Showing papers on "Titanium published in 1987"

Plasma sprayed coatings of hydroxylapatite

Abstract: The technique of plasma spraying has been applied to deposit a thin, dense layer of hydroxylapatite onto a titanium substrate. Bond strength of such apatite coatings with the substrate have been measured, as well as the (absence of) influence of the coating process on fatigue properties of the substrate. Animal studies showed similar histological reactions to apatite coatings as to (well documented) apatite bulk materials.

Hydrolysis of titanium alkoxides: modification of the molecular precursor by acetic acid

Abstract: Monolithic TiO 2 gels can be reproducibly obtained when the hydrolysis of titanium alkoxides is performed in the presence of acetic acid. This carboxilic acid does not act only as an acid catalyst, but also as a ligand and changes the alkoxide precursor at a molecular level therefore modifying the whole hydrolysis condensation process. Infra-red experiments show that bidentate acetates replace OR groups and are directly bounded to the titanium. Both, chelating and bridging acetates, are observed, leading to Ti(OR) x (Ac) y . oligomers. Hydrolysis of this new molecular precursor removes first (OR) groups and bridging acetates. Chelating acetates are still observed in the gel. They can only be removed upon heating above 200 °C.

Titanium: The implant material of today

Abstract: The use of metals for the replacement of structural components of the human body has been with us for some considerable time. The metals originally used were stainless steels which have gradually been replaced by cobalt-chromium alloys. Although titanium has been used since the late forties, it is only relatively recently that it has gained widespread interest. Titanium and its alloys are being used more and more in preference to the cobalt-chromium alloys and has broadened the field of applications. The features which make titanium such an interesting material are its excellent corrosion resistance in the biological environment, combined with an exception degree of biocompatibility which it shares with only a handful of other materials. In this review the background to the clinical use of titanium is discussed with particular attention to the biological aspects of the material. While there are now many clinical uses for titanium and its alloys their main areas of application are in the field of dentistry and orthopaedics and these are described in some detail.

The electrochemical behavior of metallic implant materials as an indicator of their biocompatibility.

Abstract: This study introduces a simple in vitro arrangement to measure current densities of implant metals. The in vivo condition of a metallic implant lying in tissues exhibiting different redox potentials is simulated in so-called straddle tests by applying a constant potential difference of 250 mV in saline containing the stable, fast-reacting redox system K4Fe(CN)6/K3Fe(CN)6. From a variety of corrosion-resistant implant metals and alloys, gold showed the highest current densities, followed by the stainless steel, the cobalt-based alloy, and the TiAIV-alloy. The pure metals titanium, niobium, and tantalum showed the lowest values. This can be explained by the stable oxide layer on these base metals, preventing an exchange of electrons and thus any redox reaction. This rating of metallic implant materials based on in vitro measurements of current densities is in good accordance with their biocompatibility rating reported from in vivo experiences. It seems that simple and cheap electrochemical tests allow an even more precise differentiation of the suitability of metallic materials for implant purposes than most of the conventional implantation tests, considering that biocompatibility is not only determined by corrosion products, but also by exchange currents and reaction products of redox processes involving tissue compounds.

The identification and characterisation of mixed oxidation states at oxidised titanium surfaces by analysis of X-ray photoelectron spectra

Abstract: The interaction of oxygen with titanium has been studied by X-ray photoelectron spectroscopy. Methods for analysing composite photoelectron spectra (curve fitting, deconvolution and spectral subtraction) are discussed and examined critically and the advantages of the ‘difference spectra’ approach highlighted. Evidence for variable oxidation states (suboxides) is obtained from an analysis of the Ti(2p) spectra observed during the formation of thin oxide films (ca. 10 A). Angular-dependent studies established that the lower oxidation states Ti2+ and Ti3+ were formed preferentially at the metal–oxide interface, whereas Ti4+ species were dominant at the oxide–gas interface. The distribution of the oxidation states within the thin oxide overlayer may be altered by thermally induced diffusion of Ti0 species from the metal substrate; the latter can occur at low temperature (ca. 200 K) for the thin oxide film regime investigated.

