The thermal decomposition of CH3ONO was studied in a static reactor at temperatures in the range 450-520 K. Stable products were analyzed by FTIR and gas-liquid chromatography to yield concentration-time profiles as functions of temperature and pressure. The species monitored included CH3ONO, CH20, CH3OH, NO, N20, and CO. The experimental data were kinetically modeled with the aid of Rice-Ramsperger-Kassel-Marcus (RRKM) calculations for pressure-dependent rate constants. The key reactions of this mechanism are the following: CH3ONO -CH30 + NO (1); CH3ONO -CH20 + HNO (2); CH30 + NO -CH3ONO (3); CH30 + NO -> CH20 + HNO (4); CH30 + HNO -» CH3OH + NO (5); HNO + HNO -* N20 + H20 (7). The results showed that the initiation reaction, (1), is clearly pressure-dependent in the temperature and pressure ranges investigated. The data are consistent with the value kx = io15-3±0•30 exp((-38 700 ± 400)/ 7") s™1 at 710 Torr of He and with the extrapolated high-pressure rate constant kf = io1601±0•30 exp((-39 600 ± 400)/RT) s-1. The rate constant ratio fc4/k3 for channels 3 and 4 was also found to depend on both temperature and pressure. At 710 Torr, k3 = 101296±0•30 exp((0 ± 200)/RT) and fc4 = 12•92*0•30 exp((-2050 ± 200)/RT), both in units of cm3/(mol s). Kinetic modeling of CH3OH and N20 formation over the entire range of temperatures and pressures investigated here yielded k¡ = 135± exp((0 ± 400)/RT) and kn = io8 9-93±0•30 exp((-3100 ± 200)/RT) cm3/(mol s).
Limited past studies have indicated that Si,N, doped with Sc,03 may exhibit high-temperature mechanical properties superior to Si,N, systems with various other oxide sintering additives. High-temperature deformation of this system was studied by characterizing the microstructures before and after deformation. It was found that elements of the additive, Sc and 0, exist in small amounts at thin grain boundary layers and within secondary phases at triple and multiple grain boundary junctions. The secondary phase is devitrified as crystalline Sc,Si,O,. Deformation of the samples was dominated by cavitation rather than dislocation processes. Thus, the excellent deformation resistance of the samples at high temperature can be attributed to the high refractories and enhanced crystallization of a secondary phase.
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