Thermal pressure is an inevitable thermodynamic consequence of heating a volumetrically constrained sample in the diamond anvil cell. Its possible influences on experimentally determined density‐mineralogy correlations are widely appreciated, yet the effect itself has never been experimentally measured. We present here the first quantitative measurements of the spatial distribution of thermal pressure in a laser‐heated diamond anvil cell (LHDAC) in both olivine and AgI. The observed thermal pressure is strongly localized and closely follows the distribution of the laser hotspot. The magnitude of the thermal pressure is of the order of the thermodynamic thermal pressure (αK_TΔT) with gradients between 0.5 and 1.0 GPa/10 μm. Remarkably, we measure a steep gradient in thermal pressure even in a sample that is heated close to its melting line. This generates consequences for pressure determinations in pressure‐volume‐temperature (PVT) equation of state measurements when using an LHDAC. We show that an incomplete account of thermal pressure in PVT experiments can lead to biases in the coveted depth versus mineralogy correlation. However, the ability to spatially resolve thermal pressure in an LHDAC opens avenues to measure difficult‐to‐constrain thermodynamic derivative properties, which are important for comprehensive thermodynamic descriptions of the interior of planets.

中文翻译：

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激光加热金刚石砧室中的热压：定量研究及其对地幔密度与矿物学相关性的意义

热压是加热金刚石砧座中体积受限的样品的必然的热力学结果。它对实验确定的密度-矿物学相关性可能产生的影响已广为人知，但该影响本身从未进行过实验测量。我们在此介绍橄榄石和AgI中激光加热的金刚石砧盒（LHDAC）中热压力的空间分布的首次定量测量。观察到的热压非常集中，并且紧随激光热点的分布。热压力的大小为热力学热压力（顺序的αK _Ť Δ Ť）的梯度介于0.5和1.0 GPa / 10μm之间。值得注意的是，即使在加热到接近其熔解线的样品中，我们也可以测量热压的陡峭梯度。使用LHDAC时，这会对压力-体积-温度（PVT）状态方程中的压力确定产生影响。我们表明，PVT实验中热压的不完整考虑会导致令人垂涎的深度与矿物学相关性出现偏差。但是，在空间上解析LHDAC中的热压力的能力为测量难以约束的热力学导数性质提供了途径，这对于全面描述行星内部热力学非常重要。