Volume 17, Issue 7
December 1994, pages 1197-1485
pp 1197-1197 December 1994
pp 1199-1213 December 1994
Blood remains fluid so long as it flows in the cardiovascular system; it clots in other situations. While this phenomenon, vascular homeostasis, has been studied for a century, the development of artificial surfaces that induce minimal or no clotting became important only with the growth of cardiovascular surgery. The advent of the graphite-benzal konium-heparin surface which employed the ionic bonding of heparin was a milestone in the effort to develop non-clotting surfaces. The technique of ionic bonding was followed over the years by the grafting of heparin molecule to surfaces and most recently, by the covalent bonding of heparin. The covalent bonding of heparin preserves the non-clotting property of prosthetic surfaces for long periods and holds promise for numerous applications in cardiovascular surgery and other branches of medicine. The introduction of covalent bonding and similar approaches will greatly improve the biocompatibility and durability of the present generation of biomedical devices.
pp 1215-1232 December 1994
The application of positron annihilation spectroscopy to the study of defects in materials is illustrated through several examples drawn from our work. These include the study of vacancy clustering in metals, clustering of He atoms to form bubbles, and solute clustering in alloys. Results of studies on novel materials such as quasicrystals, cuprate superconductors and fullerenes are also presented.
pp 1233-1249 December 1994
The advent of high intensity lasers coupled with the recent advances in crystal technology has led to rapid progress in the field of nonlinear optics. This article traces the history of materials development that has taken place over the past forty odd years and dwells on the current status in this important area. The materials aspect is discussed under three classes viz. inorganic, organic and semiorganic crystals. In the end, some of the crystal growth work that has been carried out in author’s laboratory is presented.
pp 1251-1258 December 1994
Alternative technique for studying grain-boundary scattering phenomena in high-resistivity semiconducting films has been indicated. The combined effect of the presence of electric field and mechanical stress at the grain boundaries was considered. It is shown that the grain boundary potential, density of trap states, and carrier concentration of the films can be obtained by measuring reflectances of the films deposited on non-absorbing substrates.
pp 1259-1270 December 1994
Following the phenomenological approach of Landau and Lifshitz the existence of linear magnetoelectric effect in antiferromagnetic Cr2O3 was predicted by Dzyaloshinskii which was later experimentally confirmed by Astrov and Folenet al. Magnetoelectric phenomenon has been observed in several single-phase materials in which simultaneous electric and magnetic ordering coexists and in two-phase composites in which the participating phases are the ferroelectric and magnetic. The author’s group has recently undertaken a systematic study of the preparation, characterization and detection of the (ME)H output in a few single-phase materials and two-phase composites. This article describes the magnetoelectric phenomenon in general and recent work carried out in the author’s group.
pp 1271-1285 December 1994
When examined using continuous wave electron paramagnetic resonance and nuclear magnetic resonance spectrometers, the highTc superconductors give rise to intense, low field, ‘non-resonant’ absorption signals in the superconducting state. This phenomenon can be used as a highly sensitive, contactless technique for the detection and characterization of superconductivity even in samples containing only minute amounts of the superconducting phase. Further, it can also be applied to the determination of material parameters of interest such asJc andHc2 in addition to being a powerful way of distinguishing between weak-link superconductivity and bulk superconductivity. The details of these aspects are discussed.
pp 1287-1297 December 1994
Growth and characterization of high-temperature-superconducting YBa2Cu3O7 and several metallic-oxide thin films by pulsed laser deposition is described here. An overview of substrates employed for epitaxial growth of perovskite-related oxides is presented. Ag-doped YBa2Cu3O7 films grown on bare sapphire are shown to giveTc=90 K, critical current >106 A/cm2 at 77 K and surface resistance =450µΩ. Application of epitaxial metallic LaNiO3 thin films as an electrode for ferroelectric oxide and as a normal metal layer barrier in the superconductor-normal metal-superconductor (SNS) Josephson junction is presented. Observation of giant magnetoresistance (GMR) in the metallic La0·6Pb0·4MnO3 thin films up to 50% is highlighted.
pp 1299-1306 December 1994
This paper mostly describes the research on surfactant solutions performed at this centre in the past few years. A correlation between microemulsion structure and precipitation reaction of AgCl is described. Experimental and theoretical research culminating in the development of a theme for analysing the structure of colloidal systems is described. Recent results on the discovery of new viscoelastic surfactant systems are presented.
