Suppressing H2 Evolution by Silicon Powder Dispersions

Silicon dispersions in water are used to produce pyrotechnic time delay compositions. The propensity of the silicon to react with water and to produce hazardous hydrogen gas must be suppressed. To this end, the effect of surface modifications and medium pH on the rate of corrosion of silicon was studied at ambient temperature. It was found that the rate of hydrogen evolution increased with increasing pH. Silanes proved to be more effective silicon corrosion inhibitors than alcohols, with vinyl tris (2-methoxyethoxy) silane producing the best results. Differential thermal analysis (DTA) studies were performed using a near-stoichiometric amount of lead chromate as oxidant. Comparable combustion behavior was observed when both the fuel and the oxidant powders were either uncoated or silane modified. Mixtures of neat oxidant with silane-coated silicon showed poor burn behavior and this was attributed to poor particle–particle mixing due to the mismatch in surface energies.     

Oxidation Hardening Kinetics of the Rheological Function G′/(η′/G′) in Asphalts

Abstract

The authors used 9 asphalts oxidized at various temperatures and pressures to determine the hardening kinetics for the DSR function, an easily measured and meaningful surrogate for 15°C ductility that relates well to age-related binder deterioration. For each asphalt, there is a rapid initial period that slows to a constant rate period. This constant rate period can be represented by carbonyl formation (oxidation) rate times a hardening susceptibility (HS). For the DSR function and viscosity, the HS and initial jump were pressure- but not temperature-dependent. The DSR function initial jump was relatively higher than the viscosity initial jump.     

Enhanced activity and stability of Pt/C fuel cell anodes by the modification with ruthenium-oxide nanosheets

Ruthenium-oxide nanosheet (RuO₂ns) crystallites with thickness less than 1 nm were prepared via chemical exfoliation of a layered potassium ruthenate and deposited onto carbon supported platinum (Pt/C) as a potential co-catalyst for fuel cell anode catalysts. The electrocatalytic activity towards carbon monoxide and methanol oxidation was studied at various temperatures for different RuO₂ns loadings. An increase in electrocatalytic activity was evidenced at temperatures above 40 °C, while little enhancement in activity was observed at room temperature. The RuO₂ns modified Pt/C catalyst with composition of RuO₂:Pt = 0.5:1 (molar ratio) exhibited the highest methanol oxidation activity. CO-stripping voltammetry revealed that RuO₂ns promotes oxidation of adsorbed CO on Pt. In addition to the enhanced initial activity, the RuO₂ns modified Pt/C catalyst exhibited improved stability compared to pristine Pt/C against consecutive potential cycling tests.     

Chemistry of Secondary Polyphenols Produced during Processing of Tea and Selected Foods

This review will discuss recent progress in the chemistry of secondary polyphenols produced during food processing. The production mechanism of the secondary polyphenols in black tea, whisky, cinnamon, and persimmon fruits will be introduced. In the process of black tea production, tea leaf catechins are enzymatically oxidized to yield a complex mixture of oxidation products, including theaflavins and thearubigins. Despite the importance of the beverage, most of the chemical constituents have not yet been confirmed due to the complexity of the mixture. However, the reaction mechanisms at the initial stages of catechin oxidation are explained by simple quinone–phenol coupling reactions. In vitro model experiments indicated the presence of interesting regio- and stereoselective reactions. Recent results on the reaction mechanisms will be introduced. During the aging of whisky in oak wood barrels, ellagitannins originating from oak wood are oxidized and react with ethanol to give characteristic secondary ellagitannins. The major part of the cinnamon procyanidins is polymerized by copolymerization with cinnamaldehyde. In addition, anthocyanidin structural units are generated in the polymer molecules by oxidation which accounts for the reddish coloration of the cinnamon extract. This reaction is related to the insolubilization of proanthocyanidins in persimmon fruits by condensation with acetaldehyde. In addition to oxidation, the reaction of polyphenols with aldehydes may be important in food processing.     

Application of a spectroscopic method to estimate the olive oil oxidative status

A rapid Fourier transformed infrared (FTIR) attenuated total reflectance (ATR) spectroscopic method coupled with partial least squares (PLS), was developed to estimate the oxidation degree of extra virgin olive oil (EVOO). The reference values of EVOO oxidation for the FTIR calibration were obtained by the specific absorptions at 232 and 270 nm, due to the presence of conjugated diene (CD) and conjugated triene (CT) groups, as monitored by the UV spectrophotometric determination. Specific washing procedures were applied to the EVOO to obtain EVOOP and EVOOTP samples, without phenolic compounds and without tocopherols and phenols, respectively. To obtain different oxidation degrees covering wide CD and CT ranges, EVOO, EVOOP, and EVOOTP samples were subjected to a forced oxidation at 60°C for 20 days and aliquots of the oils were daily analyzed. Regression of the FTIR/PLS‐predicted CD and CT of individual oxidized oils EVOO, EVOOP, EVOOTP, and all combined oils (EVOOALL) against UV–Visible reference values demonstrated the good quality of the models in terms of R² and RMSECV values. The results of the study indicated that a strong correlation existed between FTIR and UV–Visible peak intensities. Practical applications: The FTIR‐ATR method coupled with PLS elaboration was developed and applied to predict the oxidation degree of EVOO samples with considerable advantages in terms of simplicity, analysis time, and solvent consumption as compared to the standard method. Moreover, suitable adjustments of the equipment could permit a rapid control at‐line in oil sector.     

