Surface layers preparation chemical treatment

More uniform results may be expected if a substantial layer of metal is removed from the specimens to ehminate variations in condition of the original metaUic surface. This can be done by chemical treatment (pickling), electrolytic removal, or grinding with a coarse abrasive paper or cloth, such as No. 50, using care not to work-harden the surface. At least 2.5 X 10 mm (0.0001 in) or 1.5 to 2.3 mg/cm (10 to 15 mg/iu") should be removed. If clad alloy specimens are to be used, specif attention must be given to ensure that excessive metal is not removed. After final preparation of the specimen surface, the speci-... 

Mechanical preparation techniques such as grinding can introduce significant cold work into the surface layers e.g. the pitting resistance of ground austenitic [3] and ferritic stainless steel surfaces [4] has been shown to be inferior to that of electropolished surfaces. This was attributed to the presence of cold worked surface layers from grinding, although chemical or electrochemical surface treatments can preferentially remove less resistant phases, e.g.inclusions, which would otherwise be responsible for an inferior corrosion performance. ... 

To make an economical and practical joint, the surface preparation methods must also meet several other requirements. They must be safe to handle and should not be flammable or toxic. They should be inexpensive and provide fast processing times. The prebond processes should be easy to monitor and control in a production situation. In addition, the process should not in itself leave a weak boundary layer. If chemical solutions are used, they should rinse off easily and not continue to react with the surface past the time when the bond is made. The surface preparation process should allow for practical working time between preparation and application of the adhesive or sealant. Finally, the surface provided by the treatment should not change once the assembled joint is made and placed into service. 

A num ber of different techniques have been used to study the surface preparation techniques used prior to anodic oxidation. For device fabrication, mechanical polishing Is usually necessary to insure a relatively flat surface. Some chemical treatment is necessary to remove the mechanical damage induced by grit polishing. Often etching or chem-mechanical polishing is used to remove this damaged layer. However, it has been shown that chemical treatments do not leave a stoichiometric surface (27-30)(63). A kinetic study of the reaction of 0.1N Br in methanol with (Hg,Cd)Te under etch conditions found the relative rates of reaction of the individual constituents to be ... 

---