Showing papers in "Transactions of The Indian Ceramic Society in 1991"
TL;DR: In recent years, the use of plasma-sprayed protective coatings has gained increasing acceptance for prolonging the service life of critical components exposed to aggressive environments during normal operation as mentioned in this paper.
Abstract: In recent years, the use of plasma-sprayed protective coatings has gained increasing acceptance for prolonging the service life of critical components exposed to aggressive environments during normal operation. This paper is aimed at providing an overview of the current state-of-the-art of the plasma coating technology. It includes a brief discussion of the various important aspects associated with the development of reliable protective coatings as well as their evaluation, and outlines some noteworthy advances made in the field of plasma spray materials and equipment in the past few years. The various factors influencing the coating quality are identified and the wide-ranging utility of plasma-sprayed coatings is also highlighted.
16 citations
TL;DR: In this article, the preparation routes for making nanocrystalline materials are briefly reviewed and structural characteristics of nanomaterials are delineated, and the effect of particle size on the energy level structure of various metals are elaborated.
Abstract: The preparational routes for making nanocrystalline materials are briefly reviewed. Structural characteristics of nanomaterials are delineated. Magnetic properties, e.g. magnetization, coercivity, etc of nanoparticles of ferromagnetic metals are described and the effect of particle size thereon is discussed. Electron spin resonance (ESR) and nuclear magnetic resonance (NMR) techniques as used to investigate the effect of particle size on the energy level structure of various metals are elaborated. Lastly, the study of Mossbauer spectra of ultrafine particles of iron and related compounds is discussed in relation to their magnetic behaviour.
9 citations
TL;DR: A tilting disc artificial heart valve using a synthetic sapphire disc and a titanium nitride coated Haynes alloy cage was developed and successfully completed the accelerated durability test as per international protocol.
Abstract: A tilting disc artificial heart valve using a synthetic sapphire disc and a titanium nitride coated Haynes alloy cage was developed. Sapphire has proved to be an excellent biocompatible material in...
6 citations
TL;DR: In this article, the principle of operation of quartz crystal units is explained with the aid of an equivalent LCR circuit and the method of controlling precisely the frequency of oscillator circuits by a quartz resonator is elucidated.
Abstract: The process of hydrothermally growing single crystals of quartz in high pressure autoclaves at elevated temperatures is described in brief. Methods of cutting and processing of wafers of quartz from synthetically grown crystals for fabrication of quartz crystal resonator units are outlined. The principle of operation of quartz crystal units is explained with the aid of an equivalent LCR circuit and the method of controlling precisely the frequency of oscillator circuits by a quartz resonator is elucidated. Extensive applications of quartz in the emerging electronic era are reviewed, both for analogue and digital circuitry, and the Indian demand analysed in the perspective of production capacity of a leading developed country of the world.
5 citations
TL;DR: In this article, the densification behavior and microstructural evolution in zirconia alloyed with 3.4 wt % MgO were studied and a comparison was made of products obtained by conventional mechanical mixing and the wet-chemical method of coprecipitating the constituents as crystallized materials obtained under hydrothermal conditions.
Abstract: The aim of the present work is to study the densification behaviour and microstructural evolution in zirconia alloyed with 3.4 wt % MgO. A comparison is made of products obtained by conventional mechanical mixing and the wet-chemical method of coprecipitating the constituents as crystallized materials obtained under hydrothermal conditions. Characterizations for strength-controlling factors like densification, metastable phase retention, hardness variations etc which are necessary for predicting the reliability of the resultant component have been made and discussed.
4 citations
TL;DR: In this article, a general review of the effects induced by high fluence ion implantation in silicate and fluoride glasses is presented, where compositional changes are related to radiation enhanced diffusion processes, preferential sputtering and internal electric field formation.
Abstract: The paper presents a general review of the effects induced by high fluence ion implantation in silicate and fluoride glasses. Charged particle irradiation introduces network damage and alters the chemical composition. Compositional changes are related to radiation enhanced diffusion processes, preferential sputtering and internal electric field formation. These effects determine modifications in the mechanical, optical and chemical properties of the glasses.
4 citations
TL;DR: In this paper, the mechanical properties of flooring tiles fired in a conventional down draft kiln were compared with those produced commercially following the fast firing schedules, and it was observed that the conventional long firing operation favored dissolution of quartz, recrystallization of the secondary mullite and reduction in the amount of closed pores in the structure, thus enhancing the strength and toughness of the body as well as the resistance towards abrasion of the glazed surface.
