Showing papers in "Bulletin of Materials Science in 1993"
TL;DR: The combustion-derived oxide materials are of submicron size with a large surface area and are sinteractive as mentioned in this paper, however, they do not have a high T cuprate.
Abstract: Fine-particle ceramic powders such as chromites, manganites, ferrites, cobaltites,aluminas ($\alpha-Al_30_3 , Cr^{3+}/A1_20_3$, zirconia-toughened alumina, mullite and cordierite), ceria,titania, zirconia (t, m, c and PSZ), dielectric oxides ($MTiO_3, PZT and PLZT) as well as high T, 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.
166 citations
TL;DR: In this paper, the effects of dynamic strain aging (DSA) on low cycle fatigue (LCF) at elevated temperatures was investigated. And the influence of prior microstructure such as second phase particles and grain size on the effect of DSA on LCF was discussed.
Abstract: 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.
88 citations
TL;DR: In this paper, a novel synthetic route for fabricating dense aluminosilicate-based ceramics at relatively low temperatures (⩽1000°C) is described, which involves ion exchange of an appropriate zeolite powder, followed by fabrication and sintering, to form a dense ceramic.
Abstract: 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.
62 citations
TL;DR: In this paper, a glass fabric laminate was prepared with cashew nut shell liquid (CNSL) in the presence of succinic acid catalyst and showed good mechanical properties and dimensional stability.
Abstract: Cashew nut shell liquid (CNSL) was used to prepare a glass fabric laminate. Two fast curing model resins were prepared using cardanol and formaldehyde in the presence of succinic acid catalyst. The resins possess ortho-ortho and ortho-para linkages. The curing kinetics of the resins showed that the resin prepared with mole ratio 0·8 possesses good curing characteristics. The IR spectra of cured resin showed responses for high ortho linkage. A CNSL high ortho novolac resin was prepared with mole ratio 0·8. The glass fabric laminates prepared with CNSL resin showed good mechanical properties and dimensional stability. It is suggested that the candidate laminate can be used as secondary load bearing structures or panels.
31 citations
TL;DR: In this article, the SGMP-LTS process simultaneously minimized the radiotoxic dust hazard and fuel fabrication cost in case of UO2 and (U, Pu) O2 pellets.
Abstract: 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.
30 citations
TL;DR: An electrically conductive plastic material was obtained by the polymerization of pyrrole on insulating polymeric materials and nylon cloth impregnated with the oxidant by vapour phase technique as discussed by the authors.
Abstract: An electrically conductive plastic material was obtained by the polymerization of pyrrole on insulating polymeric materials and nylon cloth impregnated with the oxidant by vapour phase technique, resulting in a uniform, smooth and adherent coating of conducting polymer having a surface resistance ranging from 200 Ω/□ to 20 kΩ/□, which makes it suitable for applications as an antistatic material.
25 citations
TL;DR: The application of self-propagating high-temperature synthesis (SHS) to prepare a few borides of titanium was investigated in this paper using the plane wave propagation mode, and the synthesis of titanium boride in the cold-pressed cylindrical specimens of the component powder mixtures was studied as a function of boron content in the initial mix and the specimen size.
Abstract: The application of self-propagating high-temperature synthesis (SHS) to prepare a few borides of titanium was investigated. Using the plane wave propagation mode, the synthesis of titanium borides in the cold-pressed cylindrical specimens of the component powder mixtures was effected and was studied as a function of boron content in the initial mix and the specimen size. SHS reaction in compacts having diam. of 6 mm or less and high bulk density could not be initiated and/or sustained and was considered to be a result of rapid heat dissipation.
23 citations
21 citations
TL;DR: Experimental investigations have been carried out on electro-discharge machining of titanium in respect of surface finish, out-of-roundness and overcut using rotating copper-tungsten tool electrode as mentioned in this paper.
Abstract: Experimental investigations have been carried out on electro-discharge machining of titanium in respect of surface finish, out-of-roundness and overcut using rotating copper-tungsten tool electrode. An attempt has also been made to compare the results with stationary electrode.
