• Volume 16, Issue 6

      December 1993,   pages  401-707

    • Editorial

      K J Rao P Rama

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    • Foreword

      P Rama Rao K J Rao S Ranganathan A D Damodaran

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    • Four decades of research in solid state chemistry

      C N R Rao

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      Solid state chemistry was in its infancy when the author got interested in the subject. In this article, the author outlines the manner in which the subject has grown over the last four decades, citing representative examples from his own contributions to the different facets of the subject. The various aspects covered include synthesis, structure, defects, phase transitions, transition metal oxides, catalysts, superconductors, metal clusters and fullerenes. In an effort to demonstrate the breadth and vitality of the subject, the author shares his own experiences and aspirations and gives expression to the agony and ecstacy in carrying out experimental research in such a frontier area in India.

    • Some recent innovations in the Kroll process of titanium sponge production

      R B Subramanyam

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      Titanium and its alloys have emerged as cost-effective structural materials in many spheres of chemical and engineering industries including aerospace and power generation. Titanium in its pure form is invariably prepared starting from pure titanium tetrachloride. Titanium tetrachloride obtained by chlorination of the oxide mineral is purified and reduced with either liquid magnesium or sodium or electrolysed to obtain titanium in sponge form. The metal extraction processes are so complex that large scale production technology is limited so far only to a few countries in the world viz. the USA, Japan, CIS, UK and China. India is attempting to enter this arena shortly with a 1000 TPY commercial plant based entirely on home-grown technology.

      Among the extraction methods, the magnesium reduction of titanium tetrachloride, patented by W J Kroll in 1940, has received wider attention because of the inherent and relative merits of the process and its viability for economic production on an industrial scale. The original Kroll process, however, has undergone several modifications in the past few decades. The recent technological breakthroughs in the Kroll process as well as in the magnesium recycling technology has resulted in a significant reduction in the production cost of the metal. The paper describes these important innovations and also the efforts that are being put in for the establishment of a commercial plant for metal production in India based on indigenously developed technology.

    • Race of new inorganic materials towards an ultra neolithic age

      A K Chatterjee

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      Three generally accepted generic groups of competitive engineering materials—metals, inorganic ceramics, as well as plastics and polymers belonging to the organic family—have been comparatively reviewed in the context of raw materials availability, energy requirements in production, engineering properties, combustibility and environmental friendliness. The intrinsic advantages of inorganic materials have been discussed. The shortcomings of engineering properties of inorganic materials and the new technologies of making chemically bonded ceramics or biomimic compounds from inorganic materials with improved toughness have been dealt with. The expanding application horizons of inorganic materials have been illustrated with the help of several novel products.

    • Processing and properties of sintered tool steels and cemented carbides

      G S Upadhyaya

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      This paper reviews our studies in the area of sintered high speed steels and cemented carbides carried out at the Powder Metallurgy Laboratory of IIT Kanpur under the direction of the author.

    • Liquid sodium—The heat transport medium in fast breeder reactors

      C K Mathews

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      Liquid sodium is used as a coolant in fast breeder reactors on account of its excellent heat transfer properties. It must, however, be in the pure form to be compatible with structural materials. Techniques for its purification to nuclear grade and its characterization had to be developed in our laboratory before we could embark on an R&D programme.

      It is essential to monitor hydrogen at ppb levels in the sodium circuits of the fast reactor in order to detect water leaks in the steam generator in a timely manner. Similarly it is useful to make on-line measurements of oxygen and carbon at trace levels. Electrochemical sensors have been developed in our laboratory for this purpose. These compact sensors work on the principle of concentration cells and are far superior to devices used elsewhere for this purpose.

      Corrosion of structural materials in the sodium environment depends on the oxygen content of sodium. In order to understand the mechanism of this corrosion, one must have a good grasp of the thermochemistry of the ternary systems, Na-M-O, where M stands for the alloying constitutents of stainless steels. The phase diagrams of most of these systems were established in our laboratory. A specially designed sodium loop is used in the study of corrosion, activity transport and kinetics of sodium-water reaction.

