Crystal growth kinetics of iron fluoride trihydrate

Crystal growth of β-FeF₃·3H₂O has been investigated in mixtures of 3 mol kg^-1 hydrofluoric acid and 3 mol kg^-1 nitric acid at 30, 40 and 50 °C. Seeded isothermal desupersaturation experiments have been performed in the range: 1.3<S<3.6. Solution samples were analysed for total iron concentration with inductively coupled plasma atomic emission spectroscopy. The true supersaturation driving force was estimated by a proper speciation using the software SSPEC using appropriate stability constants. Growth rate parameters of the BCF surface diffusion growth rate equation and the empirical power-law equation have been estimated by fitting the supersaturation balance equation using a nonlinear optimization procedure. The results show that the growth rate is surface integration controlled. The growth rate at a supersaturation ratio of 2 was found to be 3.5×10^-12 m s^-1 at 30 °C, 7.4×10^-12 m s^-1 at 40 °C and 16×10^-12 m s^-1 at 50 °C. The activation energy of the rate constant of crystal growth was found to be 61 kJ mol^-1.