Kinetics of crystallization of FeB-based amorphous alloys studied by neutron thermo-diffractometry

Kinetics of crystallization of two amorphous alloys, Fe70Cr10B20 and Fe80Zr10B10, have been followed up by neutron thermodiffractometry experiments performed in the two axis diffractometer D20 (ILL, Grenoble). The structural changes are directly correlated with the temperature dependence of the magnetization. Fe70Cr10B20 crystallizes following a two-step process: an eutectic crystallization of alfa-Fe (bcc) and the metastable tetragonal phase (Fe0.8Cr0.2)3B followed by another eutectic transformation to the stable phase (Fe0.75Cr0.25)2B and more segregation of alfa-Fe. These tetragonal phases are magnetically anisotropic, giving rise to a large increase of the coercivity. This behaviour is similar to that of Fe80B20 alloys, with Cr atoms replacing the Fe positions in both crystalline phases. Fe80Zr10B10 shows also a two-step process in which two polymorphic transformations take place.Comment: 3 pages. Proceedings International Workshop Non-Crystalline Solids 2006, Gijon (Spain

Mössbauer Study of FeNbCuSiB Mechanical Alloying Process

In the present work we report the preparation of nanocrystalline alloys, of composition Fe73.5Nb3Cu1Si13.5B9, formed directly by mechanical alloying of the constituents. Powders of the pure elements, in the appropriate proportions, were mixed in a Reitch planetary ball mill for upto 120 hours. The composition and the amount of the crystalline phases evolve during the milling and have been followed by Mossbauer Spectroscopy. A metastable FeSi solid solution is-formed with up to 18% Si content. This phase contains about 50% of the Fe present in the sample. At the same time other Fe disordered alloys-are produced. These are characterised by an inhomogeneous distribution of hyperfine fields

Nanocrystalline FeNbCuSiB Magnetic Alloys Obtained by Ball Milling

We report the obtention of nanocrystalline FeSi alloys together with an amorphous phase by direct mechanical alloying of the constituents. Powders of the pure elements in the appropriate proportions (Fe73.5Nb3Cu1Si13.5B9 and Fe73.5Nb3Cu1Si16.5B6), were mixed in a Reitch planetary ball mill for up to 120 hours. The resulting products were analyzed by X-ray diffraction and magnetic measurements. In all the cases an FeSi crystalline phase was present after a few hours of milling. Also an amorphous alloy develops simultaneously. The composition and size of the crystalline phases as well as the amount of the amorphous phase evolves during the milling. The evolution of coercive force, magnetic moment and the Curie temperature of the FeSi phase has been monitored. The coercive force decreases with increase milling time, but never reaches the low values of nanocrystalline materials obtained by heating metallic glasses of the same composition

Magnetic entropy change and refrigerant capacity of rapidly solidified TbNi2 alloy ribbons

"The magnetocaloric effect in TbNi2 alloy ribbons synthesized by rapid solidification was investigated. This material crystallizes in a superstructure of the cubic Laves phase structure type C15 (space group F-43m). The saturation magnetization and Curie temperature are M-S = 134 +/- 2A m(2) kg(-1) and T-C = 37 +/- 1K, respectively. For a magnetic field change of 5 T, the material shows a maximum magnetic entropy change vertical bar Delta S-M(peak)vertical bar = 13.9 J kg(-1) K-1, with a full-width at half-maximum delta T-FWHM = 32 K, and a refrigerant capacity RC = 441 J kg(-1). The RC value is similar to those reported for other magnetic refrigerants operating within the temperature range of 10-80 K. Finally, it is worth noting that the use of rapid solidification circumvents the necessity for longterm high-temperature homogenization processes normally needed with these RNi2 alloys.

Investigating the magnetic entropy change in single-phase Y2Fe17 melt-spun ribbons

"The inspection of simplified fabrication and/or processing routes in order to produce materials with attractive magnetocaloric properties is of paramount importance for the development of environmentally friendly magnetic cooling technology. In this work, we have made use of the melt-spinning technique to obtain directly single-phase Y2Fe17 polycrystalline ribbons avoiding any high-temperature annealing for phase consolidation and homogenization. The melt-spun ribbons, with hexagonal Th2Ni17-type crystal structure, exhibit a moderate maximum value of the magnetic entropy change, |?SMpeak| = 2.4(4.4) J kg?1 K?1 under an applied magnetic field change of 2(5) T. Although these values are similar to those for the bulk alloy, the ?SM(T) curves are manifestly broader, thus giving rise to an expansion of the working temperature range and the enhancement of about 15% in the refrigerant capacity. We also show that the magnetic field dependence of |?SMpeak| at T = TC follows a H2/3 power-law.

