Showing papers on "Titanium published in 1986"

Titanium aluminum nitride films: A new alternative to TiN coatings

Abstract: TiAl films have been produced in various compositions by using the sputter ion plating process. Films sputtered reactively from a target with the composition of TiAl 50:50 at. % have been deposited with a composition of 27.5 at. % Ti, 28.9 at. % Al, and 43.6 at. % N. The crystal structure found was that of sodium chloride with a lattice parameter of 4.20 A; the microhardness such films was found to be HV 2100–2300. The incorporation of Al into the nitride films improves the oxidation resistance as well as the cutting performances of TiAlN coated drills. TiN films start to oxidize at a temperature level of 550 °C, whereas TiAl coatings react with hot air at a temperature of 800 °C severely. TiAlN coated drills have been tested with two different steels and performed better by a factor >2 compared with TiN coated drills.

Combustion synthesis of titanium carbide: Theory and experiment

Abstract: The combustion synthesis of titanium carbide from elemental powders has been theoretically and experimentally studied as a model system for self -propagating high temperature synthesis (SHS) of refractory compounds. Calculations of the adiabatic temperature of combustion of graphite and titanium powders to form TiC x have been made to show the effects of stoichiometry, dilution and the initial temperature of the reactants. Experimental observations on the stability of the combustion front, combined with theoretical predictions, lead to an estimated activation energy of ≤ 117 kJ mol−1 for the process. This value is at least a factor of about four too low to correspond to a diffusion-controlled process. The combustion of graphite and titanium powders was accompanied by the evolution of gases whose primary constituent was found to be hydrogen. This observation was attributed to the reaction of adsorbed moisture with titanium powder. The titanium carbide phase resulting from the combustion of compacted mixed powders of the elements was highly porous (∼ 50% porosity). It can be obtained in high density (∼5% porosity) when pressure is applied during the combustion process.

Compensating Defects in Highly Donor-Doped BaTiO3

Abstract: Nb-doped BaTiO3 has been prepared with various Ba/(Ti + Nb) ratios such that single-phase products will be obtained if the charged donor center is assumed to be compensated in turn by Ba vacancies, Ti vacancies, equal concentrations of the two cation vacancies, oxygen interstitials, or electrons. For air-Fired samples, examination by transmission electron microscopy showed that only the composition adjusted for compensation by titanium vacancies was single phase. The other compositions contained a Ti-rich second phase in order to achieve a matrix with the appropriate concentration of titanium vacancies. When sintered in a reducing atmosphere, compensation was by electrons, and a Ba-rich second phase was present hi the composition adjusted to give compensation by titanium vacancies. The results indicate that for donor concentrations greater than ∼0.5 mol% in BaTiO3, charge compensation is achieved by Ti vacancies under oxidizing conditions, and by electrons (as is well-known) under reducing conditions.' The effect of compensating defects on grain growth is also discussed.

Alkoxide Precursor Synthesis and Characterization of Phases in the Barium-Titanium Oxide System

Abstract: Barium titanate precursors with Ba/Ti ratios ranging from 2:1 to 1:9 were prepared by controlled hydrolysis of mixed barium and titanium species in an alcohol medium. Details of the synthesis and characterization of the resultant products are given. Amorphous powders precipitated by hydrolysis from ethanol solutions of barium and titanium alkoxides crystallize to single-or two-phase 1:2 and 1:5 compounds at ∼700°C. These compounds transform at higher temperatures to other known crystalline phases, the 1:5 phase being maintained metastably to ∼1100°C.

Photocatalysis over binary metal oxides. Enhancement of the photocatalytic activity of titanium dioxide in titanium-silicon oxides

Abstract: Photocatalytic reactions of alkenes and alkynes with water were investigated over titanium-silicon oxides in order to obtain information about the potential ability of binary oxides as photocatalysts. Photocatalytic activity of TiO/sub 2/ species in the titanium-silicon oxides was found to be enhanced in the region of lower Ti content. X-ray, photoluminescence, and X-ray photoelectron spectroscopy (XPS) measurements indicate that Ti ions are enriched on the surface of the oxides having a low Ti content and present separately from each other in the SiO/sub 2/ matrix. From these results, together with those obtained with highly dispersed TiO/sub 2/ anchored on support surfaces, it is suggested that the higher photocatalytic activity of such catalysts is due to the diminished radiationless transfer of the photon energy absorbed by TiO/sub 2/. 18 references, 7 figures, 3 tables.

Osseointegration of titanium implants.

Abstract: Forty-eight screws, six double cylindrical implants and six T-plates were inserted into the tibia or femur of 6 dogs. Two titanium screws were inserted into the proximal tibia of 5 patients to anchor a titanium mould. The implants were removed en bloc with adjacent bone tissue after 3 to 14 months. They were sectioned using a technique that allowed analysis of the intact tissue-to-metal specimens. Osseointegration, defined as a direct bone-to-implant contact without interposed soft tissue, was confirmed in all screw-shaped implants while the cylindres had only partial bone contact as did the T-plates. We conclude that osseointegrated implants may be applicable in joint reconstruction for arthrosis or rheumatoid arthritis.

