J. Chandradass

Effect of Clay Dispersion on Mechanical, Thermal and Vibration Properties of Glass Fiber-Reinforced Vinyl Ester Composites

Glass fiber reinforced vinyl ester polymer composites filled with clay particles were synthesized by a hand lay-up technique with the addition of methy ethyl ketone peroxide (MEKP), cobalt napthalate and benzoyl peroxide. Mechanical and thermal properties of vinyl ester-glass fiber composite and clay particles dispersed vinyl-glass fiber hybrids were investigated in the present work. The hybridization effect of nanoclay dispersion in vinyl ester-fiber composite was discussed. Enhanced mechanical, thermal and vibration properties were observed in nanoclay dispersed composites over vinyl ester-glass fiber composite.

Synthesis and Characterization of Alumina Nanoparticles by Igepal CO-520 Stabilized Reverse Micelle and Sol-Gel Processing

Nanosized alumina powders have been prepared via reverse micelle and sol-gel processing. By stepwise hydrolysis using aqueous ammonia as the precipitant, hydroxide precursor was obtained from nitrate solutions dispersed in the nanosized aqueous domains of microemulsion consisting of cyclohexane as the oil phase, poly(oxyethylene) nonylphenyl ether (Igepal CO-520) as the non-ionic surfactant, and an aqueous solution containing aluminium nitrate as the water phase. The synthesized and calcined powders were characterized by thermogravimetry-differential thermal analysis, transmission electron microscopy, and scanning electron microscopy. The XRD analysis showed that the complete transformation from γ -Al2O3 nanocrystalline to α-Al2O3 was observed at 1100°C. The resulting alumina nanopowder exhibits particle agglomerates of 135–200 nm in average diameter occur when they calcined at 1200°C. The average particle size was found to increase with increase in water to surfactant (R) molar ratio.

Synthesis and Characterization of LaAlO3 Nanopowders by Various Fuels

In this research, a sol-gel auto combustion route has been proposed to synthesize LaAlO3 nanopowders, using lanthanum nitrate, aluminum hexahydrate, and different fuels such as citric acid, oxalic acid, and tartaric acid. The formation temperature of LaAlO3 and its crystallite size in the presence of different fuels were compared together. The results showed that the lowest formation temperature as well as the smallest crystallite size in the presence of citric acid was 750°C and 28.7 nm.

Preparation and Properties of Barium Titanate Nanopowder/Epoxy Composites

This article is focused on the preparation of barium titanate nanopowder/epoxy composites and studying the effect of barium titanate nanopowder on improving mechanical and thermal characteristics of the epoxy polymer. Composites are prepared by dispersing barium titanate nanopowder in epoxy resin and, subsequently, cross-linking by using diamino diphenyl methane (DDM) curing agents. Synthesis of barium titanate nanopowder/epoxy composites is carried out for different concentrations (1, 3, and 5 by weight) of barium titanate nanopowder at high temperature. High-temperature curing (HTC) involves mixing the resin-nanopowder solution followed by DDM hardener and curing at 120°C. Tensile, flexure, and impact results showed a maximum value of 72.7 MPa, 2.98 GPa, and 2 J/cm, respectively. DSC analysis revealed that curing occurs at low temperature in the presence of barium titanate nanopowder. Thermogravimetry analysis (TGA) showed the increased thermal stability in the nanoparticle filled epoxy composites as compared with the pure epoxy counterparts. Dynamic mechanical analysis (DMA) revealed, maximum storage modulus of 6400 MPa and glass transition temperature of 154°C for 3 wt% barium titanate nanopowder.

Synthesis and Characterization of Sol–Gel Alumina Fiber by Seeding α-Alumina Through Extended Ball Milling

Alumina fibers were prepared by sol–gel process using α-Al2O3 seeded boehmite sol. The starting material used for the preparation of boehmite sol was aluminium-tri-isopropoxide. Extended ball milling of boehmite sol using alumina grinding media was carried out to incorporate nucleating seeds of α-Al2O3 to boehmite sol. Differential thermal analysis showed that the phase transition to α-Al2O3 takes place at a much lower temperature by seeding α -Al2O3. The presence of α-Al2O3 seeds decreases the sintering temperature and a relatively dense microstructure with very fine grain size is formed at 1300°C. The fibers sintered at 1300°C have the highest tensile strength.

