Oxygen In Solid Solution Research Articles

Interfacial reactions in Al 2O 3/Ti, Al 2O 3/Ti 3Al and Al 2O 3/TiAl bilayers

Interfacial reactions were studied at three different heat-treated oxide/metal bilayers (oxide: amorphous a-Al 2O 3 and metal: crystalline c-Ti, Ti 3Al or TiAl) by means of AES depth profiling. The different oxide/metal bilayers were sputter deposited on smooth silicon substrates, covered with a TiN thin-film diffusion barrier. The reactions at the oxide/metal interfaces were activated in a differential scanning calorimeter by heating the samples in an argon atmosphere at a linear heating rate of 40°C/min, between room temperature and different final temperatures (350 to 700°C). In order to characterize the reaction products, i.e. solid solution of oxygen in the α-Ti and the newly formed α 2-Ti 3Al phase, XPS and TEM investigations were performed on selected samples. The thermal stability of three interfaces was investigated in dependence of aluminium content and consequently with respect to the solubility of atomic oxygen in the metallic layers. Thermodynamic calculations revealed that the heat of solution of oxygen in the metallic layers is crucial for the interfacial reactions. The experimental results are consistent with thermodynamic data: the a-Al 2O 3/c-Ti interface shows the highest reactivity, followed by the a-Al 2O 3/c-Ti 3Al interface. In the a-Al 2O 3/c-TiAl bilayer no reaction was detected at the interface, indicating thermal stability up to 700°C. The mechanism of the chemical reaction at the interfaces of the different bilayers is discussed

Non-stoichiometry of composition and dissolution of oxygen in the cubic boron nitride crystal lattice

Powders of cubic boron nitride (cBN), synthesized from multicomponent melts, were studied with a crystallization medium containing excessive nitrogen or boron. X-ray diffraction analysis was used for precision determination of the crystal lattice constants, space factor of regular sets of points of the F43m space group, dislocation density, and stacking fault concentration. Cubic boron nitride has been found to crystallize as a variable-composition compound having vacancies in the boron sublattice. These vacancies are due to a heterovalence substitution of oxygen for nitrogen, i.e. formation of the oxygen solid solution in the cBN crystal lattice. With an increase in the number of vacancies in the boron sublattice, the cBN lattice constant decreases, and the stacking fault concentration increases.

Recombination of charge carriers in neon cryocrystals containing oxygen impurity

The recombination of electrons and holes in neon crystals containing deep electron traps due to impurity oxygen along with weakly localized electron states of the matrix is investigated experimentally. Measurements are made by the method of cathode-luminescence spectroscopy in VUV, UV, and visible wavelength ranges at temperatures varying from 2 to 8 K. It is found that the temperature dependences of integral intensities of intrinsic and extrinsic luminescence in solid solutions of oxygen in neon are similar and nonmonotonic by nature. The observed effect is analyzed in the model of two coexisting channels of energy relaxation of electron excitations: through the Γ(1/2,3/2) exciton subsystem and through the recombination of self-trapped two-center holes and electrons. It is shown that temperature variations of integral parameters of luminescence are mainly due to peculiarities of the recombination channel whose efficiency is determined by the probability of electron localization in the matrix lattice in the low-temperature regions (2.5–5 K) and by the probability of trapping at impurity centers in the temperature range 6–8 K. Additional proofs are obtained for the possibility of electron self-trapping in the Ne lattice with the formation of shallow localized states.

Interdiffusion at the Al2O3/Ti interface studied in thin-film structures

The early-stage interfacial reactions between amorphous Al 2 O 3 (a-Al 2 O 3 ) and crystalline α-Ti (c-Ti) thin films were studied in thin-film structures with two different thicknesses. Smooth silicon (111) substrates were covered firstly with a TiN thin-film diffusion barrier and then with a crystalline Ti layer. Finally, amorphous Al 2 O 3 was sputter deposited onto the crystalline Ti layer. The samples were heated in a differential scanning calorimeter with a linear heating rate of 40°C min -1 -from room temperature up to different final temperatures of 350-700°C in an argon atmosphere to activate reactions at the a-Al 2 O 3 /c-Ti interfaces-and then rapidly quenched. The interdiffusion at the a-Al 2 O 3 /c-Ti interface was studied using the rate of change of the reaction width obtained from Auger electron spectroscopy (AES) sputter depth profiles. The beginning of the reaction, which involves the diffusion of oxygen (followed by Al) into the c-Ti thin film, was observed at ∼425°C. The activation energy at the a-Al 2 O 3 /c-Ti interface was found to be 1.6 eV for the oxygen diffusion from the amorphous Al 2 O 3 into the c-Ti thin film between 425°C and 650°C, and 0.9 eV for the Al diffusion between 500°C and 625°C. The new crystalline reaction product is composed of α 2 -Ti 3 Al phase and a solid solution of oxygen in α-Ti. The influence of different sample structures on kinetic quantities is discussed. © 1998 John Wiley & Sons, Ltd.

