Luis Torres - Academia.edu (original) (raw)

Papers by Luis Torres

Chemosphere, 2008

The purpose of this investigation was to examine the proposition that creosote, emplaced in an in... more The purpose of this investigation was to examine the proposition that creosote, emplaced in an initially water saturated porous system, can be removed from the system through Pickering emulsion formation. Pickering emulsions are dispersions of two immiscible fluids in which coalescence of the dispersed phase droplets is hindered by the presence of colloidal particles adsorbed at the interface between the two immiscible fluid phases. Particle trapping is strongly favoured when the wetting properties of the particles are intermediate between strong water wetting and strong oil wetting. In this investigation the necessary chemical conditions for the formation of physically stable creosote-in-water emulsions protected against coalescence by bentonite particles were examined. It was established that physically stable emulsions could be formed through the judicious addition of small amounts of sodium chloride and the surfactant cetyl-trimethylammonium bromide. The stability of the emulsions was initially established by visual inspection. However, experimental determinations of emulsion stability were also undertaken by use of oscillatory rheology. Measurements of the elastic and viscous responses to shear indicated that physically stable emulsions were obtained when the viscoelastic systems showed a predominantly elastic response to shearing. Once the conditions were established for the formation of physically stable emulsions a ''proof-of-concept'' chromatographic experiment was carried out which showed that creosote could be successfully removed from a saturated model porous system.

Applied Physics a-Materials Science & Processing, 1992

A systematic study of the frequency dependence, from 26.5 to 60 GHz, of the ferromagnetic resonan... more A systematic study of the frequency dependence, from 26.5 to 60 GHz, of the ferromagnetic resonance linewidth for technologically useful nickel ferrites is presented in a wide range of compositions for both single-crystal and polycrystalline samples. The FMR linewidth of the polycrystalline samples appears to be virtually independent of the frequency. Theoretical approaches are applied in our range of frequencies

Applied Physics a-Materials Science & Processing, 1993

The time dependence of the field-cooled susceptibility in polycrystalline samples of YBa2Cu3O7 ha... more The time dependence of the field-cooled susceptibility in polycrystalline samples of YBa2Cu3O7 has been studied in the temperature range 77–95 K. Field-cooled and zero-field-cooled susceptibility measurements and its variation with the ac magnetic field are also reported. Measurements have been carried out by means of an inductive technique. Our fully automatic system allows us to measure the first data points

Ieee Transactions on Magnetics, 1993

Ferrimagnetic resonance (FMR) linewidths have been measured at X-band frequencies (11 GHz) from 7... more Ferrimagnetic resonance (FMR) linewidths have been measured at X-band frequencies (11 GHz) from 77 K to 400 K in single crystal nickel ferrites with composition NixFe3-xO 4 with x=0.9, 1.0, 1.2. Measurements have been carried out by means of an automatic technique based on a modified short-circuit SMA transmission line. Linewidths ranged from 40 Oe to 80 Oe in all

Journal of Applied Physics, 1993

ABSTRACT

Ieee Transactions on Magnetics, 1993

The relaxation of the initial permeability is measured in barium ferrite samples with W-hexagonal... more The relaxation of the initial permeability is measured in barium ferrite samples with W-hexagonal structure. In the temperature range between 80 and 420 K three clear relaxation processes are found; these features are influenced by sintering temperature and atmosphere. Peak C (370 K) seems to arise from long range cation diffusion processes via vacancies, with activation energies around 1.1 eV.

Journal of Applied Physics, 1994

The frequency dependence of the ac susceptibility in polycrystalline samples of YBaCuO has been s... more The frequency dependence of the ac susceptibility in polycrystalline samples of YBaCuO has been studied at the ac field range 0.06-1.2 Oe. The curve of the real part of the susceptibility x' exhibits two drops, the first one close to T, and the other well below T, which could correspond to screening behavior of the grains and grain boundaries, respectively. The imaginary part of the susceptibility shows only a peak below T, which is related to hysteresis losses at the grain boundaries. The peak corresponding to intragrains hysteresis losses is very small and appears masked by the losses of the intergrains. In the range of l-20 kHz, the onset temperature of x' showed no frequency dependence. However, the width of the transition decreases lightly and there is a small shift in the peak of f to higher temperature as the frequency increases. This behavior could be explained in terms of the thermally activated Anderson flux creep. The shift depends on the amplitude of the measuring field. The activation energy for flux creep ranges from 6.4 eV at 0.02 Oe to 3.23 eV at 1.2 Oe in the zero-field-cooled measurements and from 3.41 eV at 0.02 Oe to 1.41 eV at 1.2 Oe in the field-cooled measurements.

