Oxide defects

Another source of departure from stoichiometry occurs when cations are reduced, as for example in tire reduction of zinc oxide to yield an oxygen-defective oxide. The zinc atoms which are formed in tlris process dissolve in the lattice, Zn+ ions entering interstitial sites and the coiTesponding number of electrons being released from these dissolved atoms in much the same manner as was found when phosphorus was dissolved in the Group IV semiconductors. The Kroger-Viirk representation of dris reduction is... 

If the initiation step, the activation of H2, is fast, as may be the case on noble metal oxides or highly defective oxide surfaces, the shrinking core or contracting sphere model applies (see Figure 2.3). The essence of this model is that nuclei of reduced metal atoms form rapidly over the entire surface of the particle and grow into a shell of reduced metal. Further reduction is limited by the transport of lattice oxygen out of the particle. The extent of reduction increases rapidly initially, but slows down as the metal shell grows. 

G. Pacchioni, Modeling Doped and Defective Oxides in Catalysis with Density Functional Theory Methods Room for Improvements, J. Chem. Phys. 128... 

Peroxisomal disorders (Zellweger syndrome, Refsum s disease, neonatal adre-noleukodystrophy) are characterised by defective peroxisome biogenesis, or, being present, peroxisomes lacking / -oxidative enzymes. In the BA biosynthetic pathway, dihydroxycoprostanic acid (DHCA) and trihydroxycoprostanic acid (THCA) are /1-oxidised in peroxisomes to produce CA and CDCA, respectively, whereas peroxisomal disorders cause a defective oxidation of the BA precursor side chain, which leads to an accumulation of C27 bile acids, notably 3 ,7 -dihydroxy-5/3-cholesta-noic acid (DHCA) and 3a,7a,12a-trihydroxy-5/l-cholestanoic acid (THCA), in the plasma and urine of affected patients. 

The existence of the latter has been recognized for many years, since Wagner (20) applied his thermodynamic theory of defect oxides to the system zinc oxide-oxygen (21). According to this scheme, at sufficiently high temperature an equihbrium sets in between zinc oxide and oxygen in the gas phase, whereby excess zinc (Zn ) can be accommodated in interstitial positions of the lattice ... 

Finally, another consequence of this situation is the danger of attributing to the surface layer properties which have been established for the bulk material. This applies in particular to semiconducting characteristics of a defect oxide. Thus, with zinc oxide, the surface layer may be nearly stoichiometric and poorly conducting as a result of oxygen adsorption or conversely may present quasimetallic properties after activation in vacuo, irrespective of the composition of the bulk material. 

Fosslien E. Review mitochondrial medicine-molecular pathology of defective oxidative phosphorylation. Ann Clin Lab Sci 2001 31 25-67. 

Diffusion in the Presence of Excess Point Defects. Oxidation-Enhanced Diffusion. Oxidation generally enhances the diffusion of group III and group V elements except for antimony (Figure 13). Oxidation-enhanced diffusion is generally observed by depositing a silicon nitride mask on the silicon surface that will prohibit oxidation in the regions that it covers. 

Herndon, J., Steinberg, D., and Uhlendorf, B., Refsum s disease defective oxidation of phytanic acid in tissue cultures derived from homozygotes and heterozygotes, N. Engl. J. Med., 281, 1034, 1969. 

Fig. 6.17. Cyclic voltammograms of o-phenylenediamine (101 M) oxidation for W03 thermal-treated (350°C) anodic films (b) and smooth platinum electrode (c) first sweep (curves 1) and repeated sweep (curves 2) scan rate was 80 mV/cm2. The left picture shows a schematic representation of the morphology of thermal-treated anodic W03 film tungsten support, highly defective oxide (including the continuous donor clusters), moderately doped oxide (non-shaded region), poly-o-phenylenediamine deposits.

Defective oxidation. Variation in response to some drugs can be attributed to genetic polymorphisms involving oxidation of their carbon centres (see Metabolism p. 112). The condition was recognised by abnormal metabolism and response to a standard dose of debrisoquine. Individuals may be classed as extensive or poor oxidisers and the latter are at special risk of adverse effects from drugs whose inactivation is strongly dependent on the defective... 

Using the intensity counts integrated from 532 to 552 eV, we estimated the x value of the defective oxide SiO in the percolation path [11]. For the sample shown in Fig. 5, it is SiOu at the BD center (Position 3) and SiOi e-i.g at the outer shell. The x values imply that there are missing of 1 (SiOu) and 2 (SiOu)... 

PR By reaction of the elements in powder form in a protective atmosphere, like argon or vacuum at elevated temperature. Starting materials, their size, crystallinity, presence of defects, oxide films, and experimental conditions determine the reaction product, mechanism, and kinetics. 

Fosslien, E. Mitochondrial medicine—molecular pathology of defective oxidative phosphorylation. Annals of Clinical Laboratory Science 31 25-67 2001. 

PifYSXOLoav.—Uric acid exists in the economy chiefly in combination as its sodium salts it is occasionally found free, aud from the pipbable method of its formation it is difficult to understand how all tbe uric arid in the economy should not have existed there free, at least at the instant of its formation. It can soeu oely be doubted that uric acid is one of the products of the oxidation of the albuminoid substances-—an oxidation intermediate in the production of urea and that consequently diseases in which there is an excessive formation of uric arid, such as gout, have their origin in defective oxidation. 

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