Effect of Other Oxidants

FIGURE 7.11. Current, i, and etch rate, r, of n-Si and p-Si of stationary electrodes in lOM HF + 0.5 M HBr + lOmM Br2. Etch rate was determined after 30min. (Reprinted from Bressers et al. 1996, with permission from Elsevier Science.) 

FIGURE 7.12. Etch rate of (lll)-oriented silicon in ammonium fluoride solutions (solution composition 5 ml 30% H2O2, aliquot 40 wt % NH4F solution, diluted with H2O to total volume of 30ml). After Kern and Puotinen.  

Alkaline solutions are another major group of etchants widely used for etching of silicon materials. The most commonly used alkaline solutions have been KOH and EDP (or EPW) which is a mixture of ethylenediamine (ED or E), pyrocatechol (P), and water Other solutions such as NH4OH, hydrazine, ethanolamine, and tetram- 

A similar etch rate dependence on concentration is found for the three major surfaces in KOH-IPA solutions as shown in Fig. 7.14, but unlike at lower temperatures, solution stirring has little effect on the etch rate. ° The activation energy of the etching process is 0.56-62 eV for KOH of different concentrations indicating that the etching is controlled by a surface process. KOH solutions are often buffered with isopropyl alcohol (IPA), which results in a decrease of etch rates.  

The most characteristic feature of etching in KOH solution is its anisotropic nature, i.e., the etch rate varies with the crystal orientation of the silicon wafer. The etch rate for the major crystal planes follows 110 100 111. The exact difference between the etch rates of these planes depends on concentration, temperature, and measurement procedure. For example, in 20% KOH at 100 °C the etch rates for (110) (100) (111) are 930 560 19A/s corresponding to a ratio of 50 30 1. The difference between the etch rates of (110) and the (100) planes and that of the (111) plane is larger at room temperature, giving a ratio of 160 100 1 in 20% KOH. Addition of 

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Surface tension of binary alkali-silica melts at 1300 °C is shown in Fig. 44, The effect of other oxides on the surface tension of a sodium oxide-silica melt is demonstrated in Fig. 45. 

GPa for single crystal alumina fibers. The overall trend reflects the weight percent increase in alumina. Differences in each category reflect super-imposed effects of other oxides (not shown) or process-induced differences. 

On the other hand, clinical and laboratory studies in humans have demonstrated the development of tolerance to the amnestic and analgesic effects of nitrous oxide and isoflurane (see Arnold et al. 1993 Avramov et al. 1990 Rupreht et al. 1985 Whitwam et al. 1976) and, in the case of ether or chloroform, to its reinforcing effects (Krenz et al. 2003). No studies have shown the development of tolerance to the reinforcing effects of nitrous oxide. 

There are few reports on the effects of nitrous oxide on dopaminergic neurotransmission. A study in mice showed that nitrous oxide inhalation produced a significant increase in locomotor activity that was antagonized in a dose-dependent fashion by the dopamine synthesis inhibitor a-methyl-/)-tyrosine (Hynes and Berkowitz 1983). Moreover, administration of the D2 antagonist haloperidol also reduced the locomotor activity induced by nitrous oxide (Hynes and Berkowitz 1983). These results suggest that excitatory effects induced by nitrous oxide may be also mediated by dopaminergic neurotransmission. However, other studies have reported that exposure to nitrous oxide resulted in decreased dopamine release by neurons in the striatum (Balon et al. 2002 Turle et al. 1998). 

The underlying mechanisms involved in the activities of carotenoid oxidation products are due either to a possible role as precursors of retinoids that would be the active species for positive effects or to their own specific activities. This latter case is illustrated by the activity of non-provitamin A carotenoid oxidation products such as those derived from lycopene. However, biological effects of carotenoid oxidation products other than retinoids are only hypothesized in vivo in humans, which hypothesis has been used as the basic principle to justify in vitro studies of these compounds. 

Oxidative ageing of rubbers is limited by the rate of diffusion of oxygen into the rubber product and is usually confined to the outer 3 mm. Antioxidants are used to protect rubbers from the effects of thermal oxidation and the vast majority of compounds will contain one or more. Peroxide vulcanisates are usually protected with dihydroquinolines. Other antioxidants react adversely with the peroxide inhibiting the crosslinking reaction. 

