Oxygen Self-diffusion Coefficients Research Articles

Relationships between oxygen diffusion characteristics of polycrystalline and single crystal 2MgO · TiO 2

Self-diffusion coefficients of oxygen in both polycrystalline and single crystal 2MgO·TiO 2 have been measured at an ambient oxygen pressure of about 40 mm Hg over the temperature range 1080–1450°C. A convenient method to estimate the volume diffusion coefficient, D 1, of this polycrystal in which the relative magnitude in D g (grain boundary diffusion coefficient) with respect to D 1 falls between two extremes, i.e., D g = D 1 and D g ⪢ D 1, is newly proposed, and its plausibility is examined by comparing the resultant D 1 with that of single crystal 2MgO·TiO 2. Not only the magnitude but also the temperature dependence of the “apparent” diffusivity of these polycrystalline particles considerably varied with their particle size. The reason for this semiquantitatively interpreted in terms of the relative magnitude of D g with respect to D 1.

Oxygen self-diffusion in non-stoichiometric uranium dioxide

Abstract Oxygen self-diffusion coefficients in UO2+x were obtained using the nuclear reactions 18O(p, n)18F and 17O(d, n)18F followed by autoradiography. The activation energy for migration and the pre-exponential were 23·1 ± 3·8 kcal mole−1 and 6·25 ± 5·03 × 10−4 cm2 sec−1, respectively, at x≃0·08. The functional dependence of the oxygen self-diffusion on composition could be semiquantitatively explained on the basis of a cooperative diffusion mechanism via a Willis 2 : 2 : 2 defect cluster subject to a very short-range defect–defect interaction.

Self-diffusion of oxygen in polycrystalline MgAl2O4

Self-diffusion coefficients of oxygen in polycrystalline MgAl2O4 were determined over the temperature range 1310–1694 °C by a gas–solid isotopic exchange technique using 18O as a tracer and the results were compared with those of single crystal MgAl2O4. The apparent diffusion coefficients for the polycrystal were greater than those of the single crystal. These results were interpreted as being due to oxygen diffusion enhanced by grain boundaries.

ChemInform Abstract: OXYGEN DIFFUSION COEFFICIENTS IN ALKALI SILICATES

AbstractDie Selbstdiffusionskoeffizienten von Sauerstoff in geschmolzenen Na‐ und K‐silicaten wurden durch Isotopenaustausch mit einer an 180 angereicherten Gasphase ermittelt.

Oxygen Diffusion Coefficients in Alkali Silicates

Oxygen self-diffusion coefficients in molten alkali silicates were measured by the technique of heterogeneous isotopic exchange with a gaseous phase enriched in 18O. For the composition 64 wt% SiO2-36 wt% K2O, the diffusion coefficients from 700° to 1000°C under 100 torr O2 pressure are described by The effect of pressure on DO*, studied for the same composition at 900°C under O2 pressures of 20 to 400 torr, is described by DO*=kPO2−(0.44±0.09). For the composition 75 wt%SiO2-25 wt% K2O, the diffusion coefficients from 750° to 1000°C under 100 torr O2 pressure are described by The effect of pressure on the self-diffusion coefficients can be explained by a diffusion mechanism involving O vacancies.

ChemInform Abstract: RELATIONSHIP BETWEEN SELF‐DIFFUSION AND INTERDIFFUSION IN GASEOUS SYSTEMS

Chemischer InformationsdienstVolume 4, Issue 50 Physical Inorganic Chemistry ChemInform Abstract: RELATIONSHIP BETWEEN SELF-DIFFUSION AND INTERDIFFUSION IN GASEOUS SYSTEMS HIROMASA HIRAKAWA, HIROMASA HIRAKAWASearch for more papers by this authorYOSHINOBU KAMEI, YOSHINOBU KAMEISearch for more papers by this authorMASAYASU SUGISAKI, MASAYASU SUGISAKISearch for more papers by this authorYASUMICHI OISHI, YASUMICHI OISHISearch for more papers by this author HIROMASA HIRAKAWA, HIROMASA HIRAKAWASearch for more papers by this authorYOSHINOBU KAMEI, YOSHINOBU KAMEISearch for more papers by this authorMASAYASU SUGISAKI, MASAYASU SUGISAKISearch for more papers by this authorYASUMICHI OISHI, YASUMICHI OISHISearch for more papers by this author First published: December 11, 1973 https://doi.org/10.1002/chin.197350024Read the full textAboutPDF 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 onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume4, Issue50December 11, 1973 RelatedInformation

