Alfredo Jacas - Academia.edu (original) (raw)

Papers by Alfredo Jacas

Science and Engineering of Composite Materials, 2020

This work focuses on dip coating and further phase inversion prepared polysulfone/LTA zeolite mix... more This work focuses on dip coating and further phase inversion prepared polysulfone/LTA zeolite mixed matrix membranes (MMMs). The Linde Type A (LTA) zeolite synthesized under hydrothermal conditions by the organic free method was introduced as fillers at 10 and 20 wt.% loadings into the polysulfone polymer matrix to obtain MMMs. The x-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis indicated that the as-synthesized LTA zeolite samples were crystalline and mainly composed of crystal of predominantly cubic shape. Textural characterisation using Ar adsorption/desorption data of LTA zeolite shown the existence of mesoporous. Atomic force microscopy (AFM) in combination with the SEM characterised the membrane morphology and the dispersion of zeolite fillers. The effect of the zeolite loading on the performance of the MMMs was analysed. It points out that N2 permeability was increased with the increment of zeolite filler, also the high membranes permeability and the w...

Materials, Jul 22, 2021

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Microporous and Mesoporous Materials, Dec 1, 1998

Zinc substituted chabazite-like aluminophosphate ZnAPO-34 was synthesized hydrothermally. Rietvel... more Zinc substituted chabazite-like aluminophosphate ZnAPO-34 was synthesized hydrothermally. Rietveld refinement has been carried out over the X-ray spectrum. Atomic coordinates of the framework were refined assuming the space group R 9 3m. Results show that Zn2+, P5+ and Al3+ occupy similar tetrahedral sites in the structure. The cell is rhombohedral; in hexagonal coordinates the lattice parameters are: a=13.827 1 Å and c=15.401 3 Å. Different crystal shapes have been revealed by scanning electron microscopy, and the elemental compositions of these crystals show variations, especially in their Ca and Zn content, but all of them belong to the same solid solution.

arXiv (Cornell University), Feb 2, 2021

Conventional polycrystalline materials acquire high levels of intrinsic mechanical stress (rangin... more Conventional polycrystalline materials acquire high levels of intrinsic mechanical stress (ranging from MPa to a few GPa) during preparation and use, but this stress decays quickly (~minutes) to small residual values (~kPa) under standard resting conditions. Nanocrystalline materials reach similar or even higher levels of intrinsic stress, but surprisingly retain a significant portion of this stress over much longer time scales (~hours). This behavior directly contradicts current theoretical models that predict stress relaxation through diffusive currents. Diffusive currents, which flow mainly on the surfaces of grains, are expected to produce faster relaxation kinetics when the stress to be released is higher. In this work, we study the kinetics of intrinsic stress relaxation in nanocrystalline films and identify the limitations of this process as a preliminary step towards designing a strategy for high-stress stabilization in nanostructured systems.

Materials Letters, Oct 1, 1996

A molecular sieve including Ca in AlPO,-5 framework was synthesized. The highly crystalline synth... more A molecular sieve including Ca in AlPO,-5 framework was synthesized. The highly crystalline synthetic products were characterized by X-ray fluorescence analysis, X-ray diffraction and NH, adsorption. Sterilized CaAPO-5 was implanted in powder form in alive animals and a preliminary evaluation of their bioactive properties was made by elementary preclinical tests.

IEEE Transactions on Magnetics, May 1, 2014

Science and engineering of composite materials, 2020

This work focuses on dip coating and further phase inversion prepared polysulfone/LTA zeolite mix... more This work focuses on dip coating and further phase inversion prepared polysulfone/LTA zeolite mixed matrix membranes (MMMs). The Linde Type A (LTA) zeolite synthesized under hydrothermal conditions by the organic free method was introduced as fillers at 10 and 20 wt.% loadings into the polysulfone polymer matrix to obtain MMMs. The x-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis indicated that the as-synthesized LTA zeolite samples were crystalline and mainly composed of crystal of predominantly cubic shape. Textural characterisation using Ar adsorption/desorption data of LTA zeolite shown the existence of mesoporous. Atomic force microscopy (AFM) in combination with the SEM characterised the membrane morphology and the dispersion of zeolite fillers. The effect of the zeolite loading on the performance of the MMMs was analysed. It points out that N 2 permeability was increased with the increment of zeolite filler, also the high membranes permeability and the weak dependence upon transmembrane pressure and therefore its high selectivity. The average membrane thickness was 150 µm.

