晶粒大小对钛硅分子筛TS-1催化氧化活性的影响

采用改进后的水热晶化法合成了TS-1分子筛,研究了凝胶pH值、硅源类型对TS-1分子筛晶粒度、晶化动力学及其催化氧化性能的影响.结果表明,选择有机硅源并采用较高的凝胶pH值有利于合成晶粒较小的TS-1分子筛.有机硅源TEOS与无机硅源的晶体生长活化能的显著差异决定了合成TS-1分子筛晶粒度大小的不同.TS-1催化的氧化反应受分子筛孔内扩散的限制,晶粒越小,表面利用率越高,因而其催化氧化活性越高.     

Synthesis of TiB2 powder from a mixture of TiN and amorphous boron

TiB₂ powder was synthesized by solid state reaction using amorphous boron and TiN as a source of titanium. The TiB₂ formation did not occur at all in a nitrogen atmosphere even at 1400° C. TiB₂ formed above 1100° C in argon and hydrogen atmospheres. The only crystalline phase of TiB₂ powder was favourably synthesized at 1400° C for 360 min in an argon atmosphere from a starting powder with a composition containing excess boron (B/Ti = 2.2). The synthesized powder was well dispersed and had a particle size of 0.5 to 2 µm. The powder activity was evaluated by sintering at 4 G Pa and 1300 to 1600° C for 15 min.     

Synthesis and catalytic ammoxidation performance of hierarchical TS-1 prepared by steam-assisted dry gel conversion method: the effect of TPAOH amount

The hierarchical titanium silicalite-1 (TS-1) was synthesized by the steam-assisted dry gel conversion method in one step and characterized by XRD, SEM, N₂ adsorption/desorption, UV–Vis, FT-IR, and Raman spectroscopies. And its catalytic activity was tested for ammoxidation of methyl ethyl ketone with hydrogen peroxide as oxidant. The results show that the amount of tetrapropylammonium hydroxide (TPAOH) as template has a major influence on the physicochemical and catalytic properties of the hierarchical TS-1 prepared. When lower amount of TPAOH (TPAOH/SiO₂ = 0.08 mol) was used, hierarchical TS-1 can be successfully synthesized. With an increase in TPAOH amount in synthesis solution, the crystal size of TS-1 is decreased and mesoporous surface area is increased; if the excess template was used in the synthesis of TS-1, more extra-framework Ti would be formed in the TS-1 samples prepared. The hierarchical TS-1 exhibits higher catalytic activity than TS-1 prepared hydrothermally for ammoxidation of methyl ethyl ketone. Using hierarchical TS-1 synthesized under TPAOH/SiO₂ = 0.18 as the catalyst, which has more tetrahedrally coordinated Ti species in the TS-1 framework, 94.2 % conversion of reactant and 100 % selectivity to methyl ethyl ketone oxime can be obtained after 2 h of reaction at 70 °C.     

Epitaxial growth of titanium oxide thin films on MgO(100) single-crystal substrates by reactive deposition methods

We synthesized titanium oxide thin films on MgO(100) single-crystal substrates by two reactive deposition methods and compared the structures of the thin films formed by these methods. In one method (pulsed-molecular-beam deposition method), molecular oxygen is supplied to the substrates by using a pulsed-molecular-oxygen beam source and deposition of one unit layer of titanium and subsequent supply of molecular oxygen are repeatedly performed. In the other method (radical beam deposition method), atomic oxygen is irradiated to the substrates by using an atomic oxygen beam generated by the radical beam source and irradiation of the atomic oxygen and deposition of titanium are simultaneously performed. In the case of the pulsed-molecular-beam deposition method, the crystal structure was changed by increasing the number of oxygen pulses supplied from the beam source. We found that the crystal structure of titanium oxide depended on the composition ratio of O:Ti in the film. The maximum ratio of O:Ti attainable by this method was 1.85, and at this ratio, (100)-oriented pseudorutile was formed. In the case of the radical beam deposition method, (100)-oriented anatase was formed below the titanium deposition rate of 0.10 nm/s and pseudorutile (TiO_2−δ) was formed above 0.15 nm/s. The pseudorutile structure synthesized on this experiment was very stable in air. We concluded that the crystal structure of the pseudorutile is a new crystal structure of titanium oxide.     

