Crystal growth water

Increased pressures can lower the temperature at which crystallisation occurs. Experiments performed using Spectrosil (Thermal Syndicate Ltd.) and G.E. Type 204 (General Electric Company) fused siUcas (see Eig. 2) show that at pressures above 2.5 GPa (<25, 000 atm), devitrification occurs at temperatures as low as 500°C and that at 4 GPa (<40, 000 atm), it occurs at as low as 450°C (107). Although the temperatures and pressures were in the coesite-phase field, both coesite and quarts were observed. Both the devitrification rate and the formation of the stable phase (coesite) were enhanced by the presence of water. In the 1000—1700°C region at 500—4000 MPa (<5, 000-40,000 atm), a- and p-quarts were the primary phases. Crystal growth rates... 

Physical properties of the acid and its anhydride are summarized in Table 1. Other references for more data on specific physical properties of succinic acid are as follows solubiUty in water at 278.15—338.15 K (12) water-enhanced solubiUty in organic solvents (13) dissociation constants in water—acetone (10 vol %) at 30—60°C (14), water—methanol mixtures (10—50 vol %) at 25°C (15,16), water—dioxane mixtures (10—50 vol %) at 25°C (15), and water—dioxane—methanol mixtures at 25°C (17) nucleation and crystal growth (18—20) calculation of the enthalpy of formation using semiempitical methods (21) enthalpy of solution (22,23) and enthalpy of dilution (23). For succinic anhydride, the enthalpies of combustion and sublimation have been reported (24). 

Scale. Scale deposits are formed by precipitation and crystal growth at a surface in contact with water. Precipitation occurs when solubiUties are exceeded either in the bulk water or at the surface. The most common scale-forming salts that deposit on heat transfer surfaces are those that exhibit retrograde solubiUty with temperature. 

Scaling is not always related to temperature. Calcium carbonate and calcium sulfate scaling occur on unheated surfaces when their solubiUties are exceeded in the bulk water. Metallic surfaces are ideal sites for crystal nucleation because of their rough surfaces and the low velocities adjacent to the surface. Corrosion cells on the metal surface produce areas of high pH, which promote the precipitation of many cooling water salts. Once formed, scale deposits initiate additional nucleation, and crystal growth proceeds at an accelerated rate. 

Other processes also use the dibasic salt as an intermediate. Dibasic calcium hypochlorite can be prepared from filtrates from chlorinated lime slurries in various ways. In one process, the filtrate is returned to the slurry being chlorinated to keep it thin. This is designed to improve crystal growth. The dibasic crystals, together with water, are added to the slurry during chlorination and some dibasic salt is prepared by chlorination in addition to the dibasic salt made from filtrates (188). In another process, dibasic crystals are separated, slurried in water, and chlorinated to obtain a slurry of neutral Ca(OCl)2 2H20 in a mother Hquor of reduced calcium chloride content which is then filtered and air dried (191,192). 

Crystal growth modifiers have been employed to improve filterabiHty and water retention of Ca(OCl)2 2H20, which typically crystallizes as fine plates. Addition of zinc dust or salts produces larger square- and diamond-shaped, untwinned dihydrate crystals (215). Coarse prismatic crystals are obtained by use of carbohydrates and carboxyHc acids and thek salts (216). 

H. Nada, Y. Furukawa. Anisotropic growth kinetics of ice crystals from water studied by molecular dynamics simulation. J Cryst Growth 169 581, 1996. 

When the water is added to the final dry cement material, the hydration of the cement begins immediately. The water is combined chemically with the cement material to eventually form a new immobile solid. As the cement hydrates, it will bond to the surrounding surfaces. This cement bonding is complex and depends on the type of surface to be cemented. Cement bonds to rock by a process of crystal growth. Cement bonds to the outside of a casing by filling in the pit spaces in the casing body [163]. 

Far less than the stoichiometric amount of sequestrants precipitation of insoluble salts from water hardness can be prevented by slowing down the formation of crystals and crystal growth. This process is called the threshold effect. It has long been used in the preparation of boiler feeding water, e.g., steam vessels of railroad engines. Originally sodium pyrophosphate was used for this task, but alkylphosphonic acids and derivatives thereof are superior in their effect. 

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. 

Snow crystals [4] Their macroscopic structure is different from a bulk three-dimensional ice crystal, but they are formed by homologous pair-pair interaction between water molecules and are static and in thermodynamic equilibrium. It should be noted, however, that dendritic crystal growth is a common phenomenon for metals [5-7] and polymers. The crystals grow under non-equilibrium conditions, but the final crystal is static. 

The hypothesis was extended to nucleation of hydrates from liquid water. An alternative hypothesis was proposed by Rodger [1516]. The main difference between these two sets of theories is that Rodger s hypothesis relates the initial formation process to the surface of the water, whereas the theory of Sloan and coworkers considers clusters related to soluted hydrate formers in liquid water as the primary start for joining, agglomeration, and crystal growth. The theories of Sloan and coworkers have been discussed and related to elements of the hypothesis proposed by Rodger [1043]. 

A surfactant is a surface-active agent that is used to disperse a water-insoluble drug as a colloidal dispersion. Surfactants are used for wetting and to prevent crystal growth in a suspension. Surfactants are used quite extensively in parenteral suspensions for wetting powders and to provide acceptable syringability. They are also used in emulsions and for solubilizing steroids and fat-soluble vitamins. 

Some of the reports are as follows. Mizukoshi et al. [31] reported ultrasound assisted reduction processes of Pt(IV) ions in the presence of anionic, cationic and non-ionic surfactant. They found that radicals formed from the reaction of the surfactants with primary radicals sonolysis of water and direct thermal decomposition of surfactants during collapsing of cavities contribute to reduction of metal ions. Fujimoto et al. [32] reported metal and alloy nanoparticles of Au, Pd and ft, and Mn02 prepared by reduction method in presence of surfactant and sonication environment. They found that surfactant shows stabilization of metal particles and has impact on narrow particle size distribution during sonication process. Abbas et al. [33] carried out the effects of different operational parameters in sodium chloride sonocrystallisation, namely temperature, ultrasonic power and concentration sodium. They found that the sonocrystallization is effective method for preparation of small NaCl crystals for pharmaceutical aerosol preparation. The crystal growth then occurs in supersaturated solution. Mersmann et al. (2001) [21] and Guo et al. [34] reported that the relative supersaturation in reactive crystallization is decisive for the crystal size and depends on the following factors. 

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