Veda Ramaswamy | National Chemical Laboratory (NCL) (original) (raw)
Papers by Veda Ramaswamy
Journal of Chemical Technology & Biotechnology, 2007
... Veda Ramaswamy, Vimal Kothiyal, Indra D. Singh and Rajamani Krishna ... The authors wish to t... more ... Veda Ramaswamy, Vimal Kothiyal, Indra D. Singh and Rajamani Krishna ... The authors wish to thank J. M. Nagpal of the Crude Evaluation Laboratory of the Institute for providing the FTA data, and S. M. Nanoti and P. B. Semwal for the computational work. REFERENCES ...
Fresenius' Zeitschrift f�r Analytische Chemie, 1984
Zusammenfassang. Zur Trennung der Erd61fraktion vom Siedebereich des Gas61s in die ein-, zwei-und... more Zusammenfassang. Zur Trennung der Erd61fraktion vom Siedebereich des Gas61s in die ein-, zwei-und dreikernigen aromatischen Bestandteile wird eine Gradientenelution an einer Aluminiumoxids/iule unter standardisierten Bedingungen angewendet. Zur Charakterisierung dienen UV-spektrometrische Messungen. Das Verfahren kann auch zur Untersuchung yon Aromaten aus anderen Erd61fraktionen eingesetzt werden. Summary. The method described is a simple procedure for separating gas oil boiling range petroleum fraction into its aromatic hydrocarbons of the mono-, di-and trinucleartype. This is accomplished by gradient elution through an alumina adsorption column under established/standardised conditions. Characterisation is performed by UV-absorption. The method can be used also for investigating aromatic hydrocarbon structures from other petroleum fractions.
Fresenius' Zeitschrift f�r Analytische Chemie, 1979
Fresenius' Zeitschrift f�r Analytische Chemie, 1988
A simple and fast column chromatographic procedure for the separation of vacuum residues into sat... more A simple and fast column chromatographic procedure for the separation of vacuum residues into saturates, mono-, di-, polyaromatics and polars has been standardized using silica-alumina-bauxite adsorbents and gradient elution with n-pentane, benzene, and methanol. The cut points have been monitored employing ultraviolet and infrared spectroscopy. The method is applicable for preparative separation of short residues from processed products.
Fresenius' Zeitschrift f�r Analytische Chemie, 1987
... die Bestim-mung kfirzerer Ketten durch die aromatische CH-Bande bei 740 cm-1 gest6rt wird, so... more ... die Bestim-mung kfirzerer Ketten durch die aromatische CH-Bande bei 740 cm-1 gest6rt wird, so ergibt sich doch aus den Wer-ten ffir ... References t. Fallah A, Badakhshan A, Etemad-Moghadam P, Seyed-Ahmadi A (1969) lran Petrol Inst Bull No.44 2. Ramaswamy V, Sarowha ...
Indian Journal of Thoracic and Cardiovascular Surgery, 2012
Objective To understand the morphology and mineral content in calcified atherosclerotic plaques. ... more Objective To understand the morphology and mineral content in calcified atherosclerotic plaques. Background Recent findings suggest that plaque calcification is biologically organized and regulated. Knowledge of morphology, location and mineral content of calcification in a plaque, could provide valuable insights into developing therapeutic interventions for calcific atherosclerotic disease. Methods We studied various patterns of calcification in atherosclerotic plaques using light and electron microscopy and analyzed their mineral composition by spectroscopic techniques.