Transformation of microporous titanium glycolate nanorods into mesoporous anatase titania nanorods by hot water treatment

High surface area titanium glycolate microporous multi-faceted nanorods were synthesized from the reaction of titanium alkoxides (Ti(OEt)₄, Ti(O ⁱ Pr)₄, or Ti(O ⁿ Bu)₄) with ethylene glycol, using a sol–gel reflux method. The specific surface area of the as-synthesized titanium glycolate nanorods obtained from Ti(OEt)₄ is ~480 m²/g. A hot water treatment at 90 °C for 1 h transformed the titanium glycolate microporous nanorods into mesoporous anatase TiO₂ nanorods. The shape of the nanorods was conserved after hot water treatment and the microporous to mesoporous transformation took place without significant change in the surface area (477 m²/g). Micro Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, solid state NMR, and nitrogen adsorption/desorption were used to characterize the samples. As a demonstration of potential applications, the thus formed mesoporous anatase TiO₂ nanorods were tested for their photocatalytic efficiency in the degradation of crystal violet, and a photodegradation mechanism is proposed.     

Ion beam nitriding of titanium and titanium alloy

Titanium and Ti8A/1Mo1V alloy have been nitrided with an ion beam source of nitrogen or agon and nitrogen, at a total pressure of 2?10×10^?4 torr. The treated surface has been characterized by surface profilometry, X-ray diffractometry, Auger Electron Spectroscopy (AES), and microhardness measurements. It was found that tetragonal Ti₂N phase forms in pure titanium and Ti8A/2Mo1V alloy with traces of AIN in the alloy. Two opposite processes were found to compete during the ion beam nitriding: (a) formation of nitrides in the surface layers; (b) sputtering of the nitrided layers by the ion beam. The highest surface hardness, of about 500 kg mm^?2 in titanium and 800 kg mm^?2 in Ti8A/1Mo1V, was obtained by nitriding with an ion beam of pure nitrogen at 4.2×10^?4 torr, at beam voltage of 1000 V.     

13C and 29Si n.m.r. characterization of silicalite-1, silicalite-2, and highly siliceous ZSM-48 zeolites containing tetraalkylammonium bromide,hexamethonium bromide,and diaminododecane,in the presence of fluoride ions

Silica gels containing tetraalkylammonium bromide (TAA), hexamethonium (HM) bromide, and 1,2-diaminododecane (DADD) have been prepared in fluoride medium: 10 NaF  (x TAABr  y HMBr₂  z DADD)  10 SiO₂  330 H₂O with x + y + z = 1.25. TAA = tetramethyl-, tetraethyl-, tetrapropyl-, and tetrabutylammonium. Silicalite-1 (with TPA), silicalite-2 (with TBA), and ZSM-48 (with DADD) are the crystalline zeolites. TPA is preferentially occluded in silicalite-1, TBA in silicalite-2, and DADD in ZSM-48. However, HM and DADD are also occluded in minor amounts in silicalite-2, and some HM is always present in the channels of ZSM-48.     

水体系自组装法制备钛酸锂纳米负极材料研究

以偏钛酸粉末作为钛源,制备钛酸锂(Li4Ti5O12)纳米材料,Li4Ti5O12由含锂过氧化钛配合物分解自组装后经煅烧结晶而得。采用X射线衍射、扫描电子显微镜、氮气吸附-脱附和恒流充放电测试对材料结构、形貌和电化学性能进行表征。结果表明:水体系下,锂钛摩尔比为4∶5、于600℃煅烧5h得到的Li4Ti5O12纳米球颗粒粒径在500nm左右,且具有丰富的孔隙,比表面积达到22.947m2/g;在电流密度4000mA/g条件下,比容量为157mAh/g,电流密度500mA/g下循环400次放电容量保持率为95.2%。表明水体系自组装形成的Li4Ti5O12纳米负极材料可以缩短锂离子迁移距离,其多孔性可以增大电解液与电极活性材料的接触面积,使离子电子传输速率同时得到提高,从而获得优异的电化学性能。     

Effect of surface alteration of hydride titanium washers on discharge characteristics of plasma gun

Several titanium (Ti) hydride washers containing different amounts of both TiN and an oxide compound (Ox) are tested for the source of hydrogen (H⁺) plasmas. According to the different-looking surfaces of the washers of Ti hydride, considerable change in the required discharge voltage is observed. Slightly larger probe currents are also measured from plasmas produced with the washers having the smallest amounts of TiN and Ox, which suggests the existence of more H⁺ ions in the formed plasmas. Once apparent grain coarsening appears on the surface of Ti hydride washers at the temperature around 950°C, no successful electric discharge occurred.     