Synthesis and Characterization of CaO Doped Alumina–Zirconia Fibers by Sol-Gel Process

Calcium oxide (CaO) doped Alumina–zirconia fibers were prepared by sol-gel process. The starting materials used for the preparation of alumina and zirconia sol were aluminium-tri-isopropoxide and zirconium oxychloride, respectively. Alumina sol and zirconia sol were mixed in definite proportions, so that the final composition contains 10 wt% ZrO2. CaO was introduced into the mixed sol in the form of calcium nitrate such that the final composition contains 1 and 2 wt%. Alumina–zirconia fibers were prepared from the mixed sol containing CaO, respectively. Sintered alumina–zirconia fiber has α -Al2O3, t-ZrO2, and m-ZrO2 phases. The phase transition to α -Al2O3 takes place at lower temperature in the presence of CaO. The addition of CaO increases the grain size.

Low Temperature Synthesis and Characterization of Zirconia Doped Alumina Nanopowder by Hydrothermal Process

Al2O3-ZrO2 composite precursor powder containing 5–20 wt% ZrO2 was prepared by hydrothermal method at a reaction temperature of 190°C and pressure 4 kgf/cm2. X-ray diffraction (XRD) of as-synthesized powder confirms the formation of bayerite and boehmite. The phases present in the powders calcined at 500°C and 800°C are α-Al2O3 and t-ZrO2. The Frontier Transform Infrared (FTIR) studies revealed the formation of α-Al2O3 in corroboration with X-ray studies. The transmission electron microscopy (TEM) analysis of the calcined powders at 800°C revealed the average particle size of alumina platelets is 60–70 nm in diameter and 10–15 nm in thickness whereas zirconia is observed as clusters of size 10–20 nm. Energy Dispersive Spectroscopy (EDAX) confirms the presence of alumina and zirconia particles.

ZnO-Based Thin Film Transistor Fabricated Using Radio Frequency Magnetron Sputtering at Low Temperature

Thin film transistors (TFTs) were fabricated on a glass substrate using zinc oxide material as a channel layer. The layers were grown by radio frequency magnetron sputtering method at a temperature of 100°C. The output characteristics of a TFT device showed that there is a reduction in drain current at increased drain-source voltage and gate-source voltage. This evidenced the existence of self-heating effect which may be due to increased donor type point defects. The electrical characteristics of a device show an improved intrinsic channel mobility of 4 cm2/Vs, threshold voltage of 12 V, sub-threshold swing of 1 V/decade, and very much decreased off current of the order 10−12 A.

Synthesis of Nanocrystalline α-Al2O3 Powder Using Acetylacetone

Nanocrystalline α-Al2O3 powders have been prepared by pyrolysis of a complex compound of aluminum with acetylacetone. The volumetric ratio (alumina to acetylacetone) of the starting feedstock has been shown to be a critical factor for the formation of nano α-Al2O3 powders. The optimum calcinations temperature of the precursor powder for crystallization of nano α-Al2O3 was found to be 1000°C for 2 h. Transmission electron microscopy (TEM) micrographs showed, the obtained materials could be modified from segregated nanoparticle to aggregates of nanoparticle with decrease in the volume ratio of alumina to acetylacetone from 8:2 to 5:5 in the precursor solutions. Fourier transform infrared spectra (FTIR) analysis show peak at 450 cm−1 corresponds to α-Al2O3 at 1000°C.

Synthesis and Characterization of Alumina–Zirconia Nanopowders via an Oxalate Route

Nanocrystalline Al2O3–ZrO2 powder was synthesized by a simple method using oxalic acid as a chelating agent. The formation temperature of α - Al2O3 was investigated by differential thermal analysis. X-ray diffraction (XRD) analysis shows that t-ZrO2 was stabilized in alumina matrix with oxalic acid content 0.5 M and 1 M, respectively. In addition, the data from XRD showed α-Al2O3 and t-ZrO2 phase can be formed at 1100°C with 1 M oxalic acid content. Transmission electron microscope (TEM) micrograph of calcined powders revealed as the oxalic acid content in the precursor solutions is increased from 0.25 M to 0.5 M concentration. The obtained materials could be modified from segregated nanoparticles to agglomerated nanoparticles and finally to large agglomerate with 1 M concentration of oxalic acid. The Fourier transform infrared spectra (FTIR) confirms the formation of α-Al2O3 in corroboration with X-ray studies.