Debasish Roy

Improvement of lubrication and cooling in grinding

ABSTRACT The presence of air boundary layer around a grinding wheel impedes the proper entry of cutting fluid into grinding zone and thereby lubrication and cooling are hampered. It leads to the thermal damage to the workpiece and rapid wheel wear. This experimental work is aimed at increasing the lubrication and cooling effects in grinding by a novel method of using scraper board. The experiments are conducted, using the scraper board, to find the critical region where the air pressure is zero. The coolant jet has then impinged into the grinding zone which is maintained within the critical region. The requirement of specific energy, surface texture, and mechanical properties of the ground surface are analyzed and compared with the traditional grinding and the grinding at various positions of scraper board. Results show that the grinding ratio improved by 35.6and 119%, surface roughness decreased by 36 and 54.2%, while the requirement of specific energy is reduced by 50.8 and 57.3% when scraper board is positioned at the critical distance in comparison to the 57.5° position and no scraper board, respectively. The results indicate that the introduction of fluid in the present method can improve the process efficiency and the product quality effectively.

Structural and Optical Properties of V2O5-MoO3-ZnO Glass-Nanocomposite System

ABSTRACT The present work points to highlight the physical, structural and the optical properties of some semiconducting V2O5-MoO3-ZnO glass-nanocomposites using density, molar volume, X-ray diffraction (XRD), field effect scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and UV-VIS absorption spectra. We have observed that addition of V2O5 increases (or decreases) the density (or molar volume) of the glassy system due to structural changes. Distribution of Zn3V2MoO11, Zn2.5VMoO8 and Zn2V2O7 nanoparticles has been confirmed from FESEM and XRD studies. It has been observed from FTIR spectra that the network structure depends upon isolated strongly deformed M oO4 polyhedra and VO4 metavanadate chains. Vibrations of MoO6 octahedra, Zn2V2O6, Zn2V2O7, Zn3V2MoO11 and VO2 are observed from the Raman spectroscopic studies. The fundamental UV-VIS absorption spectra have been analyzed, which indicates indirect transitions. GRAPHICAL ABSTRACT

Positron annihilation studies and complementary experimental characterization of xAg2O–(1 − x)(0.3CdO–0.7MoO3) metal oxide glass nanocomposites

Metal oxide nanocomposites of the composition xAg2O–(1 − x)(0.3CdO–0.7MoO3) were prepared by a melt-quenching method and were characterized by different experimental techniques like X-ray diffraction, high resolution transmission electron microscopy and optical absorption spectroscopy. X-ray diffraction showed sharp diffraction peaks indicating large crystallites but transmission electron microscope images also showed crystallites of nanometer dimensions in appreciable concentrations, which confirmed the nanocomposite structure of the samples. Although the lattice constants did not show significant changes with the increase in concentration (x) of Ag2O, there is considerable relaxation of the growth-induced strain above x = 0.2. Interestingly this is also the concentration above which the optical band gap energy showed a mild decrease. One salient feature of this study is the use of positron annihilation spectroscopy for identifying and monitoring the structural defects such as vacancies and vacancy clusters as well as the free volume cavities during the change in concentration of Ag2O. Positron lifetime measurements indicated trapping of positrons initially in the interfacial defects within the 0.3CdO–0.7MoO3 nanocrystalline ensemble and then in the free volume defects within the amorphous Ag2O matrix. At higher Ag2O concentrations, positron trapping appeared to take place within the Cd2+-monovacancies in CdO and in the divacancies of neighbouring cationic and oxygen monovacancies in the α-MoO3 and CdMoO4 nanocrystallites. At x = 0.1–0.2, the effective positron trapping centres are translocated to the tetrahedral Mo6+-monovacancies instead of the Cd2+-monovacancies. The results of coincidence Doppler broadening spectroscopic measurements, which map the electron momentum distribution and its variations, indicated increasing trapping of positrons with increasing concentration of Ag2O, which again is attributed to the trapping sites in the increasing number of nanocrystallites being formed.

On the problem of a unified study of HCP metals from a perturbative approach: A possible resolution

Abstract The present work is an attempt to identify the role of pseudopotential third order energy in different lattice mechanical properties of HCP metals. Although it plays an important role in explaining the typical features of the phonon dispersion curves, the third order contribution to the individual elastic constants is found to be unphysical. The root of this unphysical contribution may be identified with the singularity in the derivative of the g -function appearing in the expression for the third order energy. A possible solution to this problem is suggested. An alternative approach of a unified study in the framework of a second order pseudopotential theory invoking the consistency condition is also examined. This method simulates the effect of some terms beyond the second order in lattice dynamics and explains typical features of the phonon dispersion curves which are believed to be manifestations of the many-ion effect.

