钛阳极氧化膜的着色研究

TA2型纯钛植入材料在葡萄糖酸钠电解液中阳极氧化可得到丰富的色彩,增强了钛植入体的美观性和功能性.分析表明:工艺参数对氧化膜质量有着重要的影响.电压是影响膜层色彩的最主要的因素,颜色随着电压的变化而发生规律性的改变.经X射线衍射分析,纯钛表面经阳极氧化处理后,其表面生成了一层非晶态的氧化钛薄膜,并且钛晶体的各个表面沿不同结晶方向的腐蚀速率不相同.通过对氧化膜层显微观察和耐蚀性研究,证明阳极氧化及热处理可大大提高钛氧化膜在模拟体液中的热力学稳定性和耐蚀性,且适当的热处理可使非晶态的钛氧化膜转化为稳定的二氧化钛.     

PbTiO3 sol-gel process studied by207Pb-NMR,IR, DTA and XRD

PbTiO₃ film and powder materials have been obtained from a sol prepared at room temperature by mixing lead(II) acetate trihydrate (LAT) and tetraisopropylorthotitanate (TPOT) in methoxyethanol. The sol-gel process was studied by means of²⁰⁷Pb nuclear magnetic resonance and infrared spectroscopy, differential thermal analysis and X-ray diffraction measurements. This investigation shows that an interaction between LAT and TPOT occurs immediately on mixing in solution and, as a result of the interaction, the lead and titanium compounds are indistinctly linked togetherthrough bidentate acetate bridging. This linkage remains unchanged during solution reactions and gelation, Pb-O-Ti bonding being absent at this stage. Pb-O-Ti bonding in the sol-gel materials is believed to be first formed between 200 and 350 °C during the decomposition of the OAc group of LAT and its removal from the gel. The gel retains its amorphous state on heating at 370 °C for 1 h. An unidentified primary crystal phase appears after heating the gel at 400 °C for 1 h, and it is transformed into perovskite PbTiO₃ crystals at 500 °C and higher temperatures.     

van der Waals epitaxy of MoS₂ layers using graphene as growth templates

We present a method for synthesizing MoS(2)/Graphene hybrid heterostructures with a growth template of graphene-covered Cu foil. Compared to other recent reports, (1, 2) a much lower growth temperature of 400 °C is required for this procedure. The chemical vapor deposition of MoS(2) on the graphene surface gives rise to single crystalline hexagonal flakes with a typical lateral size ranging from several hundred nanometers to several micrometers. The precursor (ammonium thiomolybdate) together with solvent was transported to graphene surface by a carrier gas at room temperature, which was then followed by post annealing. At an elevated temperature, the precursor self-assembles to form MoS(2) flakes epitaxially on the graphene surface via thermal decomposition. With higher amount of precursor delivered onto the graphene surface, a continuous MoS(2) film on graphene can be obtained. This simple chemical vapor deposition method provides a unique approach for the synthesis of graphene heterostructures and surface functionalization of graphene. The synthesized two-dimensional MoS(2)/Graphene hybrids possess great potential toward the development of new optical and electronic devices as well as a wide variety of newly synthesizable compounds for catalysts.     

Thermogravimetric–differential thermal analysis of the solid-state decomposition of ammonium tetrathiomolybdate during heating in argon

The formation of MoS2 by thermal decomposition of ammonium tetrathiomolybdate (ATT) solids under an argon atmosphere has been studied by simultaneous thermogravimetric and differential thermal analysis. The sequential products for the decomposition upon heating to 700 °C is ATT (hydrated)(NH4)2MoS4(NH4)HMoS4H2MoS4MoS3 Mo2S5MoS2. MoS2 forms between 230 and 260 °C and remains stable up to about 360 °C when it tends to be oxidized by residual oxygen, if present in the atmosphere. These findings suggest that the synthesis of MoS2 from (NH4)2MoS4 via formation of MoS3 is not a direct process, as previously reported, but rather a complex process involving a number of intermediate products (NH4)HMoS4, H2MoS4 and Mo2S5 which have not been reported before. That these products are only specific to the very narrow temperature regimes as revealed suggests that they are very unstable and short lived, that their presence is transient in nature and thus that ex-situ characterization of them is normally difficult. The presence of these intermediate products, as justified experimentally, is further interpreted in terms of their mutual structural similarities which improve understanding as to why MoS2 can usually be prepared from ATT by thermal decomposition, as in this case, or by other techniques, such as anodizing. Laminar morphology of MoS2 is revealed by transmission electron microscopy and its crystal structure examined by selected-area diffraction. Further ex-situ examination by X-ray photoelectron spectroscopy of this end product supports the feasibility of preparing MoS2 from aqueous solutions by anodizing. © 1998 Kluwer Academic Publishers     