Study of the Ti/Al2O3 interface

The Ti/Al₂O₃ (1 ¯1 0 2) interface formation has been investigated by X-ray photoelectron spectroscopy and Auger electron spectroscopy (AES). The results showed that when an active metal titanium was evaporated on to a room-temperature Al₂O₃ (1 ¯ 1 0 2) surface in ultrahigh vaccum, a Ti/Al₂O₃ interface region of about 200 nm was formed, and in the first several monolayers of titanium, the titanium was oxidized due to the active oxygen anions on the surface. Therefore, the pure Ti/Al₂O₃ interface was replaced gradually by a titanium oxides/Al₂O₃ interface, which has a stronger interaction than the former. The change of shape of the photoemission lines and the shift of binding energy of aluminium, oxygen and titanium with increasing coverage of titanium showed that the formation of the Ti-O bond at the interface is due to titanium transferring its electrons to Al³⁺ via O^2– anions in the Al-O bond, whereby the Al³⁺ was reduced to metallic aluminium, Al⁰. The AES intensity profile also proved the existence of the reduced species Al⁰. This suggests that the reaction layer consists of a multiphasic mixture: the Ti-O type phase, the (Ti, Al)₂O₃ phase and metallic aluminium phase.     

Effect of Ti concentration on the structure and texture of SiTiOC glasses

Five different silicon–titanium organic–inorganic hybrid materials were prepared by the reaction of tetraethoxysilane, titanium tetrabutoxide and silanol-terminated polydimethylsiloxane. Si–Ti oxycarbide glasses were prepared by pyrolysis of the hybrid materials in nitrogen atmosphere in the range of 400 to 1500 °C. The obtained Si–Ti oxycarbide materials were characterized by Fourier Transform-Infra Red spectroscopy, X-ray-diffraction, mercury porosimetry and SEM.The study indicated that the reactivity towards water increases up to 1000 °C, at higher temperatures it decreases for all samples. During the pyrolysis, Ti atoms were incorporated into the silicate network leading to the formation of Si–Ti oxycarbide glasses, except with sample containing 7% of Ti which presented also the formation of β-SiC and TiC crystalline phases.The porosity was increased up to 600 °C and then decreased tending to disappear at 1500 °C. When the titanium concentration increased from 1 to 3% in the oxycarbide glass, the porosity decreased; for higher concentration, an increase in the porosity was observed.     

Synthesis of mesoporous silicon directly from silicalite-1 single crystals and its response to thermal diffusion of ZnO clusters

This article describes the preparation of mesoporous silicon granules with a layered structure directly from silicalite-1 single crystals. The silicalite-1 single crystals were thermally reduced in vacuum at 630 °C, with the original shape retained. The samples are confirmed as crystalline silicon by X-ray diffraction and transmission electron microscope. The silicon granule is composed of a monocrystalline surface and polycrystalline layered interior. A surface area of around 66 m² g⁻¹ and the pore size centered at 3.7 nm were obtained from nitrogen porosimetry, BET and BJH analysis. The ZnO clusters have been loaded into the porous silicon granule by thermal diffusion method. The photoluminescence emission centered at 3.44 eV originates from the small particles of ZnO and the band at 2.81 eV may be due to both an oxidized surface and quantum confinement effects. The microstructure in this silicon granule is very different from those in etched samples. The synthetic design demonstrates an interesting way from the microporous zeolite to mesoporous silicon and enlarges the structural diversity of porous silicon crystal.     

A metallurgical study of the contamination zone at the surface of dental Ti castings, due to the phosphate-bonded investment material: the protection efficacy of a ceramic coating

Commercial pure (cp) titanium exhibits remarkable advantages compared to conventional dental alloys, mostly in the fields of biocompatibility and corrosion resistance. Today there exist very optimistic perspectives for the use of titanium as an ideal alternative for the conventional dental alloys. However, titanium casting procedure shows some serious difficulties related mainly with its high melting point and its great chemical reactivity at high temperatures. As a result, an extensive contamination is observed in Ti castings when SiO₂-based investment materials are used (phosphate-bonded or silica-bonded). In the present work, a detailed metallurgical study of the contamination zone of Ti castings due to Si, P and O, was performed. The new phases which formed, were investigated and analyzed using mainly light and scanning electron microscopy, as well as energy dispersion spectrometry. These phases were found to be: -Ti, -Ti and a Ti-Si compound. An attempt was done to prevent the contamination of cast Ti by using a wax pattern coating technique. The protection efficacy of a ZrO₂ coating was proven. Ti castings without contamination were obtained in this way.     

