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[Afrik.,=apartness], system of racial segregation peculiar to the Republic of South Africa, the legal basis of which was largely repealed in 1991–92. History
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in U.S. history, the goal of an organized movement to break down the barriers of discrimination and segregation separating African Americans from the rest of American society.
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segregationthe spatial separation of a RACE, CLASS OR ETHNIC GROUP by discriminatory means. Racial segregation can be enforced by law, as in the southern US until the 1950s, or in the system of APARTHEID in South Africa. Such segregation can take the form of separate facilities (schools, beaches, transport, etc.) or the establishment of racially homogeneous territories (as in the ‘Bantustan’ policy in South Africa pre-1991). In many countries, residential or educational segregation exists that does not have the force of law but results from economic and social DISCRIMINATION. See also GHETTO.
(or liquation), in metallurgy, heterogeneity in the chemical composition of alloys that occurs upon crystallization. The term has a special meaning when used with reference to steel, as first discovered by the Russian metallurgists N. V. Kalakutskii and A. S. Lavrov in 1866.
Segregation occurs because alloys, unlike pure metals, crystallize within a range of temperatures rather than at a certain fixed temperature. The composition of crystals formed during the early solidification stage may differ considerably from that of the final batches of crystallizing mother liquor. The wider the temperature range of crystallization of an alloy, the greater the development of segregation. In addition, the alloy components that have the strongest effect on the range of crystallization temperatures (for example, sulfur, oxygen, phosphorus, and carbon in the case of steel) exhibit the greatest tendency to undergo segregation. Segregation usually produces an adverse effect on the quality of metal, since it leads to irregularity of its properties.
A distinction is made between dendritic segregation, which occurs in microscopic volumes of an alloy that are approximately equal to grain sizes, and zonal segregation, which is observed throughout the ingot. In dendritic segregation, the axes of dendritic crystals differ in chemical composition from the interaxial spaces. This type of segregation can be largely eliminated by prolonged annealing of the metal (homogenization), through diffusion of impurities. Zonal segregation is characterized by the existence in the ingot of several zones with differing chemical composition, which are referred to as positive or negative segregation zones, depending on the type of deviation from the average alloy composition. Axial and extra-axial types of segregation are also distinguished. To reduce zonal liquation, ingot dimensions are limited and special metallurgical processes, such as continuous casting or electroslag or vacuum remelting in a water-cooled crystallizing tank, are used.
REFERENCESGolikov, I. N. Dendritnaia likvatsiia v stali. Moscow, 1958.
Shteinberg, S. S. Metallovedenie. Sverdlovsk, 1961.
Winegard, W. Vvedenie ν fiziku kristallizatsii metallov. Moscow, 1967. (Translated from English.)
A. IA. STOMAKHIN
in nonferrous metallurgy, the combined process of roasting an oxide ore and subsequent concentration. The aim of segregation is the conversion of valuable metals in difficult-to-concentrate ores into metallic granules 20–40 microns in size. The metals are then removed in the concentrate by flotation methods or magnetic separation.
Segregation roasting consists in heating the ore with small amounts of a chloride salt, for example, NaCl or CaCl2, and a reducing agent in the presence of moisture. Hydrogen chloride (HC1) is formed in the roasting process and chlorinates the valuable metals. Volatile chlorides form and are reduced to the metallic state by hydrogen over the solid reducing agent with the regeneration of HC1. The metallic granules increase in size with repetitions of the cycle. The process may be used to extract metals that form volatile chlorides, such as Cu, Ni, Co, Pb, Sn, Sb, Bi, Ti, Au, and Ag.
The process of segregation of copper oxide ores, which are difficult to concentrate, has acquired the name TORCO, an acronym for “treatment of refractory copper ores.” The TORCO process is used on a commercial scale in plants at Rhokana, Zambia, with a daily capacity of 500 tons of ore and at Akjoujt, Mauritania, with a daily capacity of 900 tons. The roasting is carried out in two steps. The ground ore, together with an additive of coal smalls, is first heated in a fluidized-bed furnace to a temperature up to 800°-820°C. The hot material is then transferred to the segregation reactor, where coal and rock salt are added. The duration of the reaction of the components in the reactor is approximately 10 min. The hot calcine from the reactor is then washed in a conduit by a stream of water, and sodium sulfide is added for the final stage—flotation. An extraction efficiency of up to 95 percent is possible in segregating copper ore containing 2 percent copper into a concentrate containing 60 percent.
For nickel oxide ores, which cannot be concentrated by the usual methods, the roasting should be carried out at a temperature higher than that used in roasting copper ores. The consumption of reagents in roasting and flotation is greater, and the ferronickel concentrate has a lower nickel content than the copper content in copper concentrate. In addition to nickel, some of the iron present enters the concentrate.
REFERENCESWright, J. K., “The Segregation Process.” Minerals Science and Engineering, 1973, vol. 5, no. 2, pp. 119–34. (V1NIT1 abstract Ekspress-informatsiia tsvetnoi metallurgii, 1973, no. 31.)
Pevzner, G. R. “Obogashchenie rud.” Biul. in-ta Mekhanobr, 1974, no. 1, pp. 39–45.
“Izvlechenie nikelia iz zhelezistykh okislennykh nikelevykh rud metodom segregatsii.” Tsvetnye metally, 1975, no. I, pp. 8–11.
I. D. REZNIK
in mining, the vertical distribution according to size of grains of a material within some layer. When a stack of material slides, the large pieces primarily accumulate below. In this case, the lower layers are filled with large pieces. In another case, under the action of vibration fine grains appear to be sifted to the lower part of the layer. The principle of segregation is used in the concentration of minerals, for example, in separating mineral mixtures on a concentration table.
in biology, the development of local differences in the properties of ooplasm during the period of growth and maturation in an oocyte and in a fertilized egg. Segregation is the basis for the subsequent differentiation of an embryo; in the course of the cleavage of an egg portions of the ooplasm with unlike properties enter different blastomeres. The interaction of the blastomeres with cleaved nuclei having identical potencies results in the differential activation of a genome.
Segregation occurs at different times in different animals and is manifested in varying degrees. It is most distinctly observed in animals with a mosaic type of development, although it also occurs in animals with a regulative type of development. Examples of segregation include the formation of polar plasmas in mollusks and the concentration of RNA in the future dorsal hemisphere of a mammalian egg.
REFERENCESWilson, E. Kletka i ee rol’ v ravitii i nasledstvennosti, vol. 2. Moscow-Leningrad, 1940. (Translated from English.)
Raven, C. Oogenez. Moscow, 1964. (Translated from English.)
Bodemer, C. Sovremennaia embriologiia. Moscow, 1971. (Translated from English.)
A. S. GINZBURG
in bourgeois states, the forcibly maintained separation of different racial groups in the population.
Segregation is always accompanied by discrimination against a national group, even when the principle of racial equality has been formally established, as in the USA. There are two forms of segregation. Institutional segregation is introduced in all spheres of social life, including schools, universities, hospitals, social services, and transportation, by the establishment of parallel institutions or of separate facilities for blacks and coloreds in a particular institution. Under territorial segregation, racial groups are restricted to certain territories. Territorial segregation is one expression of the policy of apartheid in the Republic of South Africa. Institutional segregation is usually accompanied by the territorial isolation of racial groups, as in the Republic of South Africa and Rhodesia.