Dr. Jacob Philip
https://dyuthi.cusat.ac.in:443/xmlui/handle/purl/2022
2024-02-07T17:28:20ZThermal Properties of Polytetrafluoroethylene/ Sr2Ce2Ti5O16 Polymer/Ceramic Composites
https://dyuthi.cusat.ac.in:443/xmlui/handle/purl/2030
Thermal Properties of Polytetrafluoroethylene/ Sr2Ce2Ti5O16 Polymer/Ceramic Composites
Jacob, Philip; Subodh, G; Manjusha, M V; Sebastian,M T
Polytetrafluoroethylene (PTFE) composites
filled with Sr2Ce2Ti5O16 ceramic were prepared by a powder
processing technique. The structures and microstructures
of the composites were investigated by X-ray diffraction
and scanning electron microscopy techniques. Differential
scanning calorimetry showed that the ceramic filler
had no effect on the melting point of the PTFE. The effect
of the Sr2Ce2Ti5O16 ceramic content [0–0.6 volume fraction
(vf)] on the thermal conductivity, coefficient of thermal
expansion (CTE), specific heat capacity, and thermal diffusivity
were investigated. As the vf of the Sr2Ce2Ti5O16 ceramic increased, the thermal conductivity of the specimen
increased, and the CTE decreased. The thermal conductivity
and thermal expansion of the PTFE/Sr2Ce2Ti5O16
composites were improved to 1.7 W m21 8C21 and 34
ppm/8C, respectively for 0.6 vf of the ceramics. The experimental
thermal conductivity and CTE were compared
with different theoretical models.
2008-01-01T00:00:00ZYoung’s modulus of silicon nitride used in scanning force microscope cantilevers
https://dyuthi.cusat.ac.in:443/xmlui/handle/purl/2029
Young’s modulus of silicon nitride used in scanning force microscope cantilevers
Jacob, Philip; Khan, A; Hess, P
The Young’s modulus and Poisson’s ratio of high-quality silicon nitride films with 800 nm thickness,
grown on silicon substrates by low-pressure chemical vapor deposition, were determined by
measuring the dispersion of laser-induced surface acoustic waves. The Young’s modulus was also
measured by mechanical tuning of commercially available silicon nitride cantilevers, manufactured
from the same material, using the tapping mode of a scanning force microscope. For this
experiment, an expression for the oscillation frequencies of two-media beam systems is derived.
Both methods yield a Young’s modulus of 280–290 GPa for amorphous silicon nitride, which is
substantially higher than previously reported (E5146 GPa). For Poisson’s ratio, a value of n
50.20 was obtained. These values are relevant for the determination of the spring constant of the
cantilever and the effective tip–sample stiffness
2004-02-15T00:00:00ZUltrasonic measurement of the elastic properties of benzoyl glycine single crystals
https://dyuthi.cusat.ac.in:443/xmlui/handle/purl/2028
Ultrasonic measurement of the elastic properties of benzoyl glycine single crystals
Jacob, Philip; Alex,A V
Certain organic crystals are found to possess high non- linear optical coefficients,often one to two orders of magnitude higher than those of the well known inorganic non-linear optical materials.Benzoyl glycine is one such crystal whose optical second-harmonic generation efficiency is much higher than that of potassium dihydrogen phosphate. Single crystals of benzoyl glycine are grown by solvent evaporation technique using N,N-dimethyl formamide as the solvent.All the nine second-order elastic stiffness constants of this orthorhombic crystal are determined from ultrasonic wave velocity measurements employing the pulse echo overlap technique.The anisotropy of elastic wave propagation in this crystal is demonstrated by plotting the phase velocity, slowness,Young's modulus and linear compressibility surfaces along symmetry planes.The volume compressibility, bulk modulus and relevant Poisson's ratios are also determined. Variation of the diagonal elastic stiffness constants with temperature over a limited range are measured and reported.
2004-01-01T00:00:00ZThermal transport across incommensurate phases in potassium selenate: photo-pyroelectric and calorimetric measurements
https://dyuthi.cusat.ac.in:443/xmlui/handle/purl/2027
Thermal transport across incommensurate phases in potassium selenate: photo-pyroelectric and calorimetric measurements
Jacob, Philip; Manjusha, M V
The thermal transport properties—thermal diffusivity, thermal conductivity and specific heat
capacity—of potassium selenate crystal have been measured through the successive phase
transitions, following the photo-pyroelectric thermal wave technique. The variation of thermal
conductivity with temperature through the incommensurate (IC) phase of this crystal is
measured. The enhancement in thermal conductivity in the IC phase is explained in terms of
heat conduction by phase modes, and the maxima in thermal conductivity during transitions is
due to enhancement in the phonon mean free path and the corresponding reduction in phonon
scattering. The anisotropy in thermal conductivity and its variation with temperature are
reported. The variation of the specific heat with temperature through the high temperature
structural transition at 745 K is measured, following the differential scanning calorimetric
method. By combining the results of photo-pyroelectric thermal wave methods and differential
scanning calorimetry, the variation of the specific heat capacity with temperature through all the
four phases of K2SeO4 is reported. The results are discussed in terms of phonon mode softening
during transitions and phonon scattering by phase modes in the IC phase.
2009-01-01T00:00:00Z