Sankar Ghatak

Development of ceramic tiles from common clay and blast furnace slag

Abstract With an objective of making ceramic tile, granulated blast furnace slag (GBFS) and common clay were mixed whereby calcia:silica ratio (w/w) varied from 0.04 to 0.86. Calcia and silica combined to form wollastonite as the major phase in the sintered microstructure. Excess silica combined with magnesia, iron oxide and alumina to form enstatite, fyalite and alumino silicates respectively during sintering. Optimum compositions were found to be where calcia-silica ratio were in the range of 0.1–0.3 where mechanical strength and water absorption of the fired specimen were in the range of 28–38 MPa and 2.5–0.1%, respectively. Physical properties of the sintered specimen are explained on the basis of XRD and SEM analysis. Formation of wollastonite in the sintered compacts with finer grain size was found to be an important parameter for increase in strength.

Microstructure and thermo mechanical properties of a talc doped stoneware composition containing illitic clay

The influence of talc on the thermo mechanical properties and microstructure of a stoneware composition containing illitic clay has been studied. It has been observed that there is an optimum addition of talc/feldspar combination to reach proper vitrification at a relatively lower temperature. The addition of 3 mass% talc resulted in increased flexural strength (69.7 MPa at 1200 °C), decreased water absorption value (0.28%) and increased relative density (94.83%). Decrease in residual quartz content with progressive addition of talc led to decrease in percent thermal expansion upto 3 mass% talc addition, beyond which reverse trend was observed due to increased proportion of the high expansion glassy phase. Addition of talc had little effect on the mullite content of the fired body. The decrease of sintering temperature of bodies containing more than 3 mass% talc led to enlargement of pores which is responsible for decrease in the fired MOR of the matured specimens.

Near net shape SiC–mullite composites from a powder precursor prepared through an intermediate Al-hydroxyhydrogel

Abstract SiC–mullite composites with low dimensional changes on sintering were fabricated by partial oxidation of SiC followed by reaction bonding using hydroxyhydrogel derived alumina keeping SiC as dispersed phase in the intermediate gel-like mass as starting material. The sintering-induced shrinkage is compensated by volume expansion caused by the silicon carbide oxidation-induced-volume expansion. This work describes a new processing route to fabricate SiC–mullite composites where in situ formation of mullite takes place that proceeds at much lower temperatures (⩽1600°C) than in normal ceramics processing routes. Specimens containing Al2O3⩽40% are not suitable due to the formation of large amount of low eutectic aluminosilicates at processing temperatures. Specimens containing ⩾40% Al2O3 yield different aluminosilicates, mainly mullite, which acted as a retarder for oxidation of SiC and at the same time it helped to consolidate SiC compacts. Final phases in fired compact were identified by XRD and different phases present were calculated on the basis of X-ray diffraction results.

Organophilic Nano Clay: A Comprehensive Review

Organophilic nano clay is an important organic-inorganic hybrid derived from intelligent combination of two dissimilar components, viz. clays and organic molecules, at the nanometric and molecular level. The clay component of this hybrid provides a 2-D lamellar structure with interesting surface chemistry, which can be engineered by organic molecules. 2:1 layered clay minerals with high cation exchange capacity, e.g. montmorillonite, possess cation exchange sites on the siloxane surface which can be exchanged with suitable organic molecules. Key aspect of this organic treatment is to swell the interlayer space of the clay mineral up to a certain extent reducing interlayer interaction, to produce nanoplatelet of aluminosilicate materials. Those engineered nanoplatelets are used in various fields of applications, viz. polymer nano clay composite, rheological modifier, thickening and gelling agent in paints and lubricants, in waste water treatment, and also as drug delivery vehicle. Intensive research activity in this complex system is attested by evergrowing number of symposia, books and specialized journals devoted to this subject. This present article is an updated review of organophilic nano clay preparation, characterization and application of the material. Important information available in the protected domain of patent is also included.

Synthesis of boron nitride from boron containing poly(vinyl alcohol) as ceramic precursor

A ceramic precursor, prepared by condensation reaction from poly(vinyl alcohol) (PVA) and boric acid (H3BO3) in 1:1, 2:1 and 4:1 molar ratios, was synthesized as low temperature synthesis route for boron nitride ceramic. Samples were pyrolyzed at 850°C in nitrogen atmosphere followed by characterization using Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD).

Prevention of Oxidation of SiC through Reaction Bonding in the SiC-Mullite Composite System by Using the Technique of Intermediate Gel Formation

Reaction bonding of silicon carbide-mullite composites with varying SiC to mullite ratio is studied. The oxidation of silicon carbide to cristobalite could be controlled by increasing the material that gives mullite after heat treatment. In the present study, the best composition was found to be that which produces SiC and mullite in the ratio of about 1:1.

Rheological Behaviour of Silicon Carbide Suspension in Relation to Particle Size Distribution

Rheological behaviour of an aqueous suspension of silicon carbide in presence of a dispersing agent has been studied to analyze the important factors related to casting. Shear stress τ and rate of shear γ were found to follow power law with two constants n and k both of which were dependent on particle size distribution.

Studies on the Suitability of Iron-rich Indian Bentonites for Synthesis of Organoclays by Intercalation

In the present study intercalation behaviour of two bentonites from Indian origin were compared with a high-puritycommercial montmorillonite. Experimental bentonites of Indian origin showed low cation exchange capacity (CEC) due to limited Mg2+ substitution. Infra-red spectral study revealed the presence of Fe3+ in octahedral positions. Organic loading of intercalated clays increased with CEC.

OXIDATION BEHAVIOUR OF SILICON CARBIDE : GEL DERIVED OXIDE COMPOSITE SYSTEMS

Consolidation of composites in the system SiC—Al2O3, SiC—ZrO2 and SiC—MgO in relation to oxidation characteristics of silicon carbide during firing in the ambient atmosphere were studied. A12O3, ZrO2 and MgO additives were derived through sol-gel route. SiC—Al2O3 system was found to be more resistant towards oxidation of SiC where ultimate fired phases were silicon carbide and mullite with traces of cristobalite as detected by XRD. Both Al2O3, and ZrO2 are prospective, but MgO in the present system is not effective.

SIMULTANEOUS INTERCALATION OF TWO QUATERNARY PHOSPHONIUM SALTS INTO MONTMORILLONITE

Intercalation of montmorillonites with a mixture of intercalates has not been studied extensively. The objective of the present investigation was to study the effects of phosphonium-based intercalate mixtures on the properties (organic loading and basal spacing) of montmorillonite. These phosphonium-intercalated montmorillonites are promising candidates as high-temperature stable nanofillers for application in clay polymer nanocomposites.Two salts with different cationic heads and chain lengths were mixed in varying molar ratios and the mixtures were intercalated into the interlayer space of montmorillonite. Two sets were chosen based on the chain length and the cationic head-group structure of the two intercalated salts (referred to hereafter as set 1 and set 2). The resultant intercalated montmorillonite was characterized by thermogravimetric analysis, X-ray diffraction, and transmission electron microscopy. The organic loading of the intercalated montmorillonite increased with the proportion of longer carbon-chain intercalate in the mixture. The intensity of the characteristic XRD peak of each intercalate varied with the mole fraction percent of that intercalate in the solution mixture. No marked synergistic effect of the intercalate mixture on the basal spacing and organic loading properties of the intercalated montmorillonite was observed — the proportional influence of individual components was found to be more prominent.