Oxygen In Solid Solution Research Articles

Technological possibilities of manufacturing high-grade ferrotitanium from crude ore

The content of metal and oxide phases that form during aluminothermic melting of a mixture of ilmenite and rutile concentrates is studied by X-ray diffraction, electron probe, and metallographic analyses. The main components of the high-grade ferrotitanium melted from the crude ore are represented by the solid solutions of oxygen and iron in titanium and the Ti4Fe2O phase, which is not reduced to TiO2. It has been shown experimentally that rich ferrotitanium (60–70% Ti) containing <5 wt % oxygen cannot be produced by the aluminothermic melting of the crude ore.

Size and concentration distributions of x-ray scattering centers in annealed Cz-Si

The kinetics of decomposition of a solid solution of oxygen in Czochralski-grown silicon (Cz-Si) is investigated using x-ray diffractometry. The samples are annealed for different times at a temperature of 900°C. A technique for processing x-ray diffraction data is proposed. Portions of the size and concentration distribution curves for oxygen-containing precipitates and dislocation loops are obtained.

Monoclinic superstructure V14O6 of the tetragonal solid solution of oxygen in vanadium

The monoclinic (space group C2/m) superstructure of V14O6, which is formed in the atom-vacancy ordering of the tetragonal solid solution of oxygen in vanadium, is studied by the methods of x-ray diffraction and symmetry analysis. It has been found that the channel of the order-disorder phase transition attributed to the formation of the monoclinic suboxide V14O6 includes six superstructure vectors belonging to three non-Lifshitz stars {k1−1}, {k1−2}, and {k1–3} of one type {k1}. The distribution function of the O atoms in the V14O6 monoclinic superstructure has been calculated. It has been shown that the displacements of V atoms distort the body-centered tetragonal metal sublattice, thus preparing the formation of the fcc sublattice and the transition from the suboxide V14O6 to the cubic vanadium monoxide with the B1 structure.

Structure and chemical analysis of aluminum wear debris: Experiments and ab initio simulations

Sliding can produce severe plastic deformation and drive material far from equilibrium. Commonly, it also involves material transfer, mechanical mixing and formation of tribomaterial that influences both friction and wear. This paper describes aluminum wear debris generated by sliding in different environments. One portion of the debris is highly strained and another portion contains a large amount of oxygen, but not in the form of a simple oxide such as α-alumina. Annealing the debris allows strain relaxation, weight loss and changed electrical conduction characteristics. Characterization of debris before and after annealing suggests that the tribomaterial and the debris consist partly of an aluminum–oxygen solid solution and partly of hydroxylated material. These constituents are not normally formed in the absence of external forces. Quantum mechanical ab initio simulations were performed to complement the experiments. The simulations indicate that tetrahedral sites in aluminum are favored for oxygen in solid solution.

Structural states and electrical conductivity of oxidized niobium nanopowders

The structure of niobium nanopowders (particle size 0.03–0.07 μm) oxidized in air is studied by X-ray diffraction. The nanopowder particles have a significant fraction of an amorphous phase. The amorphous component is likely to block the well-known mechanism of niobium oxidation Nb → Nbs.s → Nb6O → NbO → NbOx, which was proposed on the basis of the results of studying the oxidation of niobium powders at high temperatures. Here, Nbs.s is the solid solution of oxygen in niobium and NbOx are the higher niobium oxides NbO2 and Nb2O5. The amorphization of the surface of niobium nanopowders oxidized at 20°C can be one of the main causes of a rather high electrical resistivity (ρ ≈ 108 Θ cm) of the samples compacted from these powders.

