Somnath Sinhamahapatra - Academia.edu (original) (raw)

Papers by Somnath Sinhamahapatra

International Journal of Applied Ceramic Technology, Jan 21, 2014

Alumina-chrome (Al 2 O 3-Cr 2 O 3) refractories with Al 2 O 3 :Cr 2 O 3 molar ratio 1:1 were synt... more Alumina-chrome (Al 2 O 3-Cr 2 O 3) refractories with Al 2 O 3 :Cr 2 O 3 molar ratio 1:1 were synthesized in the temperature range of 1400-1700°C by conventional solid-oxide reaction route. The effect of different aluminas (viz., hydrated and calcined) on the densification, microstructure, and properties of Al 2 O 3-Cr 2 O 3 refractories was investigated without changing the Cr 2 O 3 source. The starting materials were analyzed to determine the chemical composition, mineralogy, density, surface area, and particle size. Sintered materials were characterized in terms of densification, phase assemblage, and mechanical strength at room temperature and at higher temperatures. Microstructural evolution at different sintering temperature was correlated with sintering characteristics. It can be concluded that the Al 2 O 3-Cr 2 O 3 refractories prepared with hydrated alumina as Al 2 O 3 source show better densification and hot mechanical strength than corresponding calcined variety.

Future Landscape of Structural Materials in India, 2022

Transactions of the Indian Ceramic Society

Dehydroxylated kaolin has widespread application in the synthesis of mullite ceramics. In the pre... more Dehydroxylated kaolin has widespread application in the synthesis of mullite ceramics. In the present study, a new source of highly pure kaolin from western part of India was used as a raw material to investigate the dehydroxylation-rehydroxylation behavior utilizing DTA/TGA and FTIR technique. The results showed that kaolin used in this study possesses high degree of crystalinity and retained its structure up to some extent even after dehydroxylation at 700 degrees C with a tendency to rehydrate. The DTA peak at 1000 degrees C supports the high reactivity of dehydroxylated kaolin and the peak is associated with the formation of mullite. The SEM study does not reveal any major microstructural changes after dehydroxylation. However, the XRD pattern of raw clay shown kaolin as major phase which converted to amorphous nature after dehydroxylation and subsequent grinding.

Ceramics International, 2020

Abstract The thermal conductivity of the matrix part of alumina – carbon unshaped refractory has ... more Abstract The thermal conductivity of the matrix part of alumina – carbon unshaped refractory has been estimated to accurately interpret its thermophysical and thermomechanical behavior. The properties of precalcined composite matrix containing either as-received or surface-modified graphite in equal quantity (20.0 wt%) have been investigated at three different temperatures (110,550,900 °C). The thermal compatibility or degradation of both kinds of carbonaceous matrices had been correlated with respective scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) analyses. The monolithic matrices were also subjected to X-ray diffraction (XRD) studies to distinguish between their phase evolution patterns. A synergestic study on an equivalent graphite-free formulation was also carried out. The thermal shock resistance profile of respective castables had been addressed to confirm the superiority of surface-treated graphites. Nanoengineering at graphite surface was conceived by Rietveld analysis of the (004) peak that substantiated the additional influence of calcium aluminate coating on selective clumping and partial exfoliation of graphite sheets.

