Showing papers in "Transactions of The Indian Ceramic Society in 1984"
TL;DR: In this article, the structural changes accompanying dehydration and thermal transformations in palygorskite have been reviewed and salient features of the dehydration mechanisms proposed by various authors have been discussed.
Abstract: Structural changes accompanying dehydration and thermal transformations in palygorskite have been critically reviewed. Salient features of the dehydration mechanisms proposed by various authors have been discussed. Results of some X-ray and electron microscopic studies made by the authors on this problem, clarifying some points in greater detail, have also been included.
8 citations
TL;DR: In this paper, X-ray analysis was performed on CA, CA2 and their mixes with and without alumina aggregate and the results showed that CA2, CA-CA-CA2 and CA2 mixes gave higher percentage of CAH10 and AH3.
Abstract: CA, CA2 and their mixes with and without alumina aggregate were allowed to hydrate below 25°C and in not less than 90% relative humidity. The various phases formed were determined by X-ray analysis. The data obtained showed that the hydration products of CA were C3AH6 and AH3 whereas CA2, CA—CA2 mixes gave higher percentage of CAH10 and AH3. Hydrated CA mixes with Al2O3 after firing gave CA2 and CA6, whereas CA—CA2 mixes gave CA6. The strength value of CA—CA2 mixes increased with increase in CA2 content whereas PCE value increased with increase in CA2 content.
6 citations
TL;DR: In this article, the translucency of unglazed bone-china pieces of thickness 1-2 mm, fired at different temperatures, was measured and it was found that samples fired at temperatures less than 1150°c showed hardly any translucencies for a reasonable soaking time.
Abstract: Translucency of unglazed bone-china pieces of thickness 1–2 mm, fired at different temperatures, was measured. It was found that samples fired at temperatures less than 1150°c showed hardly any translucency for a reasonable soaking time. Thickness of samples was less critical than the firing temperatures. A firing temperature of 1200° to 1250°c with one and half hours' to two and half hours' soaking time resulted in translucency of unglazed bone-china samples which compared favourably with commercial samples.
5 citations
TL;DR: In this article, Bayer's alumina of micron and submicron order formed agglomerates when the powder was calcined at sufficiently high temperatures and became increasingly stronger with increasing temperature of calcination.
Abstract: Wet ground and washed Bayer's alumina of micron and submicron order formed agglomerates when the powder was calcined at sufficiently high temperatures. The agglomerates became increasingly stronger with increasing temperature of calcination. Grinding, leaching with acid and finally washing with distilled water caused surface hydration which was evidenced by loss in weight on ignition and pycnometric density of alumina powders calcined at different temperatures. Pore volume reduction of agglomerates thus formed at temperatures above 1100°C caused remarkable improvement in the packing density of alumina bodies using the calcined powders. However, in order that a good alumina body may be formulated, the use of fused alumina grains seemed to be unavoidable.
4 citations
TL;DR: In this article, a modified route for synthesizing barium hexaferrite (BaO) through ammonium carbonate using metal chlorides is reported, and coprecipitations were studied in the range of pH 7.2-8, Fe/Ba ratio 8.55-11.5, and dilutions of 0.005M-0.5M.
Abstract: A modified route for synthesizing barium hexaferrite (BaO.6Fe2O3) through ammonium carbonate using metal chlorides is reported. The coprecipitations were studied in the range of pH 7.2–8, Fe/Ba ratio 8.55–11.5, and dilutions of 0.005M–0.5M. The average particle size of these coprecipitates ranged from 20 A to 170 A. Ferritization studies have been carried out between 850° and 1150°C. The optimum specific magnetic moments and coercive fields were in the range of 49–53 emu/gm and 3.45–3.55 K Oe respectively.
4 citations
TL;DR: In this paper, an attempt has been made to replace the use of costly fused alumina grams by dense sintered alumina grog, which was prepared by adding 1% TiO2 as a sintering aid to raw Bayer's alumina followed by wet pot-milling, drying, briquetting (600 kg/cm2).
Abstract: The study aims at developing dense high alumina refractories containing 84–85% alumina with improved thermal shock resistance. The raw materials taken were raw Bayer's alumina, i.e. technical grade alumina and Lapsaburu kyanite lumps. In this work, an attempt has been made to replace the use of costly fused alumina grams by dense sintered alumina grog. Dense sintered alumina grog was prepared by adding 1% TiO2 as a sintering aid to raw Bayer's alumina followed by wet pot-milling, drying, briquetting (600 kg/cm2) and sintering in a high temperature gas fired furnace at 1650°C for 5 hours. Raw kyanite lumps were calcined at 1550°C for a soaking period of 4 hrs and then crushed, ground and graded to required sieve fractions. Cylindrical buttons of 2″ dia × 2″ ht (approx) and quarter size bricks (4½″ × 2″ × 2″) were fabricated in a hydraulic press at a pressure of 1000 kg/cm2 from the thoroughly prepared homogeneous mix of graded dense sintered alumina grog, calcined kyanite grains and 0.5–3.0% additions of M...
