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Spaces between small rods direct gas flow. Wires for thin rods clamped in square array in precise square gooove. Spaces between wires are long, thin, parallel channels that direct flow of gas. Technique extended to such hard-to-machine refractory metals as tungsten and molybdenum.
A method is described to electrodeposit noble metals such as platinum and ordinary metals such as copper on and within plasma-sprayed ceramic materials and ceramic fiber materials. Low-density ceramic fiber bodies were vacuum impregnated with plating solution and attached to an electrode. Light micrographs illustrating the density and location of deposited materials are presented and discussed. Voids in the plasma-sprayed ceramic were filled with deposits that vary from spherical to lens-shaped circular and have particle size corresponding to the full range of void size. Multiple coatings of ceramic and metal can be sequenced.
A method is described to electrodeposit noble metals such as platinum and ordinary metals such as copper on and within plasma-sprayed ceramic materials and ceramic fiber materials. Low-density ceramic fiber bodies were vacuum impregnated with plating solution and attached to an electrode. Light micrographs illustrating the density and location of deposited materials are presented and discussed. Voids in the plasma-sprayed ceramic were filled with deposits that vary from spherical to lens-shaped circular and have particle size corresponding to the full range of void size. Multiple coatings of ceramic and metal can be sequenced.
The effect of introducing a very small amount of Ga into Au-contacted InP on the behavior of that contact system was investigated. It was found that Ga affected both the metallurgical and the electrical behavior of the system. It is shown that Ga atoms in the interstices of the Au lattice prevent the solid-state reactions that normally take place between Au and InP during contact sintering and cause an order of magnitude reduction in the specific contact resistivity. It is also shown that the presence of Ga affects the reactions of GaP and GaAs with Au contacts.
The strain behavior of three polycrystalline NiAl alloys has been investigated at temperatures between 300 and 1200 K. Yield stress plateaus, yield stress transients upon a ten-fold increase in strain rate, work hardening peaks, and dips in the strain rate sensitivity (SRS) have been observed between 700 and 800 K. These observations are indicative of dynamic strain aging (DSA) and are discussed in terms of conventional strain aging theories.
Gas trapped in the interstices of the biomaterials used for vascular prostheses causes thrombosis, and the process of eliminating this gas is known as denucleation. An apparatus was developed for testing in the in vitro effects of denucleation on 4 mm I.D. expanded polytetrafluoroethylene (ePTFE) Vitagraft (Johnson and Johnson). The apparatus was designed to ensure that neither the blood nor the grafts came in contact with air. Blood from a single donor was incubated with control and denucleated grafts for 5, 10, 15, 20, and 30 minutes. The thrombus volume in the graft lumen was measured with a computer assisted videometric system. Little thrombus formed by 5 or 10 minutes, but there was less thrombus in the denucleated graft than in the control graft at all times. The differences were statistically significant at 15 and 20 minutes (p < 0.05). Denucleation nearly doubled the thrombus formation time. Thrombus was more adherent to denucleated grafts than to control grafts. These results are consistent with in vivo observations in the rat where denucleation decreased thrombus formation and increased patency duration.
A procedure is described for the analysis of the stable carbon isotopic composition of dissolved organic carbon (DOC) in natural waters from marine and higher-salinity environments. Rapid (less than 5 min) and complete oxidation of DOC is achieved using a modification of previous photochemical oxidation techniques. The CO2 evolved from DOC oxidation can be collected in less than 10 min for isotopic analysis. The procedure is at present suitable for oxidation and collection of 1-5 micromoles of carbon and has an associated blank of 0.1-0.2 micromole of carbon. Complete photochemical oxidation of DOC standards was demonstrated by quantitative recovery of CO2 as measured manometrically. Isotopic analyses of standards by photochemical and high-temperature sealed-tube combustion methods agreed to within 0.3%. Photochemical oxidation of DOC in a representative sediment pore-water sample was also quantitative, as shown by the excellent agreement between the photochemical and sealed-tube methods. The delta 13C values obtained for pore-water DOC using the two methods of oxidation were identical, suggesting that the modified photochemical method is adequate for the isotopically non-fractionated oxidation of pore-water DOC. The procedure was evaluated through an analysis of DOC in pond and pore waters from a hypersaline microbial mat environment. Concentrations of DOC in the water column over the mat displayed a diel pattern, but the isotopic composition of this DOC remained relatively constant (average delta 13C = -12.4%). Pore-water DOC exhibited a distinct concentration maximum in the mat surface layer, and delta 13C of pore-water DOC was nearly 8% lighter at 1.5-2.0-cm depth than in the mat surface layer (0-0.5-cm depth). These results demonstrate the effectiveness of the method in elucidating differences in DOC concentration and delta 13C over biogeochemically relevant spatial and temporal scales. Carbon isotopic analysis of DOC in natural waters, especially pore waters, should be a useful probe of biogeochemical processes in recent environments.