Ceramics International, 2021

Abstract Magnesium aluminate spinel with an initial MgO: Al2O3 molar ratio of 2:1 was prepared fr... more Abstract Magnesium aluminate spinel with an initial MgO: Al2O3 molar ratio of 2:1 was prepared from its constituent oxides through a solid-state sintering process at temperatures ranging from 1550 to 1700 °C in a normal air atmosphere. The effect of varying amount (0.25–1.0 wt%) of TiO2 and Yb2O3 on densification, phase assemblage, mechanical, thermo-mechanical properties and microstructure of magnesia-rich spinel were investigated under static heating condition. The addition of TiO2 and Yb2O3 favours the densification of magnesia-rich spinel, which is discernible up to 1650 °C. This beneficial effect may be attributed to the development of the secondary phase and formation of solid solution due to the dissolution of the additive ions in the spinel structure. A marginal increase in the average grain size of the samples along with a narrower grain size distribution occurred with the incorporation of both the additives. Both the additives improved the mechanical properties of the magnesia-rich spinel; however, better room temperature flexural strength was achieved with Yb2O3 as compared to TiO2 addition. For the samples sintered at 1550 °C, 1.0 wt% Yb2O3 addition resulted in 30% increase in flexural strength; however, same amount of TiO2 addition increased the strength by 20%. In case of thermal shock resistance, 1.0 wt% TiO2 and 0.25 wt% Yb2O3 addition demonstrated promising result among all the samples.

Ceramics International, 2018

Transactions of the Indian Ceramic Society, 2020

Indian natural magnesite containing silica and lime as main impurities was beneficiated using rev... more Indian natural magnesite containing silica and lime as main impurities was beneficiated using reverse froth flotation technique. Pine oil was used as frother, Flotigam EDA as collector and sodium hexametaphosphate as depressant of carbonate group. Operating parameters were optimized using response surface methodology and a quadratic model equation was formulated for the experiment. The effect of different process parameters was studied using Box-Behnken design. Statistical analysis suggested that the model was significant. Moreover, optimum process conditions were predicted after analyzing the experimental data. The beneficiated sample for which the highest silica in froth was achieved was characterized in terms of X-ray diffraction analysis. Further, quantification of the crystalline phases showed that amount of quartz was reduced from 2.3% in raw sample to 1.8% in processed sample.

Ceramics International, 2019

Role of three rare earth oxides, viz., La 2 O 3 , CeO 2 and Yb 2 O 3 on reaction sintering of mag... more Role of three rare earth oxides, viz., La 2 O 3 , CeO 2 and Yb 2 O 3 on reaction sintering of magnesium aluminate spinel having molar ratio of MgO:Al 2 O 3 =1:2 from its solid oxide precursors was investigated in static and dynamic heating conditions. Effect of these additives (3 wt%) on densification behavior, phase assemblage and microstructure development were studied in the temperatures of 1500 to 1700 °C. Yb 2 O 3 enhanced the sintering of spinel, while La 2 O 3 and CeO 2 negatively impacted the sintering of magnesium aluminate spinel which can be discerned from the shrinkage curve of TMA as well as from static firing regime. This is ascribed to the formation of secondary phases in La 2 O 3 and CeO 2 containing samples which have different crystalline structures to that of spinel. This anisotropy due to different crystallinity hindered the pore shrinkage and pore removal and thereby retarded the densification. Whereas, the cubic structure of the secondary phase formed in Yb 2 O 3 containing sample which is isotropic with the crystalline orientation of the parental spinel phase assisted the densification.

Ceramics International, 2018

Alumina-excess magnesium aluminate spinel finds use in different high temperature applications in... more Alumina-excess magnesium aluminate spinel finds use in different high temperature applications including steel ladles. Alumina-excess spinel was prepared by solid oxide reaction using magnesia (MgO=10 wt%) and calcined alumina (Al 2 O 3 = 90 wt%), in the sintering temperature range of 1500-1700°C. The role of titania on the densification, spinelisation, evolution of microstructure and phase assemblage was investigated in this MgO-Al 2 O 3 system. Titania addition increased the rate of densification 20x compared to undoped composition at 1500°C under dynamic heating condition. However, under static firing, the beneficial effect of titania on densification could only be discerned at lower temperatures. The microstructure of titania doped sintered aluminaexcess spinel compacts contain magnesium aluminium titanate phase in the grain boundary of corundum and spinel grains. The beneficial effect of titania on densification is attributed to magnesium aluminium titanate phase (Mg x Al 2(1-x) Ti (1+x) O 5) development and also by incorporation of Ti 4+ into the spinel structure. ..

