ZnO thin film as methane sensor

Methane (CH4) sensitivity of zinc oxide (ZnO) thin film has been studied in the present work. The sensor element comprises of a chemically fabricated ZnO semiconducting layer and a layer of palladium (Pd) as catalyst. The catalyst layer was formed on the surface of semiconducting ZnO following a wet chemical process from palladium chloride (PdCl2) solution. Fundamental features of a sensor element e.g. sensitivity, response time and recovery process has been studied. The effect of operating temperature on performance of the sensor material has been investigated and a choice of optimum temperature was made at around 200 degrees C. The sensor element exhibited reasonable sensitivity of about 86% at this temperature in presence of 1 vol% methane (CH4) in air

Dynamic compressive fracture of ceramic polymer layered composites

Dynamic compressive fracture evaluation is an essential characterization technique for advanced monolithic structural ceramics like alumina. Thus, for high strain rate induced damage tolerant applications, it is needed to take care of the characteristically brittle microstructure of the alumina ceramics. Hence, a smarter design concept has been involved based on the idea that cracks can either be arrested or deflected if a weak interface or interphase can be introduced. Thus, ceramic polymer layered composites (CPLC) were fabricated from high (e.g., 97%) density alumina disks pressureless sintered from sub-micron (d50-0.6 □m) alumina powder. The dynamic fragmentation of the CPLC samples at a reasonably high e.g., 900.s-1 strain rate has been studied with the real time, high-speed, in-situ video images, obtained during their failure in SHPB tests. A new failure mechanism has been proposed based on these data and FESEM evidences of grain boundary microcrack, inter/intra-granular shear bands and micro-fracture/cleavage formation

Chemically deposited magnesium hydroxide thin film

Here we report for the first time to the best of our knowledge the processing techniques, nucleation kinetics and the nanoindentation behaviour of a 1.5 mu m magnesium hydroxide thin film chemically deposited on a commercially available soda lime silica glass substrate at room temperature. The phase and microstructure of the films were analysed by X-ray diffraction, scanning electron microscopy, field emission scanning electron microscopy as well as transmission electron microscopy. An exponential nucleation kinetics was identified for the growth of the thin films. The nanomechanical properties, e. g. nanohardness and Young's modulus of the films were measured by the nanoindentation technique at ultralow loads of 50, 70 and 100 mu N. Finally, the nature of deformation of the thin film was analysed in terms of the energetics of the nanoindentation process and the microstructure

Reversible and repeatable phase transition at a negative temperature regime for doped and co-doped spin coated mixed valence vanadium oxide thin films

Smooth, uniform mixed valance vanadium oxide (VO) thin films are grown on flexible, transparent Kapton and opaque Al6061 substrates by the spin coating technique at a constant rpm of 3000. Various elements e.g., F, Ti, Mo and W are utilized for doping and co-doping of VO. All the spin coated films are heat treated in a vacuum. Other than the doping elements the existence of only V4+ and V5+ species is noticed in the present films. Transmittance as a function of wavelength and the optical band gap are also investigated for doped and co-doped VO thin films grown on a Kapton substrate. The highest transparency (approximate to 75%) is observed for the Ti, Mo and F (i.e., Ti-Mo-FVO) co-doped VO system while the lowest transparency (approximate to 35%) is observed for the F (i.e., FVO) doped VO system. Thus, the highest optical band gap is estimated as 2.73 eV for Ti-Mo-FVO and the lowest optical band gap (i.e., 2.59 eV) is found for the FVO system. The temperature dependent phase transition characteristics of doped and co-doped VO films on both Kapton and Al6061 are studied by the differential scanning calorimetry (DSC) technique. Reversible and repeatable phase transition is noticed in the range of -24 to -26.3 degrees C

Influence of Impurity on the Properties of Chemically Synthesized Calcium Hydroxide

Here we report synthesis and characterization of chemically synthesized calcium hydroxide (Ca(OH)2) with and without deliberate presence of NaNO3 as an impurity. Calcium nitrate tetrahydrate (Ca(NO3)2.4H2O) is used as precursor and alkaline NaOH solution is used as precipitant to synthesize the Ca(OH)2 samples. The samples were characterized by XRD, FESEM, FTIR spectroscopy, DTA, TGA and UV-Vis spectroscopy techniques. From the UV-Vis spectroscopy results, it is found that the Ca(OH)2 with NaNO3 impurity has higher bandgap than the sample without NaNO3. The weight loss in TGA is also more for the Ca(OH)2 with impurity than the one for without impurity. The results are discussed in terms of composition formed during synthesis process

Nanocolumnar Crystalline Vanadium Oxide-Molybdenum Oxide Antireflective Smart Thin Films with Superior Nanomechanical Properties

Vanadium oxide-molybdenum oxide (VO-MO) thin (21-475 nm) films were grown on quartz and silicon substrates by pulsed RF magnetron sputtering technique by altering the RF power from 100 to 600 W. Crystalline VO-MO thin films showed the mixed phases of vanadium oxides e.g., V2O5, V2O3 and VO2 along with MoO3. Reversible or smart transition was found to occur just above the room temperature i.e., at similar to 45-50 degrees C. The VO-MO films deposited on quartz showed a gradual decrease in transmittance with increase in film thickness. But, the VO-MO films on silicon exhibited reflectance that was significantly lower than that of the substrate. Further, the effect of low temperature (i.e., 100 degrees C) vacuum (10(-5) mbar) annealing on optical properties e.g., solar absorptance, transmittance and reflectance as well as the optical constants e.g., optical band gap, refractive index and extinction coefficient were studied. Sheet resistance, oxidation state and nanomechanical properties e.g., nanohardness and elastic modulus of the VO-MO thin films were also investigated in as-deposited condition as well as after the vacuum annealing treatment. Finally, the combination of the nanoindentation technique and the finite element modeling (FEM) was employed to investigate yield stress and von Mises stress distribution of the VO-MO thin films

Young's modulus-porosity relations: an analysis based on a minimum contact area model

The Young's modulus-porosity relation of porous ceramic materials has been analysed based on a minimum solid area of contact model. The minimum solid area of contact developed during sintering of an assembly of monosized spheres stacked in simple cubic packing is calculated by approximating the neck area by two sine-wave functions. The first function represents the shape of a sphere and the second function signifies the shape of the neck between neighbouring spheres. The model shows excellent agreement with 12 sets of relative Young's modulus, E/E-0, versus pore volume fraction, P, data from literature on five different polycrystalline ceramic oxides, namely Lu2O3, Sm2O3, Yb2O3, Al2O3 and ThO2, whose porosities are reasonably represented by such idealized packing

Influence of some parameters on the strength and fracture-toughness of reaction-bonded silicon-nitride composites

Strength, Young's modulus and fracture toughness data in the temperature range 30–1400°C are presented for reaction-bonded silicon nitride and its particulate composites with SiC (5–20 vol.%), BN (10 vol.%) and TiC (5 vol.%). The composites of Si3N4 with SiC showed the best mechanical properties of the three types of composites. The toughening mechanism and interdependence of various mechanical properties for these composites are discussed