21 citations
TL;DR: In this paper, the effect of composition of the supernatant solution is considered and the results of the growth experiments were carried out by single diffusion method, where the Pauling radius, hydration energy and distribution coefficient of the cations are tabulated and results are described and discussed.
Abstract: Aspects of gel growth of cadmium oxalate single crystals doped with monovalent (Li+, Na+, K+ and NH
4
+
) and divalent (Ca2+, Co2+, Ni2+ and Zn2+) cation impurities are discussed. The growth experiments were carried out by single diffusion method. In this paper the effect of composition of the supernatant solution is considered. Rigorous characterization involves determination of composition of cations by employing atomic absorption spectrophotometer and of anions by titration method. The Pauling radius, hydration energy and distribution coefficient of the cations are tabulated and the results are described and discussed.
19 citations
TL;DR: In this paper, the glass-forming composition range (GFR) is found to be much wider in case of mechanical alloying in comparison with RSP, and the free energy calculations made to explain GFR are also presented.
Abstract: Mechanical alloying (MA) pioneered by Benjamin is a technique for the extension of solid solubility in systems where the equilibrium solid solubility is limited. This technique has, in recent years, emerged as a novel alternate route for rapid solidification processing (RSP) for the production of metastable crystalline, quasicrystalline, amorphous phases and nanocrystalline materials. The glass-forming composition range (GFR), in general, is found to be much wider in case of MA in comparison with RSP. The amorphous powders produced by MA can be compacted to bulk shapes and sizes and can be used as precursors to obtain high strength materials. This paper reports the work done on solid state amorphization by MA in Ti-Ni-Cu and Al-Ti systems where a wide GFR has been obtained. Al-Ti is a classic case where no glass formation has been observed by RSP, while a GFR of 25–90 at.% Ti has been obtained in this system, thus demonstrating the superiority of MA over RSP. The free energy calculations made to explain GFR are also presented.
TL;DR: In this paper, a new phase Cu2V2O7 synthesized, exhibits phase transitions between 475°C and 500°C. These phase transitions are reversible with ease in contrast toα →β phase transition at 712°C of Cu2 V2O 7 phase reported earlier.
Abstract: A new phase Cu2V2O7 synthesized, exhibits phase transitions between 475°C and 500°C. These phase transitions are reversible with ease in contrast toα →β phase transition at 712°C of Cu2V2O7 phase reported earlier. These phase transitions are identified by DTA technique and characterized by detailed XRD investigations at different temperatures. The crystal structures of these Cu2V2O7 phases are related to either thortveitite (Sc2Si2O7) type or a modification of it.
TL;DR: In this paper, the electrical conductivity of vacuum-deposited molybdenum trioxide thin films was investigated and the variation of electrical conductivities with temperature for different thicknesses of films was found to increase initially, then decreased rapidly and reached a steady value.
Abstract: Infrared spectra of vacuum-deposited molybdenum trioxide thin films have been studied. The variation of electrical conductivity with temperature for different thicknesses of films has been investigated. Electrical conductivity of the films as a function of time of UV irradiation was found to increase initially, then decreased rapidly and reached a steady value. It increased and reached a steady value with time when irradiation was cut-off.
TL;DR: In this article, the authors describe the 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.
Abstract: 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.
TL;DR: In this article, the authors present a review of the application of high resolution X-ray diffractometry, topography and diffuse Xray scattering for direct observation and characterization of real structure of single crystals of silicon, gallium arsenide, diamond and LiNbO3.
Abstract: 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 BF
2
+
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.
TL;DR: In this paper, the authors reported thermal power and electrical resistivity for the system Cu1+xSnxFeFe2−2xO4 from room temperature to 800 K. Hopping conduction phenomenon has been explained on the basis of localized model of electrons.