Application of a nondestructive single-spectrum proton activation technique to study oxygen diffusion in zinc oxide

18O diffusion coefficients were measured directly and without serial sectioning, using proton activation analysis of 18O via the nuclear reaction 18O (p, α)15N. In this technique, the α-particle spectrum recorded during proton irradiation is used to determine the 18O concentration profile; submicron resolution can be achieved. The suitability of this approach was demonstrated by studying oxygen self-diffusion along the c axis of ZnO single crystals. In the temperature range 940–1140°C and at Po2 of 700 mm, D=1.2(−0.6+1.1)10−10exp[−(29.6±1.6) kcal/RT] (cm2/sec). The results are interpreted as indicating extrinsic behavior; the activation energy is then that for oxygen mobility only. The surface exchange coefficient, characteristic of the reaction between gaseous and lattice oxygen, was also determined, in the temperature range 940–1040°C, as K=5.7(−4.6+23.8)105 exp[−(91.2±4.0 kcal)/RT] (cm/sec). A detailed analysis of the technique is presented. Using a convolution procedure, the oxygen self-diffusion coefficient, at a given temperature, is determined in a single irradiation run with a precision better than 10%, which is limited only by counting statistics. However, uncertainty in the values of the stopping powers for protons and alphas may cause an additional systematic uncertainty in D of up to [inverted lazy s]50%; since this error is identical for all temperatures, it causes an uncertainty in the preexponential but not in the activation energy. The technique is optimum for determining D in the range [inverted lazy s]5 × 10−12−[inverted lazy s]5 × 10−17 cm2/sec and is useful for testing models of the exchange kinetics.

Oxygen-diffusion characteristics of loosely-sintered polycrystalline MgO

Self-diffusion coefficients of oxygen in well-sintered and in loosely-sintered polycrystalline MgO have been measured at an ambient oxygen pressure of about 35 mm Hg over the temperature range 1020–1450°C. The oxygen diffusion coefficient as a function of temperature of the former specimen is expressed by a single Arrhenius equation with an activation energy of 55.8 kcal/mole, while that of the latter is composed of two intersecting lines ( E = 60.2 kcal/mole from 1020–1250°C; E = 102.8 kcal/mole from 1250–1450°C). The diffusivity for single-crystal grain of the well-sintered polycrystals is two orders of magnitude larger than that in the low-temperature portion of the loosely-sintered one. This fact is interpreted in terms of an insufficient dissolution of monovalent cation impurities into the loosely-sintered crystal lattice. Two ways of interpretation are given for the presence of the high-temperature portion characteristic of the loosely-sintered polycrystal.

Mesures de resistivite et de cinetique d'oxydation dans PuO 2− x

The electrical resistivity of PuO 2−x has been measured between PuO 1,77 and PuO 2,00 in the temperature range 700–1200 °C. It is concluded that the major defect species are anion vacancies. The kinetics of oxidation has been measured at 1080 °C. The chemical diffusion coefficient of oxygen was computed and the oxygen self-diffusion coefficient is derived as a function of the deviation from stoichiometry.

Preferential diffusion of oxygen along grain boundaries in polycrystalline MgO

Self-diffusion coefficient of oxygen in polycrystalline MgO can be represented by D=4.5×10−5exp(−60200/RT)cm2/sec for 80–115 mesh particles and by D=1.3×10−5exp(−60200/RT)cm2/sec for 170–200 mesh particles. These two activation energies are exactly the same, but the magnitude of the diffusion coefficients varied from one sample to another. When D was recalculated by taking a as the grain radius instead of particle radius, all the data points fall on a single solid line expressed by D=4.5×10−7exp(−60200/RT) cm2/sec. It is important to note that this line approximately meets the Arrhenius plot for oxygen diffusion in single-crystal MgO. Therefore, we conclude that the diffusion of oxygen along the grain boundaries in polycrystalline MgO is considerably faster than diffusion through the bulk.

Self-diffusion of carbon and oxygen in dolomite

Self-diffusion of carbon and oxygen in dolomite was measured by isotopic exchange with CO2 at 645-785 C at 120-935 bars pressure. Several runs were also made with calcite under comparable experimental conditions. The principal findings of this study are that (1) the self-diffusion coefficients of both carbon and oxygen in dolomite are approximately 100 times larger than the values in calcite over the temperature range investigated and (2) oxygen self-diffusion in calcite is accelerated by high CO2 pressure.