钛合金表面磁控溅射离子渗镀铜的烧蚀特性研究

针对一定条件下钛合金的易燃以及在双层辉光离子渗铜中铜源极易熔的问题,采用了磁控溅射的技术,在Ti6Al4V的表面进行铜元素的渗镀,形成的Ti-Cu阻燃合金层以提高其阻燃性能.研究溅射功率、溅射时间、工作气压等工艺参数对铜渗镀层厚度的影响后,发现0.6 Pa的工作气压、180 W的溅射功率、3 h的溅射时间为优化工艺参数.XRD结构分析表明,Ti6Al4V样品表面形成了含CuTi2相的合金层;激光烧蚀实验表明,钛合金渗铜层的阻燃性能提高了2倍以上,但表面纯铜薄膜层对阻燃性能没有帮助.     

Synthesis and characterization of nm-sized PbTiO3 crystallites

In this work attempt is made to synthesize PbTiO₃(PT) nanopowder by low temperature direct synthesis (LTDS) method already introduced by Wada et al. [8]. Various samples were prepared by precipitating a strong acidic Ti-bearing solution in an alkaline solution obtained by dissolution of Pb(NO₃)₂ in a KOH solution (pH = 14). The samples were synthesized with varying Pb/Ti atomic ratios (1.0, 2.7, 6.5 and 10) at 70 ^∘C. XRD, TEM, FTIR and DTA/TG techniques were utilized to characterize the obtained powders. The formation of single phase PT was not confirmed for the non-heat treated as precipitated samples in contrast with the results obtained by Wada et al. [8] for BaTiO₃. Further, for the as precipitated samples not subjected to washing process with a Pb/Ti ratio above 1, the formation of unknown crystalline phase/s was detected due to the reaction taken place between Ti-bearing solution and potassium plumbate formed by dissolution of Pb(NO₃)₂ in KOH solution. Applying washing process for these samples gave rise to the partial destruction of the observed structure/s and the formation of an amorphous phase as confirmed by XRD and TEM results. However, calcination of the as precipitated/washed samples at 500 ^∘C and 700 ^∘C for 1 hour gave rise to the formation of PT nanopowder as the main phase with average crystallite sizes in the range of about 11–14.5 nm respectively. Single phase PT nanopowder of an average crystallite size of 13 nm was formed for the sample with a Pb/Ti ratio = 1 when calcined at 500 ^∘C for 1 hour. For the calcined samples with Pb/Ti ratios above 1 the formation of PbO as the second phase, however, was also detected and its level of formation was found to be related to the Pb/Ti ratio.     

Re-crystallization of silicalite-1 crystals from a crystalline layered silicate using nanosized seeds

Crystallization of silicalite-1 guided by nanosized seeds has been carried out from a crystalline layered silicate. The crystallization process was investigated by crystallinity of silicalite-1 obtained by hydrothermal treatments of the seeds/crystalline layered silicate mixtures with H₂O/Si ratios of 2, 6, and 12, respectively, at 423 K. Time courses of the crystallinity revealed the improved crystallization rate: the crystallization with the seeds was completed for 24 h although it spent more than 48 h without the seeds. SEM observation of the products showed well-crystallized particles with a coffin-like shape reflecting the crystal growth of the seeds. The particles sizes were 2-4 μm for the products by the treatment with the H₂O/Si ratio of 6 and 12, although the size was < 2 μm for the product with the H₂O/Si ratio of 2, suggesting that less H₂O content brings about the limited growth. As a result, we have succeeded to control the crystallization process of silicalite-1 from the crystalline layered silicate by impregnation of the seeds.     

Influence of titanium and nitrogen on hot ductility of C–Mn–Nb–Al steels

Abstract

The influence of small additions of titanium on the hot ductility of C–Mn–Nb–Al steels has been examined. Titanium and nitrogen levels varied in the ranges 0·014–0·045 and 0·004–0·011 wt-%, respectively, so that a wide range of Ti/N ratios could be studied. The tensile specimens were cast and cooled at average cooling rates of 25, 100, and 200 K min^-1 to test temperatures in the range 1100–800°C and strained to failure at a strain rate of 2 × 10^-3 s^-1. It was found that ductility in the titanium containing niobium steels improved with a decrease in the cooling rate, an increase in the size of the titanium containing precipitates, and a decrease in the volume fraction of precipitates. Coarser particles could be obtained by increasing the Ti/N ratio above the stoichiometric ratio for TiN and by testing at higher temperatures. However, ductility was generally poor for these titanium containing steels and it was equally poor when niobium was either present or absent. For steels with ～0·005 wt-%N ductility was very poor at the stoichiometric Ti/N ratio of 3·4 : 1. Ductility was better at the higher Ti/N ratios but only two of the titanium containing niobium steels gave better ductility than the titanium free niobium containing steels and then only at temperatures below about 950–900°C. One of these steels had the lowest titanium addition (0·014 wt-%), thus limiting the volume fraction of fine Ti containing particles and the other had the highest Ti/N ratio of 8 : 1. However, even for these two steels ductility was worse than for the titanium free steels in the higher temperature range. The commercial implications of these results are discussed.     

