Influence Of Oxygen Diffusion Research Articles

Influence of Oxygen Diffusion on Thermal Ageing of Cross-Linked Polyethylene Cable Insulation.

Thermal ageing of cross-linked polyethylene (XLPE) cable insulation is an important issue threatening the safe operation of power cables. In this paper, thermal ageing of XLPE was carried out at 160 °C in air for 240 h. The influence of oxygen diffusion on thermal ageing of XLPE was investigated by Ultraviolet–visible spectrophotometer (UV–Vis), tensile testing, and Fourier transformed infrared spectroscopy (FTIR). It was observed that the degradation degree not only depended on ageing time but also on sample positions. The thermally aged samples were more oxidized in the surface region, presented a darker color, more carbon atoms appeared in the conjugate cluster, had smaller elongation at break and tensile strength, and a larger carbonyl index. As ageing time increased, the non-uniform oxidation of the XLPE samples became more prominent. The degree of non-uniform oxidation caused by oxygen diffusion was quantitatively studied by first order oxidation kinetic. The calculated results demonstrated that carbonyl index measured by FTIR was more sensitive to non-uniform oxidation with a shape parameter in the range of 1–2. The result shown in this paper is helpful for interpreting and predicting the non-uniform ageing behavior of high voltage XLPE cables.

Relationship between the volume of the unit cell of hexagonal-close-packed Ti, hardness and oxygen content after α-case formation in Ti–6Al–2Sn–4Zr–2Mo–0.1Si alloy

In this study, the influence of oxygen diffusion on the physical properties of Ti–6Al–2Sn–4Zr–2Mo–0.1Si was examined. Measurements were carried out directly on sample cross sections which were preoxidized at high temperature. The lattice parameter evolution was measured using synchrotron X-ray diffraction and was coupled with microhardness and electron probe microanalyzer results with the aim of highlighting their relationships. The results show that the hardness and oxygen gradients along the oxygen diffusion zone in the alloy are similar to the evolution of the α-phase unit-cell volume quantified by X-ray diffraction. Linear relationships were found between these three parameters.

Modeling the rate of biocorrosion and the effects of redox-reactions of metals in water environment

Laboratory studies were conducted to assess the effectiveness of biocorrosion through oxygen diffusion in zinc metal in water environment. The present investigation was undertaken to determine the corrosion rate of zinc metal in water environment with respect to Plank-Nernst Equation modified to monitor and predict the biocorrosion rate through oxygen diffusion which resulted to biofilm formation. The modified developed mathematical model of Plank-Nernst equations to evaluate the corrosion rate of zinc metal upon the influence of oxygen diffusion in a flowing system was given as CR = 534w / DAtoeλ21 where l = 0.5 when compared with the normal corrosion rate equation, CR = 534w / DAtoeλ21 then the results obtained showed a good match. The biocorrosion rate of zinc metal was tested in salt and fresh water environment and the results obtained showed that corrosion was faster on zinc metal immersed in salt water environment than the fresh water environment; this was attributed to the physicochemical parameters of the salt/fresh water environment. Key words: Modeling, corrosion, redox-reaction, biocorrosion, metal, water environment.

Influence of oxygen diffusion on residual stress for tantalum thin films

The influence of oxygen diffusion on the residual stress of 500Å thick tantalum thin films sputtered on Si substrate after annealing temperature from 200to400°C is examined in this article. The intensity of diffraction peaks for tetragonal β-Ta phase decreases when annealing temperatures increase by utilizing glancing incident angle x-ray diffraction measurements, and x-ray photoelectron spectroscopy was performed to understand the Ta2O5 oxidation layer on the surface of Ta films after the annealing processes. Furthermore, simulated x-ray reflectivity (XRR) results show that the thicker Ta2O5 oxidation layer is formed when the annealing temperature increases. The compressive stress is nearly proportional to the thickness of the Ta2O5 oxidation layer after the annealing process because of the incorporation of the oxygen into interstitial sites of β-Ta unit cell, which leads to the 5.4Å3 volume expansion of the β-Ta unit cell. Besides, Auger electron spectroscopy was also used to analyze the depth profile of oxygen diffusion which has consistent tendency with XRR results. The above results indicate that oxidation of Ta films with annealing processes will increase the compressive stress in textured β-Ta thin films.

Influence of oxygen diffusion through capping layers of low work function metal gate electrodes

This letter evaluates Ru and W capping layers for MoTa metal gate electrodes in MOS capacitor applications. The authors report that the oxygen diffusion from the capping layer plays an important role in determining the MoTa alloy effective work function value on SiO/sub 2/. A MoTa alloy metal gate with Ru capping exhibits stable effective work function up to 900/spl deg/C annealing but is not stable with W capping. Auger electron spectroscopy and Rutherford backscattering spectroscopy analyses show minimal oxygen diffusion into MoTa gate stacks with Ru capping while severe oxygen diffusion into the gate is observed with W capping metal after 900/spl deg/C annealing. Current-voltage analysis also demonstrates different barrier heights of MoTa on SiO/sub 2/ with Ru or W capping layer after 900/spl deg/C annealing, confirming the effective work function value change.

