Isabel Sobrados - Academia.edu (original) (raw)

Papers by Isabel Sobrados

Research paper thumbnail of Microstructural and mechanical properties of silica–PEPEG polymer composite xerogels

Acta Materialia, 2006

We prepared and characterized silica-polyethylene-block-polyethylene glycol (PEPEG) nanocomposite... more We prepared and characterized silica-polyethylene-block-polyethylene glycol (PEPEG) nanocomposite xerogels and investigated the role of addition of the elastic PEPEG oligomer in a brittle porous silica matrix by relating microstructure to mechanical properties. For PEPEG < 7 wt.%, the oligomer fills smaller pores in the silica matrix; but, as evidenced by atomic force microscopy and Fourier transform infrared spectroscopy, PEPEG partially disrupts matrix formation at higher concentrations. Consequently the pore size distribution shifts towards larger sizes and the specific surface area of the composite decreases. The toughness increases continuously with PEPEG addition. The elastic modulus of the composite increases twofold for 7 wt.% PEPEG, but decreases on further addition of PEPEG. Microhardness and structural loss factor also show a similar optimum for PEPEG at around 5-7 wt.%. The analytical and empirical models agree with the experimental modulus values for lower PEPEG addition, but fail to explain the maximum because of their inability to capture the observed microstructural changes in the composite structure.

Research paper thumbnail of Hybrid Cements: Mechanical Properties, Microstructure and Radiological Behavior

Molecules, 2022

The use of more eco-efficient cements in concretes is one of the keys to ensuring construction in... more The use of more eco-efficient cements in concretes is one of the keys to ensuring construction industry sustainability. Such eco-efficient binders often contain large but variable proportions of industrial waste or by-products in their composition, many of which may be naturally occurring radioactive materials (NORMs). This study explored the application of a new gamma spectrometric method for measuring radionuclide activity in hybrid alkali-activated cements from solid 5 cm cubic specimens rather than powder samples. The research involved assessing the effect of significant variables such as the nature of the alkaline activator, reaction time and curing conditions to relate the microstructures identified to the radiological behavior observed. The findings showed that varying the inputs generated pastes with similar reaction products (C-S-H, C-A-S-H and (N,C)-A-S-H) but different microstructures. The new gamma spectrometric method for measuring radioactivity in solid 5 cm cubic spec...

Research paper thumbnail of Electrical and Structural Properties of Li1.3Al0.3Ti1.7(PO4)3—Based Ceramics Prepared with the Addition of Li4SiO4

Materials, 2021

The currently studied materials considered as potential candidates to be solid electrolytes for L... more The currently studied materials considered as potential candidates to be solid electrolytes for Li-ion batteries usually suffer from low total ionic conductivity. One of them, the NASICON-type ceramic of the chemical formula Li1.3Al0.3Ti1.7(PO4)3, seems to be an appropriate material for the modification of its electrical properties due to its high bulk ionic conductivity of the order of 10−3 S∙cm−1. For this purpose, we propose an approach concerning modifying the grain boundary composition towards the higher conducting one. To achieve this goal, Li4SiO4 was selected and added to the LATP base matrix to support Li+ diffusion between the grains. The properties of the Li1.3Al0.3Ti1.7(PO4)3−xLi4SiO4 (0.02 ≤ x ≤ 0.1) system were studied by means of high-temperature X-ray diffractometry (HTXRD); 6Li, 27Al, 29Si, and 31P magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR); thermogravimetry (TG); scanning electron microscopy (SEM); and impedance spectroscopy (IS) techniq...

Research paper thumbnail of New Approach for the Determination of Radiological Parameters on Hardened Cement Pastes with Coal Fly Ash

Materials, 2021

Supplementary cementitious materials (SCMs) in industrial waste and by-products are routinely use... more Supplementary cementitious materials (SCMs) in industrial waste and by-products are routinely used to mitigate the adverse environmental effects of, and lower the energy consumption associated with, ordinary Portland cement (OPC) manufacture. Many such SCMs, such as type F coal fly ash (FA), are naturally occurring radioactive materials (NORMs). 226Ra, 232Th and 40K radionuclide activity concentration, information needed to determine what is known as the gamma-ray activity concentration index (ACI), is normally collected from ground cement samples. The present study aims to validate a new method for calculating the ACI from measurements made on unground 5 cm cubic specimens. Mechanical, mineralogical and radiological characterisation of 28-day OPC + FA pastes (bearing up to 30 wt % FA) were characterised to determine their mechanical, mineralogical and radiological properties. The activity concentrations found for 226Ra, 212Pb, 232Th and 40K in hardened, intact 5 cm cubic specimens ...

Research paper thumbnail of Polysiloxane Hybrids via Sol-Gel Process: Effect of Temperature on Network Formation

Coatings, 2020

The effect of temperature on the network formation of polysiloxane hybrids was evaluated since th... more The effect of temperature on the network formation of polysiloxane hybrids was evaluated since this type of material is currently in high demand. In the last decades, the deposition of these coatings on different substrates, mostly metals, has demonstrated anticorrosion properties. Sol-gel hybrids were prepared by mixing 3-methacryloxypropyltrimethoxysilane (MPTS) and tetramethyl orthosilicate (TMOS) with a molar ratio of 1. The formation, thickness and composition of these hybrid materials were evaluated by nuclear magnetic resonance (NMR) spectroscopy and scanning electron microscopy (SEM), respectively. The results showed that the temperature plays an important role in the network formation, the total condensation degree and the total dimensionality of the hybrid materials. At room temperature, the polysiloxane hybrids presented total condensation degrees lower than 75% and a total dimensionality (dtotal) = 2.5, while those obtained at 65 °C presented total condensation degrees h...