Formation of amorphous anodic oxide films of controlled composition on aluminium alloys

Binary, non-equilibrium Al-29at%Nb, Al-44at%Ta, Al-19at%Ti, Al-25at%Ti and Al-32at%Zr alloys were prepared by magnetron sputtering and subsequently anodized at high Faradaic efficiency to grow barrier-type anodic films. Examination in the transmission electron microscope revealed amorphous anodic films of relatively uniform compositions across the film thicknesses, except for a layer of relatively pure alumina, of about 5% of the film thickness, present at the film/electrolyte interface of the Al-Ta alloy. The film compositions, from Rutherford backscattering spectroscopy, indicate that the alloy constituents are oxidized in their alloy proportions to form films comprising intimately mixed units of the various oxides, namely alumina, niobia, titania, tantala and zirconia. The films grow by co-operative transport of metal and oxygen ions under the electric field with formation of film material by both migration of metal ions outwards and of oxygen, and possibly hydroxyl, ions inwards. The average migration rates of Al³⁺, Nb⁵⁺, Ti⁴⁺ and Zr⁴⁺ ions are similar, to within 10%, but Ta⁵⁺ ions migrate more slowly than Al³⁺ ions. The results of the study show that a wide range of compositions of amorphous oxide films can be readily formed by anodic oxidation of appropriate alloys, including compositions containing units of normally crystalline anodic oxides, namely TiO₂ and ZrO₂.     

Formation of porous anodic alumina in alkaline borate electrolyte

The growth of porous anodic films at 60 V in an alkaline 0.13 M borax electrolyte at 333 K is examined using sputtering-deposited aluminium substrates, with a fine band of incorporated tungsten tracer. The findings reveal amorphous alumina films containing approximately conical major pores incorporating finer secondary pores, with film thicknesses similar to that of the oxidized aluminium. Further, the distribution of the tungsten tracer within the film is mainly consistent with its expected migration behaviour in anodic alumina. The results indicate that pore development under the present growth conditions is dominated by field-assisted dissolution of anodic alumina, with an efficiency of film growth of about 50%. The findings are in contrast with those of porous anodic films formed in phosphoric acid electrolyte, which are significantly thicker than the layer of oxidized metal.     

Low-temperature synthesis of leucite crystals using kaolin

Synthesis of leucite crystals below 1000 °C using natural kaolin as the primary raw material was investigated. Spherical leucite crystals having a diameter of approximately 50 μm were prepared by heating a powder mixture of Al₂(SO₄)₃, kaolin and K₂SO₄ (in mass ratios of 3:3:15) at 900 °C for 3 h. Quartz, the main accessory phase in kaolin, and the amorphous metakaolin formed upon heating kaolin were found to be responsible for the decreased synthesis temperature.     

Crystallization behavior and resistance change in eutectic Si15Te85 amorphous films

Crystallization process and the corresponding electrical resistance change were investigated in eutectic Si₁₅Te₈₅ amorphous thin films. The Si₁₅Te₈₅ amorphous film showed two-stage crystallization process upon heating. In the first stage, the Si₁₅Te₈₅ amorphous crystallized into Te crystals at 175 °C. In the second stage, the residual amorphous phase crystallized into Si₂Te₃ crystals at above 300 °C accompanying the resistance drop. Before the second crystallization, the electrical resistance once increased in the temperature range of about 250-295 °C. This phenomenon can be explained by considering the formation of amorphous phase with a high electrical resistivity.     

