Mixed Ti Research Articles

Ethanol interference in light alkane sensing by metal-oxide solid solutions

A study of the sensing properties of chemoresistive metal-oxides vs. light alkanes has been undertaken under wet condition and in presence of ethanol. Screen-printed films of a solid solution of mixed Sn and Ti oxides have been selected for the purpose. We demonstrated that the films are capable of detecting 100 ppm of light alkanes or 500 ppm of methane in wet condition, two concentration levels by far lower than their alarm thresholds, respectively. Ethanol is known to be a harmful interfering gas, though its concentration can be reduced to values lower than 10 ppm by proper filtering. We show that, even in presence of 10 ppm of ethanol, the films steadily responded to alkanes.

Synthesis of nanoporous graphite-derived carbon/TiO 2–SiO 2 composites by a mechanochemical intercalation method

Nanoporous composites of carbon nanosheets and single or mixed TiO 2 and SiO 2 were synthesized from graphite oxide (GO) precursor by a mechanochemical intercalation (MCI) method and their structural and adsorption/photocatalytic properties examined. It was found that a mixed Ti and Si organic phase behaves differently from a single phase in the MCI process, with linkages of SiO 2 and TiO 2 forming between the carbon layers, leading to an intercalation structure with improved surface hydrophilicity and a composite with enhanced microporosity and a reduced total amount of oxides. Although structural regularity of intercalated GO becomes poorer by applying Ti species in the MCI method, carbon-mixed oxide composites with an appropriate pore structure and sufficient Ti content exhibit a synergy effect of adsorption concentration and photocatalysis toward organic molecules.

Photo-electrochemical investigation of anodic oxide films on cast Ti–Mo alloys. I. Anodic behaviour and effect of alloy composition

The anodic behaviour of cast Ti–Mo alloys, having different Mo contents (6–20 wt.%), was investigated in acidic and neutral aerated aqueous solutions. All sample showed a valve-metal behaviour, owing to formation and thickening of barrier-type anodic oxides displaying interference colours. Growth kinetics of passive films is influenced by both anodizing electrolyte and composition of the starting alloy. This last parameter was found to change also the solid-state properties of the films, explored by photoelectrochemical and impedance spectroscopy experiments. Thicker films ( U f = 8 V/MSE) grown on alloys richer in Mo showed more resistive character and a photocurrent sign inversion under negative bias, that revealed an insulating character, whereas corresponding films grown on alloys with lower Mo content, as well as thinner films, behaved as n-type semiconductors. Results are discussed in terms of formation of a mixed Ti–Mo oxide phase.

High-Rate Charge-Discharge Performance of Composite Electrodes of FeOOH-Based Amorphous Particles and Carbon Powder

Composite electrode materials of amorphous FeOOH-based particles and carbon powder were prepared by heat treatment of composite powder obtained by hydrolyzing of mixed aqueous solutions of FeCl3 and Ti(SO4)2 into which electron conducting carbon powder was dispersed. They exhibited high capacities over 150 mAh g-1 and good cycle performance at large charge-discharge current density of 5 mA cm-2 (ca. 1 A g-1). In this case, the heat treatment was effective process to improve the cycle performance.

Metal-oxide solid solutions for light alkane sensing

Sensing of light alkanes via chemoresistive gas sensors has been addressed. Screen-printed films of a solid solution of mixed Sn and Ti oxides have been selected for the purpose. We demonstrate that the films sensitively detect 100 ppm of such gases and 500 ppm of methane, the two levels being by far lower than the alarm limits for these gases. Information about the working mechanism of chemical reactions on the surface has been discussed under either dry or wet condition.

Microwave plasmochemical synthesis of nanopowders in the system Pb-Zr-Ti-O

Conditions for building up the composition and structure of mixed Pb, Zr, and Ti oxides in a microwave plasma-chemical process were studied. As starting substances Pb(C2H5)4, Ti(C4H9O)4, and a 80% Zr(C4H9O)4 solution in 2-propanol were used. To avoid stratification of the components the initial temperature of the flow should not exceed 1000°C. Under these conditions the crystallization of a complex structure requires a combination of a plasma-chemical synthesis with subsequent thermal treatment of the resulting powders. After the thermal treatment an average particle size of lead zirconate-titanate nanopowder was 120 nm.

