Anoop Kumar Mukhopadhyay

Chemically deposited zinc oxide thin film gas sensor

Zinc oxide (ZnO) thin films were prepared by a low cost chemical deposition technique using sodium zincate bath. Structural characterizations by X-ray diffraction technique (XRD) and scanning electron microscopy (SEM) indicate the formation of ZnO films, containing 0.05–0.50 μm size crystallites, with preferred c-axis orientation. The electrical conductance of the ZnO films became stable and reproducible in the 300–450 K temperature range after repeated thermal cyclings in air. Palladium sensitised ZnO films were exposed to toxic and combustible gases e.g., hydrogen (H2), liquid petroleum gas (LPG), methane (CH4) and hydrogen sulphide (H2S) at a minimum operating temperature of 150 °C; which was well below the normal operating temperature range of 200–400 °C, typically reported in literature for ceramic gas sensors. The response of the ZnO thin film sensors at 150 °C, was found to be significant, even for parts per million level concentrations of CH4 (50 ppm) and H2S (15 ppm).

Galvanostatic deposition and electrical characterization of cuprous oxide thin films

Abstract Semiconducting cuprous oxide (Cu 2 O) thin films, important for low cost solar cell and oxygen or humidity sensor applications, were galvanostatically deposited at 40–60 °C on copper substrates. The deposition kinetics, studied up to a film thickness of about 20 μm, was found to be linear and independent of deposition temperature. The observed film growth rate was in excellent agreement with the growth rates predicted from Faradays law of electrolysis. The deposited films exhibited a preferred (200) orientation. The current-voltage characteristics of the electrodeposited Cu 2 O/Cu diodes exhibited a metal-insulator-semiconductor type of behaviour, suggesting the presence of a thin interfacial insulating layer between Cu 2 O and copper. The electrical conductivity of Cu 2 O films was found to vary exponentially with temperature in the 145–300°C range with an associated activation energy of 0.79 eV.

On the microhardness of silicon nitride and sialon ceramics

Influences of relative density, grain size, Youngs modulus, flexural strength and fracture toughness on microhardness characteristics of hot-pressed silicon nitride, sintered silicon nitride, reaction-sintered sialon and liquid-phase sintered sialon have been discussed. Three new semi-empirical equations have been proposed to correlate microhardness to relative density. Indentation size effects on microhardness measurement have also been discussed.

Development of Hydroxyapatite Coating by Microplasma Spraying

Bioactive hydroxyapatite (HAP) coating (Ca/P-1.67) was developed on surgical grade SS316 L substrate using the microplasma spraying (MIPS) process with low (1.5 kW) plasmatron power. The MIPS-HAP coating showed both crystallinity and volume percent open porosity much higher than those usually reported for HAP coating deposited by the conventional macroplasma spraying (MAPS) process with high plasmatron power. The X-ray diffraction (XRD) data identified the coating to be nearly phase pure. The Fourier transformed infrared (FTIR) data suggested that a process of dehydroxylation and rehydroxylation might have occurred in the as-sprayed and post-heat treated coatings, respectively. The coating had a highly heterogeneous microstructure comprising of splats, completely and/or partially molten and unmelted splats retaining a nonflattened core, micropres, macropres, inter-, and intrasplat cracks.

Fracture toughness of structural ceramics

Abstract A comparative study of fracture toughness evaluation at room temperature of three different structural ceramics viz. sintered alumina, silicon carbide and silicon nitride is reported. Four methods of fracture toughness evaluation such as the single edge notched beam (SENB) technique, chevron notched beam (CNB) technique, indentation fracture (IF) technique and fractographic methods (FM) were compared. In addition, for a given method, the influence of several experimental parameters, e.g. blade width, notch tip radius, normalised notch length and the loading rate on the measured value of fracture toughness was investigated in the cases of the aforesaid materials.

