Cleaning metals chemical treatment

Again, the key to this problem lies in making all efforts to keep the metal surfaces clean. Additional chemical treatment may improve matters, but it is unlikely to be the most cost-effective long-term solution. 

The possible remedial and preventive actions are hot soaks and drains during cooldown to help remove soluble deposited material, chemical cleaning to remove corrosion products and reduce the pressure drop (see Metal surface treatments), and reduced corrosion product transport into OTSG using amines other than ammonia in feedwater (14). 

Improved nucleation within the phosphate solution itself can produce smoother coatings without the necessity of recourse to preliminary chemical treatment. This may be accomplished by introducing into the phosphating bath the sparingly soluble phosphates of the alkaline earth metals or condensed phosphates such as sodium hexametaphosphate or sodium tripolyphosphate. Such modified phosphating baths produce smoother coatings than orthodox baths and are very much less sensitive to cleaning procedures. 

Some mineral products are employed essentially in the form in which they are mined, with only shaping, crushing, cleaning or other treatments that do not change their compositions. Coal, in most of its uses, is a typical example. Most minerals are processed, however, to yield usable products - metals, chemicals or other materials from which most of the items of utility are derived. As regards coal, it may be pointed out that it is often referred to as a mineral, but unlike a true mineral, it has no fixed chemical formula. 

Alkylphenol ethoxylates are chemically stable and highly versatile surfactants that find application in a large variety of industrial products including acid and alkaline metal cleaning formulations, hospital cleaners, herbicides (qv) and insecticides, oil-well drilling fluids, synthetic latices, and many others (see Disinfectants and antiseptics Elastomers, synthetic Insect control technology Metal surface treatments Pesticides Petroleum, drilling fluids). 

Occupational exposures may occur in the production of hydrogen peroxide, in waste-water treatment, metal cleaning, and chemical synthesis, and in the textile, pulp and paper, geothermal energy and mining industries (lARC, 1985). 

Most aliphatic amines and alcohols are considered to be nonelectroactive. The reason for this is that the product of the oxidation adsorbs to the electrode surface, fouling the electrode. Therefore, most reactions of these compounds at noble metal electrodes have been transient and not amenable to direct amperometric detection. In voltammetry experiments, electrodes are cleaned between experiments by electrochemical or chemical treatment to restore the electrode response. 

The cleaning of the various catalyst samples has to be scrutinized for each material studied. For iron for example, the major impurity is sulfur, and its removal must be carried out outside the vacuum system in a furnace in a constant hydrogen flow for a long period of time (days). Trace metallic impurities or nonmetallic impurities may be removed either by argon ion bombardment in the vacuum chamber or by chemical treatment using gas-surface interactions of different types. 

The presence of polyphosphate detergent in the cleaning formulation (some of which will revert to orthophosphate) will, under most circumstances, lead to passivation of the clean metal surfaces. Additionally, as part of the water treatment program start-up procedure, it may prove useful to supplement this initial passivation with 2 to 3x the normal reserve of maintenance inhibitor chemical treatment for a period of 1 to 2 weeks. 

For metals, the nature of the active metal surface determines its reactivity, as do both surface cleanness and metal particle size (4,9-11). Finely divided metals, with their correspondingly larger surface areas, show markedly greater reactivity towards alkyl halides than do corresponding bulk metals (20). Sono-chemical treatment of metal surfaces removes impurities and renders such surfaces correspondingly more reactive (21). Various other factors about metal surfaces that affect their adsorption of organic molecules are discussed in a book by Albert and Yates (22). 

Effects of Deposits on the Catalv.sts- In describing techniques for regenerating commercial VOC oxidation catalysts of noble metals on ceramic honeycombs, Heck et al. pointed out that generally below 450 C the presence (in the gas stream) of phosphorous and other metals, particularly as oxides, leads to catalyst deactivation by simple masking as opposed to poisoning by chemical interaction. These deposits can often be removed by chemical treatment with acid or alkaline solutions and sometimes by physically cleaning with a compressed air lance. When combustible... 

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