Physica Status Solidi a-Applied Research, 1994

Ieee Transactions on Magnetics, 1994

Magnetic disaccommodation spectra (77-420 K) for YIG polycrystalline samples sintered during 8 ho... more Magnetic disaccommodation spectra (77-420 K) for YIG polycrystalline samples sintered during 8 hours in air atmosphere at different sintering temperatures ranging from 1350°C to 1450°C are presented, Samples sintered at temperatures from 1350°C to 1415°C present a relaxation process around 125 K, its amplitude decreases with increasing sintering temperature and its activation energy is close to 0.34 eV, For samples

Journal of Magnetism and Magnetic Materials, 1995

The frequency dependence of the ac susceptibility in polycrystalline samples of Bi0.7Pb0.3SrCaCu]... more The frequency dependence of the ac susceptibility in polycrystalline samples of Bi0.7Pb0.3SrCaCu].80 x has been studied in the range 1-20 kHz. The peak in the imaginary part of the susceptibility shifts slightly to higher temperature as the frequency increases. This behavior could be explained in terms of thermally activated flux creep. The activation energy for flux creep ranges from 2 eV at 0.06 Oe to 0.5 eV at 1

Applied Physics Letters, 1995

ABSTRACT

Journal of Magnetism and Magnetic Materials, 1995

Disaccommodation (DA) spectra for single crystal nickel ferrites of composition NixFe3_xO 4 with ... more Disaccommodation (DA) spectra for single crystal nickel ferrites of composition NixFe3_xO 4 with x = 0.9, 1.0 and 1.2 have been measured. Our results are compared with measurements of ferromagnetic resonance (FMR) on the same samples. Qualitative comparation between the two kinds of measurements (DA and FMR) by means of induced anisotropy formalism is provided.

Applied Physics a-Materials Science & Processing, 1995

... A pplied .s,os,e Science & I ly ~,.~1~,,~ Processing 9 Springer-Verlag 1995 Comparison be... more ... A pplied .s,os,e Science & I ly ~,.~1~,,~ Processing 9 Springer-Verlag 1995 Comparison between disaccommodation and ferromagnetic resonance measurements in polycrystalline nickel ferrites L. Torres t, M. Zazo 1, J. Ifiiguez 1, C. de Francisco 2, JM Mufioz 2 ...

Journal of Applied Physics, 1996

ABSTRACT

Applied Physics Letters, 1996

ABSTRACT

Journal of Magnetism and Magnetic Materials, 1996

The relaxation of the initial permeability after sample demagnetization has been measured in poly... more The relaxation of the initial permeability after sample demagnetization has been measured in polycrystalline strontium ferrite samples with nominal composition SrO • 6Fe203 (M-phase), sintered under different oxygen pressures, and has been represented by isochronal curves. Very different behaviours are observed. With lower oxygen pressures the isochronal spectra are similar to the curves obtained for barium ferrites, with relaxation peaks at room temperature. In higher oxygen partial pressures, the relaxation peaks are found at lower temperatures.

Journal of Applied Physics, 1996

Magnetic relaxation in ceramic cylindrical samples of BiPbSrCaCuO high Tc superconductors has bee... more Magnetic relaxation in ceramic cylindrical samples of BiPbSrCaCuO high Tc superconductors has been studied as a function of applied magnetic field for a constant decay rate of that field strength. We have analyzed the variation of the ac susceptibility versus time just after removing the magnetic field. Data have been obtained by means of an inductive technique from 1 to

Physica Status Solidi a-Applied Research, 1996

L. TORRES et al. : Ferromagnetic Resonance Linewidths of MnCd Ferrites ... Departamento de Fisica... more L. TORRES et al. : Ferromagnetic Resonance Linewidths of MnCd Ferrites ... Departamento de Fisica Aplicada, Universidad de Salamanca ') (a), Centro Electrotdcnia (INK), Departamento de Engenharia Electrotknica, Universidade, Coimbra') (b), Departamento de Electricidad ...

