Mechanical properties of struvite-K: A high-pressure X-ray diffraction study

Magnesium potassium phosphate cement (MKPC) is gaining increasing popularity for specialized applications, e.g., structural rehabilitation, waste encapsulation, and 3D printing. However, the mechanical properties of struvite-K, the binding phase of MKPC, have rarely been examined. This study utilized synchrotron-based high-pressure X-ray diffraction to determine the intrinsic mechanical properties of struvite-K at the unit-cell scale, for the first time. The deformation of the unit cell, axial incompressibility, and bulk modulus was studied under hydrostatic pressures up to ~10 GPa. The unit cell shifts from orthorhombic to monoclinic lattice below 1 GPa; phase transition and amorphization occur at ~5 and ~10 GPa, respectively. The axial incompressibility shifts from anisotropy to isotropy, and the bulk modulus increases from 27 to 37 GPa upon phase transition. The experimental results are of great importance in calibration of atomistic modelling and provide implications on the problem with nanoindentation for studying mechanical properties of struvite-K or MKPC.