Static compression of Ca(OH)2 at room temperature: Observations of amorphization and equation of state measurements to 10.7 GPa

Abstract

We report x‐ray diffraction measurements on Ca(OH)2‐portlandite as it is compressed to 37.6 gigapascals (GPa) in the diamond cell at room temperature. Between 10.7 and 15.4 GPa crystalline Ca(OH)2 transforms to a glass, and on decompression the glass recrystallizes between 3.6 and 5.1 GPa. Below pressures of 10.7 GPa we measure the elastic compression of crystalline Ca(OH)2. A finite strain analysis of these data shows that the isothermal bulk modulus and its pressure derivative are K0 = 37.8 (±1.8) GPa and K0'= 5.2 (±0.7) at zero pressure. From the change in the unit cell dimensions, we find that the linear incompressibilities of Ca(OH)2 differ by a factor of three. These data show that hydrogen bonding can produce large anisotropies in the elastic properties of hydroxides. We infer from the amorphization that dense, high‐pressure phases of Ca(OH)2 exist at pressures of 11 GPa and above.