Showing papers in "Transactions of The Indian Ceramic Society in 1986"
TL;DR: The effects of dopants, e.g. oxides of La, Sb, Nd, Gd, Y, Nb etc, on the PTC behavior of polycrystalline BaTiO3 was studied in this paper.
Abstract: The effects of dopants, e.g. oxides of La, Sb, Nd, Gd, Y, Nb etc have been studied on the PTC behaviour of polycrystalline BaTiO3. Sb-doped material showed the best characteristics under our experimental conditions. A systematic study on the effects of different electrode materials like Ag, In, In-Ga and Ni has also been carried out. The contact resistance was exceptionally high for Ag and In, but negligible in case of either In-Ga or Ni. Impedance measurement at different frequencies has been used to distinguish between the intra-grain, inter-grain and electrode-contact resistances. Power-limiting capability of the prepared specimens has been tested by measuring I-V characteristics.
13 citations
TL;DR: In this paper, the smallest size and narrowest size range of the spherical particles were observed for the product generated from methanolic solutions under a variety of experimental conditions with methanol, ethanol, 1-propanol and 2-pro panol as solvents.
Abstract: Monodisperse, ultrafine, spherical particles of amorphous silica were produced by the hydrolysis of tetraethyl orthosilicate under a variety of experimental conditions with methanol, ethanol, 1-propanol and 2-propanol as solvents. 1- and iso-butanol, acetone and 1, 4-dioxan
produced non-spherical agglomerates under equivalent conditions. The smallest size and narrowest size range of the spherical particles were observed for the product generated from methanolic solutions. Attempts were made to correlate solvent characteristics, e.g. polarity
and viscosity with the time lag of precipitation after onset of reaction, and particle size. It was indicated that under specific conditions, the nature of the solvent could also determine the nature of the polymeric aggregation in the precipitated particles.
9 citations
TL;DR: In this article, the sol-gel method has been used to synthesise zircon-based pigments having Pr, V, Ni, Cr, Fe and Cu ions as dopants and glass enamels close to the commercial composition of 27PbO.O3.8B.
Abstract: The sol-gel method has been used to synthesise zircon-based pigments having Pr, V, Ni, Cr, Fe and Cu ions as dopants and glass enamels close to the commercial composition of 27PbO.51SiO2.8B.O3.5Li2O. While these products compared reasonably with the corresponding products obtained through conventional sintering and melting, they are yet to be further developed to meet desirable qualities. The sol→gel→glass transitions have been studied spectroscopically for samples containing transition metals and the absorption spectra explained in the light of ligand field theory. The temperature of zircon formation and the extent of transformation to zircon were found to be influenced by the nature of dopants and such zircon pigments were found to have very high chemical durability. The gel derived glass enamels did not show any sign of crystallisation and adhered well on sheet glass substrate when fired at 600°C for 10 minutes.
7 citations
TL;DR: A number of TiO2 and P2O5 nucleated glass-ceramic coating compositions in the system RO-R′2O-Al2O3-SiO2 (R = Ca, Mg; R′ = Na, K, Li) have been studied for application on various grades of steel and alloy with a view to protecting them against mechanical wear and chemical corrosion as discussed by the authors.
Abstract: A number of TiO2 and P2O5 nucleated glass-ceramic coating compositions in the system RO-R′2O-Al2O3-SiO2 (R = Ca, Mg; R′ = Na, K, Li) have been studied for application on various grades of steel and alloy with a view to protecting them against mechanical wear and chemical corrosion. Good adhesion of the coating has been obtained on mild steel, stainless steel and nimonic alloy. The conventional technique has been used in the preparation and application of the coating material. The nucleation and crystal growth have been achieved by suitable heat-treatment schedule of the coated specimen. The properties of the coatings with respect to resistance towards abrasion, impact, high temperature, thermal shock and chemical corrosion have been evaluated and found to be superior to those of the conventional vitreous enamel coatings. X-ray and electron microscopic studies have been used to analyse the crystalline phases formed in the coating during the heat-treatment process. The unique combination of properties achie...
5 citations
TL;DR: The glass-ceramic material obtained under optimum conditions had high chemical resistance, micro-hardness of 7400 MPa and thermal stability as discussed by the authors, and the final product can be recommended for workshop floorings and storage vessels in chemical industries.
Abstract: Glasses containing iron oxide (12–15 wt%) have been prepared based on thermal power plant wastes, and their crystallization mechanism studied with the help of XRD, DTA and TEM. In the initial stages of crystallization, phase separation took place which led to the formation of hedenbergite. The glass-ceramic material obtained under optimum conditions had high chemical resistance, microhardness of 7400 MPa and thermal stability. The final product can be recommended for workshop floorings and storage vessels in chemical industries.
