Sintering behaviour and hydration resistance of reactive dolomite

Sintering of raw dolomite and hydroxides derived from dolomite was carried out in the temperature range 1350-1650 degrees C. The hydroxide derived from dolomite was developed through pre-calcination of dolomite followed by its hydration. For hydroxide development, after precalcination one sample was air-quenched and the other powder was furnace cooled before hydration. The air quenched samples showed better densification than that of the furnace cooling process at the same temperature. Fe2O3 addition enhances sintering by liquid formation at higher temperature. The grain size of doloma with Fe2O3 addition is bigger than that without additive. Hydration resistance was related to densification and grain size of sintered dolomite. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved

Synthesis and mechanical properties of mullite from beach sand sillimanite: Effect of TiO2

Reaction sintering of beach sand sillimanite and calcined alumina is an innovative as well as cost effective method of mullite formation. In the present investigation, beach sand sillimanite and calcined alumina in microfine state were used as starting materials to develop high alumina aggregates for refractories applications using titania additive (0-6 wt%). The raw, materials and additive (TiO2) were mixed in definite proportion and sintered in compacted form at 1400-1550 degrees C with 2 h soaking. It was determined that, alumina/silica ratio of the batch controls densification, flexural strength and microstructural development of the aggregates. Aggregates with almost zero porosity were developed at a sintering temperature of 1500 degrees C with the help of titania additive. Gradual addition of TiO2 up to 4 wt% promotes the densification process, however, TiO2 affects the high temperature-flexural strength of the aggregates. Aggregates developed from sillimanite sand at 1500 degrees C indicates that the mullites formed are not ideal 3:2 type, but are 1:1 type. Mullite formed in the silica rich composition is long and elongated in nature. At the densification temperature of 1500 degrees C up to 3.06 wt% TiO2 enters into the mullite structure as solid solution. (C) 1998 Elsevier Science Limited. All rights reserved

Synthesis and mechanical properties of mullite developed from beach sand sillimanite: effect of Fe2O3

Mullite aggregate was developed from sillimanite beach sand and calcined alumina by the reaction sintering route using 1–4 wt% Fe2O3, as additive. Effect of Fe2O3, on the densification behaviour, microstructure and thermomechanical properties of the aggregate was discussed. It was found that Fe2O3 favours densification process by liquid phase formation, thereby deteriorating the thermomechanical properties particularly at higher sintering temperature. Mullite formed without Fe2O3 additive at 1600°C was mostly equiaxed in nature whereas it was needle shaped with few occasional equiaxed mullite grains within the matrix when formed in presence of Fe2O3 at 1500°C. Up to 4.08 wt% Fe2O3 enters into the mullite structure by solid solution formation at 1500°C

Effect of chemical composition on sintering and properties of Al2O3-SiO2 system derived from sillimanite beach sand

Reaction sintering of beach sand sillimanite and alumina is an innovative as well as inexpensive method of mullite formation. Beach sand sillimanite, a by-product generated during the separation of rare earth compounds, and calcined alumina were used as starting materials and were mixed in appropriate proportion and sintered in compacted form at 1500-1575 degrees C. The study reveals that the use of submicron size powder enhances the sintering process. In this investigation, effect of chemical composition on sintering and mechanical/thermomechanical properties has been studied. It was found that the densification process is dependent on the Al2O3/SiO2 ratio. Silica rich composition achieves highest density at 1525 degrees C whereas the alumina rich composition requires 1550 degrees C. Flexural strength measured at room temperature and at 1200 degrees C initially de-creases with alumina content, with a minima at 71-74% Al2O3 and then increases again. Microstructure of the sintered is also dependent on the Al2O3/SiO2 ratio of the batch. Mullite made from silica rich composition is needle shape in nature whereas in alumina rich composition they are non-acicular in nature. (C) 1998 Elsevier Science Limited and Techna S.r.l. All rights reserved

