Aluminium and oxygen tracer diffusion in polycrystalline alpha-Al2O3

α-Al_2O_3是一种重要的耐火材料，在技术上有许多应用：作为原位生长的自愈合氧化膜、作为块体材料和作为复合材料中的增强纤维。这意味着多晶微结构在α-Al_2O_3的技术应用中至关重要。因此，非常不利的是，到目前为止，关于直接测量的氧晶界扩散系数的数据很少，而且根本没有(！)适用于铝晶界扩散。这种数据的缺乏大大阻碍了对多晶α-Al_2O_3中扩散控制过程的定量模拟。因此，为了模拟扩散控制的过程(蠕变、烧结、含铝Fe或Ni基合金上的α-Al_2O_3鳞片生长)，人们普遍推测，与整体传输类似，氧的晶界扩散比铝晶界扩散慢得多。为了定量地检验这一猜想，进行示踪剂直接扩散实验是绝对必要的。有史以来第一次(！)本项目将确定26Al晶界示踪剂在多晶α-Al_2O_3中扩散的实验数据。这将允许量化晶界扩散系数的比率Db-Al/Db-oxy，这是理论研究中的一个关键参数。从工艺角度来看，Y的掺杂具有非常积极的效果，因为它减缓了多晶α-Al_2O_3的蠕变速度和含铝Fe或Ni基合金上α-Al_2O_3层的生长速度。为了证明Y掺杂对氧晶界扩散的影响，另外两个小组进行了~(18)O示踪扩散研究，但结果是有争议的。为了充分了解Y掺杂的重要技术效应，有必要提供掺Yα-Al_2O_3中铝晶界示踪剂扩散的数据。因此，本项目将测量掺Yα-Al_2O_3中的铝晶界扩散，并对有争议的氧晶界扩散数据进行实验验证。

Alpha-Al2O3 is an important refractory material which has numerous technical applications: as an in situ growing self-healing oxide scale, as a massive material and as reinforcement fibres in composites. This means that polycrystalline microstructures are of prime importance in the technological use of alpha-Al2O3. It is therefore extremely disadvantageous that to date only very few data on directly measured oxygen grain boundary diffusivities exist and that there is no data at all (!) available on aluminium grain boundary diffusion. This lack of data considerably hinders quantitative modelling of diffusion controlled processes in polycrystalline alpha-Al2O3. Therefore, for modelling diffusion controlled processes (creep, sintering, alpha-alumina scale growth on aluminium bearing Fe or Ni base alloys) it is generally conjectured that, in analogy to bulk transport, oxygen grain boundary diffusion is much slower than aluminium grain boundary diffusion. In order to check this conjecture quantitatively, it is absolutely necessary to perform direct tracer diffusion experiments. For the first time ever (!) experimental data on the 26Al grain boundary tracer diffusion in polycrystalline alpha-Al2O3 will be determined in this project. This will allow to quantify the ratio Db-Al/Db-oxy of grain boundary diffusivities which is a key parameter in theoretical studies.Yttrium doping has, from the technological point of view, a very positive effect as it slows down both the creep rate of polycrystalline alpha-Al2O3 and the growth rate of alpha-Al2O3 scales on aluminium bearing Fe or Ni base alloys. In order to demonstrate that yttrium doping affects oxygen grain boundary diffusion two other groups performed 18O tracer diffusion studies whose results are, however, controversial. In order to fully understand the technologically important effect of yttrium doping, it is necessary to supply data for the aluminium grain boundary tracer diffusion in yttrium doped alpha-alumina. Therefore, in this project the aluminum grain boundary diffusion in yttrium doped alpha-alumina will be measured and the controversial oxygen grain boundary diffusion data will be experimentally checked.