Abstract: The mechanical properties of flooring tiles fired in a conventional down draft kiln were compared with those produced commercially following the fast firing schedules. It has been observed that the conventional long firing operation favours dissolution of quartz, recrystallization of the secondary mullite and reduction in the amount of closed pores in the structure, thus enhancing the strength and toughness of the body as well as the resistance towards abrasion of the glazed surface.
4 citations
TL;DR: In this article, the structures of TeO2 and Li2O-LiCl-TeO2 glasses have been investigated by means of Raman and 125Te MAS NMR spectroscopy.
Abstract: The structures of TeO2 and Li2O-LiCl-TeO2 glasses have been investigated by means of Raman and 125Te MAS NMR spectroscopy. Extremely large isotropic chemical shifts of 1500–1700 ppm and linewidths of 160–230 kHz were observed in the 125Te MAS NMR spectra of both TeO2 crystals and TeO2-based glasses, indicating that Te atoms in TeO4 or TeO3+1 polyhedra in oxide crystals and glasses have very low symmetry mainly due to the presence of a lone pair of electrons. The Raman spectra revealed that pure TeO2 glass has a network structure similar to that of α-TeO2 rather than β-TeO2. The present Raman and 125Te MAS NMR spectra also confirmed that not only Li2O but also LiCl modifies the TeO2 glass network, forming TeO3, trigonal pyramid.
3 citations
TL;DR: In this article, various designs for batch preheating are described and compared, and the merits of a packed bed direct exchange preheater are noted, and experiments simulating the effect of some of these factors on SO2 removal are presented.
Abstract: Batch and cullet heat exchange with the flue gas permits recycling of otherwise inaccessible flue gas enthalpy. Various designs for batch preheating are described and compared. The merits of a packed bed direct exchange preheater are noted.Heat transfer calculations reveal that significant energy savings can be realized even on efficient regenerative furnaces. The savings depend either on the temperature of the Hue gas exiting the regenerator or on batch and cullet sticking behaviour. Experimental results on sticking will be presented.Capture of SO2 and perhaps NOx by the batch depends on a number of factors, e.g. batch temperature and batch particle size. Experiments simulating the effect of some of these factors on SO2 removal will be presented.
3 citations
TL;DR: In this article, the results indicate that for both regions, it is not possible to make tiles or other products by using one type of clay alone, and a combination of both the clays available in the same region can impart appropriate properties conducive to satisfactory production.
Abstract: Thc common clays, namely blue clay and yellow clay from Kerala and red clay and black clay from Morbi, Gujarat have been selected for studying their physico-chemical properties which involve chemical analysis, plasticity test, particle size analysis, X-ray diflractometry, drying and firing characteristics, rational analysis etc. The results indicate that for both regions, it is not possible to make tiles or other products by using one type of clay alone. A combination of both the clays available in the same region can impart appropriate properties conducive to satisfactory production.
2 citations
TL;DR: The role of grain size on the extent of microcracking was illustrated in the case of niobia and lead titanate ceramics in this article, which exhibits both a phase change (paraelectric to ferroelectric) and an anisotropic thermal expansion.
Abstract: One of the limitations in the use of ceramics in critial applications is due to the presence of microcracks, which may arise from differential thermal expansion and phase changes, among others. Acoustic emission signals occur when there are abrupt microdeformations in a material and thus offer a convenient means of non-destructive detection of microcracking. Examples of a study of acoustic emission from microcracking due to anisotropic thermal expansion in low thermal expansion single phase ceramics such as niobia and sodium zirconium phosphate ceramics and due to phase changes in zirconia and superconducting YBa2Cu3O7-x ceramics are piesented, together with the case of lead titanate ceramics, which exhibits both a phase change (paraelectric to ferroelectric) and an anisotropic thermal expansion. The role of grain size on the extent of microcracking is illustrated in the case of niobia ceramics. Some indirect evidence of healing of microcracks on heating niobia and lead titanate ceramics is presented from...
