Re-deposition

Dezincification of brasses When dezincihcation occurs, regions of the brass become replaced by a porous mass of copper which, though retaining the shape of the original article, has virtually no strength. There has long been discussion as to whether there is selective corrosion of the zinc in the brass, which leaves the copper behind, or whether complete dissolution of the brass occurs, followed by re-deposition of copper. Possibly both processes occur in different circumstances. The mechanism has been investigated and discussed by Evans, Fink", Lucey , Feller" and Heidersbach , and is referred to in many other papers. ... 

Steam/CR system corrosion debris pickup, tranport, and re-deposition. Wide ranging FW line blockages and impingement/erosion Enhances risk of pre-boiler corrosion... 

Localized pre-boiler scale and corrosion debris deposits. Combination of New phosphate, iron, copper, and silica deposition Old re-deposited debris Transport of Fe, Cu, Ni, Zn, Cr oxides to HP boiler section, leading to deposition, fouling, and possible tube failures Transport of minerals and debris including malachite, ammonium carbamate, basic ferric ammonium carbonate Precipitation in FW line of phosphates, iron, and silicates... 

This method emplosrs a molten flux which dissolves the material and re-deposits it upon a seleeted substrate. That is, the molten flux acts as a transport medium. The temperature of the flux can be varied to suit the material and to promote high solubility of the solute material in the molten solvent. One example is YIG", yttrium iron garnet, i.e.- Y3FesOi2 -This material is used in the Electronics Industry as single crystals for microwave generating devices. It can be grown via the molten flux method. 

Benninger et al., [3] found values of about 1 dpm cm 2 yr for the deposition rate of 210Pb in soils and sediments near New Haven, Connecticut and Long Island. Recent measurements in Puget Sound at Sinclair Inlet by W. R. Schell (unpublished data), indicated that the deposition rate was about 0.35 dpm cnr yr. Thus, to explain the very high and variable values for the 210Pb deposition rate at the deep ocean stations, one must propose a mechanism whereby material from the topmost layers of sediments near the Atlantic Disposal Site is transported and re-deposited at these stations. 

Another important point to guarantee the long-term stability of the electrode is the procedure used to manage shutdowns. The experience gained through the laboratory tests shows that during shutdown the cell must be maintained under polarisation conditions to avoid the probable dissolution of the silver catalyst and its re-deposition... 

The related formation equilibrium constant should have a small value if it is zero no XZ would form if, on the other hand, it is very large the stable XZ would not re-decompose and no X re-deposition could be obtained. Notice that if the synthesis of XZ is endothermic, the equilibrium will be displaced to the right with increasing temperature (the opposite is true if the reaction corresponds to an exothermic formation of XZ). Therefore, in order to have the transport of X, (synthesis of the intermediate at one end of the tube and re-decomposition with deposition of X at the other end) this must be placed at the hot end if the formation of XZ is endothermic (or the cold end, if exothermic). 

Particle trapping is also a substantial economic issue, as in many countries the sUtation time scale is relatively short (about 100 yr on a global scale). In alpine reservoirs this time scale is much longer, and measures to mitigate siltation had low priority. However, in the future, sediment management, including removal, will be unavoidable. An occasionally used method is to divert the early arrival of a turbid flash flood past the reservoir, so that most of the sediment is delivered to the downstream river. Also, sediment removal and downstream re-deposition is periodically applied, especially when the downstream river suffers from erosion. 

The first two components are the active surfactants, whereas the other components are added for a variety of reasons. The polyphosphate chelate Ca ions which are present (with Mg ions also) in so-called hard waters and prevents them from coagulating the anionic surfactants. Zeolite powders are often used to replace phosphate because of their nutrient properties in river systems. Sodium silicate is added as a corrosion inhibitor for washing machines and also increases the pH. The pH is maintained at about 10 by the sodium carbonate. At lower pH values the acid form of the surfactants are produced and in most cases these are either insoluble or much less soluble than the sodium salt. Sodium sulphate is added to prevent caking and ensures free-flowing powder. The cellulose acts as a protective hydrophilic sheath around dispersed dirt particles and prevents re-deposition on the fabric. Foam stabilizers (non-ionic surfactants) are sometimes added to give a... 

The soil and air concentrations of p,p -DDT were used in a soil-air exchange model developed by Harner et al. [103] to estimate p,p -DDT emissions to air from soils under steady-state conditions. The volatilization flux of p,p -DDT from soil to air was larger than fluxes in runoff over the same time period. For example 15.7 kg of DDT was volatilized during the period March-June, if it was assumed that an area of 300 km2 of land was formerly treated with DDT the steady-state model results were used and calculated monthly, with adjustment for mean monthly temperature. Re-deposition in rainfall was about 15 g ofp,p -DDT to the watershed, based on concentrations in precipitation measured at the field station during May-August 2000. The extent of re-deposition of gas-phase DDT compounds on plants and soils was not known. 

A component in a detergent formulation that acts to help prevent re-deposition of dispersed dirt or grease. Example carboxymethyl cellulose. See also Detergent. 

The ability of a detergent or detergent component to keep foreign material away from the solid material from which it has been removed to prevent re-deposition. See also Detergent. 

With respect to the re-deposition of a coating on the first wall, the obvious advantage is the compatibility with Tokamak operation since it requires a minimum of auxiliary equipment and modification, particularly if a continuous, high frequency discharge is used. The power requirements for such an approach appear to be acceptable134. An rf heating system, if incorporated into the reactor design (e. g. 

Regardless of the analytical procedure chosen for the analysis, several advantages are derived from the ashing/re-deposition process These advantages include... 

Recirculate the solution. The solution should be recirculated at about 35 gpm per pressure vessel. In other words, for an 8-pressure vessel stage with 8-inch diameter membrane modules, the recirculation rate should be 8 times 35 gpm or 280 gpm. Recirculation should be conducted using as little pressure as possible, thereby minimizing the formation of permeate. If permeate is generated, it increases the likelihood of re-deposition of removed species on the membrane.1 If the cleaning solution comes out dark, it should be discarded and a new batch should be prepared. Temperature and pH should be monitored and adjusted during the recirculation as needed. Recirculation should continue for about 45 to 60 minutes. 

Corrosion by dealloying is common in brasses here the zinc component of the alloy is preferentially removed. Brasses with high proportions of the P phase are especially prone to this type of attack. The mechanism appears to be corrosion of both copper and zinc from the metal the zinc passes into solution but the copper is re-deposited with a porous structure of low strength. Aluminium bronzes also suffer dealloying of the aluminium component if incorrectly heat treated. Other metals which may be preferentially dissolved from their alloys are manganese from copper-manganese, nickel from copper-nickel, copper from either copper-silver or copper-gold, and tin from tin-lead (solders). It is evident from this list that it is the component which is anodic to the alloy which is removed. 

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