Amaya Sagarzazu - Academia.edu (original) (raw)

Papers by Amaya Sagarzazu

Research paper thumbnail of Infuence of Microstructure in Drug Release Behavior of Silica Nanocapsules

Journal of Drug Delivery, 2013

Meso-and nanoporous structures are adequate matrices for controlled drug delivery systems, due to... more Meso-and nanoporous structures are adequate matrices for controlled drug delivery systems, due to their large surface areas and to their bioactive and biocompatibility properties. Mesoporous materials of type SBA-15, synthesized under different pH conditions, and zeolite beta were studied in order to compare the different intrinsic morphological characteristics as pore size, pore connectivity, and pore geometry on the drug loading and release process. These materials were characterized by X-ray diffraction, nitrogen adsorption, scanning and transmission electron microscopy, and calorimetric measurements. Ibuprofen (IBU) was chosen as a model drug for the formulation of controlled-release dosage forms; it was impregnated into these two types of materials by a soaking procedure during different periods. Drug loading and release studies were followed by UV-Vis spectrophotometry. All nano-and mesostructured materials showed a similar loading behavior. It was found that the pore size and Al content strongly influenced the release process. These results suggest that the framework structure and architecture affect the drug adsorption and release properties of these materials. Both materials offer a good potential for a controlled delivery system of ibuprofen.

Research paper thumbnail of Mechanical Alloying and Thermal Treatment of the Fe-Co-Ag System

Journal of Metastable and Nanocrystalline Materials, 2004

Metastable, Mechanically Alloyed and Nanocrystalline Materials 2003: Mechanical Alloying and Ther... more Metastable, Mechanically Alloyed and Nanocrystalline Materials 2003: Mechanical Alloying and Thermal Treatment of the Fe-Co-Ag System.

Research paper thumbnail of Effect of the Milling Media on the Phases Obtained in Mechanically Alloyed Equiatomic Fe-Co

Journal of Metastable and Nanocrystalline Materials, 2001

All rights reserved. No part of contents of this paper may be reproduced or transmitted in any fo... more All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 66.249.72.21-29/04/11,06:33:21) ... 356 Metastable, Mechanically Alloyed and ...

Research paper thumbnail of Synthesis of Biomaterials by Mechanochemical Transformation

Journal of Metastable and Nanocrystalline Materials, 2002

All rights reserved. No part of contents of this paper may be reproduced or transmitted in any fo... more All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 66.249.66.44-26/04/11,06:28:44) ... 646 Metastable, Mechanically Alloyed and ...

Research paper thumbnail of Mechanochemical transformation of mixtures of Ca(OH)2 and (NH4)2HPO4 or P2O5

Materials Research Bulletin, 2006

A detailed comparative study of the mechanochemical transformation of two mixtures: Ca(OH)2–(NH4)... more A detailed comparative study of the mechanochemical transformation of two mixtures: Ca(OH)2–(NH4)2HPO4 and Ca(OH)2–P2O5, milled in a mortar dry grinder for different periods of time was carried out. The phase transformations obtained at each milling stage were studied by X-ray diffraction, infrared spectroscopy, transmission electron microscopy, differential scanning calorimetry and thermogravimetric analysis.The transformations taking place during the first periods of

Research paper thumbnail of Influence of TEA2O/SiO2 ratio on the polymorph formation and crystallization of zeolite beta

Materials Chemistry and Physics, 2013

ABSTRACT Zeolite beta is formed by different proportions of polymorphs. The influence of the synt... more ABSTRACT Zeolite beta is formed by different proportions of polymorphs. The influence of the syntheses conditions on the polymorphs formation has not been systematically studied up to now. In the present work a detailed study of the effect of the variation of TEA(2)O/SiO2 on the synthesis of zeolite beta has been carried out, for different molar ratios: 0.15, 0.27, 0.50 and 0.75. TEA(2)O concentration affects the crystallization kinetics, crystal size and morphology, polymorph proportion, textural properties and Al content in the final products. TEA(2)O/SiO2 = 027, seems to be a threshold value below or above which the nucleation rate decreases. For this ratio nanosize beta was obtained with the highest content of polymorph A, highest surface area and micropore volume. Lower or higher TEA(2)O/SiO2 ratios resulted in larger crystal size and higher content of polymorph B. The proportion of polymorphs obtained were in the range of 32%A-68%B to 51%A-49%B.