pp 1307-1315 December 1994
This paper reviews recent investigations of the factors which control gas transport in a series of highly aromatic polyarylates. The polymer physical properties which correlate with its intrinsic separation characteristics were elucidated by studying well-defined families of polyarylates. Molecular modelling was used to understand the effects of various substitutions in the polymer structure and the mechanism through which the polymer properties are affected. The effect of polymer chain mobility, conformation and packing density on the permeation characteristics are discussed.
pp 1317-1329 December 1994
The fundamental concepts related to biomaterials and blood/tissue-material interactions at the interface have been reviewed. The relevance of surface modification to enhance blood and/or tissue compatibility of materials has been discussed and its role in selected prosthetic applications described.
pp 1331-1339 December 1994
The rapid advances in technologies in various fields have also recorded significant progresses in the field of newer materials as the reliability and effective performance of industrial equipment as well as the associated components mostly depend upon their integrity over specified period.
Though the basic methods of protection of materials like use of corrosion-resistant alloys, application of surface coatings, modification of the environment and application of cathodic protection have largely remained the same, the approaches and techniques adopted in each of these fields have been so advanced that one could today advocate appropriate protection systems with high reliability and performance.
The author presents some of his contributions along with his colleagues in the fields of cathodic protection of vital structures, development of newer coatings for specific applications and new approaches to corrosion monitoring techniques, besides highlighting the corrosion behaviour of some of the heat-treated alloys which are specifically used in such strategic areas as space and defence.
The presentation would also cover briefly some of the techniques that have been employed by the author for better understanding of corrosion and passivation of metals and alloys.
pp 1341-1350 December 1994
Cast single-crystal superalloys are being used as turbine blades in modern aeroengines with 〈001〉 axis oriented along the direction of principal stress. This allows use of higher operating temperature with associated improvement in efficiency. Although 〈001〉 is the natural direction of crystal growth in these alloys it is often not possible to attain perfect alignment. Consequently, besides time-dependent deformation this would induce a change in cross-sectional shape and crystal orientation of the blade as a results of service exposure. Therefore in order to exploit their full potential it is necessary to develop a predictive system which could model effect of crystallographic anisotropy on hightemperature creep deformation of such materials. The paper reviews the recent developments in this direction and suggests that modelling not only helps in identifying the dominant mechanisms of deformation but also suggests simple experiments to verify them.
pp 1351-1367 December 1994
A research programme was initiated at the Defence Metallurgical Research Laboratory, Hyderabad, a decade ago for the indigenous development of Al-Li alloys in order to finally meet the requirements of the space and aircrft industries in the country. This paper describes the systematic studies carried out in the laboratory to overcome the initial difficulties in producing sound ingots, optimize the subsequent heat treatments and processing schedules, and to finally obtain reproducible microstructure and mechanical properties in the semi products (i.e. sheets and extrusions) developed. Laboratory-scale sheet and extrusion products meet tensile property specification of 8090 alloy. One of these semiproducts, i.e. round bar extrusion, is currently being supplied for the stallite programmes. Commercial-scale sheet products made in Russia under an Indo-Russian joint programme have been made available for the aircraft programme. Recent alloy development studies in the laboratory are discussed within the context of the present paper.
pp 1369-1378 December 1994
A number of condensed case-histories of successful materials innovations are presented to illustrate the author’s thesis that happy accident favouring the prepared mind (i.e. serendipity), or alternatively a response to a challenge from competing materials, are circumstances favouring effective innovation.
pp 1379-1391 December 1994
Deposition of diamond thin films on non-diamond substrates at low pressures (<760 torr) and low temperatures (<2000°C) by chemical vapour deposition (CVD) has been the subject of intense research in the last few years. The structural and the electrical properties of CVD diamond films grown on p-type 〈111〉 and high-resistivity (>100 kΩ-cm) 〈100〉 oriented silicon substrates by hot filament chemical vapour deposition technique are described in this review paper.
pp 1393-1399 December 1994
This paper gives a survey of the present state and new aspects of the measurement techniques for the characteristics of magnetic materials (except for recording materials) with several examples. Particular attention is paid to the aspects of reproducibility and traceability to SI units, and to the current trend of quality assurance and standardization.
pp 1401-1409 December 1994
The ever-increasing need for sensors capable of detecting and monitoring toxic and flammable gases is presented and the various techniques available are introduced. Semiconductor devices based on tin dioxide, which potentially have many desirable characteristics, are discussed in detail with particular reference to the work in Swansea which has focused on the problem of selectivity.
