Browsing by Author "Nampi, PP"

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    Aluminosilicates with varying alumina-silica ratios: synthesis via a hybrid sol-gel route and structural characterisation
    (DALTON TRANSACTIONS, 2010) Nampi, PP; Moothetty, P; Berry, FJ; Mortimer, M; Warrier, KG
    Aluminosilicates with varying Al(2)O(3):SiO(2) molar ratios (3 : 1, 3 : 2, 3 : 3 and 3 : 4) have been synthesized using a hybrid sol-gel route using boehmite sol as the precursor for alumina and tetraethyl orthosilicate (TEOS) as the precursor for silica. The synthesis of boehmite sol from aluminium nitrate, and its use as the alumina precursor, is cost effective compared to alkoxide precursors. Structural aspects, including bonding and coordination, are studied in detail for samples calcined in the temperature range 400-1400 degrees C using both NMR and FTIR spectroscopy: the results are correlated with phase formation data (spinel and high temperature phases) obtained from XRD and thermal analysis. FTIR results show a broadening of peaks at 800 degrees C indicating a disordered distribution of octahedral sites caused by crosslinking between AlO(6) octahedral and SiO(4) tetrahedral units prior to the formation of mullite. (27)Al MAS NMR spectra are consistent with a progressive decrease in the number of AlO(6) polyhedra with increasing temperature corresponding to Al in these units being forced to adopt a tetrahedral coordination due to the increasing presence of similarly coordinated Si species. XRD results confirm the formation of pure mullite at 1250 degrees C for a 3Al(2)O(3):2SiO(2) system. At 1400 degrees C, phase pure mullite is observed for all compositions except 3Al(2)O(3):SiO(2) where alpha-Al(2)O(3) is the major phase with traces of mullite. The synthesis of aluminosilicates through a hybrid sol-gel route and the detailed insight into structural features gained from spectroscopic and diffraction techniques contributes further to the development of these materials in applications ranging from nanocatalysts to high-temperature ceramics.
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    Calcination and associated structural modifications in boehmite and their influence on high temperature densification of alumina
    (CERAMICS INTERNATIONAL, 2011) Nampi, PP; Ghosh, S; Warrier, KG
    A systematic study is reported on the calcination of boehmite and its associated structural changes, and their effect on densification features. Boehmite precursor gels have been calcined in the temperature range 250-1200 degrees C. The associated structural changes are identified by FTIR and XRD. The specific surface area measurements indicated a relatively high value of 169 m(2)/g for bochmite calcined at 400 degrees C; this value reduced to 4 m(2)/g on calcination at 1200 degrees C. In the temperature range 400-1000 degrees C, the coordination of aluminium changes from a quasioctahedral to a tetrahedral nature, which reverts to octahedral at 1200 degrees C. The precursor containing gamma-alumina gives a 92.1% theoretical density, on sintering at 1500 degrees C due to the highly unstable quasioctahedral coordination. Boehmite precursors calcined at 400 degrees C and 1000 degrees C produced a density of 88.2% and 96.9%, respectively, in the sintered compact at 1500 degrees C. Boehmite calcined to a-alumina (1200 degrees C) possesses an octahedral structure having a density of 97.6% at 1500 degrees C. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
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    Effect of surface roughness on grain growth and sintering of alumina
    (BULLETIN OF MATERIALS SCIENCE, 2011) Nampi, PP; Kume, S; Hotta, Y; Watari, K
    The production of ceramic bodies with less surface roughness is industrially important when one considers the aspect of final machining processes. Hence an attempt have been made to study the variation in surface roughness parameters (R(a), R(y), R(z)) of alumina having three different kinds of roughness features at different sintering temperatures. Variation in surface roughness properties are also correlated with grain size. R(z) shows significant difference between fine and intermediate surfaces, hence predicts small difference in their microstructural features. As a general trend, average grain size increases with increase in sintering temperature, but wide distribution of grains with enhanced non-uniform grain growth is observed when the surface is coarse. Hence, creation of fine surface in the green body is necessary for homogeneously distributed grains with controlled uniform grain growth. The final roughness and grain size of the sintered alumina depend on the initial surface roughness of the green body.
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    High surface area sol-gel nano silica as a novel drug carrier substrate for sustained drug release
    (MATERIALS RESEARCH BULLETIN, 2012) Nampi, PP; Mohan, VS; Sinha, AK; Varma, H
    Among various carrier materials for drug delivery, silica has been found to be significant for loading and sustained release of the drug. In the present study, the antibiotic gentamicin was incorporated in various amounts on to a silica matrix, using a sol-gel subcritical drying route. Crack free silica rods with a length of 1-1.5 cm, diameter of 0.5 cm and density of 1.35 g/cm(3) incorporated with gentamicin were obtained. The incorporation of gentamicin into the silica matrix was revealed by FTIR. The adsorption-desorption isotherms and pore size distribution were studied in detail. The drug elution patterns were analysed and show a biphasic mode of release. After the initial burst release, a constant release pattern is observed. A release value above the minimum inhibitory concentration (MIC) is always maintained. The amount of drug released is higher than that of many other bioactive ceramic materials. An attempt has been made to correlate the functional properties with the porosity features. (C) 2012 Elsevier Ltd. All rights reserved.
