Polishing and Electropolishing

The term electropolishing is used when an electric potential is applied through the chemical solution using the specimen as the anode. A simple 

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Duboust A, Wang Y, Neo S, Chen LY. End point detection for electrochemical-mechanical polishing and electropolishing processes.U.S. Patent 20030 136684. 2003 Jul 24. 

Electrochemical polishing, or electropolishing, is conventionally used for producing shiny surfaces where mechanical polishing is difficult to perform. Examples include components with complicated surfaces, decorative items, and other special applications. For microelectronic fabrication, planarization is emphasized in addition to surface smoothness. Hence, the term electrochemical planarization (ECP) is used throughout this chapter/book. 

Fig. 5 Schematic diagram illustrating how, as electropolishing potential is increased, conditions may change from etching to polishing and, finally, to pitting.

Most HPLC columns are made of 316 grade stainless steel, which is austenitic chromium-nickel-molybdenum steel, USA standard AISI, resistant to the usual HPLC pressure and also relatively inert to chemical corrosion (chloride ions and lithium ions at low pH being important exceptions). The inside of the column should have no rough surfaces, grooves or microporous structures, so the steel mbes must be either precision drilled or polished or electropolished after common manufacturing, e.g. by drawing. 

In the early days of TEM, sample preparation was divided into two categories, one for thin films and one for bulk materials. Thin-films, particularly metal layers, were often deposited on substrates and later removed by some sort of technique involving dissolution of the substrate. Bulk materials were cut and polished into thin slabs, which were then either electropolished (metals) or ion-milled (ceramics). The latter technique uses a focused ion beam (typically Ar+) of high-energy, which sputters the surface of the thinned slab. These techniques produce so-called plan-view thin foils. 

The enormous scope of the subject of corrosion follows from the definition which has been adopted in the present work. Corrosion will include all reactions at a metal/environment interface irrespective of whether the reaction is beneficial or detrimental to the metal concerned —no distinction is made between chemical or electropolishing of a metal in an acid and the adventitious deterioration of metal plant by acid attack. It follows, therefore, that a comprehensive work on the subject of corrosion should include an account of batteries, electrorefining, chemical machining, chemical and electrochemical polishing, etc. 

Electropolishing techniques utilise anodic potentials and currents to aid dissolution and passivation and thus to promote the polishing process in solutions akin to those used in chemical polishing. The solutions have the same basic constitution with three mechanistic requirements—oxidant (A), contaminater (B) and diffusion layer promoter (C) —but, by using anodic currents, less concentrated acid solutions can be used and an additional variable for process flexibility and control is available. 

The simplest and most thoroughly studied solutions are those based on phosphoric acid at low temperatures (<35°C) which alone can fulfil all three requirements of acid solvent, film former (as metal phosphate) and diffusion agent by virtue of its viscosity. Thus copper and its main alloys of brasses and bronzes can be very effectively electropolished in 60-70% orthophos-phoric acid with the temperature maintained below 35°C under other conditions copper passivates or dissolves freely under mass transfer controlled conditions, but by varying the conditions appropriately polishing can be continued under mild agitation. An annotated polarisation curve is given in Fig. 11.7 readers are referred to recent studies for more detailed 2ispects " . 

An alternative or additional step to flame annealing is electrochemical or chemical polishing. The fundamental aspects of electropolishing were reviewed recently [185], and a list of polishing procedures and parameters is available [185,186]. This method has been successfully applied to the preparation of gold, silver, and copper electrodes for STM studies [177,180,188]. It is important to note that different mesoscopic structures may arise according to the specific preparation procedures. For example, electropolishing a mechanically prepared Au(lOO) surface followed by... 

The most convenient and effective method for preparing a tip specimen is by electrochemical polishing of a piece of thin wire of 0.05-0.2 mm diameter. Usually the methods developed for electropolishing thin film specimens in transmission electron microscopes are also applicable for polishing field ion microscope tips.7 In Table 3.1 some of the commonly used emitter polishing solutions and conditions for the polishing are listed for various materials.8... 

In electropolishing, the metal workpiece is made the anode rather than the cathode. Instead of deposition onto the surface of the workpiece, some of the metal dissolves, leaving a bright, polished surface. High points dissolve at a faster rate than recessed areas. Electropolishing is performed to improve adhesion of subsequent electroplates, to deburr and Finish parts, and for decorative purposes (Schaer 1971). 

Kummer (38) measured the rate of oxidation of ethylene on single crystals of silver prepared parallel to the (111) face, nearly parallel to the (110) face, and nearly parallel to the (211) face. The relative reaction rates between faces were found to vary by a factor of 2 at the most, and the fraction of ethylene oxidized to ethylene oxide varied between 31 and 38 %. The surfaces were prepared by mechanical polishing followed by electropolishing and were determined by an electron microscope to be smooth within the limits of 100 A. 

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