Magnetic entropy table-like shape in RNi2 composites for cryogenic refrigeration

"We have investigated the magnetocaloric (MC) effect in a two-phase composite based on melt-spun ribbons of the intermetallic DyNi2 and TbNi2 Laves phases. The temperature dependence of the isothermal magnetic entropy change, Delta S-M(T), has been calculated for the biphasic system x(DyNi2) + y(TbNi2) with 0< x < 1 (i. e., y - 1 - x). The optimum MC properties, i. e., a Delta S-M(T) curve with table-like shape, has been found in the temperature interval of 18-44K for the composite with x = 0.4 and for values of the magnetic field change mu(o)Delta H - 2 and 5 T, in good agreement with the experimental data. The refrigerant capacity, RC, reaches 221(526) J kg(-1) with a temperature span delta T-FWHM of 32(41) K for mu(o)Delta H of 2(5) T, thus improving the values obtained for the individual RNi2 ribbons. Our findings constitute a good starting point to stimulate the search for new composites with enhanced MC properties at cryogenic temperatures.

"Nací el 21 en primavera..." - Mujeres al borde de un ataque de versos / Donne sull'orlo di una crisi di versi (collana "La rosa inalcanzable")

Antologia di poesia spagnola contemporanea femminile curata e tradotta da P. Laskaris, che si inserisce nella collana "La rosa inalcanzable" e nel progetto "Nací el 21 en primavera..." avviato nel 2008. Le poetesse antologizzate sono: Carmen Camacho, Ana Gorría, Elena Medel, Sofía Rhei, Sara Toro. A queste voci si aggiungono quelle di Julia Castillo, Patricia esteban, Erika Martínez Miriam Reyes e Alejandra Vanessa

Evaluación de la actividad asistencial de un equipo multidisciplinario de soporte nutricional en el seguimiento de la nutrición parenteral total Assessment of activity of care of a nutritional support multidiciplinary team in the follow-up of total parenteral nutrition

INTRODUCCIÓN: En la Nutrición Parenteral Total (NPT) los equipos multidisciplinarios de soporte nutricional (EMSN) deben proporcionar una asistencia nutricional de calidad basada en la evidencia y en el seguimiento diario de los pacientes sometidos a NPT. Objetivos: Evaluar el grado de cumplimiento de los estándares de calidad en la asistencia prestada a los pacientes con NPT por parte del EMSN en dos períodos anuales sucesivos, de acuerdo con indicadores de estructura, proceso y resultado previamente definidos en el protocolo de trabajo del equipo. PACIENTES Y MÉTODOS: Estudio prospectivo de todos los pacientes que recibieron NPT en nuestro centro (hospital general docente con 421 camas) durante el año 2002 y durante el año 2003, utilizando los datos introducidos en NUTRIDATA© mediante el seguimiento diario de las condiciones clínicas, analíticas y complicaciones nutricionales y no nutricionales, comparando ambos períodos y considerando un nivel de significación de p INTRODUCTION: In total parenteral nutrition (TPN) nutritional support multidisciplinary teams (NSMT) must provide a high quality nutritional assistance based on evidence and daily follow-up of patients with TPN. Objectives: To assess the degree of adherence to quality standards of care provided to patients on TPN by the NSMT in two consecutive annual periods,according to structure, procedure, and outcomes indicators, previously defined in the team working protocol. PATIENTS AND METHODS: Prospective study of all patients that received TPN at our Center (421-bed general teaching hospital) during the years 2002 and 2003, using the data introduced in NUTRIDATA® by daily follow-up of clinical and analytical conditions, and nutritional and non-nutritional complications, comparing both periods and considering an statistical significance level of p <0.05. RESULTS: One hundred and sixty-three patients and 145 patients received TPN during 2002 and 2003(65.9% male), respectively, with similar parameters of gender, age, indications for TPN, baseline nutritional status, mean nutritional supply, and non-nutritional complications. As to the different quality indicators established in the comparative study, we found a significant improvement in 2003 vs. 2002 in relation to initial anthropometrical assessment (71.03% vs 51.53%; p < 0.001), initial biochemical assessment (97.93% vs. 92.63%; p < 0.04), performance of systematic monitoring analysis (84.83% vs. 71.78%; p < 0.01), hypernatremia incidence (8.27% vs. 15.34%; p = 0.05) and moderate hyperphosphatemia (26.89% vs.40.49%; p < 0.02), TPN ending for clinical improve ment (76.60% vs. 64.40%; p = 0.04), and reduction of days on TPN (15.74 &plusmn; 20.43 vs. 11.88 &plusmn; 8.34; p < 0.02), the impaired electrolyte levels significantly improving as a whole. We also observed a non-significant trend towards an improvement of adequacy of TPN indications, hyperphosphatemia, severe hypophosphatemia, total stay, and post-surgical stay, in 2003 vs. 2002. CONCLUSIONS: The NSMT experience shows that analysis of indicators based on quality standards, in two successive annual periods allows assessing the improvement of efficiency of nutritional intervention in hospital-admitted patients with TPN with regards to indication, assessment, follow-up, and course