204 research outputs found
Milling and quite-fast sintering as key production steps to obtain fully dense PZTN-CF particulate composites
No full textIn the near future (within ten years) magnetoelectric multiferroics could be implemented into the emerging technologies such as wireless power, internet of things, machine-to-machine communication services, mesh network, etc. Remarkable efforts have been done to develop laminated bi-layer and multilayer multiferroic composites as bulk or thin films. These structures lead to remarkable magneto-electric coupling coefficients of a few Volts / cm∙Oe because the ferroic layer is a "full dielectric" which can be completely poled in the conventional way. On the other hand in the particulate ceramic composites the requirement for "full dielectric" is no longer applicable, since the ferroic phases are fully separated within the composite. The strengths of particulate ceramic composites are low cost, simple production technology, higher strain mediated magneto-electric coupling (since electric order phase/magnetic phase interface density can be higher) and easy control of electrical and magnetic properties if the ferroelectric phase (generally a perovskite) and the ferromagnetic one (a ferrite with spinel structure) are mixed in a favourable proportion under the percolation threshold of the ferromagnetic phase. A great research effort is in progress to improve the fabrication of PZT-CoFe2O4 (PZT- CF) composites in order to avoid the unwanted reactions, which occur during densification of PZT-CF materials at 1100-1200 °C, and to achieve the electric saturation during the poling. Up to date, by setting a quite-fast sintering, full densification and prevention of unwanted reactions were achieved for the PZT:CF 74:26 composites,1 but achieving electric saturation is still a challenge. Further important results were: the understanding that the main cause of reactions is the PbO loss;1 the proposal of an equation to calculate the PbO loss through XRD analysis, considering the amount of ZrO2 and variation of perovskite's tetragonality;1 and the ability to design the ceramic process (milling of the CF powers in particularly) to control the CF grain size distribution, which can be mono- or bi-modal, and overgrowth.1,2 References 1. P. Galizia, C.E. Ciomaga, L. Mitoseriu and C. Galassi, "PZT-cobalt ferrite particulate composites: Densification and lead loss controlled by quite-fast sintering", J. Eur. Ceram. Soc., 37, pp. 161-168, 2016. 2. P. Galizia, C. Baldisserri, C. Capiani and C. Galassi, "Multiple parallel twinning overgrowth in nanostructured dense cobalt ferrite", Mater. Design, 109, pp. 19-26, 2016
Thick composite magnetoelectric films by electrophoretic deposition
No full textElectrophoretic deposition (EPD) from colloidal suspensions was utilized for the preparation of composite magneto-dielectric films on a conductive substrate. The present process is developed as a convenient forming process for the development of devices based on thick magneto-dielectric films [1]. The deposition parameters - using EPD - such as colloidal parameters, deposition voltage and deposition time and the post process parameters, such as drying velocity and sintering will be controlled. This work aims to control the fillers/matrix ratio during the deposition and obtain a good adhesion, compaction and functionality of the composite film after the heat treatment. Measurements results for the current transients during constant-voltage deposition and the correlated deposited mass are presented [2, 3].1] A.O. Karilainen, P.M.T. Ikonen, C.R. Simovski, S.A. Tretyakov, A.N. Lagarkov, S.A. Maklakov, K.N. Rozanov, and S.N. Starostenko, Experimental studies on antenna miniaturisation using magneto-dielectric and dielectric materials, IET Microw. Antennas Propag., vol. 5, no. 4, pp. 495-502, 2011. 2] C. Baldisserri, D. Gardini and C. Galassi, An analysis of current transients during electrophoretic deposition (EPD) from colloidal TiO2 suspensions, Journal of Colloid and Interface Science 347 (2010) 102-111 3] H. Farnoush, J.A. Mohandesi, D. H. Fatmehsari and F. Moztarzadeh, A kinetic study on the electrophoretic deposition of hydroxyapatite-titania nanocomposite based on a statistical approach, Ceramics International 38 (2012), 6753-676
Heterostructured ceramic materials based on PZTN-CFO compounds
