Zirconium carbide oxidation: Kinetics and oxygen diffusion through the intermediate layer
Zirconium carbide oxidation: Kinetics and oxygen diffusion through the intermediate layer
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DOI：
10.1111/jace.15479
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发表时间：
2018-06-01
影响因子：
3.9
通讯作者：
Lee, William E.
中科院分区：
文献类型：
--
作者：
Gasparrini, Claudia;Chater, Richard J.;Lee, William E.
研究了热压ZrC在1073- 1373 K空气中的氧化行为。动力学在1073 K是线性的，而在较高的温度下，样品最初遵循线性动力学，然后进行快速氧化，导致马耳他十字形状的氧化物。在1073 K的线性动力学是由向内的氧扩散通过ZrC和ZrO 2之间的中间层的厚度恒定，这是由无定形碳和ZrO 2纳米晶体。在O-16/O-18的双氧化实验中，使用O-18作为示踪剂，测得氧通过中间层的扩散为9 × 10（-10）cm（2）s（-1）。在1073和1173 K的氧化产生的样品由m-ZrO 2和t-或c-ZrO 2与由无定形碳和ZrO 2制成的粘附中间层制成，而在1273和1373 K的氧化产生的样品与由m-ZrO 2制成的大体积氧化物显示ZrO 2和氧化物之间的间隙。在1273 K时，在差距处发现了亚化学计量的氧化锆层，并且与顶部氧化物层相比，在该层中没有检测到碳吸收。与1173 K相比，1273 K下中间层的损失和线性速率常数（gm（-2）s（-1））的减慢与中间层处的碳的优先氧化相关，这将以CO和/或CO2的形式离开，从而在ZrC和亚化学计量氧化锆之间留下间隙。
Oxidation of hot-pressed ZrC was investigated in air in the 1073-1373K range. The kinetics were linear at 1073K, whereas at higher temperature samples initially followed linear kinetics before undergoing rapid oxidation leading to a Maltese cross shape of the oxide. The linear kinetics at 1073K was governed by inward oxygen diffusion through an intermediate layer of constant thickness between ZrC and ZrO2 which was comprised of amorphous carbon and ZrO2 nanocrystals. Diffusion of oxygen through the intermediate layer was measured to be 9x10(-10)cm(2)s(-1) using O-18 as a tracer in a double oxidation experiment in O-16/O-18. Oxidation at 1073 and 1173K produced samples made of m-ZrO2 and either t- or c-ZrO2 with an adherent intermediate layer made of amorphous carbon and ZrO2, whereas oxidation at 1273 and 1373K produced samples with a voluminous oxide made of m-ZrO2 showing a gap between ZrC and the oxide. A substoichiometric zirconia layer was found at the gap at 1273K and no carbon uptake was detected in this layer when compared with the top oxide layer. The loss of the intermediate layer and the slowdown of the linear rate constant (gm(-2)s(-1)) at 1273K compared to 1173K was correlated with the preferential oxidation of carbon at the intermediate layer which would leave as CO and/or CO2 leaving a gap between ZrC and substoichiometric zirconia.