Research paper thumbnail of Characterization of mechanically alloyed Fe–Cr–Sn alloys

Journal of Materials Processing Technology, 1999

Ferritic steels with high Cr concentration are extensively used due to their resistance to corros... more Ferritic steels with high Cr concentration are extensively used due to their resistance to corrosion, also they are much cheaper to produce than Ni alloys and austenitic stainless steels. However, the formation of the sigma phase and phase separation affect their mechanical properties deleteriously. The addition of Sn to the Fe±Cr system retards the sigma phase formation. Their mechanical properties may be further improved by decreasing the average grain size and the density of defects inside the grains, as in nano-grained Fe±Cr alloys. Nanocrystaline Fe±Cr±Sn alloys, which are prepared by mechanical alloying, are thus, worthy of investigation. In this work mechanical alloying of mixtures of elemental Fe, Cr and Sn powders was carried out in an Ar atmosphere using either untreated or hardened vials and balls, in order to obtain the following alloys: Fe 55-x Cr 45 Sn x with x 0, 3 and 6 at%. These were studied by 57 Fe Mo Èssbauer spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). It was found that the increasing of the Sn concentration leads to a reduction of particle size and grain size. Furthermore, milling in the untreated vials causes a partial amorphization of the alloys. Contamination from the balls and vials decreases with the increasing Sn concentration. # 1999 Elsevier Science S.A. All rights reserved.

Research paper thumbnail of Comparative study of NiW, NiMo and MoW prepared by mechanical alloying

Journal of Alloys and Compounds, 2007

The present work concern the amorphisation process induced by mechanical alloying in the NiW, NiM... more The present work concern the amorphisation process induced by mechanical alloying in the NiW, NiMo and MoW systems. The alloys chosen combine a group of transition elements varying from very similar atomic radius and electronic valences (MoW) to different ones (NiW and NiMo). The three systems achieved an amorphous state after 50h of milling. The mechanism of amorphisation proposed for

Research paper thumbnail of Mechanical alloying of the FeNi–Ag system

Journal of Alloys and Compounds, 2007

The Fe–Ni–Ag system is of particular interest for its potential applications as soft magnetic gra... more The Fe–Ni–Ag system is of particular interest for its potential applications as soft magnetic granular material with small magnetic grains embedded in a non-magnetic metal matrix. Under equilibrium conditions: Fe–Ag and Ni–Ag are immiscible and Fe–Ni shows complete solubility. These materials are particularly important for magnetoresistivity properties. The properties of these alloys are closely related to their microstructure; therefore, a

Research paper thumbnail of Solid state amorphisation in binary systems prepared by mechanical alloying

Journal of Alloys and Compounds, 2009

In the present work a detailed study of amorphisation in different systems prepared by mechanical... more In the present work a detailed study of amorphisation in different systems prepared by mechanical alloying under the same experimental conditions was carried out, milling up to 50 and 100 h in some cases. The systems studied were: AlTi, AlNi, AlFe, FeNi, FeCo, NiMo, NiW, NiCo, MoW, CoMo. These systems were chosen to study the effect of Al-transition metal, transition metal-transition metal and also systems with large and small negative heat of mixing, different and similar crystal structures, atomic sizes and diffusion coefficients. Calculations based on the Miedema model for alloy formation and amorphisation on all the alloys studied were performed. The experimental results from X-ray diffraction and transmission electron microscopy showed that the systems based on Fe (FeNi, FeCo and FeAl) did not amorphised, even after milling for 100 h, and formed a stable solid solution with a nanometric grain size of 7 nm. The systems NiMo, NiW, MoW and CoMo (systems with small negative heat of mixing), showed amorphisation after 50 h of milling. NiAl and TiAl form an intermediate amorphous phase after around 20 h of milling and with further milling they recrystallize into a fcc solid solution. Agreement between the theoretical calculations based on the Miedema model and the experimental results was found in most of the systems.