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    High-Surface-Area Alumina-Silica Nanocatalysts Prepared by a Hybrid Sol-Gel Route Using a Boehmite Precursor
    (JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 2010) Nampi, PP; Moothetty, P; Wunderlich, W; Berry, FJ; Mortimer, M; Creamer, NJ; Warrier, KG
    High-surface-area alumina-silica mixed oxide (Al(2)O(3):SiO(2)) nanocatalysts have been prepared by a hybrid sol-gel method using boehmite (synthesized from aluminum nitrate) as the source of alumina and tetraethyl orthosilicate as the source of silica. The gels, after calcination at 400 degrees C, result in mixed oxides with specific surface areas of 287 m2/g (Al(2)O(3):SiO(2)=3:1) and 262 m2/g (Al(2)O(3):SiO(2)=3:4). Further heating to 600 degrees C produces materials with specific surface areas of 237 and 205 m2/g, respectively. The larger specific surface areas characteristic of the 3Al(2)O(3):SiO(2) samples are attributed, via transmission electron micrograph investigations, to the presence of similar to 10 nm size, needle-like particles having an aspect ratio of 1:50. Further addition of silica leads to the formation of larger needles of 20-75 nm size. Calcination at 600 degrees C induced an approximately 5% decrease in the total pore volume for the 3Al(2)O(3):SiO(2) sample. In contrast, the material with Al(2)O(3):SiO(2)=3:4 showed an approximately 12% increase in pore volume when heated at 600 degrees C. The pore-size distribution was in the range 1-3.5 nm with r(max) at similar to 2 and similar to 2.5 nm at 600 degrees and 800 degrees C, respectively. Adsorption isotherms and pore-size distribution analyses are discussed in some detail for the aluminosilicates at different calcination temperatures. This discussion is supported by structural information determined from FTIR and 27Al MAS NMR studies. Relatively high acidity values (0.234 mmol/g for Al(2)O(3): SiO(2)=3:4) are observed for silica-rich compositions consistent with their application as efficient acid catalysts.
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    Sodium yttrium fluoride based upconversion nano phosphors for biosensing
    (6TH INTERNATIONAL CONFERENCE ON OPTICAL, OPTOELECTRONIC AND PHOTONIC MATERIALS AND APPLICATIONS (ICOOPMA) 2014, 2015) Nampi, PP; Varma, H; Biju, PR; Kakkar, T; Jose, G; Saha, S; Millner, P
    In the present study, NaYF4-Yb3+/Er3+ having the composition NaYF4-18%Yb3+/2%Er3+ and NaYF4-20%Yb3+/2%Er3+ with and without the addition of PVP (polyvinyl pyrolidone) have been synthesised by a solution method using NaF, yttrium nitrate, ytterbium nitrate and erbium nitrate as precursors. Upconversion spectra of prepared nanomaterial under 980 nm laser excitation have been studied. The variation in upconversion spectra with new born calf serum and myoglobin has been studied. Myoglobin (Mb) may be helpful when used in conjunction with other cardiac markers for rapid determination of acute myocardial ischemia, especially in patients with a typical chest pain or nonspecific ECG changes. The variation of UC fluorescence with addition of Mb indicates the suitability of using NaYF4 based UC nanoparticles in cardiac marker detection. The detailed study is currently under progress.
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    Sol-gel nanoporous silica as substrate for immobilization of conjugated biomolecules for application as fluorescence resonance energy transfer (FRET) based biosensor
    (Sensors and Actuators B: Chemical., 2013-06) Nampi, PP; Kartha, CC; Jose, G; Anilkumar, PR; Anilkumar, T; Varma, HK
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    The effect of polyvinyl alcohol as a binder and stearic acid as an internal lubricant in the formation, and subsequent sintering of spray-dried alumina
    (CERAMICS INTERNATIONAL, 2011) Nampi, PP; Kume, S; Hotta, Y; Watari, K; Itoh, M; Toda, H; Matsutani, A
    The production of ceramic components using fewer processing steps on a shorter timescale is very important when considering the industrial and economic aspects of the manufacture of these materials in bulk. Spray-dried granules are expected to give compacts with fewer defects due to their low shear strength compared to conventional powders. Several extent studies show results for product of high relative densities (similar to 50% at 10 MPa), however, this study arrives at a process for making ceramic components with comparable density (48-49%) at 10 MPa), using less processing time and fewer processing steps which becomes extremely important when one considers the industrial aspects such as bulk production and manufacturing cost. In the present investigation, 35 vol% alumina slurries with 0.5% weight dispersant (ammonium polyacrylate) have been synthesized with different contents of binder (PVA) and lubricant (stearic acid). It is found that variations in the amounts of these additives plays a significant role in the formation of spray-dried granules, as well as the subsequent consolidation and densification of the compacts made using the granule particles. There is support for adopting the concept of a 'compact process'. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.