Showing papers on "Titanium published in 1992"

Ti8C12+-Metallo-Carbohedrenes: A New Class of Molecular Clusters?

Abstract: During the course of studying the dehydrogenation reactions of hydrocarbons by titanium atoms, ions, and clusters, an exceptionally stable and abundant cluster which contains 8 titaniums and 12 carbons was discovered "Titration" reactions with ND3 reveal the uptake of eight molecules, pointing to the fact that the titanium atoms are at exposed positions of similar coordination A dodecahedral structure of Th point group symmetry is proposed to account for the unusual stability of this molecular cluster The Ti8C12+ dodecahedron has 12 pentagonal rings and each of the rings is formed by two titanium and three carbon atoms, where each titanium is bound to three carbons Based on the model, it is expected that neutral Ti8C12 would be a stable metallo-carbododecahedral molecule and may comprise one member of a new class of molecules, namely metallo-carbohedrenes

Oxo[5, 10, 15, 20-tetra(4-pyridyl)porphyrinato]titanium(IV): an ultra-high sensitivity spectrophotometric reagent for hydrogen peroxide

Abstract: The water-soluble titanium(IV)–porphyrin complex, oxo[5, 10, 15, 20-tetra(4-pyridyl)porphyrinato]titanium(IV)[TiO(tpyH4)4+], was found to enhance the spectrophotometric determination of trace amounts of hydrogen peroxide. A 0.05 mol dm–3 hydrochloric acid solution containing TiO(tpypH4)4+ was used (the Ti—TPyP reagent), the absorbance of which decreased at 432 nm as hydrogen peroxide was added. This was due to the consumption of the TiO(tpypH4)4+ complex following the formation of peroxo[5, 10, 15, 20-tetra(4-pyridyl)porphyrinato]titanium(IV). The decrease in absorbance at 432 nm (ΔA432) was proportional to the concentration of hydrogen peroxide, from 1.0 × 10–8 to 2.8 × 10–6 mol dm–3, in the sample solution (25 pmol–7.0 nmol per assay). The reaction was accelerated by hydrogen ions; the presence of 1.6 mol dm–3 perchloric acid was found to promote complexation to the greatest extent. A ΔA432 of 1.9 × 105 was found for 1 mol dm–3 hydrogen peroxide. A measurement precision of 1.2% for 1.0 × 10–6 mol dm–3 hydrogen peroxide (n= 8) was obtained. The reagent can be used for the determination of hydrogen peroxide in water samples such as tap water and rainwater over the range from 1.05 × 10–7 to 3.34 × 10–5 mol dm–3.

In Situ Raman Spectroscopy of Alumina-Supported Metal Oxide Catalysts

Abstract: The molecular structures of the surface overlayerers of rhenium(VII) oxide, molybdenum(VI) oxide, tungsten(VI) oxide, chromium(VI) oxide, vanadium(V) oxide, niobium(V) oxide, and titanium(IV) oxide on γ-alumina were determined by in situ Raman spectroscopy under dehydrated conditions. It was found that the dehydrated surface metal oxide structures of all the systems under study, except for supported titanium oxide, are different from those under ambient condition where moisture is present on the surface

Method of selectively etching titanium-containing materials on a semiconductor wafer using remote plasma generation

Abstract: A method of selectively etching titanium-containing materials without attacking aluminum or silicon dioxide is describe, wherein an atomic chlorine etching environment is generated using downstream techniques. Atomic chlorine in the absence of ion bombardment (as provided by downstream etching) etches titanium-containing materials such as titanium nitride without attacking silicon dioxide. In one embodiment of the invention, atomic chlorine is generated by the discharge of energy into molecular chlorine. In another embodiment of the invention, discharge of energy into a fluorine-containing gas causes the generation of atomic fluorine. Molecular chlorine is then added, creating a fluorine-chlorine exchange reaction which produces atomic chlorine. The presence of fluorine inhibits etching of aluminum, but does not impede the etching of titanium-containing materials.

Metallo-Carbohedrenes [M8C12+ (M = V, Zr, Hf, and Ti)]: A Class of Stable Molecular Cluster Ions.

