B. K. Samantaray

EVA/clay nanocomposite by solution blending: Effect of aluminosilicate layers on mechanical and thermal properties

Ethylene vinyl acetate (EVA)/clay nanocomposites were synthesized by blending a solution of ethylene vinyl acetate copolymer containing 12% vinyl acetate abbreviated as EVA-12 in toluene and dispersion of dodecyl ammonium ion intercalated montmorillonite (12Me-MMT) inN,N-dimethyl acetamide (DMAc). X-ray patterns of sodium montmorillonite (Na+-MMT) and 12Me-MMT exhibited d001 peak at 2θ?=7.4° and 2θ?=5.6° respectively; that is, the interlayer spacing of MMT increased by about 0.39 nm due to intercalation of dodecyl ammonium ions. The XRD trace of EVA showed no peak in the angular range of 3–10° (2θ). In the XRD patterns of EVA/clay hybrids with clay content up to 6 wt% the basal reflection peak of 12Me-MMT was absent, leading to the formation of delaminated configuration of the composites. When the 12Me-MMT content was 8 wt% in the EVA-12 matrix, the hybrid revealed a peak at about 2θ?=5.6°, owing to the aggregation of aluminosilicate layers. Transmission electron microscopic photograph exhibited that an average size of 12–15 nm clay layers were randomly and homogeneously dispersed in the polymer matrix, which led to the formation of nanocomposite with delaminated configuration. The formation of delaminated nanocomposites was manifested through the enhancement of mechanical properties and thermal stability, e.g. tensile strength of an hybrid containing only 2 wt% 12Me-MMT was enhanced by about 36% as compared with neat EVA-12.

Dehydration transformation in Ca-montmorillonite

The present work deals with the dehydration transformation of Ca-montmorillonite in the temperature range 30°–500°C. Thermal, infrared (IR), and X-ray diffraction (XRD) analyses were used to describe the thermal transformation. The microstructural and layer disorder parameters like crystallite size, r.m.s. strain (〈e2〉1/2), variation of interlayer spacing (g), and proportion of planes which were affected by the defect (γ), have all been calculated from the (001) basal reflection using the method of variance and Fourier line shape analysis. These investigations revealed that sample underwent transformation from hydrated phase to dehydrated phase at 200°C, and as a consequence, its basal spacing collapsed from 1602 Å (30°C) to around 10 Å (200°C). This transformation occurred through a wide range of temperature, i.e. within the range 120°–200°C. The crystallite size was maximum at room temperature (30°C), however, the size decreased with increasing temperature in the hydrated phase, whereas the size increased with increasing temperature for the dehydrated phase. Theg, γ and 〈e2〉1/2 of the hydrated and the dehydrated phase increased and decreased, respectively with increase of heating temperature.

Studies on layer disorder, microstructural parameters and other properties of tungsten-substitued molybdenum disulfide, Mo1−xWxS2 (0≤x≤1)

Abstract The present paper deals with the preparation of tungsten-substituted molybdenum disulfide, Mo 1− x W x S 2 (0≤ x ≤1) compounds and their characterization by various physicochemical methods. X-ray studies confirmed that these compounds crystallized in a layer type of hexagonal structure. X-ray line profile analysis techniques such as the method of variance and Fourier analysis have been used for microstructural characterization of these compounds to find out information about particle size, r.m.s. strain, variability of interlayer spacing, fraction of planes affected by such defects, dislocation density, stacking fault probability and radial distribution function analysis for calculating coupling constants and mean-square displacements, etc. Room-temperature magnetic susceptibility measurements and thermoelectric power experiments and temperature variation of conductivity (25–350°C) confirmed, respectively, diamagnetic n- and p-type semiconducting behaviour for Mo 1− x W x S 2 . Thermal stability behaviour of these compounds in air and inert atmosphere has also been carried out up to 1000°C. These studies indicated that the compounds are nearly stable up to 1000°C in inert atmosphere, whereas, in air, oxidative degradation of these compounds started at 400°C. The nature of the oxidized products has also been studied by X-ray analysis. Scanning electron micrograph studies are also reported here.

