dispersion

dispersion,

in physics: see spectrum.

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dispersion,

in chemistry, mixture in which fine particles of one substance are scattered throughout another substance. A dispersion is classed as a suspension, colloid, or solution. Generally, the particles in a solution are of molecular or ionic size; those in a colloid are larger but too small to be observed with an ordinary microscope; those in a suspension can be observed under a microscope or with the naked eye. A coarse mixture (e.g., sand mixed with sugar) is usually not thought of as a dispersion.

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Dispersion (radiation)

The separation, by refraction, interference, scattering, or diffraction, of acoustic and electromagnetic radiation or energy into its constituent wavelengths or frequencies. For a refracting, transparent substance, such as a prism of glass, the dispersion is characterized by the variation of refractive index with change in wavelength of the radiation. Refractive index (n) is defined as the ratio of the velocity of the radiation in free space (air at standard temperature and pressure for sound, and a vacuum for electromagnetic radiation) to the velocity in the substance in question. I. Newton used a small hole in a window shade and a glass prism to disperse sunlight into a visible spectrum, from violet through red. Using a second prism, he showed that no further decomposition of any of the spectral colors could be achieved. See Optical prism, Refraction of waves

The condition where the refractive index decreases as wavelength increases is termed normal dispersion. The opposite condition is termed anomalous dispersion, and almost always occurs in regions outside the range of visible wavelengths.

McGraw-Hill Concise Encyclopedia of Physics. © 2002 by The McGraw-Hill Companies, Inc.

dispersion

1. The separation of a beam of light into its component colors, i.e. into its component wavelengths, so that a spectrum is formed. It arises because of the variation of the refractive index of the transmitting medium with wavelength. It occurs in a lens or prism, causing chromatic aberration. It also occurs to a small extent in the Earth's atmosphere, producing atmospheric dispersion. Normally the refractive index of a transparent substance increases as the wavelength decreases: blue light is refracted (bent) more than red light. See also spectrograph.

2. The retardation of radio waves that occurs when they pass through ionized gas in the interstellar medium, the speed of propagation depending on frequency: the lower the frequency the greater the delay. This delay is not observable in a continuous radio signal but is detectable in a pulsed one, such as that from a pulsar. The amount of dispersion gives an indication of distance to a pulsar.

See also dispersion measure.

Collins Dictionary of Astronomy © Market House Books Ltd, 2006

dispersion

see MEASURES OF DISPERSION.

Collins Dictionary of Sociology, 3rd ed. © HarperCollins Publishers 2000

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Dispersion

 

the fine pulverization of solids or liquids in the surrounding medium, leading to the formation of disperse systems: powders, suspensions, and emulsions. The dispersion of liquids in gases (air) is usually called atomization, whereas the dispersion of liquids in liquids is called emulsification. The expenditure of work required for dispersion is proportional to the required degree of pulverization and to the surface energy at the boundary between the body being pulverized and the surrounding medium.

In industry, dispersion is accomplished using mills of various designs (such as ball, vibrating, colloid, and air-pressure mills), as well as sonic and ultrasonic vibrators. Turbulent (cyclonic) mixing and homogenizers of various types, which are devices for the preparation of homogeneous emulsions, are used to disperse liquids. Mortars are widely used in laboratories and pharmacies for dispersion.

Mechanical dispersion yields particles as small as 10-1 micron. High-efficiency pulverization is possible only in the presence of dispersants and emulsifiers, which are surface-active materials that lower the surface energy of the solids or liquids being dispersed and reduce the work of dispersion. In addition, these materials prevent aggregation—that is, the adhesion of small particles and droplets (coagulation and coalescence). Very strong reduction of the surface energy may lead to spontaneous dispersion without the expenditure of external energy as a consequence of the thermal motion.

Dispersion is used in the production of cements, pigments, fillers, flour, and many foods and fodder concentrates, in the application of agricultural pesticides, and in the combustion of liquid and solid fuels.

REFERENCES

Khodakov, G. S. Fizika izmel’cheniia. Moscow [in press].
Khodakov, G. S. Tonkoe izmel’chenie stroitel’nykh materialov. Moscow [in press].
Guiot, R. Problema izmel’cheniia i ee razvitie. Moscow, 1964. (Translated from French.)

