Crystal growth retardation

Hardness stabilization, functioning at substoichiometric levels by crystal growth retardation, (threshold effect). This attribute is useful in low heat-flux HW applications. 

Crystal growth retardation, function of all-organics 443 Crystal modification, function of all-organics 443... 

As part of the overall scale-inhibiting threshold effect, the mechanism of crystal growth retardation is complemented by crystal distortion, whereby the crystal fails to successfully agglomerate into a larger crystalline scale. 

The ability of small concentrations of chemicals such as certain phosphates and polymers to retard relatively large amounts of crystal growth and eventual deposition by incorporation of the chemical into the crystal lattice. 

An increase in viscosity usually accompanies competition. Water molecules bound by the hydrocolloid are no longer effective as solvent molecules and the concentration of the solution is thereby increased. Increase in viscosity itself has a retarding effect on crystal growth. 

According to Hoffman s crystallization theory, a drop in the heat of fusion corresponds to an exponential decrease in nucleation and crystal growth rates [63]. Implicitly, the rate of crystallization is severely retarded by the presence of 3HV comonomer [64, 69, 72]. These low crystallization rates can hamper the melt processing of these copolymers since they necessitate longer processing cycle times. 

The habit of pharmaceutical compounds has been used for purposes of identification, although the method can only be reliably used when the crystallization solvent used to generate the test crystals is carefully controlled. Since the faces of a crystal must reflect the internal structure of the solid, the angles between any two faces of a crystal will remain the same even if the crystal growth is accelerated or retarded in one direction or another. Toxicologists have made extensive use of microscopy following multiple recrystallization, and they have developed useful methods for compound identification [5]. 

Crystals grow by addition of molecules from the surroundings to the exposed faces of the crystal. When there are present in the surroundings not only substrate molecules but also impurity molecules that are stereochemically similar to the substrate, these latter molecules may also add to the surfaces. The result will be a retardation of crystal growth (267). Furthermore, since the energy of the attachment of the impurity will differ from face to face, a modification of the crystal morphology may also result (268,269). 

The level of impurity uptake can be considered to depend on the thermodynamics of the system as well as on the kinetics of crystal growth and incorporation of units in the growing crystal. The kinetics are mainly affected by the residence time which determines the supersaturation, by the stoichiometry (calcium over sulfate concentration ratio) and by growth retarding impurities. The thermodynamics are related to activity coefficients in the solution and the solid phase, complexation constants, solubility products and dimensions of the foreign ions compared to those of the ions of the host lattice [2,3,4]. 

Although most additives that have been studied retard growth on all faces of the crystal, there are some which definitely promote growth on certain faces. For example, repeated recrystallization of lactose removes growth-promoting trace substances, so that crystal growth is much slower in supersaturated solutions of this lactose than in less purified solutions. The tendency toward spontaneous nucleation is also lowered upon repeated recrystallization. 

The rate of the supercooled liquid transition to the crystalline state at T < Tm depends on two factors the number of the crystallization centres formed per unit time in unit volume, nc, and the linear rate of the crystal growth, vc. At T < Tm, v,. at first increases as the temperature decreases. This is connected with the fact that the heat which is liberated upon formation of the crystals and retards their formation dissipates more efficiently the lower is the temperature of the solution. Then, vc reaches its maximum and,... 

Retardation of crystal growth due to self-poisoning occurs preferentially on 100 faces. 

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