Determination of the elastic constants of portlandite by Brillouin spectroscopy: Fid-Bau Portal

Determination of the elastic constants of portlandite by Brillouin spectroscopy

Speziale, S. / Reichmann, H.J. / Schilling, F.R. / Wenk, H.R. / Monteiro, P.J.M.

AbstractThe single crystal elastic constants Cij and the shear and adiabatic bulk modulus of a natural portlandite (Ca(OH)2) crystal were determined by Brillouin spectroscopy at ambient conditions. The elastic constants, expressed in GPa, are: C11=102.0(±2.0), C12=32.1(±1.0), C13=8.4(±0.4), C14=4.5(±0.2), C33=33.6(±0.7), C44=12.0(±0.3), C66=(C11–C12)/2=35.0(±1.1), where the numbers in parentheses are 1σ standard deviations. The Reuss bounds of the adiabatic bulk and shear moduli are K0S=26.0(±0.3) GPa and G0=17.5(±0.4) GPa, respectively, while the Voigt bounds of these moduli are K0S=37.3(±0.4) GPa and G0=24.4(±0.3) GPa. The Reuss and Voigt bounds for the aggregate Young's modulus are 42.8(±1.0) GPa and 60.0(±0.8) GPa respectively, while the aggregate Poisson's ratio is equal to 0.23(±0.01). Portlandite exhibits both large compressional elastic anisotropy with C11/C33=3.03(±0.09) equivalent to that of the isostructural hydroxide brucite (Mg(OH)2), and large shear anisotropy with C66/C44=2.92(±0.12) which is 11% larger than brucite. The comparison between the bulk modulus of portlandite and that of lime (CaO) confirms a systematic linear relationship between the bulk moduli of brucite-type simple hydroxides and the corresponding NaCl-type oxides.