Showing papers in "Transactions of The Indian Ceramic Society in 2004"
TL;DR: In this paper, a review of state-of-the-art ceramic materials for planar solid oxide fuel cell (SOFC) power modules is presented, with special attention given to the development of planar SOFC components fabrication taking into consideration the a...
Abstract: Solid Oxide Fuel Cell (SOFC) is a solid-state electrochemical device that converts the chemical energy of a fuel directly into electrical energy. Due to its multi-fold inherent advantages SOFC is projected as the power source for the future generation. All over the world, extensive research activities are being pursued for the past decade and accordingly an immense wealth of literature is avaitable in this field of research. Though this field of research activity is very wide and multidisciplinary, this review is mainly directed towards the processing, properties and fabrication of the state of the art ceramic materials, viz., yttria stabilized zirconia (YSZ) as the electrolyte material, Sr-doped LaMnO3 as the cathode material, Ni-YSZ cermet as the anode material and Ca-doped LaCrO3 as the interconnect material, that are being considered for the development of present day SOFC power modules. Special attention is given to the development of planar SOFC components fabrication taking into consideration the a...
38 citations
TL;DR: In this paper, the combustion behavior and phase evolution with respect to the Ca/P atom ratio in the starting materials were investigated and single-phase hydroxyapatite particles were obtained when the starting batch was 1.75.
Abstract: Nanoparticles of calcium hydroxyapatite, Ca10(PO4)6(OH)2, (HA) an important material for biomedical applications and other non-medical uses were synthesized by combustion in the aqueous system Ca-nitrate—diammonium hydrogen orthophos-phate-urea. The combustion behaviour and phase evolution with respect to the Ca/P atom ratio in the starting materials were investigated. Single-phase hydroxyapatite particles were obtained when the Ca/P ratio in the starting batch was 1.75. Below this ratio the products contained mainly hydroxyapatite and tricalcium phosphate (Ca3(PO4)2, TCP), the relative abundance of these phases being dependent upon the batch composition. In all these cases, the particles were equiaxed, nanosized (60—130 nm) and occurred as easily dispersible soft agglomerates of sizes ranging from 0.1 to larger than 100 μm. The products were characterized for phase contents, particle size distribution and morphology.
20 citations
TL;DR: In this article, Sol-gel processes are used to produce ceramic fuel in the form of microspheres of controlled size and are used in the production of cheap nuclear power in the UK.
Abstract: Ceramic nuclear fuel fabrication is an important step in the production of cheap nuclear power. Sol-gel processes are used to produce ceramic fuel in the form of microspheres of controlled size and...
16 citations
TL;DR: In this paper, the use of sonochemical processes for the insertion of nanomaterials into the pores of MSPM is discussed, and how this process is conducted, to what extent the materials are deposited in the pores and what is the mechanis...
Abstract: Ultrasound radiation has been recently used for the synthesis of mesoporous materials (MSPM). The main advantages are manifested in the short preparation time and thicker walls leading to a more hydrothermally stable structure.1 This preparation method has already been reviewed.2 The discovery of MSP materials led immediately to the development of many experimental methods for the deposition of materials, especially catalytic materials, into the mesopores. Impregnation, thermal spreading, ion adsorption, and the most recent method3 in which colloidal gold solution is premixed with the precursors for the preparation of the MSPM, are among the methods used for the insertion of materials into the mesopores. Sonochemistry was also employed for this purpose. We will outline in this article the use of the sonochemical processes for the insertion of nanomaterials into the pores of MSPM. We will explain how this process is conducted, to what extent the materials are deposited in the pores and what is the mechanis...
7 citations
TL;DR: Different low thermal expansion ceramics of Ca1-xSrxZr4(PO4)6 system with x = 0, 0.25,0.5 and 0.75 were synthesized by the solid state reaction method as discussed by the authors.
Abstract: Different low thermal expansion ceramics of Ca1-xSrxZr4(PO4)6 system with x = 0, 0.25, 0.5 and 0.75 were synthesized by the solid state reaction method. After several heat treatments finished products were obtained at 1300°C. These were characterized for phase purity by X-ray Diffractometry and IR Spectroscopy. Densification parameters of the compositions with 3 and 5 wt% ZnO added as sintering aids were studied at 1100°, 1200° and 1300°C under soaking periods of 2-6 h. The corresponding effects on the physical, thermal and mechanical properties were observed. A maximum of 98% of theoretical density was obtained and flexural strength as high as 70 MPa was achieved. Thermal expansion varied from -0.47 to 2.65 x 10−6/°Cwith increase in Sr content. The results are discussed in the light of the microstructures.
