Hydrolysis of zirconium alkoxide under an uncontrolled atmosphere

The laboratory prepared zirconium n-butoxide was hydrolysed under an uncontrolled atmosphere by exposing it to air moisture (natural hydrolysis) or adding water solutions at various pH (accelerated hydrolysis) to the alkoxide solutions. Investigations were performed on the effects of the different processes and the pH of the water solutions on the products morphology, crystallinity and phase transformation. XRD, SEM, TEM and SAD were used for these investigations. A strong correlation between crystallite size, calculated with Scherrer formula, and phase transformation was observed in the present work.     

Preparation of titanium diboride powders from titanium alkoxide and boron carbide powder

Titanium diboride powders were prepared through a sol-gel and boron carbide reduction route by using TTIP and B₄C as titanium and boron sources. The influence of TTIP concentration, reaction temperature and molar ratio of precursors on the synthesis of titanium diboride was investigated. Three different concentrations of TTIP solution, 0.033/0.05/0.1, were prepared and the molar ratio of B₄C to TTIP varied from 1.3 to 2.5. The results indicated that as the TTIP concentration had an important role in gel formation, the reaction temperature and B₄C to TTIP molar ratio showed obvious effects on the formation of TiB₂. Pure TiB₂ was prepared using molar composition of Ti: B₄C = 1: 2.3 and the optimum synthesis temperature was 1200°C.     

Preparation of nanosized titania by hydrolysis of alkoxide titanium in micelles

Nanosized titania particles, with typical particle sizes in the range of 30-50 nm have been synthesized using a microemulsion-mediated process. In this process, the aqueous cores of microemulsions have been used as constrained microreactors for the precipitation of titania precursor. The microemulsion was provided by a functionalized surfactant derived from the commercially available mixtures of sorbitol monooleate and polysorbate 80 (abbreviated as Span-Tween 80). The hydroxide particles, produced by the hydrolysis of the titanium tetraisopropoxide in the water droplets containing surfactant, were separated, dried, and calcined to form nanoparticles of TiO₂. The dependence of the size of the precipitated TiO₂ particles on various structure parameters of the microemulsion was studied in detail.     

Preparation of nanosized titania powder via the controlled hydrolysis of titanium alkoxide

By controlling the hydrolysis of titanium butoxide, followed with or without an ethanol washing process, the preparation of nanoscale titania powder was studied in detail. The characteristics of different powders produced by the direct precipitation (without an ethanol wash) and ethanol wash processes were studied by X-ray diffraction, transmission electron microscopy, BET, thermogravimetry and differential thermal analysis techniques. By comparison, it was found that both the direct precipitation and ethanol wash methods can obtain slightly agglomerated nanoscale titania powders of less than 15 nm, but the ethanol wash can further reduce the agglomeration. The particle sizes of titania powders can be modified while still retaining the anatase structure.     

Microscopy,thermal and structural properties of new synthesized 1,4-dihydroxybenzene modified titanium alkoxide

Homogenous, transparent, monolithic and red titanium hybrid gel was obtained by reaction of homogenous mixture of titanium butoxide Ti(OBuⁿ)₄ with the aromatic ring (1,4-dihydroxybenzene HO–C₆H₄–OH) (DO_1,4) in n-butanol at room temperature, without the addition of catalyst and water. Infrared spectroscopy was used to characterize the obtained material. The results show that 1,4-dihydroxybenzene reacted with the titanium alkoxide leading to the transparent monolithic and red gel in which both organic and inorganic –Ti–O–C₆H₄–O–Ti-bridges are formed. The thermal analysis of the xerogel was determined by TGA and DTA. The morphology, texture and structure of the material were studied by scanning electronic microscopy (SEM), Brunauer–Emmett–Teller (BET) method and X-ray powder diffraction (XRD). The X-ray diffraction pattern of the material calcined at 600 °C is consistent with the formation of TiO₂.     

Zirconium oxides formed by hydrolytic condensation of alkoxides and parameters that affect their morphology

When zirconium oxides are formed via hydrolytic condensation of zirconium alkoxides, the particle size and morphology of the resultant zirconia is strongly affected by certain parameters during the condensation. These parameters include: the type of alkyl group in the alkoxide, water/alkoxide ratio, molecular separation of species, and the reaction temperature. The particle size and the morphology in turn affect the sintering behaviour and crystalline transformation of ZrO₂, In this work the parameters that affect the formation of ZrO₂ from zirconium alkoxides are investigated. It has been shown that the alkyl groups and molecular separations during the hydrolytic polycondensation have particular significance in the modification of monoclinic tetragonal transformation of the resultant ZrO₂. Tetragonal phase can also be stabilized by copolymerization of ZrO₂ with SiO₂ producing tough ceramic materials.     

