Marcelo Rubén Pagnola

Argentina INTECIN (UBA-CONICET)

Published in 2022
Structural and magnetic properties of a BaFe12O19/NiFe2O4 nanostructured composite depending on different particle size ratios
NIFEO BAFEO Magnetic Properties Chinese and American standards
Authors: R. Martínez García; V. Bilovol; S. Ferrari; P. de la Presa; P. Marín; M. Pagnola
Journal: Journal of Magnetism and Magnetic Materials
Description:
A nanostructured magnetic composite based on hexagonal ferrite BaFe12O19 (magnetically hard) and cubic ferrite NiFe2O4 (magnetically soft) is synthesized. The hexagonal ferrite precursor is obtained by the Sol-Gel method using citric acid as a coordinating agent. The precursor obtained is heated at different temperatures to get nanoparticles with different sizes. Cubic ferrite is obtained by chemical co-precipitation, method and the nanoparticle growth process is controlled with different heat treatments. The hexagonal and cubic ferrite nanoparticles are mixed providing low energy. Three samples of this kind of composite are obtained with a different ratio of particle size. The composites are a mixture where there are clusters of the minority phase NiFe2O4 distributed in a matrix of the main phase BaFe12O19. Both ferrite phases are composed of nanoparticles with an average size less than 50 nm without tensions in the crystal lattice. These structural parameters were compared between the composites and their precursor ferrites. The relationship between the composite microstructures and their magnetic properties is analyzed. A weak exchange coupling was detected between the component magnetic phases of the composites. Depending on the synthesis conditions, some samples exhibit monodomain or a multidomain regime. The higher BH product appears for composites from ferrites with a nanoparticle size ratio approximately equal to one. The structural characterization is carried out by X-ray diffraction. The homogeneity of the composition in the volume of the nanostructured composites is analyzed with a field emission scanning electron microscope equipped with energy dispersive spectroscopy for the analysis of the element mapping. The magnetic study is carried out through measurements of magnetization as a function of the applied field (M vs. H) at 300 K.
Verified
Published in 2022
Crack Formation in Chill Block Melt Spinning Solidification Process: A Comparative Analysis Using OpenFOAM®
Authors: M. R. Pagnola, F. Barceló, J. Useche
Journal: JOM
Verified
Published in 2021
Radial Distribution Function Analysis and Molecular Simulation of Graphene Nanoplatelets Obtained by Mechanical Ball Milling
Authors: M. R. Pagnola, F. Morales, P. Tancredi, L. M. Socolovsky
Journal: JOM
Published in 2020
A model for the simulation of the chill block melt spinning (CBMS) process using OpenFOAM®
OPEN FOAM VOLUME OF FLUIDS CBMS Vogel-Fulcher-Tammann
Authors: Marcelo Barone; Francisco Barceló; Marcelo Pagnola; Axel Larreteguy; Andrés G. Marrugo; Jairo Useche
Journal: International Journal of Thermal Sciences
Description:
This work shows the results of a numerical model developed to simulate the CBMS technique for the production of the Fe78Si9B13 metallic magnetic ribbons for application in electronics. The model proposes a numerical approximation to a Vogel-Fulcher-Tammann (VFT) expression as a method in the solidification process. This approximation is introduced into the “compressibleInterFoam” routine, included in the OpenFOAM® suite, originally developed for the simulation of two immiscible, non-isothermal and compressible fluids. This routine solves, the phase fraction transport using the Volume of Fluids (VOF) approach. The boundary conditions imposed in the model were experimentally validated by digital image analysis with a high-speed camera at 5602 fps for the determination of the temperature profiles. The phase change is represented as a growth of several orders of magnitude of the alloy viscosity (μ) as the temperature (T) decreases, reaching solidification around the crystallization temperature (Tg). Also, we establish the condition of initial stability of CBMS process (R > 1.5) for Peclet numbers close to 400, and the validity up to limits of rotation in the wheel close to 40 m s−1. The proposed methodology is validated with previous work. Encouraging results show that the solution of the CBMS process can be adequately simulated with the proposed approach.
Published in 2018
Influence of Nb, Mo, and Ti as doping metals on structure and magnetic response in NdFeB based melt spun ribbons
NEFEB magnetic properties Nb-Mo-Ti dopants Energy Product
Authors: D. Derewnicka-Krawczyńska; S. Ferrari; V. Bilovol; M. Pagnola; K. Morawiec; F. D. Saccone
Journal: Journal of Magnetism and Magnetic Materials
Description:
In this work, it is shown a comparative analysis of magnetic measurements that has been done over rapidly quenched melt-spinning alloyed ribbons with the formula NdyFe(86−y−x)B14Mx (X = 2, 4; Y = 7,8; M = Nb, Mo, Ti). The magnetic properties such as coercivity, saturation magnetization and energy product (B.H)max are analyzed for ribbons annealed for 20 min at 953 K in each case. It is observed that the sample with the highest saturation isNd7Fe77B14Mo2 (∼1400 kA.m−1) while the sample Nd8Fe74B14Nb4 has the lowest saturation value (∼600 kA.m−1). The sample Nd7Fe75B14Ti4 exhibits the lowest value (∼400 kA.m−1) while the Nd8Fe74B14Ti4 exhibits the highest value (∼700 kA.m−1) and the maximum (B.H)max value ∼110 kJ.m−3. The use of different experimental techniques, such as X-ray diffraction, Mössbauer spectroscopy, X-ray photoelectron spectroscopy, helped us to comprehend how M doping has influenced in a broad set of physical and chemical properties (e.g. crystalline phases, grain boundary doping enrichment, etc.) and how they correlate with the various observed magnetic features for these ribbons.