The mechanical strength and cyclic fatigue behavior of PIC700 commercial eco-piezoceramic disks a... more The mechanical strength and cyclic fatigue behavior of PIC700 commercial eco-piezoceramic disks are investigated under biaxial loading on unpoled and poled samples. The bending strength of unpoled samples was higher than those of poled ones. Fatigue tests were conducted under a load ratio of 10 at a frequency of 20 Hz with a sinusoidal waveform. The curve fitting for the S-N fatigue diagram is used to predict the lifetime of these eco-piezoceramics and describe their fatigue behavior. It was also found that the unpoled samples exhibited higher fatigue resistance than the poled ones. The fatigue limit of maximum load for ten million cycles of unpoled and poled samples was estimated to be 160 and 135 MPa, respectively. The detailed observations of the fatigue fracture surfaces by scanning electron microscopy (SEM) indicated that a wavy surface with a mixture of transgranular and intergranular fractures occurred preferentially in the case of the poled material. On the other hand, trans...

Materials, Apr 3, 2020

Coupling between electrically excited electromechanical resonances of piezoelectric ceramics is u... more Coupling between electrically excited electromechanical resonances of piezoelectric ceramics is undesirable for the purpose of their characterization, since the material models correspond to monomodal resonances. However, coupling takes place quite often and it is unavoidable at the shear resonance of standard in-plane poled and thickness-excited rectangular plates. The piezoelectric coefficient e 15 , the elastic compliance s 55 E and the dielectric permi ivity component ε 11 S for a piezoelectric ceramic can be determined, including all losses, using the automatic iterative method of analysis of the complex impedance curves for the shear mode of an appropriated resonator. This is the non-standard, thickness-poled and longitudinally excited, shear plate. In this paper, the automatic iterative method is modified. The purpose is to be able to deal with the analysis of the impedance curves of the non-standard plate as the periodic phenomena of coupling and decoupling of the main shear resonance and other resonances takes place. This happens when the thickness of the plate is reduced, and its aspect ratio (width of the excitation (w)/thickness for poling (t)) is increased. In this process, the frequency of the shear resonance also increases and meets those of other plate modes periodically. We aim to obtain the best approach for the shear properties of near coupling and to reveal both their validity and the limitations of the thus-obtained information. Finally, we use a plate of a Ba 0.85 Ca 0.15 Ti 0.90 Zr 0.10 O 3 eco-piezoceramic as a case study.

Boletin de la Sociedad Espanola de Ceramica y Vidrio

The effectiveness of materials based on LTA Zeolite as active phase, for their incorporation into... more The effectiveness of materials based on LTA Zeolite as active phase, for their incorporation into systems aimed at the removal of heavy metals on waste water is evaluated in a preliminary way. This type of Zeolite with the main channel of a minimum free diameter of 0,41 nm and a low SiO2/Al2O3 ratio is an interesting molecular sieve, which in turn display a high ion exchange capacity. From this point of view, LTA Zeolite crystals were obtained “in situ” by hydrothermal synthesis and characterized by x ray diffraction (XRD) and scanning electron microscopy (SEM). We have studied the effect of hydrothermal synthesis time at 378 K. Likewise, the removal capacity of heavy metal from the active phase was evaluated in as a first step on diluted solutions of cooper salts at slightly acidic pH (~ 4,7).