Formation of hydroxyapatite on low Young's modulus Ti–30Nb–1Fe–1Hf alloy via anodic oxidation and hydrothermal treatment

Hydroxyapatite (HA) on the Ti–30Nb–1Fe–1Hf alloy has been fabricated via anodic oxidation followed with the hydrothermal treatment. The anodic oxide film (AOF) containing Ca and P was formed by anodic oxidation in a solution consisting of β-glycerophosphate disodium pentahydrate(β-GP), and calcium acetate monohydrate(CA). The AOF was formed by a 2-stage growth: (1) a thin oxide film that intimately contacted the substrate formed prior to sparking; (2) after sparking, the thickness of AOF increased rapidly, accompanying with the formation of numerous craters in the AOF. When anodizing to 300 V, the AOF had a glassy amorphous structure. Increasing anodizing potential increased the Ca/P ratio and contents of Ca and P, but decreased the adhesion strength between the AOF and the substrate. After 6 h of hydrothermal treatment at 250 °C, a great number of crystalline HA precipitated on the surface of AOF anodized to 300 V. The shapes and population density of HA crystals can be controlled by modifying the anodizing potential and the solution pH of hydrothermal treatment. Increasing the pH of the solution in hydrothermal treatment enhanced the precipitation of HA crystals. Numerous needle-like HA crystals that nearly covered the surface of AOF were obtained when hydrothermally treated in the pH 13 solution.     

XRD, TEM, IR and 29Si MAS NMR characterization of NiO-SiO2 nanocomposites

The present study focuses on the structural properties of a NiO-SiO₂nanocomposite with 14 mol % of nickel oxide obtained by a sol-gel method and a gradual heating the gel in the 350–900°C range. NiO nanoparticles and their dispersion in the amorphous silica matrix were studied through TEM and XRD. The behaviour at the nanoparticle/matrix interface was investigated through IR and ²⁹Si MAS NMR spectroscopy comparing the spectra of the nanocomposite with that of a silica sample obtained with the same preparation method and submitted to the same thermal treatments. The results indicate that nanoparticles, formed in cavities of the silica matrix, act as an obstacle towards the spontaneous silica polymerization process with heat treatments.     

Formation of new carbides with diamond structure from carbon film containing transition metal

New carbide crystallites, which have a solid-solution phase with diamond structure, were formed from amorphous carbon film containing a transition metal such as Fe, Co, Mo or Ti by vacuum heating at 500-800 °C. The lattice constants for each solid-solution phase have been determined from electron diffraction patterns and high-resolution transmission electron microscope images. The formation of carbon polymorphs has been summarized as being dependent on the heat treatment temperature.     

Preparation of nanocomposite materials containing WS2, δ-WN,Fe3O4, or Fe9S10 in a silica aerogel host

Nanocomposite materials based on silica aerogel hosts have been produced using chemical vapour infiltration/decomposition methods and characterized by X-ray diffraction and electron microscopy. Amorphous tungsten in SiO₂ aerogel was formed by the decomposition of W(CO)₆ at 250 °C. Alternatively, reaction of this material with sulphur at 700 °C produced needle-shaped WS₂ crystals with lengths ranging from 25–230 nm. Reaction of the W/SiO₂ composite with anhydrous NH₃ formed crystals of -WN with diameters of 1–5 nm. Fe(CO)₅ is readily absorbed into the silica aerogel, forming an amorphous iron oxide/SiO₂ composite after slow oxidation in air. Treatment of this material with additional Fe(CO)₅ produced an Fe₃O₄/SiO₂ aerogel composite. Fe₃O₄ particle sizes were 20–55 nm. After additional heat treatment, this composite exhibited soft ferromagnetic behaviour with a coercivity of 170 Oe. Fe₉S₁₀ crystals with diameters of 30–90 nm were formed by the reaction of the amorphous iron oxide/SiO₂ composite with H₂S at 900 °C.     