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Dispersion

 

the natural deviation, or deflection, from the target, of artillery shells, mortar shells, rockets, bullets, missiles,

Table 1. Principal dispersed elements and their ores
Dispersed element	Common geochemical analogue	Nature of accumulation and occurrence	Concentrating minerals	Industrial extraction
Cadmium Cd2+	Zinc Zn2+	Complex deposits, especially skarn type	Sphalerite	As a by-product from complex and copper-zinc pyrite deposits
		Copper-zinc pyrite deposits	Sphalerite
		Oxidized zone in complex deposits	Greenockite, CdS
			Otavite, CdCO3
Gallium Ga3+	Aluminum Al3+	Nepheline syenites	Nepheline Sodalite Hackmanite
		Complex and copper-complex deposits in carbonaceous rocks	Sphalerite Gallite, CuGaS2
		Bauxites	Boehmite Hydrargillite Diaspore	Chiefly as a by-product of aluminum production from bauxites
Germanium Ge4+, Ge2+	Silicon Si4+	Complex deposits in carbonaceous rocks	Sphalerite	As a by-product from certain complex deposits
	Zinc Zn2+	Copper-germanium deposits	Germanite, Cu3(Ge, Fe)S4 Renierite, Cu3(Fe, Ge)S4	Germanite-renierite ores of the type found in the Tsumeb and Kipushi deposits
	Iron Fe2+	Coking coals		By extraction from supernatant water in the coking of coals
		Brown coals and lignites Sedimentary-metamorphic iron ores	Magnetite	From ashes of combustion coals From slag formed during the smelting of iron ores
Hafnium Hf4+	Zirconium Zr4+	Pegmatites (late stages)	Cyrtolite Alvite	As a by-product of processing zircon-group minerals
		Alkali riebeckite granites after albitization and metasomatites	Malacon
Indium In3+	Zinc Zn2+	Sphalerites rich in Fe of high-temperature complex deposits	Sphalerite	As a by-product from complex and tin-complex deposits
	Tin Sn4+	Cassiterite-sulfide (sphalerite-chalcopyrite-pyrrhotine) deposits with wood tin	Sphalerite Roquesite, CulnS2 Indite, FeIn2S4
Rhenium Re6+	Molybdenum Mo6+	Hydrothermal coppermolybdenum, uraniummolybdenum, and molybdenum deposits	Molybdenite	As a by-product from molybdenum ores
		Copper sandstones	Dzhezkazganite, Cu(Mo, Re)S4	As a by-product from copper ores
		Copper shales	Molybdenite
Rubidium Rb+	Potassium K+	Pegmatites (late stages) in potassium and cesium minerals	Microcline Rb-muscovite Lepidolite Pollucite	As a by-product from lepidolite-type and pollucite-type lithia micas during processing into Li and Cs
		Greisens	Zinnwaldite	As a by-product from lithia micas
		Sedimentary deposits of potassium salts	Sylvite Carnallite	As a by-product from potassium salts
Scandium Sc+	Rare-earth elements of yttrium group TRY3+	Rare-earth pegmatites	Samarskite Euxenite Y(Nb, Ti, Ta)2O6 Gadolinite Orthite Thortveitite, Sc[Si2O7]	As a by-product from the processing of TR-concentrates Independent scandium thortveitite ores
		Hydrothermal quartzilmenite-davidite deposits	Davidite	As a by-product of processing davidite concentrates into uranium
	Iron Fe2+ Magnesium Mg2+	Greisen cassiterite wolframite deposits	Wolframite Cassiterite Beryl	As a by-product of processing cassiterite-wolframite and wolframite concentrates
	Zirconium Zr4+	Alluvial deposits	Zircon Malacon	As a by-product of processing zircon concentrates
	Aluminum Al3+	Bauxite deposits	Aluminum minerals	As a by-product from hematite in the production of aluminum
Selenium Se2-	Sulfur S2-	Copper-nickel sulfide deposits	Pyrrhotine Chalcopyrite Pentlandite Cubanite	As a by-product from ores of copper-nickel copper-molybdenum, copper-pyrite, and pyrite-complex deposits
Tellurium Te2-		Copper-molybdenum deposits	Molybdenite
		Copper pyrite deposits	Pyrite Chalcopyrite Galenite
		Complex and complex-pyrite deposits	Galenite
		Selenide deposits	Clausthalite (PbSe) and other selenides	From independent selenide deposits of the Pacajaca type (Bolivia)
		Gold-tellurium deposits	Native tellurium and gold, silver, and bismuth tellurides	As a by-product from gold ores
		Sedimentary selenium-uranium-vanadium deposits	Native selenium and secondary selenides	As a by-product of processing ores to obtain uranium and vanadium
Thallium TI+, TI3+	Potassium K+	Pegmatites (late stages) in Rb-enriched potassium minerals	Lepidolite
	Rubidium Rb+	Pyrite-complex and stratiform complex deposits	Galenite	Chiefly as a by-product of processing ores from complex deposits
	Lead Pb2+	Low-temperature hydrothermal sulfide complex and antimony-mercury deposits	Galenite Geocronite, Pb5(Sb, As)2S8 Menaghinite, CuPb13Sb7S24 Pyrite Marcasite
		Low-temperature arsenic deposits	Lorandite, TlAsS2 Vrbaite, Tl(As, Sb)3S5
Vanadium V5+	Titanium Ti4+ Phosphorus P5+	Titanomagnetite magmatic deposits in pyroxenites and peridotites and ilmenite-magnetite deposits in gabbro and anorthosites	Titanomagnetite Magnetite	As a by-product of processing titanomagnetite ores
	Iron Fe3+	Oxidized zones of complex deposits	Descloizite, (Zn, Cu)Pb[VO4](OH) Vanadinite, Pb5[VO4]3Cl	Independent vanadium deposits
		Sedimentary carnotite and roscoelite deposits (sandstones)	Carnotite, K2(UO2)2[VO4]2·3H2O Roscoelite, KV2[AlSi3O10](OH, F)2	As a by-product of processing uranium ores
		Phosphorites		As a by-product from phosphorites
		Petroleum deposits and asphaltites	Petroleum ash Patronite VS4	As a by-product from petroleum Independent vanadium deposits in asphaltites