Journal of Applied Physics, 1996

ABSTRACT

Chemosphere, 2008

The purpose of this investigation was to examine the proposition that creosote, emplaced in an in... more The purpose of this investigation was to examine the proposition that creosote, emplaced in an initially water saturated porous system, can be removed from the system through Pickering emulsion formation. Pickering emulsions are dispersions of two immiscible fluids in which coalescence of the dispersed phase droplets is hindered by the presence of colloidal particles adsorbed at the interface between the two immiscible fluid phases. Particle trapping is strongly favoured when the wetting properties of the particles are intermediate between strong water wetting and strong oil wetting. In this investigation the necessary chemical conditions for the formation of physically stable creosote-in-water emulsions protected against coalescence by bentonite particles were examined. It was established that physically stable emulsions could be formed through the judicious addition of small amounts of sodium chloride and the surfactant cetyl-trimethylammonium bromide. The stability of the emulsions was initially established by visual inspection. However, experimental determinations of emulsion stability were also undertaken by use of oscillatory rheology. Measurements of the elastic and viscous responses to shear indicated that physically stable emulsions were obtained when the viscoelastic systems showed a predominantly elastic response to shearing. Once the conditions were established for the formation of physically stable emulsions a ''proof-of-concept'' chromatographic experiment was carried out which showed that creosote could be successfully removed from a saturated model porous system.

Applied Physics a-Materials Science & Processing, 1992

A systematic study of the frequency dependence, from 26.5 to 60 GHz, of the ferromagnetic resonan... more A systematic study of the frequency dependence, from 26.5 to 60 GHz, of the ferromagnetic resonance linewidth for technologically useful nickel ferrites is presented in a wide range of compositions for both single-crystal and polycrystalline samples. The FMR linewidth of the polycrystalline samples appears to be virtually independent of the frequency. Theoretical approaches are applied in our range of frequencies

Applied Physics a-Materials Science & Processing, 1993

The time dependence of the field-cooled susceptibility in polycrystalline samples of YBa2Cu3O7 ha... more The time dependence of the field-cooled susceptibility in polycrystalline samples of YBa2Cu3O7 has been studied in the temperature range 77–95 K. Field-cooled and zero-field-cooled susceptibility measurements and its variation with the ac magnetic field are also reported. Measurements have been carried out by means of an inductive technique. Our fully automatic system allows us to measure the first data points

Ieee Transactions on Magnetics, 1993

Ferrimagnetic resonance (FMR) linewidths have been measured at X-band frequencies (11 GHz) from 7... more Ferrimagnetic resonance (FMR) linewidths have been measured at X-band frequencies (11 GHz) from 77 K to 400 K in single crystal nickel ferrites with composition NixFe3-xO 4 with x=0.9, 1.0, 1.2. Measurements have been carried out by means of an automatic technique based on a modified short-circuit SMA transmission line. Linewidths ranged from 40 Oe to 80 Oe in all

Journal of Applied Physics, 1993

ABSTRACT

Ieee Transactions on Magnetics, 1993

The relaxation of the initial permeability is measured in barium ferrite samples with W-hexagonal... more The relaxation of the initial permeability is measured in barium ferrite samples with W-hexagonal structure. In the temperature range between 80 and 420 K three clear relaxation processes are found; these features are influenced by sintering temperature and atmosphere. Peak C (370 K) seems to arise from long range cation diffusion processes via vacancies, with activation energies around 1.1 eV.

Journal of Applied Physics, 1994

The frequency dependence of the ac susceptibility in polycrystalline samples of YBaCuO has been s... more The frequency dependence of the ac susceptibility in polycrystalline samples of YBaCuO has been studied at the ac field range 0.06-1.2 Oe. The curve of the real part of the susceptibility x' exhibits two drops, the first one close to T, and the other well below T, which could correspond to screening behavior of the grains and grain boundaries, respectively. The imaginary part of the susceptibility shows only a peak below T, which is related to hysteresis losses at the grain boundaries. The peak corresponding to intragrains hysteresis losses is very small and appears masked by the losses of the intergrains. In the range of l-20 kHz, the onset temperature of x' showed no frequency dependence. However, the width of the transition decreases lightly and there is a small shift in the peak of f to higher temperature as the frequency increases. This behavior could be explained in terms of the thermally activated Anderson flux creep. The shift depends on the amplitude of the measuring field. The activation energy for flux creep ranges from 6.4 eV at 0.02 Oe to 3.23 eV at 1.2 Oe in the zero-field-cooled measurements and from 3.41 eV at 0.02 Oe to 1.41 eV at 1.2 Oe in the field-cooled measurements.