TL;DR: In this article, three precursors of equivalent oxide composition 2ZnO.SiO2, namely, a colloidal gel prepared from zinc nitrate tetra+hexahydrate (partially crystallized) and colloidal silica sol, anamorphous colloidal mixture from zinc chloride n-hydrate and the same colloidal sol, and a mechanical mixture of quartz and ZnO, have been used for examining their relative reactivities in the formation of willemite, Zn2SiO4.
Abstract: Three precursors of equivalent oxide composition 2ZnO.SiO2, namely, (i) a colloidal gel prepared from zinc nitrate tetra+hexahydrate (partially crystallized) and a colloidal silica sol, (ii) a colloidal gel (amorphous) prepared from zinc chloride n-hydrate and the same colloidal silica sol, and (iii) a mechanical mixture of quartz and ZnO, have been used for examining their relative reactivities in the formation of willemite, Zn2SiO4. The samples were heat-treated at temperatures in the range 1000°C–1400°C and for soaking periods of less than 1 hr to 80 hours. X-ray analyses showed the nitrate-derived gel to be the most reactive, followed by the chloride-derived gel; the crystalline oxide mixture showed sluggish reaction. Attempts have been made to explain this difference in reactivity in terms of the thermal behaviour of the precursors below 1000°C.
TL;DR: In this article, the effects of several factors, i.e. temperature, humidity and time on the weathering of soda-lime glasses (float and rolled glasses) were studied by means of AAS, IRRS, XPS, EPM, SEM, EPMA and WDS.
Abstract: The effects of several factors, i.e. temperature, humidity and time on the weathering of soda-lime glasses (float and rolled glasses) were studied by means of AAS, IRRS, XPS, EPM, SEM, EPMA and WDS. Under the same weathering conditions, lead crystal glass with higher alkali content was found to be more liable to weathering. The experimental relationships between the amount of alkali generated and weathering temperature and time for the four kinds of glasses have been derived. The weathering mechanism of soda-lime and lead glasses has been discussed.
TL;DR: In this paper, the size defect of poorly crystalline goethite has been explained in terms of size defect, which is inherent in all real crystals, and the results of the measurements are compared and used to explain that with dehydration, size defect gradually diminishes, leading finally to the formation of defect free, well-crystallized hematite.
Abstract: Dehydration transformation in an oxyhydroxide of iron, i.e. goethite has been studied from X-ray line profile. The transformation of poorly crystalline goethite into a well crystallized hematite has been explained in terms of size defect which is inherent in all real crystals. Variation of particle size during the transformation has been calculated by adopting quantitative X-ray methods based on integral breadth and variance. The results of the measurements are compared and used to explain that with dehydration, the size defect gradually diminishes, leading finally to the formation of defect free, well-crystallized hematite.
TL;DR: In this paper, the properties, applications and microstructural developments of these no-cement castables are discussed, which are based on a proprietory bonding system and can be installed by a concrete pump.
Abstract: Since the advancement of monolithic refractories through low moisture/low-cement castables, the iron and steel industries have benefited significantly through improved quality and productivity. A no-cement castable has also been developed recently, which has basically similar characteristics as of low-cement castables and have better hot strengths above 1400°C, ease of drying without spalling or cracking; they are amenable to the basic installation techniques. All these no-cement castables which are based on a proprietory bonding system can be installed by a concrete pump. The advancements mentioned above have made these no-cement castables much more versatile. This paper deals with the properties, applications and microstructural developments of these no-cement castables.
TL;DR: In this paper, the phase changes and microstructure of the sintered compacts were studied and properties like degassing rate and electrical breakdown strength were measured, showing no chipping during machining.
Abstract: Studies were carried out for development of machinable ceramics from indigenous mica. A composition containing mica, 8–12% glass and sintering aids up to 10% resulted in dense and impervious bodies on heat treatment up to 1100°C. XRD patterns and SEM fractographs were used to study the phase changes and microstructure of the sintered compacts. Properties like degassing rate and electrical breakdown strength were measured. The samples were machinable and showed no chipping during machining.
TL;DR: In this article, the authors present an analysis of the world status of structural ceramics and show that the products which have already been commercialized are mainly bearing and bearing parts, cutting tools and wear resistant parts.