    • Recent investigations on some cubic Laves phase compounds of rare earth and transition metals

      K V S Rama Rao

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      Pseudobinary alloy, Tb0·27Dy0·73Fe2−δ, belonging to C-15 cubic Laves phase having MgCu2-type structure, possesses large magnetostriction and high magnetomechanical coupling coefficient. The advantages of this material over existing piezoelectric materials, particularly for SONAR applications, are highlighted. Recent results on the influence of cobalt (Co) on magnetic and magnetomechanical properties of Tb0·27Dy0·73Fe2 are discussed.

    • Biotechnology in gold processing

      K A Natarajan

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      The applicability of a biotechnological approach for extracting gold from lean grade and refractory ores and from tailings is analysed. Microbiological as well as physicochemical characteristics of various leaching bacteria are outlined. Technological aspects of bioleaching of refractory gold-bearing concentrates in specially designed bioreactors are illustrated with emphasis on control parameters and use of metal and temperature-tolerant strains. Commercial operations prevalent across the world are detailed and the relevance of biomineral technology for augmentation of gold production in India brought out.

    • Sol-gel microsphere pelletization: A powder-free advanced process for fabrication of ceramic nuclear fuel pellets

      C Ganguly

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      Hydrated gel-microspheres of U, Pu, Th oxide or oxide plus carbon mixture of diameter 400–800µ were prepared by ammonia gelation processes. They were dried and subjected to suitable treatment for obtaining free-flowing oxide, carbide or nitride micro-spheres of diameter 200–400µ suitable for direct pelletization and sintering. The oxide, carbide and nitride pellets were, in general, sintered at high temperature in Ar+8% H2. However, for UO2 and (U, Pu)O2 pellets low temperature (1200 °C), short duration (1 h) oxidative (CO2 or N2+air) sintering (LTS) was also successful, thereby reducing electrical energy and gas consumption during sintering. Thus, the combined SGMP-LTS process simultaneously minimized “radiotoxic dust hazard” and fuel fabrication cost in case of UO2 and (U, Pu) O2 pellets.

    • Sol-gel processing: A versatile concept for special glasses and ceramics

      D Ganguli

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      The various parameters related to sol-gel processing are discussed with special reference to those which usually attract less attention but depending on the final product in mind, can play important roles. The versatility of the sol-gel technique in materials preparation is demonstrated by discussing the various products developed at the author’s laboratory by using this processing method.

    • Advanced ceramics: Combustion synthesis and properties

      K C Patil

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      Fine-particle ceramic powders such as chromites, manganites, ferrites, cobaltites, aluminas (α-Al2O3, Cr3+/Al2O3, zirconia-toughened alumina, mullite and cordierite), ceria, titania, zirconia (t, m, c and PSZ), dielectric oxides (MTiO3, PZT and PLZT) as well as highTc cuprates have been prepared by the combustion of redox compounds or mixtures. The combustion-derived oxide materials are of submicron size with a large surface area and are sinteractive.

    • Solidification modelling

      O Prabhakar

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      The modelling of solidification of a metal/alloy in a mold cavity is increasingly becoming popular with numerous attempts being made to understand the phenomena that occur at the level of the casting (macro level) and that which occur at the microscopic level (micro level). In this paper, an attempt has been made to describe the phenomena occurring at both the macro and the micro levels.

      At the macro level, the effect of fluid flow on various thermal and solidification parameters has been studied. The results were compared with simulations carried out considering conduction alone and with experimental results. The relative importance of including fluid flow on solidification simulation of a casting has been brought out.

      At the micro level, an algorithm based on the macro-micro model to take the melt superheat into account while numerically predicting the grain size and dendritic arm spacing at different locations of an Al-7% Si alloy sand casting has been developed. The results are compared with the experimental values.