Media-based effects on the hydrolytic degradation and crystallization of electrospun synthetic-biologic blends

Tissue engineering scaffold degradation in aqueous environments is a widely recognized factor determining the fate of the associated anchorage-dependent cells. Electrospun blends of synthetic polycaprolactone (PCL) and a biological polymer, gelatin, of 25, 50, and 75 wt% were investigated for alterations in crystallinity, microstructure and morphology following widely used in vitro biological exposures. To our knowledge, the effects of these different aqueous-based biological media compositions on the degradation of these blends have never been directly compared. X-ray diffraction (XRD) analysis exposed that differences in PCL crystallinity were observed following exposures to phosphate buffered solution (PBS), Dulbecco’s modified eagle medium (DMEM) cell culture media, and DI water following 7 days of exposure at 37 °C. XRD data suggested that in vitro medium exposures aid in providing chain mobility and rearrangement due to hydrolytic degradation of the gelatin phase, allowing previously constrained, poorly crystalline PCL regions to achieve more intense reflections resulting in the presence of crystalline peaks. The dry, as-spun modulus of relatively soft 100 % PCL fibers was approximately 10 % of any gelatin-containing composition. Tensile testing results indicate that hydrated gelatin containing scaffolds on average had a fivefold increase in elongation compared to as-spun scaffolds. After 24-h of aqueous exposure, the elastic modulus decreased in proportion to increasing gelatin content. After 1 day of exposure, the 75 and 100 % gelatin compositions largely ceased to display measurable values of modulus, elongation or tensile strength due to considerable hydrolytic degradation. On a relative basis, common aqueous in vitro medium exposures (deionized water, PBS, and DMEM) resulted in significantly divergent amounts of crystalline PCL, overall microstructure and fiber morphology in the blended compositions, subsequently ‘shielding’ scaffolds from significant changes in mechanical properties after 24-h of exposure. Understanding electrospun PCL-gelatin scaffold dynamics in different aqueous-based cell culture medias enables the ability to tailor scaffold composition to ‘tune’ degradation rate, microstructure, and long-term mechanical stability for optimal cellular growth, proliferation, and maturation.     

Ordering effects in nonstoichiometric titanium carbide

The effect of carbon ordering on the crystal structure and resistivity of cubic TiC_y was studied. The ordering of TiC_y below 1020 K was found to yield cubic or trigonal Ti₂C or orthorhombic Ti₃C₂, depending on composition. Temperature-dependent resistivity data for compositions from TiC_0.522 to TiC_0.62 indicate that the temperature of the reversible equilibrium order-disorder transition ranges from 980 to 1000 K.     

Hydrogen effects in gamma titanium aluminides

The results of X-ray diffraction studies on Ti-48Al-1V at %(Ti-48-1) are reported. The objective of this study is to investigate the effects of hydrogen on phase changes and hydride formation in these alloys. Hydrogen-induced cracking was found to occur as a result of hydrogen charging. The cracking appears after the hydride phase formation and is observed to be dispersed throughout the material. The hexagonal hydride formed is unlike any previously reported titanium hydride. The hydride exhibits an 8% volume contraction compared to Ti₃Al which is made up of a 10% contraction in the a-direction, and a 12.5% expansion in the c-direction. This revised version was published online in November 2006 with corrections to the Cover Date.     

TA12钛合金热变形微观组织演变及变形参数优化

在应变速率为0.01~10 s-1,变形温度为870~1 070℃,最大变形量为80%的条件下,利用Gleeble-3800热模拟机对TA12合金高温压缩变形行为进行研究。依据实验结果绘制真应力-应变曲线,分析变形参数与组织的关系。同时把应力-应变曲线作为计算应变速率敏感指数m、功率耗散因子η、失稳判据ξ的底层数据,研究应变速率、变形温度、变形量共同存在对应变速率敏感指数m、功率耗散因子η的影响,绘制失稳图对失稳区域进行识别,并将功率耗散图和失稳图叠加构建热加工图。结果表明,在变形温度较低时,温度的影响主要表现为α相形态和数量的变化,在变形温度较高时,主要表现为β晶粒粗化;应变速率的影响主要表现在变形时间上;较高的η和ξ区域为良好加工区域,较低的η和ξ的失稳变形参数区域为加工避免区域。本批次合金适宜加工参数为温度910~970℃,应变速率0.01~0.3 s-1。     