Clays and Clay Minerals, 2006
ABSTRACT Alumina-pillared montmorillonite clays (Al-PILC), prepared under ultrasonic (US) agitati... more ABSTRACT Alumina-pillared montmorillonite clays (Al-PILC), prepared under ultrasonic (US) agitation and normal stirring (S) methods, have been used as a host material to encapsulate Co phthalocyanine (CoPc) complex. The amount of Co varies from 0.27 to 1.48 wt.% in the samples, depending on the input concentration of Co. Powder X-ray diffraction and other characterization techniques reveal that the structure of Al-PILC remains intact after the incorporation of the complex into the pores through a pyridine solution of the complex by ultrasonic agitation. A substantial decrease in the BET surface area and total pore volume of Al-PILC points to the occupation of the CoPc moieties within the porous structure of the pillared clay. This is further supported by the observation of a band at 1489 cm−1 in the Fourier transform infrared (FTIR) spectra of the encapsulated samples. The FTIR and diffuse reflectance ultraviolet-visible (DRUV-Vis) spectral results indicate that the encapsulated CoPc complex in the clay matrix undergoes distortion in order to accommodate itself within the pores of the Al-PILC. The encapsulated samples prepared by ultrasonification show better dispersion of the complex than the samples prepared under normal stirring conditions. Compared to the 'neat' complex, the encapsulated samples (CoPc in Al-PILC) exhibit greater turnover in the test reaction of the oxidation of benzyl alcohol to benzaldehyde with tert-butyl hydroperoxide as the oxidant at 373 K. The method of preparation and consequent site isolation of CoPc in Al-PILC influence the catalytic activity.
Materials Research Bulletin, May 1, 2007
We have carried out in situ high temperature X-ray diffraction (HTXRD) studies of silicalite-1 (S... more We have carried out in situ high temperature X-ray diffraction (HTXRD) studies of silicalite-1 (S-1) and metallosilicate molecular sieves containing iron, titanium and zirconium having Mobil Five (MFI) structure (iron silicalite-1 (FeS-1), titanium silicalite-1 (TS-1) and zirconium silicalite-1 (ZrS-1), respectively) in order to study the thermal stability of these materials. Isomorphous substitution of Si 4+ by metal atoms is confirmed by the expansion of unit cell volume by X-ray diffraction (XRD) and the presence of Si-O-M stretching band at $960 cm À1 by Fourier transform infrared (FTIR) spectroscopy. Appearance of cristobalite phase is seen at 1023 and 1173 K in S-1 and FeS-1 samples. While the samples S-1 and FeS-1 decompose completely to cristobalite at 1173 and 1323 K, respectively, the other two samples are thermally stable upto 1623 K. This transformation is irreversible. Although all materials show a negative lattice thermal expansion, their lattice thermal expansion coefficients vary. The thermal expansion behavior in all samples is anisotropic with relative strength of contraction along 'a' axes is more than along 'b' and 'c' axes in S-1, TS-1, ZrS-1 and vice versa in FeS-1. Lattice thermal expansion coefficients (a v ) in the temperature range 298-1023 K were À6.75 Â 10 À6 K À1 for S-1, À12.91 Â 10 À6 K À1 for FeS-1, À16.02 Â 10 À6 K À1 for TS-1 and À17.92 Â 10 À6 K À1 for ZrS-1. The highest lattice thermal expansion coefficients (a v ) obtained were À11.53 Â 10 À6 K À1 for FeS-1 in temperature range 298-1173 K, À20.86 Â 10 À6 K À1 for TS-1 and À25.54 Â 10 À6 K À1 for ZrS-1, respectively, in the temperature range 298-1623 K. Tetravalent cation substitution for Si 4+ in the lattice leads to a high thermal stability as compared to substitution by trivalent cations. #
Studies in Surface Science and Catalysis, 1998
ABSTRACT Powder diffraction patterns contain far poorer information than single crystal intensity... more ABSTRACT Powder diffraction patterns contain far poorer information than single crystal intensity data mainly due to equivalent and overlapping reflections. This report reviews the basic problems of powder X-ray diffraction studies of zeolites and molecular sieves, various techniques used for the refinement of the unit cell parameters encountered. Emphasis is given to the preparation of fully crystalline sample by carefully optimizing the conditions of crystallization and then collecting the data from the diffractometer. While indexing the powder patterns of known and unknown phases using computer programs, the problems encountered for indexing zeolite samples with large unit cells are discussed with examples. Scientists are still exploring new ideas and computer programs for the structural analysis of zeolites and molecular sieves from their powder x-ray diffraction profiles.
Materials Research Bulletin, 2004
... The studies either limit to the use of dilatometric technique to study the bulk thermal expan... more ... The studies either limit to the use of dilatometric technique to study the bulk thermal expansion or are related to the study of the tetragonal to monoclinic phase transition as a function of temperature, without any quantification or study of the change in lattice parameters or ...