Abstract: Thermoelectric power (α) and electrical resistivity (ρ) are reported for the system Cu1+xSnxFe2−2xO4 (wherex=0·05, 0·1, 0·15, 0·2 and 0·3) from room temperature to 800 K. The compositions withx=0·05 and 0·2 exhibitn-type conduction while the compositions withx=0·1 and 0·15 showp- ton-type conduction change after 423 K. The conduction at low temperature (i.e. 400 K), it is due to polaron. Hopping conduction phenomenon for the present system has been explained on the basis of localized model of electrons. Additional localization may arise due to Sn4+ + Fe2+ stable pairs at B-site and Cu1+ + Fe3+ pair at A-site.
TL;DR: In this paper, the phase transition of copper(II) orthovanadate was identified through detailed DTA and high temperature XRD techniques; it was observed that these structural transitions are rapid and reversible.
Abstract: Data on the polymorphs of copper(II) orthovanadate are reported. The Cu3V2O8 phase synthesized in this laboratory exhibits phase transitions between 460° and 560°C. These phase transitions are identified through detailed DTA and high temperature XRD techniques; it is observed that these structural transitions are rapid and reversible. The crystal structure of Cu3V2O8 is similar to that of Mg3V2O8, Zn3V2O8, Co3V2O8 and Ni3V2O8.
TL;DR: In this article, a kinetic study of NiCl2-containing gel was carried out and the detailed statistical as well as reduced time analysis showed that contracting geometry and nucleation and growth type of mixed mechanisms are operative.
Abstract: Isothermalin situ reduction kinetic study of NiCl2-containing gel was carried out. The detailed statistical as well as reduced time analysis show that contracting geometry and nucleation and growth type of mixed mechanisms are operative. The activation energy for reduction is in the range 158–193 kJ/mol. Thermal analysis on NiCl2-containing gel was carried out in the temperature range 800°C to 900°C.
TL;DR: Sputter deposition is currently being widely used in the microelectronics industry for the production of silicon integrated circuits as mentioned in this paper, where the highly energetic sputtered atoms enhance crystal growth and/or sintering during film growth.
Abstract: 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-T
C superconductors of layered perovskite. At present sputter deposition is one of key materials technologies for the coming century.
TL;DR: In this paper, the authors describe variation of nucleation density and growth of these crystals as a function of concentration of feed solution, gel ageing, gel density, gel pH and intermediate neutral gel column.
Abstract: As part of our work on growth of cadmium oxalate single crystals in gels, we describe here variation of nucleation density and growth of these crystals as a function of concentration of feed solution, gel ageing, gel density, gel pH and intermediate neutral gel column. While high density and high pH gels have been found to produce opaque crystals, good quality transparent single crystals have been obtained in low density and low pH gels. It was observed that the intermediate neutral gel column and gel ageing considerably reduced the number of nucleation sites and increased the size of the crystals without affecting their quality. By concentration programming the size of the crystals increased.
TL;DR: In this article, 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.
Abstract: 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.
TL;DR: In this article, a homogeneous single phase perovskite type with tetragonal structure has been fabricated for XRD, SEM, DTA and electrical studies of the sample withx=0·10 have been performed.
Abstract: 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.
TL;DR: In this article, the phase transformation observed by electrical conductivity measurements agrees well with the initial magnetization measurement, and the magnetic hysteresis values compare with those ofγ-Fe2O3 samples synthesized using established procedures.
Abstract: γ-Fe2O3 synthesized from FeC4H4O4·4H2O has been studied using various techniques. The phase transformation observed by electrical conductivity measurements agrees well with the initial magnetization measurement. The magnetic hysteresis values compare with those ofγ-Fe2O3 samples synthesized using established procedures.γ-Fe2O3 particles obtained were circular in shape showing a well resolved six narrow bands in Mossbauer spectrum. The presence of hydrogen ferrite phase was also confirmed by electrical and magnetic measurements.
TL;DR: In this paper, the degree of crystallinity of the films improves at higher substrate temperatures and the crystallites have smaller dimensions on CaF2 than on NaCl, mica and even glass, under identical conditions of deposition.