4 citations
TL;DR: In this article, structural changes in kaolinite during dehydration have been studied by calculating the radial distribution function from the X-ray diffraction intensities, and an estimate of the interatomic distances, relative strength of the couplings and the coordination numbers has been obtained for the samples at room temperature and heated at higher temperatures.
Abstract: Structural changes in kaolinite during dehydration have been studied by calculating the radial distribution function from the X-ray diffraction intensities. An estimate of the inter-atomic distances, relative strength of the couplings and the coordination numbers has been obtained for the samples at room temperature and heated at higher temperatures. The results show high stability of the silicon tetrahedral layer compared to the Al-O-(OH) octahedral one.
3 citations
TL;DR: In this article, the crystallization behavior of SiO2 52.0 (wt%) glass was studied and the principal crystal phases appeared at 760°, 835° and 930°C.
Abstract: Studies on the crystallization behaviour of SiO2 52.0, Al2O3 22.0, RO (CaO + MgO) 10.5, R2O (Na2O + K2O) 13.5, TiO2 6.0 (wt%) glass were carried out. The glass possessed fair working characteristics and corrosion of the melting pot was insignificant. The glass did not show any tendency towards deformation during crystallization. On crystallization, glass-ceramics possessing high mechanical strength (50,000 psi) and fair resistance to attack of alkali were obtained. The DTA curve exhibited exothermic peaks at 720° and 835°C. The principal crystal phases appearing at 760°, 835° and 930°C were identified as nepheline and sphene, while cordierite was also detected.
3 citations
TL;DR: In this paper, the authors measured the dielectric constant (K) and loss (tan δ) and AC conductivity of a sample of ripidolite sample as a function of frequency in the range 102-107 Hz and in the temperature range 30°-400°C.
Abstract: The dielectric constant (K) and loss (tan δ) and AC conductivity of a ripidolite sample have been measured as a function of frequency in the range 102–107 Hz and in the temperature range 30°–400°C. K and tan δ appear to decrease with increase of frequency and their values at 106 Hz are found to be 4.2 and 0.105 respectively. Variational patterns of K and tan δ reveal relatively larger changes at higher temperatures and appreciable frequency dependence, the values being larger at lower frequencies. Temperature variation of AC conductivity at different frequencies and the value of activation energy in the intrinsic range (∼ 1.0 eV) suggest that the conduction process is mainly associated with ions.
3 citations
TL;DR: In this article, surface modification of kaolinite by a controlled thermal treatment has been described, which resulted in a product of higher surface area and higher compressive strength as compared to those of composites with unmodified clay.
Abstract: Surface modification of kaolinite by a controlled thermal treatment has been described. The treatment resulted in a product of higher surface area. The surface-modified and unmodified particles have been incorporated in a polyester resin. Surface-modified clay-filled composites showed higher compressive strength as compared to those of composites with unmodified clay. Microstructures of the clay-polyester composites prepared using surface-modified and unmodified clays have also been presented.
3 citations
TL;DR: In this article, the aspect ratios of mica schist from Jhabua district of Madhya Pradesh were shown to have increased by more than three times on ultrasonic vibration.
Abstract: Mica schist from Jhabua district of Madhya Pradesh has been beneficiated through the water elutriation method. Advantages in using mica particulates from mica schist in composites are explained. The flakes are delaminated by ultrasonic vibration employing limestone and sand as cavitising aids. The aspect ratios are shown to have increased by more than three times on ultrasonic vibration. Preliminary results of mica polymer preparation are discussed.
3 citations
TL;DR: In this paper, the authors modeled the subcritical crack growth phenomenon in zirconia by deflection mechanism and found that the applied stress intensity factors in the sub critical crack growth range get affected due to scattering in KI-Vdata, biassing of N values to higher magnitude and calculating erroneous life times.
Abstract: Subcritical crack growth phenomenon in zirconia is modelled in this paper The model simulates subcritical crack growth by deflection mechanism Due to phase transformation in zirconia, KI, the applied stress intensity factors in the subcritical crack growth range get affected This is the main reason for the following observations: (i) scattering in KI—Vdata, (ii) biassing of N values to higher magnitude and (iii) calculating erroneous life times All the above mentioned experimental observations are explained by the present model
TL;DR: In this paper, a characterization of powders prepared by comminution of technical grade commercial alumina has been made with respect to wet grinding media and ratio of weight of balls to material.