Studies in Surface Science and Catalysis, 2004
ABSTRACT MgAPO-5 molecular sieves with AFI structure were crystallized at a faster rate using N, ... more ABSTRACT MgAPO-5 molecular sieves with AFI structure were crystallized at a faster rate using N, N-diisopropylethylamine as structure directing agent (SDA) for the first time. The results indicate that highly crystalline MgAPO-5 material could be obtained with the ratio x=Mg/(Mg+Al+P) varied from 0 to 0.11. Further increase in x to 0.2 molar fraction in the reaction gel yields MgAPO-5 associated with both MgAPO-47 (CHA-type) and an unknown phase. Characterization results, such as unit cell parameters, thermogravimetric analysis, pyridine adsorbed FT-IR and temperature-programmed desorption of ammonia indicate that Mg is incorporated into the framework of the molecular sieve. The 27Al MAS NMR spectra presented an intense signal at 36 ppm for the as-synthesized MgAPO-5 samples, typical of tetrahedrally coordinated aluminum. The 31P MAS NMR spectra of the as-synthesized MgAPO-5 samples exhibit a resonance at −30 ppm attributed to the P(4A1) and a shoulder or low intensity peak at −24 ppm which can be attributed to P(3Al, 1Mg) sites in the AFI framework. The signals at −7 and −2 ppm for samples with higher Mg content can be attributed to non-zeolitic phosphate species. Presence of strong structural Brönsted acid sites in MgAPO-5 samples is confirmed from the FT-IR spectra of adsorbed pyridine and temperature-programmed desorption of ammonia.
Microporous and Mesoporous Materials
The measurement of the thermal expansion behavior of silica polymorph of zeolite MFI (Silicalite-... more The measurement of the thermal expansion behavior of silica polymorph of zeolite MFI (Silicalite-1) was carried out in greater detail in the temperature range 373K–673K using high temperature X-ray diffraction (HTXRD) technique. The sample shows negative thermal expansion (NTE) in the temperature range studied, which is related to the transverse vibrations of the bridging oxygen atom between the two rigid polyhedrons. There is an anisotropy in the negative thermal expansion of this material that is contracting more along a axis than along the b and c axes. The bond angles and bond distances were determined from the Rietveld refinement data to look for any structural changes taking place as a function of temperature. The Si–O bond distances seem to play no role in the NTE, as there is no change in their distances as a function of temperature. It was observed that the Si–Si non-bonding distances for which the interatomic vectors are parallel to any of the crystallographic axes is resp...
Microporous and Mesoporous Materials
In the present investigations we have carried out the high temperature X-ray diffraction (HTXRD) ... more 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 ∞) 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 = ∞ < 100 < 75 < 50. It is concluded that by changing the composition of the framework of MFI, enhanced negative thermal expansion can be obtained.
Structural studies of Cu-doped zirconia samples with varying Cu content have been carried out. Co... more Structural studies of Cu-doped zirconia samples with varying Cu content have been carried out. Copperzirconia samples containing 2-20 mol% Cu were prepared by the co-precipitation technique using tetramethylammonium hydroxide as the precipitating agent and calcined at 773 K in air. The powder XRD data following Rietveld refinement revealed stabilization of zirconia in both tetragonal and cubic phases for all the samples with some monoclinic impurity phase. A decrease in the unit cell parameters of the cubic and tetragonal phase indicates incorporation of copper in the zirconia lattice of both the phases. An increase in the copper concentration (up to 20 mol%) stabilizes zirconia into the cubic phase at the expense of the tetragonal phase, with a decrease in the crystallite size (6-8 nm). Rietveld refinement of the high temperature XRD data reveals that both cubic and tetragonal phases exist up to 723 K with the cubic phase dominating (80% at 723 K). At temperature higher than 723 K, cubic phase gets transformed into the tetragonal phase, which further transforms into the monoclinic phase at 1173 K. At 1173 K, copper comes out of the cubic zirconia lattice forming a separate copper oxide phase and only the tetragonal and monoclinic polymorphs of zirconia exist. #
