@article { ISI:000227196900007, title = {Characterization of nanocrystalline anatase titania: an in situ HTXRD study}, journal = {Thermochimica Acta}, volume = {427}, number = {1-2}, year = {2005}, month = {MAR}, pages = {37-41}, publisher = {ELSEVIER SCIENCE BV}, type = {Article}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

Nanocrystalline titania was synthesized by the hydrolysis of titanium iso-propoxide using ultrasonication. The powder XRD patterns of the sample were recorded in static air and vacuum using a Philips X-pert Pro diffractometer equipped with a high-temperature attachment (HTK16) from room temperature (298 K) to 1173 K and were analyzed by the Rietveld refinement technique. The anatase to rutile phase transformation was observed at 1173 K for the data collected in static air. Only 3\% of anatase titania transformed to rutile when the experiments were carried out at H 73 K in vacuum. The phase transformation from anatase to rutile is accompanied by a continuous increase in the crystallite size of the anatase phase from 9 nm at room temperature to 28 nm at 873 K and then to 50 nm at 1173 K in air while the process of crystallite growth was suppressed in vacuum. A linear increase in the unit cell parameters {\textquoteleft}a{\textquoteright} and {\textquoteleft}c{\textquoteright}, and thus, an overall linear increase in the unit cell volume was observed as a function of temperature in static air as well as vacuum. The lattice and volume thermal expansion coefficients (TEC), alpha(a), alpha(c), and alpha(v) at 873 K are 8.57 x 10(-6), 8.71 x 10(-6) and 25.91 x 10(-6) K-1 in air and 18.01 x 10(-6), 14.95 x 10(-6) and 51.13 x 10(-6) K-1 in vacuum, respectively. (C) 2004 Elsevier B.V. All rights reserved.

}, keywords = {Anatase, HTXRD, Rietveld refinement, rutile, thermal expansion coefficient, titania}, issn = {0040-6031}, doi = {10.1016/j.tca.2004.08.011}, author = {Jagtap, Neelam and Bhagwat, Mahesh and Awati, Preeti and Ramaswamy, Veda} } @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:000275702600044, title = {Enhanced negative thermal expansion in MFI molecular sieves by varying framework composition}, journal = {Microporous and Mesoporous Materials}, volume = {130}, number = {1-3}, year = {2010}, month = {MAY}, pages = {322-326}, publisher = {ELSEVIER SCIENCE BV}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

In the present investigations we have carried out the high temperature X-ray diffraction (HTXRD) studies on the metallosilicate molecular sieves iron silicalite-1 (FeS-1) samples of different Si/M ratios (Si/Fe = 50, 75, 100 and infinity) for their negative thermal expansion (NTE) behavior. All the samples exhibit NTE behavior in the temperature range 373-773 K. Systematic increase in negative thermal expansion coefficient is observed as a function of increasing Fe content in the MFI framework. Strength of the negative thermal expansion increases in the order Si/Fe = infinity \< 100 \< 75 \< 50. It is concluded that by changing the composition of the framework of MFI, enhanced negative thermal expansion can be obtained. (C) 2009 Elsevier Inc. All rights reserved.

}, keywords = {HTXRD, Negative thermal expansion, Silicalite-1}, issn = {1387-1811}, doi = {10.1016/j.micromeso.2009.11.029}, author = {Bhange, Deu S. and Ramaswamy, Veda} }