Oxidation behavior of hot-pressed Si3N4 with addition of Y2O3 and Al2O3.

Abstract

Hot-pressed Si3N4 were prepared from two kinds of commercial Si3N4 with addition of Y2O3 and Al2O3. Oxidation behavior of hot-pressed Si3N4 bodies were investigated in pure dry oxygen at 1200•‹ and 1300•Ž, at several steps up to 30 days. Results of the weight gain, X-ray diffraction analysis, EPMA analysis and SEM observa tions on the oxidized layer are discussed in relation to the mechanism of oxidation.

Oxidation mechanism of Mo5Si3 particle in Si3N4 matrix composite at 750 °C

“…When Si 3 N 4 was oxidized at high temperature, a silica layer formed on the surface and subsequently reacted with the sintering additives, Y 2 O 3 and Al 2 O 3 , to form Y 2 Si 2 O 7 [7,10,11]. However, no oxygen was detected from the Si 3 N 4 grains by EDS analysis in the present study, indicating that the amorphous silicon oxide detected by XPS was a reaction product from the oxidation of the Mo 5 Si 3 particles.…”

“…Silicon nitride (Si 3 N 4 ) is the most promising material for use as structural components in tribological and high-temperature environments, and many studies concerned with tribological behavior [1][2][3][4][5] and oxidation behavior [6][7][8][9][10][11][12][13][14][15] have been conducted. However, most engineering ceramics, including Si 3 N 4 , often exhibit unsatisfactory wear performance and/or high friction coefficients, even under oil-lubricated conditions [16][17][18].…”

Identification of oxidation mechanisms in silicon nitride ceramics by transmission electron microscopy studies of oxide scales

“…We must remember that Al2O 3 as an additive in the material incorporates during sintering into Si 3 (2), the presence of alumina as an additive leads to the formation of viscous intergranular silicate. Yttrium and aluminum diffusion to the surface in an early stage of oxidation is accompanied by the creation of numerous micropores in the triple points and grain junctions, where YAG and Y 2 Si 2 0 7 were initially present.…”

“…(a,b) TEM micrographs of a 7Y2A oxidized at 1500 °C showing the outer oxidation front with cristobalite and yttrium silicate in the oxide scale and the reaction front with amorphous aluminosilicate phase (1), WC precipitates (2), and different amorphous silicate precipitates(3). EDX spectra of (1), (2), and (3) indicate the chemical composition.…”

Fabrication of highly dense Si3N4 via record low‐content additive system for low‐temperature pressureless sintering

“…Hence, we fixed the Y 2 O 3 –MgO system and added one more component to further lower the eutectic temperature in order to find a system favorable for low‐temperature pressureless sintering of Si 3 N 4 with low additive concentration. Al 2 O 3 has been used with Y 2 O 3 for preparing Si 3 N 4 with high densification by conventional sintering 30 . SiO 2 additive, in combination with Y 2 O 3 , enhances the phase transformation (α → β) as well as densification rate 31,32 .…”