Surface Engineering of Titanium with Nitrogen

Abstract: The possibilities for surface hardening of titanium alloys by alloying with nitrogen are reviewed. Alloying has been carried out in the solid state by plasma nitriding and in the liquid state by laser melting in nitrogen. Microstructure, hardness profiles, and fatigue and wear properties have been examined. Wear resistance was found to be greatly improved by both techniques, although at the expense of a drop in fatigue properties. Case depths of 0.1 mm were produced by plasma nitriding, while 0.5 mm case depths and a maximum hardness of 1400 HV0.1 were achieved by laser alloying.

Process for patterning local interconnects

Abstract: A local interconnect system for VLSI integrated circuits. After titanium is deposited for self-aligned silicidation of exposed moat and gate regions in a nitrogen atmosphere, a hardmask is deposited and patterned over the titanium. When a conductive titanium nitride layer is formed overall, it will already be patterned according to this hardmask.

Heterogeneous organometallic catalysts containing a supported titanium compound and at least one other supported organometallic compound

Abstract: Catalyst compositions are disclosed which are a combination of a supported titanium compound such as titanium tetraisopropoxide supported on magnesium dichloride and at least one other supported metallic catalyst such as dicyclopentadienyl zirconium dichloride supported on alumina and a cocatalyst such as aluminoxane. These catalysts are useful in the polymerization of α-olefins.

The reactivity of TiO2 and ZrO2 in organically modified silicates

Abstract: The objective of this investigation was to compare the influence of titania, zirconia and silica on synthesis and properties of epoxide group containing organically modified silicates. These materials were prepared from the epoxysilane ( MeO ) 3 SiC 3 OCH 2 CHCH 2 O and titanium, zirconium and silicon alkoxides by the sol-gel process. The results show that titanium and zirconium, beside their role as network formers, act as efficient catalysts for epoxide polymerization. Zirconium promotes thermically the polymerization of epoxides to polyethylene oxide crosslinking chains, whereas titanium promotes this reaction photochemically. The incorporation of crosslinking polyethylene oxide decreases the scratch resistance of the silicate condensates. The activity of silicon in both reactions is very poor.

Raman spectra of the anodic oxide film on titanium in acidic sulfate and neutral phosphate solutions

Abstract: Laser Raman spectroscopy has been applied under in situ and ex situ conditions to the anodic oxide films formed on titanium at various potentials in neutral phosphate and acidic sulfate solutions. The Raman spectra reveal that the anodic oxide film is primarily composed of an anatase type of . From the relation between the Raman band intensity, film thickness, and surface morphology, it is likely that the film changes from the amorphous state to the crystalline state beyond a certain critical potential.

Kinetics of titanium dioxide precipitation by thermal hydrolysis

Abstract: Precipitation of titanium dioxide by thermal hydrolysis from concentrated sulfuric acid solutions has been studied by considering all the factors which have influence on the rates of the process and on the characteristics of the precipitate. For this purpose a mathematical model containing three population balance equations has been defined. A population balance equation is related to the free particles that are present at any time in the system, another to the agglomerates, and the last to the total particles, that is free particles plus particles bounded into the agglomerates. In this model kinetic laws for nucleation and growth, respectively, have been introduced by considering the experimental observations that precipitation is a strongly activated process and that sulfuric acid concentration negatively affects precipitation rate. The following assumptions have then been introduced: coalescence is possible only for very small free particles; and elementary particles in aggregates can grow independently without losing their identity. The above-mentioned population balance equations have been solved by employing the method of moments and give the amount of titanium precipitated during the time, the average size of the elementary particles and of the aggregates during the time, and the evolution of the corresponding distribution function. The reliability of the mathematical model has been tested on kinetic runs performed under different conditions of temperature, titanium concentration, and sulfuric acid concentration.

Internal stress and adherence of titanium nitride coatings

Abstract: Titanium nitride coatings were deposited on various substrates by sputter ion plating and the state of stress was determined by the sin2 ψ method. The lattice distortions that occur in the nitride coatings have been resolved in terms of a macrostrain and microstrain, as determined from the breadth of the x‐ray reflections, and the origins of each are discussed. The internal stress present in a coating is shown to consist of two components, one thermal in origin and the other structural, and that its sign and magnitude varies with substrate material and bias potential. During cooling from deposition temperature partial relaxation of this internal stress (macrostrain) occurs via two mechanisms, plastic deformation of the substrate and yield of the film. The internal stress was completely relaxed on dissolution of the substrate, accompanied by a decrease in the lattice parameter of the film. By comparing the results from substrates biased and unbiased during deposition, and measurements made on adherent and free‐standing coatings, the microstrain measurements have been separated into two parts, one due to distortions at the grain boundaries and one due to defects in the crystallites. A model is proposed that accounts for all the experimental observations; this also provides an explanation for the distortions from cubic symmetry reported in titanium and hafnium nitride films.