6 citations
TL;DR: In this article, an active filler alloy, 97(Ag-28Cu)3Ti has been developed for joining of ceramic-ceramic/metal, and the microstructure of the alloy shows the presence of silver-rich bright and copper-rich dark phases.
Abstract: An active filler alloy, 97(Ag-28Cu)3Ti has been developed for joining of ceramic-ceramic/metal. The microstructure of the alloy shows the presence of silver-rich bright and copper-rich dark phases. Most of the titanium is associated with copper-rich phase as the solubility of titanium in silver is very low in comparison to that in copper. The cleaned thin foil of 0.1–0.2 mm thick alloy was used for joining of sintered Al2O3-Al2O3 at 800°, 900°, 1000°, 1100° and 1200°C. The brazed samples were characterized by using SEM, EPMA and XRD. The EPMA analyses of the brazed samples show the inter-diffusion of elements across the interface. The inter-diffusion process during brazing was found to be dependent on the concentration of silver and copper present near the interface. The diffusion of titanium from the active filler alloy towards Al2O3was found to be maximum at the centre of the interfacial zone. The XRD results revealed that during brazing TiO and Ti3Cu3O were formed at the interface.
4 citations
TL;DR: In this article, the authors used a displacement reaction between solid silica glass rods and molten aluminium to construct dense AI2O3/AI composites containing three-dimensionalally interconnected ceramic and metallic phases.
Abstract: Dense AI2O3/AI composites containing three-dimensionally interconnected ceramic and metallic phases were fabricated by a displacement reaction between solid silica glass rods and molten aluminium. These composites consist of about 69% Al2O3 and 31% Al by volume. Their mechanical properties, namely, compressive strength, bend strength and microhardness are determined by the conventional procedures. The experimentally obtained data are compared with the theoretically derived one-point method. Elastic modulus, as determined by flexure testing, falls outside the Voigt-Reuss bounds. Although the two phases are interconnected in the composites to form an interpenetrating microstructure, the metallic phase is found to govern the modulus. Thermal treatments during fabrication and the interpenetrating microstructure strongly influence both the compressive and flexural strengths and the hardness of the final composite.
4 citations
TL;DR: In this article, the effect of atmosphere on the sintering of nano-crystalline α-silicon carbide, doped with boron carbide and carbon, and prepared by attrition milling, has been studied under vacuum, argon and nitrogen atmospheres between 2000° and 2100°C.
Abstract: The effect of atmosphere on the sintering of nano-crystalline α-silicon carbide, doped with boron carbide and carbon, and prepared by attrition milling, has been studied under vacuum, argon and nitrogen atmospheres between 2000° and 2100°C. It has been found that the sintering atmosphere has a very critical influence on the sintering of silicon carbide. Sintering in vacuum provides maximum theoretical density, whereas the nitrogen atmosphere has a retarding effect and does not yield full densification. Argon atmosphere takes an intermediate role in the sintering process. The results have been explained in terms of a diffusion model.
4 citations
TL;DR: In this paper, the development of a fast fired body, incorporating 5% wollastonite in place of quartz powder in a stoneware composition, resulted in early maturing by 50°C, decrease in the fired shrinkage by around 26.67%, increase in strength by around 18.69% and bulk density by 3.93% along with reduction in percent thermal expansion by 22.12% of the test specimen fired at 1200°C in comparison to those of a conventional body.
Abstract: The development of a fast fired body, incorporating 5% wollastonite in place of quartz powder in a stoneware composition, resulted in early maturing by 50°C, decrease in the fired shrinkage by around 26.67%, increase in strength by around 18.69% and bulk density by 3.93% along with reduction in percent thermal expansion by 22.12% (at 600°C) of the test specimen fired at 1200°C in comparison to those of a conventional body. The substantial decrease in the shrinkage and thermal expansion would favourably influence the final product output by reducing losses due to deformation, thermal shock, dunting etc. The reduction in the maturing temperature will be helpful to conserve energy during firing.
3 citations
TL;DR: In this article, the additives used to control slurry rheology included sucrose and two different dispersants, Darvan 821 A (ammonium polyacrylate) and DBAC (dibasic ammonium citrate).
Abstract: Ceramic foams with porosity 95% or above could be prepared by controlling slurry rheology through additives in direct casting route. The additives used to control slurry rheology included sucrose and two different dispersants, Darvan 821 A (ammonium polyacrylate) and DBAC (dibasic ammonium citrate). In addition, slurry rheology could also be varied through variation in ceramic loading. Slurry rheology had a significant influence on the foaming behaviour resulting in sintered foams with varying microstructure and total porosity. Lower viscosity slurries foamed to a greater extent, leading to higher porosity in foams. DBAC based slurries foamed to greater extent, resulting in thinner cell walls and increased number of interconnections between the cells. Use of sucrose helped in strengthening of green ceramic foams enabling ease in handling and machining.
