Tapas Kumar Mukhopadhyay

In situ synthesis and antibacterial activity of copper nanoparticle loaded natural montmorillonite clay based on contact inhibition and ion release

Copper nanoparticle based clay composite has been synthesized by in situ reduction of a copper ammonium complex ion and characterized by different analytical instruments. The copper nanoparticles were both intercalated and adsorbed on the surface with diameters of <5nm (for intercalated) and 25-30nm (for adsorbed). The composite showed good stability for over 3 months in air. Excellent antimicrobial activity of the composite was observed on Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Enterococcus faecalis with mortality rates >90% after 12h. Cellular membrane damage permeated by direct attachment of the composite and indirect damage caused by released copper ion are the primary sources of antibacterial action. Cytotoxicity measurements showed minimal adverse effect on the two human cell lines beyond the M.B.C. value for the microorganisms studied. In the present form the clay composite shows good promise for use in therapeutic applications.

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.

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.

Strength of sillimanite sand reinforced porcelain subjected to thermal shock

Abstract An attempt has been made to eliminate quartz and gradually replace felspar by sillimanite sand to improve the thermomechanical properties of porcelains. It has been observed that the quenching temperature difference (ΔT) required to initiate thermal stress fracture in the porcelain increased greatly, when compared to classical compositions, with gradual replacement of felspar by sillimanite sand. Similar behaviour has also been observed in linear thermal expansion measurements. It was concluded that improvement in thermal shock resistance of the material was due to the absence of quartz and the presence of sillimanite — a volume-stable mineral — in addition to the decreased amount of glassy phase.

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.

Effect of vanadic anhydride and copper oxide on the development of hard porcelain composite and its antibacterial activity

Abstract A mullite-reinforced porcelain composite with antibacterial properties has been developed using transition metal oxides by solid state sintering. The composite has been characterized in terms of mullite content, hardness, color and antibacterial properties. The physico-chemical properties of the porcelain were substantially increased in the presence of V2O5 and CuO. Well-crystallized needle shaped mullite of average length ∼ 3 μm was observed in the porcelain body at 1300 °C and 1500 °C after the addition of V2O5 and CuO. Vickers hardness of the composite increased 4.2 times for 2% V2O5 at 1500 °C. The porcelain composites showed satisfactory antibacterial activity on gram negative bacteria Escherichia coli with mortality rates of 45% and 22% for V2O5 and CuO doped porcelain respectively.

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.

Non-Isothermal Kinetic Evaluation of Pyrophyllite Dehydroxylation

Dehydroxylation of clay minerals is an important process with several applications. Despite the industrial use of several well defined clay minerals, only the dehydroxylation kinetics of kaolinite has been reported. Still, the kinetics of these solid state reactions is yet to be understood using unambiguous model. In the present work, we have performed detailed kinetic analysis of dehydroxylation of pyrophyllite clay using non-isothermal kinetics by thermogravimetry (TG) at different heating rates. The TG data has been analysed initially with model-free methods (ASTM E 698, ASTM 1641, Friedman analysis and Ozawa-Flynn-Wall method). Interestingly, both the model-free methods of analysis have unequivocally indicated that activation energy (Eact) changes very marginally with progress of reaction and a single activation energy barrier is present. This surmises that the dehydroxylation process is a single stage process. A multivariate non-linear regression on the dynamic thermal data at different heating rates has been performed to determine the most probable kinetic model based on statistical fit. It has been found that, TG data provides best fit with regression coefficient (r2) value of 0.994, when a single stage Avrami type diffusion reaction model is assumed, and an activation energy of 159 kJ.mol−1.

Consideration of Alternate Raw Materials for Porcelain Tile Manufacture: The Effect of the Incorporation of Fired Scrap and Pyrophyllite

To address the problem of depleting reserves of raw materials for the manufacture of porcelain tiles a comparative analysis is made between two possible alternatives. The recycling of waste generated during tile manufacturing and the use of pyrophyllite in the composition were compared in relation to process parameters such as firing temperature and manifested properties such as linear shrinkage, porosity, bulk density and the sequence of sintering in a dilatometric study. It was found that the use of pyrophyllite in such systems is a better proposition. The conclusion was supported by microstructural and XRD phase analysis. The better ceramic properties in the pyrophyllite containing system are attributed to higher mullite formation at comparative firing temperature and a possible explanation for the same has been put forward. The use of pyrophyllite will open up an opportunity to utilize this non-conventional material in the commercial production of different porcelain products.

Influence of Kaolinitic Clay on the Physico-Mechanical Properties of Common Clay-Fly Ash Mix for Building Bricks

Kaolinitic clays of different varieties were progressively added to a 70: 30 mix of common clay and fly ash. The improvement in physico-mechanical properties upon heating in the temperature range of 1050° to 1200°C was studied by evaluating their linear shrinkage, water absorption, flexural strength and phase content. Incorporation of clay I produced better ceramic properties than that of clay II. It was observed that incorporation of kaolinitic clay up to 10% of the total batch improved the physico-mechanical properties and beyond this limit the properties, particularly fired strength, remained unchanged or marginally decreased. Microstructural features were also studied using SEM technique.