4 citations
TL;DR: In this paper, the effect of gypsum additive on specific conductivity during hydration of cement is also described, and suitable explanations for variations in conductivity, and effect of Gypsum on conductivity have been proposed.
Abstract: Variations in specific conductivity during hydration and setting of cements and clinker minerals have been reported. Measurements on the specific conductivity, for 48 hrs at regular intervals, of the suspensions of cement with adequate W/C ratio have shown two peaks in a plot of time vs specific conductivity and only one peak in case of clinker mineral. The effect of gypsum additive on specific conductivity during hydration of cement is also described. Suitable explanations for variations in conductivity, and effect of gypsum on conductivity, during hydration and setting of cements have been proposed.
3 citations
TL;DR: In this paper, the nature of attack of V2O5 melts on polycrystalline alumina and fused silica rods was studied under conditions of forced convection dissolution at several temperatures in the range 800°-1000°C.
Abstract: The nature of attack of V2O5 melts on polycrystalline alumina and fused silica rods was studied under conditions of forced convection dissolution at several temperatures in the range 800°–1000°C. The rate of corrosion as a function of the square root of angular velocity of rotation at various temperatures was found to be linear. This was in agreement with the theoretical model of forced convection dissolution. Using the experimental data, the effective diffusivities were calculated for both silica and alumina. Throughout the temperature range of the present investigation, alumina was found to have greater diffusivity. As the dissolution was diffusion-controlled, it was concluded that silica would act as a better refractory than alumina in vanadium-rich environments.
3 citations
TL;DR: In this article, the modulus spectra of the glasses in the LiF-Li2O-Al(PO3)3 system have been studied over wide ranges of frequency (100 Hz-10M Hz) and temperature (25°-200°C).
Abstract: Electrical and electrochemical characterization of the ionic conductors to be used in advanced electrochemical devices is generally carried out by complex impedance/admittance analysis which separates electrode polarisation effect from the bulk properties of the conductor. The characteristic frequency dispersion in the bulk of the vitreous electrolyte can also be examined by electric modulus which is the inverse of complex permittivity. The modulus spectra of the glasses in the LiF-Li2O-Al(PO3)3 system have been studied over wide ranges of frequency (100 Hz-10M Hz) and temperature (25°–200°C), using three different electrode materials (Ag, C, Li). An interesting feature of these modulus spectra is the appearance of a nearly perfect Debye peak indicative of a single relaxation process. This has been explained in terms of charge carrier density. The dielectric constant and the loss tangent of the glasses have also been calculated. An abrupt rise of dielectric constant at lower frequencies has been explained...
2 citations
TL;DR: In this article, structural differences occurring in vermiculite minerals of different origin are brought out in the presence of heat-treatment and the thermal domains for existence of both phyllosilicate and intermediate phases are correlated to the charge density of the mineral.
Abstract: Structural differences occurring in vermiculite minerals of different origin are brought out in this paper. Peaks obtained in DTA and TGA are attributed to the structural modifications occurring in the minerals due to heat-treatment. The thermal domains for existence of both phyllosilicate and intermediate phases are correlated to the charge density of the mineral. Exfoliation characteristic of the minerals vis-a-vis charge density is also discussed.
2 citations
TL;DR: In this paper, a low-loss ceramics of L-6 or better grade using indigenous wollastonite was developed using a combination of several heavy metal modifiers such as Pb, Ba, etc.
Abstract: Low-loss ceramics of L-6 or better grade have been developed using indigenous wollastonite. The composition consisted mainly of wollastonite, clay and a flux. It was observed that a combination of several heavy metal modifiers such as Pb, Ba, etc gave a better result when incorporated in the flux. The maturing tempeiature of the wollastonite body was much less than that of conventional steatite and other low-loss ceramics. © 1984 Taylor & Francis Group, LLC.
TL;DR: In this paper, a plan for setting up an ideal R&D center based on modern management technique is presented. And functional control and underlying decision making and execution techniques in such work area of a large electro-porcelain industry are discussed.
