Chromic acid treatment

Pyrrolizidine alcohols are readily oxidized. Stereoisomeric 1-hydroxymethylpyrrolizidines when oxidized with chromic acid afford stereoisomeric pyrrolizidine-1-carboxylic acids (see Section III, C).81,90 Secondary alcohols, when subjected to Oppenauer oxidation or chromic acid treatment, yield amino-ketones (cf. refs. 72, 77, and 81). 

For some plastics, surface treatments were necessary—for example, chromic acid treatment for polypropylene. When fillers were present in the plastics the results with cyanoacrylates often were better (this was apparent in particular with polyethylene). 

Protective effects of chromic acid and ferric chloride treatments on surface degradation also were observed on radial surfaces. The preservation of both simple and bordered pits in woods treated by these inorganic salts was observed. At a 10% chromic acid treatment concentration, the structure of the pits retained most of the original shape after 1000 h of UV irradiation. The diagonal microchecks passing through the bordered pits in radial walls of tracheids, however, can still be observed (Figure 30). 

The most widely used polymer system that bioerodes by Type I erosion or by a combination of Type I and Type III erosion is gelatin that has been insolubilized by heat treatment, aldehyde treatment, or chromic acid treatment. 

Pretreatment is particularly important for structural adhesive joints such as those used in aircraft and motor vehicle construction. Aluminum adhesive surfaces are subjected to chromic acid treatment and an anodizing process, major factors in the overall joining costs. The disposal of used pickling baths is particularly demanding and expensive, especially in view of the CrVl ions resulting from the pickling process. 

R"-CH20H by Y. The problem indicates Y becomes X upon chromic acid treatment. This is the crux of the problem. 

Treatment of the bis-epoxide (219) with hydrogen chloride in glacial acetic acid afforded the mono-chlorohydrin derivative (220). Reaction of Ha-hydroxy-16-methylene-20-ketopregnanes led to stereospecific epoxidation at C-16 by chromic acid treatment. In addition, energetic reaction conditions can lead to (165)-spiro-2 -oxirans of the androstane series. 

Chemical conversion processing is a type of surface treatment that consists only of a chemical reaction. In this respect, metal is immersed in a solution where it dissolves slightly, and an insoluble corrosion product, or an oxide film forms simultaneously on the surface. Examples of such films are corrosion resistant films, undercoat films, and lubrication films. Examples of chemical conversion processing are phosphating and chromic acid treatment. The following is an example of the use of a LCA in the phosphating of zinc plates. 

Epoxies, isocyanate cured polyester, and cyanoacrylates are used to bond acetal copolymer. Generally, the surface is treated with a sulfuric-chromic acid treatment. Epoxies have shown 150 to 500 psi shear strength on sanded surfaces and 500 to 1000 psi on chemically treated surfaces. Plasma treatment has also been shown to be effective on acetal substrates. Acetal homopolymer surfaces should be chemically treated prior to bonding. This is accomplished with a sulfuric-chromic acid treatment followed by a solvent wipe. Epoxies, nitrile, and nitrile-phenolics can be used as adhesives. 

Change in topography (e.g. roughening with chromic acid treatment of polyolefins)... 

Figure 14-2. Comparison of SDS-FRL and conventional freeze-fracture techniques (a) freeze fracturing, (b) shadowing, (c) chromic acid treatment, (c ) Cellulase and SDS treatment, (d) antibody labeling. (Figure 2 from Itoh, T. and Kimura S. 2001. Cellulose synthases are localized in terminal complexes. Journal of Plant Research 114 483-489. Reproduced with kind permission of Springer Science and Business Media and the Botanical Society of Japan).

While it is possible to bond to a freshly abraded or cleaned metal surface, chemical treatments are preferred for rendering the metal surface inactive to corrosion over time. For low carbon steel, phosphatising is the recommended pre-bond surface preparation treatment. Stainless steel should be passivated or acid etched, while titanium is usually treated with a hydrofluoric acid pickle. Almninium or magnesium are best treated with a chromate conversion coating. Zinc and cadmium are generally prepared mechanically but a phosphate or chromic acid treatment may be used. Brass and copper may be treated with an ammonium persulphate etch or an acid-ferric chloride etch. 

Brewis and Critchlow [27] investigated the locus of failure of aluminium joints bonded with epoxies and polyurethanes and measured peel strengths after water immersion. Significant differences were found between different surface-treatment techniques, which included phosphoric anodisation, chromic-acid treatment, and epoxy primers. 

Hofste JM, Schut JA, Pennings AJ. The effect of chromic acid treatment on the mechanical and tribological properties of aramid fibre reinforced ultra-high molecular weight polyethylene composite. J Mater Sci 1998 October 9(10) 561-6. 

The effects of chromic acid treatment for periods of time between 1 and 60 minutes and oxygen plasma treatment... 

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