Spinelisation and properties of Al(2)O(3)-MgAl(2)O(4)-C refractory: Effect of MgO and Al(2)O(3) reactants

The effect of particle size of MgO and Al(2)O(3) on the spinel formation associated with permanent linear change on reheating (PLCR) and microstructure of Al(2)O(3)-MgAl(2)O(4)-C refractory is investigated as a function of heating cycle at 1600 degrees C with 2 h holding at each cycle. It was found that rate of spinet formation and associated volume expansion is very much dependent on the reactivity and particle size of the reactant. When the reactants are very fine and reactive there is considerable amount of spinet formation, whereas coarser reactants with lower reactivity show negligible formation of spinel phase and associated expansion. Magnesia and alumina with moderate reactivity develops optimum PLCR of the refractory. It continuously increases with the number of heating cycles. The SEM photomicrographs show that in Al(2)O(3)-MgAl(2)O(4)-C refractory the spinel phase is formed in between the calcined bauxite grain and the EDX analysis indicates that the spinel phase formed is stoichiometric in nature. (C) 2009 Elsevier Ltd and Techna Group S.r.l. All rights reserved

Sintering of beach sand sillimanite: Effect of ZrO2

Sintering, microstructure and properties of a beach sand sillimanite have been investigated. The effect of ZrO2 on the densification behaviour and properties of the aggregate was studied. It was found that ZrO2 addition slightly reduces the densification of the beach sand sillimanite. Thermo-mechanical properties of the aggregate at 1200 degrees C also deteriorates to a little extent, particularly at higher percentage of ZrO2. Scanning electron photomicrographs show that ZrO2 occupies both the intergranular and intergranular position of the mullite matrix. Mullite formed at 1600 degrees C is elongated in nature, which suggests densification occurs through liquid phase sintering

Synthesis and densification of lutetium pyrosilicate from lutetia and silica

Cerium-doped lutetium pyrosilicate (Lu2Si2O7:Ce) powder was synthesized by solid state reaction of Lu2O3 and SiO2. Stoichiometric mixtures of the starting materials were heat treated at various different temperatures and their phase contents were measured by XRD technique. It was found that the first step in the formation of Lu2Si2O7 (LPS) is the appearance of Lu2SiO5 (LSO). This takes place at 1100 8C, fully 300 8C below the first appearance of LPS. Between 1400 and 1500 8C both LSO and LPS coexist in the calcined batch, but by 1550 8C all LSO is completely converted to LPS. LPS formation temperature does not have appreciable effect on the density of the hot pressed samples. Hot pressed samples obtained from powder synthesized at 1650 8C are nearly transparent, although the particle size of the starting powder is higher than that of the powder formed at lower temperatures

Kinetics of non-isothermal and isothermal decomposition of limestone

The kinetics of decomposition of limestone was studied using both non-isothermal and isothermal methods. The mechanism and kinetics of thermal decomposition were studied using Arrhenius equation applied to solid state reactions. It was found that in both non-isothermal and isothermal methods limestone seemed to be decomposed via a zero order reaction mechanism. The energy of activation for the non-isothermal and isothermal decompositions of limestone was 157.79 and 181.43 kJ.mol–1 respectively. Similarly, lnA values for non-isothermal and isothermal decomposition were found to be 14.2 and 13.2(s–1) respectively

Reaction sintering of different spinel compositions in the presence of Y2O3

Reaction sintering of spinels (MgO-Al2O3 molar ratio 1:1 and 2:1) was done in the temperature range of 1550-1650 degreesC using sintered sea water magnesia and commercial alumina as the starting materials and Y2O3 as additive up to 4 wt.%. An attrition mill was used for the reduction of particle size. Dilatometric study was done to evaluate the effect of additive on reaction and sintering. Sintered products were characterized in teens of densification, phase analysis, hot strength, microstructure and energy-dispersive X-ray analysis (EDAX) studies. Y2O3 was found to be beneficial for both the compositions. (C) 2004 Elsevier B.V. All rights reserved