Supersaturation-induced hydrothermal formation of α-CaSO4·0.5H2O whiskers

Abstract

The supersaturation-induced hydrothermal formation of α-CaSO₄·0.5H₂O whiskers from the CaSO₄·2H₂O precursor at 115–150 °C was investigated in this paper. The experimental results indicated that the conversion processes were carried out via dissolution–precipitation and homogeneous nucleation routes and connected with the critical supersaturation (abbreviated as S_crit, ln S_crit = a(γ/T)^3/2) of the system. In the temperature range of 115–150 °C, α-CaSO₄·0.5H₂O whiskers with a length of 200–500 μm and a diameter of 0.1–0.5 μm formed quickly within 2.0–5.0 minutes once the supersaturation (abbreviated as S) reached S_crit. The supersaturation-induced formation of α-CaSO₄·0.5H₂O is well consistent with the first-order reaction model, and the corresponding activation energy (E_a) and pre-exponential factor (A₀) were 161.7 kJ mol⁻¹ and 2.601 × 10²¹ h⁻¹, respectively.