Gel assisted fabrication of alumina and mullite matrix nanocomposites (2000-2004)
Colloidal processing offers homogeneous, fine-grained sintered ceramics haing exceptional mechanical properties at low densification temperatures. Conventional colloidal processing deals with preparation of ceramic slurries containing more than 50 vol% solids and consolidation of the ceramic by the application of simple pressures, followed by densification. In our work we used sol gel derived alumina, silica and titania colloids as media for fabricating alumina, aluminium titanate, mullite and their composites. Fine grained alumina with grain size less than 2 mm was achieved at 1450°C/2h. The fine grained aluminium titanate, alumina–aluminium titanate and mullite aluminum titanate ceramics having comparatively better mechanical strength, high thermal shock resistance, low thermal expansion coefficient and high creep resistance were developed through sol gel assisted colloidal processing.
Development of nano ZnO for high energy field varistors (2006-2009)
This is a project sponsored by a varistor company and mainly the objective was to use nano ZnO as active ingredient to improve the varistor properties. Mainly the non-ohmic characteristics of the ZnO-Bi2O3 varistors should be improved. We have synthesized nano ZnO by various techniques such as reflux, microwave decomposition, sonochemical and hydrothermal synthesis and added into industrially processed varistor mix. The optimum amount of varistor filler was arrived and in this approach the varistor non-linearity was found to improve significantly. Fig 1 shows the I-V properties of the varistor discs made only with ZnO nanoparticles and nano/micro composite powders. Sintering of nanocomposites varistors by microwave sintering, two-stage sintering and conventional sintering was also performed for achieving nano-grained sintered products.
Rare earth based composite varistors for high energy applications (2009-2012)
In this project use of rare earths La2O3 and CeO2 for varistor applications is taken up under the funding by IRELTDC, Kollam. The conventional varistors having Sb2O3 and Bi2O3 additives have problems related to Bi-evaporation, and secondary insulating spinel formation. Rare earths have already been employed for having low leakage current, high field varistors. Here we use rare earth doped ZnO nanoparticles as active fillers for developing high energy field varistors. Rare varistor particles mixed in polymer matrix also has been taken up in this work for making varistor-polymer nanocomposites for electronics applications.
Preparation of MAX Phase ceramics by Novel techniques (2010-2012)
Synthesis of Ti3SiC2 and Ti3AlC2 carbides, the two potential ‘metallic-ceramics’ belonging to 312-MAX phase family, by microwave activated displacement reaction and development of its nanocomposite engineering shapes by gel assisted ceramic extrusion and centrifugal casting processes are proposed in this project for the first time. The methodology involves milling of stoichiometric amounts of elemental Al, Ti, Si and graphite with SiC, TiC or Al4C reactants followed by compaction and microwave heating at <1200°C under argon atmosphere to form Ti3SiC2 and Ti3AlC2 phases. The phases thus formed will be provided Al2O3-TiO2, Al2O3-ZrO2 nanocomposite surface coatings through solution techniques for enhancing the poor oxidation resistance and hardness. Consolidation by simple uniaxial pressing followed by densification through microwave sintering would be engaged for fabricating dense MAX-phase ceramics. The project occupies three year duration. At the end of this project, a process for oxidation resistant, bulk Ti3SiC2 and Ti3AlC2 powders as well as dense, fine-grained MAX-phase ceramic nanocomposites for the applications as automobile engine components and thermal protection systems for the future re-usable, re-entry space vehicles will be delivered.
Development of self lubricating ceramic nanocomposites (2010-2011)
Development of high dense, load bearing, radiation and acid resistant, self-lubricating ceramic composite materials is proposed. Ceramic matrix composites based on Al2O3 / ZrO2 containing MoSi2, Ti3SiC2 ceramic reinforcements will be processed in this project. Submicron size alumina and zirconia powders will be ceramically alloyed with MoSi2 and Ti3SiC2 by planetary milling and composite fabrication will be achieved by viscous processing involving sol gel derived nano-Al2O3/NiO binders. Densification will be carried out at 1400 to 1600°C by microwave sintering at controlled atmospheres. In this project series of self-lubricating, multifunctional composites by varying amounts of reinforcements will be processed and then tested for mechanical performance such as wear resistance, coefficient of friction, compressive strength, hardness and hot-acid corrosion resistance.
ZnO nanostructures for functional applications (2006-2010)
Being a known photocatalyst and sunscreen material, ZnO nanoceramics have potential applications as functional cosmetics, fluorescent inks, antibacterial coatings and UV active bleaching agents. Compared to many functional materials, ZnO offers wide possibility for tuned morphologies into range of nanostructures like nanorods, tubes, wires and spheres. These morphologies resulted in varying BET surface area, exhibiting different catalytic properties. In our work we synthesize ZnO nanoparticles with varying morphological features by reflux, hydrothermal, sonochemical and microwave techniques. Microwave is a potential technique for obtaining functional ZnO nano coatings on glass, mica and metallic substrates including soft surfaces like paper, cloth and polymers. Since ZnO has low thermal conductivity, a heat shielding coatings can be quickly generated over any substrates by microwave technique. We have also grown ZnO nano wire assembly on a glass substrate by solution method. Other than UV active photocatalytic functional property, these ZnO nanostructures can show better adsorption of CO2 and H2 gases giving new opportunities for energy and environment applications. This is an ongoing Ph.d work.
|ZnO Morphological features grown on various substrates by microwave technique
Nanostructured ZnO-SiO2 gels and gel hybrids for energy storage applications (2010-2014)
The group also focus on the development of high surface area nanoporous ZnO-SiO2 composite materials through sol gel approach. Insitu growth of ZnO nanostructures in porous silica matrix offer excellent gas storage and sensing applications. For example the ZnO nanowire growth in porous silica shows H2 storage capability. If the ZnO nanostructure is suitably doped with organic and inorganic phase it can be used for the adsorption of CO2 as well as oily pollutants.
Nano ZnO fillers for Smart glaze (2009-2010)
ZnO is a known thermo-luminescent material and suitably doped nano ZnO can perform as smart fillers for generating bulk smart materials and fluorescent coatings. We have tested the action of nano ZnO fillers in the glaze compositions. The spray coatings made up of nano ZnO based glaze exhibits luminescent-glaze depending upon the day and night light. In this work we tuned the luminescence by doping with iron, chromium and cobalt ions. More importantly we used flyash as source for alumin and silica. In fact fly ash is largely employed as building products and cement additives. Our interest is to use flyash as smart-glaze material for country tiles and cement bonded blocks.
Smart glaze prepared using nano ZnO as fillers