Cloning,Expression and Purification of Cindoxin,an Unusual Fmn‐Containing Cytochrome P450 Redox Partner

Cytochromes P450 (P450s) belong to a superfamily of haemoproteins that catalyse a remarkable variety of oxidative transformations. P450 catalysis generally requires that cognate redox proteins transfer electrons, derived ultimately from NAD(P)H, to the P450 for oxygen activation. P450_cin (CYP176A1) is a bacterial P450 that is postulated to allow Citrobacter braakii to live on cineole as its sole carbon source by initiating cineole biodegradation. Here we report the cloning, expression, purification and characterisation of one of its postulated redox partners, cindoxin (Cdx), which has strong similarity to the FMN domain of cytochrome P450 reductase. Cindoxin reductase (CdR), which displays strong similarity to NADPH‐dependent ferredoxin reductases, was unable to be expressed in a functional form. Mass spectrometric and HPLC analyses confirmed that the flavin cofactor of cindoxin was FMN. Redox potentiometric titrations were performed with cindoxin within the range 6<pH<8; this enabled the quinone/semiquinone (E₁) and semiquinone/hydroquinone (E₂) redox potentials to be determined. Our results show that cindoxin might be somewhat different to other flavodoxins that interact with P450s, in which generally only one couple is important. Both redox states of cindoxin could be catalytically relevant. A catalytically active system was reconstituted in vitro with E. coli flavodoxin reductase (Fpr) acting as the terminal redox partner in the absence of CdR. Our results show that Cdx and Fpr support regio‐ and stereoselective P450_cin‐catalysed cineole oxidation to (1R)‐6β‐hydroxycineole with turnover rates up to 1500 min^?1. This system is tightly coupled with 80 % of NADPH reducing equivalents funnelled into substrate oxidation.     

High‐temperature oxidation behaviour of model Co?Re?Cr alloys at low oxygen partial pressure

The oxidation behaviour of four model Co? Re? Cr alloys and a commercial Co‐based alloy was investigated at 1000 °C and a low‐oxygen partial pressure of p(O₂) = 10^?16 bar, in order to prove the feasibility of a pre‐oxidation treatment. Under suitable conditions of the pre‐oxidation treatment, the oxidation of the highly reactive alloying element Cr is possible. All the studied alloys form a continuous and dense Cr₂O₃ scale on the metal surface. The transport of chromium to the surface occurs mainly from the Cr‐rich σ‐phase, which becomes completely dissolved in the surrounding matrix after long exposure times. As a result of the Cr₂O₃ scale, growth depletion of Cr occurs in the near surface region, leading to internal oxidation.     

Surface characterisation of DC plasma electrolytic oxidation treated 6082 aluminium alloy: Effect of current density and electrolyte concentration

Plasma electrolytic oxidation (PEO) is a specialised but well-developed process which has found applications in aerospace, oil/gas, textile, chemical, electrical and biomedical sectors. A novel range of coatings having technologically attractive physical and chemical properties (e.g. wear- and corrosion-resistance) can be produced by suitable control of the electrolyte as well as electrical parameters of the PEO process. Oxide ceramic films, 3 to 40 μm thick, were produced on 6082 aluminium alloy by DC PEO using 5 to 20 A/dm² current density in KOH electrolyte with varied concentration (0.5 to 2.0 g/l). Phase analysis (composition and crystallite size) was carried out using X-ray diffraction and TEM techniques. Residual stresses associated with the crystalline coating phase (α-Al₂O₃) were evaluated using the X-ray diffraction Sin²ψ method. Nanoindentation studies were conducted to evaluate the hardness and elastic modulus. SEM, SPM and TEM techniques were utilised to study surface as well as cross-sectional morphology and nano features of the PEO coatings. Correlations between internal stress and coating thickness, surface morphology and phase composition are discussed. It was found that, depending on the current density and electrolyte concentration used, internal direct and shear stresses in DC PEO alumina coatings ranged from − 302 ± 19 MPa to − 714 ± 22 MPa and − 25 ± 12 MPa to − 345 ± 27 MPa, respectively. Regimes of PEO treatment favourable for the production of thicker coatings with minimal stress level, dense morphology and relatively high content of α-Al₂O₃ phase are identified.     

The Effect of Un-saturates on Low-Temperature Oxidation of Crude Oil

Abstract

Low-temperature oxidation (LTO) of four Arabian crudes as well as blends of naphtha with a super-light crude was investigated employing differential thermal analysis. The mass fraction of un-saturates in the reactants varied between 0.2 and 0.9. All reactants showed LTO peaks between 230 and 264°C; heat flow at the peak, however, varied widely. The data revealed a clear increase in LTO-generated heat as the reactant's content of un-saturates increased. The lightest crude with 51.1 °API gravity and un-saturates fraction of 0.2 showed the least LTO reactivity. It is, therefore, concluded that the un-saturates content of a crude is an influential factor in its LTO tendency and, thus, its potential for spontaneous ignition and other enhanced-recovery techniques that rely on LTO.     

Effect of simulated gastrointestinal digestion on phenolic composition and antioxidant capacity of cooked cowpea (Vigna unguiculata) varieties

Consumption of diets rich in phenolic compounds has been associated with reduced risk of chronic diseases. The effect of cooking and simulated gastrointestinal digestion on phenolic compounds and antioxidant properties of two cowpea (Vigna unguiculata) types was determined. Phenolic acids, flavan‐3‐ols and flavonols were the main groups of phenolic compounds identified. Cooking and simulated enzyme digestion of the cooked cowpea samples rendered some phenolics less extractable (possibly by promoting binding with other food components) or more extractable (possibly by release of bound forms). Total phenolic contents and radical scavenging properties of the cowpeas were reduced upon cooking, but increased upon simulated enzyme digestion. Cowpea extracts inhibited human LDL oxidation at a concentration of 2 mg mL^?1 possibly due to their phenolic content. Phenolic compounds in cowpea can potentially protect against cardiovascular diseases for which LDL oxidation is a risk factor.