Electron donating properties and catalytic actiVity of cerium oxide and its mixed oxides with alumina

The electron donating properties of Ce02 and its mixed oxides with alumina have been determined from the studies of adsorption of electron acceptors of various electron affinities on the surface of these oxides. The catalytic activity of these oxides towards some reactions such as oxidation of alcohols and reduction of ketones have been Correlated with their surface electrondonor properties. The surface acidity/basicity of these oxides have also been determined by titration method using a set of Hammett indicators.

Basicity and electron donor properties of lanthanum oxide and its mixed oxides with alumina

The electron donating properties of La2O3 activated at 300, 500 and 800·C and its mixed oxides with alumina are reported from the studies on adsorption of electron acceptors of varying electron affinity on La203. The electron acceptors with their electron affinity values given in parenthesis are: 7,7,8,8-tetracyanoquinodimethane (2.84 eV), 2,3,5,6-tetrachloro-I,4-benzoquinone (2.40 eV) and p-dinitrobenzene(l.77eV). The basicity of the oxide has been determined by titration with n-butylamine and Ho.max values are reported. The limit of electron transfer from the oxide to the electron acceptor is between 2.40 and 1.77 eV. It is observed that La203 promotes the surface electron properties of alumina without changing its limit of electron transfer.

Surface acidity/basicity and catalytic activity of Zr-Sm mixed oxide systems

The surface acidity and basicity of oxides of Sm and Zr and their mixed oxides have been determined using a set of Hammett indicators. The data have been correlated with the catalytic activity of these oxides towards the liquid phase reduction of cyclo-hexanone in 2-propanol.

Acid-base, electron-donating and magnetic properties of Nd2O3 and its mixed oxides with alumina catalysts

The electron donor properties of Nd2O3 activated at 300, 500 and 800°C were investigated through studies on the adsorption of electron acceptors of various electron affinities - 7, 7, 8,8-tetracyanoquinodimethane (2.84 eV). 2, 3, 5, 6-tetrachloro-l , 4-benzoquinone (2.40 eV). p-dinitrobenzene (1.77 eV), and m-dinitrobenzene (1.26 eV) in solvents acetonitrile and 1, 4-dioxan. The extent of electron transfer during adsorption has been found from magnetic measurements and electronic spectral data. The corresponding data on mixed oxides of neodymium and aluminium are reported for various. compositions. The acid-base properties of catalysts were also determined using a set of Hammett indicators.

Surface acidity/basicity of yttria and its mixed oxides with alumina catalysts

Acid/base strength distribution of Y2O3 and its mixed oxides with alumina catalysts are measured on Hammett acidity function scale and expressed in terms of H0max value. Basicity of Y2O3 increases with increase in activation temperature and for mixed oxides the basicity increases with increase in concentration of Y2O3, in the catalyst.

Electron Donating Property and Catalytic Activity of Perovskite-type Mixed Oxides (ABO3 ) Consisting of Rare Earth and 3d Transition Metals

The catalytic activity of Perovskite-type mixed oxides (LaCo03 . PrCo03 and SmCo03 ) for the reduction of cyclohexanone to cyclohexanol with 2-propanol (Meerwein-Ponndorf-Verley reduction) has been studied. The data have been correlated with the surface electron donor properties of these mixed oxides.

Wet peroxide oxidation of phenol over mixed pillared montmorillonites

Wet peroxide oxidation (WPO) of phenol is an effective means for the production of diphenols, which are of great industrial importance. An added advantage of this method is the removal of phenol from wastewater effluents. Hydroxylation of phenol occurs efficiently over mixed iron aluminium pillared montmorillonites. An initial induction period is noticed in all cases. A thorough study on the reaction variables suggests free radical mechanism for the reaction.

Surface Electron Donor Properties of Dy2O3,Y2O3 and Their Mixed Oxides with Alumina Catalyst

The limit of electron transfer in electron affinity from the oxide surface to the electron acceptor (EA) are reported from the adsorption of EA on DY203, mixed oxides of DY203 with alumina and mixed oxides of Y203 with y-alumina. The extent of electron transfer is understood from magnetic measurements.

Catalytic activity of some of the perovskite-type mixed oxides (ABO3) consisting of rare earth and 3d transition metals

The catalytic activity of some of the ABO3 (A = La, Pr and Sm, B= Cr, Mn, Fe, Co and Ni) perovskite-type oxides for the liquid phase reduction of ketone and oxidation of alcohol in 2-propanol medium has been studied. The data have been correlated with the surface electron donor properties of these oxides. The surface electron donor properties have been determined from the adsorption of electron acceptors of varying electron affinities on the oxide surface.

Surface acidity/basicity and catalytic activity of mixed oxides of Zr, La and Al

The surface acidity/basicity of binary oxides of Zr and La and the ternary oxides of Zr, La and Al are reported. The data have been correlated with their catalytic activity towards liquid phase reduction of cyclohexanone.

Acidity, basicity and catalytic activity of La−Zn mixed oxides

Surface acidity/Basicity of mixed oxides of La and Zn activated at three different temperatures were determined. The data have been correlated with the catalytic activity for liquid phase reduction of cyclohexanone in isopropanol.

