Slower Oxidation Rate Research Articles

Sodium vanadate-induced corrosion of nickel and MCrAIY coatings on Inconel 600

The vanadate-induced corrosion of M Cr AIY coatings (M = Ni/Fe) on Inconel alloy 600 has been studied by using samples with preformed vanadate deposits. The samples were exposed to oxygen at 650 to 800°C for a maximum of 25 h in a thermobalance. The presence of molten vanadate ((Na2O)x·V2O5) on the surface causes accelerated corrosion. The corrosion rates increase with increasing V2O5 content of the vanadates. In the presence of molten vanadate, protective scales of Cr2O3-Al2O3 fail to develop; rather the oxide layer next to the coating consists of the oxides of all components in the coating and of vanadium both as vanadate and as vanadium sesquioxide. In most cases the molten vanadate phase fluxes the oxide scale and particularly the NiO phase in the oxide layer. Under these conditions the corrosion is probably governed by inward transport of oxygen (or oxygen species) in the vanadate melt. When the NiO concentration in the oxide layer next to the metal is high (as on nickel-base coatings with more than 75 wt-%Ni) a Ni3(VO4)2 layer gradually develops between the oxide and the melt. This is accompanied by compositional changes in the oxide layer beneath the vanadate and results in a slow oxidation rate. MST/510

Carbon Fiber Electrode for Redox Flow Battery

not Available.

Microcrystalline structure and surface area of elemental sulphur as factors influencing its oxidation by Thiobacillus albertis

The effect of particle size, surface area per unit weight, and molecular composition of S0 on the rate of S0 oxidation by Thiobacillus albertis was studied. Spherical S0 prills varying in size and surface areas were prepared and added as the sulphur source to synthetic salts medium. The rate of S0 oxidation by T. albertis was found to be a function of surface area/unit weight of sulphur. In all these experiments [Formula: see text] was produced in a linear manner with time indicating sterically favorable cell–sulphur oxidation binding sites for bacterial growth. Different powdered forms of S0 (high-purity orthohombic, high-purity polymeric, and mixed molecular sulphur) were oxidized at a significantly faster rate than the prilled S0. Also the initial oxidation was exponential up to 3 days at which point [Formula: see text] production from mixed molecular sulphur utilization fell off substantially with time as compared with similar [Formula: see text] rate curves obtained with high-purity orthorhombic and high-purity polymeric oxidation. It was implied that the increased Sx content in mixed molecular sulphur was responsible for the slower oxidation rate by altering the sulphur crystal lattice formation which affected the number of sterically favorable oxidation binding sites for T. albertis growth. Thiobacillus albertis was shown to colonize S0 surfaces as microcolonies. It was concluded that particle size, surface area/unit weight, and the crystal microstructure of S0 affects the oxidation rate of S0 by T. albertis.

The effects of 2{5(4-chlorophenyl) pentyl}oxirane-2-carbonyl-CoA on mitochondrial oxidations

2{5(4-Chlorophenyl)pentyl}oxirane-2-carbonyl-CoA (POCA-CoA) was prepared from 2{5(4-chlorophenyl)pentyl}oxirane-2-carboxylate (POCA) and characterised chromatographically. POCA-CoA does not inhibit citrate cycle oxidations or effect oxidative phosphorylation by rat liver mitochondria. POCA-CoA at low (μM) concentrations, but not free POCA −, specifically inhibits palmitoyl-CoA oxidation at the stage of carnitine palmitoyltransferase I (CPT I) situated on the outer face of the inner mitochondria membrane. Palmitoyl-carnitine oxidation was not inhibited by POCA-CoA. POCA-CoA inhibits palmitoyl-CoA oxidation in liver mitochondria from fed rats more strongly than it does in mitochondria from fasted rats, similarly to the inhibition by malonyl-CoA [E. D. Saggerson and C. A. Carpenter, FEBS Lett. 129, 225 (1981)]. Palmitoyl-CoA, by contrast with palmitoylcarnitine, is not quantitatively oxidised to acetoacetate by liver mitochondrial fractions, presumably due to competing palmitoyl-CoA hydrolase activity. In the presence of POCA-CoA the amount oxidised is decreased further because the slower rate of oxidation allows more palmitoyl-CoA to be hydrolysed to palmitate. The oxidation of palmitoyl-CoA, but not that of palmitoyl-carnitine, was strongly decreased in washed liver and muscle mitochondrial fractions from POCA-fed animals. POCA − inhibited the oxidation of {U- 14C}palmitate in cultured human fibroblasts, and caused small increases in 14CO 2 production from {1- 14C}pyruvate and {U- 14C}glucose. Inhibition of β-oxidation at the stage of CPT I by POCA-CoA can explain the powerful hypoketonaemic and hypoglycaemic effects of POCA in fasted normal and fasted diabetic animals [H. P. O. Wolf, K. Eistetter and G. Ludwig, Diabetologia 22, 456 (1982)].

