M. Balasubramanian

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.

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.

Gd2O3:Eu Nanophosphors Prepared Via Reverse Micelle Processing: Influence of Eu3+ Content on Photoluminescence Property

Europium-doped Gadolinia (Eu-Gd2O3) phosphor nanoparticles have been synthesized by a reverse microemulsion system using cyclohexane as the oil phase, a non-ionic surfactant Igepal CO 520 and the mixed aqueous solutions of gadolinium III nitrate hexahydrate and Europium III nitrate hexahydrate as the water phase. The synthesized and calcined powders were characterized by thermogravimetry-differential thermal analysis (TG-DTA), X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR). The XRD results showed that the powders were cubic phase of Gd2O3 after being calcined in the air at 1,000°C. DTA and FTIR also evidenced the formation of Gd2O3 at 1,000°C. SEM revealed that the particle size decrease with increase in Eu content. EDS confirmed the presence of Gd and Eu phase in the nanopowders calcined at 1,000°C. The photoluminescence studies indicated that a strong emission peak at 610 nm is a characteristic red emission of Eu3+, and the emission intensity increases with increase in Eu content.

Sol-Gel Based Extrusion of Alumina Fibers

ABSTRACT Alumina fibers were prepared by sol-gel method using an in-house fabricated extruder. The starting material used for the preparation of alumina sol was aluminium-tri-isopropoxide. A suitable binder was added to the sol and aged at room temperature for gelation to occur. When the sol became a paste appropriate for extrusion, the fibers were drawn through the extruder and dried at room temperature and subsequently sintered at 1200°, 1400°, and 1600°C in air. It was found that regardless of sintering temperature, the XRD traces indicated that the only phase present in sintered fibers was α-Al2O3. Thermogravimetric analysis of the extruded fibers indicated that most of the volatile compounds were burned out at 500°C. The DTA and FTIR studies confirmed the phase transition to α-Al2O3 and this was in good agreement with the XRD analysis. The SEM investigation revealed that a dense microstructure formed when fibers sintered at 1600°C. In addition, the SEM micrograph revealed that an intergranular fracture was the predominant fracture mode. Mechanical tests indicated that the optimum tensile strength was achieved for fibers sintered at 1600°C.

Solution phase synthesis of t-ZrO2 nanoparticles in ZrO2–SiO2 mixed oxide

A solution phase synthesis is used to prepare tetragonal zirconia nanoparticles. Ammonia solution and zirconia precursor solution were prepared separately and then mixed together to get colloidal hydroxide precipitate. The colloidal hydroxide was treated with silica sol and then the precipitate was separated and dried. The dried powder was then calcined at different temperatures for 2 and 6 h. The mean particle size of the powder calcined at 1000°C was found to be around 8–10 nm. The thermal analysis of dried powder indicates the formation of bulk tetragonal zirconia phase at 780°C. X-ray diffraction (XRD) and infrared spectroscopic analyses confirm the presence of 100% tetragonal zirconia phase in the powder calcined at 1000°C. The addition of silica stabilised the tetragonal zirconia phase. It is advantageous to use this powder as catalyst or catalyst support that operates at high temperatures.

Effect of Ni Doping on the Structure and Magnetic Property in Chemically Synthesized (In1-xNix)2O3 (x = 0.03, 0.05, and 0.07) Nanocrystals

In order to experimentally check the Ni doped In2O3 as a potential spintronic material and to search for high temperature ferromagnetic material, a series of (In1−x Ni x )2O3 (x = 0.03, 0.05, and 0.07) nanoparticles were prepared by sol–gel method. Lattice parameter measurement shows distinct shrinkage of the lattice constant indicating the actual incorporation of Ni ions into the In2O3 lattice. X-ray diffraction (XRD) data show that all the samples exhibit single-phase polycrystalline behavior. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses show that the particle size of the calcined powder is in the range of 10–14 nm and 8–9 nm, respectively. SEM energy dispersive x-ray spectrometer (EDS) mapping shows the presence of Ni ions in the Ni doped In2O3 sample. High resolution transmission electron microscopy (HRTEM) micrographs show lattice fringes of 0.290 and 0.322 nm corresponding to the crystallographic plane (222) and (310) of cubic In2O3. Magnetization study indicated that the Ni doped In2O3 samples exhibit diamagnetic behavior.