Oxygen gettering at defects introduced by plastic deformation in silicon

AbstractDecay of the supersaturated oxygen solid solution during annealing at 500–800 °C is studied in plastically deformed silicon crystals. The plastic deformation up to 4–5% is found to significantly increase the rate of the decay. In the samples deformed at 700 °C the decay is governed by the oxygen diffusion not to dislocations but to other defects created during deformation. These defects are recovered due to the short annealing at 1150 °C. In the annealed samples the decay of oxygen solution is determined by the oxygen diffusion to dislocations. In both cases the activation energy of oxygen transport in the temperature range (500–700) °C is about 1.5 eV. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Snoek‐Type High‐Damping Alloys Realized in β‐Ti Alloys with High Oxygen Solid Solution

High strength and a huge Snoek damping peak—properties required for high-damping alloys, which find applications in mechanical structures in attempts to eliminate noise and vibration—are reported to have been realized in β-type Ti alloys with an oxygen solid solution above 1.0 at %. The properties of some Ti–25 Nb–x O (at %) alloys (see figure) are superior to those of most previously developed high-damping alloys.

Decay of oxygen solid solution in plastically deformed silicon

AbstractDecay of the oxygen solid solution in silicon during annealing at 550–700 °C is studied by the IR absorption technique in the single crystalline samples subjected to the plastic deformation to a high dislocation density at 680 °C. The deformation is shown to significantly enhance the rate of the decay in the whole temperature range studied. Based on the simple model, which assumes the heterogeneous oxygen aggregation at dislocations, the effective oxygen diffusivity is calculated from the experimental data. The activation energy of oxygen diffusion in this temperature range is found to be about 1.6 eV, which is essentially lower than that for the isolated interstitial oxygen atom. (© 2005 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Electrochemical properties of sintered polycrystalline α-SiC

We have used potentiodynamic polarization curves and Auger electron spectroscopy to determine the characteristic features of the anodic and cathodic behavior in a 0.5 M H2SO4 solution of sintered nonporous samples of polycrystalline α-SiC. We have shown that anodic oxidation of silicon carbide first leads to formation of a surface layer of a solid solution of oxygen in α-SiC, and then a layer of a metastable oxycarbide phase SiC0.67O0.33. We have established that during cathodic polarization, the process of evolution of hydrogen first occurs according to a slow discharge mechanism, and for more extensive polarization it occurs according to a mechanism of surface recombination of atoms.

On the influence of a Si single-crystal real surface on the low-frequency internal friction and the behavior of an effective shear modulus

The spectra of low-frequency internal friction and the behavior of the effective shear modulus Geff(T) in a Czochralski grown silicon single crystal were investigated after mechanical and chemical-mechanical treatment of the surface and after natural aging at room temperature over a long period of time. The mechanical treatment of the Si surface was shown to initiate unusual structural phase transitions accompanied by an inverse hysteresis in the Geff(T) dependence. Such a behavior of Geff(T) is assumed to be associated with the formation of incommensurate phases. It was also found that aging at room temperature for more than 10000 h leads to the onset of decomposition of the supersaturated solid solution of oxygen in silicon and to the generation of substantial stresses that initiate structural phase transitions in the samples.

Diffuse x-ray scattering study of the formation of microdefects in heat-treated dislocation-free large-diameter silicon wafers

Diffuse x-ray scattering (DXS) is used to study the formation of microdefects (MDs) in heat-treated dislocation-free large-diameter silicon wafers with vacancies. The DXS method is shown to be efficient for investigating MDs in silicon single crystals. Specific defects, such as impurity clouds, are found to form in the silicon wafers during low-temperature annealing at 450°C. These defects are oxygen-rich regions in the solid solution with diffuse coherent interfaces. In the following stages of decomposition of the supersaturated solid solution, oxide precipitates form inside these regions and the impurity clouds disappear. As a result of the decomposition of the supersaturated solid solution of oxygen, interstitial MDs form in the silicon wafers during multistep heat treatment. These MDs lie in the {110} planes and have nonspherical displacement fields. The volume density and size of MDs forming in the silicon wafers at various stages of the decomposition are determined.

