Volume 21, Issue 4
August 1998, pages 263-361
pp 263-278 August 1998 Review Article
Confocal laser scanning microscope (CLSM) has great advantage over a conventional microscope because it rejects the light that does not come from the focal plane, enabling one to perform optical slicing and construction of three-dimensional (3D) images. Further its high axial resolution, sharp image quality and associated quantitative image analysis provide vital structural information in the mesoscopic range for the full 3D realization of the microstructure. Because of this unique feature, CLSM is now finding wider applications in the study of variety of materials and processes such as phase separation in binary polymer mixtures, fracture toughness in alloys, in determining residual strains in fibre-reinforced metal composites, and in microvisualization of corrosion. This paper reviews some of these recent applications and also discusses our results on colloidal dispersions. CLSM has been used to characterize the amorphous structure in highly-charged colloidal systems which have undergone gas-solid transition. CLSM images show presence of large voids deep inside the disordered suspensions. Frame averaged images reveal that the structural disorder is amorphous. The reasons for voids coexisting with dense amorphous regions and their implications on colloidal interactions are discussed. The article also reviews the use of fluorescence-CLSM in the investigation of novel materials of technological importance such as template-directed colloidal crystals with preferred orientations and multilayered structures with different crystal plane symmetries. Direct measurement of the interfacial curvatures for a bicontinuous polymer blend system as well as real space measurement of structure in phase separating polymer mixtures are now possible using CLSM. This paper reviews some of these results highlighting the unique advantages of confocal microscopy for better understanding of the microstructure and mechanistic aspects of various important phenomena in a large variety of materials.
pp 279-282 August 1998 Material Synthesis
A new hexaferrite composition, BaCoxSix+yFe12−2x−yO19 (x=0·90;y=0·05), in fine (∼μ size) powder form, is prepared. Ferrite paint formulations are made by dispersing this powder in different weight proportions in an epoxy resin. X-band (8–12 GHz) microwave absorption behaviour of the paint coatings of different thicknesses is studied. Remarkably high value, ≥10 dB, of signal absorption at 9·5 GHz is observed for a coating thickness of 0·60 mm with a ferrite fill factor of 57 wt%.
pp 283-286 August 1998 Material Synthesis
Silicon dioxide films on strained Si1−xGex have been deposited by electron cyclotron resonance (ECR) plasma-enhanced chemical vapour deposition technique using tetraethylorthosilicate (TEOS) at room temperature. The deposition rate as a function of time and substrate temperature has been studied. MOS capacitors fabricated using deposited oxides have been used to characterize the electrical properties of silicon dioxide films. Deposited oxide film shows its suitability for microelectronic applications.
pp 287-290 August 1998 Nucleation And Growth Studies
Induction periods were measured for various supersaturated aqueous solutions of ammonium dihydrogen orthophosphate doped with ammounium oxalate monohydrate by the direct vision method. Various critical nucleation parameters were calculated based on classical theory for homogeneous crystal nucleation and the results reported and discussed. The critical nucleation parameters increased with increase in doping concentration.
pp 291-295 August 1998 Nucleation And Growth Studies
Single phase copper indium disulphide (CuInS2) thin films of thickness between 60 nm and 650 nm with the chalcopyrite structure are obtained on NaCl and glass substrates by flash evaporation. The films were found to ben-type semiconducting. The influence of the substrate temperature on the crystallinity, conductivity, activation energy and optical band gap was studied. An improvement in the film properties could be achieved up to a substrate temperature of 523 K at a molybdenum source temperature of 1873 K.
pp 297-301 August 1998 Nucleation And Growth Studies
Large single crystals of a few important members (x=0, 1, 2) of the series ZrSxSe2−x compounds have been obtained by chemical vapour (iodine) transport method. The crystals have been characterized for several properties. Their semiconducting nature is inferred from resistivity vs temperature measurements, their optical absorption data reveal indirect gap transitions, their thermoscans indicate their stability over a limited temperature range, and they essentially grow by the mechanism of two dimensional layer propagation.
pp 303-308 August 1998 Nucleation And Growth Studies
Grazing incidence X-ray diffraction, performed on a 70 keV nitrogen implanted Ti-6Al-4V system, reveals phase instabilities, during the course of nitride formation. With the build up of unbound N atom concentration, for a dose of 1×1016 ions/cm2, the surface region becomesα-rich, whereas, on precipitation of Ti-nitrides at a high dose of 1×1017 ions/cm2, theβ-Ti phase reappears, at the surface and beyond the implanted zone. The low concentration of V and the strain in the nitrided zone, have led to radiation induced martensitic transformation of theβ-Ti phase.
pp 309-312 August 1998 Surfaces Of Materials
Some observations related to the decoration ofn-octacosane hydrocarbon crystal surfaces, by the same material, when crystallized from a solution containing a non-solvent in trace quantity (which is completely miscible with solvent) as impurity, are discussed.
