crystallization

Crystallization is a technique that has long been used in the purification of substances. Often, when a solid substance (single compound) is placed in a liquid, it dissolves. Upon adding more of the solid, a point eventually is reached beyond which no…

…about a certain degree of crystallization in the normally random atomic structure. Glassy materials that exhibit such a structure are called glass ceramics. Commercially useful glass ceramics are those in which a high density of uniformly sized, nonoriented crystals has been achieved through the bulk of the material, rather than…

…for a perceptible degree of crystallization to take place, there must be a finite amount of “supercooling” below the freezing point b (which is also the melting point, T_m, of the corresponding crystal). Crystallization is essentially two processes: nucleation (the adoption of a patterned arrangement by a small number of…

…is a matter of bypassing crystallization. The channel to the crystalline state is evaded by quickly crossing the temperature interval between T_f and T_g. Nearly all materials can, if cooled quickly enough, be prepared as amorphous solids. The definition of “quickly enough” varies enormously from material to material. Four techniques…

…process that occurs in the formation of a crystal from a solution, a liquid, or a vapour, in which a small number of ions, atoms, or molecules become arranged in a pattern characteristic of a crystalline solid, forming a site upon which additional particles are deposited as the crystal grows.

…pack together in an ordered crystalline arrangement. In high-density polyethylene, for example, the long sequences of ethylene units that make up the polymer spontaneously crystallize at temperatures below about 130 °C (265 °F), so that, at normal temperatures, polyethylene is a partially crystalline plastic solid. Polypropylene is another “semicrystalline” material:…

…and some other salts are crystallized from hot solutions. In all of these cases, positive and negative electric charges are produced by the mechanical separation of surfaces and during the crystallization process. Light emission then occurs by discharge, either directly, by molecule fragments, or via excitation of the atmosphere in…

The crystallization of magma is a complex process because magma is a complex substance. Certain magmas, such as those which form granites, contain several percent water dissolved in them. When a granitic magma cools, the first minerals to crystallize tend to be anhydrous (e.g., feldspar), so…

Because magmas are multicomponent solutions, they do not crystallize at a single temperature at a given pressure like water at 0 °C and one atmosphere pressure. Rather, they crystallize over a wide range of temperatures beginning at liquidus temperatures…

The crystallization of wax from lubricating oil fractions is essential to make oils suitable for use. A solvent (often a mixture of benzene and methyl ethyl ketone) is first added to the oil, and the solution is chilled to about −20 °C (−5 °F).…

…principle is used to explain recrystallization in metamorphic rocks when minerals become oriented with their long dimensions parallel. Usually, mineral deformation in a metamorphic rock is caused by a combination of slippage along minute fractures, strain of the crystal lattice, and recrystallization according to Riecke’s principle.

…and alumina combine to form crystalline clays.

Freezing is a crystallization process that begins with a nucleus or a seed derived from either a nonaqueous particle or a cluster of water molecules (formed when the temperature is reduced below 0 °C). This seed must be of a certain size to provide an adequate site for…

…run through a series of crystallizing pans, usually four in number, where the salt is deposited as evaporation proceeds. In the first crystallizing pan, the brine is concentrated to a specific gravity of 1.23 and remains partly contaminated with calcium sulfate. The specific gravity of the solution in the pan…