Metals pretreatment processes

The metal pretreatment process requires ceneful selection, particularly with the cathodic process. BS4479 1990, Part 3, Recommendations for Conversion Coatings should be consulted. 

Eor the cover-coat direct-on process, a ferric sulfate [10028-22-5] Ee2(S0 2> etch is included in the metal pretreatment for rapid metal removal. It is designed to remove ca 20 g/m (2 g/ft ) of iron from the sheet metal surface. Hydrogen peroxide [7722-84-1/, H2O2, is added intermittently to a 1% ferric sulfate solution to reoxidize ferrous sulfate [7720-78-7] EeSO, to ferric sulfate. 

He concluded that for aluminium and titanium certain etching or anodization pretreatment processes produce oxide films on the metal surfaces, which because of their porosity and microscopic roughness, mechanically interlock with the polymer forming much stronger bonds than if the surface were smooth . 

The study of corrosion is essentially the study of the nature of the metal reaction products (corrosion products) and of their influence on the reaction rate. It is evident that the behaviour of metals and alloys in most practical environments is highly dependent on the solubility, structure, thickness, adhesion, etc. of the solid metal compounds that form during a corrosion reaction. These may be formed naturally by reaction with their environment (during processing of the metal and/or during subsequent exposure) or as a result of some deliberate pretreatment process that is used to produce thicker films or to modify the nature of existing films. The importance of these solid reaction products is due to the fact that they frequently form a kinetic barrier that isolates the metal from its environment and thus controls the rate of the reaction the protection afforded to the metal will, of course, depend on the physical and chemical properties outlined above. 

One ore pretreatment process involves heating metal carbonates, hydroxides and some sulfides to metal oxides, which are more easily reduced to their elemental metal forms.. 

Organic compounds, sulphur-, phosphorous- and nitrogen-compounds may be present as soluble, suspended or colloidal particles. This also holds for salts, bases and heavy metals. Pretreatment can change the physical state of pollutants in the wastewater. This gives a possibility for guiding the treatment process. 

A large segment of the metal parts produced by industry are painted for both decorative purposes as well as to increase the corrosion resistance and extend the useful life of the product. To obtain maximum quality from painted metal articles, it is of paramount importance to pretreat the metal parts with a conversion coating process. ( 1,2) Pretreatment processes contribute a significant improvement in corrosion protection and durability to metal articles by ... 

Depending upon the quality level desired, the type of paint and the application method used, and the metal mix treated, a number of different types of pretreatment processes are available. For use as a paint base, the phosphate processes are either of the "iron phosphate" or the "zinc phosphate" type. 

Reverse osmosis can remove dissolved metals to very low levels. It can also remove a variety of pollutants such as cyanide and residual organics from refinery wastewater. However, because it is an expensive process, it would be competitive only if removal of total dissolved solids is also required. It also requires extensive pretreatment to prevent membrane fouling and deterioration [52]. The pretreatment processes may include filtration to remove suspended solids, pH adjustment, softening, and activated carbon treatment to remove organics and chlorine. A major drawback of the RO process is the handling and disposal of the reject stream, which can amount to 20-30% of the influent flow. 

On the other hand, new combined coupling agent — corrosion inhibitor pretreatment processes 29 125 have provided a new approach to increasing metal/epoxy adhesion systems with limits that are not yet known. 

The high electrical resistivity of aluminum oxide is believed to be the major reason why coatings continue to exhibit very strong adhesion to aluminium substrates even when localized corrosion is observed to occur. Therefore, by developing a pretreatment process for any metal substrate which produces a metal oxide with high electrical... 

A simple and effective way of incorporating such a cation-exchange material into the interfacial region would be to apply it to the metal surface as a final pretreatment process. This way the released hydrogen ions would be present in the immediate vicinity of the hydroxide ion generation sites. Therefore, the hydroxide ions could be promptly neutralized and the hydrolysis of the epoxy coating by strong alkali minimized 91>. 

In order to metallize a polymer surface, electroless plating can be applied. This process typically consists of a pretreatment process in order to improve the adhesion. In the second step a surface seeding of the electroless catalyst is done. Wet chemical methods of pretreatment are using strong acids such as chromic acid, sulfuric acid and acidified potassium permanganate in order to achieve a surface modification of the polymers (96). 

Keegan et al. studied the calcination and reduction of the same Pt(NH3)4 on HZSM-5 system with energy dispersive Extended X-ray Absorption Fine Structure (EXAFS). They showed that during calcination the Pt-Pt coordination rises, indicating agglomeration. The final metal particle size obtained after direct reduction (no calcination prior to the reduction) was smaller than the particle size obtained after calcination prior to the reduction. The authors did not clarify the chemistry of the pretreatment process. 

QEXAFS scans (30-90 seconds per scan) is suitable to study reactions like pretreatment processes. The whiteline area gives information concerning the oxidation state. The EXAFS region represents the geometrical structure of the Pt atom. The final metal particle size was obtained from the Pt-Pt first shell coordination number, H2 chemisorption26 as well as HRTEM. 

In selecting a pretreatment process for aluminum or any other substrate, both the initial strength and the permanence in a specific operating environment must be considered. Mechanical abrasion is a useful pretreatment in that it removes the oxide and exposes bare aluminum. When this is done, however, many of the benefits of the protective oxide layer are lost. For example, if bare abraded aluminum is bonded, the reactive metal at the joint interface can potentially become hydrolyzed and oxidized, which will displace the adhesive. Hence, this bonded joint may initially be much stronger than one made with unabraded metal, but it will deteriorate rapidly when exposed to a harsh environment such... 

Foreign materials such as metals, sand, etc., are removed from domestic waste plastics in the pretreatment process. Mikasa does not have a large population and thus waste plastics have to be collected from various municipalities in Hokkaido. 

Another pretreatment process involves chemical modification. This converts metal compounds to more easily reduced forms. Carbonates and hydroxides may be heated to drive off CO2 and H2O, respectively. 

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