Peter Koshy

Tearing behavior of blends of isotactic polypropylene and nitrile rubber: influence of blend ratio, morphology and compatibilizer loading

Tearing behavior of blends of isotactic polypropylene (PP) and nitrile rubber (NBR) has been investigated with special reference to the effect of blend ratio and addition of compatibilizing agents. It has been observed that the tear strength of blends depends on the rubber concentration. Attempts have been made to correlate the tear strength with the morphology of the blends. Various composite models such as parallel model, series model, Halpin-Tsai equation and Corans model have been used to fit the experimental values. The effect of addition of phenolic modified polypropylene (Ph-PP) as a compatibilizer on the tear strength of PP/NBR blend was investigated. The observed increase in tear strength with increase of Ph-PP concentration has been explained in terms of the reduction in particle size of dispersed NBR domains.

Electrical conductivity and impedance spectroscopy studies of cerium based aeschynite type semiconducting oxides: CeTiMO6 (M=Nb or Ta)

Complex ceramic oxides, CeTiMO6 (M=Nb or Ta) having aeschynite type mineral structure were prepared by the conventional ceramic route. Complex impedance analysis in the frequency range 10 Hz–1 MHz over a wide temperature range (30–600 °C) indicates the presence of grain boundary effect along with the bulk contribution and also confirms the presence of non-Debye type of multiple relaxations in the material. The frequency dependent conductivity plots exhibit double power law dependence suggesting three types of conduction mechanisms: low frequency (10 Hz–1 kHz) conductivity owing to long range translational motion of electrons (frequency independent), mid-frequency conductivity (1–10 kHz) due to short-range hopping, and high frequency (10 kHz–1 MHz) conduction due to localized orientation hopping mechanism. The hopping model can explain the nature of the conduction mechanism completely. The electrical conductivity measurements with temperature suggest the negative temperature coefficient of resistance behav...

Influence of cation substitution and activator site exchange on the photoluminescence properties of Eu3+-doped quaternary pyrochlore oxides.

Stannate-based pyrochlore-type red phosphors CaGd(1-x)SnNbO7:xEu(3+), Ca(1-y)Sr(y)Gd(1-x)SnNbO7:xEu(3+), and Ca(0.8-x)Sr0.2GdSnNbO(7+δ): xEu(3+) were prepared via conventional solid-state method. Influence of cation substitution and activator site control on the photoluminescence properties of these phosphors are elucidated using powder X-ray diffraction, Rietveld analysis, Raman spectrum analysis, and photoluminescence excitation and emission spectra. The Eu(3+) luminescence in quaternary pyrochlore lattice exemplifies as a very good structural probe for the detection of short-range disorder in the lattice, which otherwise is not detected by normal powder X-ray diffraction technique. The Eu(3+) emission due to magnetic dipole transition ((5)D0-(7)F1 MD) is modified with the increase in europium concentration in the quaternary pyrochlore red phosphors. (5)D0-(7)F1 MD transition splitting is not observable for low Eu(3+) doping because of the short-range disorder in the pyrochlore lattice. Appearance of narrow peaks in Raman spectra confirms that short-range disorder in the crystal lattice disappears with progressive europium doping. By using Sr as a network modifier ion in place of Ca we were able to increase the f-f transition intensities and europium quenching concentration. The influence of effective positive charge of the central Eu(3+) ions when it replaces a metal ion having lower oxidation state such as Ca(2+) was also investigated. The relative intensities of A1g (∼500 cm(-1)) and F2g (∼330 cm(-1)) Raman vibrational modes get inverted when Eu(3+) ions replaces Ca(2+) ions instead of Gd(3+) as trivalent europium ions can attract the electron cloud of oxygen ions strongly in comparison with divalent calcium ions. The influence of positive charge effect of Eu(3+) in Ca0.7Sr0.2GdSnNbO7+δ:0.1Eu(3+) phosphor is greatly strengthened the charge transfer band and (7)F0-(5)L6 transition intensities than that of the Ca0.8Sr0.2Gd0.9SnNbO7:0.1Eu(3+) phosphor. Our results suggest that the photoluminescence properties can be enhanced by simple compositional adjustments in the quaternary pyrochlore-type red phosphors.