On the mechanical properties of selenite glass nanocomposites

In this paper the room temperature micro-hardness of selenite glass-nanocomposites has been measured using a Vickers and Knoop micro hardness tester where the applied load varies from 0.01N to 0.98 N. A significant indentation size effect was observed for each sample at relatively low indentation test loads. The classical Meyer’s law and the proportional specimen resistance model were used to analyze the micro-hardness behavior. It was found that the selenite glass-nanocomposite becomes harder with increasing CuI composition and the work hardening coefficient and mechanical properties like Young modulus, E, were also calculated. Our results open the way for the preparation, application and investigation of significant mechanical properties of new type of glass-nanocomposites.

Lattice mechanical properties of yttrium and scandium

Abstract Our previous three-body force model [8] is modified and used to calculate the elastic constants and phonon dispersion curves of yttrium and scandium. It is demonstrated that the interpretation of the volume strain as the local strain, as the adiabatic hypothesis demands, leads to an effective three-body interaction which is essential to guarantee the equality of the static and dynamic elastic constants. This model satisfies the two equilibrium conditions and the symmetry properties of the dynamical matrix. The results obtained with this model are in good agreement with the available experimental data. The experimental phonon dispersion curves for these metals do not provide a clear picture along the [1 1 2 0] direction. Out of the six possible branches only two are measured; the other four which would provide valuable informations about the importance of three-body forces are not available. As for these branches, the calculated results may provide useful information.

V 2 O 5 -MoO 3 -ZnO thick film resistors as highly selective trace level ethanol gas sensors

The Glass nanocomposite materials in the form of fine granular powders were synthesized by conventional melt quenching technique. Thick films of the synthesized powders were fabricated by screen printing technique, followed by firing at 100oC, for 2 hours. Upon exposure to 50 ppm ethanol gas, due to oxidation or reduction reaction at the surface of the as prepared nanocomposite materials with the target gas, exchange of electrons take place thereby affecting the sensors resistance greatly leading to drastic change in conductance. The glass nanocomposite of composition xV2O5-(1−x) (0.05MoO3-0.95ZnO) where x = 0.95 (sample-C) was observed to most sensitive to ethanol at room temperature. The surface misfits, operating temperature, gas concentrations, etc. affect the microstructure and gas sensing performance of the sensing element. The quick response and fast recovery are the main features of this sensor. The microstructure of the as prepared glass nanocomposites was analyzed to study the gas response and selectivity of the sensor in the presence of ethanol and some other gases also.

Electrical and mechanical properties of ZnO doped silver-molybdate glass-nanocomposite system

Zno doped silver-molybdate glass-nanocomposites, 0.3 Ag2O - 0.7 [0.075 ZnO – 0.925 MoO3] have been prepared by melt-quenching method. Ionic conductivity of these glass-nanocomposites has been measured in wide temperature and frequency windows. Vicker’s hardness methods have been employed to study micro-hardness of the as-prepared samples. Heat-treated counterparts for this glass-nanocomposites system has been analyzed in different temperature to observe the changes in conductivity as well as micro-hardness for that system.

Relaxation of Cu+2 in selenite glass nanocomposites

The present study mainly focuses on the electrical relaxation data of some glass-nanocomposites. We have prepared xCuI- (1-x)(0.5CuO - 0.5SeO2) where x = 0.2 and 0.5 using melt-quenching method. Ionic relaxation data of these glass-nanocomposites have been analyzed in the framework of the electric modulus formalism. Conductivity relaxation frequency (τc) has been computed from the maximum value (M//max) of the imaginary modulus M//. It is also observed that the conductivity relaxation process is highly non-exponential. The variation of conductivity relaxation time is correlated with their structure.

An adiabatic formulation of the quadrupolar charge deformation in the study of lattice dynamics of covalent solids

Abstract An adiabatic formulation of the dipolar charge deformation has been found to be quite important in solids. The present formulation is quite general and may be applied to cases where in addition to the dipole deformation the quadrupole is also important. However, as a preliminary application of the formulation we consider homopolar crystals where the symmetry indicates that the dominant multipole deformation of the charge cloud is quadrupolar, dipolar deformation being totally absent. The results obtained give us an idea about the order of magnitude of this effect.