Electrochemical co-deposition of Tin+ phases with gold in ionic liquids

The electro-deposition of titanium from two different classes of ionic liquids has been studied. Gold ions in solution have been used as an additive in order to provide a stable nucleation site for titanium to deposit on via a co-deposition process. Despite evidence from previous literature, it was found that it was not possible to reduce titanium from the +4 state to titanium (0) due to problems of redox cycling and solubility of reduced titanium species in the various ILs trialled. It was however found that gold was a very effective nucleating agent for these reduced titanium species and that successful mixed Ti(n+)/gold electro-deposits were obtained. The content of titanium in these species could be varied according to the conditions and IL used.

Sensing of volatile alkanes by metal-oxide semiconductors

Abstract Sensing of volatile alkanes via chemoresistive gas sensors has been addressed. Screen-printed films of Au- and Pd-added SnO 2 and a solid solution of mixed Sn and Ti oxides have been selected for the purpose. We demonstrate that the films sensitively detect 200 ppm of such gases, a value which is by far lower than their alarm limits. Information about the working mechanism of chemical reactions at surface has been discussed.

Liquid injection MOCVD of TiO 2 and SrTiO 3 thin films from [Ti(OPr i) 2(tbaoac) 2]: Film properties and compatibility with [Sr(thd) 2

Different mixed alkoxide β-ketoester Ti precursors were synthesized and titanium bis (isopropoxide) bis (tert-butylacetoacetate) was selected for detailed CVD studies of TiO 2 and SrTiO 3 films. Films were deposited on Pt/ZrO 2/SiO 2/Si substrates and special emphasis was directed on low deposition temperatures (≤ 500 °C). TiO 2 films were amorphous for deposition temperatures ≤ 450 °C and crystallized in the tetragonal anatase structure above that. The film growth was homogeneous over large areas and columnar growth was found for the crystalline films. SrTiO 3 films could be grown within the wide temperature range from 450 to 700 °C. High growth rates and (100) textured films were achieved at T ≥ 600 °C. However, at lower temperature (450–500 °C), stoichiometry is strongly influenced by a decrease of the Ti incorporation efficiency. This effect could be attributed to the interaction with the Sr precursor and could be avoided only by long separation times between the Ti and Sr injection pulses.

Property change in multifunctional TiC xO y thin films: Effect of the O/Ti ratio

TiC x O y films with various O/Ti ratios have been deposited by DC magnetron sputtering, using C pieces incrusted in a Ti target erosion area. Composition analysis revealed the existence of three different growth regimes: (i) zone I, corresponding to films with metallic-like appearance, and atomic ratios O/Ti below one; (ii) zone II, with films revealing interference-like colours, and atomic ratios O/Ti higher than 2. Between these two regions, there was a transition zone T, where the atomic ratio O/Ti is between one and two. The films within this zone revealed a brown colour. X-ray diffraction (XRD) structural characterization results showed an evolution from a mixed Ti(C,O) phase at lower O/Ti ratio, to a quasi-amorphous structure within zone T, and poorly crystallized rutile and anatase TiO 2 at the highest O/Ti ratios (zone II). These different structural arrangements resulting from different film's compositions had clear effects on electrical resistivity, whose values increased from about 7 × 10 2 to 2 × 10 11 μΩ cm with increase of the O/Ti ratio. Fourier-transform infrared spectroscopy (FTIR) was used to further confirm the different nature of films structure and, thus, to better understand their properties variation. The observed behaviour was found to be in straight correlation with those of XRD.

Niobia-stabilised anatase TiO 2 highly porous mesostructured thin films

The thermal stability of anatase TiO 2 mesoporous thin films has been considerably increased up to 800 °C by substituting a fraction of Ti cations by Nb. Mesoporous mixed oxide films Ti 1− x Nb x O 2, with x = Nb/(Nb + Ti) ranging from 0 to 1, and homogeneous crystalline walls have been successfully prepared from chloride precursors and non-ionic block copolymer templates. They all exhibit a uniaxially distorted Im3m bcc mesostructure with the a lattice parameter ranging from 14 to 19 nm. Films have been characterised by simultaneous in situ SAXS and WAXS investigations during thermal treatment. Transmission electron microscopy and UV–visible ellipsometry were used to confirm the structure, the porosity and the good optical quality. A high porosity of 40% (pore size estimated at 7 nm) was maintained for the 10% Nb-doped films above the temperature of crystallisation and a bandgap of 3.40 eV has been measured after annealing at 500 °C.

