Effect of additives in supersaturated binary and ternary solutions on cluster growth by gravity driven concentration gradient studies

Abstract

The concentration gradients formed in long column supersaturated solutions of the binary systems Potassium dihydrogen phosphate -Water, Benzophenone -Ethanol, Ammonium dihydrogen phosphate -Water, Potassium hydrogen phthalate -Water and ternary systems Potassium dihydrogen phosphate -Potassium chloride -Water, Benzophenone -Urea -Ethanol, Ammonium dihydrogen phosphate -Urea -Water, Potassium hydrogen phthalate -Ethylenediaminetetraacetic acid -Water under stirred and non-stirred conditions have been studied. The solution concentration was measured at different heights, at different degrees of supersaturation and at different times. Weight average molecular weight, Degree of Association, Number average molecular weight, Average number of molecules per cluster and weight average cluster diameter were calculated for binary and ternary supersaturated solutions under stirred and non-stirred conditions. Under stirred conditions concentration gradient of all the above mentioned systems decrease compared to non-stirred conditions. The cluster sizes are estimated from concentration gradient data in the presence and absence of additives and also corresponding changes in metastable zonewidths are studied. The changes in concentration gradients of supersaturated solutions appear to be a reliable indicator of the effect of additives on cluster growth and nucleation. As long column of solution is used in growing crystal by Sankaranarayanan-Ramasamy method the effect of gravity driven concentration gradient on critical column length is investigated.

Novel Approach to Analyze Metastable Zone Width Determined by the Polythermal Method: Physical Interpretation of Various Parameters

“…This behavior has been observed for all of the investigated systems. ,,,,,, Equation also predicts that the quantity Δ T max / T 0 decreases with an increase in saturation temperature T 0 and a decrease in cooling rate R . This general trend has been observed in numerous publications. ,,,, …”

“…In this method, metastable zone can also be measured directly from the initially preset temperature difference when spontaneous nucleation occurs immediately after attaining the preset temperature. However, in the polythermal method, the solution is cooled at a constant cooling rate from saturation temperature T 0 to a temperature when visible crystals appear in the solution, − or there is sudden discontinuity at a temperature T lim in the temperature dependence of some property such as electrical conductivity, , ultrasound velocity, , density or turbidity of the solution. ,, The temperature difference ( T 0 − T lim ) is taken as the metastable zone width.…”

The Effect of EDTA on the Nucleation Kinetics and Mechanical Properties of KDP Crystal

“…Nucleation occurs when clusters reach a critical size where the Gibbs free energy changes for growth of the clusters is negative. Eventually, a critical size is reached and a crystal is born [3].…”