Abstract: All successful electroceramic industries have a common denominator at the core of their success—a well-organised, effective R&D laboratory. This article re-emphasises this issue and chalks out a plan for setting up an ideal R&D centre based on modern management technique. The article also elaborates functional control and underlying decision making and execution techniques in such work area of a large electro-porcelain industry.
TL;DR: In this paper, the authors correlate various rheological parameters such as Bingham yield stress, thixotropic breakdown at upper plastic limit consistency, cation exchange capacity, liquid limit with specific s...
Abstract: Investigations to correlate various rheological parameters as Bingham yield stress, thixotropic break-down at upper plastic limit consistency, cation exchange capacity, liquid limit with specific s...
TL;DR: In this paper, a critical study has been made on the extraction of elemental copper with silver salt in a silicate glass and a new method for its estimation in copper-ruby silicates glass is described.
Abstract: A critical study has been made on the extraction of elemental copper with silver salt in a silicate glass and a new method for its estimation in copper-ruby silicate glass is described. The method consists of extraction of elemental copper with saturated silver sulphate solution in 0.04 N sulphuric acid and its subsequent estimation by Atomic Absorption Spectrophotometry. The results showed that only about 5-6 of total copper was present as elemental copper in both types of copper glasses melted with or without tin. Opposite trends in the extraction values have been observed in the two types of heat-treated glasses (with or without tin), which was presumably due to the structural rearrangement during heat-treatment. © 1984 Taylor & Francis Group, LLC.
TL;DR: The suitability of these cements in the preparation of castables was also studied by measuring high-temperature strength retaining capacities of the cements using different aggregates as mentioned in this paper.
Abstract: Bauxite is an important raw material for the production of high- alumina cements. Purer grade bauxites are mainly used for industries like aluminium, alum, etc. Use of low grade bauxites increases the titania content of high-alumina cements to an unusual extent.High-alumina cements containing varying amounts of titania were prepared from analytical grade chemicals and the phases were identified by X-ray measurements. It was found that TiO2 had a beneficial role in the hydraulic and other related properties of high-alumina cements up to a certain limit. The suitability of these cements in the preparation of castables was also studied by measuring high-temperature strength retaining capacities of the cements using different aggregates. The maximum allowable limit of titania content may be suggested to be 4 per cent.
TL;DR: In this paper, the authors studied the crystallization of MgO-Al2O3-SiO2 glasses containing small amounts of ZrO2 with or without TiO2 or Cu2O. X-ray diffraction studies revealed the presence of β-quartz and tetragonal zirconia or Cu 2O at the initial stages of crystallization.
Abstract: Crystallization of MgO-Al2O3-SiO2 glasses containing small amounts of ZrO2 with or without TiO2 or Cu2O was studied. In addition to high mechanical strength and indentation hardness the crystallized glasses possessed ultra-high alkali resistance. X-ray diffraction studies revealed the presence of β-quartz and tetragonal zirconia or Cu2O at the initial stages of crystallization, while cordierite, zircon, cristobalite etc appeared at elevated temperatures. DTA curves showed that crystallization was accelerated on addition of TiO2 or Cu2O while scanning electron micrographs also exhibited dense crystallization below 1000°C. Partial substitution of TiO2 by ZrO2 improved the working characteristics of glasses melted for the production of conventional cordierite glass-ceramics; corrosion of refractories was also significantly reduced.
TL;DR: Suitably glazed alumino-silicate glass-ceramic compositions were developed in the laboratory scale as mentioned in this paper, and the materials possessed high mechanical strength and resistance to thermal shock.
Abstract: Suitably glazed alumino-silicate glass-ceramic compositions were developed in the laboratory scale. The materials possessed high mechanical strength and resistance to thermal shock.
TL;DR: In this paper, 14 cationic forms of an alumino-silicate gel were subjected to heat-treatment, and characteristic changes in dehydrations, rehydrations, bulk densities and cation exchange capacities were studied.
Abstract: Fourteen cationic forms of an alumino-silicate gel were subjected to heat-treatment, and characteristic changes in dehydrations, rehydrations, bulk densities and cation exchange capacities were studied. A correlation was established between the hydration energy values of the exchangeable cations and their characteristic changes on heat-treatment.
TL;DR: In this paper, experimental parameters to produce monolithic pure silica and multi-component silicate glasses by controlled hydrolysis of ethyl orthosilicate have been discussed in detail.
Abstract: Experimental parameters to produce monolithic pure silica and multi-component silicate glasses by controlled hydrolysis of ethyl orthosilicate have been discussed in detail. Preliminary results of an attempt to produce Uv transparent pure silica discs are presented. Amount of water used for hydrolysis, acid concentration and concentration of ethyl orthosilicate have been found to be the main parameters which control the process.