Oxidation of Reduced Perovskite-type Ferrites

The oxidation of the reduced solid solution Sr1-xMxFeO2.5+x/2(MY3+ and La3+) was studied by means of the high temperature X-ray diffractometry and the thermogravimetry. The end member SrFeO2.5, which is isostructural with the brownmillerite having orthorhombic symmetry, changes to the cubic perovskite-type structure when Sr is substituted for Y in the composition range of 0.15<x<0.25 and for La in the range of 0.30<x<0.60. When the samples were heated at a constant rate in air, the oxidation reaction of SrFeO2.5 started at 356°C and ceased at 458°C and the structure of SrFeO2.5 then transformed into the cubic perovskite-type. The increase of the M content in this solid solution lowered both the starting and the ceasing temperature of the oxidation. Oxygen self-diffusion coefficient was successfully evaluated by a diffusion equation derived from the observation of the weight gains due to the incorporation of oxygen. The activation energy for the mobility of oxygen in the oxygen-deficient perovskite- type structure was obtained to be 6∼8 kcal/mole. The energy required for the structural change from the brownmillerite-type phase to the cubic perovskite-type one was estimated to be 43 kcal/mol which decreased with the increasing M content.

Autodiffusion de l'oxygene dans le dioxyde d'uranium surstoechiometrique

Self-diffusion of oxygen in hyperstoichiometric uranium-dioxide UO 2+ x (0.006 ⩽ x < 0.16) has been investigated with tracer oxygen-18, in the temperature range between 400 and 900 °C. 18O diffusion profiles were analyzed by two different methods: either mass spectrometry or nuclear reactions. The activation energy for self-diffusion of 18O, 21 kcal · mole −1, is independent of x ( x ⩾ 0.006). The apparent diffusion coefficient is lowered when a second phase U 4O 9 is present in UO 2+ x . No grain boundary diffusion of oxygen was evidenced. The oxygen self-diffusion coefficient in UO 2+ x may be expressed as a function of x ( x > 0) and temperature with a semi-empirical equation.

Oxygen diffusion in single crystals of titanium dioxide

The self-diffusion coefficient of oxygen has been determined for non-reduced and reduced single crystals of rutile at 806°C. The rate of exchange between 18O enriched gas, solid single crystal plates and grains of the pure, non-doped, material has been measured. The influence of the particle size and the degree of reduction of the rutile samples on the diffusion rate has been determined. The diffusion coefficient for the stoichiometric, non-reduced samples was 1·7 × 10 −15cm 2/sec in the direction perpendicular to the crystallographic c-axis and 3·2 × 10 −16 cm 2/sec parallel to it. After short-term reduction at 1200°C an increase in the diffusion rate was observed. This increase appeared to be independent of the duration of the heating (between 1–10 hr), but the amount of the increase was the same whether the reduction was performed in vacuum or in air. No influence of the particle size on the diffusion rates was observed but marked effects were noted for the surface exchange coefficients.

Surface-controlled oxidation-reduction of UO 2

The oxidation and reduction rates of UO 2 in CO 2-CO mixtures were measured between 900 and 1400 °C and O/U ratios of 2.01 and 2.14. A statistically significant stoichiometry gradient within the UO 2 was never found on sectioning mercury quenched specimens. The oxidation rates were proportional to the surface: volume ratio of the specimens and to the (CO 2 + CO) partial pressure in a (CO 2 + CO + inert gas) atmosphere. In CO 2 -CO the oxidation within the single phase field is, therefore, controlled by the solid-gas interface reaction. The reduction kinetics could not be so interpreted. An O/U gradient was never found, but the reduction rates with increasing inert gas concentrations and increasing sample sizes were too rapid to be surface-controlled. From sectioning experiments a lower limit was determined for the chemical oxygen diffusion coefficient which was in agreement with that calculated from the oxygen self-diffusion coefficient.

Self-diffusion of carbon and oxygen in calcite by isotope exchange with carbon dioxide

Carbon self-diffusion coefficients were determined by exchange between calcite grains and a large reservior of C14-labeled CO2 at 250°–750°C. The progress of diffusion and the surface area of the grains were measured by the C14 uptake of the solid. Both carbon and oxygen self-diffusion coefficients were determined by exchange between calcite grains and a limited reservoir of C13- and O18-enriched CO2 at 650°–850°C. The progress of diffusion was measured by the change in isotope composition of the gas. On an Arrhenius plot of log D versus 103/T°K, the carbon self-diffusion coefficients are fitted to two straight lines. Carbon diffusivity determined by both methods in unannealed and annealed material at temperatures above 550°C are given by D = 1.3 × 103 exp(−88,000/RT)cm2/sec. Oxygen self-diffusion coefficients were higher than the corresponding carbon values by up to a factor of 4. Carbon diffusivity determined by the C14 method in unannealed calcite below 550°C are given by D = 4.6 × 10−16 exp(−17,000/RT)cm2/sec. Diffusivity in annealed material is lower by a factor of 50. The relative rates of oxygen and carbon self-diffusion indicate that there may be several mechanisms of oxygen migration in calcite in the high temperature region. A detailed examination of the C14 uptake results suggest that carbon self-diffusion is depth-dependent for the shallow penetration distances obtained in these experiments. Extrapolation of these results suggests that solid-state diffusion will not significantly alter the isotopic record of calcite under a wide range of geologic environments.