Sintered Tantalum and Niobium Sub-micron Powders of Solid Electrolite Capacitors

ABSTRACTThe results of x-ray study and electrical measurements are brought together in order to understand a difference in performance and failures of solid electrolyte capacitors made of sintered tantalum and niobium sub-micron powders. It is shown that bulk Ta and Nb exhibit different abilities for the formation and decomposition of oxygen solid solution during manufacturing steps which may be critical for stability of metal/oxide interface of capacitor.

Generation and motion of dislocations in nitrogen-doped silicon singlecrystals

Characteristic peculiarities of the generation and propagation of dislocations innitrogen-doped silicon wafers (grown by the Czochralski method) wereinvestigated by the four-point bending method. The critical stresses for thedislocation generation and dislocation velocity in nitrogen crystals are less than innon-doped crystals for equal loads. It was proposed that the strengtheningof nitrogen-doped crystals is caused by the influence of nitrogen on thedecomposition of the supersaturated oxygen solid solution during the cooling ofthe growing single crystals. As a result, many dispersed oxygen precipitates aregenerated in the crystal volume and harden it by hindering dislocation generationand propagation.

Specific features in the generation and motion of dislocations in silicon single crystals doped with nitrogen

The specific features in the generation and motion of dislocations are investigated in Si: N single crystals grown by the Czochralski method. The motion of dislocation loops is analyzed by the four-point bending technique in the temperature range 500–800°C. The dislocation loops are preliminarily introduced into the samples with the use of a Knoopp indenter at room temperature. It is found that doping with nitrogen leads to a considerable increase in the critical stress of the onset of dislocation motion from surface sources (indentations) and in the stress of the generation of dislocations from internal sources. The velocity of dislocation motion in Si: N crystals is less than that in undoped crystals (under comparable loads). The hardening effect of nitrogen is explained by the fact that nitrogen promotes the decomposition of a solid solution of oxygen in silicon during postcrystallization cooling.

Reactions of TiNi with Oxygen

X-ray diffraction and metallography have been applied to study the formation conditions for the η phase in Ti4Ni2O in the reaction of TiNi with oxygen. The phase diagram for the Ti ― Ni ― O system indicates that the η phase (Fe3W3C structure type) is a solid solution of oxygen in Ti2Ni. For TiNi made in an oxygen-bearing medium or from initial materials contaminated with oxygen, one gets the η phase and Ni3Ti. Those phases are formed also in surface oxidation as products from the initial interaction of the alloy with oxygen. They occur when there is a low oxygen partial pressure, as on annealing TiNi powder in a vacuum given by a rotary pump or in a layer under scale formed on a cast TiNi specimen on oxidation in air. The layer under the scale is formed because of the preferential loss of titanium from the TiNi and consists of Ti4Ni2O, Ni3Ti, and an Ni(Ti) solid solution, which in turn occurs because of preferential loss of titanium from Ni3Ti. In the subsequent oxidation stages, there is selective oxidation of Ti4Ni2O to lower titanium oxides. The decomposition of TiNi alloy containing oxygen when the composition is varied near the equiatomic one can be used for practical purposes. For example, the segregation of the hydride-forming η phase may improve the hydrogen uptake by the alloy, while the dispersed segregation of Ni3Ti and the lower oxides may favor hardening.

Specific features of oxygen dissolution in refractory metals in gas-phase deposition

The phase composition of niobium specimens obtained by crystallization from the gaseous chloride-hydrogen mixture with regular addition of oxygen has been studied by the method of X-ray phase analysis. It is established that the oxygen-containing niobium contains a solid solution of oxygen in niobium monoxide. The specific feature of the phases revealed is an unusually pronounced deformation of the crystal lattice (with an increase in the oxygen content in the specimen, the lattice parameter increases by 0.5–0.6%). It is concluded that oxygen possesses elevated solubility in niobium and that during their gas-phase crystallization oxygen is present in niobium monoxide in a “superstoichiometric” concentration. The results obtained are compared with the known data on oxygen-enriched tungsten and chromium also obtained by various modifications of gasphase technology.