Age-related changes in the composition of proteins in the trabecular meshwork of the human eye

The composition of the trabecular meshwork proteins of human eyes ranging in age from 36 days to 84 years was examined by polyacrylamide gel electrophoresis and amino acid analysis. Proteins of different molecular weights could be extracted from the tissue with acetic acid. Although their electrophoretic patterns became less distinct with increasing age, proteins of molecular weights ranging from 50 000 to 69 000 always prevailed. The amino acid compositions of the acetic acid-insoluble trabecular meshwork residues revealed the prevalence of collagenous proteins. The peptide maps produced by treatment with cyanogen bromide indicate that most of the fragments solubilized from the trabecular meshwork of younger eyes are derived from type I collagen. Beyond 40 years of age, the trabecular meshwork was resistant to cyanogen bromide and pepsin digestion. A rough estimate of the distribution of collagen types in the trabecular meshwork was based on 3-hydroxyproline/4-hydroxyproline ratios, indicating an age-related increase of type I collagen from about 55 to 70 per cent, and of type IV collagen from about 2 to 5 per cent of the total protein present. During ageing, some of the protein-bound methionine is oxidized to methionine sulfoxide, reaching about 35 per cent of the total methionine content at the age of 20 years and, with a slower rate of oxidation, a mean value of 40 per cent at 80 years of age. Electron-microscopic analysis of specimens remaining undissolved after cyanogen bromide cleavage and pepsin treatment no longer revealed regular collagenous fibrils but rather elastic-like fibers surrounded by wide sheaths consisting of fine fibrils with a regular cross-banding periodicity of 40–50 nm. In addition, clusters of so-called curly (lattice) collagen were found. The amino acid composition of this insoluble material suggests that altered collagen-like molecules prevail among the proteins of the residues.

RIBOFLAVIN‐PHOTOSENSITIZED OXIDATIVE DEGRADATION OF A VARIETY OF LIGNIN MODEL COMPOUNDS

AbstractOxidation of several lignin model compounds with alkylated paraphenolic groups by photosensitizing riboflavin (RF). rose bengal (RB) and methylene blue (MB) was examined. Photosensitizing RF cleaved l–(3‘‐4’‐diethoxyphenyl)‐1.3 dihydroxy‐2‐(4‐methoxyphenyl)propane (I). 4‐ethoxy‐3‐methoxyphenylglycerol‐(3‐guaiacyl ether (II) and l‐(4‘‐ethoxy‐3’‐methoxyphenyI)‐1,3 dihydroxypropane (IV) at their respective Cα‐Cβ bonds. Riboflavin also oxidized 3.4‐diethoxy‐benzaldehyde (VI) to the corresponding acid, and hydroxylated the conjugated olefin l‐(4‘‐ethoxy‐3’‐methoxyphenyl)1.2 propene (III) to yield the initial product IV. In contrast, MB and RB hydroxylated III but had no effect on I, II, IV or VI under identical conditions. This suggested RF effected transformations via a hydrogen radical abstraction (Type I) rather than a 1O2 mediated reaction.To confirm this, the effects of deuterium oxide (D:0) and oxygen pressure on the photosensitizing dye reactions were examined. The effect of D20 on tryptophan (Trp) oxidation and hydroxylation of III by MB and RB was significant, indicating involvement of 1O2. D2O had no significant effect on cleavage of the diarylpropane (I) and the olefin (III) by RF, indicating these reactions did not proceed by a Type II mechanism. While O2 pressure effect on Trp oxidation by MB was insignificant, it had a large negative effect on cleavage of I by RF. These results, coupled with the relatively slow oxidation rate of Trp by RF. indicate that photosensitizing RF produces 1O2 inefficiently and is not effecting oxidation of these lignin model compounds via a Type II mechanism.

Postbreakaway oxidation kinetics of two ferritic steels

The time needed to reach breakaway oxidation, weight gain at the breakaway point, and the postbreakaway oxidation rate are three important variables which, along with others, play an important role in causing boiler tube failure. In this paper an attempt has been made to study the behavior of two ferritic steels-21/4Cr-1Mo and 9Cr-1Mo. Postbreakaway oxidation kinetics of these two alloys have been studied at temperatures in the range 900–1100°C in pure oxygen for a short duration (maximum of 3 hr). No breakaway was observed at 900°C under these conditions. Postoxidation kinetics are linear at first, followed by a slower oxidation rate. The results have been substantiated by the postoxidation studies using SEM, EDAX, and X-ray diffraction.

