Density and ultrasonic velocity of undersaturated and supersaturated solutions of fluoranthene in trichloroethylene, and study of their metastable zone width

Abstract

The density ( d) and ultrasonic velocity ( u) of undersaturated, saturated and supersaturated solutions of fluoranthene in trichloroethylene have been measured with the help of two microprocessor instruments. Moreover, the same instruments and an apparatus for measuring transparency and turbidity were used to investigate the metastable zone width, as well as the solubility of fluoranthene in this solvent. It was found that the temperature dependencies of both the density and ultrasonic velocity in the range of undersaturation and supersaturation may be described by first-order equations. In the undersaturation range, the density linearly decreases and the ultrasonic velocity linearly increases with an increase in solution concentration. The second-order equations relating these quantities to solution supersaturation can satisfactorily be used for describing the data. Moreover, the first precipitation temperatures ( T p) determined from the density, ultrasonic velocity and transparency measurements as well as the metastable zone widths (Δ Θ max) are strongly dependent on the detection manner of the onset of crystallisation. Their mean values are 12.58, 5.76 and 4.62 K for density, ultrasonic velocity and transparency methods, respectively. This parameter was assessed as a function of cooling rate ( b). Hence, the linear dependence between log b and log (Δ Θ max) was established. The solubility temperature of fluoranthene determined from the change in turbidity of solution is generally lower by about 3 K than those measured with the help of the synthetic–dynamic method.