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Molecular dynamics simulations are conducted to study the effects of alloying elements on the primary damage behaviors in three Fe-based ferritic alloy systems: (1) a Fe-Cr system in which the heat of mixing changes its sign with the Cr concentration; (2) a Fe-Cu system that has a positive heat of mixing; and (3) an ideal but artificial Fe-Cr system that has a zero heat of mixing, which is used as a reference system to investigate solute interstitial formation based on probability. It is found that in these alloys, the solute type and concentration do not have a significant effect on the total number of surviving Frenkel pairs. However, the fraction of solute interstitials has distinct behaviors. In Fe-Cr, the Cr interstitial fraction is much higher than the Cr solute concentration and the Cr interstitial production efficiency decreases with the increasing Cr concentration. By contrast, in Fe-Cu, Cu interstitials are barely produced. In the ideal alloy, the solute interstitial fraction is close to the solute concentration. The defect formation energies in both dilute and concentrated alloys, interstitial binding energies, liquid diffusivities of Fe and solute atoms, and heat of mixing have been calculated for both Fe-Cr and Fe-Cu alloys. Among them, we find that the relative thermodynamic stability between Fe self-interstitials and solute interstitials plays the most important role in the solute interstitial production behaviors. The decrease of Cr interstitial production efficiency with increasing Cr concentration can be explained by the probability distribution functions of solute interstitial formation energy in concentrated alloys.
Oxygen transport is central to many properties of oxides such as stoichiometric changes, phase transformation, and ionic conductivity. In this paper, we report a mechanism for oxygen transport in uranium dioxide (UO{sub 2}) in which the kinetics is mediated by defect clustering dynamics. In particular, the kinetic Monte Carlo method has been used to investigate the kinetics of oxygen transport in UO{sub 2} under the condition of creation and annihilation of oxygen vacancies and interstitials as well as oxygen interstitial clustering, with variable off-stoichiometry and temperature conditions. It is found that in hypo-stoichiometric UO{sub 2−x}, oxygen transport is well described by the vacancy diffusion mechanism while in hyper-stoichiometric UO{sub 2+x}, oxygen interstitial cluster diffusion contributes significantly to oxygen transport kinetics, particularly at high temperatures and high off-stoichiometry levels. It is also found that di-interstitial clusters and single interstitials play dominant roles in oxygen diffusion while other larger clusters have negligible contributions. However, the formation, coalescence, and dissociation of these larger clusters indirectly affects the overall oxygen diffusion due to their interactions with mono and di-interstitials, thus providing an explanation of the experimental observation of saturation or even drop of oxygen diffusivity at high off-stoichiometry.
The interstitial chemical impurities hydrogen, oxygen, nitrogen, and carbon are important for niobium metal production and particularly for the optimization of niobium SRF technology. These atoms are present in refined sheets and can be absorbed into niobium during processing treatments, resulting in changes to the residual resistance and the performance of SRF cavities. A first-principles approach is taken to study the properties of carbon in niobium, and the results are compared and contrasted with the properties of the other interstitial impurities. The results indicate that C will likely form precipitates or atmospheres around defects rather than strongly bound complexes with other impurities. On the basis of the analysis of carbon and hydrogen near niobium lattice vacancies and small vacancy chains and clusters, the formation of extended carbon chains and hydrocarbons is not likely to occur. Association of carbon with hydrogen atoms can, however, occur through the strain fields created by interstitial binding of the impurity atoms. Calculated electronic densities of states indicate that interstitial C may have a similar effect as interstitial O on the superconducting transition temperature of Nb.
