Passivating effect

In the case of CaCl2 and NaCl, the order corresponds with the corrosion behaviour expected from cathodic polarisation curves . The order of aggressiveness of chlorides can also be explained on the basis of redox potentials of the melts, calculated on thermodynamic grounds from the free energies of formation of the appropriate oxides and chlorides . The order of aggressiveness of nitrates is complicated by passivity effects , while that of alkalis in contact with air is... 

Access of air to the melt can be reduced by fitting a cover over it, or by floating a layer of powdered graphite on the melt surface. Diffusion rates in the melt can be reduced only by lowering the temperature, and this invariably reduces the amount of corrosion (except in certain cases in nitrate melts where passivity effects occur ). 

The cleanliness of the surface produced by emulsifiable cleaners is rarely of a very high standard, and additional cleaning may well be necessary before further finishing operations. Success has been achieved, however, in the use of these products prior to some immersion phosphating operations, where the crystal growth can be quite refined due to the absence of the passivation effect often encountered with some heavy-duty alkali cleaners. The supplier of the phosphating solution should be asked to advise on the suitability of any particular cleaning/pretreatment combination. 

Sulfite is not recommended above 850 to 900 psig because it decomposes to form corrosive sulfur compounds. In the absence of erythorbate, it begins to provide a magnetite-passivation effect above 300 to 325 psig above 400 psig, it starts to break down in the boiler (see equation 1), although initially the level of decomposition is not particularly serious. 

The temperature is again raised, aeration begins, or 0.5 to 1.0% sodium nitrite is added to dissolve the copper, which is then com-plexed by ammonia to [CuOIXNFyj. The solvent is circulated for 2 to 3 hours before draining, and rinsing with hot condensate follows this. Rinsing requirements are minimal because of the passivating effects of the alkaline conditions. 

Ammonia/hydrazine passivator An alkaline hydrazine solution (pH over 9.0, 0.5% N2H2) provides a useful passivator. If there are concerns over the use of hydrazine, diethylhydroxylamine (DEHA), erythorbate, or carbohydrazide may be substituted. Air blowing improves the passivating effect. 

Change of material removal rate with pH value is very interesting. Neither low nor high pH value exhibits the high MRR, which may be attributed to a passivation effect on the disk surfaces under the low pH value and a slow chemical dissolution rate under the high pH value. 

We have found that dendrimers can be used to encapsulate active moieties, thereby preventing them from interacting. This passivation effect limits inter-molecular interactions such as self-aggregation and molecular clustering. We also found that dendrimers can be made dipolar. This asymmetry in molecular orientation enables dendrimers to be used in NLO. In this chapter we describe our application of dendrimers to lasers and NLO. 

The passivation of n-type dopants in Si was reported by Johnson et al. (1986) several years after it was well recognized that deep defects and shallow acceptors were passivated following exposure to an H2 plasma. Donor passivation effects had been missed by previous workers presumably because the in-diffusion of H into heavily n-doped Si is impeded when compared to undoped or p-type material. 

Staniforth JN. Improvements in dry powder inhaler performance surface passivation effects. Paper presented at Drug Delivery to the Lungs VII, 1996 London. 

Supramolecular catalysis can involve passive effects such as the confining of two reactive molecules within a cavity and active effects where the catalyst interacts with the substrate via an active site. The active site may be metal-based as in other kinds of homogeneous catalyst based on transition metals or Lewis acids, or my involve interactions such as hydrogen bonding to bring about both polarisation of the reactants and their mutual spatial organisation. 

Table II. Antimony Metals Passivation Effects on Charge Rate...

In another report, it was found that the addition of PEG 8000 or PVP 40 in the PCR mixture produced a significant surface passivation effect in either native or Si02-precoated Si-glass chips. Using this passivation method, PCR of the nitric oxide synthase gene (human endothelial) in human lymphocytes was demonstrated [936]. 

The method of providing detector elements as disclosed in GB-A-1559473, shown above, is further improved in GB-A-1568958 in which an anodic surface treatment is used to form a passivation layer. This layer is found to have a protective or passivating effect which allows the device to be subjected to elevated temperatures (90°C) without severe degradation in the detectivity of the detector elements. 

If desired, plasma oxide films can be doped much as the plasma nitride film we discussed earlier. In fact, doping with boron and phosphorus has been carried out as an alternative to the standard atmospheric-pressure thermal CVD process for BPSG.11 12 The latter process has the drawbacks of high defect density and poor thickness uniformity, so it was hoped that plasma BPSG would be an improvement. However, there are differences in the films in terms of H2 and N2 content, and their effect on reflow temperature, intrinsic stress and passivation effectiveness had to be examined. 

The passivating effect is attributed to the formation of an insoluble oxide film on the silicon. The chemical attack by the hot alkaline solution on the silicon does not resume immediately after the anodic bias is removed. Several minutes are required before the passive layer breaks down and chemical attack resumes. A brief cathodic treatment, however, reactivates the silicon immediately. 

Apart from physical roughness and chemical passivation effects, phase transformation or structural changes can also play a major role in the friction and wear performance of diamond coatings.The extent of such changes may be dominated by environmental species or by ambient temperature. 

A similar passivation effect was reported by Mezey et al. for silicon implanted with 10 - 10 Ge" and The tendency for thermal oxidation at 900°C... 

A thermodynamic analysis was conducted for corrosion of iron alloys in supercritical water. A general method was used for calculation of chemical potentials at elevated conditions. The calculation procedure was used to develop a computer program for display of pH-potential diagrams (Pourbaix diagrams). A thermodynamic analysis of the iron/water system indicates that hematite (Fe203> is stable in water at its critical pressure and temperature. At the same conditions, the analysis indicates that the passivation effect of chromium is lost. For experimental evaluations of the predictions, see the next paper in the symposium proceedings. 

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