Anodic film formation on high strength aluminium alloy FVS0812

Barrier-type film growth on the high strength aluminium alloy FVS0812 has been studied by a combination of transmission electron microscopy and Rutherford backscattering spectroscopy. The film is composed mainly of amorphous anodic alumina, but is contaminated with iron species incorporated into the film from the alloy. The film may also be contaminated with silicon and vanadium species at levels below the detection limit of the present experiments. The contaminant species are primarily incorporated locally into the film during oxidation of Al₁₃(Fe, V)₃Si dispersoids and the resulting film material is of reduced resistivity compared with anodic alumina of high purity. As a consequence of the presence of regions of film material of differing resistivities, the film is of irregular thickness. The average thickness corresponds to a nm/V ratio of about 1.3. Iron species incorporated into the film migrate outwards at roughly 2.1 times the rate of Al³⁺ ions. The iron species are not ejected in significant amounts to the electrolyte on reaching the film/electrolyte interface and hence, a thin layer of film material highly enriched in iron species develops at the film surface. The layer may also be enriched in vanadium species, if these are incorporated into the film and migrate more rapidly than Al³⁺ ions. Enrichment of iron, and possibly other alloying element atoms, is found in a thin layer of alloy immediately beneath the anodic film, paralleling enrichments of alloying element atoms found following anodic oxidation of other aluminium alloys. The enrichments at both the alloy/film and film/electrolyte interfaces do not appear to be continuous across the macroscopic surface of the specimens, probably due to the non-uniformity of film growth on the two-phase substrate. The maximum voltage for the selected conditions of anodizing was limited to 68 V as a result of oxygen generation at flaws which are present extensively in the anodic film. This revised version was published online in November 2006 with corrections to the Cover Date.     

Synthesis of anodic films in the presence of aniline and TiO2 nanoparticles on AA2024-T3 aluminium alloy

Coatings, comprising an inner porous anodic alumina film and an outer polyaniline/TiO₂ nanoparticle layer, were electrochemically synthesised on an AA2024-T3 aluminium alloy by single-step, anodic polarisation in an oxalic acid-based electrolyte. The morphology and composition of the coatings were examined by TEM, SEM and XPS, with the size and zeta-potential of the TiO₂ nanoparticles in the oxalic acid solution also measured. Observation of the growth of the coating during of anodic polarisation revealed that a distinct, two-layered coating is formed from the early stages of polarisation, with the anodic film forming at a constant rate and the outer layer developing at a rate that decreases markedly with times beyond about 30 min. Nanoparticles, agglomerated in the electrolyte, migrate to the anode due to the negative zeta-potential and form the nanoparticle-containing layer at the surface of anodic film. Such particles are not incorporated in the pores due to agglomeration and disordered film porosity at the outer layer of the anodic film.     

Growth of large-area and highly crystalline MoS2 thin layers on insulating substrates

The two-dimensional layer of molybdenum disulfide (MoS(2)) has recently attracted much interest due to its direct-gap property and potential applications in optoelectronics and energy harvesting. However, the synthetic approach to obtain high-quality and large-area MoS(2) atomic thin layers is still rare. Here we report that the high-temperature annealing of a thermally decomposed ammonium thiomolybdate layer in the presence of sulfur can produce large-area MoS(2) thin layers with superior electrical performance on insulating substrates. Spectroscopic and microscopic results reveal that the synthesized MoS(2) sheets are highly crystalline. The electron mobility of the bottom-gate transistor devices made of the synthesized MoS(2) layer is comparable with those of the micromechanically exfoliated thin sheets from MoS(2) crystals. This synthetic approach is simple, scalable, and applicable to other transition metal dichalcogenides. Meanwhile, the obtained MoS(2) films are transferable to arbitrary substrates, providing great opportunities to make layered composites by stacking various atomically thin layers.     

Thermal and X-ray studies of the pyrolysis process for bismuth-substituted iron garnet films

The thermal decomposition and crystallization processes of two types of films with various thicknesses prepared by spin-coating aqueous and acetylacetonic solutions made by dissolving metal nitrate hydrates of appropriate ratios for the garnets, are described. It was found that the aqueous films decomposed with endothermic reactions over a broad temperature range from 80–500 °C, while the acetylacetonic films decomposed at two strong exothermic reactions at temperatures of 130 °C and 250 °–400 °C. Both films decomposed to become amorphous oxides, which then began to crystallize at a temperature of about 600 °C. It was also found that when the amorphous oxide films were thinner than 0.3 m, the garnets were formed directly from the amorphous oxides. When the films were thicker than 0.3 m, intermediate orthoferrites were formed which, upon further heating, transformed to the garnets. Differential thermal analysis, thermogravimetry, and X-ray diffraction data in the temperature range 20–750 °C are given and discussed.     