3 citations
TL;DR: In this paper, the microwave-sol vothermal (M-S) process is used to synthesize nanopowders of different sizes and shapes, which can then be processed by microwave sintering to achieve good mechani...
Abstract: There are two main keys for step function advances in ceramic materials science, i.e., new materials and new processing techniques. This paper focuses on new synthesis and processing techniques. Since 1991, we have been very active in the synthesis of various ceramics, metals and semiconductor powders using microwave-assisted solvothermal process. The main advantages of microwave-sol vothermal (M-S) process over the conventional process are: (a) it can lead to energy savings through rapid heating to the temperature of treatment and enhanced kinetics of phase formation by one to two orders of magnitude, (b) it can lead to formation of new phases and (c) it can eliminate metastable phases. These advantages of the M-S process will be illustrated with several examples of ceramic materials synthesized by this process. Ceramic powders including nanopowders of different sizes and shapes can be synthesized by the novel M-S process. These powders can then be processed by microwave sintering to achieve good mechani...
TL;DR: In this paper, the mechanism and kinetics of thermal decomposition of limestone were studied using Arrhenius equation applied to solid state reactions, and it was found that in both non-isothermal and isothermal methods limestone seemed to be decomposed via a zero order reaction mechanism.
Abstract: The kinetics of decomposition of limestone was studied using both non-isothermal and isothermal methods. The mechanism and kinetics of thermal decomposition were studied using Arrhenius equation applied to solid state reactions. It was found that in both non-isothermal and isothermal methods limestone seemed to be decomposed via a zero order reaction mechanism. The energy of activation for the non-isothermal and isothermal decompositions of limestone was 157.79 and 181.43 kJ.mol−1respectively. Similarly, In A values for non-isothermal and isothermal decomposition were found to be 14.2 and 13.2(s−1) respectively.
TL;DR: The reaction between SiO and CO vapours in an argon atmosphere has been employed for the synthesis of SiC nanofibres as discussed by the authors, where the raw materials for the vapour-state formation were silicon and graphite powders.
Abstract: The reaction between SiO and CO vapours in an argon atmosphere has been employed for the synthesis of SiC nanofibres. The raw materials for the vapour-state formation were silicon and graphite powd...
TL;DR: In this article, protein coagulation casting (PCC) was applied for consolidation of green silicon carbide bodies, which utilizes aqueous ceramic slurries based on egg whitening.
Abstract: A new ceramic forming process, protein coagulation casting (PCC), has been applied for consolidation of green silicon carbide bodies. The process utilizes aqueous ceramic slurries based on egg whit...
TL;DR: In this paper, a fly ash waste material generated from thermal power stations was used as a complete replacement of quartz and partial replacement of china clay and potash feldspar in the semi-vitreous tile body composition.
Abstract: An investigation was carried out to incorporate fly ash, a waste material generated from thermal power stations, as a complete replacement of quartz and partial replacement of china clay and potash feldspar in the semi-vitreous tile body composition. Further, a non-conventional flux talc was gradually incorporated in the body mix containing 40 wt% of fly ash. Dry and fired thermo-mechanical properties of the fired specimens were studied and compared with those of a standard body mix. It was observed that the incorporation of fly ash to the tune of 15 wt% in the standard composition led to an increase in the fired strength by 14% without any increase to the maturing temperature of the specimens. The incorporation of talc in a body mix containing 40 wt% fly ash increased the fired strength by 32.4% and decreased the maturing temperature of specimen by 50°C in comparison to those of the parent body.
TL;DR: In this article, an attempt has been made to evaluate the rheological characteristics of a cordierite-mullite precursor oxides based dough with appropriate proportions of additives using an indigenously designed and fabricated capillary extrusion die coupled with a universal testing machine.
Abstract: An attempt has been made to evaluate the rheological characteristics of a cordierite-mullite precursor oxides based dough with appropriate proportions of additives using an indigenously designed and fabricated capillary extrusion die coupled with a universal testing machine. Further, the pressure profile of the extrusion process was analyzed using Benbow's paste flow model, which showed a clear dependence of die land region and negligible effect of die entry on extrusion velocity with respect to L/d ratios. The flow characteristics were also analyzed using power law model after incorporating Bagley's entry correction. Viscosity-shear rate data show that the variation is towards Newtonian behaviour with a power law exponent of 0.63 for shear rates < 50 s−1, while at higher shear rates, it is distinctly non-Newtonian with a power law exponent of typically 0.31.