Abstract: Thin films of (Pb1 −x Sn x )1 −y Te y have been deposited by vacuum evaporation onto glass, mica, CaF2 and NaCl substrates heated to various temperatures at low deposition rates. Transmission HEED, TEM and SEM studies have been carried out for as-grown films. HEED photographs show that (i) the degree of crystallinity of the films improves at higher substrate temperatures and (ii) the crystallites have smaller dimensions on CaF2 than on NaCl, mica and even glass, under identical conditions of deposition. SEM studies reveal that with increasingT sub, grains tend to form clusters through mobility coalescence. Needleshaped grains are formed when the deposition rate exceeds a certain critical value. Formation of needle-like grains has been attributed to the excess Te atoms possessing trigonal structure so that such grains can be observed only inp-type PbSnTe films.
TL;DR: In this paper, the authors reviewed their 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.
Abstract: 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.
TL;DR: In this article, the average bond distance was used to obtain the exact cation distribution, in conformity with X-ray diffraction data, in the case of a cation occupying both the sites of the first coordination shell.
Abstract: In oxidic spinels containing transition metal ions, the tetrahedral and octahedral bond distances differ by less than 0·25 A. Therefore, in the case of a cation occupying both the sites, the normalized EXAFS for first coordination shell gives the average bond distance and average coordination number respectively over all the bonds and the positions of the cation under investigation. EXAFS analysis of fourteen mixed lithium ferrite spinels was carried out to show how the average bond distance can fruitfully be used to obtain the exact cation distribution, in conformity with X-ray diffraction data.
TL;DR: In this paper, the dielectric breakdown strength and diffusion characteristics were measured for polyimides and polyimide fluorocarbon polymer film at different weathering conditions and different diffusion characteristics as well as breakdown mechanisms were observed on both sides in the PMF-1 polymer film.
Abstract: 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.
TL;DR: An indigenous sol-gel derived yttria-partially stabilized zirconia (Y-PSZ) powder has been characterized and its suitability for plasma spraying applications evaluated as discussed by the authors.
Abstract: An indigenous sol-gel derived yttria-partially stabilized zirconia (Y-PSZ) powder has been characterized and its suitability for plasma spraying applications evaluated. The powder, determined to have about 5·1% yttria content, predominantly consisted of spherical particles with an average equivalent particle diameter close to 25µm. Furthermore, it was found that the powder did not contain any particles >50µm, which is considered the ideal upper size limit for spray-grade ceramic powders in order to ensure complete melting during spraying. The sol-gel produced powder exhibited good flow characteristics and the plasma sprayed coatings developed using this powder were also found to have excellent thermal shock resistance. The corresponding results obtained using an imported Y-PSZ powder are also presented for the purpose of comparison.
TL;DR: In this article, the first operation of light emitting p-n junction diode in porous silicon fabricated by diffusion was reported, where the diode was a light emitting polygonal diode.
Abstract: We report the first operation of light emittingp-n junction diode in porous silicon fabricated by diffusion.
TL;DR: In this article, the same authors provided evidence that zeaxanthin, lutein and fucoxanthin form molecular charge transfer (CT) complexes with iodine in the solid state and the identical values of thermal activation energies for dark and photoconduction have been obtained for the complexes.
Abstract: Spectroscopic evidence has been provided to confirm that zeaxanthin, lutein and fucoxanthin form molecular charge-transfer (CT) complexes with iodine in the solid state. The semiconductive and photoconductive properties of CT complexes have been investigated in polycrystals in a sandwich cell configuration. Both dark and photoconductivity increases by several orders of magnitude on complex formation. The identical values of thermal activation energies for dark and photoconduction have been obtained for the complexes and this has been attributed to spontaneous carrier generation by CT interaction and their migration by trapping and detrapping mechanisms. Photoconduction action spectra in pure polyene and in polyene-iodine complex suggest that photoinjection from the electrode and direct electron hole pair production are the two photocarrier generation mechanisms operative in these crystals. The second mechanism predominates in pure materials whereas the first one becomes important in the complexes.