Materials Research Bulletin, 2007
We have carried out in situ high temperature X-ray diffraction (HTXRD) studies of silicalite-1 (S... more We have carried out in situ high temperature X-ray diffraction (HTXRD) studies of silicalite-1 (S-1) and metallosilicate molecular sieves containing iron, titanium and zirconium having Mobil Five (MFI) structure (iron silicalite-1 (FeS-1), titanium silicalite-1 (TS-1) and zirconium silicalite-1 (ZrS-1), respectively) in order to study the thermal stability of these materials. Isomorphous substitution of Si 4+ by metal atoms is confirmed by the expansion of unit cell volume by X-ray diffraction (XRD) and the presence of Si-O-M stretching band at $960 cm À1 by Fourier transform infrared (FTIR) spectroscopy. Appearance of cristobalite phase is seen at 1023 and 1173 K in S-1 and FeS-1 samples. While the samples S-1 and FeS-1 decompose completely to cristobalite at 1173 and 1323 K, respectively, the other two samples are thermally stable upto 1623 K. This transformation is irreversible. Although all materials show a negative lattice thermal expansion, their lattice thermal expansion coefficients vary. The thermal expansion behavior in all samples is anisotropic with relative strength of contraction along 'a' axes is more than along 'b' and 'c' axes in S-1, TS-1, ZrS-1 and vice versa in FeS-1. Lattice thermal expansion coefficients (a v ) in the temperature range 298-1023 K were À6.75 Â 10 À6 K À1 for S-1, À12.91 Â 10 À6 K À1 for FeS-1, À16.02 Â 10 À6 K À1 for TS-1 and À17.92 Â 10 À6 K À1 for ZrS-1. The highest lattice thermal expansion coefficients (a v ) obtained were À11.53 Â 10 À6 K À1 for FeS-1 in temperature range 298-1173 K, À20.86 Â 10 À6 K À1 for TS-1 and À25.54 Â 10 À6 K À1 for ZrS-1, respectively, in the temperature range 298-1623 K. Tetravalent cation substitution for Si 4+ in the lattice leads to a high thermal stability as compared to substitution by trivalent cations. #
Materials Research Bulletin, 2006
In situ high temperature X-ray diffraction (HTXRD) studies on monoclinic silicalite-1 (S-1, silic... more In situ high temperature X-ray diffraction (HTXRD) studies on monoclinic silicalite-1 (S-1, silica polymorph of ZSM-5) and an orthorhombic metallosilicate molecular sieve, zirconium silicalite-1 (ZrS-1) with MFI structure (Si/Zr = 50) have been carried out using a laboratory X-ray diffractometer with an Anton Parr HTK 1600 attachment. While the structure of the S-1 collapsed at 1123 K forming a-cristobalite. S-1 and ZrS-1 showed a complex thermal expansion behavior in the temperature range 298-1023 K, ZrS-1 was stable. Powder X-ray diffraction (PXRD) data taken in this region have shown strong negative lattice thermal expansion coefficient, a V = À6.75 Â 10 À6 and À17.92 Â 10 À6 K À1 in the temperature range 298-1023 K À1 for S-1 and ZrS-1 samples, respectively. The thermal expansion behavior of S-1 and ZrS-1 is anisotropic, with the relative strength of contraction along a axis is more than that along b and c axes. Three different thermal expansion regions could be identified in the overall temperature range (298-1023 K) studied, corroborating with the three steps of weight loss in the TG curve of ZrS-1 sample. While the region between 298 and 423 K, displays positive thermal expansion coefficient with a V = 2.647 Â 10 À6 and 4.24 Â 10 À6 K À1 , the second region between 423 and 873 K shows strong negative thermal expansion (NTE) coefficient a V = À7.602 Â 10 À6 and À15.04 Â 10 À6 K À1 , respectively, for S-1 and ZrS-1 samples. The region between 873 and 1023 K, shows a very strong NTE coefficient with a V = À12.08 Â 10 À6 and À45.622 Â 10 À6 K À1 for S-1 and ZrS-1, respectively, which is the highest in the whole temperature range studied. NTE seen over a temperature range 298-1023 K could be associated with transverse vibrations of bridging oxygen atoms in the structure which results in an apparent shortening of the Si-O distances. #
Journal of Chemical Technology & Biotechnology, 2007
... Veda Ramaswamy, Vimal Kothiyal, Indra D. Singh and Rajamani Krishna ... The authors wish to t... more ... Veda Ramaswamy, Vimal Kothiyal, Indra D. Singh and Rajamani Krishna ... The authors wish to thank J. M. Nagpal of the Crude Evaluation Laboratory of the Institute for providing the FTA data, and S. M. Nanoti and P. B. Semwal for the computational work. REFERENCES ...