Materials Letters, 2005

MCM-41 mesostructured materials were prepared by confined space synthesis into the cavities of αA... more MCM-41 mesostructured materials were prepared by confined space synthesis into the cavities of αAl2O3-mullite supports by hydrophobing the matrix surfaces prior to be immersed in a precursor solution. The obtained samples were characterized by X-ray Powder Diffraction (XRPD), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM) and Nitrogen Adsorption techniques. XPS results demonstrated the effectiveness of hexamethyldisilazane (HMDS) to modify

Journal of Materials Science Letters, 1995

Bulletin of Materials Science, 2013

Biphase wires consisting of a soft magnetic amorphous nucleus surrounded by a hard magnetic CoNi ... more Biphase wires consisting of a soft magnetic amorphous nucleus surrounded by a hard magnetic CoNi layer of variable thickness were obtained by means of rotating water-quenching method and subsequent electroplating technique. Magnetization processes for all the biphase wires were resolved in terms of reversible bulging of magnetic domains and spin rotation by means of complex permeability measurements within the frequency range of 10 Hz-13 MHz. Results are interpreted in terms of CoNi layer effect on the magnetic anisotropy of the soft core.

Materials

Achieving good piezoelectric properties, such as the widely reported d33 charge coefficient, is a... more Achieving good piezoelectric properties, such as the widely reported d33 charge coefficient, is a good starting point in establishing the potential applicability of piezoceramics. However, piezoceramics are only completely characterized by consistent piezoelectric-elastic-dielectric material coefficient matrices in complex form, i.e., including all losses. These matrices, which define the various alternative forms of the constitutive equations of piezoelectricity, are required for reliable virtual prototyping in the design of new devices. To meet this need, ten precise and accurate piezoelectric dielectric and elastic coefficients of the material, including all losses, must be determined for each alternative. Due to the difficulties arising from the coupling of modes when using the resonance method, this complete set of parameters is scarcely reported. Bi0.5Na0.5TiO3-based solid solutions are already commercially available in Europe and Japan. Here, we report a case study of the det...

Boletín de la Sociedad Española de Cerámica y Vidrio, 2012

En este trabajo se evalúa de forma preliminar la efectividad del empleo de materiales basados en ... more En este trabajo se evalúa de forma preliminar la efectividad del empleo de materiales basados en zeolita LTA, como fase activa para su incorporación en sistemas orientados a la eliminación de metales pesados presentes en aguas residuales. Este tipo de zeolitas con el canal principal de un diámetro mínimo libre de 0,41 nm y una baja relación SiO 2 /Al 2 O 3 se presenta como un tamiz molecular interesante, que a su vez manifiesta una gran capacidad de intercambio iónico. Partiendo de este punto de vista, cristales de zeolita LTA fueron obtenidos "in situ" por síntesis hidrotermal y caracterizados por difracción de rayos X (DRX), y microscopia electrónica de barrido (MEB). Se ha estudiado el efecto del tiempo de tratamiento hidrotermal a 378 K. Asimismo, la capacidad de eliminación de metales pesados de la fase activa de los sistemas obtenidos fue evaluada en una primera etapa en soluciones diluidas de sales de cobre a pH ácido (~ 4,7). Palabras claves: zeolita, membrana, síntesis hidrotermal, remoción, metales pesados, intercambio iónico. Synthesis of LTA zeolite on corundum supports: Preliminary assessment for heavy metal removal from waste water The effectiveness of materials based on LTA Zeolite as active phase, for their incorporation into systems aimed at the removal of heavy metals on waste water is evaluated in a preliminary way. This type of Zeolite with the main channel of a minimum free diameter of 0,41 nm and a low SiO 2 /Al 2 O 3 ratio is an interesting molecular sieve, which in turn display a high ion exchange capacity. From this point of view, LTA Zeolite crystals were obtained "in situ" by hydrothermal synthesis and characterized by x ray diffraction (XRD) and scanning electron microscopy (SEM). We have studied the effect of hydrothermal synthesis time at 378 K. Likewise, the removal capacity of heavy metal from the active phase was evaluated in as a first step on diluted solutions of cooper salts at slightly acidic pH (~ 4,7).