Catalyst on the basis of silicon and titanium having high mechanical strength

Abstract: The invention discloses a catalyst on the basis of silicon and titanium having the form of microspheres and constituted by oligomeric silica and by titanium-silicalite crystals having an oligomeric silica/titanium-silicalite molar ratio comprised within the range of from 0.05 to 0.11, wherein the crystals of titanium-silicalite are encaged by means of Si--O--Si bridges.

Higher nitrides of hafnium, zirconium, and titanium synthesized by dual ion beam deposition

Abstract: We report the preparation and properties of higher nitrides of Hf, Zr, and Ti synthesized by dual ion beam deposition. For Hf and Zr, evidence is given for the existence of a metastable nitride phase with composition of approximately Hf3 N4 and Zr3 N4. These two materials are insulating and transparent straw colored, in contrast to the well-known mononitrides, which are shiny, gold colored, and highly conducting. For Ti-N we do not reach as high an N content and do not obtain an insulating, transparent phase. The higher nitrides of Hf and Zr are synthesized under energetic nitrogen ion bombardment (200 e V) of a growing film and do not form in the presence of molecular nitrogen gas alone. Several variations of the ion beam deposition process are used to obtain a wide range of film composition and to study the transition from the mononitride to the higher nitride phase. Transmission electron diffraction shows the structure of Hf3N4 and Zr3N4 to be very close to the Bl (NaCl) structure of the mononitrides, but with a slight rhombohedral distortion. Additional evidence from noble gas incorporation (Ne, Ar, and Xe) supports a model of these higher nitrides as containing a large number of vacancies on the metal atom sites.

Iridium oxide coated electrodes for neural stimulation

Abstract: A metallic electrode made of platinum, platinum iridium alloy, stainless steel, stainless steel alloys, titanium, titanium alloys, tantalum or tantalum alloys is coated with iridium oxide. Ir(III) trichloride is heated in 5.5M HCl until 75-80% of the solution is evaporated. Isopropyl or ethyl alcohol is added to the evaporated solution to restore the solution to its original volume. This restored acid/alcohol solution is aged for 1-2 weeks. The metallic electrode is soaked in the aged acid/alcohol solution for 16 hours, dried for one hour at room temperature and annealed in air at 320° C. for 80-90 minutes.

Alteration of detrital Fe-Ti oxides in sedimentary rocks

Abstract: Scanning electron microscope study has revealed that in Proterozoic sandstones, shales, and carbonate rocks of the Visingso Group in southern Sweden, detrital Fe-Ti oxides have undergone alteration by dissolution and/or replacement mainly by titanium oxides, hematite (reddish rocks), or pyrite (greenish sandstones, shales, and carbonate rocks). The titanium oxides occur as either poorly crystalline masses, cryptocrystalline aggregates, or discrete, euhedral crystals of anatase, brookite, and rutile that attain a variety of crystal habits. Microprobe analyses have shown that the alteration of ilmenite occurs through several intermediate phases, each successively enriched in titanium and depleted in iron, to an almost pure form of TiO 2 . Some of the iron and titanium which is released during alteration of the Fe-Ti oxides is incorporated in associated clay minerals.

Casting of reactive metals into ceramic molds

Abstract: Mold coatings that are relatively unreactive with titanium and titanium alloys during casting are prepared from zirconia or yttria sols, or mixtures thereof as a binder for a refractory such as zirconium oxide, yttrium oxide and mixtures thereof.

Behavior of surface peroxo species in the photoreactions at titanium dioxide

Abstract: The electrochemical behavior of the surface species photogenerated at a polycrystalline titanium dioxide film electrode in alkaline solution was investigated by means of cyclic voltammetry. The obtained results are consistent with the same surface peroxo titanium species being formed when an illuminated TiO/sub 2/ electrode is subjected to an anodic bias or left in open circuit both in the presence and in the absence of oxygen. The decay of these species after the cutoff of illumination was observed to occur relatively slowly, about half of their initial amount being still detectable after 16 h of electrode immersion in sodium hydroxide solution. It was shown that the cathodic reduction of the surface peroxo species, photogenerated at the TiO/sub 2/ electrode, takes place at distinctly more negative potentials than that of dissolved molecular oxygen and that of both preadsorbed and dissolved hydrogen peroxide. The latter species (present mainly as HO/sub 2//sup -/ ions) were also observed to undergo rapid photooxidation at the TiO/sub 2/ photoanode, competing efficiently for positive holes with OH/sup -/ ions. These findings do not support the earlier postulated involvement of the hydrogen peroxide as an intermediate of the photoreaction leading to oxygen evolution. The pathways for the photooxidationmore » reactions at TiO/sub 2/ are briefly discussed in connection with the proposed mechanism of formation of the surface peroxo titanium species. Their role in controlling the surface electron-hole recombination, particularly at dispersed TiO/sub 2/ photocatalysts, is pointed out.« less