Insights onto the magnetic coupling at hexaferrite-based hard/soft bilayer systems

IBERTRIVA 2019 X Iberian Conference on Tribology – IBERTRIB, XI Iberian Vacuum Conference - RIVA, Seville, Spain,June 26-28Magnets are used in a variety of applications, such as generators, magnetic recording media, components in RF and microwave devices. However, many of these magnets contain s rare earths, critical elements whose extraction is environmentally harmful and that present price volatility risks. Their replacement by cheaper and more environmentally friendly materials is therefore sought. In our case, we have focused on magnetically hard strontium hexaferrite (SrFe 12O19, SFO) as the base for alternative permanent magnets (Figure 1a). The atomic arrangement of this ferrite results in a high magnetocrystalline anisotropy and a coercive field, however, its magnetization is moderate (1). It is well known that the coupling between a magnetically hard and soft material improved magnetization while avoiding a high cost in coercitivity loss (2). However, results have been disappointing so far as structural and geometrical limitations make it extremely challenging to fabricate. In this work, we aim at further understanding the magnetic coupling at hard -soft interfaces involving ferrites, for which we have deposited soft iron and cobalt metals on top of SrFe12O19 thin films with controlled easy-axis of magnetization. SFO thin films have been obtained by RF magnetron sputtering at 260W followed by a subsequent annealing in air of 850ºC. Their structure and composition was characterized by Raman spectroscospy (Figure 1b), Mössbauer spectroscopy, X-ray photoemission spectroscopy and low-energy electron microscopy (LEEM). We have grown the magnetically soft layer by molecular-beam epitaxy and we have analyzed the resulting bilayer system through photoemission electron microscopy, LEEM and vibrating-sample magnetometry. References [1] R.C. Pullar, Hexagonal ferrites: a review of the synthesis, properties and applications of hexaferrite ceramics, Progress in Materials Science 57 (2012), pp 1191¿1334. [2] Eric E. Fullerton, J. S. Jiang, M. Grimsditch, C. H. Sowers, and S. D. Bader, Exchange-spring behavior in epitaxial hard/soft magnetic bilayers, Phys. Rev. B 58 (1998) 1219

Substituent and ring effects on enthalpies of formation: 2-methyl- and 2-ethylbenzimidazoles versus benzene-and imidazole-derivatives

The enthalpies of combustion, heat capacities, enthalpies of sublimation and enthalpies of formation of 2-methylbenzimidazole (2MeBIM) and 2-ethylbenzimidazole (2EtBIM) are reported and the results compared with those of benzimidazole itself (BIM). Theoretical estimates of the enthalpies of formation were obtained through the use of atom equivalent schemes. The necessary energies were obtained in single-point calculations at the B3LYP/6-311+G(d,p) on B3LYP/6-31G* optimized geometries. The comparison of experimental and calculated values of benzenes, imidazoles and benzimidazoles bearing H (unsubstituted), methyl and ethyl groups shows remarkable homogeneity. The energetic group contribution transferability is not followed, but either using it or adding an empirical interaction term, it is possible to generate an enormous collection of reasonably accurate data for different substituted heterocycles (pyrazole-derivatives, pyridine-derivatives, etc.) from the large amount of values available for substituted benzenes and those of the parent (pyrazole, pyridine) heterocycles.We acknowledge the financial support of the DGI/MCyT (project nos. BQU-2003-00976, 01251 and 05827). This work has been partially supported by the DGI project no. BQU-2003-00894. A generous allocation of computational time at the CCC of the Universidad Auto´noma de Madrid is also gratefully acknowledged. Thanks are also due to Instituto de Cooperac¸a˜o Cientı´fica e Tecnolo´gica Internacional (ICCTI), Lisbon, Portugal, and Consejo Superior de Investigaciones Cientı´ficas (CSIC), Madrid, Spain, for a joint research project ICCTI/CSIC. MLPFA thanks Fundac¸a˜o para a Cieˆncia e Tecnologia (FCT), Lisbon, Portugal, for the award of a postdoctoral fellowship (PRAXIS XXI/BPD/16319/98) and MT thanks MECD/SEEU (AP 2002-0603), Spain, for financial support

Experimental thermochemical study of two 2-alkylbenzimidazole isomers (alkyl = propyl and isopropyl)