Physica Status Solidi a-Applied Research, 1994

Ieee Transactions on Magnetics, 1994

Magnetic disaccommodation spectra (77-420 K) for YIG polycrystalline samples sintered during 8 ho... more Magnetic disaccommodation spectra (77-420 K) for YIG polycrystalline samples sintered during 8 hours in air atmosphere at different sintering temperatures ranging from 1350°C to 1450°C are presented, Samples sintered at temperatures from 1350°C to 1415°C present a relaxation process around 125 K, its amplitude decreases with increasing sintering temperature and its activation energy is close to 0.34 eV, For samples

Journal of Magnetism and Magnetic Materials, 1995

The frequency dependence of the ac susceptibility in polycrystalline samples of Bi0.7Pb0.3SrCaCu]... more The frequency dependence of the ac susceptibility in polycrystalline samples of Bi0.7Pb0.3SrCaCu].80 x has been studied in the range 1-20 kHz. The peak in the imaginary part of the susceptibility shifts slightly to higher temperature as the frequency increases. This behavior could be explained in terms of thermally activated flux creep. The activation energy for flux creep ranges from 2 eV at 0.06 Oe to 0.5 eV at 1

Applied Physics Letters, 1995

ABSTRACT

Journal of Magnetism and Magnetic Materials, 1995

Disaccommodation (DA) spectra for single crystal nickel ferrites of composition NixFe3_xO 4 with ... more Disaccommodation (DA) spectra for single crystal nickel ferrites of composition NixFe3_xO 4 with x = 0.9, 1.0 and 1.2 have been measured. Our results are compared with measurements of ferromagnetic resonance (FMR) on the same samples. Qualitative comparation between the two kinds of measurements (DA and FMR) by means of induced anisotropy formalism is provided.

Applied Physics a-Materials Science & Processing, 1995

... A pplied .s,os,e Science & I ly ~,.~1~,,~ Processing 9 Springer-Verlag 1995 Comparison be... more ... A pplied .s,os,e Science & I ly ~,.~1~,,~ Processing 9 Springer-Verlag 1995 Comparison between disaccommodation and ferromagnetic resonance measurements in polycrystalline nickel ferrites L. Torres t, M. Zazo 1, J. Ifiiguez 1, C. de Francisco 2, JM Mufioz 2 ...

Journal of Applied Physics, 1996

ABSTRACT

Applied Physics Letters, 1996

ABSTRACT

Journal of Magnetism and Magnetic Materials, 1996

The relaxation of the initial permeability after sample demagnetization has been measured in poly... more The relaxation of the initial permeability after sample demagnetization has been measured in polycrystalline strontium ferrite samples with nominal composition SrO • 6Fe203 (M-phase), sintered under different oxygen pressures, and has been represented by isochronal curves. Very different behaviours are observed. With lower oxygen pressures the isochronal spectra are similar to the curves obtained for barium ferrites, with relaxation peaks at room temperature. In higher oxygen partial pressures, the relaxation peaks are found at lower temperatures.

Journal of Applied Physics, 1996

Magnetic relaxation in ceramic cylindrical samples of BiPbSrCaCuO high Tc superconductors has bee... more Magnetic relaxation in ceramic cylindrical samples of BiPbSrCaCuO high Tc superconductors has been studied as a function of applied magnetic field for a constant decay rate of that field strength. We have analyzed the variation of the ac susceptibility versus time just after removing the magnetic field. Data have been obtained by means of an inductive technique from 1 to

Physica Status Solidi a-Applied Research, 1996

L. TORRES et al. : Ferromagnetic Resonance Linewidths of MnCd Ferrites ... Departamento de Fisica... more L. TORRES et al. : Ferromagnetic Resonance Linewidths of MnCd Ferrites ... Departamento de Fisica Aplicada, Universidad de Salamanca ') (a), Centro Electrotdcnia (INK), Departamento de Engenharia Electrotknica, Universidade, Coimbra') (b), Departamento de Electricidad ...

Journal of Applied Physics, 1996

ABSTRACT