Delay of oxidation

The distance between falKng current in the cathodic cycle and rising current of the subsequent anodic cycle increases more and more. This potential difference corresponds directly to a delay of oxide formation indicating a kinetic hindrance, in spite of the constant potential sweep rate. 

This study allowed the comparative evaluation of different polyolefin substrate in respect to their thermal oxidation. As it was expected, ultrahigh molecular weight polyethylene shows the most significant thermal resistance to oxidative degradation [04G2]. The order of increase in the delay of oxidation is ... 

Rubber Chemicals. Sodium nitrite is an important raw material in the manufacture of mbber processing chemicals. Accelerators, retarders, antioxidants (qv), and antiozonants (qv) are the types of compounds made using sodium nitrite. Accelerators, eg, thiuram [137-26-8J, greatly increase the rate of vulcaniza tion and lead to marked improvement in mbber quaUty. Retarders, on the other hand (eg, /V-nitrosodiphenylamine [156-10-5]) delay the onset of vulcanization but do not inhibit the subsequent process rate. Antioxidants and antiozonants, sometimes referred to as antidegradants, serve to slow the rate of oxidation by acting as chain stoppers, transfer agents, and peroxide decomposers. A commonly used antioxidant is A/,AT-disubstituted Nphenylenediamine which can employ sodium nitrite in its manufacture (see Rubber chemicals). 

The placement of the NOx bed ahead of the oxidation bed causes a delay of the warm-up of the oxidation bed from a cold start. Since many of the materials considered for the reduction of NO are also excellent oxidation catalysts, the NOx bed is often used as the oxidation bed by the injection of secondary air during the first two minutes from a cold start. After the oxidation bed is warmed up, the secondary air is diverted from upstream of the first bed to upstream of the second bed. This procedure helps the emission reduction when the catalysts are fresh, but hastens the aging of the NOx catalyst as it is being exposed repeatedly to oxidation and reduction conditions. 

The time-scale of this haem conversion is related to the antioxidant status of the LDL and that of the erythrocyte lysate. The incorporation of lipid-soluble antioxidants, such as tocopherol and butylated hydroxy-toluene (BHT) at specific time points during the LDL-erythrocyte interaction, prolongs the lag phase to oxidation, eliminates the oxy to ferryl conversion of the haemoglobin and delays the oxidative modification of the LDL. 

Figure 18. A 0.2-s delayed COSY spectrum of the aliphatic region of 10 (2mg, CDCLj). Long-range "W-type" coupling of 19 and 21 axial protons to 30-CHj and coupling across the gem dimethyls from I9eq to 21 eq establish the position of oxidation at C-22. The spectrum was obtained under conditions similar to those in Figure 1, except that 32 transients were acquired for each of 128 x 512 data point spectra (17).

A recent series of experiments with cats, chickens, or rats exposed to [uniformly labeled 14C-phenyl]-TOCP shows that a complex array of oxidized and dearylated metabolites are found in excreta and various tissues including the liver, kidney, testis, and brain (Abou-Donia et al. 1990a, 1990b Nomeir and Abou-Donia 1986 Somkuti and Abou-Donia 1990). Cats and chickens, like humans, are sensitive to TOCP-induced delayed neuropathy (Baron 1981). A similar array of oxidized and dearylated derivatives of tri-para-cresyl phosphate (but no cyclic metabolites) were identified by mass spectrometry in the urine and... 

After chlorination, beakers were removed from the sunlight at regular (usually 30-min) intervals, placed in a dark box, and the contents analysed for bromate and residual oxidants without delay. Residual oxidants analyses were performed by the Ij spectrophotometric titration procedure described by Carpenter [19] with a pH of 2 and potassium iodide concentration of 4 g/1. Bromate... 

The increase in char yield, the decrease in exothermicity, and the delay of the peak oxidative-pyrolysis rate by the zinc... 

Compelling evidence suggesting that the breakdown of hydroperoxyl groups is not related to polymer destruction, at least in the initial period of oxidation at temperatures below 400 K, comes from experiments on the initiated oxidation of polymers. It was found that the destruction of polymers develops in parallel with their oxidation from the very onset of the process, but not after a delay related to the accumulation of a sufficient amount of hydroperoxyl groups [129]. These experiments also demonstrated that it is free macroradicals that undergo destruction. Oxidation of polymers gives rise to alkyl, alkoxyl, and peroxyl macroradicals. Which radicals undergo destruction can be decided based on the kinetics of initiated destructive oxidation. 

The above data demonstrate an important, possibly even critical role of oxidative stress in AD pathogenesis. Therefore, it is reasonable to suggest that antioxidant administration could be useful for the treatment of AD patients. Grundman [320] recently summarized the results of clinical trial, in which vitamin E was administrated to AD patients with moderately severe disease. It has been concluded that the treatment with vitamin E may delay and slow disease progress in these patients. 

With the possible exception of delay fuses, any pyrotechnic mixture represents a hazard worthy of report. Although the cause of frequent accidents reviewed in [2], compositions intended to explode or deflagrate are generally outside the field of this work and few are listed. Numerous reviews and specialist texts exist and hundreds of patents appear yearly. The account [1] of the theory and practice of pyrotechnics contains much useful information on the performance and potential hazards of a great variety of oxidant-fuel combinations which burn very rapidly or explosively. Safety measures are found in [2], Other reviews written from a functional viewpoint are found in [3] and [4], Some hazardously incompatible pyrotechnic mixes are reported [5], Detonability of pyrotechnic compositions has... 

In Pt(lOO) and PKllO), therefore, the delay of platinum oxidation is likely the cause of the delay of the COad oxidation. As for Pt(lll), however, water is considered as the oxygen source. Therefore, the large potential shift is considered as the result of difficulty in using water as the oxygen source. In other words, using more concentrated acid affects more the COad oxidation by water than the COad oxidation by Pt-OH. 

No one pollutant can be blamed as the major cause of ozone formation. Replacing the more reactive hydrocarbons with less reactive ones would delay the formation of ozone, but would not prevent it. Reducing the NO, concentration seems to reduce the maximal oxidant concentrations observed, but the effect is nonlinear. Heavy injections of nitric oxide into the air can temporarily reduce the local ozone concentration, as often happens in urban centers, but additional oxidant formation can be expected later downwind. Although these effects can be understood qualitatively, it is not yet possible to make accurate predictions of oxidant formation, even in lalx)ratoty experiments. 

Arsine is the most acutely toxic form of arsenic. It binds with oxidized hemoglobin, causing profound hemolysis of sudden onset. Inhalation of 250ppm may be fatal within 30 minutes, whereas 10-50 ppm may cause anemia and death with more prolonged exposure. Human experience has indicated that there is usually a delay of 2-24 hours after exposure before the onset of headache, malaise, weakness, dizziness, and dyspnea, with abdominal pain, nausea, and vomiting. Dark red urine is frequently noted 4—6 hours after exposure. This often progresses to brown urine, with jaundice appearing at 24-48 hours after exposure. 

In the context of vascular disease, numerous studies have focused on the ability of phenolic compounds, as pure aglycones and as glycosides, to delay the oxidation of LDL in This work has been paralleled by studies investigating the propensity with... 

A. Iwama K. Yamazaki, Effect of Some Parameters on the Ignition Delay of Hyper-golic Bipropellants. I. The Variation With Liquid Temperature, Oxidant Concentration, Subatmos-pheric Pressure and Fuel Composition , KKZ 63, 1879-83 (1960) CA 57, 1140(1962)... 

---