@article { ISI:000257362100009, title = {Non-isothermal kinetic studies of the template decomposition from silicalite-1 framework-high temperature X-ray diffraction and thermogravimetric analysis}, journal = {Microporous and Mesoporous Materials}, volume = {113}, number = {1-3}, year = {2008}, month = {AUG}, pages = {64-71}, publisher = {ELSEVIER SCIENCE BV}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

Non-isothermal decomposition of the tetrapropylammonium cations (TPA(+)) intercalated in silicalite-1 framework has been carried out using thermogravimetric (TG) analysis and high temperature powder X-ray diffraction (HTXRD) techniques. Conversion factor for template decomposition is calculated using two methods viz., \% weight loss from the thermogravimetric analysis and changes in the intensities of the Bragg reflections 101/011 and 200/020 in the HTXRD patterns scanned at different temperatures (range 298823 K). The calculated apparent activation energy for template decomposition in air was 129 and 125 kJ mol(-1), respectively, for the two techniques TG and HTXRD, calculated using the Kissinger method. By Flynn-Wall-Ozawa approach of isoconversion, apparent activation energy for template decomposition in air was 123 and 124 U mol-1, respectively, for TG and HTXRD data. The reaction order was determined using the method of Kennedy and Clark and it is similar to 2 by both the techniques. The second order of template decomposition can be attributed to the fact that TPA+ is positioned in two different orientations inside the silicalite-1 framework. Template removal occurs with a contraction in unit cell dimensions. There is a decrease in the lattice parameters of the as-synthesized silicalite-1 sample after removal of template from the framework. (C) 2007 Elsevier Inc. All rights reserved.

}, keywords = {HTXRD, non-isothermal kinetics, Silicalite-1}, issn = {1387-1811}, doi = {10.1016/j.micromeso.2007.11.002}, author = {Bhange, Deu S. and Pandya, N. A. and Jha, Ratnesh Kumar and Ramaswamy, Veda} } @article { ISI:000257365900027, title = {Novel hydroxide precursors for low temperature synthesis of selected ternary oxides}, journal = {Materials Research Bulletin}, volume = {43}, number = {7}, year = {2008}, month = {JUL}, pages = {1842-1849}, publisher = {PERGAMON-ELSEVIER SCIENCE LTD}, address = {THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, ENGLAND}, abstract = {

A novel method of using hydroxide precursors to reduce the synthesis temperature for few selected ternary oxides has been presented here. This technique is very useful and advantageous when the ternary oxides contain an alkaline earth element. The selected compositions for this method are BaCeO3 (BC), BaBiO3 (BB), La0.7Sr0.3CoO3 (LSCO) and BaBi2Nb2O9 (BBN). Commercially purchased strontium (or barium) hydroxide and freshly prepared lanthanum, cobalt, bismuth and niobium hydroxides were mixed thoroughly in stoichiometric ratio and heated at different temperatures ranging from 100 to 700 degrees C for 10 h for corresponding compositions. The sequence of the reaction and evolution of the product phase were studied by the X-ray diffraction (XRD) studies. The phase purity and lattice parameters were also determined by XRD investigations. All the product phases in each case were formed at relatively low temperature than when they were prepared by co-precipitation or solid state method. The morphology and average particle size of these powders were investigated by scanning electron microscopy (SEM). (C) 2007 Elsevier Ltd. All rights reserved.

}, keywords = {Ceramics, Chemical synthesis, Electron microscopy, Oxides, X-ray diffraction}, issn = {0025-5408}, doi = {10.1016/j.materresbull.2007.07.006}, author = {Muthurajan, H. and Rao, N. Koteswara and Gupta, U. N. and Pradhan, Sivaram and Jha, Ratnesh Kumar and Kumar, H. H. and Mirji, S. A. and Ravi, V.} } @article { ISI:000253478500012, title = {Novel synthesis of SrBi2Nb2O9 powders from hydroxide precursors}, journal = {International Journal of Applied Ceramic Technology}, volume = {5}, number = {1}, year = {2008}, month = {JAN}, pages = {101-104}, publisher = {BLACKWELL PUBLISHING}, address = {9600 GARSINGTON RD, OXFORD OX4 2DQ, OXON, ENGLAND}, abstract = {

Simple hydroxide precursors were used for the first time for the synthesis of a typical Aurivillius compound (SrBi2Nb2O9 (SBN)) at a low temperature. This method is very advantageous because it circumvents the use of SrCO3 in the case of conventional ceramics as well in the coprecipitation methods, thereby lowering the formation of the product phase. Commercially purchased strontium hydroxide is mixed thoroughly with freshly precipitated bismuth and niobium hydroxides in a stoichiometric ratio and heated at different temperatures ranging from 100 degrees C to 750 degrees C for 12 h. The sequence of the reaction and evolution of the product phase was monitored by X-ray diffraction (XRD) studies by recording the XRD for samples calcined at different temperatures. The incipient SBN phase begins to form at temperatures as low as 400 degrees C, and phase formation was complete only at 650 degrees C as revealed by the XRD observations. The differential thermal/thermogravimetric analyses) also corroborate this result. The morphology and average particle size of these powders were investigated by transmission electron microscopy studies.

}, issn = {1546-542X}, doi = {10.1111/j.1744-7402.2008.02182.x}, author = {Gupta, Upendra Nath and Rao, Koteswara and Pradhan, Sivaram and Jha, Ratnesh Kumar and Muthurajan, Harries and Ravi, Venkat} }