Abstract: Findings of magic peaks corresponding to M 8 C 12 + (M = V, Zr, and Hf) formed from reactions of the respective metals with various small hydrocarbons, in conjunction with recent findings for the titanium system, establish metallo-carbohedrenes as a stable general class of molecular cluster ions. A dodecahedral structure of T h point symmetry accounts for the stability of these ionic clusters.

dc reactive magnetron sputtering of titanium‐structural and optical characterization of TiO2 films

Abstract: This paper deals with the reactive sputtering of titanium in an argon and oxygen mixture. The variation in cathode potential as a function of oxygen partial pressure has been explained in terms of cathode poisoning effects. The titania films deposited during this process have been studied for their structural and optical characteristics. The effect of substrate temperature (from 25 to 400 °C) and annealing (from 250 to 700 °C) on the packing density, refractive index, extinction coefficient, and crystallinity has been investigated. The refractive index varied from 2.24 to 2.46 and extinction coefficient from 2.6 × 10−3 to 10.4× 10−3 at 500 nm as the substrate temperature increased from 25 to 400 °C. The refractive index increased from 2.19 to 2.35 and extinction coefficient changed from 3.2× 10−3 to 11.6 × 10−3 at 500 nm as the annealing temperature was increased from 250 to 700 °C. Anatase and rutile phases have been observed in the films deposited at 400 °C substrate temperature and annealed at 300 °C. ...

Effect of surface processing on the attachment, orientation, and proliferation of human gingival fibroblasts on titanium.

Abstract: The adhesion, orientation, and proliferation of human gingival fibroblasts was studied on electropolished (elpTi), etched (etchTi), and sandblasted (sblTi) titanium surfaces. The texture, chemical state, and composition of the titanium surfaces were analyzed using a surface tracing instrument and electron spectroscopy for chemical analysis. Considerable differences were evident in the surface texture and chemical composition of the differently treated titanium plates. Electropolishing produced the smoothest and cleanest surface. Human gingival fibroblasts attached, spread, and proliferated on all titanium surfaces. However, cells on elpTi exhibited an extremely flat morphology and seemed to form cellular bridges with adjacent cells, whereas the etchTi and sblTi surfaces harbored both round and flat cells with many long processes. Cells on elpTi appeared to grow in thick layers with no specific orientation, whereas on etchTi surfaces they were migrating along the parallel, irregular minor grooves caused by mechanical polishing, and on sblTi surfaces they seemed to grow in clusters. Stress-fiber type actin bundles and vinculin-containing focal adhesions were present in cells spreading on elpTi and etchTi surfaces but not in cells spreading on sblTi surfaces. Cell shape, orientation, and proliferation appear to depend on the texture of the titanium surface and probably also on the properties of the oxide layer and adjacent bulk material. Our findings suggest that smooth or finely grooved titanium surfaces could be optimal in implants adjacent to soft tissues as they support the attachment and growth of human gingival fibroblasts.

Corrosion between the components of modular femoral hip prostheses.

Abstract: We studied the tapered interface between the head and the neck of 139 modular femoral components of hip prostheses which had been removed for a variety of reasons. In 91 the same alloy had been used for the head and the stem; none of them showed evidence of corrosion. In contrast, there was definite corrosion in 25 of the 48 prostheses in which the stem was of titanium alloy and the head of cobalt-chrome. This corrosion was time-dependent: no specimens were corroded after less than nine months in the body, but all which had been in place for more than 40 months were damaged. We discuss the factors which may influence the rate of these changes and present evidence that they were due to galvanically-accelerated crevice corrosion, which was undetected in previous laboratory testing of this type of prosthesis.

Enhanced extracellular matrix production and mineralization by osteoblasts cultured on titanium surfaces in vitro.

Abstract: Long-term stability of orthopaedic and dental implants depends on the integration of the artificial material into the surrounding bone tissue. The physical and chemical properties of implants, including those made of metals such as titanium, are thought to influence osseointegration. Despite the known importance of this interface, little is known about the factors that promote its formation. In this study, chick embryonic calvarial osteoblasts were cultured in vitro on smooth, rough-textured and porous-coated titanium surfaces and examined for morphology, biosynthesis of extracellular matrix and mineralization as a function of culture time. Scanning electron microscopy revealed that osteoblasts adhered securely to the titanium surface and frequently bridged the uneven surface by means of cellular processes. The osteoblast phenotype was retained in the cell cultures on titanium. In addition, the synthesis of extracellular matrix and subsequent mineralization were both substantially enhanced in the cultures on rough-textured and porous-coated titanium. These results strongly suggest that porous or rough titanium implant surfaces may act like "natural" substrata to permit microscopic tissue/cell ingrowth to improve clinical implant fixation.