Published in 2016
Biot number behaviour in the Chill Block Melt Spinning (CBMS) process
BIOT NUMBER CBMS OPEN FOAM MELT SPINNING
Authors: M.Pagnola; M.Malmoria; M.Barone
Journal: Applied Thermal Engineering
Description:
This paper shows the change obtained in the Biot number (Bi) during the adhesion interface and the contact between phases, where the cooling and solidification of the ribbon obtained by the CBMS process occurs. This change shows an increase in the number of Bi according to the tangential velocity of the copper wheel (Vx) in the pressure range of the tests that define the ejection speeds in the nozzle (Vo). The present study demonstrates that a zone where Vo is close to 2 m/s appears, and a transition of the Bis/l numbers from magnitudes below unity until this value is exceeded can be observed. In this study, the Bis/l > 1 values indicate that Newtonian cooling occurs during the ribbon’s solidification process and show that the convective forces on the external part of the solidifying mass begin to influence the amount of heat transferred during the liquid/solid phase in the adhesion zone.
Published in 2015
Influence of z/w relation in Chill Block Melt Spinning (CBMS) process and analysis of thickness in ribbons
SOLIDIFICATION MAGNETIC MATERIALS 2D MODELING THIN FILMS
Authors: Marcelo R. Pagnola; Marcelo Barone; Mariano Malmoria; Hugo Sirkin
Journal: Multidiscipline Modeling in Materials and Structures
Description:
The purpose of this paper is to present an analysis over own and other authors data related to the process of Chill Block Melt Spinning (CBMS) and propose a model of analysis for interpretation. The similarity between our own experimental data. with others data reported by other authors, both z/w ratio and the thicknesses of the films produced has been found. This allows us to establish an exponential decay of the parameters studied and possibly link it to the Newtonian cooling to which the samples are subjected in its production.
Published in 2014
Analysis of Fe78Si9B13 (%at.) ribbons of noncommercial scrap materials produced by melt spinning equipment
AMORPHOUS MATERIALS MAGNETIC MATERIALS MOSSBAUER EFFECT NANOSTRUCTURES
Authors: Marcelo R. Pagnola; Mariano Malmoria; Marcelo Barone; Hugo Sirkin
Journal: Multidiscipline Modeling in Materials and Structures
Description:
The purpose of this paper is to present a ribbons production route of composition Fe78Si9B13 (%at.) using low-cost noncommercial scrap materials to obtain usable magnetic cores by melt spinning technique and their characterization. This way, these may compete with the materials produced by conventional casting processes. The methodology is to design a master alloy with scrap different starting compositions, to which Fe is added to get the desired atomic ratio of components. With this starting alloy, using the method of melt spinning, in its variant of chill block melt spinning, are achieved amorphous ribbons with desired soft magnetic behavior. Then these ribbons are thermally treated for achieving nanocrystalline structures to improve the performance in the magnetic cores.
Published in 2009
Improvement to the second‐order rational functions approximation for hysteresis cycles of magnetic materials
Hysteresis Cycles Magnetic Measurement Physical Properties Semi‐empirical Approach
Authors: M.R. Pagnola; F. D. Saccone; A. Ozols; H. Sirkin
Journal: COMPEL
Description:
The purpose of this paper is to introduce a simplified method, based on an improvement to the actual second‐order approximation to magnetic hysteresis curves, to calculate an estimation of quasi‐static hysteresis loops of ferromagnetic materials. The addition of a new dB(B) function is proposed to second‐order rational approximation for the upward and downward magnetic quasi‐static hysteresis loop. The new semi‐empirical approach is tested with typical cycles of commercial Ni‐ferrites (ferroxcube) and Ni standards using a vibrating sample magnetometer (VSM). The model is simple and a fast tool to reproduce with reasonable accuracy the hysteresis loops based on appropriate parameters of materials under analysis. The proposed extension to the Rivas model has reduced the maximum difference between experimental and modeled values from 19 to 0.08 per cent in the approximation to different hysteresis cycles of the magnetic materials studied here.
Published in 2009
Nanocrystals magnetic contribution to FINEMET-type soft magnetic materials with Ge addition
FINEMET Nanocrystals Ge addition Structural Properties
Authors: D. Muraca; J. Silveyra; M. Pagnola; V. Cremaschi
Journal: Journal of Magnetism and Magnetic Materials
Description:
Over the last years several works have been published in which magnetic and structural properties of soft magnetic nanocrystalline alloys were reported. Among these, there are a series of articles where the nanocrystals composition of FINEMET-type alloys with Ge addition was obtained by Mössbauer spectroscopy (MS) and X-ray diffraction (XRD). By considering a linear relationship between the magnetic moments of the nanocrystals and the composition of various elements in these crystallites, the magnetic moment of the nanocrystals was calculated. This paper reviews results obtained by different authors since 1980 and they are compared with ours. In turn, we revised some elements not previously considered for the calculus of the nanocrystals composition that allowed us to obtain the magnetic moment of the crystallites in the alloy. In particular, we analyzed FINEMET-type alloys with replacement of B for Ge: Fe73.5Si13.5Ge2B7Nb3Cu1 and Fe73.5Si13.5Ge4B5Nb3Cu1. The nanocrystalline structure was obtained by isothermal annealing of melt-spun ribbons at 823 K for 1 h. From MS and XRD we obtained the atomic composition of the nanocrystals in the magnetic material. The magnetic contribution of the nanocrystals to the alloy was calculated using a linear model and the results were compared with experimental measurements of the samples.