No full textMultiferroic composites are currently one of the hot research topics [1]. Particulate ceramic composites have the advantages of low cost, simple production technology, good magnetoelectric effect and easy control of electrical and magnetic properties if the ferroelectric phase (generally a perovskite) and the ferromagnetic one (a ferrite with spinel structure) are mixed in a favourable proportion under the percolation threshold of the ferromagnetic phase. A great research effort is in progress to improve the fabrication of PZT-CoFe2O4 (PZT-CF) composites due to the excellent piezoelectric properties showed by the PZT material class and the large magnetostrictive coefficient of the CF. Unfortunately unwanted reactions occur during densification of PZT-CF materials at 1100-1200 °C. They are promoted by initial PbO loss that is calculated through XRD analysis, considering the amount of ZrO2 and variation of perovskite's tetragonality. The resulting titania reacts with CF to form cobalt titanate [2]. The microstructure of the composites at 26-81 mol % CF content was thoroughly investigated; the CF grain size distribution can be mono- or bi-modal and overgrowth [3] occurs. By setting a quite-fast sintering full densification and prevention of unwanted reactions was achieved for the PZT:CF 74:26 composites. The high coercivity (789 Oe) shown by these composites is correlated to the good dispersion of euhedral CF grains (250 nm) in the PZT matrix that is affected as well by limited grain growth (240 nm). [1] G. Schileo, Recent developments in ceramic multiferroic composites based on core/shell and other heterostructures obtained by sol-gel routes. Prog. Solid State Ch. 41 (2013) 87-98. [2] P. Galizia, et al., PZT-cobalt ferrite particulate composites: Densification and lead loss controlled by quite-fast sintering. J. Eur. Ceram. Soc. (2016). doi:10.1016/j.jeurceramsoc.2016.08.025 [3] P. Galizia, C. Baldisserri, C. Capiani, C. Galassi Multiple parallel twinning overgrowth in nanostructured dense cobalt ferrite. Mater. Design 109 (2016) 19-26. doi:10.1016/j.matdes.2016.07.05
Reduction of PbO loss in PZT-cobalt ferrite composites through quite-fast sintering and its quantification by means of XRD analysis
No full textNowadays, considerable efforts have been devoted to design and control the fabrication of multifunctional materials in order to fulfil the needs of modern technology for novel sensors, microwave devices, energy harvesting, photovoltaic technologies, solid-state refrigeration, data storage recording technologies and multiferroic random access multistate memories (MFRAM) [1]. Particulate ceramic composites are low cost, simple production technology, higher strain mediated magnetoelectric coupling (since electric order phase/magnetic phase interface density can be higher) and easy control of electrical and magnetic properties if the ferroelectric phase and the ferromagnetic one are mixed in a favourable proportion under the percolation threshold of the ferromagnetic phase. A great research effort is in progress to improve the fabrication of PZT-CoFe2O4 (PZT-CF) composites due to the excellent piezoelectric properties showed by the PZT material class and the large magnetostrictive coefficient of the CF. Unfortunately, during the sintering process particulate PZT-CF composites, side reactions do occur that are detrimental to the properties of the so-obtained material. In this study, we have avoided such reactions and PbO loss by setting a quite-fast sintering process [2]. The extent of PbO loss was determined by means of XRD analysis of the densified samples taking into account the amount of ZrO2 and the variations of the perovskite's tetragonality [2]. The calculated PbO loss values are in agreement with the final density and the microstructure of PZT-CF composites. In particular, microstructural characterization showed that CF grain size distribution can be mono- or bi-modal, and CF overgrowth was found to affect the coercivity of the material [3]. [1] M. M. Vopson, Fundamentals of Multiferroic Materials and Their Possible Applications. Crit. Rev. Solid State 4:40 (2015) 223-250 doi:10.1080/10408436.2014.992584 [2] P. Galizia, et al., PZT-cobalt ferrite particulate composites: Densification and lead loss controlled by quite-fast sintering. J. Eur. Ceram. Soc. (2016). doi:10.1016/j.jeurceramsoc.2016.08.025 [3] P. Galizia, C. Baldisserri, C. Capiani, C. Galassi, Multiple parallel twinning overgrowth in nanostructured dense cobalt ferrite. Mater. Design 109 (2016) 19-26. doi:10.1016/j.matdes.2016.07.05
La reologia dei materiali ceramici tradizionali
No full textraccolta di contributi sulla misura delle caratteristiche reologiche di sospensioni ceramich
De aldea silenciosa a urbe moderna: los inicios del transporte urbano (1850-1906)
No full textDeclarada ciudad en agosto de 1852, Rosario se destacaba de otras poblaciones argentinas por carecer de una tradición colonial. Su origen se mostraba desligado de conquistadores, funcionarios reales y familias con títulos nobiliarios. La ciudad fue receptora, particularmente a partir de las últimas décadas del siglo XIX, de numerosos contingentes inmigratorios provenientes de Europa y del progreso técnico generado por la revolución industrial, que alcanzaba esferas cada vez más amplias de la modernización social. Estas particularidades influyeron sobre los distintos grupos sociales que integraron los trayectos, imágenes y símbolos que determinaron el carácter cosmopolita y moderno de la urbe. La actividad del transporte y la comunicación de Rosario estuvieron íntimamente ligadas a su desarrollo como centro portuario desde los primeros años de la Confederación Argentina. En un comienzo, el gobierno de Paraná le adjudicó funciones que