Fresenius' Zeitschrift f�r Analytische Chemie, 1984
Zusammenfassang. Zur Trennung der Erd61fraktion vom Siedebereich des Gas61s in die ein-, zwei-und... more Zusammenfassang. Zur Trennung der Erd61fraktion vom Siedebereich des Gas61s in die ein-, zwei-und dreikernigen aromatischen Bestandteile wird eine Gradientenelution an einer Aluminiumoxids/iule unter standardisierten Bedingungen angewendet. Zur Charakterisierung dienen UV-spektrometrische Messungen. Das Verfahren kann auch zur Untersuchung yon Aromaten aus anderen Erd61fraktionen eingesetzt werden. Summary. The method described is a simple procedure for separating gas oil boiling range petroleum fraction into its aromatic hydrocarbons of the mono-, di-and trinucleartype. This is accomplished by gradient elution through an alumina adsorption column under established/standardised conditions. Characterisation is performed by UV-absorption. The method can be used also for investigating aromatic hydrocarbon structures from other petroleum fractions.
Fresenius' Zeitschrift f�r Analytische Chemie, 1979
Fresenius' Zeitschrift f�r Analytische Chemie, 1988
A simple and fast column chromatographic procedure for the separation of vacuum residues into sat... more A simple and fast column chromatographic procedure for the separation of vacuum residues into saturates, mono-, di-, polyaromatics and polars has been standardized using silica-alumina-bauxite adsorbents and gradient elution with n-pentane, benzene, and methanol. The cut points have been monitored employing ultraviolet and infrared spectroscopy. The method is applicable for preparative separation of short residues from processed products.
Fresenius' Zeitschrift f�r Analytische Chemie, 1987
... die Bestim-mung kfirzerer Ketten durch die aromatische CH-Bande bei 740 cm-1 gest6rt wird, so... more ... die Bestim-mung kfirzerer Ketten durch die aromatische CH-Bande bei 740 cm-1 gest6rt wird, so ergibt sich doch aus den Wer-ten ffir ... References t. Fallah A, Badakhshan A, Etemad-Moghadam P, Seyed-Ahmadi A (1969) lran Petrol Inst Bull No.44 2. Ramaswamy V, Sarowha ...
Indian Journal of Thoracic and Cardiovascular Surgery, 2012
Objective To understand the morphology and mineral content in calcified atherosclerotic plaques. ... more Objective To understand the morphology and mineral content in calcified atherosclerotic plaques. Background Recent findings suggest that plaque calcification is biologically organized and regulated. Knowledge of morphology, location and mineral content of calcification in a plaque, could provide valuable insights into developing therapeutic interventions for calcific atherosclerotic disease. Methods We studied various patterns of calcification in atherosclerotic plaques using light and electron microscopy and analyzed their mineral composition by spectroscopic techniques.
