Swapan Kumar Das

Differences in densification behaviour of K- and Na-feldspar-containing porcelain bodies

Abstract Porcelain bodies fabricated from triaxial mixtures of clay, quartz and feldspar with different amounts of Na 2 O and K 2 O were investigated to study their densification behaviour on thermal treatment at which the bodies achieve full vitrification. The high temperature dilatometric study has shown a distinct behaviour in their densification rate. The degree of vitrification of the densified samples and samples separately heated at different temperatures was determined by measuring the shrinkage, bulk density (BD), percent water absorption (%WA) and flexural strength. It was found that Na-rich feldspar containing body composition achieve full vitrification at lower temperature compared to K-rich feldspar containing composition with improved flexural strength. Differential thermal analysis–thermogravimetric analysis (DTA–TGA) confirms similar reaction steps for both the compositions up to 1000xa0°C, beyond which feldspar forms eutectic melt and starts reacting. As the purity of raw materials has a strong influence on the colour of the fired bodies, the bodies were also subjected to colour measurement and their differences in whiteness also compared, and is discussed in this paper. The scientific and technological importance of such vitrified porcelain products has also been touched upon, highlighting their industrial application.

Vanadium doped tin dioxide as a novel sulfur dioxide sensor

Considering the short-term exposure limit of SO2 to be 5 ppm, we first time report that semiconductor sensors based on vanadium doped SnO2 can be used for SO2 leak detection because of their good sensitivity towards SO2 at concentrations down to 5 ppm. Such sensors are quite selective in presence of other gases like carbon monoxide, methane and butane. The high sensitivity of vanadium doped tin dioxide towards SO2 may be understood by considering the oxidation of sulfur dioxide to sulfur trioxide on SnO2 surface through redox cycles of vanadium-sulfur-oxygen adsorbed species.

Effect of addition of pond ash and fly ash on properties of ash-clay burnt bricks

Two industrial solid waste products generated by Indian coal-fired power plants, namely pond ash and fly ash, were used in combination with local clay to develop building bricks. The clay were mixed with the two different ashes in the range 10 to 90 wt.%, hydraulically pressed and fired at 1000°C. The fired products were characterized for various quality properties required for building bricks. The properties of the optimal compositions were compared with conventional red clay bricks including the developed microstructures and the comparative study generally showed that te ash-clay bricks were of superior quality to the conventional products.

Thermal shock behaviour of high alumina aggregates derived from sillimanite beach sand with and without Fe2O3 doping

Abstract In this investigation, three types of high alumina aggregates namely sillimanite, mullite and alumina rich aggregates were developed from sillimanite beach sand and calcined Al2O3 by reaction sintering route. The various phases present in the sintered compacts were identified by X-ray diffraction study in conjunction with infrared study. Thermal shock behaviour of the aggregates with and without Fe2O3 doping were measured by the room temperature flexural strength retention on ambient air quenching from 1000°C against the number of cycles. The results obtained are presented and discussed in this paper. It was found that all Fe2O3 containing samples show a strength enhancement on quenching by means of tempering. Attempts have been made to correlate this parameter with the microstructure and phase assembly of the product. ©

Evolution of microstructure in flyash-containing porcelain body on heating at different temperatures

Abstract15 wt% flyash (a calcined byproduct of thermal power plant) was incorporated in a normal triaxial kaolin-quartz-feldspar system by replacing equivalent amount of quartz. The differences in microstructural evolution on heating the compact mass of both normal and flyash-containing porcelain at different temperatures (1150–1300°C) were examined using scanning electron microscopy (SEM) operating in secondary electron image (SEI) mode. Microstructure of normal porcelain did not show the presence of mullite and quartz grains at 1200°C and the viscosity of silica-rich glass restricted the growth of mullite crystals at 1250°C. Flyash porcelain, on the other hand, shows the presence of primary mullite aggregates in the clay relict and a significant growth of mullite crystals in a low viscosity glassy matrix at 1200°C itself. At 1300°C, both the bodies show a larger region of more elongated (> 1 μm) secondary mullite along with clusters of smaller sized primary mullite (< 1 μm). Small primary mullite crystals in the clay relict can be distinguished from elongated secondary mullite crystals in the feldspar relict in their size. Primary mullite aggregates remain stable also at higher temperatures. XRD studies were carried out for quantitative estimation of quartz, mullite and glass, which supported the SEM observations. An attempt was also made to correlate their mechanical strength with the constituent phases.

Paper pulp waste - A new source of raw material for the synthesis of a porous ceramic composite

A synthetic porous ceramic composite material consisting of the mullite, cordierite and cristobalite phases is produced from a mixture of paper pulp waste and clay by reaction sintering at 1400°C. Physicomechanical properties such as bulk density, porosity, cold crushing strength and cold modulus of rupture have been studied. The presence of mullite, cordierite, cristobalite and quartz as major phases and montellecite, tatanite, forsterite and anorthite as minor phases have been confirmed by X-ray diffraction pattern. SEM studies revealed the presence of well developed needle shaped mullite and quartz crystals. The paper also discusses the possible uses of this type of porous composite material.