Aluminium titanate formation by the gas-phase hydropyrolysis method

A novel process of aluminium titanate formation by thermal decomposition of an aqueous nitric-hydrofluoric solution containing stoichiometric amounts of aluminium and titanium is described. The solution is decomposed by spraying it into a heated reactor with subsequent oxide formation and recycling of the corresponding nitric and hydrofluoric acids by means of an absorption system. The oxides formed were mostly amorphous, in a fine dispersed, homogeneously distributed form of highly reactive state. X-ray (RDA) analysis showed crystalline forms of TiO₂ (anatase), complex titanium oxides, such as Ti₃O₅, Al₂TiO₅ (tialite) and AlO(OH) (boehmite). Complete formation of tialite from this oxide mixture was studied by thermogravimetry, differential thermogravimetry and differential thermal analysis. RDA of compounds formed after the successive and stepwise heating of this powder in a muffle helped in the understanding of tialite formation. The reaction was found to be time dependent and to be completed at 1400° C. Decomposition of the tialite formed into Al₂O₃ (corundum) and TiO₂ (rutile) was observed in the temperature range 900 to 1070° C.     

Hydrothermal precipitation of hydroxyapatite on anodic titanium oxide films containing Ca and P

Highly-crystallized hydroxyapatite (HA) can be precipitated during heat treatment in high-pressure steam at 300 °C on an anodic titanium oxide film containing Ca and P (AOFCP), which has been electrochemically formed on a titanium substrate prior to the hydrothermal treatment. Factors affecting the precipitation, such as a percentage of distilled water in the autoclave and additives in the AOFCP, were evaluated by scanning electron microscopy. Ca²⁺ and PO^3– ₄ ions were leached from the AOFCP into a water layer covering the film surface, and nucleate HA heterogeneously on the porous TiO₂ matrix of the AOFCP which was made by the ion leaching. The morphology of the precipitated crystals was significantly affected by the water volume ratio because the concentrations of the Ca²⁺ and PO₄ ^3– ions varied depending on the thickness of the water layer. The amount of the precipitation decreased on the AOFCP which was formed in the solution containing a small amount of Mg²⁺ ions or formed on Ti-6Al-4V alloy instead of titanium.     

Synthesis of yttrium iron garnet precursor particles by homogeneous precipitation

Yttrium iron garnet (YIG) precursor particles were obtained by homogeneous precipitation in a nitrate salt solution by a reaction involving the thermal decomposition of urea. Chemical analysis indicated that solid phases were initially precipitated with sequential iron ion content. The precipitate formed was an amorphous mixed iron oxide phase. The complex composition and the thermal decomposition of the precipitate were studied by thermogravimetry-differential thermal analysis, differential scanning calorimetry, X-ray diffraction, and Fourier transform-infrared spectroscopy. Precipitate morphology was observed by SEM and TEM. Fine-grained single-phase yttrium iron garnet (YIG:Y₃Fe₅O₁₂) powders were obtained by calcination of the precipitate at 1200 °C. YFeO₃ intermediate compound was formed at 600 °C prior to the final crystallization of YIG.     

Nanostructured ZnO network films deposited on Al2O3 substrates by chemical bath deposition

Nanostructured ZnO network films have been fabricated on Al₂O₃ substrates by the combination of chemical bath deposition and thermal decomposition process. Layered basic zinc nitrate (LBZN) network films were deposited on the Al₂O₃ substrates with LBZN crystal seeds in methanol solution of zinc nitrate hexahydrate and hexamethylenetetramine. The LBZN precursor films were then transformed into nanostructured ZnO films by heating at 260 °C in air. During the thermal decomposition process abnormal exothermic heat effect was observed at 200-210 °C and CH₃ groups were found in the as-deposited films. We propose that methanol molecules are integrated in the LBZN films forming LBZN-CH₃OH complex and that the heat effect comes from the exothermic release of the methanol.