Mithun Nath

Nanometal-Glass Hybrid Nanocomposites: Synthesis, Properties and Applications

In recent past research on nanometal-glass hybrid composites has been the centre of attention across the globe particularly in the area of nanoscience and for the future nanotechnology. In this review, with a short historical background, its preparation by various multi-step techniques, properties and applications are briefly described. In addition, recently developed single-step in situ thermochemical reduction methodology by these authors for synthesis of various nanometal-glass hybrid nanocomposites are described in detail with their significant characteristic properties, relevant theories and applications. Here Au, Ag and Bi metals are considered and the synthesized glasses are mostly based on antimony, bismuth and phosphorus oxides. Some of them are dichroic in nature, that is, they exhibit blue to green colourations in transmitted light and brown to reddish brown colourations in reflected light. The appropriate reasons for their dichroic character are still remained unsolved. Nanometal-antimony oxide glass nanocomposites have been found to enhance the photoluminescence upconversion intensities up to 11 fold when co-doped with rare earth (RE) ions due to the plasmonic induced local field as enhanced by the effects of doped metal nanoparticles. The nanometal-glass hybrid nanocomposites, therefore, seem to be very promising for various nanophotonic applications (such as nanometal enhanced rare earth luminescence, solar cell, light emitting diode, plasmonic integrated circuit, plasmon slot waveguide, etc) that have presently emerged into a major field called ‘plasmonics’.

Synthesis and characterization of mullite–zirconia composites by reaction sintering of zircon flour and sillimanite beach sand

Mullite–zirconia composites containing 10–30 wt% zirconia were prepared by reaction sintering of zircon flour, sillimanite beach sand and calcined alumina. Raw materials were attrition milled, shaped into pellets and bars and sintered in the temperature range of 1450–1600∘C with 2 h soaking at peak temperature. Sintered products were analysed in terms of various physical, mechanical and thermo-mechanical properties. The analyses of phases developed and microstructural analyses were carried out by X-ray diffraction (XRD) and scanning electron microscope (SEM), respectively. It was observed that the addition of ZrO2 up to 20 wt% significantly improves flexural strength and fracture toughness. The transformation of t → m zirconia was found to be the dominant mechanism for enhancement in mechanical properties. ZrO2 occupies both the intergranular as well as intragranular positions. However, intragranular zirconias are much smaller compared to intergranular zirconias.

Thermo-mechanical properties of mullite—zirconia composites derived from reaction sintering of zircon and sillimanite beach sand: Effect of CaO

Abstract Mullite—zirconia composites containing 20% zirconia (mass fraction) were prepared by reaction sintering route utilizing Indian coastal zircon flour and sillimanite beach sand. 4%–12% of CaO (mole fraction) with respect to zirconia was used as additive. The effect of additive on densification, microstructure as well as various mechanical and thermo-mechanical properties was studied. Incorporation of CaO reduced the densification temperature of the composites to 1550 °C compared to 1600 °C (for CaO free samples). CaO formed small amount of liquid phase (calcium aluminosilicate), which facilitated sintering. Average grain size of the composites decreased up to 4% CaO addition, afterwards grain size increased with further addition of CaO. Samples with 4% CaO exhibited ∼225 MPa of flexural strength, ∼6 MP·m 1/2 of fracture toughness and significant improvement in thermal shock resistance. CaO stabilized the tetragonal zirconia phase and thus improved the mechanical properties.