Formation Gibbs energy of K 2NbF 7, K 2NbOF 5, and K 2NbO 2F 3 from electrochemical measurements

The formation Gibbs energies of molten K 2NbF 7, K 2NbOF 5, and K 2NbO 2F 3 at the temperature of 750°C were calculated from the previously performed voltammetric and chronopotentiometric measurements in the system LiF–NaF–K 2NbF 7–Na 2O [1–3] and from the equilibrium constants of reactions leading to the formation in the melts of the individual oxyfluoroniobates. For the formation Gibbs energy of K 2NbF 7 the average value Δ f G 0(K 2NbF 7)=−(1340±25) kJ mol −1 was obtained. For K 2NbOF 5 the formation Gibbs energy is Δ f G 0(K 2NbOF 5)=−(1526±16) kJ mol −1. This value may, however, not be exactly correct since the product of the electrochemical reduction was not pure niobium, but the solid solution of oxygen in niobium. For the formation Gibbs energy of K 2NbO 2F 3 the value Δ f G 0(K 2NbO 2F 3)=−(1100±100) kJ mol −1 was calculated. This value may be charged by a substantial error as well due to the probably incorrect value of the formation Gibbs energy of K 2NbOF 5.

The Behavior of Uranium Dioxide in Various Gases

The behavior of uranium dioxide in an oxidative medium in air and a neutral medium in argon for several thousands of hours was studied. Negligible additional oxidation of pellets occurred at room temperature; this was indicated by an increase of the stoichiometric mixture ratio of uranium dioxide near the surface. The oxidation rate constant at 295 K was k = 2.77·10–7 in air and 5·10–8 g/(cm2·h) in argon. For oxidation in air at 295–503 K only solid solutions of oxygen in uranium dioxide were formed. The temperature dependence of the oxidation rate constant was determined. The threshold temperature above which higher oxides of uranium form was determined. The stoichiometric mixture ratio has no effect on the oxidation rate constant of uranium dioxide in air. 1 figure, 3 tables, 9 references.

The parameters of equilibrium between oxygen solid solutions in cubic and graphite-like hexagonal boron nitrides

Abstract A decrease in the onset temperature of the cBN-to-hBN solid-phase transformation with increase in the oxygen content of cBN samples has been found experimentally. This dependence might be attributable to the existence of oxygen solid solutions in cBN and hBN. From the experimental data and taking into account the kinetics of solid-phase transformations, the equilibrium onset temperature of the cBN-to-hBN transition has been derived for samples with different oxygen contents. In the framework of phenomenological thermodynamics, the model parameters have been determined and the lines of equilibrium between oxygen solid solutions in cubic and graphite-like hexagonal boron nitride have been calculated. It has been shown that a decrease in the oxygen content of the boron nitride–solvent system usually used for cBN synthesis should induce an increase in the thermodynamic stimulus to the hBN-to-cBN transformation at high pressures.

Investigation of atomic and electronic structure of films generated on a cutting tool surface

Abstract It is established that oxygen-containing films named as secondary structures (SS) are developed on the surface of deformed composite powder material based on high-speed steel (HSS-based DCPM) tools during their operation at cutting. The composition, nearest atomic surrounding, and electronic structure features of these films were investigated by means of SEM, AES, ELS, and EELFS methods. It was found that structural features of these films differ from those of TiC, TiO2 (rutile), and films formed on the surface of the TiC powder heated in air. Disordering of atoms at long interatomic distances (beyond the third coordination sphere) and low localisation of π-electrons make it possible to arrive at a conclusion on the amorphous-like structure of the films. Evolution of the atomic structure of DCPM tools at friction was revealed. It was discovered that favourable frictional properties and a high wear resistance of DCPM tools are followed from developing SSs that consist of the oversaturated solid solution of oxygen in titanium that possesses metal-like characteristics.