Si‐C‐O‐N High‐Pressure Equilibria and ΔG_f^o for Si₂ON₂

Abstract

Phase relations in the Si-C-0-N system were studied by subjecting mixtures of carbon and silica (C/Si02 = 2 to 3) to high temperatures (up to 2000 K) and elevated nitrogen pressures (0.5 to 2.0 MPa) in a gas autoclave. The condensedphase assemblages obtained at different temperatures, pressures, and N/Si ratios are reported and compared with thermodynamic calculations. Values of AGf"(Si20N2) consistent with the experimental data are -397 kJ/mol at 1780 K and -369 kJ/mol at 1890 K. The influence on the synthesis of seeding the starting material is discussed.

Three-Dimensional Reticulated, Spongelike, Resilient Aerogels Assembled by SiC/Si3N4 Nanowires

“…The formation of SiC nuclei could follow eqs and , and eq will occur under high pressure of SiO circumstances . A previous study proposed that, above the critical temperature which is below 1500 °C at 0.1 MPa atmosphere, both SiC and Si 3 N 4 could be achieved in the Si–C–O–N system, and the former becomes the major phase. , Equations – are responsible for the formation of Si 3 N 4 , and eq could be prior to others in consideration of its Gibbs free energy change remaining negative in the reaction temperature. ,, Further growth of SiC and Si 3 N 4 nanowires will obey the vapor–solid mechanism because of the raw materials free of catalysts. − The formed nuclei would deposit on the surface of solid carbon, which was prevented from further reacting, leading to the growth of nanowires according to gas–gas reactions . The above-mentioned reactions are dynamic process; e.g., the consumption of gaseous SiO would accelerate in eq , and CO achieved in eqs and would participate in the following eqs and .…”

“…31 A previous study proposed that, above the critical temperature which is below 1500 °C at 0.1 MPa atmosphere, both SiC and Si 3 N 4 could be achieved in the Si−C−O−N system, and the former becomes the major phase. 34,35 Equations 10−13 are responsible for the formation of Si 3 N 4 , and eq 10 could be prior to others in consideration of its Gibbs free energy change remaining negative in the reaction temperature. 33,36,37 Further growth of SiC and Si 3 N 4 nanowires will obey the vapor−solid mechanism because of the raw materials free of catalysts.…”

Carbothermic Production of Silicon Oxynitride

“…In addition, when the data of Ekelund et al [II] are extrapolated to 1673 and 1723 K the values of~G~(SizN20) are found to be -425" and -412 kJ mol-1, respectively. This represents a difference of 2.80/0 for GHSizNzO) at 1673 K and 1.50/0for~G~(Si2N20) at 1723 K between the values calculated here at atmospheric pressure and the values extrapolated from the results of Ekelund et al [11] which were calculated at higher pressures. Therefore, the free energy of formation of silicon oxynitride calculated here can be considered to be reasonably accurate.…”

“…Ekelund et al [11] investigated the high pressure eqUIlIbna in the Si-C-O-N system and calculated the free energies of formation of Si2N20 at 1780, 1890, and 2000 K from experimental observations. The values calculated by Ekelund et al [11] are -396.5 kJ mol-1 at 1780 K, -369 kJ mol-1 at 1890 K, and -340 kJ mol-l at 2000 K (Table 4).…”

Effect of nitrogen gas pressure during heat treatment on the morphology of silicon nitride fibers synthesized by carbothermal nitridation

“…For these reactions, the thermodynamic Gibbs's free energy of formation was calculated based on the JANAF data and the data presented by Ekelund [13] for the standard conditions of various silicon nitride formation, i.e. the whole reaction of silica reduction nitridation (Equation ( 1)), the SiO 2 partial reduction reaction to form Si at low temperatures, while the formation of Si 3 N 4 (Equation ( 1)) with the β-phase is favored when the temperatures are high.…”