and bombs when fired, launched, or dropped from the same weapon under essentially identical conditions.

Natural dispersion is caused by random factors, such as differences in the weight of the charge and quality of the powder; differences in the weight, shape, and dimension of shells and missiles; differences in the degree of heating and in the condition of the barrel or guide tube; differences in vertical and horizontal laying in repeated shots, missile launches, or bombing; differences in jump angles; and changes in wind velocity and direction and air temperature and density. Dispersion follows the normal distribution; in relation to the dispersion of shells, missiles, and bombs this principle is called the law of dispersion.

In long-range noncontact firing at aerial or underwater targets, the dispersion of shells, missiles, and the like in space is limited to a three-dimensional area called the ellipsoid of dispersion. When firing at flat targets, the corresponding area is called the ellipse of dispersion. A distinction is made between natural dispersion and deliberate man-made dispersion, which is used in firing machine guns at wide, deep targets.

G. M. SHINKAREV

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

dispersion

[də′spər·zhən]

(aerospace engineering)

Deviation from a prescribed flight path; specifically, circular dispersion especially as applied to missiles.

(astronomy)

The frequency dependence of the retardation of radio waves (such as those emitted by a pulsar) when they pass through an ionized gas.

(chemistry)

A distribution of finely divided particles in a medium.

(communications)

The entropy of the output of a communications channel when the input is known.

(electromagnetism)

Scattering of microwave radiation by an obstruction.

(mineralogy)

In optical mineralogy, the constant optical values at different positions on the spectrum.

(physics)

The separation of a complex of electromagnetic or sound waves into its various frequency components.

Quantitatively, the rate of change of refractive index with wavelength or frequency at a given wavelength or frequency.

The rate of change of deviation with wavelength or frequency.

In general, any process separating radiation into components having different frequencies, energies, velocities, or other characteristics, such as the sorting of electrons according to velocity in a magnetic field.

(statistics)

The degree of spread shown by observations in a sample or a population.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

dispersion

1. Any gas, liquid, or solid containing finely dispersed particles in suspension.

2. A paint containing finely dispersed particles of pigment or latex.

McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.

dispersion

i. Spreading or scattering shots about a target in air-to-air or air-to-ground gunnery.
ii. The average distance from the aiming point of bombs or other armament dropped under identical conditions.
iii. The process in which electromagnetic radiation is separated into its components.

An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved

dispersion

In optical fibers, the broadening of the waveforms over long distances by the time they reach the receiving end, which makes them difficult to interpret. There are three major causes. One is the multiple transmission paths (modes) possible in large-core multimode fibers where each path results in a different travel distance.

A second cause has to do with the varying of the refractive index due to changes in frequency (or correspondingly, changes in wavelength). The speed of light in a fiber is based on the frequency of light and the refractive index of the fiber. Thus, different frequencies travel at different speeds. The problem is that there are always multiple frequencies. Analog signals are naturally many frequencies, but digital pulses are also more than one frequency, because it is difficult to create a perfect single frequency.

The third cause of dispersion is the random fluctuations of light polarization inside the fiber. Following are the common types of dispersion.

Modal Dispersion (or Intermodal Dispersion)
Occurs in multimode fibers, because light travels in multiple modes (reflective paths), and each path results in a different travel distance. Modal dispersion is a major problem with multimode fibers.

Chromatic Dispersion
The sum of material dispersion and waveguide dispersion. "Material dispersion" is caused by the variation in refractive index of the glass in the fiber. "Waveguide dispersion" is due to changes in the distribution of light between the core and the cladding of a singlemode fiber.

Polarization Mode Dispersion (PMD)
Light travels in two polarization states in singlemode fibers. Over long distances, conditions such as stress and slight irregularities in the fiber core cause random fluctuations in how the two polarizations travel through the fiber. As a result, they gradually spread over the square root of the distance. See refractive index, dispersion compensator, step index fiber, graded-index fiber, dispersion-shifted fiber and fiber optics glossary.

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