Showing papers on "Titanium published in 1991"

Characterization of DSA-type oxygen evolving electrodes: choice of a coating

Abstract: In the search for a DSA®-type electrode for oxygen evolution in acidic solutions, nine binary coatings with IrO2, RuO2, Pt as conducting component, and TiO2, ZrO2, Ta2O5 as inert oxides, have been deposited on titanium, examined for their microstructural properties and tested for their electrocatalytic activity and anodic stability. Electrochemical “true” surfaces of the coatings were found to be dependent on structure and morphology: the mixtures that form a solid solution (RuO2−TiO2), or allow limited miscibility (IrO2−TiO2), show the lowest dispersion of active material. Differences in service lives, were attributed to differences in wear mechanism of the electrodes. It was found that Ti/IrO2 (70 mol%)-Ta2O5 (30 mol%) is by far the best electrode.

Sensitivity to titanium. A cause of implant failure

Abstract: Tissues from five patients who underwent revision operations for failed total hip replacements were found to contain large quantities of particulate titanium In four cases this metal must have come from titanium alloy screws used to fix the acetabular component; in the fifth case it may also have originated from a titanium alloy femoral head Monoclonal antibody labelling showed abundant macrophages and T-lymphocytes, in the absence of B-lymphocytes, suggesting sensitisation to titanium Skin patch testing with dilute solutions of titanium salts gave negative results in all five patients However, two of them had a positive skin test to a titanium-containing ointment

Plasma-sprayed coatings of tetracalciumphosphate, hydroxyl-apatite, and alpha-TCP on titanium alloy: an interface study

Abstract: In order to study the interaction of calcium phosphate coatings with bone tissue, coated titanium cylinders with a standard size were implanted in dog femora. Coatings were made by plasma spraying powders of hydroxylapatite, beta-whitlockite, and tetracalciumphosphate particles. The plasma spraying process turns beta-whitlockite into alpha-TCP. Bone bonding and bone formation were evaluated by mechanical push-out tests and histological observations. Hydroxylapatite and tetracalciumphosphate coatings show an interface strength after 3 months of implantation of 34.3 +/- 6.5 MPa and 26.8 +/- 3.9 MPa, respectively, while alpha-TCP and blanco titanium lead to an interface strength of 10.0 +/- 3.5 MPa and 9.7 +/- 1.3 MPa, respectively. Histological examinations revealed that hydroxylapatite and tetracalciumphosphate give rise to an excellent bone formation, while alpha-TCP and blanco titanium evoked remodeling and less bone contact.

Histologic evaluation of the osseous adaptation to titanium and hydroxyapatite-coated titanium implants.

Abstract: The aim of this study was to obtain more information about the bone reaction to titanium and hydroxyapatite (HA)-coated titanium implants during the first 3 months after implantation. Therefore, uncoated and coated implants were inserted into the tibia of rabbits for various implantation periods. The histological results demonstrated that although there were no marked differences in bony reaction at the cortical level to the different implant materials, HA-coating appeared to induce more bone formation in the medullary cavity. It was also noted, that 3 months after insertion loss of coating thickness had occurred.

New high-refractive-index organic/inorganic hybrid materials from sol-gel processing

Abstract: New hybrid materials (ceramers) can be prepared by reacting titanium alkoxides with triethoxysilane-capped poly(arylene ether ketone) or poly(arylene ether sulfone). By using titanium tetraisopropoxide, a considerable increase in the refractive index can be systematically induced. Also, these new materials have an optical dispersion behavior between that of organic polymers and inorganic glasses

Problems in DSA® coating deposition by thermal decomposition

Abstract: Several DSA® coatings were prepared by thermal decomposition of metallic chloride salts on titanium base. It was shown that the painting composition does not necessarily correspond to the final coating composition. Thermogravimetric and fluorescent X-ray measurements were used to identify and characterize the material losses. It was found that IrO2, Ta2O5 and RuO2 compounds can be deposited with almost 100% yield, while SnO2 and Pt precursors give high material losses. The influence of parameters affecting the deposition yield are discussed.