Thermo-mechanical behaviour of low cement castables derived from mullite aggregates synthesised from beach sand sillimanite

Mullite aggregates were synthesised from beach sand sillimanite, a by-product generated during rare earth extraction, by reaction sintering with calcined alumina. The aggregates were characterised in terms of chemical composition, mineral phases, microstructure and important thermo-mechanical properties critical for refractory applications. To evaluate its suitability in castable refractories, low cement castables were prepared using the aggregates with commercial high alumina cement. The physical and thermo-mechanical properties such as bulk density, apparent porosity, cold crushing strength, hot modulus of rupture and compressive creep was studied in relation to temperature. The castables exhibited good modulus of rupture and excellent creep resistance at 1400 °C. Attempts were made to correlate these properties with corresponding microstructure and phases.

Effect of titania on fired characteristics of triaxial porcelain

Titania was progressively added in the range 3–9 wt% into a triaxial porcelain body consisting of clay, quartz and feldspar. The composed bodies were heated at five different temperatures in the range 1200-1400°C and their fired properties as well as phases evolved were studied. The results revealed that beyond 1300°C, formation of more liquid phases caused bloating in samples which led to generation of pores. This effect is more pronounced in TiO2 containing samples. In the present system, 1300°C appeared to be the optimum temperature at which porosity was almost negligible and strength was maximum (45 MPa), particularly in presence of TiO2. From the results of XRD studies, it was revealed that quartz content primarily decreased with increase in TiO2 content due to excess glass formation and its subsequent dissolution. Mullite content increased with increase in TiO2 content. No significant effect was observed beyond 6 wt% addition. Microstructure primarily showed the presence of quartz grain and cluster of smaller sized primary mullite crystals in both the samples without and with TiO2. Very few secondary mullite crystals were also observed. SEM picture of sample containing 9 wt% TiO2 showed some grain boundary crack due to cooling stress generated in the glassy phase. The drastic reduction of residual strength after 8 cycles of heating at 800°C and cooling particularly in TiO2 containing samples suggests controlled heat treatment of the vitrified samples necessary to promote secondary crystallization process for the enhancement of strength. Attempts have also been made to correlate the constitutional parameters with the properties.

DTA study of kinetics of transformation of silica gel to cristobalite

The activation energy for the transformation of silica gel to cristobalite, a partial reaction of first order, was determined from a single DTA curve by the methods available in the literature. The values obtained were not in agreement with those obtained by the isothermal method. This suggested that the methods were not applicable to reactions which are partial. A modified equation was derived which could be utilized for the determination of the activation energy of first-order reactions from a single DTA curve, if the fraction transformed during the reaction was known.RésuméOn a déterminé à laide dune seule courbe ATD lénergie dactivation de la transformation du gel de silice en cristobalite, réaction partiellement du premier ordre, en utilisant les méthodes décrites dans la littérature. Les valeurs obtenues ne sont pas en accord avec celles obtenues par la méthode isotherme. On a déduit que les méthodes utilisées ne sont pas valables dans le cas des réactions partielles. On établit une équation modifiée qui permet de déterminer lénergie dactivation de réactions du Ier ordre à partir dune seule courbe ATD si les fractions transformées pendant la réaction sont connues.ZusammenfassungDie Aktivierungsenergie der Umwandlung von Kieselgel in Cristobalit, einer Teilreaktion erster Ordnung, wurde aus einer einzigen DTA-Kurve unter Anwendung einer in der Literatur beschriebenen Methode bestimmt. Die erhaltenen Werte standen mit den durch isotherme Methoden ermittelten nicht in Übereinstimmung. Daraus wurde gefolgert, daß die Methoden bei Teilreaktionen nicht einzusetzen sind. Eine modifizierte Gleichung wurde abgeleitet, die sich zur Bestimmung der Aktivierungsenergie von Reaktionen erster Ordnung aus einer einzelnen DTA-Kurve eignet, wenn der während der Reaktion umgewandelte Anteil bekannt ist.РезюмеЭнергия активации пр евращения силикагел я в кристобалит, частная реакция первого порядка, была определена из единст венной кривой ДТА, используя методы, известные в литерату ре. Полученные значен ия не согласуются с данным и, полученными изотопическим метод ом. Это доказывает, что эти методы не применимы к реакци ям, которые являются час тными. Было выведено модифицированное ур авнение, которое может быть использов ано для определения э нергии активации реакций пе рвого порядка из одной кривой ДТА, если известна фракция пре вращаемая во время реакции.

Effect of silica sol of different routes on the properties of low cement castables

Silica sols synthesized through different routes viz. inorganic, organic and ion-exchange routes, have been incorporated in the low cement alumina castable composition in various proportions and cast samples in the form of 2 inch cube briquettes were prepared. The cast briquettes after curing were subjected to heat treatment at various temperatures. The effect of different sources of such sols on the important physico-mechanical properties of the castables such as bulk density, apparent porosity, compressive strength, volume shrinkage and residual strength after spalling have been studied. Some of the selected samples were also subjected to microstructural evaluation. It is observed that silica sol synthesized through cation exchange routes has significant beneficial role on the properties of castable with 3% addition.