Damage of materials due to neutron irradiation occurs via energetic cascades caused by energetic primary knock-on atoms (PKA) created by the energetic neutron as it passes through the material. These cascades result in creation of Frenkel Pairs (interstitials and vacancies). The interstitials and vacancies diffuse and recombine to (I) nullify the damage when an interstitial recombines with a vacancy, (II) form interstitial clusters when two or more interstitials recombine, and (III) form vacancy clusters when several vacancies come together. The latter two processes result in change of material properties. Interstitial diffusion has reported time-scales of microseconds and vacancy diffusion has diffusion time-scales of the order of seconds. We have carried out molecular dynamics (MD) simulations of interstitial diffusion in crystal Cu to study the mechanism of diffusion. It is found that interstitialcy diffusion – wherein an interstitial displaces a lattice atom thereby making the lattice atom an interstitial – has time-scales of a few tens of pico-seconds. Therefore we propose that the “interstitialcy diffusion” mechanism could play a major part in the diffusive-recombinations of the Frenkel Pairs created during the cascade.
In this paper, the influence of calcination parameters on the synthesis of N:TiO{sub 2} catalysts obtained through the polymeric precursors method was evaluated. The powders were prepared by annealing Ti{sup 4+} precursor resins at different temperature-time conditions in air, resulting in powders with different degrees of crystallinity for N doping, which was done by adding urea to the as-prepared powders and calcining in N{sub 2} atmosphere. The N doping process resulted in band gap narrowing of TiO{sub 2} and, varying annealing temperature and time, can be an alternative method for preferential formation of substitutional N or interstitial N. It was found that the percentage of interstitial N increased with an increase in annealing temperature, resulting in the complete absence of substitutional N at 400 °C. The photocatalytic performance of the powders was evaluated using Rhodamine-B and Atrazine solutions under ultraviolet and visible irradiations. The coefficients revealed that interstitial N had a positive correlation to both ultraviolet and visible photoactivity. In contrast, substitutional N showed a negative correlation. Further, the ratio of substitutional N to interstitial N indicated a strong negative correlation to ultraviolet light photoactivity and no correlation to visible light photoactivity. However, substitutional N should be controlled for better photocatalytic properties. - Graphical abstract: The temperature influences to promote higher quantities of Interstitial N doped TiO{sub 2} than Substitutional and due to difference between energies levels for substitutional N doped TiO{sub 2} and Interstitial N doped TiO{sub 2}, it is presented difference on photocatalytic activity. - Highlights: • Temperature and time of synthesis of N doping TiO{sub 2} could affect the type of N (interstitial and substitutional N). • The percentage of interstitial N increased with an increase in annealing temperature. • Interstitial N improves ultraviolet and visible light degradation of color and colorless substrates (Rhod and Atraz). • Visible photoactivity may not depend only on band gap narrowing but on several factors.
The defect energetics in y-LiAlO2, Li2 TiO3, and Li2ZrO3 materials used in tritium-producing burnable absorber rods and fusion solid breeder applications was investigated using density functional theory calculations. A comprehensive analysis of the charged defects was performed for cation and anion vacancies, interstitials, antisite defects, and 3H interstitial and substitutional defects to understand the defect structures at different charge states and their stability as a function of the electron chemical potential across the electronic band gap of crystals at operating temperature and oxygen partial pressure conditions. Through investigation of the local bonding configurations and projected electronic density of states of the 3H related charged defects, including 3H interstitial (3Hint), 3Hint bound with an oxygen interstitial, and substitutional 3H defects on the Li, O, and M (M¼ Al, Ti, and Zr) sites (3HLi, 3HO, and 3HM), the 3H states of these defects were distinguished, i.e. triton (3Hþ), neutral 3H (3H0), and tritide (3H-). The two stable 3H related defects under the Li2O-LiOH rich condition at T ¼ 1000 K, between P(O2) ¼ 10^-5 and 10^-25 atm were found to be 3H interstitial (3Hint) with charge of þ1 and neutral 3HLi (substitutional 3H on the Li site) in g-LiAlO2, Li2ZrO3, and Li2TiO3 materials. For Li2TiO3, the stability of the 3HO with charge of þ1 and 3HM with charge of 3 becomes comparable to that of 3Hint atm at P(O2) ¼ 1025 atm. Overall, our results indicate the energy cost to form the stable 3H defect species (3Hint with charge of þ1 and neutral 3HLi) in g-LiAlO2 material are higher than those of Li2TiO3 and Li2ZrO3 materials at T ¼ 1000 K, between P(O2) ¼ 10^-5 and 10^-25 atm. Interactions between the point defects and the 3H species as a function of the electron chemical potential across the band gap of the materials were also examined. All the three materials exhibit strong interactions between the 3Hint and the O vacancy, Li vacancy, and O interstitial defects with the strongest interactions found in the case of y-LiAlO2 phase, indicating a higher tendency to trap 3H at such point defects in y-LiAlO2.