Corrosion performance of some titanium-based hard coatings

Abstract: Tools and machine parts which could benefit from wear-resistant titanium-based hard films are often subject to corrosive environments. Physically vapour-deposited coatings frequently exhibit porosity and even small defects, which can cause rapid local corrosion of the substrate material; there is therefore a requirement for dense and chemically inert coatings. This paper presents corrosion data for titanium-based hard coatings such as TiN, (Ti,Al)N, Ti(B, N) and TiB2 and also for multilayered structures where additional aluminium-based insulating surface layers (AlN and Al2O3) were deposited. The corrosion resistance and porosity of the films were analysed by electrochemical techniques. The degree of metallic bonding can play a significant role in influencing the corrosion resistance of refractory transition-metal-based ceramic coatings. Here we demonstrate that, under potentiodynamic corrosion test conditions, resistance to corrosive attack was relatively poor for TiB2, better for (Ti, Al)N and Ti(B, N) and best for TiN. It is also shown that applying the additional protective aluminium-based insulating surface layers on the coating can further improve corrosion resistance.

A removal torque and histomorphometric study of commercially pure niobium and titanium implants in rabbit bone

Abstract: Screw-shaped commercially pure (c.p.) niobium and c.p. titanium implants were inserted in rabbit bone. After a healing period of 3 months, a significantly higher removal torque was demonstrated to unscrew the niobium implants (average 32.9 Ncm) compared to the c.p. titanium implants (average 25.3 Ncm). In the histomorphometric part of the study, there were no significant differences in bone-to-metal contact between the 2 implant materials. An average of 41.1% bony contact was demonstrated for the niobium screws compared to an average of 37.2% for the c.p. titanium ones. Our removal torque findings could be related to the differences that we observed between the 2 implant surfaces as indicated by SEM. Since niobium implants showed a more irregular surface topography and niobium is a softer metal than c.p. titanium, this seems the most probable reason for the differences observed in removal torque between the 2 metals. Hypothetically, a more “positive biocom-patibility” of the c.p. niobium in comparison to the c.p. titanium remains as another possible reason for the observed differences. However, against such a difference in biocompatibility between c.p. niobium and c.p. titanium, there is the very similar amount of bony contact registered 1 in the histomorphometric analysis.

Stability of protective oxide films on Ti-base alloys

Abstract: Thermodynamic calculations are performed to estimate isothermal sections of Ti-Al-O, Ti-Si-O, and Ni-Al-O phase diagrams. Very small aluminum levels (<10−10 at. %) are needed to stabilize alumina on Ni-Al alloys. However, much higher aluminum (≳50%) and silicon (≳40%) levels are needed to stabilize alumina and silica on Ti-Al and Ti-Si alloys, respectively. These calculations suggest that the mechanism of formation of the protective oxide films on titanium-based alloys is radically different from that on nickel-based alloys. The aluminum levels needed to form a continuous film of alumina on nickel-based alloys are dominated by kinetic factors. On the other hand, thermodynamic factors appear to dominate the alloy compositions needed to form protective films of alumina and silica on titanium-based alloys. Further work is needed to evaluate any possible role of kinetic factors.

Joint, a laminate, and a method of preparing a nickel-titanium alloy member surface for bonding to another layer of metal

Abstract: A joint and a laminate including a nickel-titanium alloy such as nitinol and a method for preparing the surface of a nickel-titanium alloy member for bonding solder material and, electively, another similar or dissimilar member thereto. The method includes applying an aluminum paste flux to the titanium oxide coated surface of a nickel-titanium alloy member and heating the flux to its activation temperature. The flux removes and suspends the titanium oxide therein along with leaching titanium from the base alloy member surface to form a nickel-rich interface surface. The activated flux also coats the nickel-rich interface layer for protection from further oxidation. A bonding material such as a tin-silver solder is flowed onto the nickel-rich interface surface to displace the activated flux. Electively, another member is applied to the molten solder to form a joint between the two members. The residual flux is cleaned from the joint to prevent further deterioration of the base metal. The solder joint includes the base nickel-titanium alloy metal, the nickel-rich interface surface, and the solder material. Electively, any other member may be applied to this joint in the molten state to form a metallic bond therebetween.