Characterization of acid-base properties of the hydrated oxides on iron and titanium metal surfaces

Abstract: Energy and angular resolved X-ray photoelectron spectroscopy of iron and titanium metals oxidized to produce hydroxylated oxide surfaces showed the concentration of hydroxyl to be 2.6/nm/sup 2/ for iron and 4.3/nm/sup 2/ for titanium. Exchange of the hydroxyl hydrogens with potassium ions as a function of pH was used to determine the acid strength of these surface hydroxyls. The iron and titanium surfaces, behaving as acids, were found to have pK values of 11.5 and 10.0, respectively. The more acidic nature of titanium is consistent with the higher charge/radius ratio of Ti/sup 4 +/ compared to Fe/sup 3 +/ in the respective metal oxides. The strongest chemical interaction between organic coatings and metal surfaces is considered to be via hydrogen bonding of polar groups in the coating with surface hydroxyls. On this basis, the acid strengths of the iron and titanium surfaces measured in this study and the base strength from reported phosphate exchange on iron were used to predict the relative stabilities of organic coatings containing different functional groups.

Sputtered titanium oxynitride films

Abstract: A sputtered titanium oxynitride film is disclosed, as well as a low emissivity coated article comprising a titanium oxynitride film in combination with a highly infrared reflective metal film, such as silver.

Semiconductor contact silicide/nitride process with control for silicide thickness

Abstract: A titanium silicide/titanium nitride process is disclosed wherein the thickness of the titanium nitride can be regulated with respect to the titanium silicide. In particular, a control layer is formed in the contact opening during a reactive cycle to form a relatively thin (20 to 50 angstrom) control layer. Titanium is thereafter deposited and in another thermal reaction the control layer retards the development of titanium silicide without retarding the development of titanium nitride so that the thickness of titanium silicide is kept small. A double titanium process can also be used.

Comparison of cutting performance of ion-plated NbN, ZrN, TiN and (Ti, Al)N coatings

Abstract: Three binary nitrides of the refractory materials titanium, zirconium and niobium and ternary (Ti, Al)N as well as quaternary (Ti, Al, V)N coatings were deposited by reactive triode ion plating on powder metallurgically produced high-speed steel (PM-HSS) inserts. The coated tools were then tested by dry turning of hardened and tempered AISI 4140 steel. The effect of the deposition parameters on coating properties was studied in detail. The results showed that NbN coating does not seem to improve the wear resistance in the turning of steel. Titanium-based nitride films such as TiN and (Ti, Al)N, however, appeared very suitable, as they showed increasing cutting performance and finer structures with increasing substrate current density. ZrN, however, showed the opposite effect. The best turning properties were achieved with a substrate bias of −100 V. Increasing thickness improved cutting performance almost linearly in the range from 1 to 5 μm. Substrate polishing before the deposition of the TiN layer had a strong effect, almost corresponding to doubling of the coating thickness. For example, a thickness increase from 3 to 5 μm yielded a performance improvement which could also be achieved simply by polishing the substrates carefully before coating. The three best coating materials in decreasing order of performance were ZrN, (Ti, Al)N and TiN. The differences between the best coating materials were generally not large.

Abnormalities of pulmonary function and pleural disease among titanium metal production workers.

Abstract: The authors conducted a cross-sectional survey of respiratory disease among 209 titanium metal production workers. Work in areas where there was exposure to titanium tetrachloride and titanium dioxide particulates was associated with reductions in ventilatory capacity. Pleural disease (plaques and diffuse thickening) was present in the chest radiographs of 17% of the subjects and was associated with the duration of work in titanium manufacturing. It was also associated with past asbestos exposure. After control for asbestos exposure, it remained associated with titanium manufacturing. The findings are consistent with the hypothesis that titanium tetrachloride and titanium dioxide particulates may be associated with a reduction in ventilatory capacity and that the overall process of titanium manufacturing may be associated with unexpected pleural disease.

Organometallic Route to the Chemical Vapor Deposition of Titanium Carbide Films at Exceptionally Low Temperatures