Clays and Clay Minerals, 2006
ABSTRACT Alumina-pillared montmorillonite clays (Al-PILC), prepared under ultrasonic (US) agitati... more ABSTRACT Alumina-pillared montmorillonite clays (Al-PILC), prepared under ultrasonic (US) agitation and normal stirring (S) methods, have been used as a host material to encapsulate Co phthalocyanine (CoPc) complex. The amount of Co varies from 0.27 to 1.48 wt.% in the samples, depending on the input concentration of Co. Powder X-ray diffraction and other characterization techniques reveal that the structure of Al-PILC remains intact after the incorporation of the complex into the pores through a pyridine solution of the complex by ultrasonic agitation. A substantial decrease in the BET surface area and total pore volume of Al-PILC points to the occupation of the CoPc moieties within the porous structure of the pillared clay. This is further supported by the observation of a band at 1489 cm−1 in the Fourier transform infrared (FTIR) spectra of the encapsulated samples. The FTIR and diffuse reflectance ultraviolet-visible (DRUV-Vis) spectral results indicate that the encapsulated CoPc complex in the clay matrix undergoes distortion in order to accommodate itself within the pores of the Al-PILC. The encapsulated samples prepared by ultrasonification show better dispersion of the complex than the samples prepared under normal stirring conditions. Compared to the 'neat' complex, the encapsulated samples (CoPc in Al-PILC) exhibit greater turnover in the test reaction of the oxidation of benzyl alcohol to benzaldehyde with tert-butyl hydroperoxide as the oxidant at 373 K. The method of preparation and consequent site isolation of CoPc in Al-PILC influence the catalytic activity.
Materials Research Bulletin, May 1, 2007
We have carried out in situ high temperature X-ray diffraction (HTXRD) studies of silicalite-1 (S... more We have carried out in situ high temperature X-ray diffraction (HTXRD) studies of silicalite-1 (S-1) and metallosilicate molecular sieves containing iron, titanium and zirconium having Mobil Five (MFI) structure (iron silicalite-1 (FeS-1), titanium silicalite-1 (TS-1) and zirconium silicalite-1 (ZrS-1), respectively) in order to study the thermal stability of these materials. Isomorphous substitution of Si 4+ by metal atoms is confirmed by the expansion of unit cell volume by X-ray diffraction (XRD) and the presence of Si-O-M stretching band at $960 cm À1 by Fourier transform infrared (FTIR) spectroscopy. Appearance of cristobalite phase is seen at 1023 and 1173 K in S-1 and FeS-1 samples. While the samples S-1 and FeS-1 decompose completely to cristobalite at 1173 and 1323 K, respectively, the other two samples are thermally stable upto 1623 K. This transformation is irreversible. Although all materials show a negative lattice thermal expansion, their lattice thermal expansion coefficients vary. The thermal expansion behavior in all samples is anisotropic with relative strength of contraction along 'a' axes is more than along 'b' and 'c' axes in S-1, TS-1, ZrS-1 and vice versa in FeS-1. Lattice thermal expansion coefficients (a v ) in the temperature range 298-1023 K were À6.75 Â 10 À6 K À1 for S-1, À12.91 Â 10 À6 K À1 for FeS-1, À16.02 Â 10 À6 K À1 for TS-1 and À17.92 Â 10 À6 K À1 for ZrS-1. The highest lattice thermal expansion coefficients (a v ) obtained were À11.53 Â 10 À6 K À1 for FeS-1 in temperature range 298-1173 K, À20.86 Â 10 À6 K À1 for TS-1 and À25.54 Â 10 À6 K À1 for ZrS-1, respectively, in the temperature range 298-1623 K. Tetravalent cation substitution for Si 4+ in the lattice leads to a high thermal stability as compared to substitution by trivalent cations. #
Studies in Surface Science and Catalysis, 1998
ABSTRACT Powder diffraction patterns contain far poorer information than single crystal intensity... more ABSTRACT Powder diffraction patterns contain far poorer information than single crystal intensity data mainly due to equivalent and overlapping reflections. This report reviews the basic problems of powder X-ray diffraction studies of zeolites and molecular sieves, various techniques used for the refinement of the unit cell parameters encountered. Emphasis is given to the preparation of fully crystalline sample by carefully optimizing the conditions of crystallization and then collecting the data from the diffractometer. While indexing the powder patterns of known and unknown phases using computer programs, the problems encountered for indexing zeolite samples with large unit cells are discussed with examples. Scientists are still exploring new ideas and computer programs for the structural analysis of zeolites and molecular sieves from their powder x-ray diffraction profiles.
Materials Research Bulletin, 2004
... The studies either limit to the use of dilatometric technique to study the bulk thermal expan... more ... The studies either limit to the use of dilatometric technique to study the bulk thermal expansion or are related to the study of the tetragonal to monoclinic phase transition as a function of temperature, without any quantification or study of the change in lattice parameters or ...