Research paper thumbnail of Density Functional Theory Modeling of Solid-State Nuclear Magnetic Resonances for Polycyclic Aromatic Hydrocarbons

The Journal of Physical Chemistry C, 2018

Experimental Solid State Nuclear Magnetic Resonance (SS-NMR) has been used to analyze different t... more Experimental Solid State Nuclear Magnetic Resonance (SS-NMR) has been used to analyze different theoretical models for Polycyclic Aromatic Hydrocarbon crystals of similar structure (naphthalene, anthracene, phenanthrene, picene, and triphenylene). We compare the accuracy of four modeling approaches to compute SS-NMR chemical shifts using ab-initio Density Functional Theory (DFT). Models based on X-Ray cell parameters, on optimization of cell with Perdew, Burke and Ernzerhof (PBE) approximation and on two methods adding dispersion forces were compared (using Pearson's and Mean Absolute Deviation correlation factors). Even if the intermolecular distances and cell volumes are different depending on the model, there is an overall good agreement between theoretical and experimental 13 C chemical shifts for all of them. An analysis of intermolecular distances and deviation from planarity in different models and their influence on theoretical chemical shieldings is also performed.

Research paper thumbnail of Structural transition in orthorhombic Li5−xHxLa3Nb2O12 garnets induced by a concerted lithium and proton diffusion mechanism

Journal of Materials Chemistry A, 2018

Li5−xHxLa3Nb2O12 (x ≈ 2.8) transforms from an orthorhombic into a cubic symmetry through a phase ... more Li5−xHxLa3Nb2O12 (x ≈ 2.8) transforms from an orthorhombic into a cubic symmetry through a phase transition driven by concerted Li and H diffusion.

Research paper thumbnail of Comprehensive investigation of the lithium insertion mechanism of the Na2Ti6O13 anode material for Li-ion batteries

Journal of Materials Chemistry A, 2018

Sodium hexatitanate Na2Ti6O13 with a tunnel structure has been proposed to be an attractive anode... more Sodium hexatitanate Na2Ti6O13 with a tunnel structure has been proposed to be an attractive anode material for lithium ion batteries because of its low insertion voltage, structural stability and good reversibility.

Research paper thumbnail of Acid-based geopolymers: Understanding of the structural evolutions during consolidation and after thermal treatments

Journal of Non-Crystalline Solids, 2019

Materials such as ceramic matrix composites are developed for mechanical applications at high tem... more Materials such as ceramic matrix composites are developed for mechanical applications at high temperature, but their cost remains a limitation. Consequently, the use of acid-based geopolymer matrices may be an alternative to reduce costs. In this study, the sample was prepared from metakaolin and phosphoric acid. FTIR and NMR spectroscopies, XRD and thermal measurements were used to understand the structural evolution of acid-based geopolymers (binders) during consolidation and after thermal treatments. According to the results, the consolidation of the binder has been divided into four steps: the dissolution of the metakaolin, the polycondensation reactions forming AlPO 4 entities and hydrated phases, the breakdown of Si-O-Al bonds with formation of various hydrated silica *Manuscript Click here to download Manuscript: manuscript.docx Click here to view linked References

Research paper thumbnail of Water-Free Proton Conduction in Discotic Pyridylpyrazolate-based Pt(II) and Pd(II) Metallomesogens

Inorganic Chemistry, 2016

Research paper thumbnail of Synthesis and Characterization of NaNiF3·3H2O: An Unusual Ordered Variant of the ReO3 Type

Inorganic Chemistry, 2015

A new hydrated sodium nickel fluoride with nominal composition NaNiF 3 3H 2 O was synthesized us... more A new hydrated sodium nickel fluoride with nominal composition NaNiF 3 3H 2 O was synthesized using an aqueous solution route. Its structure has been solved by means of ab initio methods from powder X-ray diffraction and neutron diffraction data. NaNiF 3 3H 2 O crystallizes in the cubic crystal system, space group Pn-3 with a = 7.91968(4) Å. The framework, derived from the ReO 3 structure type, is built up by NaX 6 and NiX 6 (X=O,F) corner-shared octahedra, in which F and O atoms are randomly distributed on a single anion site. The 2a x 2a x 2a superstructure arises from the strict alternate 3D-link-up of NaX 6 and NiX 6 octahedra together with the simultaneous tilts of the octahedra from the cube axis ( = 31.1°), with a significant participation of hydrogen bonding. NaNiF 3 3H 2 O corresponds to a fully cation ordered variant of the In(OH) 3 structure, easily recognizable when formulated as NaNi(XH) 6 (X=O,F). It constitutes one of the rare examples for the a + a + a + tilting scheme with 1:1 cation ordering in perovskite-related compounds. The Curie-like magnetic behavior well reflects the isolated paramagnetic Ni 2+ centers without worth mentioning interactions. While X-ray and neutron diffraction data evidence Na/Ni order in combination to O/F disorder as a main feature of this fluoride, results from Raman and MAS-NMR spectroscopies support the existence of specific anion arrangements in isolated square windows identified in structural refinements. In particular, formation of water molecules derives from unfavorable FH bond formation.

