Oxygen In Solid Solution Research Articles

Oxygen Influence on Titanium Silicide Formation

ABSTRACTThe oxygen behaviour and its influence on the annealing properties of the TiO2/Si and Ti/TiO2/Si systems have been investigated. For the TiO2/Si system no reaction at all could be evidenced after vacuum annealing up to 900°C for 30'. In the Ti/TiO2/Si system metallic Ti reacts with the TiO2 film above 400°C and at 600°C a uniform oxygen solid solution at the solubility limit was obtained without any Si reaction. Silicide formation occurs for annealing temperatures higher than 650°C and causes oxygen expulsion from the reacted layer and consequently a rise in its concentration at the surface where Ti oxide precipitation takes place. This surface oxide layer prevents a further growth of the silicide up to 850°C. The reaction of the whole metal film is attained only by annealing at 900°C or above, when the oxide is completely reduced and an important oxygen loss takes place. A model explaining this behaviour is proposed.

Modeling oxygen activities in ternary solid solutions: Niobium-vanadium-oxygen system

The quasi-chemical model for ternary solid solutions proposed by Alex and McLellan [1] J. Phys. Chem. Solids 32, 449 (1971), was extended to include next-nearest neighbor interactions between interstitial and lattice atoms. It is shown that this model can describe the behavior of dilute oxygen solid solutions in niobium-vanadium-oxygen alloys. The analysis shows that the interaction between oxygen and lattice atoms may extend to the next-nearest neighbor shell. These thermodynamic results are compared with the diffusion results obtained for niobium-rich and vanadium-rich alloys.

Borrmann effect in elastically bent silicon crystals with structural defects

The Borrmann effect peculiarities in elastically bent silicon crystals containing structural defects appearing as a result of decay of oxygen solid solution are investigated by means of a double-crystal spectrometer. Linearity of the thickness dependences of the integral intensity logarithms In IR = f(t) at fixed level of elastic strain ϵ is established in such samples. This fact allows to determine the most important parameters μi and α describing respectively the absorption and scattering of intensity IR in an elastically bent crystal. The effect of non-additive influence of the localized and distributed distortions of lattice periodicity as well as the sensibility attenuation of IR to elastic strain in real samples with respect to perfect crystals are explained on the basis of decreasing of the effective volume scattering the radiation dynamically. [Russian Text Ignored]

Titanium-Tungsten Carbide/Silver: A New Electric Contact Material

The performance of a new contact material (Ti,W)C-Ag, has been evaluated. Two compositions of this contact, 50 percent by weight Ag and 35 percent by weight Ag, haye been Used. The former contact showed good performance under switching duty (20 A, 110 V, 99 percent power factor). The latter contact had insufficient Ag, however, to maintain a low contact resistance throughout the switching experiments. Both contact structures showed excellent resistance to arc erosion under short circuit conditions. Microchemical (EDAX, EMA, DIMA), metallographic, and X-ray diffraction techniques have been used to analyze the chemical and micr0structural factors. These have been used to explain the good electrical contact characteristics. Gravimetric oxidation tests have also been conducted to characterize the new contacts. Several factors have been identified that contribute to the improved contact material: a) good wetting of (Ti,W)C with silver; b) higher oxidation resistance of (Ti,W)C; c) wide stability range of the mixed Ti-W carbide phase; d) formation of oxygen solid solutions and/or suboxides of titanium; and e) the generation of a CO/CO2 gas blanket during oxidation. This new contact material is shown to be a significani addition to the family of materials used for electric contact applications.

Interaction de l'oxygène aux basses pressions avec la solution solide niobium-oxygène à haute température: I. Èquilibre de segrégation — chimisorption

Interactions between oxygen under low pressure and a niobium-oxygen solid solution had been studied, in the regime where adsorption is the rate-determining step, from 1000 to 1700 K. It is shown that at saturation of solid solution, there exists a constant limiting value Θ l of superficial coverage, comparable to a limiting bulk concentration c l. The ratios θ = Θ/Θ l and ∄ = c/ c l are called “relative ratio of occupation” (superficial and bulk). K SV is the equilibrium constant of segregation between adsorbed and dissolved oxygen atoms: (O diss −v ) + σ ⇌ (O chim−σ) + v (σ and v being respectively surface and bulk sites), K SV = [(1 − θ)/θ] [œ/(1 − œ)]. The experimentally determined expression: K SV = 5.7 exp[−(22.1 − 12.1 θ)/ RT] shows that lateral superficial interactions have a large influence on the enthalpy of transfer between the bulk and the surface of the sample. Adsorption is direct and non activated. At the solubility limit, only a fraction of the superficial sites is occupied. We estimate it to be one half. The sticking probability b of oxygen on a niobium oxygen solid solution is given by b = (1 − θ/2) 2, its value at zero coverage being estimated as unity.