Studies in Surface Science and Catalysis, 2004
ABSTRACT MgAPO-5 molecular sieves with AFI structure were crystallized at a faster rate using N, ... more ABSTRACT MgAPO-5 molecular sieves with AFI structure were crystallized at a faster rate using N, N-diisopropylethylamine as structure directing agent (SDA) for the first time. The results indicate that highly crystalline MgAPO-5 material could be obtained with the ratio x=Mg/(Mg+Al+P) varied from 0 to 0.11. Further increase in x to 0.2 molar fraction in the reaction gel yields MgAPO-5 associated with both MgAPO-47 (CHA-type) and an unknown phase. Characterization results, such as unit cell parameters, thermogravimetric analysis, pyridine adsorbed FT-IR and temperature-programmed desorption of ammonia indicate that Mg is incorporated into the framework of the molecular sieve. The 27Al MAS NMR spectra presented an intense signal at 36 ppm for the as-synthesized MgAPO-5 samples, typical of tetrahedrally coordinated aluminum. The 31P MAS NMR spectra of the as-synthesized MgAPO-5 samples exhibit a resonance at −30 ppm attributed to the P(4A1) and a shoulder or low intensity peak at −24 ppm which can be attributed to P(3Al, 1Mg) sites in the AFI framework. The signals at −7 and −2 ppm for samples with higher Mg content can be attributed to non-zeolitic phosphate species. Presence of strong structural Brönsted acid sites in MgAPO-5 samples is confirmed from the FT-IR spectra of adsorbed pyridine and temperature-programmed desorption of ammonia.
Microporous and Mesoporous Materials
The measurement of the thermal expansion behavior of silica polymorph of zeolite MFI (Silicalite-... more The measurement of the thermal expansion behavior of silica polymorph of zeolite MFI (Silicalite-1) was carried out in greater detail in the temperature range 373K–673K using high temperature X-ray diffraction (HTXRD) technique. The sample shows negative thermal expansion (NTE) in the temperature range studied, which is related to the transverse vibrations of the bridging oxygen atom between the two rigid polyhedrons. There is an anisotropy in the negative thermal expansion of this material that is contracting more along a axis than along the b and c axes. The bond angles and bond distances were determined from the Rietveld refinement data to look for any structural changes taking place as a function of temperature. The Si–O bond distances seem to play no role in the NTE, as there is no change in their distances as a function of temperature. It was observed that the Si–Si non-bonding distances for which the interatomic vectors are parallel to any of the crystallographic axes is resp...
Microporous and Mesoporous Materials
In the present investigations we have carried out the high temperature X-ray diffraction (HTXRD) ... more 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 ∞) 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 = ∞ < 100 < 75 < 50. It is concluded that by changing the composition of the framework of MFI, enhanced negative thermal expansion can be obtained.
Structural studies of Cu-doped zirconia samples with varying Cu content have been carried out. Co... more Structural studies of Cu-doped zirconia samples with varying Cu content have been carried out. Copperzirconia samples containing 2-20 mol% Cu were prepared by the co-precipitation technique using tetramethylammonium hydroxide as the precipitating agent and calcined at 773 K in air. The powder XRD data following Rietveld refinement revealed stabilization of zirconia in both tetragonal and cubic phases for all the samples with some monoclinic impurity phase. A decrease in the unit cell parameters of the cubic and tetragonal phase indicates incorporation of copper in the zirconia lattice of both the phases. An increase in the copper concentration (up to 20 mol%) stabilizes zirconia into the cubic phase at the expense of the tetragonal phase, with a decrease in the crystallite size (6-8 nm). Rietveld refinement of the high temperature XRD data reveals that both cubic and tetragonal phases exist up to 723 K with the cubic phase dominating (80% at 723 K). At temperature higher than 723 K, cubic phase gets transformed into the tetragonal phase, which further transforms into the monoclinic phase at 1173 K. At 1173 K, copper comes out of the cubic zirconia lattice forming a separate copper oxide phase and only the tetragonal and monoclinic polymorphs of zirconia exist. #
