Thermal studies on melting and crystallization of polyamide fibres

Effect of heating rate on melting and crystallization of polyamide fibres has been examined using differential scanning calorimetric (DSC) technique. Peak temperature for melting (T m) and crystallization (T k) get suppressed with the increase in the heating rate which has been explained on the basis of chain orientation. Heat of melting (DeltaH m) and crystallization (DeltaH k) have been measured.DeltaH m vs. T m shows a nonlinear dependence which has been explained on the basis of entropy change. Quantitative difference inDeltaH m andDeltaH k values has been explained on the basis of orientation and degradation of the polymer.

Differential thermal analysis of potassium perchlorate

A study has been made of the differential thermal analysis of (i) potassium perchlorate in powdered form, (ii) potassium perchlorate in pelletized form, (iii) potassium perchlorate recrystallized from liquid NH3, and (iv) potassium perchlorate preheated for 24 hours at 375°. Pretreatment of potassium perchlorate leads to a desensitization of both endothermic and exothermic processes. Additionally, the pretreatment tends to convert the symmetric exotherm into an asymmetric exotherm due to merging of the two exotherms. An analysis of the factors causing asymmetry in the exotherm has thrown fresh light on the mechanism of thermal decomposition of potassium perchlorate.

Structure-thermal behaviour studies on the salicylato complex of cobalt

The salicylato complex of cobalt was synthesized and its structure established to be [Co(sal)2] · 4 H2O, where, sal =, from elemental analysis, IR spectroscopy, magnetic susceptibility, cryoscopy and conductivity. The X-ray diffractogram of the complex has been given. Thermal decomposition has been studied in air by thermogravimetry (TG), differential thermal analysis and differential scanning calorimetry. TG shows three main steps of decomposition. The intermediates formed at various stages were collected and analysed. From the TG results and chemical analysis of the intermediates, a mechanism has been proposed for the thermal decomposition of the complex, leading to the oxide formation in the final stage.

Crystallization behaviour of polyethylene and i-polybutene-1 blends

The mutual influence of the components on the crystallization behaviour of polyblends, namely, isotactic polybutene-1 (PB) with low-density and high-density polyethylene (LDPE and HDPE), has been studied using techniques such as differential scanning calorimetry, infra-red spectroscopy, wide-angle X-ray diffraction, scanning electron microscopy, etc. Each component in the blend is observed to crystallize independently. There is phase separation and incompatibility, as shown from tensile properties and scanning electron microscopic observation of the fracture surface of the blend. For HDPE-PE blends (<30% HDPE), unusual form I′ crystals of PB are observed along with the usual form II.

Mechanism of the thermal decomposition of polystyrene peroxide

The thermal degradation of polystyrene peroxide was carried out using differential scanning calorimetry. The activation energy (E) was found to be 136 kJ mole–1 at all extents of decomposition. TheE value was found to correspond to-O-O-dissociation. The order of reaction was found to decrease from 2 to 1 as the decomposition progresse.

Silica from rice husk through thermal decomposition

The thermal decomposition characteristics of rice husk have been investigated by dynamic thermoanalytical techniques: DTA, TG, DTG and isothermal heating. The observed thermal behaviour is explained on the basis of a superposition of the decomposition of cellulose and lignin, which are the major organic constituents of rice husk. Morphological features of silica in husk as well as the ash are examined by scanning electron microscopy. Silica in the residual ash has been characterised by X-ray diffraction and infrared spectroscopy. Controlled thermal decomposition of rice husk has been shown to be a convenient method for the liberation of silica.

Competing tetragonal and monoclinic phases in Ni2.2Mn0.80Ga

Temperature dependent synchrotron x-ray powder diffraction, differential scanning calorimetry, and magnetic measurements were performed on Ni2+xMn1-xGa (x=0.20 and 0.35) magnetic shape memory alloys. For x=0.20, though the monoclinic phase is thermodynamically stable, a trace of residual stress can stabilize a tetragonal phase. The residual-stress-induced tetragonal phase transforms to the cubic austenite phase over an unusually large temperature range (348 K < T < 693 K), suggesting extremely slow kinetics of transformation. In contrast to x=0.20, the thermodynamically stable phase of x=0.35 is tetragonal and this composition exhibits the usual features of a reversible martensitic transformation. The results suggest that for x=0.20 the monoclinic and tetragonal phases are nearly degenerate.

A chitotetrose specific lectin from Luffa acutangula :Physico-chemical properties and the assignment of orientation of sugars in the lectin binding site

A chitooligosaccharide specific lectin (Luffa acutangula agglutinin) has been purified from the exudate of ridge gourd fruits by affinity chromatography on soybean agglutininglycopeptides coupled to Sepharose-6B. The affinity purified lectin was found homogeneous by polyacrylamide gel electrophoresis, in sodium dodecyl sulphate-polyacrylamide gels, by gel filtration on Sephadex G-100 and by sedimentation velocity experiments. The relative molecular weight of this lectin is determined to be 48,000 ± 1,000 by gel chromatography and sedimentation equilibrium experiments. The sedimentation coefficient (S20, w) was obtained to be 4·06 S. The Stokes’ radius of the protein was found to be 2·9 nm by gel filtration. In sodium dodecyl sulphate-polyacrylamide gel electrophoresis the lectin gave a molecular weight of 24,000 in the presence as well as absence of 2-mercaptoethanol. The subunits in this dimeric lectin are therefore held by non-covalent interactions alone. The lectin is not a glycoprotein and circular dichroism spectral studies indicate that this lectin has 31% α-helix and no ß-sheet. The lectin is found to bind specifically to chitooligosaccharides and the affinity of the lectin increases with increasing oligosaccharide chain length as monitored by near ultra-violetcircular dichroism and intrinsic fluorescence titration. The values of ΔG, ΔΗ and ΔS for the binding process showed a pronounced dependence on the size of the oligosaccharide. The values for both ΔΗ and ΔS show a significant increase with increase in the oligosaccharide chain length showing that the binding of higher oligomers is progressively more favoured thermodynamically than chitobiose itself. The thermodynamic data is consistent with an extended binding site in the lectin which accommodates a tetrasaccharide. Based on the thermodynamic data, blue shifts and fluorescence enhancement, spatial orientation of chitooligosaccharides in the combining site of the lectin is assigned.