Tin dioxide thin film gas sensor

Abstract Tin dioxide (SnO 2 ) is the singular, most important material utilised in commercially manufactured sensors for toxic and combustible gases. In the present work, tin dioxide thin film sensors with porous microstructure and thickness of 0.22 μ m have been fabricated on commercially available glass slides by a novel, low-cost, modified chemical deposition technique. Here we report, for the first time, the details of structural and deposition characteristics of the same films as a function of experimental parameters such as the number of dippings, bath temperature and bath concentration. In addition, the electrical properties were studied for both as deposited and palladium sensitised films as a function of temperature (300–500 K) in a closed quartz tube furnace. Further, the gas sensitivity of the palladium sensitised tin dioxide thin film sensors was evaluated in air inside the same closed quartz tube furnace as a function of the operating temperature (150–300°C) for a fixed concentration (3 vol%) of hydrogen gas with nitrogen as the carrier gas. The sensor response could be recorded at an operating temperature of as low as 150°C. Maximum sensitivity of 90% was found to occur at a low temperature of only 200°C. Above this cut-off temperarure, sensitivity of the present thin film sensors was found to suffer only moderate degradation.

Wear and friction behaviour of UHMWPE-alumina combination for total hip replacement

Abstract The wear and friction behaviour of ultra high molecular weight polyethylene (UHMWPE) against high purity fine grained alumina, the ideal material combination for total hip joint prosthesis, were studied under different contact pressures and sliding velocities using a pin-on-disc type wear and friction monitor. The wear heights in wet conditions were found to be much lower than those in dry conditions, which followed a power law relationship with load after 3–5 km of sliding. Efforts were also made to find out the sequence of dominating wear mechanisms.

An analysis of microstructural parameters in the minimum contact area model for ultrasonic velocity–porosity relations

The relationship between the normalised ultrasonic velocity (v=v0) and the volume fraction (P) of pores in porous materials has been derived on the basis of a minimum solid area of contact model. It considers the development of the minimum solid area of contact during the sintering of an assembly of monosized spheres stacked in simple cubic packing. It is shown that by using a single model parameter ‘‘c’’, related to the eAective aspect ratio ‘‘’’ of spheroidal pores; it is possible to predict the trends in variation of the experimental (v=v0 versus P) data of hot pressed silicon carbide (SiC), hot pressed silicon nitride (HPSN), reaction bonded silicon nitride (RBSN), porcelain, ceramic superconductors based on YBCO system, sintered iron and tungsten powder compacts as well as alumina. In addition, it was found that a single relation describes the behaviour of both longitudinal and transverse wave velocity as a function of pore volume fraction in all but the ceramic superconductors of the aforesaid materials. Finally, it is proposed that for all practical purposes, the analytical relation derived in the present work, can be eAciently approximated by an empirical relationship: v=v0a 1ˇ a1P OU n , where the subscript zero refers to the material of theoretical density and a1, n are fitting

Mechanical characterization of microwave sintered zinc oxide

The mechanical characterization of microwave sintered zinc oxide disks is reported. The microwave sintering was done with a specially designed applicator placed in a domestic microwave oven operating at a frequency of 2.45 GHz to a maximum power output of 800 Watt. These samples with a wide variation of density and hence, of open pore volume percentage, were characterized in terms of its elastic modulus determination by ultrasonic time of flight measurement using a 15 MHz transducer. In addition, the load dependence of the microhardness was examined for the range of loads 0.1–20 N. Finally, the fracture toughness data (KIC) was obtained using the indentation technique.

Electrodeposition and characterisation of cuprous oxide films

Abstract Semiconducting cuprous oxide films were prepared by electrodeposition onto copper substrates from an alkaline CuSO4 bath at temperatures between 40 and 60°C. The Cu2O films, which were deposited using a potentiostatic method, were found to exhibit exponential growth kinetics. X-ray diffraction studies revealed the formation of only Cu2O films with (200) preferred orientation. The observed current-voltage characteristics of the Cu 2 O Cu device structures were found to be similar to that of a metal-insulator-semiconductor (MIS) tunnel diode, indicating the presence of a thin unidentified interfacial insulating layer between the copper substrate and the cuprous oxide film.