Materials Research Bulletin, 2007
We have carried out in situ high temperature X-ray diffraction (HTXRD) studies of silicalite-1 (S... more We have carried out in situ high temperature X-ray diffraction (HTXRD) studies of silicalite-1 (S-1) and metallosilicate molecular sieves containing iron, titanium and zirconium having Mobil Five (MFI) structure (iron silicalite-1 (FeS-1), titanium silicalite-1 (TS-1) and zirconium silicalite-1 (ZrS-1), respectively) in order to study the thermal stability of these materials. Isomorphous substitution of Si 4+ by metal atoms is confirmed by the expansion of unit cell volume by X-ray diffraction (XRD) and the presence of Si-O-M stretching band at $960 cm À1 by Fourier transform infrared (FTIR) spectroscopy. Appearance of cristobalite phase is seen at 1023 and 1173 K in S-1 and FeS-1 samples. While the samples S-1 and FeS-1 decompose completely to cristobalite at 1173 and 1323 K, respectively, the other two samples are thermally stable upto 1623 K. This transformation is irreversible. Although all materials show a negative lattice thermal expansion, their lattice thermal expansion coefficients vary. The thermal expansion behavior in all samples is anisotropic with relative strength of contraction along 'a' axes is more than along 'b' and 'c' axes in S-1, TS-1, ZrS-1 and vice versa in FeS-1. Lattice thermal expansion coefficients (a v ) in the temperature range 298-1023 K were À6.75 Â 10 À6 K À1 for S-1, À12.91 Â 10 À6 K À1 for FeS-1, À16.02 Â 10 À6 K À1 for TS-1 and À17.92 Â 10 À6 K À1 for ZrS-1. The highest lattice thermal expansion coefficients (a v ) obtained were À11.53 Â 10 À6 K À1 for FeS-1 in temperature range 298-1173 K, À20.86 Â 10 À6 K À1 for TS-1 and À25.54 Â 10 À6 K À1 for ZrS-1, respectively, in the temperature range 298-1623 K. Tetravalent cation substitution for Si 4+ in the lattice leads to a high thermal stability as compared to substitution by trivalent cations. #
Materials Research Bulletin, 2006
In situ high temperature X-ray diffraction (HTXRD) studies on monoclinic silicalite-1 (S-1, silic... more In situ high temperature X-ray diffraction (HTXRD) studies on monoclinic silicalite-1 (S-1, silica polymorph of ZSM-5) and an orthorhombic metallosilicate molecular sieve, zirconium silicalite-1 (ZrS-1) with MFI structure (Si/Zr = 50) have been carried out using a laboratory X-ray diffractometer with an Anton Parr HTK 1600 attachment. While the structure of the S-1 collapsed at 1123 K forming a-cristobalite. S-1 and ZrS-1 showed a complex thermal expansion behavior in the temperature range 298-1023 K, ZrS-1 was stable. Powder X-ray diffraction (PXRD) data taken in this region have shown strong negative lattice thermal expansion coefficient, a V = À6.75 Â 10 À6 and À17.92 Â 10 À6 K À1 in the temperature range 298-1023 K À1 for S-1 and ZrS-1 samples, respectively. The thermal expansion behavior of S-1 and ZrS-1 is anisotropic, with the relative strength of contraction along a axis is more than that along b and c axes. Three different thermal expansion regions could be identified in the overall temperature range (298-1023 K) studied, corroborating with the three steps of weight loss in the TG curve of ZrS-1 sample. While the region between 298 and 423 K, displays positive thermal expansion coefficient with a V = 2.647 Â 10 À6 and 4.24 Â 10 À6 K À1 , the second region between 423 and 873 K shows strong negative thermal expansion (NTE) coefficient a V = À7.602 Â 10 À6 and À15.04 Â 10 À6 K À1 , respectively, for S-1 and ZrS-1 samples. The region between 873 and 1023 K, shows a very strong NTE coefficient with a V = À12.08 Â 10 À6 and À45.622 Â 10 À6 K À1 for S-1 and ZrS-1, respectively, which is the highest in the whole temperature range studied. NTE seen over a temperature range 298-1023 K could be associated with transverse vibrations of bridging oxygen atoms in the structure which results in an apparent shortening of the Si-O distances. #