Research paper thumbnail of Selective destruction and differentiation of clay minerals from natural diaspore admixture by mortar grinding

International Journal of Mineral Processing, 1983

Mendelovici, E., . Selective destruction and differentiation of clay minerals from natural diaspo... more Mendelovici, E., . Selective destruction and differentiation of clay minerals from natural diaspore admixture by mortar grinding. Int, J. Miner. Process., 11: 131--138.

Research paper thumbnail of Mössbauer study of Fe–Co alloys with Cr additions synthesized by mechanical alloying

Hyperfine Interactions, 2010

Cr has been added to FeCo substituting 10 at.% of Co or Fe in the alloy. The alloys Fe 50 Co 40 C... more Cr has been added to FeCo substituting 10 at.% of Co or Fe in the alloy. The alloys Fe 50 Co 40 Cr 10 , Fe 40 Co 50 Cr 10 and Fe 50 Co 50 were prepared by mechanical alloying for 2, 5, 10, 20, 40 and 60 h. The formation of the alloy and the incorporation of the elements have been followed by X-Ray Diffraction (XRD) and Mössbauer Spectroscopy. The kinetics of mixing occurs by incorporation of Co and Cr into the Fe structure. After prolonged milling it seems that Cr incorporates itself into both α-Fe and α-FeCo structures and a mixture of FeCoCr rich in Cr and FeCoCr rich in Co solid solutions is obtained.

Research paper thumbnail of Aluminum Content on the Crystallization of Zeolite Beta

Microscopy and Microanalysis

The zeolite beta is a very important material for catalytic processes; it was described for the f... more The zeolite beta is a very important material for catalytic processes; it was described for the first time in 1.967 according to patent [1]. It is a microporous solid that can be synthesized in an extensive range of Si/Al ratios, its structure is formed by an intergrowth of two or three polymorphs ...

Research paper thumbnail of Study of the mechano-chemical transformation of goethite to hematite by TEM and XRD

Materials Research Bulletin, 2000

A study of the mechano-chemical transformation of goethite to hematite was carried out using tran... more A study of the mechano-chemical transformation of goethite to hematite was carried out using transmission electron microscopy (TEM) and X-ray diffraction (XRD). Synthetic goethite was dry-ground in air for different times up to 104 h and characterized with the aim of understanding the mechanisms taking part in the transformation, the phases formed, and particle distribution, morphology and size. It was

Research paper thumbnail of Infuence of Microstructure in Drug Release Behavior of Silica Nanocapsules

Journal of Drug Delivery, 2013

Meso-and nanoporous structures are adequate matrices for controlled drug delivery systems, due to... more Meso-and nanoporous structures are adequate matrices for controlled drug delivery systems, due to their large surface areas and to their bioactive and biocompatibility properties. Mesoporous materials of type SBA-15, synthesized under different pH conditions, and zeolite beta were studied in order to compare the different intrinsic morphological characteristics as pore size, pore connectivity, and pore geometry on the drug loading and release process. These materials were characterized by X-ray diffraction, nitrogen adsorption, scanning and transmission electron microscopy, and calorimetric measurements. Ibuprofen (IBU) was chosen as a model drug for the formulation of controlled-release dosage forms; it was impregnated into these two types of materials by a soaking procedure during different periods. Drug loading and release studies were followed by UV-Vis spectrophotometry. All nano-and mesostructured materials showed a similar loading behavior. It was found that the pore size and Al content strongly influenced the release process. These results suggest that the framework structure and architecture affect the drug adsorption and release properties of these materials. Both materials offer a good potential for a controlled delivery system of ibuprofen.

Research paper thumbnail of Mechanical Alloying and Thermal Treatment of the Fe-Co-Ag System

Journal of Metastable and Nanocrystalline Materials, 2004

Metastable, Mechanically Alloyed and Nanocrystalline Materials 2003: Mechanical Alloying and Ther... more Metastable, Mechanically Alloyed and Nanocrystalline Materials 2003: Mechanical Alloying and Thermal Treatment of the Fe-Co-Ag System.

Research paper thumbnail of Effect of the Milling Media on the Phases Obtained in Mechanically Alloyed Equiatomic Fe-Co

Journal of Metastable and Nanocrystalline Materials, 2001

All rights reserved. No part of contents of this paper may be reproduced or transmitted in any fo... more All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 66.249.72.21-29/04/11,06:33:21) ... 356 Metastable, Mechanically Alloyed and ...

