Thermoelastic properties of synthetic single crystal portlandite Ca(OH)₂ - Temperature-dependent thermal diffusivity with derived thermal conductivity and elastic constants at ambient conditions
Breuer, S. / Schwotzer, M. / Speziale, S. / Schilling, F. R. (2020)
Cement and concrete research, 2020, 137, 106199
- Datum: August 2020
Synthetic portlandite single crystals were used to measure thermal diffusivity and elastic constants. The full tensor of elastic constants cijkl is derived by Brillouin pectroscopy at ambient conditions. The resultant aggregate bulk and shear moduli are K(S,VRH)= 32.2(3) GPa and G(VRH)= 21.2(2) GPa, respectively. The thermal diffusivity D was measured from −100 °C to 700 °C parallel  and perpendicular  to the crystallographic c-axis using laser flash method. The dehydration of the crystals influences the thermal diffusivity determination depending on sample size, orientation and heating rate. Thermal diffusivity and the derived thermal conductivity show a pronounced anisotropy with a maximum perpendicular to the c-axis, i.e. in the plane of the [CaO6] octahedral layers. In the same direction the highest sound velocities (v(P) and v(mean)) and longest mean free path length of phonons are determined. The thermal diffusivity as well as the derived thermal conductivity show a distinct temperature dependence.