enfatizaban las actividades postales y sentaban las bases de una cierta regionalización. Luego se priorizó desde el Estado nacional la producción de las colonias agrícolas cercanas a Rosario, que junto a la llegada de la fuerza de trabajo europea resultó uno de los elementos centrales del programa de inserción del país en la «división internacional del trabajo». La ciudad se convirtió así en el puerto de exportación de los cereales argentinos y en un nodo del trazado ferroviario. Todos estos factores condujeron a un proceso de urbanización acelerado entre 1870 y 1890, y que continuaría su desarrollo en los años posteriores, simultáneamente con el crecimiento demográfico. Según los respectivos censos, Rosario contaba en 1858 con 9.780 habitantes, pasando a tener 23.169 en 1869 y alcanzando los 112.461 en 1900. Semejante aumento poblacional demandó, en función de un mercado laboral en formación, el desarrollo de un sistema de transporte, primero a nivel regional y, más tarde, en el ejido urbano.Fil: Galassi, Gisela Elisabet. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Investigaciones Socio-Históricas Regionales. Centro de Estudios Sociales Regionales - Nodo Cesor - Ishir; ArgentinaFil: Sonzogni, Elida Sofia del Carmen. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Investigaciones Socio-Históricas Regionales. Centro de Estudios Sociales Regionales - Nodo Cesor - Ishir; Argentin
Heating rate dependence of anatase to rutile transformation
No full textCommercial titania powders were calcined in order to investigate the influence of the heating history on the thermally stable phase (rutile). Temperatures from 620 to 700 °C and heating rates from 50 to 300 °C/h were used in order to evaluate their influence on the kinetics of transformation and microstructure evolution. The quantitative analysis of anatase-rutile mixtures based on X-ray diffraction intensities was performed. The results were plotted as cumulative transformation rate vs. cumulative coarsening rate in order to address the heating history of the anatase to rutile transformation. As the main result it was found that the amount of anatase transformed into rutile increases with increasing heating rate at fixed soaking time and temperature of calcination. Through linear extrapolation of experimental data obtained from the calcined commercial titania Degussa P25, it was found that 83 nm for the rutile crystallite size is the lowest limit needed for getting 100% of rutile powders. A substantial improvement in the anatase to rutile kinetic transformation was achieved after pressing the starting powders in order to exploit the interface nucleation
Magnetoelectric composite bilayer film by electrophoretic deposition
No full textIn the recent years the interest of the research community towards multiferroic composite materials was growing fast [1,2]. A number of papers relates to bulk materials while less attention is focused on films. Electrophoretic deposition (EPD) was applied to prepare magnetoelectric (ME) composite bilayer thick films based on perovskite phase and spinel cobalt ferrite as some of the best piezoelectric and magnetostrictive oxides belong these crystal groups. The co-deposition of titanium oxide (TO) and cobalt ferrite (CFO) nanoparticles and the deposition of niobium-doped lead titanate zirconate (PZTN) were made from colloidal suspensions in ethanol keeping constant voltage and recording the current. Good adhesion and compaction of the green film were achieved by optimization of deposition voltage and time while high density of the film and minimized interphase reactions occurred after sintering. The deposited volume, the mixing of dielectric and magnetic phases and the density and ordering of the films have been verified by electron scanning microscopy after heat treatment. No reactions between the different phases was found. The piezoelectric properties were measured on the sintered films. [1] N.A. Spaldin, M. Fiebig, Science 309 (2005) 391. [2] R. Ramesh, N.A. Spaldin, Nat. Mater. 6 (2007) 2
Microstructure development in novel titania-cobalt ferrite ceramic materials
No full textThe system cobalt ferrite (CFO)–titania (TO) has been studied in view to produce new in situ ceramic composites by conventional solid state reaction. To synthesize the CFO–TO composite, the processing parameters are optimized to yield a reliable and repeatable homogeneous distribution of the phases. Composition, crystalline structure and microstructure of the sintered bodies were investigated by XRD, SEM, microprobe analysis; the image analysis was performed to quantify the phase volume content and grain size. The final compositions after sintering differ significantly from the starting ones as a consequence of the reaction of titania with the ferrite and the formation of a new ternary compound Fe2CoTi3O10 (FCTO). In this work we report for the first time the preparation of almost pure (about 95 vol%) single phase FCTO ceramics, its XRD patterns, and the microstructural characterization
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