Mathematical modelling of diffusion-driven oxidation in metals

这个由工业赞助的项目旨在提供金属表面保护性氧化层形成的预测性定量描述。在纯氧、纯湿和两者的混合物(如潮湿空气)中的氧化是有意义的。过去，人们对这些氧化反应的动力学性质进行了广泛的研究，并提出了大量描述反应速率的模型。然而，除了几个值得注意的例外，这些模型本质上都是经验性的，而不是对看似合理的潜在物理机制的数学描述。在没有水分的情况下，氧化主要是氧离子通过氧化物基材向金属迁移，而在有水分的情况下，羟基阴离子的离子扩散可能是速率限制步骤。因此，整个过程是在不同组成的生长衬底内结合温度和时间相关的化学和离子扩散的过程。至关重要的是，对主要的物理机制进行良好的建模，以提供对长期材料老化的定性理解和定量预测能力。

This industrially-sponsored project is aimed at providing a predictive quantitative description of the formation of a protective oxide layer on a metal surface. Oxidation in pure oxygen, pure moisture, and mixtures of the two (e.g. humid air) are of interest. The kinetic properties of these oxidation reactions have been studied extensively in the past, and a large number of models describing the rates of reaction have been proposed. However, with just a few notable exceptions, these models have been empirical by their nature rather than mathematical descriptions of plausible underlying physical mechanisms. Oxidation in the absence of moisture is dominated by migration of oxygen anions through the oxide substrate towards the metal, while in the presence of moisture it is likely that ionic diffusion of hydroxyl anions is the rate limiting step. The overall process is thus one of combined temperature- and time-dependent chemical and ionic diffusion within a growing substrate of variable composition. It is vital that the dominant physical mechanisms are well modelled to provide both qualitative understanding and a quantitative predictive capability for long-term material ageing.