Abstract— In situ high-temperature powder X-ray diffraction (HTPXRD), differential scanning calorimetry (DSC), and thermogravimetry (TG) of three natural borosilicates have been performed in the temperature range of 25–1200°С. Axinite-(Mn) melts incongruently at 900°С with the formation of anorthite and bustamite. Leucosphenite decomposes at 850°С to form fresnoite and cristobalite. According to DSC data, kornerupine decomposes at 1177°С to form sapphirine, indialite, and spinel as the products of heating kornerupine. The values of the thermal expansion tensor and its orientation were determined using the HTPXRD data. The study showed that the three borosilicates expand weakly and almost isotropically. The average bulk thermal expansion coefficients are 21.3, 22.7, and 32.9 × 10^–6°С^–1 for axinite-(Mn), kornerupine, and leucosphenite, respectively. Leucosphenite has the maximum volumetric expansion, most likely due to the pronounced layered character of its crystal structure. The least symmetric structure of axinite-(Mn) has the maximum anisotropy of thermal expansion in the temperature range of 600–900°С.

摘要—在25–1200°С的温度范围内对三种天然硼硅酸盐进行了原位高温粉末X射线衍射（HTPXRD），差示扫描量热法（DSC）和热重分析（TG）。滑石（Mn）在900°С融化不均匀，形成钙长石和白云母。白云母在850°C分解，形成方铁矿和方石英。根据DSC数据，核仁素在1177°C分解，形成蓝宝石，辉绿岩和尖晶石，作为加热核仁素的产物。使用HTPXRD数据确定热膨胀张量的值及其方向。研究表明，三种硼硅酸盐几乎没有各向同性地膨胀。平均整体热膨胀系数为21.3、22.7和32.9×10 ^–6 °С ^–1分别用于无水硫酸镁（Mn），红景天碱和无色石。白云母具有最大的体积膨胀，很可能是由于其晶体结构具有明显的分层特性。在600-900°С的温度范围内，最小对称结构的axinite-（Mn）具有最大的热膨胀各向异性。