The mechanisms of passive dissolution of titanium in a model physiological environment

Abstract: The surface chemistry, oxidation, and disolution kinetics of titanium were measured to establish the mechanisms of passive dissolution in physiological environments. Titanium thin films were immersed in 8.0 mM ethylenediamine-tetraacetic acid in simulated interstitial electrolyte (EDTA/SIE) and maintained at 37 degrees C, 10% O2, 5% CO2 and 7.2 pH for periods of time up to 3200 h (133 days). Two immersion schemes were employed: the integral sequentially determined the titanium released into a solution of accumulated dissolution products; and the differential continuously replenished the test solution. The solutions were analyzed for titanium by electrothermal atomic absorption spectrometry (EAAS), and the sample surfaces were analyzed by Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) to determine oxide composition, stoichiometry, and thickness. Prior to immersion two types of hydroxyl (OH) groups were distinguished on the TiO2 surface. Upon immersion, the chemistry of the surface changed as a function of immersion: the presence of OH groups increased and P (nonelemental) was detected at the surface. The dissolution kinetics obeyed a two-phase logarithmic model, where the transition between phases occurred simultaneously with the adsorption of the P-containing species. The dissolution kinetics depended on surface reactions, electric field strength, and molecular diffusion. These mechanisms explain the observed dependence of dissolution kinetics on the properties of the surface oxide and solution ligands.

The use of titanium fixtures for intraoral anchorage to facilitate orthodontic tooth movement.

Abstract: The use of endosseous implants to facilitate orthodontic tooth movement has been periodically reported in the scientific literature for over 40 years. The predictable achievement of rigid bone-implant anchorage was first applied by Branemark in 1965. Using the osseointegration method, a prospective study was conducted involving seven adult patients who were treated with titanium implants used as rigid anchorage units. Orthodontic forces were directed off the implants to correct a variety of malocclusions. All 14 implants placed remained stable during the course of treatment with loading forces of 150 to 400 g. No significant complications occurred. Desirable occlusal and facial results were achieved in all cases. The results obtained over a 3-year period of treatment indicate that intraoral rigid anchorage in the absence of observed reciprocal action is possible.

Microstructural characterization of hydroxyapatite coating on titanium

Abstract: The microstructure of hydroxyapatite plasma sprayed onto titanium alloy has been studied by using transmission electron microscopy. It has been shown that while substantial portions of the coating are crystalline hydroxyapatite, regions of amorphous calcium phosphate with Ca/P ratios of 0.6–1.0 are also present, both in the coatings and at the metal-ceramic interface. The microstructures observed have also been found to be consistent with devitrification of the amorphous calcium phosphates producing regions of very fine grained hydroxyapatite. A calcium titanate phase has also been detected at the metal-ceramic interface produced by the chemical reaction of hydroxyapatite to titanium.

Light and Transmission Electron Microscopy of the Intact Interfaces Between Non-submerged Titanium-coated Epoxy Resin Implants and Bone or Gingiva

Abstract: This experiment was aimed at studying the intact tissue/implant interface of non-submerged dental implants with a titanium surface. Epoxy-resin replicas were fabricated from 3.05 x 8 mm cylindrical titanium implants with a plasma-sprayed apical portion and a smooth coronal collar. The replicas were coated with a 90-120-nm-thick layer of pure titanium and autoclaved. The coated replicas were inserted as non-submerged endosseous implants in the edentulous premolar region of dog mandibles and allowed to heal for three months. Jaw sections containing the implants were processed for light and electron microscopic study of the intact tissue/implant interface with and without prior demineralization. Gingival connective tissue fibers were closely adapted to the titanium layer, in an orientation more or less parallel to the implant surface. There was no evidence of any fiber insertions into the surface irregularities of the smooth or rough titanium surface. Undemineralized bone was intimately adapted to the titanium surface without any intervening space. In demineralized sections, the collagen fibers of the bone matrix tended to be somewhat thinner and occasionally less densely packed in the vicinity of the implant surface. However, they extended all the way to the titanium surface, without any intervening fibril-free layer.

Synthesis of titanium-containing ZSM-48

Abstract: Titanium-containing ZSM-48 is synthesized with silicon to titanium ratios of 26 or larger; changes in unit cell volume and IR data show that titanium is incorporated into framework positions.

