Bonatti L, Brugman B L, Subramani T, Leinenweber K D, Navrotsky A
School of Molecular Sciences and Center for Materials of the Universe, Arizona State University, Tempe, Arizona 85287, USA.
Eyring Materials Center, Arizona State University, Tempe, Arizona 85287, USA.
Rev Sci Instrum. 2023 May 1;94(5). doi: 10.1063/5.0131946.
Quantitative scanning calorimetry on microgram-sized samples opens a broad, new range of opportunities for studying the thermodynamic properties of quantity-limited materials, including those produced under extreme conditions or found as rare accessory minerals in nature. We calibrated the Mettler Toledo Flash DSC 2+ calorimeter to obtain quantitative heat capacities in the range 200-350 °C, using samples weighing between 2 and 11.5 μg. Our technique is applied to a new set of oxide materials to which it has never been used before, without the need for melting, glass transitions, or phase transformations. Heat capacity data were obtained for silica in the high pressure stishovite (rutile) structure, dense post-stishovite glass, standard fused quartz, and for TiO2 rutile. These heat capacities agree within 5%-15% with the literature values reported for rutile, stishovite, and fused SiO2 glass. The heat capacity of post-stishovite glass, made by heating stishovite to 1000 °C, is a newly reported value. After accurate calibrations, measured heat capacities were then used to calculate masses for samples in the microgram range, a substantial improvement over measurement in conventional microbalances, which have uncertainties approaching 50%-100% for such small samples. Since the typical uncertainty of heat capacities measured on 10-100 mg samples in conventional differential scanning calorimetry is typically 7% (1%-5% with careful work), flash differential scanning calorimetry, using samples a factor of 1000 smaller, increases the uncertainty of heat capacity measurements by a factor of <3, opening the door for meaningful measurements on ultra-small, high-pressure samples and other quantity-limited materials.
对微克级样品进行定量扫描量热法，为研究数量有限的材料的热力学性质开辟了广泛的新机会，这些材料包括在极端条件下产生的材料或自然界中罕见的副矿物。我们校准了梅特勒托利多Flash DSC 2+量热仪，以获得200-350°C范围内的定量热容，使用的样品重量在2至11.5微克之间。我们的技术应用于一组以前从未使用过的新型氧化物材料，无需熔化、玻璃化转变或相变。获得了高压斯石英（金红石）结构中的二氧化硅、致密的后斯石英玻璃、标准熔融石英以及TiO2金红石的热容数据。这些热容与文献报道的金红石、斯石英和熔融SiO2玻璃的值在5%-15%范围内一致。通过将斯石英加热到1000°C制成的后斯石英玻璃的热容是一个新报道的值。经过精确校准后，测量得到的热容随后被用于计算微克范围内样品的质量，这比传统微量天平的测量有了实质性的改进，传统微量天平对于如此小的样品的不确定性接近50%-100%。由于传统差示扫描量热法中对10-100毫克样品测量的热容的典型不确定性通常为7%（仔细操作时为1%-5%），使用小1000倍的样品的快速差示扫描量热法将热容测量的不确定性增加不到3倍，为对超小、高压样品和其他数量有限的材料进行有意义的测量打开了大门。