pp 1411-1414 December 1994
In the form of a succinct overview the structure and symmetry requirements of magnetic ferroelectrics are discussed. Boracites are the best-studied examples and have phases being simultaneously ferroelectric, ferromagnetic and ferroelastic. One of the salient features of such materials is the obligatory occurrence of the linear and bilinear magnetoelectric effects. They represent an invaluable auxiliary information for magnetic symmetry determination by neutron diffraction. Owing to the complexity of property combinations, work with single crystals and polarized light microscopy is obligatory. Key references of the field are given.
pp 1415-1434 December 1994
Ion beam-assisted deposition offers a novel and unique process to prepare diamond-like carbon (DLC) films at room temperature, with particularly good interface adhesion. This advantage was explored in this study to deposit highly wear-resistant coating on bearing 52100 steel. Both dual ion beam sputtering and ion beam deposition were employed. Various bombarding species and energy were investigated to optimize the process. Raman, X-ray photoelectron and Auger electron spectroscopy were used to characterize the bonding structure of DLC. Extensive experiments were carried out to examine the tribological behaviour of the DLC/52100 system. A metal intermediate layer can help tremendously in wear resistance. The results are optimistic and may lead to useful applications.
pp 1435-1439 December 1994
Al2O3:ZrO2 ceramics have been prepared from physically mixed pure oxide powders. The results indicate that careful processing of the starting powders and a two-stage sintering process can avoid expensive processing methods like hot pressing/hot isostatic pressing used for achieving high densification. The mechanical properties were measured and the resultant microstructure studied to explain the toughening behaviour of this material.
pp 1441-1446 December 1994
Sintering of yttria-containing tetragonal zirconia polycrystal (Y-TZP) ceramics was performed in a single-mode cylindrical cavity applicator CMPR-250 operating at 2·45 GHz in the TM012 mode. High heating rates at low power levels were achieved. Rapid heating and cooling resulted in a fine-grain microstructure.
High-purity submicron Y-TZP powders were sintered from an initial green density of 60% to final sintered density close to the theoretical density. Microwave sintering offers potential for improving microstructural properties through controlled development of uniform microstructure.
pp 1447-1455 December 1994
Sparingly soluble neodymium copper oxalate (NCO) single crystals were grown by gel method, by the diffusion of a mixture of neodymium nitrate and cupric nitrate into the set gel containing oxalic acid. Tabular crystal, revealing well-defined dissolution figures has been recorded. X-ray diffraction studies of the powdered sample reveal that NCO is crystalline. Infrared absorption spectrum confirmed the formation of oxalato complex with water of crystallization, while energy dispersive X-ray analysis established the presence of neodymium dominant over copper in the sample. X-ray photoelectron spectroscopic studies established the presence of Nd and Cu in oxide states besides (C2O4)2− oxalate group. The intensities of Nd (3d5/2) and Cu (2p3/2) peaks measured in terms of maximum photoelectron count rates also revealed the presence of Nd in predominance. The inductively coupled plasma analysis supports the EDAX and XPS data by the estimation of neodymium percentage by weight to that of copper present in the NCO sample. On the basis of these findings, an empirical structure for NCO has been proposed. The implications are discussed.
pp 1457-1465 December 1994
(Zn, Cd)S: Au, Cl mixed phosphors were prepared in nitrogen atmosphere with various concentrations of impurities. Photoluminescence (PL) spectra were obtained. The peak of the PL spectrum shifts towards longer-wavelength values with increasing replacement of zinc by cadmium in the host lattice. The PL efficiency was found to decrease with increasing. CdS content whereas lattice constants increased with increasing CdS concentration.
pp 1467-1471 December 1994
A simple and sensitive spectrophotometric method for the determination of cerium(IV) was developed. Witho-phenylenediamine cerium(IV) gives an orange-red colour with an absorption maximum at 470 nm. The system obeys Beer’s law in the range 7 ppm to 500 ppm with a molar absorptivity of 2·4 × 103l mol−1 cm−1 and Sandell sensitivity of 0·5 ppm. Interference by various ions was studied. This method was used for the determination of cerium in low-alloy steels and the results are in good agreement with the certified values.
pp 1473-1485 December 1994
The small-angle X-ray scattering (SAXS) curves for ultralongn-alkanes obtained by Ungar and Keller at different times after reaching the crystallization temperature have been Fourier analysed. The correlation curves so obtained at different temperatures and different annealing times reflect sensitively all those morphological features which are broadly characteristic of the scattering curves. In addition the correlation curves clearly show a transition from a non-integer-fraction length to extended chain structure. Crystalline and amorphous lengths, degree of order and half-widths which characterize kinetics of morphological changes are also reported.
Volume 42 | Issue 6
Click here for Editorial Note on CAP Mode