The corrosion of group 5a metals in flowing sodium

The corrosion of vanadium, niobium and tantalum in flowing, liquid sodium has been examined. The ternary oxides, Na 4VO 4 and NaVO 2 have been observed on the surface of vanadium, through a matrix of sodium, by X-ray diffraction, together with an oxygen solid solution in the vanadium. For niobium and tantalum, only a single, ternary oxide corrosion product, Na 3MO 4(M = Nb, Ta), was observed, together with an oxygen solid solution. It has been concluded that Group 5A metals will form ternary oxide corrosion products when exposed to liquid sodium at 600 °C containing more than five parts per million of oxygen.

The role of dissolved oxygen in the corrosion of vanadium by liquid sodium

The corrosion of vanadium in liquid sodium is strongly influenced by the quantity of dissolved oxygen in the liquid metal. The ternary oxide, Na 4VO 4, has been observed on the surface of vanadium after immersion in liquid sodium containing dissolved oxygen at 600°C; it was identified by its X-ray powder-diffraction pattern which was recorded through a matrix of sodium. Vanadium oxides were observed beneath the ternary oxide layer. Measurement of the lattice constant of the vanadium metal enabled the extent of oxygen solid solution to be calculated. A mechanism for the corrosion of vanadium in liquid sodium is postulated.

Electron probe microanalysis and X‐ray diffraction of nitrides, oxides, and sulfides in steels

AbstractThe aim of the present work was to show the possibilities for the determination of the chemical and phase composition of oxygen, nitrogen and sulphur compounds in steels by a parallel application of electron microanalysis and X‐ray structure analysis methods. The application of both methods makes it possible to identify composed phases with regard to the chemical composition, i. e. solid solutions of oxygen and nitrogen in precipitations and inclusions occurring in steel.

The role of dissolved oxygen in the corrosion of titanium and zirconium by liquid sodium

The corrosion of titanium and zirconium by liquid sodium containing dissolved oxygen has been shown to take place by the formation of non-adherent ternary oxides, in addition to the well known binary oxides, and oxygen solid solution in the metals. The compounds Na4TiO4 and Na2ZrO3 have been identified on the surface of titanium and zirconium after immersion in liquid sodium containing dissolved oxygen at temperatures close to 600 °C. The oxides were identified by their X-ray powder diffraction patterns which were recorded through a matrix of sodium. The lattice parameters of the underlying transition metal were measured enabling the approximate amount of oxygen in solid solution in the metal to be calculated. The characterisation of ternary oxide corrosion products, in addition to binary oxides and solid solutions of oxygen in the metal, enables a comprehensive mechanism of corrosion for titanium and zirconium in the presence of liquid sodium to be postulated.

The role of dissolved oxygen in the corrosion of niobium and tantalum by liquid sodium

The corrosion of niobium and tantalum in liquid sodium is strongly influenced by the quantity of dissolved oxygen in the liquid metal. The oxides Na3TaO4 and Na3NbO4 have been identified on the surface of tantalum and niobium after immersion in liquid sodium containing dissolved oxygen at temperatures in excess of 300°. The oxides were identified by their X-ray powder diffraction patterns which were recorded through a matrix of sodium. Measurement of the lattice constant of the underlying transition element enabled the extent of oxygen solid solution to be calculated. The formation of an oxide, together with oxygen in solid solution, enables a mechanism of corrosion for niobium and tantalum in the presence of liquid sodium to be established.