Abstract: Characteristics of powders play an important role in the densification and grain growth during the sintering process of oxide ceramics. During the process of grinding for reduction of particle size, factors like impurity, hydration etc have to be controlled by the comminution period, ratio of material to grinding media (balls) as well as the use of proper liquid medium.In this investigation characterization of powders prepared by comminution of technical grade commercial alumina has been made with respect to wet grinding media and ratio of weight of balls to material. Powders thus obtained were examined by chemical analysis (purity), BET (surface area), SEM (shape and size), particle size distribution by X-ray (Sedigraph) methods. The influence of powder properties on the sintering behaviour of compacts was studied at 1400° and 1500°C for two hours.It was observed that an increased amount of balls reduced the particle size to a limiting stage with characteristic size distribution; a corresponding increase...
TL;DR: In this article, the effects of processing parameters and additions like clay, pyrophyllite and magnesium carbonate on densification have been studied in the range of 1500°-1800°C with a view to the utilization of these compositions for electrical applications.
Abstract: Alumina bodies have been prepared from commercially available, technical grade alumina. Effects of processing parameters and additions like clay, pyrophyllite and magnesium carbonate on densification have been studied in the range of 1500°–1800°C with a view to the utilization of these compositions for electrical applications.The bodies have been evaluated for microstructures and electrical properties at room temperature for 20 MHz. It was observed that alumina bodies containing 91–93% Al2O3 densified to the extent of 3.4–3.5 gm.cm−3 with imperviousness at 1500° to 1600°C. Bodies containing pyrophyllite exhibited dissipation factor as low as 0.0002 along with dielectric constant (K), in the range 6–7, while bodies containing alumina over 97% had a dissipation factor as low as 0.0001 having K in the range 7–8 when densities of these bodies exceeded 3.6 gm.cm−3 and open porosity decreased below 1%.
TL;DR: In this paper, the effect of volatiles present in the kiln atmosphere on the sinterability and microstructure of alumina ceramics was studied, and the results when compared with the corresponding properties under a pure environment have been presented.
Abstract: The effect of volatiles present in the kiln atmosphere on the sinterability and microstructure of alumina ceramics was studied. The experiments were so designed that the volatile impurities generated from the respective salts of Na, Cu, Zn, Ni, Cr and Fe were allowed to act on pure alumina ceramics.
The properties studied included porosity, density, fired shrinkage, microhardness, power factor, loss factor, volume resistivity and dielectric strength. Scanning Electron Microscopy was used for the characterization of the resulting microstructures. The results when compared with the corresponding properties of alumina ceramics fired under a pure environment have been presented.
TL;DR: The feasibility of utilizing this resource in the preparation of vitrified flooring tiles, refractory bricks, silicon carbide, optical and ophthalmic glasses and in foundry applications has been discussed as mentioned in this paper.
Abstract: Quartz sand deposits of Kerala are mainly confined to the Alleppey-Chavakkad belt on the western coast of Kerala. For evaluating this rich deposit, extensive physico-chemical characterization has been carried out. The feasibility of utilizing this resource in the preparation of vitrified flooring tiles, refractory bricks, silicon carbide, optical and ophthalmic glasses and in foundry applications has been discussed.
TL;DR: In this article, the sintering behavior of Bayer grade alumina in the temperature range 1400°-1800°C in a partially reducing atmosphere was reported, and a 1 wt% addition of titania was found to improve the sintability of alumina appreciably.
Abstract: The sintering behaviour of Bayer grade alumina in the temperature range 1400°—1800°C in a partially reducing atmosphere is reported. A 1 wt% addition of titania is found to improve the sinterability of alumina appreciably. The pellet density after two hours of sintering was the highest at 1475°C. The microstructure of the sintered pellets showed enhanced but uneven grain growth compared to that of similar alumina pellets without the titania addition. They also showed that the titania addition did not form any eutectic phase with the impurities in the Bayer alumina during the sintering.
TL;DR: In this paper, generalized relations between the strength distribution function and derivatives of the fracture probability have been obtained for cylindrical specimens tested in 3-point bending and derived relations have been used to evaluate the probability of failure during dynamic loading using a fracture mechanics approach.
Abstract: Generalised relations between the strength distribution function and derivatives of the fracture probability have been obtained for cylindrical specimens tested in 3—point bending. The derived relations have been used to evaluate the probability of failure during dynamic loading using a fracture mechanics approach. The theoretical and experimental results indicate that subcritical flaw growth during loading causes the strength degradation and the failure probabilities in impact test can be used to determine ‘safe working stress’ for the application of glass as a structural component.