Abstract: Titanium carbide, TiC, is one of the hardest materials known (9-10 Mohs), possesses remarkable thermal stability (mp 3067/sup 0/C), and is essentially unaffected by acids and aqueous alkali. These properties make TiC a very useful material for such applications as first-wall coatings for fusion reactors. Unfortunately, crystalline TiC is also brittle, and this limits its structural applications at low temperatures. With present industrial technology, only crystalline TiC coatings can be deposited on complex shapes; the commercial process involves chemical vapor deposition from hydrogen, methane, and titanium tetrachloride at 1000/sup 0/C. More recently, plasma-assisted chemical vapor deposition techniques have been applied to the synthesis of TiC coatings, but these methods also require high temperatures, in excess of 1200/sup 0/C. They now report a simple and powerful chemical vapor deposition (CVD) method for preparing thin films of TiC using an organometallic precursor at exceptionally low temperatures (approx. 150/sup 0/C). Tetraneopentyltitanium, Ti(CH/sub 2/C(CH/sub 3/)/sub 3/)/sub 4/ was chosen for metal-organic chemical vapor deposition (MOCVD) studies since it volatilizes easily and has been reported to thermolyze at low temperature. They have devised an improved synthesis of Ti(CH/sub 2/C(CH/sub 3/)/sub 3/)/sub 4/: interaction of Ti(OCH/sub 2/CH/sub 3/)/sub 4/ with 4 equi of LiCH/sub 2/C(CH/sub 3/)/submore » 3/ in pentane followed by sublimation at 50/sup 0/C (10/sup -3/ torr) gives yellow crystals of the titanium alkyl.« less

Nature of large precipitates in titanium-containing HSLA steels

Abstract: Samples of concast Nb–V, Nb–V–Ti, and Nb–Ti steels have been examined using analytical electron microscopy. It has been shown that the addition of titanium to niobium-containing high-strength low-alloyed (HSLA) steels results in undesirable precipitation in the steels, i.e. precipitation of large precipitates with various morphologies. The composition and distribution of the large precipitates has been determined. The thermal stability of these large precipitates has been assessed by carrying out various heat treatments such as annealing at and quenching from temperatures between 1050 and 1250°C, and using heat cycles which simulate the heat affected zone in welds. It has been found that some of these large precipitates are stable up to 1150°C and some up to the melting point of the steels. The significance of these observations is discussed in terms of the addition of titanium to HSLA steels.MST/641

Structural effects on the adsorption of alcohols on titanium dioxides

Abstract: The infrared spectra of methanol, isopropanol and t-butanol adsorbed on TiO2 anatase and rutile are reported and discussed. The irreversible adsorption at room temperature is completely dissociative in all cases on rutile, while undissociatively coordinated molecules are also formed together with alkoxide groups on anatase. This shows the presence on the anatase surface of particular sites whose presence might explain the different behaviour in some surface phenomena reported in the literature of the two crystal modifications.

