Long Time Oxidation Study of Ti[sub 3]SiC[sub 2], Ti[sub 3]SiC[sub 2]/SiC, and Ti[sub 3]SiC[sub 2]/TiC Composites in Air

Abstract

We report herein on the oxidation kinetics and morphology of the oxide phases that form after long term ͑up to 1500 h͒ oxidation in ambient air of fine and coarse-grained samples of Ti 3 SiC 2 , Ti 3 SiC 2 , with 30 vol % TiC and Ti 3 SiC with 30 vol % SiC in the 875-1200°C temperature range. In all cases, the oxidation resulted in a duplex scale, an outer rutile and an inner rutile/silica layer. At 875°C, and up to at least 100 h, the oxidation kinetics of the Ti 3 SiC 2 /30 vol % TiC samples are parabolic; at 925°C, the oxidation kinetics of the Ti 3 SiC 2 /30 vol % SiC are subparabolic, up to at least 500 h. The oxidation kinetics of all other runs are initially parabolic, but at times Ͼ30 h they become linear. The reason for the transition is not entirely clear, but could be due to the buildup of stresses in the external oxide scales. Comparison with previously published results indicate that the rate limiting step, when the oxidation kinetics are parabolic, is most probably the inward diffusion of oxygen and the simultaneous outward diffusion of titanium. The results also strongly suggest that the activation energies for diffusion of oxygen and titanium in rutile are almost identical over at least the 1000-1200°C temperature range.

Oxidation of Ti3SiC2 between 900 and 1200 °C in Air

“…Ti 3 SiC 2 materials have been synthesized by hot pressing or hipping processes using various starting material systems such as Ti/SiC/graphite, [1][2][3] Ti/Si/graphite, [4][5][6][7][8][9][10] Ti/Si/TiC, 11,12 TiH 2 /Si/ graphite 13 and TiC/Si, 14,15 However, it is known that the synthesis of high-purity Ti 3 SiC 2 is difficult, since it requires a relatively long reaction time at high temperatures to synthesize thermodynamically stable Ti 3 SiC 2 through the formation of intermediate phases, when the powder-metallurgical route is employed. In this study, we successfully synthesized high-purity Ti 3 SiC 2 materials by the hot pressing of a newly developed starting-material system consisting of a TiC x (x=0.6)/Si powder mixture.…”

“…Oxidation at temperatures ranging from 900°C to 1500°C in air generally resulted in the formation of a duplex scale, an outer TiO 2 (rutile) layer and an inner (TiO 2 + SiO 2 ) layer. 2,4,5,7,[9][10][11]14,[16][17][18] Depending on the investigators, the SiO 2 formed was either amorphous, 2,8,9,14,15 tridymite, 5 or cristobalite. 2,8,11,18 The oxidation was controlled by the inward diffusion of oxygen ions and the simultaneous outward diffusion of Ti and carbon.…”

“…The silicon atoms were oxidized in situ by the inwardly diffusing oxygen ions. 2,4,5,[17][18][19] Good oxidation resistance was obtained up to 1100°C in air.…”

High‐temperature oxidation of Ti3Al0.7Si0.3C2 compound at 900 and 1000 °C in air

“…On the other hand, a-Al 2 O 3 is generally known to grow very slowly by the inward diffusion of oxygen [13]. However, the non-stoichiometry in Al 2 O 3 is very small, and the unequivocal defect structure of a-Al 2 O 3 is not yet known [14].…”

“…It is electrically and thermally conductive, easily machinable, ductile with a high stiffness-to-hardness ratio, thermally stable up to at least 1700 8C in an inert atmosphere, damage tolerant, maintains its strength at high temperatures, and is resistant to thermal shock and chemical attack including high-temperature oxidation. The scales formed on Ti 3 SiC 2 are typically composed of an outer TiO 2 layer and an inner (TiO 2 þ SiO 2 ) mixed layer [2][3][4]. Ti 3 SiC 2 displays good oxidation resistance because of the presence of SiO 2 .…”