    • Role of dynamic strain ageing in low cycle fatigue

      S L Mannan

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      Low cycle fatigue (LCF) at elevated temperatures is known to be influenced by time-dependent processes like creep, oxidation and metallurgical instabilities. Another time-dependent phenomenon namely, dynamic strain ageing (DSA) has been found to exert an influence on LCF behaviour at high temperatures. Research activities carried out in the present author’s laboratory with a view to understanding the effects of DSA on LCF are highlighted in this paper. Occurrence of DSA manifests during total strain-controlled fatigue tests in the form of serrated plastic flow in stress-strain hysteresis loops, increased cyclic work hardening and reduced plastic strain range. Further, DSA causes localization of plastic flow leading to enhanced planarity of slip and widely-spaced slip bands. Impingement of slip bands on grain boundaries causes increased grain boundary decohesion, leading to reduced fatigue life. The influence of prior microstructure such as second phase particles and grain size on the effects of DSA on LCF is also discussed.

    • The unique features of textures in low-carbon steels

      Sanak Mishra

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      Textures in low-carbon steels are of great significance in view of their strong influence on important physical properties such as formability and magnetic induction. Recent studies on the formation and evolution of textures through different processing stages of hot rolling, cold rolling and annealing have brought out many unique features, e.g. presence of complete and almost ideal fibre axes, inheritance of texture, texture memory effect and parallels between single crystal and polycrystalline situations. In particular, it has been possible to develop a fairly cogent picture of the genesis and perpetuation of the Goss texture.

    • Probing exotic magnetic phases in ferrites with neutrons

      L Madhav Rao

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      The decades of the sixties and early seventies saw the neutron diffraction technique playing a major role in the elucidation of magnetic structures in a variety of ferrites in our laboratory. In 1979, Villain in his seminal paper on insulating spin glasses argued that the spinel structure affords topological frustration which can give rise to a variety of perturbed magnetic ordering, depending upon magnetic dilution in the ferrite. The neutron is a unique probe to explore the nature of spatial correlations of magnetic moments in such systems. This paper describes the exciting work carried out at Trombay recently in mixed ferrites which have led to the discovery of exotic magnetic phases like the uniaxial random ferrimagnetic phase and the canted random ferrimagnetic phase involving the coexistence of long-range magnetic order and disorder.

    • High resolution X-ray diffraction studies of real structure of nearly perfect single crystals

      Krishan Lal

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      Real structure together with composition and elemental purity of single crystals controls their properties. This paper reviews recent work carried out at the National Physical Laboratory on application of high resolution X-ray diffractometry, topography and diffuse X-ray scattering for direct observation and characterization of real structure of single crystals of silicon, gallium arsenide, diamond and LiNbO3. A series of six multicrystal X-ray diffractometers have been designed, developed and fabricated indigenously. The most versatile of these systems is a five crystal X-ray diffractometer with state-of-the-art level resolution. These techniques and equipments have been applied in studying several interesting problems. Even in dislocation-free crystals of silicon, remarkable differences in the defect structure have been observed if the growth method was changed from float zone to Czochralski. Study of effect of externally applied electric fields and ion implantation on real structure of crystals has yielded interesting results. Images of ‘filaments’ which show nonhomogeneous distribution of electric current through semiconductors and insulators have been recorded for the first time in high resolution traverse topographs. Diffracted X-ray intensities could be modified by externally applied electric fields. It has been shown that implantation of BF2+ ions in silicon for producing shallow junctions does not produce homogeneous distribution of boron. The impurity is partially in clustered form. Biaxial stress introduced by thin depositions in substrate crystals are of considerable applied concern. The value and nature of stress have been determined in a number of systems. Typical results obtained on GaAs: multilayer metallizations are described. Also, degradation of perfection of substrates has been monitored. This work has shown that the stress is not homogeneously distributed and is quite anisotropic. A new high resolution X-ray diffraction technique has been developed for direct observation and study of forward diffracted X-ray beam and anomalous transmission of X-rays through ‘thin’ diamond crystals of varying degrees of perfection.

    • Sputter deposition technology as a materials engineering

      Kiyotaka Wasa

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      Sputter deposition is currently being widely used in the microelectronics industry for the production of silicon integrated circuits. Recently interest has been focused on sputter deposition as a new materials processing technique. The highly energetic sputtered atoms enhance crystal growth and/or sintering during film growth. This results in lowering of the growth temperature of high temperature materials including cubic diamonds. Single crystals of complex ceramics materials could be prepared by sputter deposition through epitaxial growth process. Atomically controlled deposition using multi-target sputter enables to make man-made superlattice including high-TC superconductors of layered perovskite. At present sputter deposition is one of key materials technologies for the coming century.

