Sarama Bhattacharjee

Facile synthesis of ultra-small monodisperse ceria nanocrystals at room temperature and their catalytic activity under visible light

An optimized facile method has been developed to synthesize ultra-small monodisperse ceria nanocrystals (3 to 4 nm) strictly at RT. The presence of well resolved broad peaks ([111], [200], [220] and [311]) for as-synthesized samples reveal the formation of the cubic phase of ceria. The detailed characterization by TEM exhibited the formation of monodisperse and crystalline ceria nanocrystals. These as-synthesized nanocrystals have shown autocatalytic behaviour and photocatalytic activity under visible sunlight, hence appears to be potential candidates for biomedical (antioxidant), solar cell applications.

Factorial design of experiments on the effect of surface charges on stability of aqueous colloidal ceramic suspension

The present investigation was aimed at studying the synergistic effects of different surface-active agents (SAA) on the stability of aqueous alumina suspensions. The SAA used were dibasic ammonium citrate as dispersant, albumin as binder and octanol-2 as an antifoaming agent. Stability of suspensions was assessed through measurement of the specific surface charge of the system, using the fact that the particles exhibit maximum repulsion between them at high magnitude of surface charge. The experiments were statistically designed to bring out the effect of each variable as well as the effect due to interactions. The results show that the strongest affects on stability of aqueous colloidal suspension is that of dibasic ammonium citrate and albumin. The effect of interactional parameters, though slightly favourable for increasing the stability of the suspension, is very small. Dibasic ammonium citrate and albumin, both highly negatively charged SAA, stabilise the suspension by increasing the overall surface charges of the ceramic particles which inturn increases the overall repulsive forces. On the other hand, the positive charge of octanol-2 neutralises/decreases the magnitude of negative surfaces charge and, consequently, decreases the stability of the suspension. It has been shown that factorial design of experiment approach is very helpful in defining conditions for an optimum performance in such complex systems.

Influence of surface charge on maximizing solids loading in colloidal processing of alumina

Abstract Stability of concentrated aqueous colloidal alumina powder suspensions with and without dispersant (albumin and dibasic ammonium citrate (DAC)) has been investigated by measuring surface charge at different solids loading and pH values. The iso-electric point (iep) of alumina powder was found to be pH iep =8.5. The surface charge of alumina powder changed significantly with anionic polyelectrolyte and iep shifted towards more acidic pH range under different dispersion conditions. The study illustrated that albumin is more effective as dispersant than DAC at all solid loading conditions. The computed specific interaction energies −Δ G SP 0 of albumin (7.5) and DAC (3.5) indicate strong adsorption of albumin compared to DAC on alumina powder surface, leading to higher solid loading.

Optimisation of performance of dispersants in aqueous plasma dissociated zircon suspension

Abstract Plasma dissociated zircon (PDZ) is a unique product obtained during in-flight dissociation of zircon sand in a plasma reactor. In PDZ, submicron zirconia crystallites are intimately mixed with glassy silica. This paper describes the selection and optimisation of dispersants in controlling stability of an aqueous suspension of PDZ. It has been observed that inorganic dispersants and organic additives give clearly distinct behaviour. In both cases, optimum dispersant dosages can be obtained from the streaming potential characteristics. It is shown that there is a critical concentration of each dispersants, which gives the highest streaming-potential/surface charge and hence optimum performance. Studies showed that the isoelectric point of PDZ particulate is at pH 2.8. Additions of dispersant increase the charge in magnitude and modified the surface to have more negative charge in the pH range 2.8–9.4. An assessment of particle/additive interactions, overall stability, and optimised chemical additive required to obtain homogeneous, well-stabilized suspension can be derived from the streaming potential characteristics.

Preparation of zirconia toughened mullite by thermal plasma

Abstract A method for preparation of zirconia toughened mullite using DC plasma is presented. An indigenously developed 50 kW thermal plasma reactor is used for preparation of zirconia toughened mullite (ZTM) from premixed zircon and alumina mixture. ZTM of different compositions were prepared by varying alumina content in the mixture. Finer grain size (

Facile synthesis of nanostructured hydroxyapatite–titania bio-implant scaffolds with different morphologies: their bioactivity and corrosion behaviour