Multiband Orange-Red-Emitting Phosphors SrY3SiP5O20 : Eu3 + under Near-UV Irradiation

The photoluminescence properties of silicon-based xenotime-type rare-earth phosphate as an orange-red-emitting phosphor material, Sry 3 Sip 5 O 20 :xEu 3+ (0.2, 0.6, 1, 2, 3, 5, 10, and 15 mol %), are reported. The photoluminescence spectra of the silicon phosphate indicated the simultaneous occurrence of six predominant orange-red band emissions due to doubly split magnetic-dipole ( 5 D 0 - 7 F 1 ), electric-dipole ( 5 D 0 - 7 F 2 ), and unusual ( 5 D 0 - 7 F 4 ) transitions under a near-UV wavelength excitation. The multiband emission of Eu 3+ at 5 D 0 - 7 F 1,2,4 is attributed to the odd-parity distortions of the Eu 3+ surrounding environment. With high Eu3+ concentration, the phosphor has a strong excitation due to f-f transitions appearing at around 396 nm, which correspond to the popular emission line from a near-UV light-emitting diode (LED) chip. Thus, the intense orange-red emission of the silicon phosphate phosphors under near-UV excitation suggests them to be a potential candidate for white light generation by using near-UV LEDs.

EDAX versus FTIR in mixed stones

Mixed stones form a significant number of all urinary stones. Accurate analysis of individual areas of stones is fraught with uncertainties. Scanning electron microscopy with elemental distribution analysis (SEM-EDAX) is a very important tool in assessing stone composition. The objective of this paper is to project the role of the combination of Fourier transform infrared (FTIR) spectroscopy and SEM-EDAX combination in achieving a total understanding of mixed stone morphology. Ten mixed urinary stones were washed and dried and the composition recognized by analysis of FTIR spectra by comparing with the spectra of pure components. Spectra for different layers were obtained. Then the stone samples were further studied by SEM-EDAX analysis. The findings of FTIR were correlated with SEM-EDAX and detailed data generated. Using SEM-EDAX, the spatial distribution of major and trace elements were studied to understand their initiation and formation. As much as 80% of the stones studied were mixtures of calcium oxalate monohydrate (whewellite) and calcium phosphate (hydroxyapatite) in various proportions. Quantitative evaluation of components was achieved through FTIR and SEM-EDAX analysis. It was possible to get an idea about the spatial distribution of molecules using SEM analysis. The composition of different areas was identified using EDAX. Analyzing with EDAX, it was possible to obtain the percentage of different elements present in a single sample. The study concludes that the most common mixed stone encountered in the study is a mixture of calcium oxalate monohydrate and calcium phosphate in a definite proportion. The combination identified not only the molecular species present in the calculus, but also the crystalline forms within chemical constituents. Using EDAX, the amount of calcium, phosphorus, oxygen and carbon present in the stone sample could be well understood.

Role of bond strength on the lattice thermal expansion and oxide ion conductivity in quaternary pyrochlore solid solutions.