TL;DR: Laterite constitutes a mixture of hydrous iron and aluminium oxides and kaolinite along with quartz and has been used for the consolidation of clays as discussed by the authors, but this method is not suitable for laterites.
Abstract: Laterite constitutes a mixture of hydrous iron and aluminium oxides and kaolinite along with quartz. Since the normal firing schedules used for the consolidation of clays are not suitable for laterites, attempts have been made to use a chemical binder for their consolidation. Studies based on thermal analysis and infrared spectroscopy reveal that phosphoric acid could react with kaolinite and hydrous iron oxide and the products formed from the reaction could act as tile binding phase. The increase in compressive strength of the blocks of laterite after reaction with phosphoric acid has been explained on the basis of differential thermal analysis, infrared spectral data and certain mineralogical investigations.
TL;DR: In this paper, the authors attributed the lack of proper assessment of the needs of ceramic engineers to the fact that there is a growing need of personnel with sound ceramic education in order to cope with the modern highly mechanized and diversifial ceramic industry having a high rate of technical obsolescence.
Abstract: The ceramic industry is a core industry in the sense that the performance of many other basic industries depends to a large extent on it. Although the growth of the ceramic industry in India has been fairly satisfactory, manpower development programme for this industry appears to be inadequate, in spite of the fact that during the past twentyfive years the overall growth of technical education in the country has been quite significant. This has been attributed to the lack of proper assessment of the needs of ceramic engineers.There is a growing need of personnel with sound ceramic education in order to cope with the modern highly mechanized and diversifial ceramic industry having a high rate of technical obsolescence. Existing facilities for ceramic education in the country are meagre. It is high time that the requirements of technical manpower for ceramic industry are assessed and the education programme is properly planned and implemented so that like other major engineering disciplines, self-reliance i...
TL;DR: In this article, the effects of a number of inorganic and organic acids (HCl, HNO3, HClO4, CH3COOH, Cl3CCOOH) on the peptization of aluminium monohydroxide derived from aluminium secondary butoxide were examined.
Abstract: The effects of a number of inorganic and organic acids (HCl, HNO3, HClO4, CH3COOH, Cl3CCOOH) on the peptization of aluminium monohydroxide derived from aluminium secondary butoxide were examined. The efficiency of peptization, given inversely by the optical density of the sols, varied in the series HClO4> HNO3> HCl for inorganic acids and CH3COOH > Cl3CCOOH for organic acids. A similar series was also valid for the shrinkage pattern of the sols during sol-gel transformation, pointing towards a proportionality between colloidal particle size and the degree of flocculation. The rate of escape of the volatiles, i.e. gelling time as a function of gel volume, could be expressed by a linear regression equation with a correlation coefficient r = -0.9658, indicating a strong relationship, when gelation under the action of low concentrations of the acid was ignored. © 1984 Taylor & Francis Group, LLC.
TL;DR: In this article, Bauxites from the different profiles in Western India have been studied for the first time with a view to examining their potential as a refractory material, and the results show that the sintering behaviour of these Gibbsite-Boehmite-Halloysite (GBH) assemblages proceeded in two stages with (i) a decomposition stage at 400°-1200°C and (ii) mullite formation stage at 1200°-1600°C.
Abstract: Bauxites from the different profiles in Western India have been studied for the first time with a view to examining their potential as a refractory material. The results show that the sintering behaviour of these Gibbsite—Boehmite—Halloysite (GBH) assemblages proceeded in two stages with (i) a decomposition stage at 400°–1200°C and (ii) mullite formation stage at 1200°–1600°C. Microstructures of the raw materials and sintered pellets were studied to evaluate the possibility of utilizing them in the ceramic industry.
TL;DR: In this paper, a low cost cold face insulation bricks from common clay, which could be manufactured in the rural sector, were used for increasing the porosity of the bricks and the firing was done at 900°, 1000°, 1050° and 1100°C Thermal conductivity values varied between 18 and 72 gm cal/sec/cm2/°Ccm X 10−4 which is similar to that of conventional insulation bricks.