A facile synthesis to fabricate HAp–titania scaffolds with different morphological features has been presented. The hydrothermal approach explored for HAp growth leads to the formation of HAp coating onto titania substrate with distinct morphological features such as cauliflower, urchin, porous nanofibres network, nanorods, etc. under different reaction microenvironments. The XRD analysis done for all HAp–titania scaffold samples revealed the formation of hydroxyapatite phase. Furthermore, the detailed FTIR, SAED and EDS analysis performed confirmed the formation of hydroxyapatite. The addition of H2O2 to the reaction mixture led to the high degree of self-assembly of the formed nanosheets into urchin or consolidated sphere like structures when NaOH or KOH was used in hydrothermal reaction, respectively. The detailed TEM analysis reveals that the formation of such HAp structures takes place by (i) formation of localized corrosion sites on titanium substrate with NaOH/KOH and (ii) the subsequent recrystallization of HAp sol onto the corrosion sites which act as nucleation site. The Tafel plot measurements and MTT assay test indicate that the HAp–titania scaffold samples are corrosion resistance as compared to bare titanium foil and are biocompatible. The structural characterization, growth mechanism, corrosion behaviour in SBF medium and cellular biocompatibility of these scaffold samples are discussed in detail.

Characterization and Dispersion of Multiwalled Carbon Nanotubes (MWCNTs) in Aqueous Suspensions: Surface Chemistry Aspects

Dispersability of multiwalled carbon nanotubes (MWCNTs) in aqueous suspensions was investigated with gum arabic GA (anionic) and polydiallyldimethylammonium chloride (PDADMAC) cationic dispersants. The isoelectric point (iep) of MWCNTs was at pH 4.5. The surface charge of MWCNTs changed to highly negative and iep shifted to pH < 1.5 with GA, whereas with PDADMAC highly positive and iep is shifted to pH 10.2. The interaction energy of MWCNTs with GA and PDADMAC was 9.79 and 10.35 RT unit, respectively. The higher interaction energy with PDADMAC shows more favorable interaction with them. Stabilization mechanism with GA is attributed mainly by electrostatic repulsive forces, whereas with PDADMAC, electrostatic and steric effect.

Performance Evaluation of Dispersants Through Streaming Potential Measurements

Stability of 5% (w/v) colloidal alumina suspension was examined in the presence of three organic dispersants; Dispex N‐40, Darvan C, and tribasic ammonium citrate (TAC), and three inorganic dispersants; sodium tri‐polyphosphate, sodium silicate, and Calgon (sodium hexameta phosphate). The performance and the required dosage for the maximum dispersibility were evaluated by streaming potential measurement. It was shown that there is a critical concentration of each dispersant indicated by the attainment of the highest streaming potential for maximum stability conditions of the suspension. Dispersion quality of the suspension in the presence of dispersant Darvan C was investigated in detail using the sedimentation technique. It was observed that the magnitude of the charge developed on a particle surface at the dosage indicated by the inflection point is the minimum dosage required for the maximum stability of the suspension.

Nanotitania-coated multi-walled carbon nanotube composite by facile colloidal processing route for photocatalytic applications

Multi-walled carbon nanotubes (MWCNTs) and titanium dioxide nanocomposites (MWCNTs/TiO2) were fabricated by a simple novel colloidal processing route and tested as a photocatalyst for degradation of methylene blue under UV irradiation. The novel idea behind this work is to make MWCNTs and TiO2 nanoparticle suspensions separately highly oppositely charged and utilize the electrostatic force of attraction between two entities to deposit nanotitania onto MWCNTs surface. Particle charge detector, scanning electron microscopy, transmission electron microscope, energy dispersive X-rays, X-rays diffraction (XRD), and Raman spectroscopy were used to characterize the composite. XRD and Raman spectroscopic analysis showed the crystalline structure of deposited TiO2 over MWCNTs surface structure as anatase phase. It was found that MWCNTs/TiO2 composite structure have much higher photocatalytic activity compared to TiO2 nanoparticles. The composite material developed may find potential applications in the degradation of organic pollutants in aqueous medium under UV irradiation.

Correlation between Dispersion Stability of Concentrated Ceramic Suspension and Capillary Suction Time

Dispersion stability of highly concentrated ceramic suspensions using different dispersants required for colloidal processing can be assessed by measuring capillary suction time (CST). A systematic evaluation of dispersibility characteristics of colloidal alumina suspension is reported in the presence of three commonly used dispersants, namely, Dispex N 100, Darvan C, and Aluminon by employing the CST technique. The correlation between dispersibility of ceramic suspension and capillary suction time has been established. It has been found that higher the CST value of a suspension, the greater is the stability of the suspension and viceversa. In this investigation, this technique is employed both to choose suitable dispersant and to characterize the suspension. It has been concluded that higher the dispersion ratio (DR) of a suspension above unity the better is the stability and the lower the DR value below unity, the better is the aggregation tendency of the suspension. Quantitative estimation of dispersibility of an aqueous suspension is reported in terms of dispersion ratio. The CST technique has been found to be very useful and suitable for obtaining information for assessing stability of ceramic suspensions and characterizing concentrated ceramic slurry.