Mechanical and dielectric properties of pineapple fibres

Pineapple fibres are well known for their commercial uses in making fabrics especially in northeastern India. Although other natural cellulose fibres like cotton, jute, ramie, hemp, etc., have been widely studied for their various properties [1-4], no work appears to have been reported on these industrially potential fibres. Hence a study of the structure and various mechanical and dielectric properties of the fibres was undertaken to help the users to better utilize this commercially cheaper variety of fibres. For this purpose a specimen of pineapple fibres from Manipur, India was selected. The fibres were first purified from fat, wax and lignin by successively treating them with an alcohol-benzene mixture and sodium chlorite solutions, respectively. The purified sample was then first subjected to thermal and X-ray analyses. The differential thermal analysis (DTA) curve showed two endothermal peaks at 150 and 250°C, respectively, indicating a two stage dehydration of the fibres and an exothermal peak at 500 ° C which is due to the burning of the organic matter and possible emergence of some new phase. X-ray diffraction patterns were recorded with the help of a Philips X-ray diffractometer adopting the procedures as described by Mukherjee and Mitra [5]. The values of the lattice parameters obtained from the X-ray diffraction pattern after due correction are a = 8.32A.U., b = 10.3A.U., c = 7.93A.U. and ~ = 82.6 ° . These data conform well with the structure of cellulose type-I [4]. An estimation of the degree of crystallinity [Icryst/Ito~] was made from the X-ray diffractogram by applying the technique

Thermal transformation in a chrysotile asbestos

Structural changes accompanying thermal transformation in a chrysotile asbestos sample of Indian origin upto a temperature of 900°C have been investigated by x-ray method. The changes in lattice parameters have been systematically measured by applying a least square refinement technique and the crystallite size and strain defects at different stages have been estimated by line profile analysis of the diffraction peaks. The present study also confirms the earlier results on stepwise transformation of chrysotile fibres. This sequence of transformation has been explained assuming two different types of crystallites as reported in kaolinite.

Electrical properties of ramie fibres

We make a in-depth systematic study of the electrical properties of powdered ramie fibre samples instead of a bundle of fibres, under different conditions, to achieve a better understanding of the structure property relation in this cellulosic fiber

Structure of vacuum deposited SnSe films

Tin selenide (SnSe) thin films prepared on mica and glass substrates by vacuum sublimation technique and examined by scanning electron microscopy and transmission electron diffraction techniques showed epitaxial and polycrystalline nature respectively irrespective of substrate temperature. Grain size of the films deposited on glass substrate increased with increase in substrate temperature.

Dehydration and phase transformation in chrysotile asbestos—A radial distribution analysis study

Radial distribution analysis of x-ray intensities diffracted by chrysotile samples untreated and treated at different temperatures upto 900°C has been carried out. Interatomic distances, coordination numbers, mean square displacements and the interatomic coupling constants for different pairs of atoms have been calculated from the radial distribution curves. The interatomic distances and octahedral co-ordination number is found to decrease marginally upto 640°C and thereafter decrease steadily upto 800°C. The hydroxyl water is completely expelled from the structure and the original chrysotile structure breaks down. The entire process of dehydration has been interpreted in terms of RDF data.

Microstructural features of Cd0·8Zn0·2Te thin films studied by X-ray diffraction and electron microscopy

Thin films of synthesized Cd0·8Zn0·2Te have been deposited on glass substrate at different substrate temperatures. Different microstructural parameters like crystallite size, rms strain, dislocation density, stacking fault probability and stacking fault energy are determined by XRD, SEM, TEM and TED. XRD and XPS have been used to determine the composition. Variations of the microstructural parameters with film thickness and substrate temperature have been studied in order to obtain optimum growth condition for maximum particle size and least microstructural defects. An effort has been made to correlate the experimental results.