Research paper thumbnail of An X-ray and 13C CP/MAS NMR study of C,C-linked bipyrazoles and bispyrazolylmethanes

Spectrochimica Acta Part A: Molecular Spectroscopy, 1994

4,4'-Methylene-bispyrazole (1) crystallizes in the P2,ln space group with 2=4, a=5.4199(8) A, b =... more 4,4'-Methylene-bispyrazole (1) crystallizes in the P2,ln space group with 2=4, a=5.4199(8) A, b = 16.194(6) A, c = 8.381(5) A, B = 98.18(S)". 4,4'-Methylene-bis (3,5-dimethylpyrazole) (2) crystallizes in the Pbca space group with Z= 8, a= 8.350(3) A, b = 16.078(3) 8, and c= 17.154(5) A. Finally, 3,3'-bipyrazole (4) crystallizes in the P2,ln space group with Z=2, a =5.465(2) A, b= 5.491(3) A, c= 10.058(4) 8, and /?= 92.88(2)". The packing adopted by molecules 1 and 2 is related to the disposition of the pyrazole rings. In compound 4, all the molecules are joined to their neighbors by two double hydrogen bond systems forming zigzag chains. Using solid state '% NMR spectroscopy, no dynamic proton transfer was observed in these crystals, and not on those of 3,5,3',5'-tetramethyl-4,4'-bipyrazole (3) either.

Research paper thumbnail of FTIR and NMR Study of the Adsorbed Water on Nanocrystalline Anatase

The Journal of Physical Chemistry C, 2007

A hydrated anatase sample with crystal size of 11 nm, prepared by a method involving a calcinatio... more A hydrated anatase sample with crystal size of 11 nm, prepared by a method involving a calcination treatment, has been studied by FTIR, 1 H MAS NMR, and TPD techniques, to determine the characteristics of the hydroxyls and water adsorbed on its surface. The 1 H NMR and FTIR spectra of the sample, hydrated and evacuated at increasing temperature, show that most of the hydrated anatase water, weakly adsorbed and highly mobile, is forming the multilayer of water molecular arrangements (MAs). The easy desorption of this water at roomtemperature facilitates the observation of less mobile adsorbed water, whose removal originates two overlapped water desorption peaks, with maxima at 353 and 373 K, observed in the TPD profile. Most of this less weakly adsorbed water is desorbed from the MAs second layer, originating the low-temperature maximum. On the other hand, the removal of some water bound to bridging O 2anions, interacting with terminal hydroxyls, contributes to the maximum at 373 K. The TPD peak with maximum at 430 K is mainly formed by the desorption of water interacting with bridging hydroxyls. The TPD shoulder observed at 540 K is originated by the desorption of water coordinated to Ti 4+ cations, forming the first layer of the water MAs. The anatase 1 H MAS NMR spectrum obtained after evacuation at 473 K is mainly formed by the signals of bridging and terminal hydroxyls.

Research paper thumbnail of Ion exchange between tectosilicates with the nepheline-kalsilite framework and molten MNO3 or MO (M = Li, Na, K, Ag)

Physics and Chemistry of Minerals, 1993

Natural nepheline, a synthetic Na-rich nepheline, and synthetic kalsilite were ion exchanged in m... more Natural nepheline, a synthetic Na-rich nepheline, and synthetic kalsilite were ion exchanged in molten MNO3 or MC1 (M=Li, Na, K, Ag) at 220-800 ~ C. Crystalline products were characterized by wet chemical and electron microprobe analysis, single crystal and powder X-ray diffraction, and transmission electron microscopy and diffraction. Two new compounds were obtained: Li-exchanged nepheline with a formula near (Li,Ko.3,D)Li~[A13(A1,Si)Si~O16] and a monoclinic unit cell with a=951.0(6) b=976.1(6) c=822.9(5) pm 7= 119.15 ~ and Ag-exchanged nepheline with a formula near (K,Na, D)Ag3[At3(A1,Si)Si40~6] and a hexagonal unit cell with a = 1007.4(8) c = 838.2(1.0) pm. Both compounds apparently retain the framework topology of the starting material. Ion exchange isotherms and structural data show that immiscibility between the end members is a general feature in the systems Na-Li, Na-Ag, and Na-K. For the system Na-K, a stepwise exchange is observed with (K,D)Na3[A13(AI,Si)Si40~6] as an intermediate composition which has the nepheline structure and is miscible with the sodian end member (Na,D)Na3[A13-(A1,Si)Si40~6], but not with the potassian end member (K,D)4[A13(A1,Si)Si4Oa6] which shows the kalsilite structure; there was no indication for the formation of trior tetrakalsilite (K/(K + Na) ~ 0.7) at the temperatures studied (350 and 800 ~ C). The exact amount of vacancies [] on the alkali site depends upon the starting material and was found to be conserved during exchange, with ca 0-0.2 and 0.3-0.4 vacancies per 16 oxygen atoms for the synthetic and natural precursors, respectively. Thermodynamic interpretation of the Na-K exchange isotherms shows, as one important result, that the sodian end member is unstable with respect to the intermediate at K/(K +Na)~ 0.25 by an amount of ca 45 kJ/mol Na in the large cavity at 800 ~ C (52 kJ/mol at 350 ~ C).