On the spinodal nature of the phase segregation and formation of stable nanostructure in the Ti–Si–N system

The free energy of the mixed Ti–Si–N system is calculated according to a semi-empirical thermodynamic formula based on the sub-lattice model for different activities of nitrogen. The results show that the phase segregation in the ternary Ti–Si–N systems is of chemically spinodal nature at a nitrogen pressure and deposition temperature typically used for the deposition of the superhard nc-TiN/a-Si 3N 4 nanocomposites, i.e. p N 2 ≥ 10 − 3 mbar and T dep 550–600 °C, respectively. Only at much lower nitrogen pressure and much higher temperature, can the chemically spinodal decomposition be restrained. A simple estimate of the interfacial strain energy for a semi-coherent interface, as expected for this system, shows that this contribution is unlikely to hinder the system being also coherently spinodal. It is further shown that kinetic constraints, such as T dep ≤ 300 °C and low p N 2 , although within the range where the stoichiometric nitrides should be fully spinodally segregated, will kinetically hinder the system to reach the thermodynamically driven equilibrium.

Electron microscopy investigation of the TiBAl and TiCAl grain refiner master alloys

The present work brings a detailed statistical analysis of the microstructural characteristics and chemistry of the second phase particles present in the Al-5Ti-1B and Al- 3Ti-0.15C (wt.%) commercial grain refiner rods used in the Al casting industry. The investigation was performed using the TEM, EDS, STEM and HREM techniques. Both refiner rods contained large, blocky Al3Ti DO22 particles. Borides present in the TiBAl rod, known to be main α-Al nucleation substrates, exhibited a facetted, hexagonal platelet morphology and largely represented a mixed (Ti,Al)B2 phase, with Ti and Al contents changing continuously across the particle dimensions. There were two distinct families of small particles observed in the TiCAl rod. The coarser, facetted particles corresponded to cubic TiC crystal structure and these are believed to be major α-Al nucleation sites. The family of finer, round particles appeared to correspond to orthorhombic Al6Fe phase and their role in the nucleation process remains to be clarified. The results obtained may be used in optimising the grain refiner rod microstructures that would ensure improved refining performance during casting.

Martensitic transformation of grain-size mixed Ti 51Ni 49 melt-spun ribbons

The as-spun and annealed ribbons of grain-size mixed Ti 51N 49 SMA exhibit the multiple martensitic transformations in which the annealed ribbons possess more obvious transformation peaks and less transformation hysteresis. According to the partial-cycled DSC test, transformation peaks are associated with B2 → R transformation, R → B 19 1 ′ transformation for large grains and R → B 19 2 ′ transformation for small grains during cooling, and B 19 1 ′ → B 2 transformation for large grains and B 19 2 ′ → B 2 transformation for small grains during heating.

Ｔｉ‐６Ａｌ‐４Ｖ射出成形材の焼結挙動と機械的特性

In this study, the metal injection molding process was applied to produce the sintered titanium alloy compacts using pre-alloyed Ti-6Al-4V powders obtained by gas atomization. The effect of sintering conditions on the density, mechanical properties, and oxygen and carbon contents were investigated as compared to using mixed Ti and 60Al-40V powders. The mechanical properties (Tensile strength of 890 Mpa, Elongation of 10%) of injection molded compacts using pre-alloyed powder were comparable to the wrought Ti-6Al-4V material of JIS 60 grade. In such a case, the injection molded compacts using mixed powders showed high density and high properties (Relative density of 98%, Tensile strength of 910Mpa, Elongation of 14%) as compared to the compacts using pre-alloyed powder.

H 2O 2-based allylic oxidation of α-pinene over different single site catalysts

Catalytic properties of different solids, containing Ti(IV), Zr(IV), and Fe(III) isolated in inorganic matrixes, have been assessed in allylic oxidation of α-pinene with aqueous H 2O 2. Among the catalysts studied were mesostructured metal silicates Ti-MMM-2 and Fe-MMM-2, TiO 2–SiO 2 mixed oxides, Ti and Zr grafted on mesoporous silica cellular foams (Ti- and Zr-MCF), and a new composite material, H 5PW 11TiO 40/silica, prepared by a sol–gel method. The catalysts were characterized by elemental analysis, N 2 adsorption, and DRS-UV. The Ti- and Zr-containing materials showed catalytic properties superior to those of Fe-MMM-2. The reaction selectivity strongly depended on the solvent properties, substrate/oxidant molar ratio, reaction temperature, and α-pinene conversion. In optimized reaction conditions (MeCN, 30 °C), the total selectivity toward verbenol/verbenone reached the maximal value of 80–82% at 8–15% conversion. The H 5PW 11TiO 40/silica catalyst can be used repeatedly without loss of activity and selectivity. No leaching of the active species occurs, and the oxidation is a true heterogeneous process operating via a radical nonchain mechanism.