Defect structure model for nickel oxide

Nickel oxide is regarded as a model compound for semiconductors of low current carrier mobility. Owing to this fact and due to the practical applications of this oxide, its t ransport properties have been the subject of numerous studies. The knowledge of defect structure in nickel oxide is also necessary for a better understanding of the mechanism of nickel oxidation. In spite of this, the structure of native defects in NiO has not been as yet satisfactorily elucidated. Taking into account the fact that the self-diffusion coefficient of nickel in NiO 1-5 is significantly larger than the oxygen self-diffusion coefficient, 6 it may be assumed that in this compound only the cation sublattice is substantially defected. On the basis of theoretical consideration, Kr6ger v concludes that nickel oxide should exhibit only an excess of oxygen. Furthermore, because NiO is a p-type semiconductor, it is assumed that in this oxide the nickel vacancies and holes are the predominant defects. However, the degree of ionization of the vacancies in nickel oxide has been a matter of discussion. On the basis of studies on the dependence of electrical conductivity of single crystals of NiO on oxygen pressure, Mitoff 8 assumes that nickel vacancies are doubly ionized at high temperatures. Pizzini and Morlott i 9 interpret their results obtained f rom polycrystalline material in a similar way. On the other hand, the results of experiments of Baumbach and Wagner, 1~ of Duquesnoy and Marion, 11 of Eror, 12 of Uno, 13 and recently of Bransky and Tallan 14 and of Cox and Quinn a5 indicate that the defects in NiO are singly ionized. This hypothesis is based on the confirmed fact that in the equation = const p l /~ (1) ~ 0 ~

Oxygen diffusion in monoclinic zirconia

Oxygen self-diffusion coefficients have been determined for near-stoichiometric monoclinic zirconia exposed in an oxygen atmosphere at 300 mm. Hg. pressure at temperatures in the range 800–1000°C. These evaluations obeyed the equation: D( cm 2 sec ) = 9.73 × 10 −3 exp − 56,000/ RT . The results were interpreted by an anti-Frenkel type defect model, the transport number for oxygen ions being 4.5 × 10 −3 at 990°C.

Oxidation Kinetics of Single-Crystal SrTiO3

The oxidation kinetics were determined for single-crystal SrTiO3 by measuring the time and temperature dependence of the weight gain of reduced crystals. The oxidation can be described as a diffusion-controlled process. The calculated diffusion coefficients between 850° and 1460°C are represented by D= 0.33 exp (-22.5 ± 5.0 kcal/RT) cm2/sec. Directly measured oxygen ion diffusion coefficients in the same temperature interval reported earlier are interpreted as being extrinsic and can be represented by D= 5.2 × 10−6 exp (-26.1 ± 5.0 kcal/RT) cm2/sec, where the activation energy is for mobility only. Assuming that the calculated diffusion coefficients are for vacancy diffusion and the two activation energies are equivalent within experimental error, a vacancy concentration (fraction of vacant lattice sites), [O□], fixed by impurities in the fully oxidized crystal is calculated to be 1.6 × 10−5 by virtue of the relation between the oxygen self-diffusion coefficient, D02-, and the oxygen vacancy diffusion coefficient, Do□; Do2-= [O□]Do□ where the oxygen ion concentration [O2-] is taken as unity.

Kinetics of Initial Sintering of Vacuum‐Reduced Titanium Dioxide

Observations of sphere‐to‐plate bonding of vacuum‐reduced monocrystalline rutile have been carried out over the temperature range 1200° to 1275°C. The rate law governing the interfacial growth between sphere and plate indicates that the predominant mechanism of material transport in this sintering process is volume diffusion. In the light of the reasonably satisfactory agreement between the oxygen self‐diffusion coefficients calculated from the present sintering data and those directly observed by Haul and Just utilizing an isotopic exchange technique, it is likely that oxygen ion diffusion is the rate‐determining step in the sintering experiments described.