Rate-limiting step in oxidation of physiological and artificial reductants by Azotobacter vinelandii membrane vesicles

The respiration of Azotobacter vinelandii membrane vesicles was investigated in order to determine the partial rates of electron fluxes at each segment of its branched respiratory chain. It is concluded that under physiological conditions only 20 to 30% of the total flux is carried through the c 4, c 5 → a 1, o chain. Steady state analysis indicates that the limited capacity of the chain is due to the slow rate of oxidation of the cytochromes c by the a 1, o oxidases. This rate-limiting step is bypassed by the artificial electron donors, ascorbate-2,6-dichlorophenol indophenol and ascorbate- N,N,N′,N′-tetramethyl- p-phenylenediamine, which directly reduce the highly active a 1, o oxidases. During the oxidation of ascorbate- N,N,N′,N′-tetramethyl- p-phenylenediamine by the membrane vesicles, an accumulation of oxidized N,N,N′,N′-tetramethyl- p-phenylenediamine occurs. Such accumulation of positively charged molecules should lead to a generation of a membrane potential. This fact and previous data concerning coupling site III of A. vinelandii are discussed.

Effect of Phosphate and Uncouplers on Substrate Transport and Oxidation by Isolated Corn Mitochondria

A study was made to determine conditions under which malate oxidation rates in corn (Zea mays L.) mitochondria are limited by transport processes. In the absence of added ADP, inorganic phosphate increased malate oxidation rates by processes inhibited by mersalyl and oligomycin, but phosphate did not stimulate uncoupled respiration. However, the uncoupled oxidation rates were inhibited by butylmalonate and mersalyl. When uncoupler was added prior to substrate, subsequent O(2) uptake rates were reduced when malate and succinate, but not exogenous NADH, were used. Uncoupler and butylmalonate also inhibited swelling in malate solutions and malate accumulation by these mitochondria, which were found to have a high endogenous phosphate content. Addition of uncoupler after malate or succinate produced an initial rapid oxidation which declined as the mitochondria lost solute and contracted. This decline was not affected by addition of ADP or AMP, and was not observed when exogenous NADH was substrate. Increasing K(+) permeability with valinomycin increased the P-trifluoromethoxy (carboxylcyanide)phenyl hydrazone inhibition. Kinetic studies showed the slow rate of malate oxidation in the presence of uncoupler to be characterized by a high Km and a low V(max), probably reflecting a diffusion-limited process.The results indicate that rapid malate and succinate oxidation require the operation of both the phosphate and dicarboxylate transporters, which in turn depend on maintenance of a proton motive force across the inner membrane. In addition, phosphate can stimulate acceptorless malate oxidation by reaction with the coupling mechanism, and in uncoupled mitochondria which are depleted of substrate there is a slow rate of oxidation which appears to be limited by diffusive entry.

Maghemite in soils and its origin

AbstractThe products of air oxidation of mixed Fe(II)-Fe(III) chloride solutions at pH 6 and 7, at 20 and 60°C and at normal pressure contain green rust, maghemite, lepidocrocite, goethite and a paracrystalline ferric hydroxide (ferrihydrite). Among these maghemite, a cubic ferromagnetic iron oxide (Fe2O3) found in many soils, is favoured by slow oxidation rate, high total Fe concentration, the presence of small amounts of Fe(III) in the original predominantly Fe(II) solution, higher temperature and at pH 7 rather than pH 6. The green rust is believed to be an essential precursor of maghemite. On slow oxidation it will form maghemite probably via magnetite. Fast oxidation prevents the cubic phase from being formed and lepidocrocite is the end product. At higher Fe(III) proportions ferrihydrite can be formed which under certain influences converts to goethite and/or hematite. The common iron oxides are seen to form from the same system from small variations in environment which is to be expected from their common associations in soils

The kinetics of the oxidation of molecular bromine by aquocobalt(III) ions in perchlorate media

The slow rate of oxidation of molecular bromine by cobalt(III) ions is first order in both [CoIII] and [Br2], and the bimolecular rate constant is inversely proportional to [H+]2. This is interpreted as the reaction of a hydrolysed dimer of CoIII with Br2, and the latter is converted into the bromate condition. At high acidity this slow reaction is followed by a very rapid oxidation initiated by the reaction of the hydroxyl radical with bromine. Evidence exists for the formation of a complex between CoIII and Br2: the variation of optical density with [CoIII], [Br2], and [HClO4] suggests a 1 : 1 complex between unhydrolysed dimer and molecular bromine.