IEEE Transactions on Magnetics, 2000

Microporous and Mesoporous Materials, 1998

Science and Engineering of Composite Materials, 2020

This work focuses on dip coating and further phase inversion prepared polysulfone/LTA zeolite mix... more This work focuses on dip coating and further phase inversion prepared polysulfone/LTA zeolite mixed matrix membranes (MMMs). The Linde Type A (LTA) zeolite synthesized under hydrothermal conditions by the organic free method was introduced as fillers at 10 and 20 wt.% loadings into the polysulfone polymer matrix to obtain MMMs. The x-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis indicated that the as-synthesized LTA zeolite samples were crystalline and mainly composed of crystal of predominantly cubic shape. Textural characterisation using Ar adsorption/desorption data of LTA zeolite shown the existence of mesoporous. Atomic force microscopy (AFM) in combination with the SEM characterised the membrane morphology and the dispersion of zeolite fillers. The effect of the zeolite loading on the performance of the MMMs was analysed. It points out that N2 permeability was increased with the increment of zeolite filler, also the high membranes permeability and the w...

Materials, Jul 22, 2021

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Microporous and Mesoporous Materials, Dec 1, 1998

Zinc substituted chabazite-like aluminophosphate ZnAPO-34 was synthesized hydrothermally. Rietvel... more Zinc substituted chabazite-like aluminophosphate ZnAPO-34 was synthesized hydrothermally. Rietveld refinement has been carried out over the X-ray spectrum. Atomic coordinates of the framework were refined assuming the space group R 9 3m. Results show that Zn2+, P5+ and Al3+ occupy similar tetrahedral sites in the structure. The cell is rhombohedral; in hexagonal coordinates the lattice parameters are: a=13.827 1 Å and c=15.401 3 Å. Different crystal shapes have been revealed by scanning electron microscopy, and the elemental compositions of these crystals show variations, especially in their Ca and Zn content, but all of them belong to the same solid solution.

arXiv (Cornell University), Feb 2, 2021

Conventional polycrystalline materials acquire high levels of intrinsic mechanical stress (rangin... more Conventional polycrystalline materials acquire high levels of intrinsic mechanical stress (ranging from MPa to a few GPa) during preparation and use, but this stress decays quickly (~minutes) to small residual values (~kPa) under standard resting conditions. Nanocrystalline materials reach similar or even higher levels of intrinsic stress, but surprisingly retain a significant portion of this stress over much longer time scales (~hours). This behavior directly contradicts current theoretical models that predict stress relaxation through diffusive currents. Diffusive currents, which flow mainly on the surfaces of grains, are expected to produce faster relaxation kinetics when the stress to be released is higher. In this work, we study the kinetics of intrinsic stress relaxation in nanocrystalline films and identify the limitations of this process as a preliminary step towards designing a strategy for high-stress stabilization in nanostructured systems.

Materials Letters, Oct 1, 1996

A molecular sieve including Ca in AlPO,-5 framework was synthesized. The highly crystalline synth... more A molecular sieve including Ca in AlPO,-5 framework was synthesized. The highly crystalline synthetic products were characterized by X-ray fluorescence analysis, X-ray diffraction and NH, adsorption. Sterilized CaAPO-5 was implanted in powder form in alive animals and a preliminary evaluation of their bioactive properties was made by elementary preclinical tests.

IEEE Transactions on Magnetics, May 1, 2014

Science and engineering of composite materials, 2020

This work focuses on dip coating and further phase inversion prepared polysulfone/LTA zeolite mix... more This work focuses on dip coating and further phase inversion prepared polysulfone/LTA zeolite mixed matrix membranes (MMMs). The Linde Type A (LTA) zeolite synthesized under hydrothermal conditions by the organic free method was introduced as fillers at 10 and 20 wt.% loadings into the polysulfone polymer matrix to obtain MMMs. The x-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis indicated that the as-synthesized LTA zeolite samples were crystalline and mainly composed of crystal of predominantly cubic shape. Textural characterisation using Ar adsorption/desorption data of LTA zeolite shown the existence of mesoporous. Atomic force microscopy (AFM) in combination with the SEM characterised the membrane morphology and the dispersion of zeolite fillers. The effect of the zeolite loading on the performance of the MMMs was analysed. It points out that N 2 permeability was increased with the increment of zeolite filler, also the high membranes permeability and the weak dependence upon transmembrane pressure and therefore its high selectivity. The average membrane thickness was 150 µm.