This paper reports the values of the standard (p∘=0.1 MPa) molar enthalpy of formation in the condensed, at T=298.15 K, for 2-R-benzimidazoles (R=propyl, isopropyl), derived from, the respective enthalpies of combustion in oxygen, measured by static bomb combustion calorimetry and the standard molar enthalpies of sublimation, at T=298.15 K, obtained using Calvet microcalorimetry in the case of 2-isopropylbenzimidazole and, by the variation of vapour pressures, determined by the Knudsen effusion technique, with temperatures between (344 and 365) K for 2-propylbenzimidazole. Heat capacities, in the temperature ranges from T=268 K to near their respective melting temperatures, T=421 K for 2-propylbenzimidazole and T=464 K for 2-isopropylbenzimidazole, were measured with a differential scanning calorimeter. These values were used to derive the standard molar enthalpies of formation, of the two 2-benzimidazole derivatives, in gaseous phase.Thanks are due to Instituto de Cooperação Cientı́fica e Tecnológica Industrial (ICCTI), Lisbon, Portugal, and Consejo Superior de Investigaciones Cientı́ficas (CSIC), Madrid, Spain for a joint research project CSIC/ICCTI; M.L.P.F.A. thanks Fundação para a Ciência e Tecnologia (FCT), Lisbon, Portugal, for the award of a postdoctoral fellowship (SRFH/BPD/5595/2001). The Spanish DGI/MCyT is acknowledged under projects BQU2000-0252, 0906 and 1497; M.T. thanks MECD/SEEU, AP2002-0603, Spain for financial support

Substituent effects on enthalpies of formation of nitrogen heterocycles: 2-substituted benzimidazoles and related compounds

The enthalpies of combustion, heat capacities, enthalpies of sublimation and enthalpies of formation of 2-tert-butylbenzimidazole (2tBuBIM) and 2-phenylimidazole (2PhIM) are reported and the results compared with those of benzene derivatives and a series of azoles (imidazoles, pyrazoles, benzimidazoles and indazoles). Theoretical estimates of the enthalpies of formation were obtained through the use of atom equivalent schemes. The necessary energies were obtained in single-point calculations at the B3LYP/6-311++G(d,p) on B3LYP/6-31G* optimized geometries. The comparison of experimental and calculated values of all studied compounds bearing H (unsubstituted), methyl (Me) ethyl (Et), propyl (Pr), isopropyl (iPr), tert-butyl (tBu), benzyl (Bn) and phenyl (Ph) groups show remarkable homogeneity. The remarkable consistency of both the calculated and experimental results allows us to predict with reasonable certainty the missing experimental values. The crystal and molecular structure of the 2-benzylbenzimidazole (2BnBIM) has been determined by X-ray analysis. The observed molecular conformation permits the crystal being built up through N−H···N hydrogen bonds and van der Waals contacts between the molecules. An attempt has been made to relate the crystal structure to the enthalpies of sublimation.Thanks are due to Instituto de Cooperac¸a˜o Cientı´fica e Tecnolo´gica International (ICCTI), Lisbon, Portugal, and Consejo Superior de Investigaciones Cientı´ficas (CSIC), Madrid, Spain. L.M.P.F.A. thanks Fundac¸a˜o para a Cieˆncia e Tecnologia (FCT), Lisbon, Portugal, for the award of a postdoctoral fellowship (PRAXIS XXI/BPD/16319/98). This work has also been financed by DGICYT (BQU-2003- 00894, -00976 and -01251)

Phenylisoxazole-3/5-Carbaldehyde Isonicotinylhydrazone Derivatives: Synthesis, Characterization, and Antitubercular Activity

14 pags, 5 figs, 3 tabs, 1 schEight new phenylisoxazole isoniazid derivatives, 3-(2′-fluorophenyl)isoxazole-5-carbaldehyde isonicotinylhydrazone (1), 3-(2′-methoxyphenyl)isoxazole-5-carbaldehyde isonicotinylhydrazone (2), 3-(2′-chlorophenyl)isoxazole-5-carbaldehyde isonicotinylhydrazone (3), 3-(3′-clorophenyl)isoxazole-5-carbaldehyde isonicotinylhydrazone (4), 3-(4′-bromophenyl)isoxazole-5-carbaldehyde isonicotinylhydrazone (5), 5-(4′-methoxiphenyl)isoxazole-3-carbaldehyde isonicotinylhydrazone (6), 5-(4′-methylphenyl)isoxazole-3-carbaldehyde isonicotinylhydrazone (7), and 5-(4′-clorophenyl)isoxazole-3-carbaldehyde isonicotinylhydrazone (8), have been synthesized and characterized by FT-IR, 1H-NMR, 13C-NMR, and mass spectral data. The 2D NMR (1H-1H NOESY) analysis of 1 and 2 confirmed that these compounds in acetone-d6 are in the trans(E) isomeric form. This evidence is supported by computational calculations which were performed for compounds 1-8, using DFT/B3LYP level with the 6-311++G(d,p) basis set. The in vitro antituberculous activity of all the synthesized compounds was determined against the Mycobacterium tuberculosis standard strains: sensitive H37Rv (ATCC-27294) and resistant TB DM97. All the compounds exhibited moderate bioactivity (MIC = 0.34-0.41 μM) with respect to the isoniazid drug (MIC = 0.91 μM) against the H37Rv sensitive strain. Compounds 6 (X = 4′-OCH3) and 7 (X = 4′-CH3) with MIC values of 12.41 and 13.06 μM, respectively, were about two times more cytotoxic, compared with isoniazid, against the resistant strain TB DM97.W. H. and F. C. acknowledge Universidad de Lima Scientific Research Institute for the financial support to carry out this research work. E. S. thanks Financiamiento Basal para Centros Cientificos y Tecnologicos de Excelencia, AFB10008. J. Z. D. thanks Consejo Superior de Investigacion Cientifica (CSIC, Spain). S. O. thanks Ministerio de Ciencias, Innovacion y Universidades (MICINN (RTI2018-094356-B-C21)) and Cabildo de Tenerife (Agust ' in de Betancourt Program).Peer reviewe