Research paper thumbnail of Synthesis of Biomaterials by Mechanochemical Transformation

Journal of Metastable and Nanocrystalline Materials, 2002

All rights reserved. No part of contents of this paper may be reproduced or transmitted in any fo... more All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 66.249.66.44-26/04/11,06:28:44) ... 646 Metastable, Mechanically Alloyed and ...

Research paper thumbnail of Mechanochemical transformation of mixtures of Ca(OH)2 and (NH4)2HPO4 or P2O5

Materials Research Bulletin, 2006

A detailed comparative study of the mechanochemical transformation of two mixtures: Ca(OH)2–(NH4)... more A detailed comparative study of the mechanochemical transformation of two mixtures: Ca(OH)2–(NH4)2HPO4 and Ca(OH)2–P2O5, milled in a mortar dry grinder for different periods of time was carried out. The phase transformations obtained at each milling stage were studied by X-ray diffraction, infrared spectroscopy, transmission electron microscopy, differential scanning calorimetry and thermogravimetric analysis.The transformations taking place during the first periods of

Research paper thumbnail of Influence of TEA2O/SiO2 ratio on the polymorph formation and crystallization of zeolite beta

Materials Chemistry and Physics, 2013

ABSTRACT Zeolite beta is formed by different proportions of polymorphs. The influence of the synt... more ABSTRACT Zeolite beta is formed by different proportions of polymorphs. The influence of the syntheses conditions on the polymorphs formation has not been systematically studied up to now. In the present work a detailed study of the effect of the variation of TEA(2)O/SiO2 on the synthesis of zeolite beta has been carried out, for different molar ratios: 0.15, 0.27, 0.50 and 0.75. TEA(2)O concentration affects the crystallization kinetics, crystal size and morphology, polymorph proportion, textural properties and Al content in the final products. TEA(2)O/SiO2 = 027, seems to be a threshold value below or above which the nucleation rate decreases. For this ratio nanosize beta was obtained with the highest content of polymorph A, highest surface area and micropore volume. Lower or higher TEA(2)O/SiO2 ratios resulted in larger crystal size and higher content of polymorph B. The proportion of polymorphs obtained were in the range of 32%A-68%B to 51%A-49%B.

Research paper thumbnail of Characterization of mechanically alloyed Fe–Cr–Sn alloys

Journal of Materials Processing Technology, 1999

Ferritic steels with high Cr concentration are extensively used due to their resistance to corros... more Ferritic steels with high Cr concentration are extensively used due to their resistance to corrosion, also they are much cheaper to produce than Ni alloys and austenitic stainless steels. However, the formation of the sigma phase and phase separation affect their mechanical properties deleteriously. The addition of Sn to the Fe±Cr system retards the sigma phase formation. Their mechanical properties may be further improved by decreasing the average grain size and the density of defects inside the grains, as in nano-grained Fe±Cr alloys. Nanocrystaline Fe±Cr±Sn alloys, which are prepared by mechanical alloying, are thus, worthy of investigation. In this work mechanical alloying of mixtures of elemental Fe, Cr and Sn powders was carried out in an Ar atmosphere using either untreated or hardened vials and balls, in order to obtain the following alloys: Fe 55-x Cr 45 Sn x with x 0, 3 and 6 at%. These were studied by 57 Fe Mo Èssbauer spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). It was found that the increasing of the Sn concentration leads to a reduction of particle size and grain size. Furthermore, milling in the untreated vials causes a partial amorphization of the alloys. Contamination from the balls and vials decreases with the increasing Sn concentration. # 1999 Elsevier Science S.A. All rights reserved.

Research paper thumbnail of Comparative study of NiW, NiMo and MoW prepared by mechanical alloying

Journal of Alloys and Compounds, 2007

The present work concern the amorphisation process induced by mechanical alloying in the NiW, NiM... more The present work concern the amorphisation process induced by mechanical alloying in the NiW, NiMo and MoW systems. The alloys chosen combine a group of transition elements varying from very similar atomic radius and electronic valences (MoW) to different ones (NiW and NiMo). The three systems achieved an amorphous state after 50h of milling. The mechanism of amorphisation proposed for

