10 6 K/s. These types of sharp nano/micro needles are observed for the first time in this shock tube experiment. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy show no change in electronic structure and chemical composition of ZrO2 which indicates that the reaction is fully catalytic. This unique experimental methodology can be used to study the chemistry of materials under extreme thermodynamic conditions which is of seminal importance in space, nuclear and other high temperature applications.
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