Anomalous variation of thermal lens signal with concentration from rhodamine B in methanol solution

Thermal lens signals in solutions of rhodamine B laser dye in methanol are measured using the dual beam pump-probe technique. The nature of variations of signal strength with concentration is found to be different for 514 and 488 nm Ar + laser excitations. However, both the pump wavelengths produce an oscillatory type variation of thermal lens signal amplitude with the concentration of the dye solution. Probable reasons for this peculiar behaviour (which is absent in the case of fluorescent intensity) are mentioned.

Photoacoustic signal saturation and optical limiting in C70-toluene solution

Pulsed photoacoustic studies in solutions of C70 in toluene are made using the 532-nm radiation from a frequency-doubled Nd:YAG laser. It is found that contrary to expectation, there is no photoacoustic (PA) signal enhancement in the power-limiting range of laser fluences. Instead, the PA signal tends to saturate during optical power-limiting phenomenon. This could be due to the enhanced optical absorption from the photoexcited state and hence the depletion of the ground-state population. PA measurements also ruled out the possibility of multiphoton absorption in the C70 solution. We demonstrate that the nonlinear absorption leading to optical limiting is mainly due to reverse saturable absorption.

Photopyroelectric study of thermal properties and phase transitions in selected solids

This thesis presents in detail. the theoretical developments and calculations which are used for the simultaneous determination of thermal parameters, namely thermal diffusivity (a). thermal effusivity (e), thermal conductivity (K) and heat capacity (cr ) employing photopyroelectric technique. In our calculations. we have assumed that the pyroelectric detector is supported on a copper backing. so that there will be sufficient heat exchange between the heated pyroelectric detector and the backing so that the signal fluctuations are reduced to a minimum. Since the PPE signal depends on the properties of the detector that are also temperature dependent. a careful temperature calibration of the system need to be carried out. APPE cell has been fabricated for the measurements that can be used to measure the thermal properties of solid samples from ~ 90 K to ~ 350 K. The cell has been calibrated using standard samples and the accuracy of the technique is found to be of the order of± 1%.In this thesis, we have taken up work n photopyroelectric investigation of thermal parameters of ferroelectric crystals such as Glycine phosphite (NH3CH2COOH3P03), Triglycine sulfate and Thiourea as well as mixed valence perovskites samples such as Lead doped Lanthanum Manganate (Lal_xPb~Mn03) Calcium doped (Lal_xCaxMnOJ) and Nickel doped Lanthanum Stroncium Cobaltate (Lao~Sro5Ni,Col_x03).The three ferroelectric crystals are prepared by the slow evaporation technique and the mixed valence perovskites by solid state reaction technique.Mixed valence perovskites, with the general formula RI_xA~Mn03 (R = La. Nd or Pr and A = Ba, Ca, Sr or Pb) have been materials of intense experimental and theoretical studies over the past few years. These materials show . colossal magneloresis/ance' (CMR) in samples with 0.2 < x < 0.5 in such a doping region, resistivity exhibits a peak at T = T p' the metal - insulator transition temperature. The system exhibits metallic characteristics with d %T > Oabove Tp (wherep is the resistivity) and insulating characteristics with d % T < 0 above T p. Despite intensive investigations on the CMR phenomena and associated electrical properties. not much work has been done on the variation of thermal properties of these samples. We have been quite successful in finding out the nature of anomaly associated with thermal properties when the sample undergoes M-I transition.The ferroelectric crystal showing para-ferroelectric phase transitions - Glycine phosphite. Thiourea and Triglycine sulfate - are studied in detail in order to see how well the PPE technique enables one to measure the thermal parameters during phase transitions. It is seen that the phase transition gets clearly reflected in the variation of thermal parameters. The anisotropy in thermal transport along different crystallographic directions are explained in terms of the elastic anisotropy and lattice contribution to the thermal conductivity. Interesting new results have been obtained on the above samples and are presented in three different chapters of the thesis.In summary. we have carried investigations of the variations of the thermal parameters during phase transitions employing photopyroelectric technique. The results obtained on different systems are important not only in understanding the physics behind the transitions but also in establishing the potentiality of the PPE tool. The full potential of PPE technique for the investigation of optical and thermal properties of materials still remains to be taken advantage of by workers in this field.

Permutation entropy based real-time chatter detection using audio signal in turning process

Machine tool chatter is an unfavorable phenomenon during metal cutting, which results in heavy vibration of cutting tool. With increase in depth of cut, the cutting regime changes from chatter-free cutting to one with chatter. In this paper, we propose the use of permutation entropy (PE), a conceptually simple and computationally fast measurement to detect the onset of chatter from the time series using sound signal recorded with a unidirectional microphone. PE can efficiently distinguish the regular and complex nature of any signal and extract information about the dynamics of the process by indicating sudden change in its value. Under situations where the data sets are huge and there is no time for preprocessing and fine-tuning, PE can effectively detect dynamical changes of the system. This makes PE an ideal choice for online detection of chatter, which is not possible with other conventional nonlinear methods. In the present study, the variation of PE under two cutting conditions is analyzed. Abrupt variation in the value of PE with increase in depth of cut indicates the onset of chatter vibrations. The results are verified using frequency spectra of the signals and the nonlinear measure, normalized coarse-grained information rate (NCIR).