Malahalli Vijaya Kumar

Hydrothermal synthesis of meso/macroporous BiVO4 hierarchical particles and their photocatalytic degradation properties under visible light irradiation

An ordered hierarchical meso/macroporous monoclinic bismuth vanadate (BiVO4) particle was fabricated for the first time by a simple two-step melamine template hydrothermal method followed by calcination. The physiochemical parameters of as-prepared porous materials were characterized by means of X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, Raman, Barrett–Emmett–Teller, and UV–vis techniques. The nitrogen adsorption–desorption measurement and pore size distribution curve suggest that meso/macropores exist in these hierarchical microarchitectures. Further, it is found that melamine plays a significant role in the formation of porous BiVO4 particles, and when a known amount of melamine was added, the surface area and pore size of such porous BiVO4 particles were increased. The photocatalytic activities of the as-prepared hierarchical BiVO4 samples were measured for the photodegradation of Congo red aqueous dye solution under visible light irradiation. Surprisingly, the porous BiVO4 particles showed outstanding photocatalytic activities than polycrystalline BiVO4 sample. The possible enhancement of such catalytic performance has also been further discussed.

Thermal and optical properties of glass and crystalline phases formed in the binary R2O3-Al2O3 (R = La-Lu and Y) system

Rare-earth aluminate (RAlO3, R = La–Lu and Y) glass and crystalline phases were prepared by containerless levitation in an aerodynamic levitation furnace. In the RAlO3 system, La, Nd and Sm aluminum perovskites solidified as glass and Eu–Lu and Y aluminum perovskites solidified as crystalline phases. The glass forming region decreased with decreasing ionic radius of the rare-earth element. Scanning electron microscopy images and x-ray diffraction results revealed the formation of a single RAlO3 phase from the undercooled melt. The glass transition temperature, Tg, and density increased and the molar volume decreased with decreasing rare-earth element ionic radius. The refractive index at 589 nm exceeds 1.85 in each composition and a transparency of approximately 72% was achieved for the LaAlO3 glass.

Density measurement of glass and liquid CaAl2O4 using a pressurized electrostatic levitator

A pressurized electrostatic levitation furnace (PESLF) was used to measure the density of calcium aluminate with a composition of CaAl2O4 (CA) over a wide temperature range of 673?2300?K with an ultraviolet-based imaging technique. The density was measured in various gas atmospheres of O2, air and N2 at a chamber pressure of 4???105?Pa. The measurements under these different atmospheres suggested that the density increased when decreasing the oxygen atmosphere. The density obtained under N2, air and O2 gas atmosphere can be expressed as??(T)?N2?=?2.91???103???0.073(T???Tm), ?(T) air?=?2.76???103???0.075(T???Tm) and ?(T) O2?=?2.70???103???0.1(T???Tm) (kg?m?3) (?2%) with Tm?=?1878?K, over the range 2200 to 673?K.

Surface Tension Measurement Using sample Rotation Combined with Electrostatic Levitation

In order to measure the surface tension of high temperature melts with high viscosity, a sample rotation method was developed. An electrostatically levitated melt was spun with a rotating magnetic field, and the shape evolution of the sample was observed. Especially, the bifurcation behavior (shape transformation from axisymmetric to non-axisymmetric) was closely monitored by a high speed camera. The experiments confirmed that the rotation frequency at the bifurcation could be precisely measured by monitoring the fluctuation of the power of the beam of a He–Ne laser reflected at the sample surface, and thus, the surface tension could be calculated based on the theory by Brown and Scriven. The validity of this measurement technique was demonstrated with ZrCoAl bulk glass forming alloy.

Nano-structure formation of an oxide ceramics with unprecedented magnetization by supercooling

We report a unique microstructure and a specific magnetization behavior resulting from containerless solidification of a deeply super-cooled BiFeO3 sample under microgravity conditions. The microstructure of the solidified material revealed a mixed structure consisting of 10 nm-size crystalline particles and amorphous matrix. More importantly, the nano-structural material exhibited a magnetization phenomenon which has never observed so far: a reversal in the magnetization jump direction occurred at 50 K when the sample temperature was increased from 5 K to 100 K.

Real-time x-ray diffraction of metastable phases during solidification from the undercooled LuFeO3 melt by two-dimensional detector at 1 kHz

In-situ identification of metastable phases formed from the undercooled LuFeO3 melt under controlled oxygen partial pressure Po2 was studied by x-ray diffraction measurements at a synchrotron radiation source. Real-time observation of the formation and growth of individual phases during the single recalescence of Lu3Fe2O7 and LuFe2O4 phases at Po2 of 1 × 103 Pa has been revealed by a high speed imaging system at 1 kHz. The obtained diffraction pattern of the metastable phase in the LuFeO3 system was consistent with that of the metastable and stable phases reported in the Lu-Fe-O system.