Non‐Isotropic Contraction and Expansion of Samples in Diamond Anvil Cells: Implications for Thermal Conductivity at the Core‐Mantle Boundary
Non‐Isotropic Contraction and Expansion of Samples in Diamond Anvil Cells: Implications for Thermal Conductivity at the Core‐Mantle Boundary
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DOI：
10.1029/2022gl100379
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发表时间：
2022-09
影响因子：
5.2
通讯作者：
S. Lobanov;Z. Geballe
中科院分区：
文献类型：
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作者：
S. Lobanov;Z. Geballe
地幔和地核物质的导热系数对行星演化有重要影响，但它们的实验测定需要高压下样品厚度的精确知识。尽管它很重要，但在大多数金刚石砧座(DAC)实验中，厚度并不是测量的，而是从状态方程推导出来的，假设压缩时各向同性收缩，或减压时各向同性膨胀。在这里，我们提供的证据表明，在DAC实验中，这两个假设对于一系列不同的机械材料(KCl、NaC、Ar、MgO、石英玻璃、Al_2O_3)都是无效的。在压缩时，这些样品的∼比各向同性收缩时预期的要薄30-50%。最令人惊讶的是，所有被研究的样品在减压到10-20 Gpa时都会继续变薄。我们的结果部分解释了在地核条件下铁的热传导值之间存在的一些差异，这些值极具争议。更广泛地说，我们认为样品几何结构的原位表征对于高压下的电导率测量是必不可少的。
The thermal conductivities of mantle and core materials have a major impact on planetary evolution, but their experimental determination requires precise knowledge of sample thickness at high pressure. Despite its importance, thickness in most diamond anvil cell (DAC) experiments is not measured but inferred from equations of state, assuming isotropic contraction upon compression or assuming isotropic expansion upon decompression. Here we provide evidence that in DAC experiments both assumptions are invalid for a range of mechanically diverse materials (KCl, NaCl, Ar, MgO, silica glass, Al2O3). Upon compression, these samples are ∼30–50% thinner than expected from isotropic contraction. Most surprisingly, all the studied samples continue to thin upon decompression to 10–20 GPa. Our results partially explain some discrepancies among the highly controversial thermal conductivity values of iron at Earth's core conditions. More generally, we suggest that in situ characterization of sample geometry is essential for conductivity measurements at high pressure.