Studies of the coupling of final d*-states in mixed Hf and Ti oxides (HfO 2) x(TiO x) 1− x and other complex oxides

X-ray absorption spectroscopy and vacuum ultra-violet spectroscopic ellipsometry are used to study the electronic structure of complex oxides comprised of mixed TM/TM and TM/RE oxides. Experimental spectra for HfTiO 4 and Gd(Dy)ScO 3 indicate multiple d-state features in the O K 1 edge. These are compared with the empirical models for atomic d-state mixing. It is concluded that a mean field, virtual alloy model does not apply, and that the effects associated with the differences in atomic coordination and deviations from ideal octahedral or cubic bonding play a determinant role in d-state atom mixing. The results are applied band edge engineering options for high- k dielectric applications.

Effect of elemental iron on the carbothermic reduction of the anatase and rutile forms of titanium dioxide

Effect of iron on the carbothermic reduction of anatase and rutile forms of titanium dioxide was studied. Differential thermogravimetric analysis indicated a significantly different reduction route in the presence of iron with a number of clear minima in the rate of mass loss observed. X-ray diffraction of the products at these minima indicated that rutile initially formed FeTiO 3 which reduced to γ-Ti 3O 5, whilst anatase reduced through the mixed Ti(III/IV) phases of general formula Ti n O 2 n−1 to d-Ti 3O 5. The final stage was the reduction of Ti 3O 5 to the sub-stoichiometric carbide, TiC 0.5. Iron was found to stabilise the Ti 3O 5 phases which were absent from an iron-free system, this is presumed to be due to partial substitution of trivalent iron for trivalent titanium.

Preparation and crystallization characteristics of mesoporous TiO2 and mixed oxides

Mesoporous TiO2 and mixed Ti oxides are prepared by a modified sol-gel method using a block copolymer as a mesoporous template. Calcination of the material at 400 °C for template removal is shown to induce crystallization of pure TiO2, resulting in the destruction of the original mesoporous structure and the development of larger pores (7.5 nm) as inter-particle voids. The addition of tri-, tetra- and penta-valent metals (Al, Zr and Nb) to Ti oxide in the amorphous phase in the ratio Ti : M = 1 : 2 (M = Al, Zr or Nb) increases the thermal stability of the material by elevating the crystallization temperature above that for pure TiO2. The formation of Al2TiO5, TiZr2O6 and TiNb2O7 crystal phases without phase separation is confirmed in these materials, demonstrating the homogeneous mixing of TiO2 and the additive element at the atomic level. The mixed mesoporous oxides are thermally stable at 400 °C, although the porous structure is still destroyed due to crystallization. Thus, a homogeneous mixture of Ti with another element (Al, Zr or Nb) in mesoporous amorphous Ti-mixed oxide is observed.

Photo-electrochemical and impedance investigation of passive layers grown anodically on titanium alloys

The anodic behaviour of two titanium cast alloys, obtained by fusion in a voltaic arc under argon atmosphere, was analyzed in aerated aqueous solutions having different pH values. In all solutions the alloys, having nominal compositions Ti–50Zr at.% and Ti–13Zr–13Nb wt.%, displayed a valve-metal behaviour, owing to the formation of barrier-type oxide films. Passive films, grown potentiodynamically up to about 9 V, were investigated by photocurrent spectroscopy (PCS) and electrochemical impedance spectroscopy (EIS). These passive layers show photoactivity under anodic polarizations, with optical gaps close to 3.55 and 3.25 eV for the binary and the ternary alloy, respectively, independent of the anodizing electrolyte. Films grown on the binary alloy present insulating behaviour and anodic impedance spectra with one time constant; this was interpreted in terms of a single-layer mixed Ti–Zr oxide enriched in Ti with respect to the alloy composition. Also for the ternary alloy the results are consistent with the formation, upon anodization, of Ti–Nb–Zr mixed oxide films, but they display n-type semiconducting behaviour, owing to their poor content of ZrO 2 groups.