dispersion

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dispersion,

in physics: see spectrumspectrum,
arrangement or display of light or other form of radiation separated according to wavelength, frequency, energy, or some other property. Beams of charged particles can be separated into a spectrum according to mass in a mass spectrometer (see mass spectrograph).
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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 suspensionsuspension,
in chemistry, mixture of two substances, one of which is finely divided and dispersed in the other. Common suspensions include sand in water, fine soot or dust in air, and droplets of oil in air. A suspension is different from a colloid or solution.
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, colloidcolloid
[Gr.,=gluelike], a mixture in which one substance is divided into minute particles (called colloidal particles) and dispersed throughout a second substance. The mixture is also called a colloidal system, colloidal solution, or colloidal dispersion.
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, or solutionsolution,
in chemistry, homogeneous mixture of two or more substances. The dissolving medium is called the solvent, and the dissolved material is called the solute. A solution is distinct from a colloid or a suspension.
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. 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.

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.

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.

dispersion

see MEASURES OF DISPERSION.

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.)

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 elementCommon geochemical analogueNature of accumulation and occurrenceConcentrating mineralsIndustrial extraction
Cadmium Cd2+Zinc Zn2+Complex deposits, especially skarn typeSphaleriteAs a by-product from complex and copper-zinc pyrite deposits
  Copper-zinc pyrite depositsSphalerite 
  Oxidized zone in complex depositsGreenockite, CdS 
   Otavite, CdCO3 
Gallium Ga3+Aluminum Al3+Nepheline syenitesNepheline
Sodalite
Hackmanite
 
  Complex and copper-complex deposits in carbonaceous rocksSphalerite
Gallite, CuGaS2
 
  BauxitesBoehmite
Hydrargillite
Diaspore
Chiefly as a by-product of aluminum production from bauxites
Germanium Ge4+, Ge2+Silicon Si4+Complex deposits in carbonaceous rocksSphaleriteAs a by-product from certain complex deposits
 Zinc Zn2+Copper-germanium depositsGermanite, 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
MagnetiteFrom 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 metasomatitesMalacon 
Indium In3+Zinc Zn2+Sphalerites rich in Fe of high-temperature complex depositsSphaleriteAs a by-product from complex and tin-complex deposits
 Tin Sn4+Cassiterite-sulfide (sphalerite-chalcopyrite-pyrrhotine) deposits with wood tinSphalerite
Roquesite, CulnS2
Indite, FeIn2S4
 
Rhenium Re6+Molybdenum Mo6+Hydrothermal coppermolybdenum, uraniummolybdenum, and molybdenum depositsMolybdeniteAs a by-product from molybdenum ores
  Copper sandstonesDzhezkazganite, Cu(Mo, Re)S4As a by-product from copper ores
  Copper shalesMolybdenite 
Rubidium Rb+Potassium K+Pegmatites (late stages) in potassium and cesium mineralsMicrocline
Rb-muscovite
Lepidolite
Pollucite
As a by-product from lepidolite-type and pollucite-type lithia micas during processing into Li and Cs
  GreisensZinnwalditeAs a by-product from lithia micas
  Sedimentary deposits of potassium saltsSylvite
Carnallite
As a by-product from potassium salts
Scandium Sc+Rare-earth elements of yttrium group TRY3+Rare-earth pegmatitesSamarskite
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 depositsDaviditeAs a by-product of processing davidite concentrates into uranium
 Iron Fe2+
Magnesium Mg2+
Greisen cassiterite wolframite depositsWolframite
Cassiterite
Beryl
As a by-product of processing cassiterite-wolframite and wolframite concentrates
 Zirconium Zr4+Alluvial depositsZircon
Malacon
As a by-product of processing zircon concentrates
 Aluminum Al3+Bauxite depositsAluminum mineralsAs a by-product from hematite in the production of aluminum
Selenium Se2-Sulfur S2-Copper-nickel sulfide depositsPyrrhotine
Chalcopyrite
Pentlandite
Cubanite
As a by-product from ores of copper-nickel copper-molybdenum, copper-pyrite, and pyrite-complex deposits
Tellurium Te2- Copper-molybdenum depositsMolybdenite 
  Copper pyrite depositsPyrite
Chalcopyrite
Galenite
 
  Complex and complex-pyrite depositsGalenite 
  Selenide depositsClausthalite (PbSe) and other selenidesFrom independent selenide deposits of the Pacajaca type (Bolivia)
  Gold-tellurium depositsNative tellurium and gold, silver, and bismuth telluridesAs a by-product from gold ores
  Sedimentary selenium-uranium-vanadium depositsNative selenium and secondary selenidesAs a by-product of processing ores to obtain uranium and vanadium
Thallium TI+, TI3+Potassium K+Pegmatites (late stages) in Rb-enriched potassium mineralsLepidolite 
 Rubidium Rb+Pyrite-complex and stratiform complex depositsGaleniteChiefly as a by-product of processing ores from complex deposits
 Lead Pb2+Low-temperature hydrothermal sulfide complex and antimony-mercury depositsGalenite
Geocronite, Pb5(Sb, As)2S8
Menaghinite, CuPb13Sb7S24
Pyrite
Marcasite
 
  Low-temperature arsenic depositsLorandite, 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 anorthositesTitanomagnetite
Magnetite
As a by-product of processing titanomagnetite ores
 Iron Fe3+Oxidized zones of complex depositsDescloizite, (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 asphaltitesPetroleum ash Patronite VS4As 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

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.

dispersion

1. Any gas, liquid, or solid containing finely dispersed particles in suspension.
2. A paint containing finely dispersed particles of pigment or latex.

dispersion

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.

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.