Enthalpies of formation of N-substituted pyrazoles and imidazoles

Accurate experimental enthalpies of formation measured using static bomb combustion calorimetry, the “vacuum sublimation” drop calorimetry method, and the Knudsen-effusion method are reported for the first time for four azoles:  1-methylimidazole (1MeIMI), 1-methylpyrazole (1MePYR), 1-benzylimidazole (1BnIMI), and 1-benzylpyrazole (1BnPYR). These values and those corresponding to imidazole (1HIMI), pyrazole (1HPYR), 1-ethylimidazole (1EtIMI), 1-ethylpyrazole (1EtPYR), 1-phenylimidazole (1PhIMI), and 1-phenylpyrazole (1PhPYR) are compared with theoretical values using the G2(MP2) and the B3LYP/6-311*G(3df,2p)//6-31G(d) approaches. In general, there is a very good agreement between calculated and experimental values for the series of N-substituted imidazoles, while the agreement is less good for the series of the N-substituted pyrazoles. Experimentally, the gap between the enthalpies of formation of imidazoles and pyrazoles decreases significantly upon N-substitution, while the theoretical estimates indicate that this decrease is smaller.This work has been partially supported by the DGES Projects PB 96-0001-C03-03, PB96-0067, and PB96-0927-C02-01. A generous allocation of computational time at the Centro de Computacio´n Cientı´fica de la Facultad de Ciencias (CCCFC) de la UAM is also gratefully acknowledged. Thanks are due to Junta National de Investigac¸a˜o Cientı´fica e Tecnolo´gica (JNICT), Lisbon, Portugal and Consejo Superior de Investigaciones Cientı´ficas (CSIC), Madrid, Spain, for a joint research project CSIC/JNICT. Financial support from the Praxis XXI, Project 2/2.1/qui/54/94, is acknowledged. L.M.P.F.A. thanks Fundac¸aˆo para a Cieˆncia e Tecnologia, Lisbon, Portugal for the award of a postdoctoral fellowship (Praxis XXI/BDP/16319/98). J.F.L. acknowledges funding from “Dow Chemical Company” for partial support of his thermochemical studies

Antioxidantes y la Química Computacional

Ciclo de conferencias virtuales por los 60 años de la Facultad de ciencias de la Universidad Nacional de Ingeniería, Perú, 21 - 25 de setiembre de 202

Microcalorímetro de combustión

Referencia OEPM: P200001506.-- Fecha de solicitud: 15/06/2000.-- Titular: Consejo Superior de Investigaciones Científicas (CSIC).Microcalorímetro de combustión caracterizado por ser de tipo isoperibol que consta de: un baño termostático, que contiene agua agitada y termorregulada, con una cámara submarina hecha de acero inoxidable. Una vasija calorimétrica con un volumen interno de, aproximadamente, 0.59 dm3. Tanto la vasija calorimétrica como la camisa, tienen forma elíptica y permiten que por todas partes haya una separación entre las paredes de, aproximadamente, 10 mm de aire. Las paredes están pulidas para evitar radiación térmica. En la vasija se sitúa una bomba de combustión.Peer reviewe

Ciencia y Tecnología: simbiosis perfecta del conocimiento humano

Ciencia y Tecnología: simbiosis perfecta del conocimiento humano, Conferencia virtual, Universidad Nacional de San Antonio Abad del Cusco, 27 de abril, 2020; https://www.youtube.com/watch?v=Z8zl3hwQJ9

Propiedades energéticas de las harinas de pseudocereales andinos con alto valor nutricional

I Simposio Internacional-Perspectivas de la Investigación y Seguridad Alimentaria, Perú, 25 Septiembre 2020Estudiamos propiedades energéticas y estructurales de harinas de quinua (Chenopodium quinoa Willd), achita/kiwicha/amaranto (Amaranthus caudatus) y cañihua (Chenopodium pallidicaule Allen) suministrados por agriculrotes de Tambillos-Huamanga (Ayacucho). Usamos técnicas experimentales como, i/espectrometría de masas para determinar sus contenidos en semi-metales y metales pesados, ii/ calormetría de combustión para evaluar el contenido energético total (¿valor calórico neto¿) de cada producto, iii/ calorimetría diferencial de barrido DSC para determinar calores específicos, temperaturas de descomposición, temperaturas y entalpías de gelatinización. Es importante mencionar que los valores energéticos determinados de manera directa y precisa son significativamente más altos que las estimaciones reportadas (en páginas webb y publicaciones diversas), particularmente para la quinua (438 kcal/100g) que es similar para la achita (436 kcal/100g) y ligeramente menor para la cañihua (443 kcal/100g)