Effect of sample volume on the metastable zone width of potassium nitrate aqueous solutions

• Effect of sample volume on metastable zone width of KNO3 aqueous solutions is studied.
• Measurements of metastable zone width were made by the polythermal method.
• UV–vis spectrophotometry and visual observation were used for detection of nucleation.
• Data are analyzed using recent approaches proposed for metastable zone width.

Results of an experimental study of the effect of sample volume on the metastable zone width of pure unstirred potassium nitrate aqueous solutions investigated as functions of cooling rate R and saturation temperature T0 of the solution by the polythermal method are described and discussed. The metastable zone width was measured as the maximum undercooling ΔTmax during the cooling of 4 and 100 mL solutions at constant predefined rates between 5 and 40 K/h by registering changes in the intensity of transmitted light using the UV–vis spectrophotometer and observation of visible nuclei by the visual method, respectively. The experimental data of the maximum undercooling ΔTmax corresponding to saturation temperature T0 for the two investigated volumes as a function of cooling rate R were analyzed by employing self-consistent Nývlt-like approach and an approach based on the classical three-dimensional nucleation theory. The results suggest that the dependence of the value of the metastable zone width of unstirred solutions on their volume is associated with the diffusion processes in the solution.