International Journal of Applied Ceramic Technology, 2018

Natural magnesite is the primary source for magnesia based refractory materials. India has vast d... more Natural magnesite is the primary source for magnesia based refractory materials. India has vast deposit of magnesite in Salem and Almora region. However due to presence of large amount of impurities which form low melting compounds at elevated temperature, its high temperature application is restricted. Raw magnesite was evaluated in terms of chemical analysis, differential thermal analysis, thermo gravimetric analysis and phase assemblage. 1 to 5 wt % zirconia was added to Indian natural magnesite of Salem region to minimize the low melting phase formation at high temperatures. Samples were sintered in the temperature range of 1550 to 1700 °C. Sintered samples were characterized in terms of densification, mechanical and thermo-mechanical properties, phase assemblage and microstructure. It was found that addition of zirconia reduced the formation of detrimental phases like monticellite and thereby improved the high temperature mechanical properties.

Ceramics International, 2016

The kinetic pathway for magnesia-excess magnesium aluminate spinel (MgAl 2 O 4) formation is dete... more The kinetic pathway for magnesia-excess magnesium aluminate spinel (MgAl 2 O 4) formation is determined from the dilation behaviour of MgO-Al 2 O 3 (34:66 w/w) oxide compacts during reaction sintering under dynamic heating regime at different constant heating rates (β). It is calculated from expansion values at different β, analysed through model-free and model-based kinetic methods to arrive at the most suitable and unambiguous kinetic pathway, where spinelisation is best described (r 2 ¼0.986) with Avrami model with exponent n ¼ 0.65 and activation energy (E a) 409 kJ mol À 1. To validate the kinetic model, an isothermal heat treatment of the oxide compact was done and % spinelisation was determined by Rietveld refinement of the XRD data. The results matched the predicted values very closely and validate our kinetic model. This method can be extended to several industrially important thermally activated solid state reactions which require thermal treatment in order to minimise the energy requirement by optimising the heating protocol.

Ceramics International, 2016

The rationalization of selection of sintering additives for α-alumina was investigated using two ... more The rationalization of selection of sintering additives for α-alumina was investigated using two oxides (MgO and TiO 2) to discern their individual roles. Using both dynamic heating study in a thermomechanical analyzer and static heat treatment, the precise role of each oxide was established. Grain growth trajectory of different doped samples sintered at 1700°C revealed that MgO neither significantly affected densification nor facilitated grain growth upto 1700°C. MgO reacted with alumina to form spinel prior to the densification process. Thus it could not generate further extrinsic defects in corundum lattice during sintering, which usually facilitate densification. In contrast, TiO 2 significantly enhanced the densification and promoted grain growth in α-alumina. At 1700°C, the average grain size of titania doped samples were 7.7x larger than undoped ones and 10x larger than magnesia dopes samples. The sintered grains developed higher aspect ratio when TiO 2 was used which may be ascribed to preferred growth of the 012 and 024 planes of corundum. The nearly perfect junction of grain boundaries meeting at $ 120°indicates absence of liquid phase and that the entire sintering process most probably took place in solid state for both MgO and TiO 2 doped samples.

International Journal of Mineral Processing, 2015

Indian magnesite mineral has substantial amount of impurities like CaO, SiO 2 & Fe 2 O 3. During ... more Indian magnesite mineral has substantial amount of impurities like CaO, SiO 2 & Fe 2 O 3. During sintering at elevated temperature these impurities react to form low melting phases like monticellite (CMS), which can degrade the high temperature properties of magnesite. In the present study, ZrO 2 was added to reduce the formation of low melting phase in order to improve the hot strength. Amount of additive was varied between 2 to 6 wt % with respect to raw magnesite. It was observed that addition of ZrO 2 reduces the formation of low melting CMS at higher temperature and improves the flexural strength at 1200°C. Periclase grain shape also changed from rounded to subrounded in presence of zirconia.

