Degradation metals

It may be noted that although the human organism is capable of degrading metal-containing porphyrins such as heme, it has no means of degrading porphyrins containing no metal, for example coproporphyrins and uroporphyrins. These must be excreted as such. The latter two are water-soluble and are thus found in urine and to some extent in the feces. Protoporphyrins, however, are largely water-insoluble and are excreted in the feces. Finally, it may be mentioned that porphyrias make their appearance after puberty. This has been associated with the appearance of 5/3-steroid reductases, as discussed above. 

Products of thermal degradation metal chlorides produced fiom thermal stabilizers, products of degradation of some antioxidants, hydrogen chloride (autocatalytic product of PVC degradation)... 

A new versatile solution based strategy for in situ preparation of metal-organic molecular precursors based on butyldithiocarbamic acid has been reported. Carbon disulfide (CS2) and 1-butylamine undergo a facile reaction producing butyldithiocarbamic acid which reacts with a variety of metal oxides and hydroxides to form thermally degradable metal-organic molecular precursors. This approach has been used for the fabrication of CIGSSe based absorber layer in thin film solar cells. In a... 

Acrylic, nylon and polyester are especially susceptible to hydrolysis and metals, such as iron and copper, catalyse this degradation. Metal impurities which are present as a result of the manufacturing process, or in a composite material, accelerate degradation. Many polymers are alkali and acid sensitive, and acid can cause the hydrolysis of polymer chains. Organic vapours and fumigants can dissolve or swell plastics. 

Total hip arthroscopy surgeries are often associated with mechanical complications due to mismatched mechanical properties, as they often use non-degradable metallic or polymer (or combinations of these) implants (Knight et al., 2011). Metals are often much harder than the bone tissue and can cause stress shielding, meaning that the bone essential receives little mechanical stress and therefore starts to remodel, becoming less dense and often encouraging osteolysis (resorption of the bone). 

Bremner J, Williams RB, Young BW (1977) Distribution of copper and zinc in the liver of the developing sheep foetus. Br. J. Nutr. 38 87-92 Cain K, Holt DE (1979) Mfetallothionein degradation Metal composition as a controlling factor. Chem. Biol. Interact. 28 91-106 Cousins RJ (1979) Regulatory aspects of zinc metabolism in liver and intestine. 

EHmcan JR, Ballance JA. Marine salts contribution to atmospheric corrosion. In Dean SW, Lee TS, eds. Degradation ( Metals in the Atmosphere. Philadelphia, Pa. ASTM, 1988 316-26. 

Metals (copper and copper alloys, nickel, iron) have a strong adverse effect on PE because they accelerate degradation. Metal deactivators (organic molecnles containing heteroatoms or functional groups such as hydroxyl or carboxyl) act by chelation of the metal to form inactive or stable complexes. The concentration used is about 1 %. Acid scavengers (or antiacids) are used to neutralise acidic catalyst residues. Calcium or zinc stearate are commonly used, and also function as internal lubricants. Inserts should be made of light metal or he nickel or chromium plated. 

One solution to this problem of oxidative degradation has been to add compounds which deactivate the metals, particularly copper, thereby suppressing their catalytic capacity and substantially reducing oxidative degradation. Metal deactivators act by complexing the respective metals as shown in Figure 18.1. 

Key words degradable metals, biocompatibility, in vivo corrosion, in vitro corrosion, magnesium implant. 

One can utilize this process for two different purposes. The first application is protecting a metal from corrosion, whereas the second is to employ the reverse effect for plating the degrading metal on another metal. The former application is referred to as cathodic protection and the latter is known as electroplating. 

---