Thermodynamic properties of oxygen in RE–O (RE=Gd, Tb, Dy, Er) solid solutions

The oxygen potentials of four rare-earth metal – oxygen (RE–O: RE=Gd, Dy, Tb, Er) solid solutions have been measured by equilibration with yttrium – oxygen (Y–O) and titanium – oxygen (Ti–O) solid solutions. Rare-earth metal, yttrium and titanium samples were immersed in calcium-saturated CaCl 2 melt at temperatures between 1093 and 1233 K. Homogeneous oxygen potential was established in the metallic samples through the fused salt, which contains some dissolved CaO. The metallic samples were analyzed for oxygen after quenching. The oxygen potentials of RE–O solid solutions were determined using either Y–O or Ti–O solid solution as the reference. This method enabled reliable measurement of extremely low oxygen potentials at high temperature (circa p O 2 =10 −48 atm at 1173 K). It was found that the oxygen affinity of the metals decreases in the order: Y>Er>Dy>Tb>Gd>Ti. Values for the standard Gibbs energy of solution of oxygen in RE metals obtained in this study, permit assessment of the extent of deoxidation that can be achieved with various purification techniques. It may be possible to achieve an oxygen level of 10 mass ppm using an electrochemical deoxidation method.

Mechanism of oxygen dissolution in metallic zirconium

The oxygen dissolution in metallic zirconium has been investigated by electrochemical and X-ray techniques. The mechanism of the zirconium oxidation process is proposed. It is shown that during the first stage of the process, oxygen dissolves in the metal matrix acting as an electron donor. The region of oxygen solid solutions in zirconium reaches 25 at.% oxygen. After oxygen saturation of the metal surface the second stage starts; zirconium oxides form.

Influence of interstitial elements on hydrogen solubility in the Group IV metals

A comparison of hydrogen solubility and enthalpy of solution of hydrogen was performed for (Ti, Zr, Hf)-(O, N, C) binary solid solutions. Oxygen addition into titanium and hafnium decreased the hydrogen solubility at a fixed pressure. The hydrogen solubility in zirconium first increased with oxygen content, and then decreased at a higher oxygen content. The enthalpy of solution of hydrogen was lower for oxygen solid solutions than for pure metals. For all the metals, the presence of nitrogen and carbon increased the hydrogen solubility and provided a negative effect on the enthalpy of solution of hydrogen. Partial thermodynamic functions of hydrogen in (Ti, Zr, Hf)-(O, N, C)-H ternary solid solutions were estimated using a dilute solution model. The partial molar enthalpy and the partial molar excess entropy decreased with nitrogen and carbon contents in the solid solutions. The oxygen effect on partial molar quantities was more complex. The changes in the partial molar quantities with the composition of the solution were discussed in terms of vibrational. dilatometric, and configurational contributions.

Thermodynamic assessment of the Silicon — Oxygen system

A thermodynamic assessment of the Si-O system has been made using a computerized CALPHAD (calculation of phase diagrams) technique. The liquid phase is described by a two-sublattice model for ionic liquids and the solid solution of oxygen in silicon is described by a regular solution model. A set of parameters describing the Gibbs energies of the different phases is given and calculated phase diagrams are presented.

Oxygen Solid Solution Hardening in Titanium by Heat Treatment

Oxygen Solid Solution Hardening in Titanium by Heat Treatment

Quadrupolar effects in interstitial solid solutions of oxygen and nitrogen in vanadium

The51V NMR in dilute solid solutions of O and N in V was used to study quadrupolar effects due to alloying. The foils with the strong texture showed the discernible structure in the wings of the observed NMR spectra. The metallic site neighbour positions were selectively identified. Electric field gradients (EFG'S) and Knight shifts at these sites were measured. The origin of EFG's is discussed. The experimental data were used to construct the impurity potentials. The energy of O−O bonds in vanadium was estimated.