TL;DR: In this paper, the molar extinction coefficients of Co2+ ion were calculated using Bouger-Beer's equation and the intensities of the bands were reported quantitatively in glasses at their wavelength maxima.
Abstract: Co2+ ion was found to produce a variety of colour shades ranging form pinkish blue to intense blue to greenish blue in a series of binary alkali silicate glasses. The optical absorption characteristics of divalent cobalt produce three strong bands in the visible and two weak bands in the near infrared region, respectively in lithium silicate, sodium silicate and potassium silicate glasses. In the present study, the molar extinction coefficients of Co2+ ion were calculated using Bouger-Beer's equation and the intensities of the bands were reported quantitatively in glasses at their wavelength maxima. The absorption bands in the molar extinction curves for Co2+ ion were found to shift more towards longer wavelengths with an increase in ionic radius of alkali ion on replacing lithium by sodium and sodium by potassium in glasses. The results were explained with reference to Ilse and Hartmann equation. Further, the values of molar extinction coefficients were found to increase with increasing basicity of the a...
TL;DR: In this article, the authors provide a brief overview of the global research going on for the development of sol-gel technologies as superior alternatives to the conventional commercial ones and discuss the major host structures and colouring components selected in solgel research, necessary preparative steps for their synthesis in the form of pigments, the major advantages that accompany this processing technique and the apparent directions this research is taking.
Abstract: Ceramic pigments are one of the conventional ceramic products widely used for decoration of tiles, tableware etc and the quality of this decoration is one of the factors that governs the market of the products. These pigments, prepared commercially through solid state reactions among constituent oxides, are known to often fall short of expectations regarding homogeneity and brightness of colour, preparative temperature etc. This minireview provides a brief description of the global research going on for the development of sol-gel technologies as superior alternatives to the conventional commercial ones. The areas dealt with are the major host structures and colouring components selected in sol-gel research, necessary preparative steps for their synthesis In the form of pigments, the major advantages that accompany this processing technique and the apparent directions this research Is taking.
TL;DR: In this paper, physicochemical and mineralogical characteristics of the raw materials, viz., clays, fly ash, sandstone and marble waste were studied with a view to finding out their possible utilization in the manufacture of earthenware wall tiles.
Abstract: Physicochemical and mineralogical characteristics of the raw materials, viz., clays, fly ash, sandstone and marble waste were studied with a view to finding out their possible utilization in the manufacture of earthenware wall tiles. The studies included plastic and dry properties, particle size distribution, chemical analyses, XRD, DTA as well as fired (at 1350°C) properties. The results showed that the clays selected were highly plastic in nature and contained predominantly kaolinite mineral associated with illite/muscovite as minor minerals. The study also revealed that fly ash contained a substantial amount of mullite, while marble waste contained calcareous minerals like dolomite, akermanite etc.
TL;DR: In this article, intermediate powder precursors of three different compositions in the system Li2O-Al2O3-SiO2 were synthesized in the form of gellike mass by wet-interaction technique in an aqueous medium.
Abstract: Intermediate powder precursors of three different compositions in the system Li2O-Al2O3-SiO2 were synthesized in the form of gellike mass by wet-interaction technique in an aqueous medium. These intermediate powder precursors were zeolitic type materials, which were found to exhibit dehydration-rehydration behaviour up to considerably high temperatures, thus establishing the fairly high stability of the network forming structure. The substances retained their amorphous character up to around 600°C, the temperature at which the material became completely dehydrated. The rehydration studies of the dehydrated specimens were carried out at different relative humidities. The dehydration-rehydration characteristics revealed the existence of large cavities and channels which hold the water molecules. The skeleton structure that remains after dehydration consists of silica tetrahedra linked to alumina octahedra and alumina tetrahedra. The amorphous character of the material was found to persist up to around 600°C...
TL;DR: The performance of the additives in effecting the desired purpose depends mainly on their chemical nature and functionality, the nature of mineral surface and the aqueous environment, therefore, it is necessary to have a thorough understanding of the chemistry of dispersants, flocculants, binders, wetting and antifoaming agents in order to maximize the effectiveness of the polymeric and other organic additives as mentioned in this paper.