Research paper thumbnail of Tautomerism of 1-(2′,4′-dinitrophenyl)-3-methyl-2-pyrazolin-5-one: theoretical calculations, solid and solution NMR studies and X-ray crystallography

New Journal of Chemistry, 1998

ABSTRACT To gain a better understanding of the tautomerism of 1-(2′,4′-dinitrophenyl)-3-methyl-2-... more ABSTRACT To gain a better understanding of the tautomerism of 1-(2′,4′-dinitrophenyl)-3-methyl-2-pyrazolin-5-one, 2, different studies were performed. In order to simulate the gas phase, several MO calculations at the semiempirical (AM1 and PM3) and abinitio (HF/6-31G* and B3LYP/6-31G*) levels were carried out on the different tautomers of this compound and on those of the corresponding 1-phenyl derivative 4. The 1H and 13C NMR spectra were recorded in solution for compound 2. Finally, to investigate the solid state, 13C CPMAS NMR studies and the crystal structure analysis of this pyrazolinone and that of its isomer [1-(2′,4′-dinitrophenyl)-3-hydroxy-5-methylpyrazole, 3, whose chemical structure was incorrectly reported in the literature] were performed. In solution, the most abundant tautomer for both pyrazolinones, 2 and 4, depends on the solvent used. For compound 2 it was found that the CH tautomer was the most stable in the gas and solid states as opposed to its 1-phenyl analogue, which appears as the CH form in the gas phase and as NH and OH tautomers in the crystal.

Research paper thumbnail of Synthesis, characterization and oxide conduction in Ba doped apatite-type silicates Ca2La6Bi2(SiO4)6O2

Materials Chemistry and Physics, 2014

Research paper thumbnail of C-S-H Gels: Interpretation of 29Si MAS-NMR Spectra

Journal of the American Ceramic Society, 2012

Page 1. C–S–H Gels: Interpretation of 29Si MAS-NMR Spectra Ines Garcı´a-Lodeiro, ‡,† Ana Ferna´nd... more Page 1. C–S–H Gels: Interpretation of 29Si MAS-NMR Spectra Ines Garcı´a-Lodeiro, ‡,† Ana Ferna´ndez-Jime´nez, ‡ Isabel Sobrados, § Jesus Sanz, § and Angel Palomo ‡ ... References 1T. Mitsuda and HFW Taylor, “Normal and Anormalous Tobermor-ites,” Min. ...

Research paper thumbnail of Structural Changes Induced on Mullite Precursors by Thermal Treatment: A 27Al MAS-NMR Investigation

Journal of the American Ceramic Society, 1991

NMR study of mullite precursors has shown that local arrangement of A1 in samples synthesized by ... more NMR study of mullite precursors has shown that local arrangement of A1 in samples synthesized by spray pyrolysis differs considerably from the one adopted by samples obtained by polymeric or colloidal routes. Aluminum is tetraand pentahedrally coordinated in the first type of samples but is tetra-and octahedrally coordinated in the second ones. Segregation of S O z and AIz03 is directly produced in colloidal preparation; however, this phenomenon occurs only in polymeric gels when they are heated between 980" and 1100°C. In polymeric samples, thermal treatment at-980°C produces the formation of y-A1203. A similar treatment in spray-pyrolized powders gives directly 3: 2 mullite. From these results, exothermic and expansive effects detected at-980°C were ascribed to changes in coordination of Al produced during the atomic rearrangement that accompanies formation of these two phases (y-A1203 or mullite). Above 1200"C, incorporation of Si in the Al-rich phase induces the formation of 3:2 mullite in polynieric and colloidal samples.

Research paper thumbnail of Alkaline Activation of Fly Ashes: NMR Study of the Reaction Products

Journal of the American Ceramic Society, 2004

Page 1. Alkaline Activation of Fly Ashes: NMR Study of the Reaction Products A´ ngel Palomo, Sant... more Page 1. Alkaline Activation of Fly Ashes: NMR Study of the Reaction Products A´ ngel Palomo, Santiago Alonso, and Ana Fernandez-Jiménez ... (2) Alkali Activation In Table II, the reaction degree attained in activated ashes is showed as a function of curing conditions. ...

