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In these small volumes, the time until the first crystal appears is usually defined to be the nucleation time. Calcium carbonate crystal nucleation depends not only on degree of supersaturation but also the ratio of calcium to carbonate ions in aqueous solutions. [11] In larger volumes many nucleation events will occur.
For perceptible growth rates, this mechanism requires a finite driving force (or degree of supercooling) in order to lower the nucleation barrier sufficiently for nucleation to occur by means of thermal fluctuations. [5] In the theory of crystal growth from the melt, Burton and Cabrera have distinguished between two major mechanisms: [6] [7] [8]
Tank crystallization is an old method still used in some specialized cases. Saturated solutions, in tank crystallization, are allowed to cool in open tanks. After a period of time the mother liquor is drained and the crystals removed. Nucleation and size of crystals are difficult to control. [citation needed] Typically, labor costs are very high.
This candy is formed by allowing a supersaturated solution of sugar and water to crystallize onto a surface suitable for crystal nucleation, such as a string, stick, or plain granulated sugar. Heating the water before adding the sugar allows more sugar to dissolve thus producing larger crystals. Crystals form after six to seven days.
An example is the nucleation of the crystal phase in a system of hard spheres, which is a simple model of colloids consisting of perfectly hard spheres in thermal motion. The agreement of CNT with the simulated rates for this system confirms that the classical theory is a reasonable approximation. [ 26 ]
i.e., crystallization takes a time that decreases as one over the one-quarter power of the nucleation rate per unit volume, ˙, and one over the three-quarters power of the growth velocity ˙. Typical crystallites grow for some fraction of the crystallization time t X {\displaystyle t_{X}} and so have a linear dimension G ˙ t X {\displaystyle ...
Critical radius is the minimum particle size from which an aggregate is thermodynamically stable. In other words, it is the lowest radius formed by atoms or molecules clustering together (in a gas, liquid or solid matrix) before a new phase inclusion (a bubble, a droplet or a solid particle) is viable and begins to grow.
Molasses is a by-product of the process and the fiber from the stems, known as bagasse, [88] is burned to provide energy for the sugar extraction process. The crystals of raw sugar have a sticky brown coating and either can be used as they are, can be bleached by sulfur dioxide, or can be treated in a carbonatation process to produce a whiter ...