Effect of thermal treatments on tensile strength of commercially cast pure titanium and Ti-6Al-4V alloys

Heating titanium structures is assumed to relieve tensions induced by the casting process as well as possibly optimizing some mechanical properties. The aim of this investigation was to evaluate the effect of thermal treatments on tensile strength of commercially pure titanium (CP Ti) and Ti-6Al-4V alloy. Thirty dumbbell rods, with diameters of 3.0 mm at the central segment and lengths of 42 mm, were cast for each metal using the Rematitan System. CP Ti and Ti-6Al-4V specimens were randomly divided into three groups of ten: a control group that received no thermal treatment and two test groups. One (T1) was heated at 750 ^∘C for 2 h and the other (T2) was annealed at 955 ^∘C for 1 h and aged at 620 ^∘C for 2 h. Tensile strength was measured with a universal testing machine (MTS model 810). Tensile strength means and standard deviations were statistically compared using a Kruskal-Wallis test at a α = 0.05 significance level. No statistically significant differences in tensile strength were observed among CP Ti groups. For the Ti-6Al-4V alloy, the control and T1 groups revealed statistically higher tensile strengths when compared to the T2 group, with no significant difference between the control and T1 groups.     

Preparation of uniform Silicalite-1 microspheres with large secondary pore architecture using monodisperse porous polystyrene particles as template

A new method was developed for preparation of silicalite-1 microspheres with uniform diameter about 2.5 μm using monodispersed micron-sized poly- styrene-co-divinylbenzene (PSD) porous particles as template. In this method, the PSD particles were impregnated first with tetraethoxysilane (TEOS) and then with tetrapropylammonium hydroxide (TPAOH). After crystallization and calcination, the silicalite-1 microspheres, possessing a regularly spherical morphology similar to the original silicalite-1, were successfully synthesized. More importantly, the silicalite-1 microspheres have large secondary pores in the range of 40 to 120 nm and high pore volume up to 0.7 cm³g^− 1. All these would facilitate the applications of microspheres in catalysis avoiding diffusion limitation.     

Investigation of boundary conditions for biomimetic HA deposition on titanium oxide surfaces

To improve the clinical outcome of metal implants, i.e. earlier loading and reduction of the incidence of revision surgery, better bone bonding ability is wanted. One method to achieve this is to change the surface chemistry to give a surface that facilitates bone bonding in vivo, i.e. a bioactive surface. Crystalline titanium oxide has recently been proven to be bioactive in vitro and is an interesting option to the more common hydroxylapatite (HA) coatings on implants. A materials possible in vitro bioactivity is tested through soaking in simulated body fluid and studies of possible HA formation on the surface. For bioactive materials, the formed HA layer can also be used as a coating. The aim of the current paper is to investigate some boundary conditions for HA formation on crystalline titanium oxide surfaces regarding influence from coating thickness, soaking time and soaking temperature. The influence from soaking time and temperature on the HA growth were investigated on oxidised Ti samples, (24 h at 800°C) resulting in a rutile surface structure. The oxidised samples were tested at three temperatures (4, 37 and 65°C) and four times (1 h, 1 day, 1 week and 4 weeks). The influence from titanium coating thickness on the HA growth was investigated via depositing thin films of crystalline titanium dioxide on Ti plates using a reactive magnetron sputtering process. Four different PVD runs with coating thicknesses between 19 and 74 nm were tested. The soaking temperature had an effect on the HA formation and growth on both rutile surfaces and native oxide on Ti substrates. Higher temperatures lead to easier formation of HA. It was even possible, at 65°C, to grow HA on native titanium oxide from soaking in PBS. The coating quality was better for HA formed at 65°C compared to 37°C. All PVD-coatings showed HA growth after 1 week in PBS at 37°C, thus even very thin coatings of crystalline titanium oxide coatings are bioactive.

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