Research paper thumbnail of Molecular structure of 4-(3,5-dimethylpyrazol-1-yl)benzoic acid trifluoroacetate

Journal of Chemical Crystallography, 1996

Molecular structure of 4-(3,5-dimethylpyrazol-l-yl)benzoic acid trifluoroacetate Foces-~oce~, Car... more Molecular structure of 4-(3,5-dimethylpyrazol-l-yl)benzoic acid trifluoroacetate Foces-~oce~, Carlos Cativiela, (2)* Maria Mar Zurbano, (2) Concepci6n-(1), Isabel Sobrados, (3) Nadine Jagerovic, (4) and Jos6 Elguero (4)

Research paper thumbnail of Microstructural and mechanical properties of silica–PEPEG polymer composite xerogels

Acta Materialia, 2006

We prepared and characterized silica-polyethylene-block-polyethylene glycol (PEPEG) nanocomposite... more We prepared and characterized silica-polyethylene-block-polyethylene glycol (PEPEG) nanocomposite xerogels and investigated the role of addition of the elastic PEPEG oligomer in a brittle porous silica matrix by relating microstructure to mechanical properties. For PEPEG < 7 wt.%, the oligomer fills smaller pores in the silica matrix; but, as evidenced by atomic force microscopy and Fourier transform infrared spectroscopy, PEPEG partially disrupts matrix formation at higher concentrations. Consequently the pore size distribution shifts towards larger sizes and the specific surface area of the composite decreases. The toughness increases continuously with PEPEG addition. The elastic modulus of the composite increases twofold for 7 wt.% PEPEG, but decreases on further addition of PEPEG. Microhardness and structural loss factor also show a similar optimum for PEPEG at around 5-7 wt.%. The analytical and empirical models agree with the experimental modulus values for lower PEPEG addition, but fail to explain the maximum because of their inability to capture the observed microstructural changes in the composite structure.

Research paper thumbnail of Hybrid Cements: Mechanical Properties, Microstructure and Radiological Behavior

Molecules, 2022

The use of more eco-efficient cements in concretes is one of the keys to ensuring construction in... more The use of more eco-efficient cements in concretes is one of the keys to ensuring construction industry sustainability. Such eco-efficient binders often contain large but variable proportions of industrial waste or by-products in their composition, many of which may be naturally occurring radioactive materials (NORMs). This study explored the application of a new gamma spectrometric method for measuring radionuclide activity in hybrid alkali-activated cements from solid 5 cm cubic specimens rather than powder samples. The research involved assessing the effect of significant variables such as the nature of the alkaline activator, reaction time and curing conditions to relate the microstructures identified to the radiological behavior observed. The findings showed that varying the inputs generated pastes with similar reaction products (C-S-H, C-A-S-H and (N,C)-A-S-H) but different microstructures. The new gamma spectrometric method for measuring radioactivity in solid 5 cm cubic spec...

Research paper thumbnail of Electrical and Structural Properties of Li1.3Al0.3Ti1.7(PO4)3—Based Ceramics Prepared with the Addition of Li4SiO4

Materials, 2021

The currently studied materials considered as potential candidates to be solid electrolytes for L... more The currently studied materials considered as potential candidates to be solid electrolytes for Li-ion batteries usually suffer from low total ionic conductivity. One of them, the NASICON-type ceramic of the chemical formula Li1.3Al0.3Ti1.7(PO4)3, seems to be an appropriate material for the modification of its electrical properties due to its high bulk ionic conductivity of the order of 10−3 S∙cm−1. For this purpose, we propose an approach concerning modifying the grain boundary composition towards the higher conducting one. To achieve this goal, Li4SiO4 was selected and added to the LATP base matrix to support Li+ diffusion between the grains. The properties of the Li1.3Al0.3Ti1.7(PO4)3−xLi4SiO4 (0.02 ≤ x ≤ 0.1) system were studied by means of high-temperature X-ray diffractometry (HTXRD); 6Li, 27Al, 29Si, and 31P magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR); thermogravimetry (TG); scanning electron microscopy (SEM); and impedance spectroscopy (IS) techniq...

Research paper thumbnail of New Approach for the Determination of Radiological Parameters on Hardened Cement Pastes with Coal Fly Ash

Materials, 2021

Supplementary cementitious materials (SCMs) in industrial waste and by-products are routinely use... more Supplementary cementitious materials (SCMs) in industrial waste and by-products are routinely used to mitigate the adverse environmental effects of, and lower the energy consumption associated with, ordinary Portland cement (OPC) manufacture. Many such SCMs, such as type F coal fly ash (FA), are naturally occurring radioactive materials (NORMs). 226Ra, 232Th and 40K radionuclide activity concentration, information needed to determine what is known as the gamma-ray activity concentration index (ACI), is normally collected from ground cement samples. The present study aims to validate a new method for calculating the ACI from measurements made on unground 5 cm cubic specimens. Mechanical, mineralogical and radiological characterisation of 28-day OPC + FA pastes (bearing up to 30 wt % FA) were characterised to determine their mechanical, mineralogical and radiological properties. The activity concentrations found for 226Ra, 212Pb, 232Th and 40K in hardened, intact 5 cm cubic specimens ...

Research paper thumbnail of Polysiloxane Hybrids via Sol-Gel Process: Effect of Temperature on Network Formation

Coatings, 2020

The effect of temperature on the network formation of polysiloxane hybrids was evaluated since th... more The effect of temperature on the network formation of polysiloxane hybrids was evaluated since this type of material is currently in high demand. In the last decades, the deposition of these coatings on different substrates, mostly metals, has demonstrated anticorrosion properties. Sol-gel hybrids were prepared by mixing 3-methacryloxypropyltrimethoxysilane (MPTS) and tetramethyl orthosilicate (TMOS) with a molar ratio of 1. The formation, thickness and composition of these hybrid materials were evaluated by nuclear magnetic resonance (NMR) spectroscopy and scanning electron microscopy (SEM), respectively. The results showed that the temperature plays an important role in the network formation, the total condensation degree and the total dimensionality of the hybrid materials. At room temperature, the polysiloxane hybrids presented total condensation degrees lower than 75% and a total dimensionality (dtotal) = 2.5, while those obtained at 65 °C presented total condensation degrees h...

