Oxygen Bulk Diffusion Research Articles

Interaction of oxygen with a Ru(OO1) surface

The interactions of oxygen with a Ru(001) surface were investigated at 300–1300 K by AES, thermal desorption spectroscopy (TDS) and work function measurements. A single second-order TD peak was observed at coverages θ lower than 0.25. The considerable changes in the shapes of the TD curves recorded at θ < 0.25 suggested a multistate oxygen desorption. It was demonstrated that oxygen diffusion into the Ru lattice, which began at T ⩾ 1150 K, substantially affected the TD data. It was found that oxygen bulk diffusion was much more probable for the binding state existing at θ < 0.25 than for those appearing in the θ range between 0.25 and 0.5.

Ultraviolet (193 nm) laser-induced oxygen exchange and bulk diffusion in gallium arsenide native oxides: 18O experiments

Pulsed laser irradiation (193 nm, t=14 ns) at low fluence (0.045 J/cm2) of GaAs 18O enriched native oxides leads to a very efficient oxygen exchange between 18O in the oxides and 16O coming from the surrounding atmosphere. 1000 laser pulses caused a complete exchange of oxygen from an oxide layer of ∼30-nm thickness. This showed a very high rate of oxygen self-diffusion under laser irradiation although the total oxygen content in the oxide was preserved. As this process is believed to have a threshold fluence, a model based on the hole-pair mechanism of Itoh and Nakayama [Phys. Lett. A 92, 471 (1982)] is suggested. Preferential loss of As and preferential oxidation of Ga are also observed to some extent.

Mathematical modelling of rate-limiting mechanisms of pyritic oxidation in overburden dumps

The mining of valuable minerals often leads to major environmental pollution problems especially when pyritic material is associated with the orebody being mined. In this thesis mathematical equations are formulated which describe a dual region model of pyritic oxidation within a waste rock dump, where it is assumed that oxygen transport is the rate-limiting step in the oxidation process, and that oxygen transport to reaction sites occurs in two stages; bulk diffusion of oxygen from the atmosphere, at the top surface of the dump, through the pore space of the dump to particles within the dump, and then diffusional transport of oxygen from the surface of particles to oxidation sites within the particles. A moving boundary (shrinking-core) formulation, describing transport and reaction processes within a single particle of the dump, is solved by a new analytic series solution technique involving a change of coordinates leading to a non-linear partial differential equation with fixed boundaries. Based on this analysis a pseudo-steady state assumption is made with respect to diffusion within the particles giving a simplified system of equations for the dump model. The system of equations is solved both in an approximate analytic way and numerically. An approximate analytic result is obtained by solving a planar moving boundary formulation which in turn comes from approximation of the position of the moving reaction front within the particles of the dump. The position of the planar front within -vthe dump is given by a transcendental equation which is shown to I collapse on the (time)2 classical planar moving boundary result when the particle size tends to zero. A combined Crank-Nicolson and Backward Euler discretisation of the system of equations is adopted for the numerical scheme. The approximate and numerical solutions

Oxygen adsorption on a Pd(111) surface

The interaction of oxygen with Pd(111) has been studied by means of AES, ELS, thermal desorption (TD), electron stimulated desorption (ESD) and work function measurements. It was found that a very small part ( ∼ 2–3%) of the available adsorption sites are contributing to the O + electron stimulated yield, the population of the latter being accompanied by enormously large work function changes (up to ∼ 0.9 eV). A mechanism of adsorption and depopulation of these sites involving oxygen bulk and surface diffusion has been proposed.