High-Temperature Physicochemical Mechanics of Materials

We propose to regard investigations in the field of high-temperature strength of structural metals and alloys interacting with corrosive media as high-temperature physicochemical mechanics of materials (HTPCMM). The most important feature of HTPCMM is the principle of correlation between deformation processes and physicochemical phenomena, which allows one to describe the features and regularities of changes in the properties of materials under service conditions most completely and correctly. We emphasize the most important role of diffusion as a controlling factor in a metal–medium system at high temperatures. Results of analytical investigations aimed at the development and investigation of physicomathematical models of elastic and elastoviscous multicomponent solid solutions with inherent degradation processes (accumulation of damage) are presented. The fact that, as a rule, these models are constructed within the framework of continuum mechanics on the basis of principles of nonequilibrium mechanics is noted Experimental data obtained, in particular, on refractory metals and titanium interacting actively with components of a vacuum or an inert atmosphere testify to the intensification of saturation of metals by interstitial impurities under conditions of long-term loading and to significant changes in the character of their creep, namely, under the influence of oxygen diffusion the creep rate decreases as stresses increase.

Effects of oxygen diffusion on recombinant E. coli B (pTG201) plasmid stability, growth rate, biomass production, and enzyme activity in immobilized and free bacteria during continuous culture

AbstractThe influence of oxygen diffusion on kinetic properties, plasmid instability, biomass production and enzyme production of recombinant Escherichia coli B containing plasmid pTG201 was investigated. The experiments were carried out using continuous cultures and two types of medium, with immobilized bacteria in carrageenan gel and free bacteria. The specific growth rate of immobilized bacteria was a monotonic function of dissolved oxygen (DO) level from 0% DO to 100% DO, and it increased 63% in L‐Broth medium and 70% in minimal medium with respect to 0% DO, but the growth rate was quickly reduced above 75% DO (L‐Broth medium) or 50% DO (minimal medium) in free bacteria. The specific growth rate was generally higher for free bacteria than for immobilized bacteria. The plasmid was substantially more stable at 0% than at 50% or 100% DO in both immobilized and free bacteria. Biomass production was proportional to the growth rate, and this in turn was greatly influenced by the DO concentration. Measurements of enzyme production showed that the enzyme activity was diminished in both immobilized and free bacteria when oxygen was eliminated. The observed increase in plasmid stability may have resulted from the disturbance of low growth rate and decreased expression of the enzyme.

The effects of oxygen diffusion on the surface photooxidation of polystyrene

AbstractThis paper further illustrates the applicability of multiple internal reflectance infrared spectroscopy to the analysis of near‐surface photooxidation. The results are compared with transmission infrared spectra to evaluate compositional gradients resulting from photooxidation and the influence of oxygen diffusion. The sample was a solvent‐cast film of atactic, narrow distribution polystyrene, Mw of 100,000, that had been drawn to a ratio of 3.0 at 110°C by solid state coextrusion. Irradiation of these thin films, ∼25μm thickness, was performed on exposure to air at 35°C for periods of up to 6 h using a mercury source emitting at 254 nm. On photooxidation, a board peak appears at 3200–3500 cm−1, attributable to hydroperoxide formation. The most dramatic increase in the infrared spectra is found for a carbonyl band at 1730 cm−1. It appears to result from an aromatic acid group since it is shifted to 1660 cm−1 on immersion of the oxidized polystyrene films in aqueous ammonium hydroxide. It is confirmed that the photooxidation of polystyrene occurs preferentially at the surface and that this reaction rate is greatly reduced in the drawn polystyrene film.

Ester Oxidation Under Simulated Boundary-Lubrication Conditions

Measurement of lubricant oxidation rates at high temperatures is complicated by the influence of oxygen diffusion. Consequently, determination of kinetic rates of oxidation above 450 K has previously been limited to reactions conducted to only 2-percent conversion of the reactant. Using the Penn State microoxidation test, we quantified the effect of oxygen diffusion on the oxidation of two esters at temperatures of 448 to 518 K. Reaction rates and product compositions were followed for reactant conversions of up to 50 percent. The rate coefficients and activation energies for the initial reactions (approximately first order) were determined using a diffusion-reaction model to separate kinetics from oxygen diffusion. Oxidation intermediates react with the iron surface, which catalyzes formation of a polymeric precursor of sludge and varnish. Proximity of the primary oxidation reaction to the iron surface influences the amount of iron-corrosion product and the molecular weight of the polymer. Differences ar...