Transport chromium

Soluble forms and suspended chromium can undergo intramedia transport. Chromium(VI) in water will eventually be reduced to chromium(in) by organic matter in the water. It has been estimated that the residence time of chromium (total) in Lake Michigan ranges from 4.6 to 18 years (Fishbein 1981 Schmidt and Andren 1984). 

Sodium Bisulfite, CHRIS Hazardous Chemical Data, Coast Guard, U.S. Dept, of Transportation, Washington, D.C., data sheet revised 1978. Treatment of Chromium Waste Eiquors, General Chemical Corp., Claymont, Del., 1989. 

Mukherjee studied the gas phase equilibria and the kinetics of the possible chemical reactions in the pack-chromising of iron by the iodide process. One conclusion was that iodine-etching of the iron preceded chromis-ing also, not unexpectedly, the initial rate of chromising was controlled by transport of chromium iodide. Neiri and Vandenbulcke calculated, for the Al-Ni-Cr-Fe system, the partial pressures of chlorides and mixed chlorides in equilibrium with various alloys and phases, and so developed for pack aluminising a model of gaseous transport, solid-state transport, and equilibria at interfaces. 

In the hydraulic transport of solids through steel pipelines, inhibitors of the sodium-zinc-phosphate glass type have been shown" to be effective. In the case of coal slurries the polyphosphate type was rejected because the de-oxygenating action of the coal lowered the inhibitor effectiveness. Hexavalent chromium compounds at 20 p.p.m. were more effective". ... 

The transport of pre-boiler corrosion debris to the boiler section includes the oxides of iron, copper, nickel, zinc, and chromium and results from the corrosion of pre-heaters and condensers, and the like. Specifically, equipment components variously fabricated from admiralty brass, aluminum brass, cupronickels, and stainless steels are most affected. 

Many types of oxide layers have a certain, not very high electrical conductivity of up to 10 to 10 S/cm. Conduction may be cationic (by ions) or anionic (by or OH ions), or of the mixed ionic and electronic type. Often, charge transport occurs by a semiconductor hole-type mechanism, hence, oxides with ionic and ionic-hole conduction are distinguished (in the same sense as p-type and n-type conduction in the case of semiconductors, but here with anions or cations instead of the electrons, and the corresponding ionic vacancies instead of the electron holes). Electronic conduction is found for the oxide layers on iron group metals and on chromium. 

Srinath T, Verma T, Ramteke PW, Garg SK (2002) Chromium biosorption and bioaccumulation by chromate resistant bacteria. Chemosphere 48 427-435 Stephen JR, Macnaughton SJ (1999) Developments in terrestrial bacterial remediation of metals. Curr Opinion Biotechnol 10 230-233 Tabak HH, Lens P, van Hullebusch ED, Dejonghe W (2005) Developments in bioremediation of soils and sediments polluted with metals and radionuclides 1. Microbial processes and mechanisms affecting bioremediation of metal contamination and influencing metal toxicity and transport. Rev Environ Sci Bio/Technol. 4 115-156... 

Another problem in the construction of these devices, is that materials which do not play a direct part in the operation of the microchip must be introduced to ensure electrical contact between the electronic components, and to reduce the possibility of chemical interactions between the device components. The introduction of such materials usually requires an annealing phase in the construction of the device at a temperature as high as 600 K. As a result it is also most probable, especially in the case of the aluminium-silicon interface, that thin films of oxide exist between the various deposited films. Such a layer will act as a barrier to inter-diffusion between the layers, and the transport of atoms from one layer to the next will be less than would be indicated by the chemical potential driving force. At pinholes in the A1203 layer, aluminium metal can reduce Si02 at isolated spots, and form the pits into the silicon which were observed in early devices. The introduction of a thin layer of platinum silicide between the silicon and aluminium layers reduces the pit formation. However, aluminium has a strong affinity for platinum, and so a layer of chromium is placed between the silicide and aluminium to reduce the invasive interaction of aluminium. 

It is known that part of this process involves the 80-kDa blood serum protein transferrin that tightly binds and transports two ferric iron ions. Because the iron binding uses only 30% of transferrin s metal binding capacity, it has long been thought to bind and transfer other metal ions (including perhaps chromium) in vivo, although this has not been demonstrated by experiment. 

Functionally, as shown in Figure 4.10, the protection layer is intended first to serve as a mass barrier to both chromium cation outward and oxygen inward transport... 

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