Effect of platinum distribution on the hydrogen gas sensor properties in tin oxide thin films

Tin oxide and platinum layers were deposited on oxidized silicon wafers by ion-beam sputtering. The hydrogen gas sensing properties of undoped films and platinum-doped films were examined at 300°C for films annealed at 500°C. It was observed that the surface platinum when annealed together with the tin oxide film increased the sensitivity and reduced the response time compared with those of undoped films. Longer annealing tended to shift the optimum sensor thickness to a thicker side; the optimum thickness changed from 17 to 37 nm as the annealing time increased from 2 to 50 h. The interdiffusivity between the platinum and the tin atoms in the bulk was negligibly small at 300°C.     

Liquid-liquid extraction of divalent manganese,cobalt, copper,zinc and cadmium from aqueous chloride solutions by tricaprylmethylammonium chloride

The distribution of divalent manganese, cobalt, copper, zinc and cadmium between aqueous solutions of hydrochloric acid and/or lithium chloride and the solutions of tricaprylmethylammonium chloride (Aliquat-336, R₃R′NCl) in benzene has been investigated under different conditions. It is found that the extraction of these metals by Aliquat-336 proceeds as MCl₄^2?(aq) + 2 R₃R′NCI(org) ? (R₃R′N)₂MCI₄ (org) + 2 Cl^?(aq). The extraction curves have been examined utilizing a modified chemical model on the basis of this equilibrium equation. In addition, the electronic, electron spin resonance and infrared spectral results suggest that all the complexes formed in the organic phases are in a tetrahedral arrangement.     

Rate constants of elementary steps by pulse technique

Two methods for measuring the rate constants of the elementary steps by the pulse technique are proposed. The first gives the adsorption and the desorption rate constants from the retention time and the half width of the chromatographic peak, and was applied to the adsorption of benzene on HY and CaY zeolites. The second gives the surface reaction rate constant and the desorption rate constant of the reactant from the peak of the product which is not adsorbed on the catalyst surface. The method was applied to the cracking of cumene on HY and CaY.     

Grain-Size Dependence of Thermal-Shock Resistance of Yttria-Doped Tetragonal Zirconia Polycrystals

Thermal-shock fracture behavior of yttria-doped tetragonal zirconia polycrystals (Y-TZP) of various grain sizes was evaluated by the quenching method using water as the quenching solvent. The tetragonal-to-monoclinic phase transformation behavior of Y-TZP around cracks introduced by thermal stress was investigated by using Raman microprobe spectroscopy. The critical quenching temperature difference (Δ T _c ) of Y-TZP ceramics increased from 250° to 425°C with increasing grain size of zirconia from 0.4 to 3.0 μm, while the fracture strength decreased from 900 to 680 MPa. The improvement of Δ T _c of Y-TZP with increasing grain size of zirconia corresponded with the quantity of tetragonal-to-monoclinic phase transformation around cracks introduced by thermal stress.     

Strain disturbances due to viscoelastic crack propagation

Local strain disturbances near a running crack in a viscoelastic material were investigated in PMMA. Specimens having different initiation crack tip radii and under different tensile strain rates were examined by use of a series of strain gauges placed parallel and close to the expected crack path, and by velocity gauges. The strain disturbance, which was observed ahead of the running crack front, diminished gradually owing to the viscoelastic damping. The maximum strain disturbances increased with increase in gross breaking load.     

Domain structure and crystalline morphology of AB and ABA type block copolymers of ethylene oxide and isoprene cast from solutions

The domain structure and crystalline morphology of AB and ABA type block copolymers of ethylene oxide (EO) and isoprene (Ip) were investigated by using two kinds of casting solvents, non-selective (benzene) and selective (ethyl benzene) solvents. The domain structures of both types of block copolymers are identical, as in the case of amorphous block copolymers, depending mostly on the fractional compositions of each block segment but hardly on the sequence arrangements.When benzene is used as a cast solvent, the change of domain structure with increase of Ip fraction follows, in general, a role established for amorphous block copolymers, except for the fact that the EO segment is crystallizable so that the above role is considerably modified, especially when the EO fraction is dominant, to form spherulitic crystalline texture. The domain structure of mixed system of block copolymer with homo-PEO, cast from benzene solution, also follows the above role, simply depending on fractional composition as a whole, of each component, unless the molecular weight of the homopolymer is much larger than that of corresponding block segment.On the other hand, when ethyl benzene is used as a cast solvent, the domain structure is quite different from that cast from benzene solution, giving single crystal-like texture of EO segments on which Ip segments are segregated to form Ip layer even for a copolymer having an EO fraction as small as 20%. The above contrast of domain formation mechanism between the two kinds of casting solvents is interpreted in terms of an interrelation of two binodal surfaces, critical concentration of crystallization of EO segments and critical concentration of micelle formation of EO and Ip segments, in the phase diagram of the system at a given temperature.     

Bioactivity and Mechanical Properties of Poly(dimethylsiloxane)-Modified Calcia–Silica Hybrids with Added Titania

Hydrolysis and polycondensation of poly(dimethylsiloxane) (PDMS), tetraethoxysilane (TEOS), and calcium nitrate, added with tetraisopropyltitanate (TiPT) at a TiPT/(TiPT + TEOS) molar ratio of 0.15, gave a pore- and crack-free transparent monolithic organic-inorganic hybrid material. It was speculated to be composed of a Si–O–Ti–O⁻ network modified with methyl groups, and a Ca²⁺ ion ionically bonded to the network. The hybrid obtained showed a high apatite-forming ability on its surface in a simulated body fluid that is indicative of high bioactivity, as well as mechanical properties such as bending strength, Young's modulus, and strain at failure, analogous to those of the human cancellous bone. This hybrid material is expected to be useful as a new type of bioactive bone-repairing material.     

Sintering and Mechanical Properties of Yttria-Doped Tetragonal ZrO2 Polycrystal/Mullite Composites

Yttria-doped tetragonal ZrO₂ polycrystal (Y-TZP)lmullite composites were sintered at 1450° to 1500°C in air to disperse rodlike mullite grains at the grain boundary of Y-TZP and the mechanical and thermal properties were investigated. The aspect ratios of mullite grain were >2. High fracture strength of 1000 MPa and fracture toughness of 12 MPa·m^1/2 were obtained by dispersing <20 vol% of mullite into Y-TZP. The thermal expansion coefficient of Y-TZP/mullite composites decreased with increasing mullite content. The thermal shock resistance of Y-TZP was greatly improved by dispersion of rodlike mullite grains.     

Fabrication of CNT-carbon composite microstructures using Si micromolding and pyrolysis

A fabrication method of carbon nanotube (CNT)-carbon composite microstructures has been developed. CNT-carbon composite microstructures with dimensions from 10 micrometers to several hundred micrometers have been fabricated by pyrolysis process from the patterned SU-8 photoresist mixed with 1 wt% of CNTs at temperature of ~600 °C under inert atmosphere. The resulting composite microstructures with a high aspect ratio of ~34 can be successfully fabricated by this novel fabrication method. This research provides a simple approach that is compatible with microfabrication technology and is capable of fabricating composite microstructures with reproducible shape and dimensions, at desired locations. This approach has potential for the further exploring of applications of composite micro/nano structures as functional units in various microdevices. Also the ultramicroindentation hardness of the CNT-carbon composite films was investigated by nanoindentation measurement.