Flavonoids protect LDL from oxidation, delaying the onset of lipid peroxidation, however, the prevention of atherosclerosis by flavonoids occurs not only by the inhibition of LDL oxidation, but also by the increase of cellular resistance to harmful effects of the oxidized LDL (de Luis and Aller, 2008). The antioxidant activity of anthocyanidins, as well as their protective role against LDL oxidation, has been well demonstrated in different in vitro systems (Aviram and Fuhrman, 2002 Satue-Gracia and others 1997 Teissedre and others 1996). 

Similar to reactive oxygen species, nitric oxide, peroxynitrite, and other nitrogen oxide species produced by mitochondria are able to stimulate or inhibit apoptosis. Proapoptotic effect of nitric oxide was probably first shown by Albina et al. [138], who demonstrated NO-induced... 

Thus the competition between stimulatory and inhibitory effects of NO depends on the competition between two mechanisms the direct interaction of NO with free radicals formed in lipid peroxidation and the conversion of NO into peroxynitrite or other reactive NO metabolites. Based on this suggestion, Freeman and his coworkers [42-44] concluded that the prooxidant and antioxidant properties of nitric oxide depend on the relative concentrations of NO and oxygen. It was supposed that the prooxidant effect of nitric oxide originated from its reaction with dioxygen and superoxide ... 

Besides this protective mechanism, there is the possibility of the effect of other inhibitors, such as oxidized phenolic compounds,297-300... 

The stability constants of the mono- and bis-complexes between Cu(II) and catecholate were determined under anaerobic conditions and were found to be the same as reported earlier, i.e. log p1 = 13.64 (CuC) and log p2 24.92 (CuC2+) (36,39). A comparison of the speciation and oxidation rate as a function of pH clearly indicated that the mono-catechol complex is the main catalytic species, though the effect of other complexes could not be fully excluded. The rate of the oxidation reaction was half-order in [02] and showed rather complex concentration dependencies in [H2C]0, [Cu(II)]0 and pH. The experimental data were consistent with the following rate equation ... 

Other Compounds The effect of other compounds (such as those containing nitrogen) on PAFC performance has been adequately reviewed by Benjamin et al. (35). Molecular nitrogen acts as a diluent but other nitrogen compounds (e.g., NH3, HCN, NOx) may not be as innocuous. NH3 in the fuel or oxidant gases reacts with H3PO4 to form a phosphate salt, (NH4)H2P04,... 

The data base on health effects of photochemical oxidants and ozone was reviewed by the Subcommittee on Ozone and Other Photochemical Oxidants in a report prepared in September 1974 for the Committee on Public Works, U.S. Senate.The following discussion repeats some of the material in that report, to exemplify the need for further work, including controlled human studies. 

Asthma, a disease featuring sudden and dramatic variations in respiratory symptoms and pulmonary function, is well known to be related to environmental factors in many cases. Many other factors, however, may play a significant role in the precipitation of asthma attacks, including meteorologic factors, emotional factors, infection, allergy, and physical activity. It has also been demonstrated that there is a significant ethnic variation in factors associated with acute asthma attacks. Nevertheless, between 2 and 5% of the population is subject to asthma attacks, so it has been examined as an indicator of health effects of photochemical-oxidant pollution. 

Research on photochemical oxidants, including o ne, was confined primarily to California during the 19S0 s. By 1959, ozone was known to be an important pollutant in the eastern United States and southern Canada. It is now known as a ubiquitous pollutant and has been widely studied throughout the United States and Canada. By 1972, several other countries had recognized the potential effects of photochemical oxidants on v etation and initiated research. 

Laboratory studies of effects of photochemical oxidants other than ozone—e.g., PAN, peroxybenzoylnitrate, atomic oxygen, excited molecular oxygen, Oj( A ), and hydroperoxy and hydroxyl radicals—on specific materials should be conducted. 

One case-control study in humans found no significant associations between exposure and various cancers no information was given on exposure levels or possible confounding effects of other exposures. The lARC has determined that there is inadequate evidence in humans for the carcinogenicity of propylene oxide but that it is possibly carcinogenic to humans. ... 

In this special field, earlier work had been done in other laboratories, such as by the Schering Company, Berlin (36), and by Ipatieff (37) in connection with his work on the hydrogenation of camphor and of other organic compounds. At both places, the favorable effect of alkali oxides and earth alkali oxides on nickel, cobalt and copper has been investigated. Similarly, Paal and his coworkers (38) have used a palladium-aluminum hydroxide catalyst in 1913 for the hydrogenation of double bonds. Bedford and Erdman (39) had reported that the catalytic action of nickel oxide is enhanced by the oxides of aluminum, zirconium, titanium, calcium, lanthanum, and magnesium. 

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