Material effects in fretting wear : application to iron, titanium, and aluminum alloys

Abstract: Fretting wear tests were performed on several alloys (low alloyed and stainless steels, Ti6A14V titanium alloy, 2024 and 7075 aluminum alloys) slid against themselves in air under relatively low stresses for various displacements (±15 to ±50 μm). Friction logs, where tangential force is plotted as a function of displacement and number of cycles, were used to characterize the fretting behavior of the materials. Wear scars and cross sections were characterized by optical and scanning electron microscopy. Depending on the amplitude of displacement, sticking, partial slip, or gross slip occurs at the interface. Gross slip leads to debris formation. Metallic particles are detached from localized, very highly deformed areas whose properties and structures are different from those of the initial material. Sticking is observed on titanium and aluminum alloys tested under the smallest displacement. Samples are only deformed elastically. During partial slip, cracks can initiate and propagate in titanium and aluminum alloys. Millimeters-long cracks are observed on aluminum alloys after 106 cycles. Mechanisms for crack formation and propagation are described in terms of fatigue properties.

Electrochemical synthesis and in situ Raman spectroscopy of thin films of titanium dioxide

Abstract: Raman spectra of thin films of the TiO 2 crystal modifications anatase and rutile are reported. The oxides are easily synthesized by electrochemical oxidation of titanium electrodes under controlled conditions. Evidence for the formation of a third crystal modification, possibly brookite, is presented

Formation of titanium and zirconium nitrides by mechanical alloying

Abstract: Using a novel ball mill with controlled ball movement, titanium and zirconium nitrides were synthesized by simple milling, at room temperature, of titanium and zirconium elemental powders in molecular nitrogen atmosphere The structural evolution during milling is studied using x‐ray diffractometry

Preparation of Highly Dispersed Gold on Titanium and Magnesium Oxide

Abstract: Gold could be highly dispersed on titanium oxide and magnesium oxide in their aqueous dispersion containing Mg citrate. The mean diameter of gold particles are smaller than 5nm. These gold catalysts are active for the oxidation of CO even at a temperature below 0°C. On magnesia support, Mg citrate acts not as a reducing agent but as a sticking agent which blocks the coagulation of gold particles. On titania support dispersed in neutral solution Mg2+ ions instead of citrate ions are mainly adsorbed. It is likely that Mg2+ ion suppresses the transformation of amorphous titania to anatase during calcination and prevent gold particles from coagulation caused by earthquake effect.

Titanium metal foils and method of making

Abstract: A high strength titanium alloy or titanium aluminide metal foil having improved strength and density is produced, preferably in coilable strip form, by plasma-depositing the selected titanium-based material on a receiving surface, separating the deposited material from the receiving surface to provide two metal foil preforms each having a relatively smooth side as cast against the receiving surface and a relatively rough, opposite side as deposited from the plasma, disposing the two metal preforms together with the relatively rough sides of the two metal preforms in facing engagement with each other, and squeezing the two preforms together between pressure bonding rolls to metallurgically bond the preforms to each other and to consolidate the materials of the preforms to form a fully dense metal foil.

LPCVD process for depositing titanium films for semiconductor devices

Abstract: The present invention describes a CVD process to deposit a titanium film at a high deposition rate that has excellent uniformity and step coverage while avoiding gas phase nucleation and coating of the reactor chamber walls. The vapor of a heated liquid titanium source enters a modified, plasma enhanced, cold wall reaction chamber and is mixed with H2 as it reaches a wafer substrate surface. As the gas vapors reach the heated wafer substrate a chemical reaction of TiCl4 +2H2 →Ti+4HCl is triggered, thereby depositing a uniform titanium film upon the substrate surface. The deposition rate is further enhanced by the presence of rf plasma above the substrate's surface.