Time dependent effects in fatigue of titanium and nickel alloys

The paper explores fatigue at both low and high temperature where creep and environmental damage interact with the normal cyclic processes of crack development. This is achieved by studying two contrasting material systems: the titanium alloys (Ti685, Ti834, Ti6246) and the nickel alloys (Udimet 720Li). Particular attention is given to both load and strain control fatigue response and crack development at stress concentration features. In each case there is an interesting balance between the beneficial effects of stress relaxation and the damaging effects of creep and environmental factors. On the crack growth side, the relative contributions of creep and environment are highlighted through measurements made in air and vacuum and by varying R value and dwell time. At the same time, any complications due to closure are removed by careful measurement of closure levels for each condition. The inadequacy of linear damage models for combining cyclic and time dependent effects is highlighted.     

Preparation of Fe3+-doped TiO2 catalysts by controlled hydrolysis of titanium alkoxide and study on their photocatalytic activity for methyl orange degradation

Fe3+-doped TiO2 (Fe-TiO2) porous microspheres were prepared by controlled hydrolysis of Ti(OC4H9)4 with water generated "in situ" via an esterification reaction between acetic acid and ethanol, followed by hydrothermal treatment. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic absorption flame emission spectroscopy (AAS), electron paramagnetic resonance (EPR) spectrum, X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy (DRS), and nitrogen adsorption-desorption methods. All of the undoped TiO2 and Fe-TiO2 samples exclusively consist of primary anatase crystallites, which further form porous microspheres with diameters ranging from 150 to 500 nm. The photocatalytic activity of Fe-TiO2 catalysts was evaluated from the photodegradation of methyl orange (MO) aqueous solution both under UV and visible light irradiation. Fe3+ doping effectively improves the photocatalytic activity under both UV light irradiation and visible light irradiation with an optimal doping concentration of 0.1 and 0.2%, respectively. The photocatalytic mechanisms of Fe-TiO2 catalysts were tentatively discussed.     

Influence of parameters of modifying oxygen-containing atmosphere on oxynitriding of titanium alloys

We study the influence of the parameters of modifying oxygen-containing atmosphere (the degree of rarefaction, temperature and time of modification) on the oxynitriding of titanium alloys. It is shown that, as the degree of rarefaction of the atmosphere increases and the temperature of modification decreases, the process of phase formation on the surface of titanium alloys evolves in the direction of formation of oxynitrides, whereas the period of modification does not affect the structural and phase state. As the oxygen content decreases, the composition of titanium oxynitride approaches the equiatomic composition. This guarantees the increase in surface microhardness and the improvement of the corrosion resistance of titanium alloys in oxygen-free acids.     

Fabrication and performances of MWCNT/TiO<Subscript>2</Subscript> composites derived from MWCNTs and titanium (IV) alkoxide precursors

Multi-walled carbon nanotubes (MWCNTs)/TiO₂ composites were synthesized by sol-gel technique using titanium (IV) n-butoxide (TNB), titanium (IV) isopropoxide (TIP) and titanium (IV) propoxide (TPP) as different titanium alkoxide precursors. The as-prepared composites were comprehensively characterized by BET surface area, SEM, XRD, EDX and UV-Vis absorption spectroscopy. The samples were evaluated for their photocatalytic activity towards the degradation of methylene blue (MB) under UV irradiation. The results indicated that the sample MPB had best excellent photocatalytic activity among the three kinds of samples. Furthermore, we also used piggery waste to determine the photocatalytic activity for the MWCNT/TiO₂ composites by using a chemical oxygen demand (COD) method. It seemed all of the samples have an excellent removal effect of COD. From the results of the bactericidal test, MWCNT/TiO₂ composites with sunlight had a greater effect on E. coli than any other experimental conditions.     

TiO2纳米管阵列的制备工艺对其光催化性能的影响

采用阳极氧化法,在醇(丙三醇、乙二醇)-水-NH4F电解液体系中制备高度有序的TiO2纳米管阵列。采用场发射扫描电子显微镜(SEM)、X射线衍射仪(XRD)对TiO2纳米管阵列的形貌和晶型结构进行表征,讨论了阳极氧化法制备工艺(阳极氧化电压、氧化时间、电解液)对TiO2纳米管的形貌、结构及其甲基橙光催化降解性能的影响;分析了退火温度对TiO2阵列的物相及其光催化性能的影响。研究结果表明,采用高电压、增加氧化时间有利于TiO2纳米管阵列光催化的提高,在其它参数相同的情况下,采用丙三醇作为电解液制备获得的TiO2纳米管阵列较乙二醇体系具有更加优异的光催化性能。