Research paper thumbnail of Density Functional Theory Modeling of Solid-State Nuclear Magnetic Resonances for Polycyclic Aromatic Hydrocarbons

The Journal of Physical Chemistry C, 2018

Experimental Solid State Nuclear Magnetic Resonance (SS-NMR) has been used to analyze different t... more Experimental Solid State Nuclear Magnetic Resonance (SS-NMR) has been used to analyze different theoretical models for Polycyclic Aromatic Hydrocarbon crystals of similar structure (naphthalene, anthracene, phenanthrene, picene, and triphenylene). We compare the accuracy of four modeling approaches to compute SS-NMR chemical shifts using ab-initio Density Functional Theory (DFT). Models based on X-Ray cell parameters, on optimization of cell with Perdew, Burke and Ernzerhof (PBE) approximation and on two methods adding dispersion forces were compared (using Pearson's and Mean Absolute Deviation correlation factors). Even if the intermolecular distances and cell volumes are different depending on the model, there is an overall good agreement between theoretical and experimental 13 C chemical shifts for all of them. An analysis of intermolecular distances and deviation from planarity in different models and their influence on theoretical chemical shieldings is also performed.

Research paper thumbnail of Structural transition in orthorhombic Li5−xHxLa3Nb2O12 garnets induced by a concerted lithium and proton diffusion mechanism

Journal of Materials Chemistry A, 2018

Li5−xHxLa3Nb2O12 (x ≈ 2.8) transforms from an orthorhombic into a cubic symmetry through a phase ... more Li5−xHxLa3Nb2O12 (x ≈ 2.8) transforms from an orthorhombic into a cubic symmetry through a phase transition driven by concerted Li and H diffusion.

Research paper thumbnail of Comprehensive investigation of the lithium insertion mechanism of the Na2Ti6O13 anode material for Li-ion batteries

Journal of Materials Chemistry A, 2018

Sodium hexatitanate Na2Ti6O13 with a tunnel structure has been proposed to be an attractive anode... more Sodium hexatitanate Na2Ti6O13 with a tunnel structure has been proposed to be an attractive anode material for lithium ion batteries because of its low insertion voltage, structural stability and good reversibility.

Research paper thumbnail of Acid-based geopolymers: Understanding of the structural evolutions during consolidation and after thermal treatments

Journal of Non-Crystalline Solids, 2019

Materials such as ceramic matrix composites are developed for mechanical applications at high tem... more Materials such as ceramic matrix composites are developed for mechanical applications at high temperature, but their cost remains a limitation. Consequently, the use of acid-based geopolymer matrices may be an alternative to reduce costs. In this study, the sample was prepared from metakaolin and phosphoric acid. FTIR and NMR spectroscopies, XRD and thermal measurements were used to understand the structural evolution of acid-based geopolymers (binders) during consolidation and after thermal treatments. According to the results, the consolidation of the binder has been divided into four steps: the dissolution of the metakaolin, the polycondensation reactions forming AlPO 4 entities and hydrated phases, the breakdown of Si-O-Al bonds with formation of various hydrated silica *Manuscript Click here to download Manuscript: manuscript.docx Click here to view linked References

Research paper thumbnail of Water-Free Proton Conduction in Discotic Pyridylpyrazolate-based Pt(II) and Pd(II) Metallomesogens

Inorganic Chemistry, 2016

Research paper thumbnail of Synthesis and Characterization of NaNiF3·3H2O: An Unusual Ordered Variant of the ReO3 Type

Inorganic Chemistry, 2015

A new hydrated sodium nickel fluoride with nominal composition NaNiF 3 3H 2 O was synthesized us... more A new hydrated sodium nickel fluoride with nominal composition NaNiF 3 3H 2 O was synthesized using an aqueous solution route. Its structure has been solved by means of ab initio methods from powder X-ray diffraction and neutron diffraction data. NaNiF 3 3H 2 O crystallizes in the cubic crystal system, space group Pn-3 with a = 7.91968(4) Å. The framework, derived from the ReO 3 structure type, is built up by NaX 6 and NiX 6 (X=O,F) corner-shared octahedra, in which F and O atoms are randomly distributed on a single anion site. The 2a x 2a x 2a superstructure arises from the strict alternate 3D-link-up of NaX 6 and NiX 6 octahedra together with the simultaneous tilts of the octahedra from the cube axis ( = 31.1°), with a significant participation of hydrogen bonding. NaNiF 3 3H 2 O corresponds to a fully cation ordered variant of the In(OH) 3 structure, easily recognizable when formulated as NaNi(XH) 6 (X=O,F). It constitutes one of the rare examples for the a + a + a + tilting scheme with 1:1 cation ordering in perovskite-related compounds. The Curie-like magnetic behavior well reflects the isolated paramagnetic Ni 2+ centers without worth mentioning interactions. While X-ray and neutron diffraction data evidence Na/Ni order in combination to O/F disorder as a main feature of this fluoride, results from Raman and MAS-NMR spectroscopies support the existence of specific anion arrangements in isolated square windows identified in structural refinements. In particular, formation of water molecules derives from unfavorable FH bond formation.

