Crystal, habit system

Ammonium sulfate [7783-20-2], (NH 2 U4, is a white, soluble, crystalline salt having a formula wt of 132.14. The crystals have a rhombic stmcture d is 1.769. An important factor in the crystallization of ammonium sulfate is the sensitivity of its crystal habit and size to the presence of other components in the crystallizing solution. If heated in a closed system ammonium sulfate melts at 513 2° C (14) if heated in an open system, the salt begins to decompose at 100°C, giving ammonia and ammonium bisulfate [7803-63-6], NH HSO, which melts at 146.9°C. Above 300°C, decomposition becomes more extensive giving sulfur dioxide, sulfur trioxide, water, and nitrogen, in addition to ammonia. 

In the host/additive systems described above, such as (/ ,S)-ser/(/ ,S)-thr and glycine/(/ ,S)-a-amino acids, the change in crystal habit and the enantiomeric segregation of occluded additive indicates that only a subset of the possible symmetry-related sites may be occupied by an additive depending on through which faces the additives are occluded. Such an effect would lead to a reduction in the overall symmetry of the host/additive crystal. 

Because the rate of growth depends, in a complex way, on temperature, supersaturation, size, habit, system turbulence and so on, there is no simple was of expressing the rate of crystal growth, although, under carefully defined conditions, growth may be expressed as an overall mass deposition rate, RG (kg/m2 s), an overall linear growth rate, Gd(= Ad./At) (m/s) or as a mean linear velocity, // (= Ar/At) (m/s). Here d is some characteristic size of the crystal such as the equivalent aperture size, and r is the radius corresponding to the... 

The ciystal habit of sucrose and adipic add crystals were calculated from their intern structure and from the attachment energies of the various crystal faces. As a first attempt to indude the role of the solvent on the crystal habit, the solvent accessible areas of the faces of sucrose and adipic add and were calculated for spherical solvent probes of difierent sizes. In the sucrose system the results show that this type of calculation can qualitatively account for differences in solvent (water) adsorption hence fast growing and slow growing faces. In the adipic add system results show the presence of solvent sized receptacles that might enhance solvent interadions on various fares. The quantitative use of this type of data in crystal shape calculations could prove to be a reasonable method for incorporation of solvent effeds on calculated crystal shapes. 

The factors which influence the rate of dissolution of iron oxides are the properties of the overall system (e. g. temperature, UV light), the composition of the solution phase (e.g. pH, redox potential, concentration of acids, reductants and complexing agents) and the properties of the oxide (e. g. specific surface area, stoichiometry, crystal chemistry, crystal habit and presence of defects or guest ions). Models which take all of these factors into account are not available. In general, only the specific surface area, the composition of the solution and in some cases the tendency of ions in solution to form surface complexes are considered. 

Exploiting ATRP as an enabling technology, we have recently synthesised a wide range of new, controlled-structure copolymers. These include (1) branched analogues of Pluronic non-ionic surfactants (2) schizophrenic polymeric surfactants which can form two types of micelles in aqueous solution (3) novel sulfate-based copolymers for use as crystal habit modifiers (4) zwitterionic diblock copolymers, which may prove to be interesting pigment dispersants. Each of these systems is discussed in turn below. 

When suspensions are formulated to provide a stable system, the particle size becomes critical. Flocculated suspensions also require careful particle size control either in the process of manufacturing or in the starting material. Equally important is the crystal habit — the outward appearance of an agglomeration of crystals. Crystal structure can be altered during the manufacturing process, particularly if the product is subject to temperature cycling, and this can alter the stability of suspensions. 

The various members of the feldspar group show many characteristics in common. Crystallizing in the monoclime and irieiinie systems, they show similarity of crystal habit, cleavage and other physical properties as well as similar chemical relationships,... 

PROUSTITE. This ruby-silver mineral crystallizes in the hexagonal system its name is a product of its scarlet-to-vermilion color when first mined It is a silver arsenic sulfide. AgjAsS, of adamantine luster Hardness of 2-2,5 specific gravity of 5.55-5.64. Usual crystal habit is prismatic to rhombohedral more commonly occurs massive. Conchoidal to uneven fracture transparent to translucent color, scarlet to vermilion red. Light sensitive must be kept in dark environment to maintain its primary character. A product of low-tcmpcraturc formation in most silver deposits. Notable world occurrences include the Czech Republic and Slovakia, Saxony, Chile and Mexico. Found in minor quantities in the United States the most exceptional occurrence at the Poorman Mine, Silver City District. Idaho where a crystalline mass of some 500 pounds (227 kilograms) was recovered m 1865, It was named for the famous French chemist, Louis Joseph Proust. 

Because the parameter depends on temperature, crystal habit will normally change when the growth temperature changes drastically. Crystal defects (dislocations, twins, and inclusions) are also responsible for morphological changes. The flow of solution around a crystal also influences its shape as is discussed in the next section. But the most important factor that can be used to change crystal habit is the addition of impurities to the precipitating system. 

System Orthorhombic Crystal Habit Columnar Optical sign + Axial angle ... 

System Orthorhombic Crystal Habit columnar Optical Sign - Axial Angle 69 Optic orientation (assigned acc.to crystal habit) XX c YY a ZZ b. Dispersion None observed Refractive Indexes a (w) = 1.517 (3 ( e) = 1.567 y = 1.592 Density 1.379 Refraction Experimental = 111.90 Calculated = 113.99. 

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