Abstract: Analysis of the world status of structural ceramics shows that the products which have already been commercialized are mainly bearing and bearing parts, cutting tools and wear resistant parts. The worldwide sale of structural ceramic products today is worth about one billion dollars. This is expected to increase to over three billion dollars in the next five years. The rate of growth after that is expected to be even more rapid due to the expected commercialisation of the heat engine components.Some of the emerging technologies in the area of structural ceramics are high performance ceramic coatings, sol-gel technology and ceramic matrix composites. The market for the coatings is growing at the rate of 9.5% and should grow faster after 1995 with their application in the heat engines. The sol-gel technology products are just beginning to get commercialized but are predicted to achieve the fastest growth rate of 117% per year. In view of the large resources needed to develop a structural ceramic product fro...
TL;DR: In this article, the crystallization behavior of lithia-alumina-silica glasses with 0-19 wt% zirconia was studied by X-ray diffraction, differential thermal analysis and infrared spectroscopy.
Abstract: The crystallization behaviour of lithia-alumina-silica glasses with 0–19 wt% zirconia was studied by X-ray diffraction, differential thermal analysis and infrared spectroscopy. The principal crystalline phases were identified as lithium metasilicate and cubic or tetragonal zirconia, as also a lithium aluminium silicate (β-spodumene). The addition of zirconia to the glass changed the crystallization behaviour and transition temperature of the glasses.
TL;DR: In this paper, the application of X-ray photoelectron spectroscopy (XPS) for understanding ionic conduction in glasses is discussed, and two major experimental concerns with this technique are discussed.
Abstract: The purpose of this article is to illustrate the application of X-ray photoelectron spectroscopy (XPS) for understanding ionic conduction in glasses. First, we briefly describe the kinds of information one may expect to obtain from XPS on glasses; this is followed by comments on two major experimental concerns with this technique. Two examples are discussed wherein XPS data contribute significantly to the understanding of ionic conductivity.
TL;DR: An allalkoxide sol-gel route to barium silicate glass has been developed in this article, where a highly reactive barium disilicate (BS2) composition gel was densified into glass with 97% density at 725°C (Tg=695°C).
Abstract: An all-alkoxide sol-gel route to barium silicate glass has been developed. A highly reactive barium disilicate (BS2) composition gel was densified into glass with 97% density at 725°C (Tg=695°C). DTA, XRD, TKM and optical studies reveal that the phase separation and crystallization behaviour of the gel glass is similar to that of the corresponding melt glass, although the peak crystallization temperature (Tc) from DTA is lower for the gel glass.
TL;DR: In this paper, the machinable ceramics were carried out with compositions containing steatite and pyrophyllite with minor additions such as barium carbonate and calcium oxide.
Abstract: Developmental work on machinable ceramics was carried out with compositions containing steatite and pyrophyllite with minor additions such as barium carbonate and calcium oxide. Cold pressed compac...
TL;DR: The effect of bismuth oxide on the sheet resistivity and TCR of ruthenium dioxide-based resistors has been studied in this paper, where it has been observed that Bismuthoxide decreases the sheet resistance and shifts the TCR towards the positive direction.
Abstract: The effect of bismuth oxide on the sheet resistivity and TCR of ruthenium dioxide based resistors has been studied. It has been observed that bismuth oxide decreases the sheet resistivity and shifts the TCR towards the positive direction. It also enhances the formation of complex ruthenates and results in much lower requirement of RuO2 than otherwise found necessary. An excess of bismuth oxide, on the other hand, may often result in the flow of glass which in turn will impair the geometry of the print.
TL;DR: In the context of the energy crunch a need is felt today to explore the possibilities of substituting alternative materials for more energy-intensive metals, plastics and high-fired ceramics as discussed by the authors.
Abstract: In the history of materials used in our society the hydraulic binders appeared much later but fulfilled the societal needs as the most extensively used and cheapest constructional materials. In the background of the energy crunch a need is felt today to explore the possibilities of substituting alternative materials for more energy-intensive metals, plastics and high-fired ceramics. Newer composites, developed from hydraulic binders with proper manipulation of properties, have now appeared in the scene for such replacement. The present discourse is an attempt to highlight such perspectives of hydraulic binder-based composites.
TL;DR: A case study of an R&D activity and its successful commercialization in the area of high technology ceramic component taking the specific example of a PTC device development is presented in this paper.
Abstract: Commercialization of indigenous R&D for technological needs particularly in advanced materials and component areas is yet to receive significant attention in our country. The present paper discusses a case study of an R&D activity and its successful commercialization in the area of high technology ceramic component taking the specific example of a PTC device development.