Research paper thumbnail of An X-ray and 13C CP/MAS NMR study of C,C-linked bipyrazoles and bispyrazolylmethanes

Spectrochimica Acta Part A: Molecular Spectroscopy, 1994

4,4'-Methylene-bispyrazole (1) crystallizes in the P2,ln space group with 2=4, a=5.4199(8) A, b =... more 4,4'-Methylene-bispyrazole (1) crystallizes in the P2,ln space group with 2=4, a=5.4199(8) A, b = 16.194(6) A, c = 8.381(5) A, B = 98.18(S)". 4,4'-Methylene-bis (3,5-dimethylpyrazole) (2) crystallizes in the Pbca space group with Z= 8, a= 8.350(3) A, b = 16.078(3) 8, and c= 17.154(5) A. Finally, 3,3'-bipyrazole (4) crystallizes in the P2,ln space group with Z=2, a =5.465(2) A, b= 5.491(3) A, c= 10.058(4) 8, and /?= 92.88(2)". The packing adopted by molecules 1 and 2 is related to the disposition of the pyrazole rings. In compound 4, all the molecules are joined to their neighbors by two double hydrogen bond systems forming zigzag chains. Using solid state '% NMR spectroscopy, no dynamic proton transfer was observed in these crystals, and not on those of 3,5,3',5'-tetramethyl-4,4'-bipyrazole (3) either.

Research paper thumbnail of FTIR and NMR Study of the Adsorbed Water on Nanocrystalline Anatase

The Journal of Physical Chemistry C, 2007

A hydrated anatase sample with crystal size of 11 nm, prepared by a method involving a calcinatio... more A hydrated anatase sample with crystal size of 11 nm, prepared by a method involving a calcination treatment, has been studied by FTIR, 1 H MAS NMR, and TPD techniques, to determine the characteristics of the hydroxyls and water adsorbed on its surface. The 1 H NMR and FTIR spectra of the sample, hydrated and evacuated at increasing temperature, show that most of the hydrated anatase water, weakly adsorbed and highly mobile, is forming the multilayer of water molecular arrangements (MAs). The easy desorption of this water at roomtemperature facilitates the observation of less mobile adsorbed water, whose removal originates two overlapped water desorption peaks, with maxima at 353 and 373 K, observed in the TPD profile. Most of this less weakly adsorbed water is desorbed from the MAs second layer, originating the low-temperature maximum. On the other hand, the removal of some water bound to bridging O 2anions, interacting with terminal hydroxyls, contributes to the maximum at 373 K. The TPD peak with maximum at 430 K is mainly formed by the desorption of water interacting with bridging hydroxyls. The TPD shoulder observed at 540 K is originated by the desorption of water coordinated to Ti 4+ cations, forming the first layer of the water MAs. The anatase 1 H MAS NMR spectrum obtained after evacuation at 473 K is mainly formed by the signals of bridging and terminal hydroxyls.

Research paper thumbnail of Ion exchange between tectosilicates with the nepheline-kalsilite framework and molten MNO3 or MO (M = Li, Na, K, Ag)

Physics and Chemistry of Minerals, 1993

Natural nepheline, a synthetic Na-rich nepheline, and synthetic kalsilite were ion exchanged in m... more Natural nepheline, a synthetic Na-rich nepheline, and synthetic kalsilite were ion exchanged in molten MNO3 or MC1 (M=Li, Na, K, Ag) at 220-800 ~ C. Crystalline products were characterized by wet chemical and electron microprobe analysis, single crystal and powder X-ray diffraction, and transmission electron microscopy and diffraction. Two new compounds were obtained: Li-exchanged nepheline with a formula near (Li,Ko.3,D)Li~[A13(A1,Si)Si~O16] and a monoclinic unit cell with a=951.0(6) b=976.1(6) c=822.9(5) pm 7= 119.15 ~ and Ag-exchanged nepheline with a formula near (K,Na, D)Ag3[At3(A1,Si)Si40~6] and a hexagonal unit cell with a = 1007.4(8) c = 838.2(1.0) pm. Both compounds apparently retain the framework topology of the starting material. Ion exchange isotherms and structural data show that immiscibility between the end members is a general feature in the systems Na-Li, Na-Ag, and Na-K. For the system Na-K, a stepwise exchange is observed with (K,D)Na3[A13(AI,Si)Si40~6] as an intermediate composition which has the nepheline structure and is miscible with the sodian end member (Na,D)Na3[A13-(A1,Si)Si40~6], but not with the potassian end member (K,D)4[A13(A1,Si)Si4Oa6] which shows the kalsilite structure; there was no indication for the formation of trior tetrakalsilite (K/(K + Na) ~ 0.7) at the temperatures studied (350 and 800 ~ C). The exact amount of vacancies [] on the alkali site depends upon the starting material and was found to be conserved during exchange, with ca 0-0.2 and 0.3-0.4 vacancies per 16 oxygen atoms for the synthetic and natural precursors, respectively. Thermodynamic interpretation of the Na-K exchange isotherms shows, as one important result, that the sodian end member is unstable with respect to the intermediate at K/(K +Na)~ 0.25 by an amount of ca 45 kJ/mol Na in the large cavity at 800 ~ C (52 kJ/mol at 350 ~ C).