TL;DR: In this article, the critical stress intensity factor, crack velocity-stress intensity relations for any glass can be predicted from the fracture stress and fracture surface mirror of specimens tested in 3-point bending.
Abstract: An analysis has been presented which enables the critical stress intensity factor, crack velocity-stress intensity relations for any glass to be predicted in a very simple manner from the fracture stress and fracture surface mirror of specimens tested in 3-point bending. A comparison of fracture energies and crack velocity parameter calculated from the mirror data with measured values supports the accuracy of the method.
TL;DR: In this article, it has been observed that for high silica content, increase in porosity or reduction in cold crushing strength improves spalling resistance whereas for low silica magnesite refractories, the reverse relationship is valid.
Abstract: It has been observed that for magnesite refractories with high silica content, increase in porosity or reduction in cold crushing strength improves spalling resistance whereas for low silica magnesite refractories, the reverse relationship is valid. Attempt has been made to explain these anomalies from their chemical and mineralogical characteristics.
TL;DR: In this paper, Boric oxide was used as a low melting additive to enhance the densification of forsterite, and the results of liquid phase sintering have been compared with those of Al2O3 addition.
Abstract: Boric oxide was used as a low melting additive to enhance the densification of forsterite. Results of liquid phase sintering have been compared with those of Al2O3 addition. Optimum density in case of pure Al2O3- and B2O3-added forsterite was found to be 2.06, 2.50 and 3.22 gm.cm−3 respectively under analogous thermal conditions. The maximum density was obtained at 3 wt% of B2O3 addition. Further addition of B2O3 reduced the density due to the development of excess vitreous phase.
TL;DR: In this paper, preliminary studies were carried out on bio-glasses with a view to developing suitable compositions which could be used as orthopaedic implants using DTA and gradient furnace techniques.
Abstract: Preliminary studies were carried out on bio-glasses with a view to developing suitable compositions which could be used as orthopaedic implants. Studies to establish conditions necessary for nucleation and proper crystal growth were carried out using DTA and gradient furnace techniques. Ceramization of the glasses was done by thermally treating the glass in such a way as to produce glass-ceramics consisting of more than one microcrystal that were differently oriented. The crystallized samples were put to X-ray analysis, scanning and transmission electron microscopy in order to find out the type and the size of the crystals. This study mainly pertains to the glass-ceramics composed of primarily Na2O—CaO—SiO2 and P2O5 in suitable composition ranges. In the present communication, the data pertaining to the studies on nucleation and crystallization of some glasses have been reported.
TL;DR: In this paper, the influence of CaO on the sintering behavior of BeO derived from beryllium sulphate was studied at temperatures between 1100° and 1500°C in vacuum and air atmospheres.
Abstract: Beryllium oxide, by virtue of its electrical resistivity and high thermal conductivity has a unique place in its application as a material for insulator components in electronics for which impervious high density bodies are requested. As BeO is a difficult material to sinter to high densities at temperatures less than 1600°C, CaO was considered as one of the additives that enhance densification without impairing the electrical properties. The influence of 0.5 to 5 wt% addition of CaO on the sintering behaviour of BeO derived from beryllium sulphate was studied at temperatures between 1100° and 1500°C in vacuum and air atmospheres. It was found that CaO addition substantially enhanced densification with concurrent grain growth and reduced open porosity.
TL;DR: Among the clay minerals present in the deltaic alluvium of Manmathanagar soil (West Bengal), the presence of halloysite has been detected in the fifth horizon with the help of transmission electron microscopy as discussed by the authors.
Abstract: Among the clay minerals present in the deltaic alluvium of Manmathanagar soil (West Bengal), the presence of halloysite has been detected in the fifth horizon with the help of transmission electron microscopy This seems to be the first report on halloysite in deltaic alluvium
TL;DR: Amorphous precursor materials for pure and MgO and CeO containing Zr02 were prepared via alkoxide hydrolysis, gel formation and solution spray drying techniques in this paper.
Abstract: Amorphous precursor materials for pure and MgO and CeO" containing Zr02 were prepared via alkoxide hydrolysis, gel formation and solution spray drying techniques. The crystallization behaviour of such precursor powders was studied by calcining them at 700°, 1000° and noocc. It was shown that the initial product(s) of crystallization,
as well as the conversion product(s) at higher temperatures could depend significantly not only on the overall mode of precursor preparation, but also on subtle differences within the same preparative technique.