Quaternary pyrochlore-type solid solutions, CaGdZrNb(1-x)Ta(x)O(7) (x = 0, 0.2, 0.4, 0.6, 0.8, 1), were prepared by a high-temperature ceramic route. The pyrochlore phases of the compounds were confirmed by powder X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy. The crystallographic parameters of the pyrochlore compounds were accurately determined by Rietveld analysis of the powder XRD data. The isovalent substitution of Ta in place of Nb at the B site can reveal the effect of chemical bonding on lattice thermal expansion and oxide ion conductivity because both Nb and Ta have the same ionic radius (0.64 Å). Lattice thermal expansion coefficients of the samples were calculated from high-temperature XRD measurements, and it was found that the thermal expansion coefficient decreases with substitution of Ta. Oxide ion conductivity measured by a two-probe method also shows the same trend with substitution of Ta, and this can be attributed to the high bond strength of the Ta-O bond compared to that of the Nb-O bond. Microstructural characterization using scanning electron microscopy proves that the size of the grains has a small effect on the oxide ion conductivity. Our studies established the role of chemical bonding in deciding the conductivity of pyrochlore oxides and confirmed that the 48f-48f mechanism of oxide ion conduction is dominant in pyrochlore oxides.

Preparation and characterization of bismuth rare earth tungstate (BiREWO6) dielectric ceramics

BiREWO6[RE=La, Nd, Pr, Sm, Gd, Dy, Tb, Yb, Y] ceramics have been prepared by the conventional solid-state ceramic route. The sintered samples are characterized by X-ray diffraction and SEM methods. The ceramics have high dielectric constants in the range 25–55 depending on the rare earth element. The dielectric losses of these ceramics increase with increase in the frequency and with increase in the rare earth crystal radii.

Ba3Ce3Ti5Nb5O30—a novel ceramic oxide semiconductor

A novel ceramic oxide semiconductor Ba3Ce3Ti5Nb5O30 was prepared by solid state route. XRD shows that it has tetragonal tungsten bronze-type crystalline structure. The electrical conductivity at 30 °C is 3.49×10−7 ohm−1 cm−1 and at 600 °C is 1.2×10−2 ohm−1 cm−1. The activation energy of the carriers has been found to be 0.41 eV Ce+3 and is probably structurally stabilized in this compound.

Pyrochlore-based oxides with small temperature coefficient of dielectric constant

Pyrochlore based oxides with small temperature coefficient of dielectric constant (TCK) in Ca–RE–Ti–M–O (RE=Sm or Dy and M=Nb or Ta) system are reported. The 1MHz dielectric constants of these oxides vary from 26 to 102. The TCK in the vicinity of room temperature (20°C) dramatically decreases, from more than −200 for CaRETiMO7 to less than −3ppm∕°C in the solid solutions of CaRETiNbO7–CaRETiTaO7 phases. Rietveld analysis of the x-ray diffraction data establishes a cubic pyrochlore-type phase in the space group Fd3m (No. 227).

Optical microscopy versus scanning electron microscopy in urolithiasis.

Stone analysis is incompletely done in many clinical centers. Identification of the stone component is essential for deciding future prophylaxis. X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy (SEM) still remains a distant dream for routine hospital work. It is in this context that optical microscopy is suggested as an alternate procedure. The objective of this article was to assess the utility of an optical microscope which gives magnification of up to 40× and gives clear picture of the surface of the stones. In order to authenticate the morphological analysis of urinary stones, SEM and elemental distribution analysis were performed. A total of 250 urinary stones of different compositions were collected from stone clinic, photographed, observed under an optical microscope, and optical photographs were taken at different angles. Twenty-five representative samples among these were gold sputtered to make them conductive and were fed into the SEM machine. Photographs of the samples were taken at different angles at magnifications up to 4,000. Elemental distribution analysis (EDAX) was done to confirm the composition. The observations of the two studies were compared. The different appearances of the stones under optical illuminated microscopy were mostly standardized appearances, namely bosselations of pure whewellite, spiculations of weddellite, bright yellow colored appearance of uric acid, and dirty white amorphous appearance of phosphates. SEM and EDAX gave clearer pictures and gave added confirmation of the stone composition. From the references thus obtained, it was possible to confirm the composition by studying the optical microscopic pictures. Higher magnification capacity of the SEM and the EDAX patterns are useful to give reference support for performing optical microscopy work. After standardization, routine analysis can be performed with optical microscopy. The advantage of the optical microscope is that, it is easy to use and samples can be analyzed in natural color.