Research paper thumbnail of Tautomerism of 1-(2′,4′-dinitrophenyl)-3-methyl-2-pyrazolin-5-one: theoretical calculations, solid and solution NMR studies and X-ray crystallography

New Journal of Chemistry, 1998

ABSTRACT To gain a better understanding of the tautomerism of 1-(2′,4′-dinitrophenyl)-3-methyl-2-... more ABSTRACT To gain a better understanding of the tautomerism of 1-(2′,4′-dinitrophenyl)-3-methyl-2-pyrazolin-5-one, 2, different studies were performed. In order to simulate the gas phase, several MO calculations at the semiempirical (AM1 and PM3) and abinitio (HF/6-31G* and B3LYP/6-31G*) levels were carried out on the different tautomers of this compound and on those of the corresponding 1-phenyl derivative 4. The 1H and 13C NMR spectra were recorded in solution for compound 2. Finally, to investigate the solid state, 13C CPMAS NMR studies and the crystal structure analysis of this pyrazolinone and that of its isomer [1-(2′,4′-dinitrophenyl)-3-hydroxy-5-methylpyrazole, 3, whose chemical structure was incorrectly reported in the literature] were performed. In solution, the most abundant tautomer for both pyrazolinones, 2 and 4, depends on the solvent used. For compound 2 it was found that the CH tautomer was the most stable in the gas and solid states as opposed to its 1-phenyl analogue, which appears as the CH form in the gas phase and as NH and OH tautomers in the crystal.

Research paper thumbnail of Synthesis, characterization and oxide conduction in Ba doped apatite-type silicates Ca2La6Bi2(SiO4)6O2

Materials Chemistry and Physics, 2014

Research paper thumbnail of C-S-H Gels: Interpretation of 29Si MAS-NMR Spectra

Journal of the American Ceramic Society, 2012

Page 1. C–S–H Gels: Interpretation of 29Si MAS-NMR Spectra Ines Garcı´a-Lodeiro, ‡,† Ana Ferna´nd... more Page 1. C–S–H Gels: Interpretation of 29Si MAS-NMR Spectra Ines Garcı´a-Lodeiro, ‡,† Ana Ferna´ndez-Jime´nez, ‡ Isabel Sobrados, § Jesus Sanz, § and Angel Palomo ‡ ... References 1T. Mitsuda and HFW Taylor, “Normal and Anormalous Tobermor-ites,” Min. ...

Research paper thumbnail of Structural Changes Induced on Mullite Precursors by Thermal Treatment: A 27Al MAS-NMR Investigation

Journal of the American Ceramic Society, 1991

NMR study of mullite precursors has shown that local arrangement of A1 in samples synthesized by ... more NMR study of mullite precursors has shown that local arrangement of A1 in samples synthesized by spray pyrolysis differs considerably from the one adopted by samples obtained by polymeric or colloidal routes. Aluminum is tetraand pentahedrally coordinated in the first type of samples but is tetra-and octahedrally coordinated in the second ones. Segregation of S O z and AIz03 is directly produced in colloidal preparation; however, this phenomenon occurs only in polymeric gels when they are heated between 980" and 1100°C. In polymeric samples, thermal treatment at-980°C produces the formation of y-A1203. A similar treatment in spray-pyrolized powders gives directly 3: 2 mullite. From these results, exothermic and expansive effects detected at-980°C were ascribed to changes in coordination of Al produced during the atomic rearrangement that accompanies formation of these two phases (y-A1203 or mullite). Above 1200"C, incorporation of Si in the Al-rich phase induces the formation of 3:2 mullite in polynieric and colloidal samples.

Research paper thumbnail of Alkaline Activation of Fly Ashes: NMR Study of the Reaction Products

Journal of the American Ceramic Society, 2004

Page 1. Alkaline Activation of Fly Ashes: NMR Study of the Reaction Products A´ ngel Palomo, Sant... more Page 1. Alkaline Activation of Fly Ashes: NMR Study of the Reaction Products A´ ngel Palomo, Santiago Alonso, and Ana Fernandez-Jiménez ... (2) Alkali Activation In Table II, the reaction degree attained in activated ashes is showed as a function of curing conditions. ...

Research paper thumbnail of Molecular structure of 4-(3,5-dimethylpyrazol-1-yl)benzoic acid trifluoroacetate

Journal of Chemical Crystallography, 1996

Molecular structure of 4-(3,5-dimethylpyrazol-l-yl)benzoic acid trifluoroacetate Foces-~oce~, Car... more Molecular structure of 4-(3,5-dimethylpyrazol-l-yl)benzoic acid trifluoroacetate Foces-~oce~, Carlos Cativiela, (2)* Maria Mar Zurbano, (2) Concepci6n-(1), Isabel Sobrados, (3) Nadine Jagerovic, (4) and Jos6 Elguero (4)