dispersion(redirected from molecular 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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[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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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.
..... Click the link for more information. . 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.
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.
See also dispersion measure.
dispersionsee MEASURES OF 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.
REFERENCESKhodakov, 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.)
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|
|Gallium Ga3+||Aluminum Al3+||Nepheline syenites||Nepheline|
|Complex and copper-complex deposits in carbonaceous rocks||Sphalerite|
|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|
|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|
|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|
|Rubidium Rb+||Potassium K+||Pegmatites (late stages) in potassium and cesium minerals||Microcline|
|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|
|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
|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|
|Greisen cassiterite wolframite deposits||Wolframite|
|As a by-product of processing cassiterite-wolframite and wolframite concentrates|
|Zirconium Zr4+||Alluvial deposits||Zircon|
|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|
|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|
|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
|Low-temperature arsenic deposits||Lorandite, TlAsS2|
Vrbaite, Tl(As, Sb)3S5
|Vanadium V5+||Titanium Ti4+|
|Titanomagnetite magmatic deposits in pyroxenites and peridotites and ilmenite-magnetite deposits in gabbro and anorthosites||Titanomagnetite|
|As a by-product of processing titanomagnetite ores|
|Iron Fe3+||Oxidized zones of complex deposits||Descloizite, (Zn, Cu)Pb[VO4](OH)|
|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
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.
dispersionIn 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.
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.