Temperatures of Shock-induced Shear Instabilities and Their Relationship to Fusion Curves

New emission spectra for MgO and radiation propagates through the unshocked portion CaA12Si208(glass ) are observed from 430 to 820 nm. of the sample to a mirror which reflects the light Taken with previous data, we suggest that out of the tank. The light is focused upon a transparent solids display three regimes of light diffraction grating and is dispersed to illuminate emission upon shock compression to successively a charge coupled detector. The detector is gated higher pressures' (1) characteristic radiation to collect radiation only while the shock front is such as observed in MgO and previously in other near the sample center. The light beam gives, via minerals, (2) heterogeneous hot spot (greybody) a photodiode, an analog signal of the total radiation observed in CaA12Si208 and previously in intensity versus time. all transparent solids undergoing shock-induced Wavelength calibration of the system relies phase transformations, and (3) blackbody emission upon standard gas emission lamps and a He-Ne observed in the high pressure phase regime in laser. Radiation intensity calibration was NaC1, Si02, CaO, CaA12Si208, and Mg2SiO 4. The obtained with a standard tungsten ribbon lamp. onset of regime (2) may delineate the onset of Samples of CaA12Si208 glass (Corning Co.) and shock-induced polymorphism whereas the onset of single crystal MgO (Norton Co.) were epoxied on regime (3) delineates the Hugoniot pressure the driver plates. Driver plates and samples were required to achieve local thermal equilibrium in ground to an optical finish and polished. the shocked solid. We also propose that the hot Color temperatures and emissivities were spot temperatures and corresponding shock determined by a least squares fit of the data to pressures determined in regime (2) delineate the Planck formula: points on the fusion curves of the high pressure phase. R = s C 1%-5 [exp (C2/%T)-l]-i (1) Introduction where R is the spectral radiance in W/m2'ster'nm. Here % is the wavelength, s is the wavelength Although shock wave techniques have been used independent emissivity, c 1 = 1.191 x 10 -16 to study the pressure-density relations of Wm2/ster, C 2 = 1.438 x 10 -2 mK, and T is the important minerals, shock temperatures have, to temperature in K. date, largely been calculated. Continuum temperatures were calculated (Table Recently, methods for temperature measurement 1) by the method of Ahrens et al. (1969) using have been described by Lyzenga and Ahrens (1979) the parameters given by Jeanloz and Ahrens (1980) who used a six channel optical pyrometry' system, for CaA12Si208 and Vassiliou and Ahrens (1981) for and Sugiura et al. (1982) who used a 500 channel MgO. Pressures were determined by the impedance spectrophotometer to measure radiance over the match method using Hugoniots of CaA12Si208 optical range. Kondo and Ahrens (1983) and Kondo et al. (in press) constructed a similar system with radiance magnitude calibration (Fig. 1) to measure the shock temperatures of various minerals. They found much higher temperatures and lower emissivities than expected for a continuum thermodynamic state in Si02, NaC1, CaSO4'2H20 and CaCO 3. Their results implied that localized shear deformation (Grady, 1980) occurred in the pressure range over which minerals undergo shock-induced phase changes. Here we report on emissions from shocked CaA12Si208 (glass) and single-crystal MgO and a new hypothesis on the significance of the color-temperature of shear bands.