The effects of temperature upon NiO formation and oxygen removal on Ni(110)

Oxygen chemisorption and NiO nucleation and growth on Ni(110) have been studied with low energy electron diffraction and Auger electron spectroscopy. Changes in the Auger peak energies and shapes were shown to occur only upon NiO formation. The effects of step-changes in temperature upon NiO nucleation and growth were studied and it was shown that temperature steps or annealing during the chemisorption regime did not significantly affect either chemisorption or NiO formation. During NiO growth, temperature steps to a higher temperature caused reduced growth rates, while steps to lower temperature caused increased growth rates. The reaction rate constant from the island growth model was calculated and shown to agree with literature data. The values obtained from temperature step measurements agreed within a factor of two with those obtained for reactions without temperature steps. Therefore, no systematic temperature effect upon the NiO nuclei density was observed for Ni(110). The activation energy for growth of NiO was found to be 5.5 kcal/mole. Dissolution of oxygen into bulk nickel was also studied and it was shown that bulk diffusion of oxygen in nickel was not rate controlling. Rather, surface phase transitions were observed which allowed incorporation of oxygen over the temperature range of 150°C to greater than 800°C, depending on the quantity of oxygen already incorporated.

The K-absorption edge of vanadium in some vanadium compounds

Fine vanadium nitride powders (particle size 11 nm) have been prepared by temperature programmed reduction and nitridation of V2O5 by gaseous ammonia. The reaction was followed by monitoring gas phase reaction products by on-line mass spectroscopy. X-ray diffraction and elemental analysis were used to identify various solid-state reaction intermediates, V6O13, V2O4, VO2, V2O3, and VO, and to establish that the final reaction step was the nitridation of VO to VN. Heating rate had a substantial effect on product specific surface area and a rate of 0.083 K sec−1 resulted in an optimal value of 90 m2g−1. The activation energy for nitridation was not constant, but rose from 203 to 243 kJ mol−1 as the extent of reaction increased from 0.25 to 0.75. The transformation was limited by the bulk diffusion of oxygen and nitrogen and not by a surface process.

The creep of quartz single crystals, with special reference to the mechanism by which water accommodates dislocation glide

Abstract A geometrical description is presented which demonstrates that the core structure of static dislocations in α- and β-quartz can be electrostatically neutral. However, to preserve neutrality during dislocation multiplication and glide, it is postulated that water has to be extracted from nearby sources. This is relatively easy if the water is distributed as water molecules in interstitial solution but not if it is present in the form of droplets of second phase, because extraction of water from bubbles requires simultaneous bulk diffusion of silicon and oxygen. As a consequence, the activation energy for secondary creep is increased from 18 kcal mole−1, the value for diffusion of hydroxyl ions, to 31 kcal mole−1, the value for self-diffusion of oxygen in quartz. The direct observation of phase separation of water suggests a new interpretation for the well-known effect of superposed hydrostatic pressure on the plasticity of quartz, namely that it suppresses such phase separation and thereby maintains the supply of water to dislocations.

Barium, strontium, and calcium as getters in electron tubes

Strontium and calcium getters have possible use replacing barium as gas sorbers in color picture tubes and other electron tubes. Stable getters were made of a calcium–aluminum or strontium–aluminum alloy, which was powdered, mixed with nickel powder, and pressed into a ring‐shaped channel of stainless steel. After exhaust pumping and tip‐off of the picture tube, the getter was heated to form a gas‐sorbing film of strontium or calcium, which was deposited by evaporation onto the internal surfaces of the picture tube. Strontium and calcium getters were evaluated and compared to barium getters in color picture tubes by the oxygen sorbtion test, which determined the maximum oxygen quantity that can be absorbed by the film without damage to the tube’s oxide cathode. When flashed in 25‐in. color tubes, barium and strontium showed the same oxygen capacity, both initially and after 11 and 25 weeks of life test. When flashed in tubes of smaller size and surface area, strontium showed lower oxygen capacity than barium, a result indicating slower bulk diffusion of oxygen through thick films of strontium oxide than through barium oxide. Calcium showed satisfactory gettering speed allowing normal tube operation out to 25 weeks of life test; however its gettering capacity was lower, being about 1/4 that of barium and indicating even slower diffusion of oxygen in calcium oxide than in strontium oxide.

The role of oxygen transport in oxidation of Fe-Cr alloys

Abstract A nuclear technique has been used to study the oxidation of Fe-Cr alloys having Cr contents of 16, 19, 28, 38, 50 and 100 wt.%. The yield of the lgO(p, α)l5N reaction was used to determine the 180 distribution in the oxide scale. Specimens were oxidized at 850°C and 950°C first in natural oxygen and then in 18O and vice versa. Any diffusion of oxygen would have shown as a mixing of the oxygen isotopes in the scale. The evidence indicates that bulk oxygen diffusion plays a negligible role in the oxidation reaction. Evidence for penetration of oxygen through the existing scale is found for the alloys of high Cr content (≥ 38%) oxidized at 950°C and it seems that this is due to cracking of the scale giving short-circuit gas diffusion paths.