Abstract: Attempts have been made in this work to develop low cost cold face insulation bricks from common clay, which could be manufactured in the rural sector Different combustible materials were used for increasing the porosity of the bricksFiring was done at 900°, 1000°, 1050° and 1100°C Thermal conductivity values varied between 18 and 72 gm cal/sec/cm2/°Ccm X 10−4 which is similar to that of conventional insulation bricks Bulk density varied from 055 to 085 gmcm−3, while apparent porosity varied between 60 and 78% Cold crushing strength was between 4 and 11 kgcm−2 Permanent change after reheating for 24 hrs was almost nil Three compositions satisfied the IS specification 2042 (1972) type 3 of low temperature insulation bricks to be used at a maximum hot face temperature of 850°C These bricks can be used as back up insulation in industrial ceramic kilns and furnaces This type of raw mix-insulation can also be used as monolithic in potters' “puans” and other furnaces
TL;DR: In this paper, the major aspects in the design and construction of a high temperature solar furnace are discussed and various applications of solar furnace as a research facility are described, and an account of different types of concentrators and different solar furnace configurations is presented.
Abstract: The available data on physico-chemical properties of materials at high temperatures are scarce, particularly for solids. This is due to constraints arising from containment or support environment, the effect of heating techniques, and the difficulty in precision control of temperatures. These difficulties could be overcome in a solar furnace to a large extent. An account of different types of concentrators and different solar furnace configurations is presented. The major aspects in the design and construction of a high temperature solar furnace are discussed and various applications of solar furnace as a research facility are described. © 1984 Taylor & Francis Group, LLC.
TL;DR: SEM study together with EDAX analysis on some carbon electrodes have been made before and after use in submerged arc furnace and the results showed that interaction of molten metal with electrode surface, porosity and localized trace elements (like Fe in this case) had marked effect in disintegration of carbon particles leading to mass surface erosion followed by the initiation of cracks as discussed by the authors.
Abstract: SEM study together with EDAX analysis on some carbon electrodes have been made before and after use in submerged arc furnace. The results showed that interaction of molten metal with electrode surface, porosity and localized trace elements (like Fe in this case) had marked effect in disintegration of carbon particles leading to mass surface erosion followed by the initiation of cracks.
TL;DR: The importance of positron annihilation techniques in investigating the defect structure of solids is now well established as discussed by the authors, and the potential of this new and powerful technique in understanding the lattice defect structure in ceramics is highlighted.
Abstract: The importance of positron annihilation techniques in investigating the defect structure of solids is now well established. The distinct advantage of these techniques in such studies arises due to the sensitivity of positrons to changes in the local electron density near the defect. Metals and alloys are the most extensively studied materials by these techniques. In recent years, however, the interest is steadily growing in the ceramic systems. The present paper highlights the potential of this new and powerful technique in understanding the lattice defect structure of ceramics.
TL;DR: In this paper, the authors measured visible light transmission in dispersions of sand particles (67-250 μm) in clear medium and found that optical density was linearly related to dispersion concentration and depth.
Abstract: Measurement of visible light transmission in dispersions of sand particles (67–250 μm) in clear medium has been described. Optical density has been shown to be linearly related to dispersion concentration and depth. Furthermore, for coarser particles, optical density was approximately governed by the total surface area of particles in unit volume. It has been shown that one could estimate, approximately, the concentration of solids in a dispersion and surface area of particles using a calibration procedure based on light transmission data.
TL;DR: In this article, the physical and thermal properties of a low grade kyanite, clays and combustibles were evaluated and the product was found to conform to the standard specifications.
Abstract: Physico-chemical characteristics of a low grade kyanite, clays and combustibles were determined. Volume changes vis-a-vis other properties were studied to ascertain the optimum firing temperature for insulating refractories. Mix compositions and other processing variables were standardised for the production of bricks of standard size. The different physical and thermal properties of the product were evaluated, and were found to conform to the standard specifications.
TL;DR: In this article, the laser cross-sections of a series of Nd3+-containing silicate glasses were estimated using the Landenburg-Fuchtbauer relationship, and the results indicated that the damage threshold is sufficiently high to suggest that this glass may be a viable alternative to CaWO4.
Abstract: δL, the laser cross-section and δF, the cross-section derived from absorption and fluorescence measurements through Landenburg-Fuchtbauer relationship have been estimated for a series of Nd3+—containing silicate glasses. A direct correlation between δL and δF for Nd3+ in silicate glasses could be established. A technique has been developed for producing glasses of good optical quality on a small scale over a wide range of composition. Laser rods were cut from glass made by this technique and their cross-sections measured. The laser cross-section varied from 1 × 10−20 cm2 to 3.2 × 10−20 cm2. The rod did not thermally fracture when operated at a repetition rate of 10 p.p.s. with 30J per pulse input power. The results also indicate that the damage threshold is sufficiently high to suggest that this glass may be a viable alternative to CaWO4 in a laser range finder.