Zinc salts, inhibitive effect

Decomposition of Peroxides by Various Stabilizers. The efficiency of tert-butyl hydroperoxide decomposition in tert-butyl alcohol by various additives was determined (Table 9). Under the conditions of these experiments, the phenolic antioxidants and dilauryl thiodipropionate had little or, often, no effect on the hydroperoxide decomposition. The three zinc salts effectively inhibited peroxide decomposition. This effect might briefly inhibit the onset of substrate oxidation under weathering-test conditions, but the peroxide would decompose whenever its concentration reached a sufficient level to permit significant light... 

The radical (RO)2PS2 in indene would thus effectively act as a chaincarrying radical and is therefore not considered to be an intermediate in chain-breaking inhibition by dithiophosphates. A two-stage mechanism was therefore proposed, involving a stabilized zinc salt-peroxy complex, either a radical or an ion pair as illustrated in structures V and VI. 

Cl or S04 anions, which enhance the corrosion rate. Anions such as carbonates and phosphates increase the formation of solid-salts and have an inhibitive effect. The reaction of chromate with the zinc surface produces passive layers, which reduce the corrosion rate strongly. 

Sodium polyphosphate is often used in a concentration of about lO-lOOppm, sometimes with added zinc salts to improve inhibition. The pH value is adjusted to 5-6 in order to minimize pitting and tubercle formation, as well as scale deposition. Polyphosphates decompose slowly into orthophosphates, which, in the presence of calcium or magnesium ions, precipitate insoluble calcium or magnesium orthophosphate, causing scale formation on the warmer parts of the system. Unlike chromates, they favor algae growth, which necessitates the addition of algaecides to the water. Corrosion inhibition with polyphosphates is less effective than that by chromates, but polyphosphates in low concentration are not toxic, and the required optimum amount of inhibitor is less than that for chromates. 

In immersion conditions, the time of protection depends on the zinc content in the film and on its dissolution rate. The mechanism is different for films exposed to the atmosphere, because after the cathodic protection in the first stage, the action is restricted substantially to a barrier effect (inhibition resistance) generated by the soluble zinc salts from corrosion by sealing the pores controlling access to water, water vapor and various pollutants. Due to the... 

The inhibition of metal corrosion in industrial water systems was first achieved by the use of inorganic salts or their blends, including chromates (Evans, 1936 Mayne and Pryor, 1949), nitrites (Hatch, 1952), phosphates (Patterson and Jones, 1952), borates (Mercer, 1990), silicates (Lehrman and Shuldenen, 1952), zinc salts (Hatch, 1965 a) and other cations (Hinton, 1989). Additionally, chromates and nitrites were mainly applied, and from the end of the 1950s the use of polyphosphates increased (May et al., 1981 Hwa, 1971). Treatments with anodic inhibitors such as nitrites or chromates require a high initial dose and a relatively high continuous dose in order to achieve an effective passive layer on the metal surface. The concentration of chromate and nitrite can be decreased in the presence of polyphosphates and zinc ions. 

Zinc salts are well-known cathodic inhibitors in cooling vrater systems. They are, however, not used alone as the films formed by them are unstable. They are, however, used very effectively with polyphosphate as a synergistic blend to maximize the effect of inhibition. These synergistic blends... 

Gonzalez, Y., Lafont, M.C., Pebere, N., and Moran, F., A synergistic effect between zinc salt and phosphonic acid for corrosion inhibition of a carbon steel. Journal of Applied Electrochemistry, 1996. 26(12) 1259-1265. 

Cathodic protection is a useful supplement to other forms of water treatment, as a general corrosion inhibiting device in HW boilers, or where specific design configurations can lead to inadequately protected localized metal in steam boilers. Where BW makeup demands are minimal and boiler output is fairly constant, cathodic protection devices can also provide some measure of protection against hardness scales. Calcium carbonate salt is formed as a floc-culant or soft sludge rather than a hard scale, due to the peptizing effects of a zinc hydroxide complex formed from zinc ions in alkaline BW. 

Thus, the mechanism of MT antioxidant activity might be connected with the possible antioxidant effect of zinc. Zinc is a nontransition metal and therefore, its participation in redox processes is not really expected. The simplest mechanism of zinc antioxidant activity is the competition with transition metal ions capable of initiating free radical-mediated processes. For example, it has recently been shown [342] that zinc inhibited copper- and iron-initiated liposomal peroxidation but had no effect on peroxidative processes initiated by free radicals and peroxynitrite. These findings contradict the earlier results obtained by Coassin et al. [343] who found no inhibitory effects of zinc on microsomal lipid peroxidation in contrast to the inhibitory effects of manganese and cobalt. Yeomans et al. [344] showed that the zinc-histidine complex is able to inhibit copper-induced LDL oxidation, but the antioxidant effect of this complex obviously depended on histidine and not zinc because zinc sulfate was ineffective. We proposed another mode of possible antioxidant effect of zinc [345], It has been found that Zn and Mg aspartates inhibited oxygen radical production by xanthine oxidase, NADPH oxidase, and human blood leukocytes. The antioxidant effect of these salts supposedly was a consequence of the acceleration of spontaneous superoxide dismutation due to increasing medium acidity. 

Conjugate hydrogenation. The combination of zinc and NiCl2 (9 1) effects conjugate reduction of a,(3-enones in an aqueous alcohol in which both the enone and product are completely soluble. Ultrasound increases the rate and the yields. Presumably the salt is reduced to a low-valent form that is absorbed on the zinc. No reduction takes place with a 1 1 Zn-NiCl2 couple. The method is not applicable to a,(3-unsaturated enals. Isolated double bonds are also reduced by this method, but this hydrogenation can be inhibited by addition of ammonia or triethylamine. 

Kratzer studied the effect of different phosphorus salts on zinc utilization in turkey poults. They fed diets which contained marginal (15 pg/g)levels of zinc. Hence they assumed any factor that inhibited zinc absorption would create a zinc deficient state in the animals and growth would be depressed. They observed if they mixed the zinc and phosphorus salts prior to their addition to the dry diet, most phosphorus salts, especially tripolyphos-phate, would depress growth in the turkey poults. However, if they did not mix the zinc and phosphorus salts prior to their addition to the dry diet, the phosphorus salts did not significantly affect growth of the animals. 

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