Correlation of the electrical properties of metal contacts on diamond films with the chemical nature of the metal-diamond interface. I. Gold contacts: A non-carbide-forming metal.

Abstract: The I-V characteristics of titanium contacts on polycrystalline diamond have been correlated with x-ray-photoelectron-spectroscopy (XPS) and Auger-electron-spectroscopy (AES) characterizations of the interface. As-deposited titanium contacts were rectifying in nature because of minimal interaction between as-deposited titanium and diamond as confirmed via XPS and AES. Once annealed, however, these contacts became Ohmic. The change was related to the formation of a carbide at the interface as observed by XPS. The Schottky-barrier height of the titanium contacts, which was determined by valence-band XPS, decreased from 1.3 to 0.8 eV as a result of the postdeposition annealing. It is believed that the carbide formation at the interface creates a diamond surface layer rich in electrically active defects which lower the barrier height of the metal and increase the leakage current. The interface between titanium and an argon-sputtered diamond surface was also characterized. Titanium formed as-deposited Ohmic contacts on the sputtered surface. A high density of ion-radiation-induced defects and a formation of a carbide during deposition both contributed to the Ohmic-contact formation. These contacts remained Ohmic after postdeposition annealing despite the fact that the annealing did not increase the carbide formed at the interface. It is believed that the carbide formed by the deposition of titanium behaved as a diffusion barrier to prevent the damaged layer from being annealed out into the titanium overlayer. It is concluded that most materials will yield rectifying contacts on a clean diamond surface. Ohmic contacts can be obtained by modifying the interface in some way (i.e., carbide formation, sputtering, etc.).

Hydroxyapatite coatings by a polymeric route

Abstract: A new polymeric route using calcium nitrate and phenyldichlorophosphine as initial compounds and acetone as solvent is described. Hydrolysis and subsequent oxidation with air led to the formation of a viscous solution which could be transformed to a solid polymer by subsequent drying. Calcining this polymer at temperatures in the range of 900 to 1100°C led to the formation of hydroxyapatite possessing a slightly distorted lattice. Dip-coating of alumina and titanium substrates using highly viscous solutions, or repeatedly carried out dipcoating, led to the formation of thick, highly porous hydroxyapatite layers.

Ti/Ti‐N Hf/Hf‐N and W/W‐N multilayer films with high mechanical hardness

Abstract: Ti/Ti‐N, Hf/Hf‐N, and W/W‐N multilayer films with very thin individual metal and metal‐nitride layers were developed, with hardness of the structure much higher than that of single‐layer nitride films. Hardnesses with value between 3500 and 5000 kg/mm2 or higher were observed in the multilayer films. This is an improvement over that of single‐layer metal‐nitride films where hardnesses between 2200 and 2800 kg/mm2 are typically achieved. The improvement is thought to be due to the fact that the grains are restricted to a very small size in the thin individual layers of the sandwich structure. The multilayer films, in general, have better adhesion and less defects than the single‐layer films. These films were prepared on room‐temperature substrates by a simple sputtering process and have potential applications, as in hard coatings.

Comparative Cell Culture Effects of Shape Memory Metal (Nitinol®), Nickel and Titanium: A Biocompatibility Estimation

Abstract: Nitinol® is an equiatomic alloy of nickel and titanium which has been attracting increasing interest in the field of biomedical engineering. To quantify toxicity as a preliminary evaluation of biocomp

Method for the formation of tin barrier layer with preferential (111) crystallographic orientation

Abstract: A process is described for forming, over a silicon surface, a titanium nitride barrier layer having a surface of (111) crystallographic orientation. The process comprises: depositing a first titanium layer over a silicon surface; sputtering a titanium nitride layer over the titanium layer; depositing a second titanium layer over the sputtered titanium nitride layer; and then annealing the structure in the presence of a nitrogen-bearing gas, and in the absence of an oxygen-bearing gas, to form the desired titanium nitride having a surface of (111) crystallographic orientation and a sufficient thickness to provide protection of the underlying silicon against spiking of the aluminum. When an aluminum layer is subsequently formed over the (111) oriented titanium nitride surface, the aluminum will then assume the same (111) crystallographic orientation, resulting in an aluminum layer having enhanced resistance to electromigration.