The mechanical strength and cyclic fatigue behavior of PIC700 commercial eco-piezoceramic disks a... more The mechanical strength and cyclic fatigue behavior of PIC700 commercial eco-piezoceramic disks are investigated under biaxial loading on unpoled and poled samples. The bending strength of unpoled samples was higher than those of poled ones. Fatigue tests were conducted under a load ratio of 10 at a frequency of 20 Hz with a sinusoidal waveform. The curve fitting for the S-N fatigue diagram is used to predict the lifetime of these eco-piezoceramics and describe their fatigue behavior. It was also found that the unpoled samples exhibited higher fatigue resistance than the poled ones. The fatigue limit of maximum load for ten million cycles of unpoled and poled samples was estimated to be 160 and 135 MPa, respectively. The detailed observations of the fatigue fracture surfaces by scanning electron microscopy (SEM) indicated that a wavy surface with a mixture of transgranular and intergranular fractures occurred preferentially in the case of the poled material. On the other hand, trans...

Materials, Apr 3, 2020

Coupling between electrically excited electromechanical resonances of piezoelectric ceramics is u... more Coupling between electrically excited electromechanical resonances of piezoelectric ceramics is undesirable for the purpose of their characterization, since the material models correspond to monomodal resonances. However, coupling takes place quite often and it is unavoidable at the shear resonance of standard in-plane poled and thickness-excited rectangular plates. The piezoelectric coefficient e 15 , the elastic compliance s 55 E and the dielectric permi ivity component ε 11 S for a piezoelectric ceramic can be determined, including all losses, using the automatic iterative method of analysis of the complex impedance curves for the shear mode of an appropriated resonator. This is the non-standard, thickness-poled and longitudinally excited, shear plate. In this paper, the automatic iterative method is modified. The purpose is to be able to deal with the analysis of the impedance curves of the non-standard plate as the periodic phenomena of coupling and decoupling of the main shear resonance and other resonances takes place. This happens when the thickness of the plate is reduced, and its aspect ratio (width of the excitation (w)/thickness for poling (t)) is increased. In this process, the frequency of the shear resonance also increases and meets those of other plate modes periodically. We aim to obtain the best approach for the shear properties of near coupling and to reveal both their validity and the limitations of the thus-obtained information. Finally, we use a plate of a Ba 0.85 Ca 0.15 Ti 0.90 Zr 0.10 O 3 eco-piezoceramic as a case study.

Boletin de la Sociedad Espanola de Ceramica y Vidrio

The effectiveness of materials based on LTA Zeolite as active phase, for their incorporation into... more The effectiveness of materials based on LTA Zeolite as active phase, for their incorporation into systems aimed at the removal of heavy metals on waste water is evaluated in a preliminary way. This type of Zeolite with the main channel of a minimum free diameter of 0,41 nm and a low SiO2/Al2O3 ratio is an interesting molecular sieve, which in turn display a high ion exchange capacity. From this point of view, LTA Zeolite crystals were obtained “in situ” by hydrothermal synthesis and characterized by x ray diffraction (XRD) and scanning electron microscopy (SEM). We have studied the effect of hydrothermal synthesis time at 378 K. Likewise, the removal capacity of heavy metal from the active phase was evaluated in as a first step on diluted solutions of cooper salts at slightly acidic pH (~ 4,7).