Properties of isolated skeletal-muscle mitochondria from rat

The method to isolate mitochondria from rat skeletal muscle has been modified in such a way as to distinguish between a “heavy” (3500 × g) and a “light” (14,000 × g) mitochondrial subfraction. The 3500 × g fraction represents relatively intact mitochondria and is characterized by a high oxidation rate and good respiratory control with pyruvate + l-malate, compared to a relatively slow rate of DPNH oxidation in the presence of cytochrome c. It exhibits a relatively low ATPase activity, which is greatly stimulated by 0.1 m M 2,4-dinitrophenol, and, to a lesser degree by Mg 2+. The 14,000 × g subfraction, after removal of 3500 × g mitochondria, has a relatively low concentration of intact mitochondria. It is mainly composed of fragments of cell organelles. It is characterized by a high cytochrome c-stimulated DPNH oxidation, and a relatively slow oxidation and poor respiratory control with pyruvate + l-malate, as well as a high Mg 2+-stimulated ATPase activity.

Some features of the gas phase oxidation of n -butenes

Conventional kinetic techniques (static and flow systems) have been used in conjunction with an integral gas chromatographic analytical system in a study of the oxidation behaviour of butene-1, cis butene-2 and trans butene-2. The cis and trans isomers of butene-2 behaved indistinguishably. All three olefins gave qualitatively the same products, but butene-1 differed in the proportions of the individual products formed, and also in oxidation rate. A mechanism, based on that previously proposed for the ethylene + oxygen system, has been found to account for these differences. The ethylene mechanism is only possible, however, because of the slow rate of oxidation of the allylic type radicals easily formed in the reactions. The relative stability of these radicals provides a natural explanation of the phenomenon of self-inhibition observed in olefin + oxygen reactions. The discontinuous production of intermediate substances noted during the oxidation of butene-2 at high reaction rates, provides further evidence for a thermal theory of cool-fiame formation. Acetaldehyde has been found to be the degenerate branching agent and the maximum reaction rate of these systems was found to be identically related to the concentration of this substance.

Influence of Clay Binders on the Oxidation of Sintered Silicon Carbide Bodies

In order to investigate some preventive measures against the oxidation of silicon carbide refractories the sintered specimens of fine SiC powders bonded by Kibushi clay, a popular binder in Japan, were heated at 1175°-1450°C for 50-100 hours in the current of dry oxygen to measure the weight increase, apparent porosity, length and the expansion up to 500°C. The results were compared with those obtained with the bondless bodies formed by adding a small amount of Syton 2X, a silica gel preparation. They weres ubjected to oxydation under the same conditions (as before).Based on the following experimental results, and on some additional considerations the author advanced a tentative plan of improving the characteristics of clay bonded refractories.(1) The bondless body used in this experiment was liable to oxidation with a large volume change. But, at the temperatures higher than 1400°C a small amount of impurity promoted remarkably the lowering of apparent porosity during the process of oxydation, so that the oxydation itself was held back to some degree.(2) Sintered body with 15-30% Kibushi clay as binder showed only a small volume change after long hour's heating at 1300°-1350°C or higher, because of the slow rate of oxidation. At a lower temperature (1175°C) the crystallization of the oxidation product, SiO2, and the influence of cristobalite liberated from the clay were corelative to show a larger expansion than bondless bodies. At higher temperatures (above 1400°C) a melt of low viscosity came out from the body making the surface more porous. The author concluded that the increase of clay substance gave practically no merit of preventing the oxidation of SiC. Taking into other important points the amount of clay should be as low as possible.(3) Kibushei clay used as bond failed to prevent the oxidation at the temperatures lower than about 1230°C. The bodies of low porosity produced by maturing sufficiently at a temperature higher than 1450°C the material added by the components such as Na2O and K2O, which effectively glassify SiO2, may be expected to improve the defects at least to some degree.

Efflorescence Resulting from Pyrite in Clay Raw Materials

In opening this investigation on the effect of pyrite on the efflorescence of structural clay products, the oxidation behavior of this sulfide was studied. The slow oxidation rate and the evolution of 2 moles of sulfur dioxide for every mole of pyrite present combined to make this impurity the major source of efflorescing salts. The retention of part of the sulfur dioxide by the clay material and the subsequent efflorescence tendency were found to depend on the composition, on the concentration of sulfurous gases, on the temperature of firing, on the time of firing, and on the duration of exposure to sulfur dioxide in the manufacturing process. The conditions necessary to reduce efflorescence from this source are described. The use of ammonium chloride to assist in the control of efflorescence was studied in detail.

Oxidation of acetate and malonate in extrahepatic tissues.

Summary1. Oxidation of acetate to CO2 by the eviscerated-nephrectomized rabbit is unaffected by malonate. 2. Studies on the fate of carbon-14 labeled malonate indicate that the intracellular transfer rate of malonate is low. 3. Conversion of radioactive malonate to CO2. has been demonstrated in the eviscerated-nephrectomized rabbit. 4. The slow rate of cell entry and subsequent oxidation of malonate is offered as a possible explanation for the non-inhibitory effect of malonate on acetate oxidation.