Titanium-base coating on plane silica substrates

Plane silica substrates were coated with a titanium-based deposit by gaseous cementation at temperatures ranging from 600 to 800 ° C, over 1 h to several tens of hours. The cement consisted of hydrogen chloride and titanium. The bilayer structure of the coating was established by X-ray diffraction, X-ray electron microprobe analysis, scanning electron microscopy, low-energy electron-induced X-ray spectroscopy. X-ray photoelectron spectroscopy, optical microscopy and X-ray fluorescence spectroscopy. Thin coatings were amorphous and the composition of the outer zone was close to TiO. Thicker coatings ranging from 2 to 30 μm were crystalline. In this case, the outer layer, designated α-Ti(O) or TiO x with 0.44 ⩽ × ⩾ 0.49, corresponded to an ordered solid solution of oxygen in a close-packed hexagonal titanium. The inner layer in contact with the substrate was Ti5Si3. At fixed temperatures (600, 650, 700, and 800 ° C), the thickness of the coating increased according to a parabolic law. Activation energy and diffusion coefficient were calculated. Thermodynamic considerations concerning the interactions between the gaseous phase of cementation and the silica substrate, are presented from theoretical calculations and from Ti-Si-O phase diagrams experimentally constructed at 800, 1000 and 1300 ° C.

KINETICS OF OXYGEN EXCHANGE IN HIGH TEMPERATURE SUPERCONDUCTOR YBa2Cu3O6+x

Kinetics of oxygen absorption in YBa 2 Cu 3 O 6+x has been described. Experiments were performed in the high pressure reactor with constant volume in the temperature range of 150–700°C and oxygen pressure 1.4–10.7 atm. Two stages of oxygen absorption in tetraphase have been discovered. The first is related to the formation of a solid solution of oxygen in Cu(I) layers with the activation energy 0.07 ± 0.01 eV . The second one is oxygen diffusion in the system of short disordered chains ( Cu − O )n with the activation energy 0.30 ± 0.01 eV . Growths of chains and their interaction during the second stage results in the formation of ortho-phase accompanied by further decrease of the reaction rate. Structure-chemical reasons for the multistage mechanism of oxygen absorption are discussed.

Praseodymium 1-2-3: Intrinsic structure, oxygen concentration effects, and solid solutions with yttrium, calcium and zinc

Abstract PrBa 2 Cu 3 O 7−y is probably the most enigmatic member of the 1-2-3 family of compounds. It is the only non-superconducting example in this lanthanide series of isomorphic structures. We have studied its structural details, and dependence of its physical properties on oxygen concentration and solid solutions with Y, Ca and Zn, with the objective of understanding its peculiar behavior and the role Pr plays in suppressing superconductivity.

Oxidation kinetics of zirconium in water vapour between 750 and 1250°C

The zirconium oxidation has been followed in H 2/H 20 gas mixtures by microgravimetry and morphological observations between 750 and 1250°C. The reaction rate is governed by a mixed regime of oxygen diffusion through multiplex oxide layers of zirconia and an oxygen solid solution. After the metal core has disappeared the reaction proceeds by direct oxidation of the solid solution. Different kinetic behaviours have been shown according to the phase couples present.

Effect of coatings on oxidation of Ti-6Al-2Sn-4Zr-2Mo foil

The viability of using coated Ti-6Al-2Sn-4Zr-2Mo foils at 620°C in air was established through mechanical and thermogravimetric testing. Weight-grained and oxygen embrittlement were significantly reduced by the coatings. The residual tensile elongation of coated specimens was 2.5 times that of uncoated specimens. Comparison depth-profiling with X-ray diffraction verified the reduction of oxygen solid-solution in the α-phase for a selection of coated specimens.

The mutual interactions of oxygen and hydrogen in α-titanium during heat treatment

Oxygen and hydrogen dissolve in α-phase titanium at different concentrations up to 34 at.% and 0.14 at.% respectively. Oxygen is an alphagene element while hydrogen is betagene. Firstly, the oxygen diffusion coefficient in hydrided titanium TiH 1.46 has been measured at 750 °C and additional tests have been carried out on TiH 0.2. Secondly, the hydrogen diffusion coefficient (in fact for tritium) has been determined at 400 °C in solid solutions of oxygen in titanium at 1 at.% and 2 at.%. For the case of oxygen diffusion in Ti-H, the chief effect is the disappearance of hydrides when the oxygen concentration is over 5 at.% (for TiH 0.2 by analogy with titanium) or at 2 at.% (for TiH 1.46 by direct measurement). The diffusion conditions of tritium depend greatly on the oxygen content of the metal. A value of 1–2 at.% seems to be critical; for higher oxygen concentrations, the quantity of tritium dissolved diminishes markedly. Diffusion coefficients have been measured.