    • Better ceramic substrates through zeolites

      M A Subramanian D R Corbin U Chowdhry

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      A novel synthetic route for fabricating dense aluminosilicate-based ceramics at relatively low temperatures (⩽1000°C) is described. The method involves ion exchange of an appropriate zeolite powder, followed by fabrication and sintering, to form a dense ceramic. Anorthite, cordierite- andβ-spodumene-based ceramic substrates with attractive physical properties for microelectronic packaging are obtained using these unusual precursors. A brief overview on the property requirements for substrates used in microelectronic packaging is outlined at the beginning of the article.

    • Synthesis and electrical studies of modified PbTiO3 ceramics: (Pb1−xCax) (Mn0·05W0·05Ti0·90) O3

      K Prasad R Sati R N P Choudhary T P Sinha

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      Modified ceramics (Pb1−xCax)[(Mn0·5W0·5)0·10Ti0·90]O3 have been fabricated forx=0, 0·05, 0·10 and 0·15 by high temperature solid state reaction technique. XRD, SEM, DTA and electrical studies of the sample withx=0·10 have been performed. These studies show that the sample is homogeneous single phase perovskite type with tetragonal structure. The phase transition occurs at 330°C. Electrical behaviour of other samples have also been investigated as a function of frequency (1 kHz to 1 MHz) and temperature (26°C to 300°C). The samples withx=0·05 and 0·10 have low loss, low dielectric constant, and show negligible pyroelectric effect. The sample withx=0·15 has minimum values ofɛ and loss which are temperature independent up to about 200°C. It also shows good pyroelectric behaviour. Hence it may be of use in pyroelectric infrared sensors.

    • Oxygen incorporation duringin situ growth of YBCO films on both sides of substrates

      S P Pai R Pinto P R Apte C P D’Souza A G Chourey D Kumar

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      Oxygen out-diffusion during cooling and heating ofin situ grown {ie685-1} (YBCO) films in low oxygen pressure used during growth by pulsed laser deposition was studied in the temperature range 700−450°C usingin situ resistance measurements. Results indicate that irrespective of the number of cooling and heating cycles seen by the films, full oxygenation of the films can be realized by the final cooling from the growth temperature in 500 torr oxygen pressure. This result has been successfully used to sequentially grow high quality YBCO films on both sides of LaAlO3 substrates. These films have been used for the fabrication of X-band microstrip resonators with superconducting ground plane.

    • X-ray powder diffraction study of ZnLi0·5Mn0·5SnO4

      Sangeetha Sampath M P Tare R R Tripathi S M Tare

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      X-ray crystallographic investigation of the title complex oxide composition reveals the presence of two phases. The first is a spinel phase which is somewhat consistent with Zn2SnO4 witha0=8·646 Å. The other phase has been identified as a non-spinel phase of LiMnSnO4, the presence of which was confirmed by synthesizing it and comparing its XRD pattern with that of the title composition. The exact composition of the two phases has been determined by intensity calculations. It seems that while cooperative J-T effect is responsible for the observed symmetry of LiMnSnO4, the distribution of phase along with separation of phases is attributed to the solubility limit of Sn4+ in such quaternary compositions.

    • Effect of humidity on the breakdown strength and diffusion characteristics of polymer film

      M M Hossain

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      Dielectric breakdown strength and diffusion characteristics were measured for polyimide and polyimide fluorocarbon polymer film at different weathering conditions. The dielectric breakdown strength and the diffusion coefficient were found to decrease in humid conditions. Different diffusion characteristics as well as breakdown mechanisms were observed on both sides in the PMF-1 polymer film. The permeation coefficient and diffusion coefficient decrease, thereby increasing the breakdown strength in more humid conditions that may be due to the formation of double potential well in the polymer film.

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