Research paper thumbnail of Mechanical alloying of the FeNi–Ag system

Journal of Alloys and Compounds, 2007

The Fe–Ni–Ag system is of particular interest for its potential applications as soft magnetic gra... more The Fe–Ni–Ag system is of particular interest for its potential applications as soft magnetic granular material with small magnetic grains embedded in a non-magnetic metal matrix. Under equilibrium conditions: Fe–Ag and Ni–Ag are immiscible and Fe–Ni shows complete solubility. These materials are particularly important for magnetoresistivity properties. The properties of these alloys are closely related to their microstructure; therefore, a

Research paper thumbnail of Solid state amorphisation in binary systems prepared by mechanical alloying

Journal of Alloys and Compounds, 2009

In the present work a detailed study of amorphisation in different systems prepared by mechanical... more In the present work a detailed study of amorphisation in different systems prepared by mechanical alloying under the same experimental conditions was carried out, milling up to 50 and 100 h in some cases. The systems studied were: AlTi, AlNi, AlFe, FeNi, FeCo, NiMo, NiW, NiCo, MoW, CoMo. These systems were chosen to study the effect of Al-transition metal, transition metal-transition metal and also systems with large and small negative heat of mixing, different and similar crystal structures, atomic sizes and diffusion coefficients. Calculations based on the Miedema model for alloy formation and amorphisation on all the alloys studied were performed. The experimental results from X-ray diffraction and transmission electron microscopy showed that the systems based on Fe (FeNi, FeCo and FeAl) did not amorphised, even after milling for 100 h, and formed a stable solid solution with a nanometric grain size of 7 nm. The systems NiMo, NiW, MoW and CoMo (systems with small negative heat of mixing), showed amorphisation after 50 h of milling. NiAl and TiAl form an intermediate amorphous phase after around 20 h of milling and with further milling they recrystallize into a fcc solid solution. Agreement between the theoretical calculations based on the Miedema model and the experimental results was found in most of the systems.

Research paper thumbnail of Selective destruction and differentiation of clay minerals from natural diaspore admixture by mortar grinding

International Journal of Mineral Processing, 1983

Mendelovici, E., . Selective destruction and differentiation of clay minerals from natural diaspo... more Mendelovici, E., . Selective destruction and differentiation of clay minerals from natural diaspore admixture by mortar grinding. Int, J. Miner. Process., 11: 131--138.

Research paper thumbnail of Mössbauer study of Fe–Co alloys with Cr additions synthesized by mechanical alloying

Hyperfine Interactions, 2010

Cr has been added to FeCo substituting 10 at.% of Co or Fe in the alloy. The alloys Fe 50 Co 40 C... more Cr has been added to FeCo substituting 10 at.% of Co or Fe in the alloy. The alloys Fe 50 Co 40 Cr 10 , Fe 40 Co 50 Cr 10 and Fe 50 Co 50 were prepared by mechanical alloying for 2, 5, 10, 20, 40 and 60 h. The formation of the alloy and the incorporation of the elements have been followed by X-Ray Diffraction (XRD) and Mössbauer Spectroscopy. The kinetics of mixing occurs by incorporation of Co and Cr into the Fe structure. After prolonged milling it seems that Cr incorporates itself into both α-Fe and α-FeCo structures and a mixture of FeCoCr rich in Cr and FeCoCr rich in Co solid solutions is obtained.

Research paper thumbnail of Aluminum Content on the Crystallization of Zeolite Beta

Microscopy and Microanalysis

The zeolite beta is a very important material for catalytic processes; it was described for the f... more The zeolite beta is a very important material for catalytic processes; it was described for the first time in 1.967 according to patent [1]. It is a microporous solid that can be synthesized in an extensive range of Si/Al ratios, its structure is formed by an intergrowth of two or three polymorphs ...

Research paper thumbnail of Study of the mechano-chemical transformation of goethite to hematite by TEM and XRD

Materials Research Bulletin, 2000

A study of the mechano-chemical transformation of goethite to hematite was carried out using tran... more A study of the mechano-chemical transformation of goethite to hematite was carried out using transmission electron microscopy (TEM) and X-ray diffraction (XRD). Synthetic goethite was dry-ground in air for different times up to 104 h and characterized with the aim of understanding the mechanisms taking part in the transformation, the phases formed, and particle distribution, morphology and size. It was