LEED structures due to interaction of CO and O 2 with (0001) and (101̄0) Re at 20°C to 920°C

The interaction of CO and O 2 with clean (0001) and (101̄0) Re surfaces, produced by the Ar + ion bombardment technique, was studied with a combined LEED-MS system. The results reported previously by Farnsworth and Zehner for the adsorption of CO and O 2 on the (0001) Re surface were confirmed. The exposure of a (0001) Re surface to CO at elevated crystal temperatures produced no additional structures. After a (0001) Re surface was exposed to O 2 in the temperature range 425°C to 920°C, half-order beams from a multiple spaced structure were first observed, as in the case at 20°C. A (1 × 1)ReO structure was present after additional exposures. Adsorption results are compared with McRae's predictions based on the double diffraction model. Adsorption of CO at 20°C on the (101̄0) Re surface occurred with a sticking coefficient close to unity. A (2 × 2)CO structure formed initially and was eventually followed by a (1 × 1)CO structure. Heating a CO covered surface at 200°C to 615°C produced a (1 × 2)CO structure. Additional heating at 780°C produced a (2 × 2)CO structure which was extinguished by heating at 960°C. A comparison of the α and β binding states for CO on Re is made with the desorption temperatures for the CO structures on both surfaces. Only a (1 × 3)O structure was formed on a (101̄0) Re surface exposed to O 2 at 20°C and was extinguished after heating at 780°C. When the (101̄0) Re surface was exposed to oxygen at pressures of 10 −4 Torr or higher at temperatures of 615°C or greater, facets parallel to the (101̄1) plane were formed. The facets could be removed, and a (1 × 3)O structure formed, by heating at 1025°C. Bulk diffusion of oxygen occurred when either crystal surface was exposed to oxygen at temperatures of 615°C or higher. Neither increased surface defect densities nor excitation of the adsorbate enhanced the adsorption characteristics of CO or O 2 on either surface.

Degassing of copper wires in an ultrahigh vacuum: Part I. Diffusion

Degassing characteristics of commercially available copper products have been studied in an ultrahigh vacuum system at temperatures greater than 700°C. Gases evolved are identified and relative quantities of H, O, C, and N evolved from nine different copper products during a 1-hr anneal at 930°C are reported. Qualitatively the evolved nitrogen originated on the surface, the hydrogen originated principally from the bulk, the carbon originated in the bulk and the oxygen originated both on the surface and in the bulk. Bulk diffusion of oxygen and hydrogen to the surface is not rate controlling. The degassing process seems sensitive to an impurity element, carbon being highly suspect.

Enhanced Bulk Diffusion of Oxygen in the Defect Structure Ba0.9La0.067□0.033TiO3

Journal of the American Ceramic SocietyVolume 48, Issue 8 p. 434-435 Enhanced Bulk Diffusion of Oxygen in the Defect Structure Ba0.9La0.067□0.033TiO3 HIROMU SASAKI, HIROMU SASAKISearch for more papers by this authorYOSHIHIRO MATSUO, YOSHIHIRO MATSUOSearch for more papers by this author HIROMU SASAKI, HIROMU SASAKISearch for more papers by this authorYOSHIHIRO MATSUO, YOSHIHIRO MATSUOSearch for more papers by this author First published: August 1965 https://doi.org/10.1111/j.1151-2916.1965.tb14785.xCitations: 17 Presented at the 3d meeting of Basic Science in Ceramics, The Ceramic Association of Japan, Kyoto, Japan, January 28–30, 1965. The writers are, respectively, group leader and research chemist, Ceramics Study Group, Research Laboratory, Wireless Division, Matsushita Electric Industrial Company, Ltd., Kadoma, Osaka, Japan. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume48, Issue8August 1965Pages 434-435 RelatedInformation