Materials Letters, 2005

MCM-41 mesostructured materials were prepared by confined space synthesis into the cavities of αA... more MCM-41 mesostructured materials were prepared by confined space synthesis into the cavities of αAl2O3-mullite supports by hydrophobing the matrix surfaces prior to be immersed in a precursor solution. The obtained samples were characterized by X-ray Powder Diffraction (XRPD), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM) and Nitrogen Adsorption techniques. XPS results demonstrated the effectiveness of hexamethyldisilazane (HMDS) to modify

Journal of Materials Science Letters, 1995

Bulletin of Materials Science, 2013

Biphase wires consisting of a soft magnetic amorphous nucleus surrounded by a hard magnetic CoNi ... more Biphase wires consisting of a soft magnetic amorphous nucleus surrounded by a hard magnetic CoNi layer of variable thickness were obtained by means of rotating water-quenching method and subsequent electroplating technique. Magnetization processes for all the biphase wires were resolved in terms of reversible bulging of magnetic domains and spin rotation by means of complex permeability measurements within the frequency range of 10 Hz-13 MHz. Results are interpreted in terms of CoNi layer effect on the magnetic anisotropy of the soft core.

Materials

Achieving good piezoelectric properties, such as the widely reported d33 charge coefficient, is a... more Achieving good piezoelectric properties, such as the widely reported d33 charge coefficient, is a good starting point in establishing the potential applicability of piezoceramics. However, piezoceramics are only completely characterized by consistent piezoelectric-elastic-dielectric material coefficient matrices in complex form, i.e., including all losses. These matrices, which define the various alternative forms of the constitutive equations of piezoelectricity, are required for reliable virtual prototyping in the design of new devices. To meet this need, ten precise and accurate piezoelectric dielectric and elastic coefficients of the material, including all losses, must be determined for each alternative. Due to the difficulties arising from the coupling of modes when using the resonance method, this complete set of parameters is scarcely reported. Bi0.5Na0.5TiO3-based solid solutions are already commercially available in Europe and Japan. Here, we report a case study of the det...

Boletín de la Sociedad Española de Cerámica y Vidrio, 2012

En este trabajo se evalúa de forma preliminar la efectividad del empleo de materiales basados en ... more En este trabajo se evalúa de forma preliminar la efectividad del empleo de materiales basados en zeolita LTA, como fase activa para su incorporación en sistemas orientados a la eliminación de metales pesados presentes en aguas residuales. Este tipo de zeolitas con el canal principal de un diámetro mínimo libre de 0,41 nm y una baja relación SiO 2 /Al 2 O 3 se presenta como un tamiz molecular interesante, que a su vez manifiesta una gran capacidad de intercambio iónico. Partiendo de este punto de vista, cristales de zeolita LTA fueron obtenidos "in situ" por síntesis hidrotermal y caracterizados por difracción de rayos X (DRX), y microscopia electrónica de barrido (MEB). Se ha estudiado el efecto del tiempo de tratamiento hidrotermal a 378 K. Asimismo, la capacidad de eliminación de metales pesados de la fase activa de los sistemas obtenidos fue evaluada en una primera etapa en soluciones diluidas de sales de cobre a pH ácido (~ 4,7). Palabras claves: zeolita, membrana, síntesis hidrotermal, remoción, metales pesados, intercambio iónico. Synthesis of LTA zeolite on corundum supports: Preliminary assessment for heavy metal removal from waste water The effectiveness of materials based on LTA Zeolite as active phase, for their incorporation into systems aimed at the removal of heavy metals on waste water is evaluated in a preliminary way. This type of Zeolite with the main channel of a minimum free diameter of 0,41 nm and a low SiO 2 /Al 2 O 3 ratio is an interesting molecular sieve, which in turn display a high ion exchange capacity. From this point of view, LTA Zeolite crystals were obtained "in situ" by hydrothermal synthesis and characterized by x ray diffraction (XRD) and scanning electron microscopy (SEM). We have studied the effect of hydrothermal synthesis time at 378 K. Likewise, the removal capacity of heavy metal from the active phase was evaluated in as a first step on diluted solutions of cooper salts at slightly acidic pH (~ 4,7).

IEEE Transactions on Magnetics, 2000

Microporous and Mesoporous Materials, 1998