The influence of hydrofluoric acid and nitric acid on the growth kinetics of iron(III) fluoride trihydrate

The influence of hydrofluoric acid and nitric acid concentration on the growth rate of β-FeF3·3H2O crystals has been studied in different hydrofluoric acid (4.7-10.7 mol/(kg H2O)) and nitric acid (2.1-4.6 mol/(kg H2O)) mixtures at 50 °C. Seeded desupersaturation experiments were performed and the results were evaluated by considering the chemical speciation using two different speciation programs. The growth rate at 50 °C at a supersaturation ratio of 2, expressed in terms of free FeF3, was found to be in the range of (0.4-3.8)×10−11 m/s. The growth rate order was found to be two or higher in all experiments. The low growth rate and high growth rate order indicate that the growth rate is governed by the surface integration step. The growth rate was found to be independent of variations in acid concentrations; this is in accordance with the assumption of a surface integration controlled growth rate.