Mechanical properties of manganese sulphides in the temperature range between room temperature and 1000.DEG.C.

Manganese sulphide powders, prepared by a sulphur deoxidation of MnSO4, were melted at 1700°C in a graphite crucible, and then solidified into buttons, about 20mm diameter and 15mm long. Several kinds of bulk manganese sulphide with additives were prepared from powder mixtures of MnS and one of Al2O3, SiO2, MnO, CaO, CaS, and FeS. In the temperature range from room temperature to about 1000°C, their microhardness and nominal yield strength were measured and the following results were obtained.(1) Purified MnS samples had almost the same hardness as those reported so far. Their nominal yield strength varied with temperature from about 9kgf/mm2 at room temperature to about 2kgf/mm2 around 1000°C.(2) Additions of impurities into MnS brought about increases in both hardness and nominal yield strength. The hardening is presumably caused by solid solution of oxygen and calcium. The nominal yield strength varied with temperature from about 11 to 12kgf/mm2 at room temperature, to about 2 to 5kgf/mm2 around 1000°C depending on kinds of additives.

Structure and properties of rapidly solidified dispersion strengthened titanium alloys: Part II. tensile and creep properties

The effects of incoherent dispersoids on tensile and creep properties were determined in rapidly solidified Ti-Er and Ti-Nd alloys. Uniform distributions of. fine incoherent dispersoids in Ti matrix were produced by rapid solidification at cooling rates > 103 °C per second and subsequent annealing at 700 to 800°C of Ti-1.0Er, Ti-2.0Er, Ti-1.5Nd, and Ti-3.0Nd alloys. The rapidly solidified particulates consolidated by vacuum hot pressing were isothermally forged, rolled, and annealed to produce fully recrystallized microstructures. The incoherent dispersoids in Ti-Er and Ti-Nd alloys increase by 40 to 110 pct the yield strength and ultimate tensile strength of Ti with no significant loss in ductility. The strength increments were analyzed in terms of the superposition of dispersion-, solid solution-, and fine grain-strengthening. Dispersion strengthening is offset to some extent by the reduction in interstitial oxygen solid solution strengthening caused by the scavenging of oxygen by Er and Nd. The dispersoids decrease the creep rates and increase the stress rupture lifetimes of Ti at 482 to 700 °C.

Titanium silicide formation: Effect of oxygen distribution in the metal film

The oxygen behavior and its influence on Ti silicide formation is systematically studied in the TiO2/Si and Ti/TiO2/Si systems using Rutherford backscattering, nuclear reaction analysis, and x-rays diffraction techniques. After annealing in vacuum ( p<5×10−7 Torr), no reaction was observed up to 900 °C in the TiO2/Si system, whereas in the Ti/TiO2/Si system, metallic titanium reacts with the TiO2 film above 400 °C and at 600 °C a uniform oxygen solid solution is formed. The silicide formation starts at 650 °C and up to 750 °C the only phase formed is Ti5Si3. We found that this phase is kinetically favored as long as the Ti is being supplied by the unreacted film. The growth rate kinetics was found to have parabolic behavior and was therefore controlled by Si volume diffusion. Above 750 °C, TiSi2 forms very rapidly, its growth being nucleation controlled. During the growth of the silicide layer, a diffusion of oxgen toward the surface region was observed. When the oxygen concentration in the surface layer exceeded the solubility limit, Ti oxide precipitated and the silicide growth nearly stopped, even if some silicon reached the surface. At a temperature higher than 850 °C, a marked oxygen loss takes place, most probably via SiO sublimation. The sublimation process is favored by the presence of Si in the surface region and prevents the formation of a stable SiO2 diffusion barrier at the TiSi2/TiOx interface.

High temperature thermodynamics of H 2 and D 2 in titanium, and in dilute titanium oxygen solid solutions

The Tian Calvet microcalorimetric method has been improved in order to determine Δ H H( D), the partial molar enthalpy of mixing of hydrogen (deuterium) in the Ti-H 2( D 2) solid systems for compositions 0 < (H/Ti) < 1.85, at 713 K and in the α TiO y + H 2 solid solutions ( y = (O/Ti)) at 745 K. The combined calorimetric and equilibrium method allows a precise evaluation of the partial molar entropies. The results of this study differ substantially from earlier published data.