Cathodic Reduction of Anodic Oxide Films Formed on Titanium

Abstract: Cathodic reduction behavior of the anodic oxide film on titanium has been investigated by using ellipsometry combined with electrochemistry. In acidic sulfate solution, the anodic oxide film reductively dissolves into the solution as Ti(III) ion, resulting in the thinning of its thickness without any significant change of the optical property of the remaining film. In neutral phosphate solutiofi, the anodic oxide film absorbs hydrogen in the hydrogen evolution potential region, resulting in a change of the optical property without thinning its thickness. The amount of hydrogen absorbed per unit volume of the film does not depend on the film thickness but on the cathodic potential. The composition change estimated from measurements of anodJc charge during the hydrogen release process indicates that the hydrogen absorption begins to occu r at a b o u t -0 .25V (vs. RHE) a n d t h a t t he a n o d i c fi lm c h a n g e s in its c o m p o s i t i o n f rom TiO~ to T iOOH at -0 .9V. The h y d r o g e n a b s o r p t i o n i n d u c e s a dec rea se of t he re f rac t ive i n d e x a n d an inc rease of t h e e x t i n c t i o n i n d e x of the a n o d i c film. T i t a n i u m is o n e of t h e m a t e r i a l s e x h i b i t i n g t h e h i g h c o r r o s i o n r e s i s t i v i t y c a u s e d b y f o r m a t i o n of a p r o t e c t i v e o x i d e f i lm in o x i d a t i v e e n v i r o n m e n t s (1). H o w e v e r , if tit a n i u m is p l a c e d u n d e r c a t h o d i c b ias c o n d i t i o n s or in red u c t i v e e n v i r o n m e n t s , t h e o x i d e fi lm c h a n g e s in i ts p rop e r t y b e c a u s e of t he h y d r o g e n a t t ack . U n d e r c a t h o d i c b ias c o n d i t i o n s , h y d r o g e n is a b s o r b e d i n t o t h e t i t a n i u m m e t a l t h r o u g h a m o d i f i e d o x i d e f i lm layer , r e s u l t i n g in h y d r o g e n b r i t t l e n e s s . F u k u z u k a et al. (2) h a v e p o i n t e d ou t t h a t t h e o x i d e fi lm f o r m e d by air oxid a t i o n at e l e v a t e d t e m p e r a t u r e s ac t s as a b a r r i e r a g a i n s t t h e h y d r o g e n a b s o r p t i o n in to t h e t i t a n i u m m e t a l b u t t h a t t h e o x i d e f i lm a n o d i c a l l y f o r m e d lo se s i t s b a r r i e r p r o p e r t y d u r i n g c a t h o d i c r e d u c t i o n in a t i m e p e r i o d s h o r t e r t h a n t h a t of t h e a i r o x i d a t i o n film. D y e r et al. (3) h a v e s u g g e s t e d t h a t h y d r o g e n can be a b s o r b e d by t h e a n o d i e o x i d e f i lm in t h e h y d r o g e n e v o l u t i o n p o t e n t i a l r e g i o n a n d t h a t h y d r o g e n in t h e o x i d e f i lm c a n b e r e v e r s i b l y d e s o r b e d in t h e a n o d i c p o t e n t i a l r eg ion . T h e y o b s e r v e d , u s i n g e l l i p s o m e t r y , a s i gn i f i c an t c h a n g e of op t i c a l p rop e r t y of t h e f i lms d u r i n g t h e e l e c t r o c h e m i c a l h y d r o g e n a b s o r p t i o n d e s o r p t i o n p r o c e s s . T h e y a lso o b s e r v e d t h e e l e c t r o d e i m p e d a n c e r e s p o n s e , w h i c h c h a n g e s dep e n d i n g on t h e c a t h o d i c p o t e n t i a l (4). F o r a p h o t o e l e c t r o c h e m i c a l e l e c t r o d e of TiO.,, i t h a s b e e n r e p o r t e d t h a t t h e e l e c t r o c h e m i c a l r e d u c t i o n t r ea t m e n t m a r k e d l y i n f l u e n c e s t h e s e m i c o n d u c t i v e p r o p e r t y o f t h e TiO~, r e s u l t i n g i n a n i n c r e a s e of p h o t o r e s p o n s e c u r r e n t (5, 6). T h e h y d r o g e n a b s o r p t i o n p r o c e s s of TiO2 h a s a lso b e e n d i s c u s s e d f r o m a v i e w p o i n t of e l ee t r~ c h r o m i c r e a c t i o n s b y O h z u k u et al. (7) a n d of h y d r o g e n gas d e t e c t o r s b y H o r r i n (8). T h e s e r e s u l t s i n d i c a t e t h a t TiO~ c h a n g e s i ts co lo r a n d e l ec t r i ca l c o n d u c t i v i t y , if hyd r o g e n is a b s o r b e d in t h e TiO2. In t h i s paper , t he op t i ca l p r o p e r t y a n d c o m p o s i t i o n of t h e a n o d i c o x i d e f i lm on t i t a n i u m d u r i n g c a t h o d i c r e d u c t i o n h a s b e e n i n v e s t i g a t e d b y e l l i p s o m e t r y a n d e o u l o m e t r y . E x p e r i m e n t a l T h e t i t a n i u m e l e c t r o d e u s e d w a s a s h e e t 99.85% p u r e a n d 0.5 m m t h i c k w i t h a s m a l l t u b for e l ec t r i ca l c o n n e c t ion . T h e p r e t r e a t m e n t of t h e e l e c t r o d e was t he s a m e as t h a t d e s c r i b e d in a p r e v i o u s p a p e r (1). T h e e l e c t r o l y t e s w e r e a 0.1 m o l d m -3 su l fu r i c ac id a n d a p h o s p h a t e b u f f e r s o l u t i o n (a m i x t u r e of 0.1 m o l d m -3 Na2HPO4 a n d 0.1 mo l d m 3 NaH2PO4) p r e p a r e d f r o m analy t ica l g r a d e r e a g e n t s a n d r e d i s t i l l e d water . B e f o r e u se in e x p e r i m e n t s , t h e e l e c t r o l y t e s w e r e d e o x y g e n a t e d b y b u b b l i n g p u r i f i e d g a s e o u s n i t r o g e n in e l e c t r o l y t e r e se r vo i r s c o n n e c t e d to t he e l e c t r o c h e m i c a l cell. T h e e l l i p s o m e t e r u s e d w as of t h e h o r i z o n t a l t y p e (Mizoj i r i T y p e DV-36). T h e m a n u a l s t a n d a r d nu l l m e t h o d was a d o p t e d for m e a s u r i n g ~ a n d A w i t h a l i gh t of wavel e n g t h X = 546.1 n m at a n a n g l e of i n c i d e n c e d~ = 70.36. T h e e x p e r i m e n t a l t e m p e r a t u r e w a s 25.0 ~ -+ 0.2~ T h e p o t e n t i a l w a s m e a s u r e d in r e f e r e n c e to a Ag/AgC1 elec*Electrochemical Society Active Member. trode and converted into the reversible hydrogen electrode scale in the same solution at PH2 = 1 atm (RHE). Titanium ions dissolved into the electrolytes during cathodic reduction were analyzed by the col0rimetric method using tiron. Results Cathodic reduction in acidic solution.--Figure 1 s h o w s t h e r e s u l t of e l l i p s o m e t r i c m e a s u r e m e n t s d u r i n g t h e o p e n c i r c u i t d e c a y for 100 r a in a n d t h e f o l l o w i n g galv a n o s t a t i c r e d u c t i o n at 1 0 ~xA c m ~ of an a n o d i c o x i d e f i lm on t i t a n i u m in 0.1 too l d m 3 s u l f u r i c ac id s o l u t i o n , in which the loci of the ellipsometric parameters, ~ and h, are plotted. The original anodic oxide film, 18.0 nm thick, was formed at E = 5.65V (vs. RHE) for lh in the phosphate buffer solution at pH 6.9. The loci in Fig. 1 change with time along a theoretical line which is computed with the complex refractive indexeS of the oxide film, n,. = 2.10-0.03i, and of the titanium substrate, n, = 2.7-2.9i (i), as a function of the film thickness. The result shows that the oxide film is thinned in the acidic sulfuric solution during the open-circuit or the gaivanostatic reduc= tion without any significant change of its optical property. The decay of W and h during the open circuit for i00 rain indicated that the oxide film was thinned gradually at a rate of about 1 nm h -I in the acidic sulfate solution. The decay rate of 9 and A was found to be much higher fo r g a l v a n o s t a t i c r e d u c t i o n t h a n for o p e n c i r cu i t , w h i c h

