NISCAIR Online Periodicals Repository Collection: IJEMS Vol.19(3) [June 2012]

Synthesis, characterization and catalytic properties of Cr-containing silica gel

Title: Synthesis, characterization and catalytic properties of Cr-containing silica gel

Authors: Bai, Yongxiao; Hu, Weiwei; Hu, Xinjun; Bao, Yan; Zhu, Bochao; Yao, Peihong; Jia, Junji

Abstract: Chromium-containing silica gel with variable Si/Cr ratios has been synthesized at ambient temperature by a sol-gel method with the addition of different amounts of Cr precursor. A combination of measurements is used to characterize the chromium-containing silica gel. All the analysis indicates following this synthesis route, it is possible to prepare materials without forming extra wall Cr₂O₃. And the results show that polychromate is absent in the silica gel materials, while the Cr (VI) of calcined chromium-containing silica gel is present as a monochromate species. Also, it has high activity for the selective oxidation of styrene, which is analyzed periodically by means of gas chromatograph.

Page(s): 209-214

Effect of crystallite size on electron spin resonance of Gd³⁺ and luminescence of Eu³⁺ doped in La₆WO₁₂

Title: Effect of crystallite size on electron spin resonance of Gd³⁺ and luminescence of Eu³⁺ doped in La₆WO₁₂

Authors: Devi, V Rama; Kumar, B Vijaya; Velchuri, Radha; Suresh, Palla; Ravi, G; Vithal, M

Abstract: Nano-sized Eu³⁺ and Gd³⁺ doped lanthanum tungstates of composition La_6-xLn_xWO₁₂ (Ln = Eu, Gd; 0 ≤ x ≤ 0.2) are prepared by sol-gel complexation method. These samples are characterized by powder X-ray diffraction (XRD). The average crystallite size is calculated from the XRD using Scherer’s equation. The electron spin resonance (ESR) spectrum of Gd³⁺ doped lanthanum tungstate (La₆WO₁₂) gives characteristic “U” type spectrum. The luminescence spectrum of Eu³⁺ doped La₆WO₁₂ gives characteristic ⁵D₀→⁷F_n (n = 0 to 4) bands due to trivalent europium ions. The intensity of ⁵D₀→⁷F₂ transition decreases with increase in the sintering temperature due to depletion of surface Eu³⁺ ions. The intensity of ⁵D₀→⁷F₂ sintered at 700°C has highest intensity and may have laser applications.

Page(s): 204-208

Investigation on the structural, electrical and magnetic properties of layered perovskite manganite DySr₂MnCrO₇

Title: Investigation on the structural, electrical and magnetic properties of layered perovskite manganite DySr₂MnCrO₇

Authors: Singh, Devinder; Sharma, Meena; Singh, Rajinder; Sharma, Sushma

Abstract: The layered perovskite oxide DySr₂MnCrO₇ has been prepared by the standard ceramic method. The powder X-ray diffraction studies suggest that the phase crystallizes with tetragonal unit cell in the space group I4/mmm. The electrical transport properties show that the phase is an electrical insulator and the electrical conduction in the phase occurs by a 3D variable range hopping mechanism. The magnetic properties suggest that the ferromagnetic interactions are dominant.

Page(s): 199-203

Characterisation of BiFeO₃ synthesised by microcontroller based thermogravimetric analyser

Title: Characterisation of BiFeO₃ synthesised by microcontroller based thermogravimetric analyser

Authors: Suresha, P H; Ramani; Radhakrishna, M C; Angadi, Basavaraj; Devaraj, J T

Abstract: Microcontroller based thermogravimetric analyser (MTGA) is a home built technique extensively used to study the thermal decomposition of inorganic solids and preparation of nanomaterials. This paper reports the characterization of bismuth ferrite BiFeO₃ (BFO) synthesized by microcontroller based thermogravimetric analyser. The synthesized nanopowder is characterized by X-ray diffraction (XRD) method for phase confirmation, crystallite size calculations and scanning electron microscope (SEM) for morphology study. The structure and thermal properties of BFO precursor are studied by using Fourier transform infrared (FTIR) spectroscopy, differential thermal analysis (DTA) and thermogravimetric analysis (TGA). The results of nano BiFeO₃ synthesized by microcontroller based TGA are in good agreement with that synthesized by other techniques.

Page(s): 196-198

NISCAIR Online Periodicals Repository Collection: IJEMS Vol.19(3) [June 2012]

Synthesis, characterization and catalytic properties of Cr-containing silica gel

Effect of crystallite size on electron spin resonance of Gd3+ and luminescence of Eu3+ doped in La6WO12

Investigation on the structural, electrical and magnetic properties of layered perovskite manganite DySr2MnCrO7

Characterisation of BiFeO3 synthesised by microcontroller based thermogravimetric analyser

Effect of crystallite size on electron spin resonance of Gd³⁺ and luminescence of Eu³⁺ doped in La₆WO₁₂

Investigation on the structural, electrical and magnetic properties of layered perovskite manganite DySr₂MnCrO₇

Characterisation of BiFeO₃ synthesised by microcontroller based thermogravimetric analyser