Ceramics International, 2016

Abstract Magnesia rich magnesium aluminate spinel (MgO: Al 2 O 3 =2:1) was developed by reaction ... more Abstract Magnesia rich magnesium aluminate spinel (MgO: Al 2 O 3 =2:1) was developed by reaction sintering of Indian natural magnesite of Salem region as well as from synthetic caustic magnesia with calcined alumina. Dilatometric study of the green compacts was carried out to evaluate the spinelisation and sintering behaviour of both the samples. Green samples were heat treated between 1400 to 1600 °C and characterised in terms of densification behaviour, high temperature flexural strength, microstructure and phase development. Spinel and periclase are the major phases in both the samples, where as forsterite is found only in the sample developed from Indian magnesite due to presence of silica as impurities.

Materials Characterization, 2016

Abstract Densification behavior of (Al1 − xCrx)2O3 (where, x = 0, 0.1, 0.3, 0.5) compacts in the ... more Abstract Densification behavior of (Al1 − xCrx)2O3 (where, x = 0, 0.1, 0.3, 0.5) compacts in the temperature range 1000–1700 °C under reducing condition were studied. Up to 1300 °C, densification behavior followed the normal trend, i.e., bulk density increases with increase in Cr2O3 content. Anomaly in the densification behavior was observed from 1400 °C onwards. Al2O3 samples showed high densification; but the addition of 10 mol% Cr2O3 resulted in a sharp decrease in densification; while further Cr2O3 addition showed a steady rise in densification. XRD studies revealed the solid solution formation starts at 1400 °C. A broad endothermic peak at around 1400 °C in DTA thermogram corresponds to the formation of solid solution which actually absorbs extra heat energy resulting less dense Al2O3–Cr2O3 compacts. The average grain size of sintered Al2O3–Cr2O3 samples increases with increase in Cr2O3 content.

Ceramics International, 2015

Natural Indian magnesite contains large amount of impurities like CaO, SiO 2 and Fe 2 O 3. On hea... more Natural Indian magnesite contains large amount of impurities like CaO, SiO 2 and Fe 2 O 3. On heat treatment, these impurities chemically react and form low melting phases like monticellite (CMS), merwinite (C 3 MS 2) and vitreous phases, which degrade the refractory properties of magnesite like hot modulus of rupture, corrosion resistance etc. In the present investigation, TiO 2 was used to reduce the formation of low melting phases. Compacted green pellets and bars of magnesite containing 0À 5 wt% TiO 2 were sintered in the temperature range of 1500À1600 1C with 2 h soaking at peak temperature. It was observed that TiO 2 slightly increased the apparent porosity and decreased the bulk density by reducing the formation of low melting phases. High temperature flexural strength increases with TiO 2 content upto 3 wt% followed by slight decrease in strength after further increase in the amount of additive.

Transactions of the Indian Ceramic Society, 2014

ABSTRACT The inorganic phases belonging to the binary alumina-silica system exhibit a plethora of... more ABSTRACT The inorganic phases belonging to the binary alumina-silica system exhibit a plethora of excellent high temperature properties that make them useful for refractory applications. Synthesized from abundant aluminosilicate minerals, these refractories are ubiquitous in high temperature industrial applications. The refractories of alumina-silica system can be engineered to generate a range of high temperature properties by varying the Al2O3/SiO2 ratio, presence of other oxides and texture. This versatility is unique to this system and is reflected in widely varied fields of applications of these refractories. Composed predominantly of mullite and corundum phases, the non crystalline phases also play important role in determining the property and end use of these refractories. This review covers different theoretical and practical aspects of refractories of aluminosilicate system spanning 30-100% alumina. Important role of microstructure in aluminosilicate refractory has been discussed in light of phase diagram, raw materials and thermo-chemical reactions. The applications of these refractories in different areas have been discussed in detail with structure-property correlation.