Corrosion of metallic implants

Abstract: The human body is a mildly corrosive environment with a certain salt level and a low oxygen content. High corrosion resistance is demanded for implants to obtain biocompatibility and because even minor corrosive attack and low failure frequency are unacceptable. Degradation processes of the commonly used implant materials titanium, cobalt alloys, and 316L stainless steel are described.

Ceramic shell mold facecoat and core coating systems for investment casting of reactive metals

Abstract: An yttria-based slurry comprising a dense grain yttria powder and a non-aqueous-based binder is used as a mold facecoat and corecoat for investment casting of reactive metals such as titanium and titanium alloys.

Electroplating silicon and titanium in molten fluoride media

Abstract: The electrolytic reduction mechanisms of K2SiF6 and K2TiF6 solutions in LiF-KF and LiF-NaF-KF eutectic mixtures have been studied at temperatures between 550 and 850°C.

Temperable low emissivity and reflective windows

Abstract: The invention relates to using titanium as a protective layer on either side of a layer of silver for making temperable low emissivity windows. The titanium layers will protect the silver layer from oxidizing when the glass is heated to shape the glass. The invention also can be used to protect a layer of stainless steel when making temperable reflective windows.

Brazing of pressureless-sintered SiC using Ag-Cu-Ti alloy

Abstract: A pressureless-sintered SiC was brazed to itself using Ag-Cu alloy foil to which titanium had been added. The results obtained revealed the following. (i) Increasing the titanium addition to the base metal from 2 to 8 wt % improved the wettability greatly, but the bonding generally became weaker. (ii) With 2 wt % Ti addition, a reaction layer about 1 μm thick was formed, regardless of which brazing temperature was used, while bond strength reached was over linearly with temperature. The maximum room-temperature bend strength reached was over 350 MPa. (iii) In the case of the alloy with only 2 wt % Ti additive, bonding was greatly influenced not only by improvement of the wettability at high temperatures and longer holding times, but also the composition and thickness of the resultant reaction layer.