An Electron Microscopic Investigation of Phenomena Associated with Solid Solution of Oxygen in Niobium

AbstractA transformation process in the solid solution period of the niobium oxygen reaction was investigated by electron microscopy and diffraction. In thin foils submitted to a heat treatment under reduced air pressure ordering of the introduced oxygen interstitials took place. This process could be followed in transmission.The transformation starts with a nucleation mechanism where by small nuclei composed of small parallel domains in crystallographic directions are formed. These nuclei grow together to form a cross hatch pattern. Selected area diffraction reveals superlattice reflections of an ordered phase. The formation of irregular shaped superlattice nuclei and an epitaxial grown suboxide phase is also described. It is supposed that all these phenomena represent a transient stage in the transformation to more stable suboxyde and oxyde phases of niobium.

X-Ray Measurement of the Static Lattice Distortion in the Solid Solution of Oxygen in Titanium*

AbstractOxygen was introduced into a single crystal of titanium in successive stages. The intensities of the h00 and 00l reflections were measured with a single-crystal diffractometer. The observed variation of the intensities with oxygen concentration was attributed to three factors: (1) the additional scattering from the oxygen atoms, (2) a change in the Debye-Waller factor, and (3) an exponential factor originating from the distortion around the oxygen atom. The theory of X-ray scattering from crystals containing centers of distortion was applied to the hexagonal titanium containing interstitial oxygen atoms. Using the variation of the lattice constant with oxygen concentration, it was possible to predict the intensity reduction due to lattice strains. It was concluded that it would have been possible to obtain an estimate of the defect concentration from the X-ray measurements of lattice expansion and intensity reduction.

Disorder and Order in Solid Solutions of Oxygen in alpha-Titanium.

Disorder and Order in Solid Solutions of Oxygen in alpha-Titanium.

The oxidation of titanium in oxygen at high temperatures

The oxidation of titanium has been studied in the range 850°–1000°C and the results compared with those of earlier investigations. The oxidation rate is initially parabolic, the parabolic rate constant being the sum of two terms; one representing the formation of a rutile scale by the migration of anion defects with an activation energy of 25,400 ± 1000 cal/mole, and one representing the formation of an oxygen solid solution by the diffusion of interstitial oxygen atoms in alpha titanium with an activation energy of 61,800 ± 2000 cal/mole. Eventually the scale detaches by blistering away from the metal surface and reacts with oxygen to become stoichiometric. When this is repeated, a white laminar porous film forms and the rate law becomes linear. Finally it appears that gaseous diffusion of oxygen through the porous scale becomes the controlling step, and a new rate law is established, initially parabolic, but tending to linear at very long times. A model is suggested for this step and a rate law of the right form derived. When the pores are identified with screw dislocation cores, quantitative agreement is obtained between calculated and observed rates.

Studies on the lower oxides of titanium∗

Pure TiO is face-centered cubic above ~ 950°C. The structure of samples annealed below this temperature is complex, consisting of two or possibly three phases not in equilibrium. Impurities and excess of oxygen stabilize the face-centered cubic form at room temperature. The electrical resistivity of TiO (prepared by melting) is 2.81 × 10 −4Ω cm at room temperature, and increases with temperature between —162 and 362°C. The thermoelectric e.m.f. of TiO is of the same order of magnitude as that of metals. The measured density is less than the X-ray density, indicating that 14.6 per cent of the lattice positions are unoccupied. The properties of our products suggest that the TiO-phase oxides may be considered solid solutions of oxygen in titanium. X-ray investigations indicate that Ti 3O 4 probably does not exist. The trigonal unit cell of Ti 2O 3 between room temperature and 350°C is confirmed. The lattice parameters change rapidly between 160 and 200°C, corresponding to the rapid increase in magnetic susceptibility. Ti 2O 3 is antiferromagnetic ; χ m = 1.09 × 10 −6 cgs units at 20°C. The thermal activation energy of electrical conduction of Ti 2O 3 in the room-temperature region is about half of the observed optical activation energy. The material is a p-type semiconductor at room temperature.

Hydrogen Evolution from Dissolving Titanium‐Oxygen Alloys in Hydrofluoric Acid and the Constitution of Ti‐O Alloys

Titanium‐oxygen alloys dissolve in according to the reaction , with a maximum for , which means that dissolves without hydrogen evolution. Higher titanium oxides do not dissolve in . The determination of the end point of the above reaction was affected by a secondary, but very slow reaction . Nevertheless, the experimental results agreed within ±2% for the first reaction for titanium containing oxygen up to 33 at.%. Titanium‐oxygen alloys do not represent titanium oxygen solid solutions but solid solutions of titanium oxides and titanium metal.