International Journal of Applied Ceramic Technology, Jan 21, 2014

Alumina-chrome (Al 2 O 3-Cr 2 O 3) refractories with Al 2 O 3 :Cr 2 O 3 molar ratio 1:1 were synt... more Alumina-chrome (Al 2 O 3-Cr 2 O 3) refractories with Al 2 O 3 :Cr 2 O 3 molar ratio 1:1 were synthesized in the temperature range of 1400-1700°C by conventional solid-oxide reaction route. The effect of different aluminas (viz., hydrated and calcined) on the densification, microstructure, and properties of Al 2 O 3-Cr 2 O 3 refractories was investigated without changing the Cr 2 O 3 source. The starting materials were analyzed to determine the chemical composition, mineralogy, density, surface area, and particle size. Sintered materials were characterized in terms of densification, phase assemblage, and mechanical strength at room temperature and at higher temperatures. Microstructural evolution at different sintering temperature was correlated with sintering characteristics. It can be concluded that the Al 2 O 3-Cr 2 O 3 refractories prepared with hydrated alumina as Al 2 O 3 source show better densification and hot mechanical strength than corresponding calcined variety.

Future Landscape of Structural Materials in India, 2022

Transactions of the Indian Ceramic Society

Dehydroxylated kaolin has widespread application in the synthesis of mullite ceramics. In the pre... more Dehydroxylated kaolin has widespread application in the synthesis of mullite ceramics. In the present study, a new source of highly pure kaolin from western part of India was used as a raw material to investigate the dehydroxylation-rehydroxylation behavior utilizing DTA/TGA and FTIR technique. The results showed that kaolin used in this study possesses high degree of crystalinity and retained its structure up to some extent even after dehydroxylation at 700 degrees C with a tendency to rehydrate. The DTA peak at 1000 degrees C supports the high reactivity of dehydroxylated kaolin and the peak is associated with the formation of mullite. The SEM study does not reveal any major microstructural changes after dehydroxylation. However, the XRD pattern of raw clay shown kaolin as major phase which converted to amorphous nature after dehydroxylation and subsequent grinding.

Ceramics International, 2020

Abstract The thermal conductivity of the matrix part of alumina – carbon unshaped refractory has ... more Abstract The thermal conductivity of the matrix part of alumina – carbon unshaped refractory has been estimated to accurately interpret its thermophysical and thermomechanical behavior. The properties of precalcined composite matrix containing either as-received or surface-modified graphite in equal quantity (20.0 wt%) have been investigated at three different temperatures (110,550,900 °C). The thermal compatibility or degradation of both kinds of carbonaceous matrices had been correlated with respective scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) analyses. The monolithic matrices were also subjected to X-ray diffraction (XRD) studies to distinguish between their phase evolution patterns. A synergestic study on an equivalent graphite-free formulation was also carried out. The thermal shock resistance profile of respective castables had been addressed to confirm the superiority of surface-treated graphites. Nanoengineering at graphite surface was conceived by Rietveld analysis of the (004) peak that substantiated the additional influence of calcium aluminate coating on selective clumping and partial exfoliation of graphite sheets.

