Shock Wave Synthesis and Exploration of High-pressure Nitrides and Related Materials
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1040-Q05-04
Shock Wave Synthesis and Exploration of High-pressure Nitrides and Related Materials Toshimori Sekine Nano Materials Lab, National Institute for Materials Science, Namiki 1-1, Tsukuba, 305-0044 Japan ABSTRACT We have successfully developed a method to manufacture spinel-type Si3N4 and also a chemical treatment method to separate the spinel-type phase from the low-pressure phases. Similar methods could be applied for the SiAlON systems. In order to explore high-pressure nitrides and oxynitrides, we extended toward the system Si3N4-AlN-Al2O3- SiO2. According to the results of in situ measurements of the high-pressure behavior up to pressures of 200 GPa, there appears to be post-spinel phase in the system. This is consistent with the results from the first principles calculations. However we could not obtain the post-spinel phase by the shock recovery experiments at present. We also carried out shock recovery experiments on carbon nitrides and related materials. Experimental results showed formation of a new carbon nitride, high stability of melamine up to a shock pressure of 37 GPa, and production of amorphous C-N materials with the highest N/C ration of 1.26 from the reaction between carbon tetrahalide and sodium dicyanoamide. We tried further to extend toward the systems C3N4-Si3N4 and Mg2SiO4Si3N4, after taking into account the results on shock wave synthesis of spinel-type nitrides. INTRODUCTION Shock wave achieves high pressure and high temperature states that give us unique conditions for material synthesis even in a limited availability of reaction time [1]. We have carried out shock wave synthesis of the high-pressure phases in the system Si3N4-AlN-Al2O3SiO2 and explored the high-pressure nitrides and oxynitrides recently. The results as well as those at high static high pressures have been reviewed recently [2]. We investigated the highpressure phases using the techniques of shock recovery and in situ measurements of shocked materials. The shock high-pressure studies on nitrides and oxynitrides revealed several important issues for applications including industrial and basic research interests. Their hardness and physical properties have been evaluated experimentally and theoretically [2]. We also carried out shock recovery experiments on carbon nitrides. We employed several N-rich materials including a C-N-O amorphous precursor, dicyandiamide, melamine, and a mixture of carbon tetrahalide and sodium dicyanoamide. We extended toward the system C3N4Si3N4 after taking into account the results on shock synthesis of spinel-type nitrides. The two systems of Mg2SiO4-Si3N4 and Mg2SiO4-SiAlON at high pressures were investigated experimentally to check nitrogen incorporation into silicate spinles. These results are reported. EXPERIMENTS We employed a propellant gun for recovery experiments [1] and a two-stage light-gas gun for the Hugoniot equation of state experiments [3]. These guns accelerate projectiles to a high velocity up to 6 km/s. Hypervelocity impacts generate strong shock waves in target contai
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