Thermal decomposition and ignition of coal

A study of the thermal decomposition and ignition of coal as functions of pelletizing pressure and dwell time has revealed that: (1) ignition and thermal behaviour are related to the apparent density of the pelletized coal; (2) for a given apparent density of pelletized coal, the ignition temperature is related to the rate constants of thermal decomposition. Isothermal decomposition in air at 550 °C has been shown to fit the Avrami-Erofeev equation for three-dimensional growth of nuclei.

Effect of inclination on laminar film condensation

The effect of inclination on laminar film condensation over and under isothermal flat plates is investigated analytically. The complete set of Navier Stokes equations in two dimensions is considered. Analysed as a perturbation problem, the zero-order perturbation represents the boundary layer equations. First and second order perturbations are solved to bring about the leading edge effects. Corresponding velocity and temperature profiles are presented. The results show decrease in heat transfer with larger ∥inclinations∥ from the vertical. Comparison with experimental data of Gerstmann and Griffith indicates a closer agreement of the present results than the analytical results of the same authors.

Investigation of surface activity and photoinduced diffusion of metals in solution deposited amorphous films of As2S3

Surface activity of solution deposited (SD) amorphous films of As2S3 has been investigated. Silver and copper are readily deposited on such films from appropriate aqueous ionic solutions. The metals diffuse into the films upon irradiation with energetic photons. Structure and properties of SD films have been investigated using electron microscopy, optical spectroscopy and differential scanning calorimetry. The amorphous films tend to crystallize upon metal diffusion. The stability of amorphous films, the deposition of metals on their active surfaces and the photo-induced diffusion may all be attributed to the presence or production of charged defects in amorphous chalcogenide films.

Effect of ion temperature on propagation of ion-acoustic solitary waves of small amplitudes in collisionless plasma

By using a perturbation technique, the Korteweg-de Vries equation is derived for a mixture of warm-ion fluid and hot, isothermal electrons. Stationary solutions are obtained for this equation and are compared with the corresponding solutions for a mixture consisting of cold-ion fluid and hot, isothermal electrons.

Crystallization Kinetics and Electrical Relaxation of BaO-0.5Li(2)O-4.5B(2)O(3) Glasses

Transparent glasses in the composition BaO-0.5Li(2)O-4.5B(2)O(3) (BLBO) were fabricated via the conventional melt-quenching technique. X-ray powder diffraction combined with differential scanning calorimetric (DSC) studies carried out on the as-quenched samples confirmed their amorphous and glassy nature, respectively. The crystallization behavior of these glasses has been studied by isothermal and nonisothermal methods using DSC. Crystallization kinetic parameters were evaluated from the Johnson-Mehl-Avrami equation. The value of the Avrami exponent (n) was found to be 3.6 +/- 0.1, suggesting that the process involves three-dimensional bulk crystallization. The average value of activation energy associated with the crystallization of BLBO glasses was 317 +/- 10 kJ/mol. Transparent glass-ceramics were fabricated by controlled heat-treatment of the as-quenched glasses at 845 K/40 min. The dielectric constants for BLBO glasses and glass-ceramics in the 100 Hz-10 MHz frequency range were measured as a function of the temperature (300-925 K). The electrical relaxation and dc conductivity characteristics were rationalized using electric modulus formalism. The imaginary part of the electric modulus spectra was modeled using an approximate solution of the Kohlrausch-Williams-Watts relation. The temperature-dependent behavior of stretched exponent (beta) was discussed for the as-quenched and heat-treated BLBO glasses.

Crystal growth and characterization of two-leg spin ladder compounds: Sr14Cu24O41 and Sr2Ca12Cu24O41

Single crystals of Sr14−xCaxCu24O41 (x=0 and 12) are grown by the travelling solvent floating zone technique using an image furnace. The grown crystals are characterized for their single crystallinity by the X-ray and Neutron Laue method. The magnetic susceptibility measurements in Sr14Cu24O41 show considerable anisotropy along the main crystallographic axes. Low-temperature specific heat measurement and DC susceptibility measurement in Ca-doped crystal showed antiferromagnetic ordering at 2.8 K at ambient pressure. High-pressure AC susceptibility measurement on Ca-doped crystal showed a sharp superconducting transition at 2 K under 40 kbars. Tc onset reached a maximum value of 9.9 K at 54 kbars. The bulk superconductivity of the sample is confirmed by the high-pressure AC calorimetry with Tc max=9.4 K and TN=5 K at 56 kbars.

Properties of the gold related acceptor level in silicon

The apparent thermal activation energy of 0.56 eV and the electron thermal capture cross section of 2.0 × 10-16 cm2 are measured for the gold related acceptor level in p+ nn+ silicon diodes by isothermal current transient and DLTS techniques. Using the emission and capture rate data and a degeneracy ratio of 2, the energy separation of the trap level from the conduction band is calculated and found to have the same temperature dependence as the band gap indicating that the acceptor level is pinned with respect to the valence band a t Ev + 0.637 eV.