Ceramics International, 2021

Abstract Magnesium aluminate spinel with an initial MgO: Al2O3 molar ratio of 2:1 was prepared fr... more Abstract Magnesium aluminate spinel with an initial MgO: Al2O3 molar ratio of 2:1 was prepared from its constituent oxides through a solid-state sintering process at temperatures ranging from 1550 to 1700 °C in a normal air atmosphere. The effect of varying amount (0.25–1.0 wt%) of TiO2 and Yb2O3 on densification, phase assemblage, mechanical, thermo-mechanical properties and microstructure of magnesia-rich spinel were investigated under static heating condition. The addition of TiO2 and Yb2O3 favours the densification of magnesia-rich spinel, which is discernible up to 1650 °C. This beneficial effect may be attributed to the development of the secondary phase and formation of solid solution due to the dissolution of the additive ions in the spinel structure. A marginal increase in the average grain size of the samples along with a narrower grain size distribution occurred with the incorporation of both the additives. Both the additives improved the mechanical properties of the magnesia-rich spinel; however, better room temperature flexural strength was achieved with Yb2O3 as compared to TiO2 addition. For the samples sintered at 1550 °C, 1.0 wt% Yb2O3 addition resulted in 30% increase in flexural strength; however, same amount of TiO2 addition increased the strength by 20%. In case of thermal shock resistance, 1.0 wt% TiO2 and 0.25 wt% Yb2O3 addition demonstrated promising result among all the samples.

Ceramics International, 2018

Transactions of the Indian Ceramic Society, 2020

Indian natural magnesite containing silica and lime as main impurities was beneficiated using rev... more Indian natural magnesite containing silica and lime as main impurities was beneficiated using reverse froth flotation technique. Pine oil was used as frother, Flotigam EDA as collector and sodium hexametaphosphate as depressant of carbonate group. Operating parameters were optimized using response surface methodology and a quadratic model equation was formulated for the experiment. The effect of different process parameters was studied using Box-Behnken design. Statistical analysis suggested that the model was significant. Moreover, optimum process conditions were predicted after analyzing the experimental data. The beneficiated sample for which the highest silica in froth was achieved was characterized in terms of X-ray diffraction analysis. Further, quantification of the crystalline phases showed that amount of quartz was reduced from 2.3% in raw sample to 1.8% in processed sample.

Ceramics International, 2019

Role of three rare earth oxides, viz., La 2 O 3 , CeO 2 and Yb 2 O 3 on reaction sintering of mag... more Role of three rare earth oxides, viz., La 2 O 3 , CeO 2 and Yb 2 O 3 on reaction sintering of magnesium aluminate spinel having molar ratio of MgO:Al 2 O 3 =1:2 from its solid oxide precursors was investigated in static and dynamic heating conditions. Effect of these additives (3 wt%) on densification behavior, phase assemblage and microstructure development were studied in the temperatures of 1500 to 1700 °C. Yb 2 O 3 enhanced the sintering of spinel, while La 2 O 3 and CeO 2 negatively impacted the sintering of magnesium aluminate spinel which can be discerned from the shrinkage curve of TMA as well as from static firing regime. This is ascribed to the formation of secondary phases in La 2 O 3 and CeO 2 containing samples which have different crystalline structures to that of spinel. This anisotropy due to different crystallinity hindered the pore shrinkage and pore removal and thereby retarded the densification. Whereas, the cubic structure of the secondary phase formed in Yb 2 O 3 containing sample which is isotropic with the crystalline orientation of the parental spinel phase assisted the densification.

Ceramics International, 2018

Alumina-excess magnesium aluminate spinel finds use in different high temperature applications in... more Alumina-excess magnesium aluminate spinel finds use in different high temperature applications including steel ladles. Alumina-excess spinel was prepared by solid oxide reaction using magnesia (MgO=10 wt%) and calcined alumina (Al 2 O 3 = 90 wt%), in the sintering temperature range of 1500-1700°C. The role of titania on the densification, spinelisation, evolution of microstructure and phase assemblage was investigated in this MgO-Al 2 O 3 system. Titania addition increased the rate of densification 20x compared to undoped composition at 1500°C under dynamic heating condition. However, under static firing, the beneficial effect of titania on densification could only be discerned at lower temperatures. The microstructure of titania doped sintered aluminaexcess spinel compacts contain magnesium aluminium titanate phase in the grain boundary of corundum and spinel grains. The beneficial effect of titania on densification is attributed to magnesium aluminium titanate phase (Mg x Al 2(1-x) Ti (1+x) O 5) development and also by incorporation of Ti 4+ into the spinel structure. ..