Abstract: Polymeric and other organic additives are used in ceramic slurry processing for a wide range of oxides, carbides, nitrides etc as dispersants, flocculants, binders, wetting agents and antifoaming agents. The performance of the additives in effecting the desired purpose depends mainly on their chemical nature and functionality, the nature of mineral surface and the aqueous environment. Therefore, it is necessary to have a thorough understanding of the chemistry of dispersants, flocculants, binders, wetting and antifoaming agents in order to maximize the effectiveness of the polymeric and other organic additives. Apart from the polymeric additives other non-polymeric additives are also used. They may be wetting agents, antifoaming agents or even dispersants.Mutual interactions between the additives in any system are usually considered negligible. In many cases, however, interactions that occur can affect the process and ultimately the product performance. This could be the root cause of some common ceramic ...
TL;DR: In this paper, an attempt has been made to develop a singular blended clay having all the plastic and dry properties required for the casting of traditional ceramic products, especially sanitaryware and table wares.
Abstract: An attempt has been made to develop a singular blended clay having all the plastic and dry properties required for the casting of traditional ceramic products, especially sanitaryware and table wares. One semi-processed china clay, one plastic ball clay and one plastic fireclay from Indian origin were crushed and blended together in a predetermined proportion and beneficiated using the existing techniques of levigation, sieving, hydrocycloning, deironing and filter pressing. The physico-chemical properties of feed raw materials as well as blended clays were studied. The investigation also included the rheological properties of the blended clay. The results indicated that the blended and beneficiated clay obtained by levigation as well as by hydrocycloning, apart from ensuring consistency, showed higher unfired strength and increased particle fineness. The content of alumina in the levigated blend and the levigation-cum-hydrocycloned blend increased by 41 and 72% respectively in comparison to that of the feed. The investigation regarding their use in a standard sanitaryware body showed an increase in unfired strengths by 23.4 and 77.2%.
TL;DR: In this article, a diffuse phase transition has been observed in Ba1-xCuxTiO3 within a certain concentration range of copper, and the maximum frequency dispersion has been found for the composition Ba0.9Cu0.1 TiO3-.
Abstract: A diffuse phase transition has been observed in Ba1-xCuxTiO3 within a certain concentration range of copper. The maximum frequency dispersion has been found for the composition Ba0.9Cu0.1TiO3-. For...
TL;DR: In this article, the electrochemical and electrokinetic determination of the charges of ceramic nano-filtration membranes under varying electrochemical conditions and the influences of these effects on the filtration properties were characterized.
Abstract: Membrane separation in the nanofiltration range does not only result from a pure sieving effect of the pore structure, but is also strongly influenced by the surface charge properties of the membrane surface and the surface of the pore waits. In the case of liquid saturated oxide ceramic membranes, a surface charge results from dissociated surface groups and adsorbed ions. The aim of the present research therefore is the electrochemical and electrokinetic determination of the charges of ceramic nano-filtration membranes under varying electrochemical conditions and the influences of these effects on the filtration properties. Oxide ceramic nanofiltration membranes of TiO2 were characterized. Direct methods for determining the membrane charges use electrokinetic effects like streaming potential (tangential and perpendicular method). Indirect methods use measurements of the etectromotive force and the salt rejection during permeation measurements. The investigations show the possibility for adjusting the sep...
TL;DR: In this paper, four types of mullite precursors are synthesized by mechanochemically processed mixtures consisting of kaolinite with or without heat treatment and AI(OH)3.
Abstract: Mullite bonded white fused alumina based castables have been prepared by adding four types of mullite precursors synthesized by mechanochemically processed mixtures consisting of kaolinite with or without heat treatment and AI(OH)3. DTA, TG and IR data of different mullite precursors have been analysed. Apparent porosity, bulk density, cold compressive strength and strength retainment after spelling test of castables have been compared to identify the possible beneficial role of these additives. XRD and SEM studies of some selected castables have been performed to substantiate the effect of mechanochemically processed mullite precursors.
TL;DR: In this paper, the α-hemihydrate form of calcium sulphate is a more suitable candidate for such applications, and ceramic shapes with requisite porosity and strength were fabricated in the laboratory and characterized for their morphology and microstructure respectively.
Abstract: The use of calcium sulphate externally on the human body in the form of Plaster of Paris (POP) has been well established, but its possible use inside the human body as bone void filler is a recent idea. It has been realized that the quality of the calcium sulphate and its physical characteristics are the key factors for its reproducible performance inside human body, and most commercial powders may not be suitable. Controlling the size and shape of the calcium sulphate hemihydrate/bihydrate crystals is necessary to obtain a product, which will get resorbed in human body at a rate consistent with the new bone growth.It has been realized that the α-hemihydrate form of calcium sulphate is a more suitable candidate for such applications. Hence, α-hemihydrate of calcium sulphate was prepared in the laboratory and ceramic shapes with requisite porosity and strength were fabricated. The powders and pellets were characterized for their morphology and microstructure respectively. These shapes after radiation steri...