pp 313-316 August 1998 Surfaces Of Materials
InxGa1−xAs (0·06≤x≤0·35) epilayers were grown on GaAs substrates by atmospheric pressure metal organic chemical vapour deposition technique. Surface morphology and lattice mismatch in the InGaAs/GaAs films of different compositions were studied. Cross-hatched patterns were observed on the surface of the epilayers for bulk alloy composition up tox≈0·25. Forx>0·3, a rough textured surface morphology was observed.
pp 317-322 August 1998 Surfaces Of Materials
Cadmium sulphide is a promising semiconductor material. In the photovoltaic solar cells it can be used as a window material. In this paper the preparation of CdS film by chemical bath deposition and its solid state properties by taking XRD, SEM, XPS and optical properties has been reported. The XRD and SEM analyses of as deposited and annealed at 400°C clearly indicate the polycrystalline hexagonal phase of the film with (002) orientation. The surfaces are uniform. The XPS measurements indicate the ratio of Cd/S in both the films to be equal to 1·1 at the surface and bulk. It is observed that the thickness of the film depends upon the deposition duration and 5 min deposited films are good for device applications.
pp 323-327 August 1998 Mechanical Properties
Various models for the prediction of strengthening mechanism of metal matrix composites (MMCs) containing either fibres or particulates are analysed. Assuming that the matrix strengthening by dislocations could be treated as equivalent to the effect of different volume fraction of dispersoids, as well as by considering the effect of morphology of reinforcement on the Young’s modulus, an expression for Young’s modulus for MMCs has been derived. The Young’s modulus values thus predicted, using this model, have been validated by ultrasonically-derived values of Young’s modulus of an Al-alloy matrix composite containing 5, 8 and 12 wt% chopped carbon fibre (Cf) dispersoids, in as cast and extruded conditions. Further, the theoretically- and ultrasonically-derived Young’s modulus of cast Al-alloy-Cf composites with 5 and 8 wt%Cf have been found to be comparable with the reported values of Young’s modulus for these weight fractions.
pp 329-333 August 1998 Mechanical Properties
Inadequacy of the rule of mixtures to estimate the true values of composite properties having a large concentration of defects has led to numerous tests being performed costing time and money. Statistical average of the properties from the Weibulls distribution law has thus been relied upon so far for the design of composite structures. Yet, to estimate the properties of a fibre reinforced composite material having sufficient flaw densities due to the methodologies adopted for its processing, more so for fibres, has long been appreciated. To avoid this inadequacy a modified rule of mixtures is developed incorporating defect concentration in the fibre and matrix enabling to arrive at a more realistic value of the composite.
pp 335-339 August 1998 Mechanical Properties
The work reports the wear occurring in a glass-epoxy composite system as a function of sliding distance for a constant sliding velocity and applied load. It is seen that the weight loss increases with increasing distance, but the gradient maintained all through is not the same. An attempt has therefore been made to correlate the weight loss with the scanning microscopic observations on the worn surfaces. It is found that in the early part, the wear of the resin/mat layer contributes to the phenomenon. The process of breakage of fibre into fragments and the resin debris formation accounts for the wear at a much later stage. The phenomenon occurring in between these two stages, is attributed to some of the broken fibres getting lodged in the matrix and agglomeration of the debris formed from the matrix material. Other features of interest are highlighted and discussed in this report.
pp 341-347 August 1998 Electrical Properties
Dielectric constantɛ, loss tanδ and a.c. conductivityσ of LiF-B2O3: Ln3+ (where Ln=Ce, Pr, Nd and Tb) glasses are studied as functions of frequency (in the range 102–106 Hz) and temperature (range 30–200°C). The dielectric breakdown strength of these glasses was also determined at room temperature in an air medium. The rate of increase ofɛ and tanδ with temperature decreases with decrease in the ionic radius of RE3+ ion whereas the dielectric breakdown strength, the activation energy for a.c. conduction in the high temperature region decreases with increase in the ionic radius of RE3+ ion. An attempt has been made to explain the a.c. conduction in these glasses on the basis of quantum mechanical tunnelling (QMT) model.
pp 349-354 August 1998 Glasses And Ceramics
The vast quantities of different beach sand minerals left behind after the extraction of rare earth compounds are industrial wastes. These can be utilized to develop various products in the form of synthetic raw materials or finished product, for applications in glass and ceramic industries. In this paper, the present research work on sillimanite sand, garnet sand and zircon sand are discussed. Attempts have been made to find out the possible uses of these minerals, particularly in the field of glass and ceramic as the materials developed from these minerals are cost competitive. Properties and microstructure of the products developed are systematically discussed.
pp 355-361 August 1998 Catalyst Materials
The adsorption behaviour of iodine on chemically modified swelling type of clays has been studied. Chemical modification was brought about by interacting the clay with surfactants such as tween-80 and polyethylene glycol. Adsorption of iodine was found to increase by several orders of magnitude on chemical modification which remained constant between pH 1 and 10. The adsorption isotherms were non-linear and fitted the Freundlich equation for swelling clays. Scatchard analysis of the data indicated minimum two types of active sites with the tween-80 modified clay and one type with the polyethylene glycol modified one. The iodine sorbed on the surface was found to get desorbed almost completely on leaching with water. Modification of the clay surface with surfactant thus offers a method of designing a recyclable adsorbent for iodine.
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