International Journal of Applied Ceramic Technology, 2018

Natural magnesite is the primary source for magnesia based refractory materials. India has vast d... more Natural magnesite is the primary source for magnesia based refractory materials. India has vast deposit of magnesite in Salem and Almora region. However due to presence of large amount of impurities which form low melting compounds at elevated temperature, its high temperature application is restricted. Raw magnesite was evaluated in terms of chemical analysis, differential thermal analysis, thermo gravimetric analysis and phase assemblage. 1 to 5 wt % zirconia was added to Indian natural magnesite of Salem region to minimize the low melting phase formation at high temperatures. Samples were sintered in the temperature range of 1550 to 1700 °C. Sintered samples were characterized in terms of densification, mechanical and thermo-mechanical properties, phase assemblage and microstructure. It was found that addition of zirconia reduced the formation of detrimental phases like monticellite and thereby improved the high temperature mechanical properties.

Ceramics International, 2016

The kinetic pathway for magnesia-excess magnesium aluminate spinel (MgAl 2 O 4) formation is dete... more The kinetic pathway for magnesia-excess magnesium aluminate spinel (MgAl 2 O 4) formation is determined from the dilation behaviour of MgO-Al 2 O 3 (34:66 w/w) oxide compacts during reaction sintering under dynamic heating regime at different constant heating rates (β). It is calculated from expansion values at different β, analysed through model-free and model-based kinetic methods to arrive at the most suitable and unambiguous kinetic pathway, where spinelisation is best described (r 2 ¼0.986) with Avrami model with exponent n ¼ 0.65 and activation energy (E a) 409 kJ mol À 1. To validate the kinetic model, an isothermal heat treatment of the oxide compact was done and % spinelisation was determined by Rietveld refinement of the XRD data. The results matched the predicted values very closely and validate our kinetic model. This method can be extended to several industrially important thermally activated solid state reactions which require thermal treatment in order to minimise the energy requirement by optimising the heating protocol.

Ceramics International, 2016

The rationalization of selection of sintering additives for α-alumina was investigated using two ... more The rationalization of selection of sintering additives for α-alumina was investigated using two oxides (MgO and TiO 2) to discern their individual roles. Using both dynamic heating study in a thermomechanical analyzer and static heat treatment, the precise role of each oxide was established. Grain growth trajectory of different doped samples sintered at 1700°C revealed that MgO neither significantly affected densification nor facilitated grain growth upto 1700°C. MgO reacted with alumina to form spinel prior to the densification process. Thus it could not generate further extrinsic defects in corundum lattice during sintering, which usually facilitate densification. In contrast, TiO 2 significantly enhanced the densification and promoted grain growth in α-alumina. At 1700°C, the average grain size of titania doped samples were 7.7x larger than undoped ones and 10x larger than magnesia dopes samples. The sintered grains developed higher aspect ratio when TiO 2 was used which may be ascribed to preferred growth of the 012 and 024 planes of corundum. The nearly perfect junction of grain boundaries meeting at $ 120°indicates absence of liquid phase and that the entire sintering process most probably took place in solid state for both MgO and TiO 2 doped samples.

International Journal of Mineral Processing, 2015

Indian magnesite mineral has substantial amount of impurities like CaO, SiO 2 & Fe 2 O 3. During ... more Indian magnesite mineral has substantial amount of impurities like CaO, SiO 2 & Fe 2 O 3. During sintering at elevated temperature these impurities react to form low melting phases like monticellite (CMS), which can degrade the high temperature properties of magnesite. In the present study, ZrO 2 was added to reduce the formation of low melting phase in order to improve the hot strength. Amount of additive was varied between 2 to 6 wt % with respect to raw magnesite. It was observed that addition of ZrO 2 reduces the formation of low melting CMS at higher temperature and improves the flexural strength at 1200°C. Periclase grain shape also changed from rounded to subrounded in presence of zirconia.

