Recrystallization

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recrystallization

[rē‚krist·əl·ə′zā·shən]
(chemistry)
Repeated crystallization of a material from fresh solvent to obtain an increasingly pure product.
(crystallography)
A change in the structure of a crystal without a chemical alteration.
(metallurgy)
A process which takes place in metals and alloys following distortion and fragmentation of constituent crystals by severe mechanical deformation, in which some fragments grow at the expense of others, so that larger, strain-free grains are formed; it progresses slowly at room temperature, but is greatly speeded by annealing.
(petrology)
The formation of new mineral grains in crystalline form in a rock under the influence of metamorphic processes.

Recrystallization

 

(1) Recrystallization in the solid state is the change in the crystal structure of a substance that takes place upon heating or cooling, without a change in the state of aggregation. It is determined by the polymorphic (allotropic) transformations of the components forming the solid.

(2) Recrystallization from solutions is a process involving the dissolution of a crystalline substance with the subsequent precipitation of its crystals from the solution. It is used to remove impurities from crystalline substances.


Recrystallization

 

the process of the formation and growth, or only the growth, of single crystalline grains (crystallites) of a polycrystal at the expense of other grains of the same phase. The rate of recrystallization increases exponentially with temperature. Recrystallization is especially rapid in plastically deformed materials.

Three stages of recrystallization are distinguished: the primary stage, in which new, nondeformed crystallites are formed in the deformed material and grow by absorbing the deformed grains; the accumulative stage, in which the nondeformed grains grow at each other’s expense, as a result of which the average size of the grain increases; and secondary recrystallization, which differs from the accumulative stage in that only a few of the nondeformed grains have the capacity to grow. In the course of secondary recrystallization the structure is characterized by grains of different sizes.

Recrystallization eliminates structural defects, alters the size of the grains, and may alter the crystallographic orientation of the grains (texture). Recrystallization changes the state of a substance to one of greater thermodynamic stability. In the primary stage this change is due to a reduction in the distortions produced by the deformation, and in accumulative and secondary recrystallization it is due to a reduction in the total surface area of the boundaries between the grains. Recrystallization alters all the structurally sensitive properties of the deformed material and often restores the predeformation structure, texture, and properties. Sometimes the structure and texture after recrystallization differ from the original structure and texture and thus there is also a difference in properties.

Recrystallization is widely used in industry in metal and alloy technology to regulate the shape and size of the grains and the texture and properties of the metals and alloys.

REFERENCE

Gorelik, S. S. Rekristallizatsiia metallov i splavov. Moscow, 1967.

S. S. GORELIK

References in periodicals archive ?
Long residence times allow the molten PP derived from the melted beta crystals to recrystallize into alpha crystals, and this recrystallization diminishes the benefits resulting from the beta crystals in the extruded sheet.
At the poem's end, the salts conceived as destructive at its beginning dissolve and recrystallize to suggest the reviving power of smelling salts, the liveliness, freshness, and wit that salt figuratively gives.
If the relative humidity varies seasonally in these structures, as it often does, he says, the salt that's accumulated will alternately dissolve and recrystallize. This can damage a wall by fracturing the porous material.
In the process of annealing treatment, the oriented crystals obtain enough energy to rearrange the molecular chains, to recrystallize, and finally form more regular crystals.
Sometimes he dissolves or melts them, then slowly cools them until they recrystallize. Other times he slices thin, transparent sections.
Dental researchers have long sought a way to make calcium phosphate dissolve and then recrystallize on teeth.
Then the researchers apply very high pressure to dissolve and recrystallize a cluster into a single gem.
If the crystals thicken at the solid state or melt and recrystallize during the heating from [T.sub.c], to [T.sub.m], it results that erroneous TG plots are generated as the [T.sub.m] values do not correspond to the measured lamellar thickness.
Then when the sun heats the stone in the day, the salts recrystallize, creating pressure in the pores of the stone that can break the limestone apart.
Molecular nucleation occurs when chains or chain segments melt near or on high-melting crystals, and then with negligible cooling, they can nucleate and recrystallize on these existing unmelted crystals.
On the other hand, the lower melting phase of rubber B (peak temperature of 110 [degrees] C) would recrystallize without epitaxy, while the ring pattern on Fig.
It has been suggested that these are longitudinal regions of lower density or lower constraint, which melt before and recrystallize within the surrounding rigid cage of material, possibly associated with a rigid stretched molecular network of entangled molecules.