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Interfacial Phenomena of High-Temperature Melts and Materials Processing
Published in Mukai Kusuhiro, Matsushita Taishi, Interfacial Physical Chemistry of High-Temperature Melts, 2019
Mukai Kusuhiro, Matsushita Taishi
The supersaturation phenomenon in aluminum deoxidation can be explained by adding the contribution of the change in free energy of the matrix phase produced accompanied by the nucleation reaction to the above-mentioned classical nucleation theory.12 One form of the supersaturation phenomenon is that the system is in a state where the reaction cannot thermodynamically progress in the first place, i.e., the system is practically in the supersaturated state because the total free energy of the system is always increasing when the nucleation reaction is progressing. Another form of the supersaturation phenomenon can be explained as follows. The free energy of the system initially decreases as the nucleation reaction progresses but reaches a minimum when the nucleus grows to a certain size, unlike the case shown in Figure 2.18. Then, when the nucleus grows further, it reaches the state in which it cannot grow anymore because the free energy increases (see Figure 4.712). The size of the nucleus corresponding to the minimum free energy state is said to be a few nanometers in diameter both theoretically12 and experimentally.13 When the fine Al2O3 particles of this size are suspended, an apparent supersaturated state emerges.
Force-System Resultants and Equilibrium
Published in Richard C. Dorf, The Engineering Handbook, 2018
For crystallization to occur, a solution must be supersaturated. Supersaturation means that, at a given temperature, the actual solute concentration exceeds the concentration under equilibrium or saturated conditions. A supersaturated solution is metastable, and all crystallization occurs in the metastable region. A crystal suspended in saturated solution will not grow. Supersaturation may be expressed as the ratio between the actual concentration and the concentration at saturation [Equation (62.1)] or as the difference in concentration between the solution and the saturated solution at the same temperature [Equation (62.2)] S=C/CsΔC=C-C s
Protein Crystallization
Published in Jay L. Nadeau, Introduction to Experimental Biophysics, 2017
Oliver M. Baettig, Albert M. Berghuis
Protein crystallization makes use of the metastable nature of supersaturation. A solution is supersaturated if it contains a higher concentration of solubilized molecules, in our case proteins, than would usually be possible in a given solvent at a given temperature. One common way of creating a supersaturated sodium chloride solution, for example, is to dissolve generous amounts of salt in water while heating it. Supersaturation will be reached once the solution is allowed to cool down. Supersaturation is a metastable state, and small disturbances such as vibration or addition of some more salt will force the dissolved salt out of solution, a phenomenon called precipitation.
Effect of process parameters on phase behavior and particle size of aspirin during freeze concentration
Published in Drying Technology, 2020
Sandeep S. Zode, Samarth D. Thakore, Arvind K. Bansal
Supersaturation is an important kinetic factor affecting crystallization and crystal size. It is reported that the supersaturation achieved during freeze concentration depends on the degree of supercooling (DoS), which is defined as retention of liquid state below equilibrium freezing point of the solution.[21,35] ASP solution contained dissolved ASP in 40 parts of TBA and 60 parts of water. According to phase diagram reported by Kasraian and DeLuca, decreasing the ASP solution temperature leads to crystallization of TBA hydrate and TBA-water eutectic. Similar observations were obtained in the present work, as reported previously in the earlier section (Figure 1). Crystallization of either TBA hydrate or TBA-water eutectic leads to decrease in the amount of solvent available for solvation of ASP. Hence, solubility of ASP decreases in the apparent system at specific temperature. Moreover, the freezing point of the solution depends on DoS, which in turn depends on the rate of cooling. Table 2 lists the freezing point of the ASP solution at different cooling rates.
Single- and multi-objective optimisation for a combined cooling and antisolvent semi-batch crystallisation process with an ACADO toolkit
Published in Indian Chemical Engineer, 2020
Kashinath Barik, Pallishree Prusti, Soumya S. Mohapatra
Crystallisation is an important unit operation for the purification and production of solid particles from a solution. Crystallisation can be carried out by various modes and crystallisation from a solution is very common in chemical process industries. The physical system of solution crystallisation can have one or more solutes dissolved in a solvent. A solution at a given temperature is said to be saturated, undersaturated or supersaturated depending on whether the dissolved solute concentration(C) is equal to, less than or greater than the saturation concentration (C#) at that temperature. Crystallisation occurs only if the system is supersaturated [1]. Supersaturation is the difference in the chemical potential between the solution and the solid phase. The supersaturation can be achieved by a variety of methods such as cooling, evaporation, antisolvent addition and chemical reaction. Cooling crystallisation is generally applied to the solution where the change of solubility depends on the temperature variation and also for the thermally stable solute. Alternatively, the supersaturation can be generated by adding an antisolvent (a solvent in which the crystallising solute has significantly lower solubility) to the solution.
Effect of crystallizer design and operational parameters on the batch crystallization of ibuprofen I: experimental
Published in Indian Chemical Engineer, 2022
Achyut Pakhare, Channamallikarjun Mathpati, Vishwanath H. Dalvi, Jyeshtharaj Joshi, Raosaheb Patil, Ekambara Kalekudithi
In the case of open impellers, the conduction of heat through the deposited crystal controls the overall heat transfer [24]. The supersaturation depends on the local solute concentration and the local temperature determining the solubility. The deposited crystals are at a much lower temperature than the liquid bulk. Hence, significantly higher supersaturation near the wall governs the nucleation and growth by deposition. The deposited crystals are not available for growth using supersaturation from liquid bulk. This also leads to additional nucleation in liquid bulk. Both these phenomena eventually produce crystals of relatively smaller size compared to HR impeller. In the case of HR, the wall is cleaned by agitation and hence supersaturation is uniform throughout the crystallizer.