Ceramics International, 2016

Abstract Magnesia rich magnesium aluminate spinel (MgO: Al 2 O 3 =2:1) was developed by reaction ... more Abstract Magnesia rich magnesium aluminate spinel (MgO: Al 2 O 3 =2:1) was developed by reaction sintering of Indian natural magnesite of Salem region as well as from synthetic caustic magnesia with calcined alumina. Dilatometric study of the green compacts was carried out to evaluate the spinelisation and sintering behaviour of both the samples. Green samples were heat treated between 1400 to 1600 °C and characterised in terms of densification behaviour, high temperature flexural strength, microstructure and phase development. Spinel and periclase are the major phases in both the samples, where as forsterite is found only in the sample developed from Indian magnesite due to presence of silica as impurities.

Materials Characterization, 2016

Abstract Densification behavior of (Al1 − xCrx)2O3 (where, x = 0, 0.1, 0.3, 0.5) compacts in the ... more Abstract Densification behavior of (Al1 − xCrx)2O3 (where, x = 0, 0.1, 0.3, 0.5) compacts in the temperature range 1000–1700 °C under reducing condition were studied. Up to 1300 °C, densification behavior followed the normal trend, i.e., bulk density increases with increase in Cr2O3 content. Anomaly in the densification behavior was observed from 1400 °C onwards. Al2O3 samples showed high densification; but the addition of 10 mol% Cr2O3 resulted in a sharp decrease in densification; while further Cr2O3 addition showed a steady rise in densification. XRD studies revealed the solid solution formation starts at 1400 °C. A broad endothermic peak at around 1400 °C in DTA thermogram corresponds to the formation of solid solution which actually absorbs extra heat energy resulting less dense Al2O3–Cr2O3 compacts. The average grain size of sintered Al2O3–Cr2O3 samples increases with increase in Cr2O3 content.

Ceramics International, 2015

Natural Indian magnesite contains large amount of impurities like CaO, SiO 2 and Fe 2 O 3. On hea... more Natural Indian magnesite contains large amount of impurities like CaO, SiO 2 and Fe 2 O 3. On heat treatment, these impurities chemically react and form low melting phases like monticellite (CMS), merwinite (C 3 MS 2) and vitreous phases, which degrade the refractory properties of magnesite like hot modulus of rupture, corrosion resistance etc. In the present investigation, TiO 2 was used to reduce the formation of low melting phases. Compacted green pellets and bars of magnesite containing 0À 5 wt% TiO 2 were sintered in the temperature range of 1500À1600 1C with 2 h soaking at peak temperature. It was observed that TiO 2 slightly increased the apparent porosity and decreased the bulk density by reducing the formation of low melting phases. High temperature flexural strength increases with TiO 2 content upto 3 wt% followed by slight decrease in strength after further increase in the amount of additive.

Transactions of the Indian Ceramic Society, 2014

ABSTRACT The inorganic phases belonging to the binary alumina-silica system exhibit a plethora of... more ABSTRACT The inorganic phases belonging to the binary alumina-silica system exhibit a plethora of excellent high temperature properties that make them useful for refractory applications. Synthesized from abundant aluminosilicate minerals, these refractories are ubiquitous in high temperature industrial applications. The refractories of alumina-silica system can be engineered to generate a range of high temperature properties by varying the Al2O3/SiO2 ratio, presence of other oxides and texture. This versatility is unique to this system and is reflected in widely varied fields of applications of these refractories. Composed predominantly of mullite and corundum phases, the non crystalline phases also play important role in determining the property and end use of these refractories. This review covers different theoretical and practical aspects of refractories of aluminosilicate system spanning 30-100% alumina. Important role of microstructure in aluminosilicate refractory has been discussed in light of phase diagram, raw materials and thermo-chemical reactions. The applications of these refractories in different areas have been discussed in detail with structure-property correlation.