COMPOSITE MATERIALS

Author: GIMENEZ LAZARRAGA MONICA.
Year: 2004.
University: AUTÓNOMA DE MADRID [www.uam.es].
Place of defense: FACULTAD DE CIENCIAS.
Place of preparation: FACULTAD DE CIENCIAS.

Summary: We have studied composite solid electrolyte and cathode. The composite materials are solid electrolyte binary systems which consist of a driver with ion type structure Nasicon and composition LiSn2 (PO4) 3 and a polymer insulator (Teflon). The composite cathode ternary systems are being trained by the cathode active material (LiMn2O4), a polymer (PVDF) and a driver-mail (NC). The composite materials formed by LiSn2 (PO4) 3 and Teflon show a microstructure in which there are individual particles of ionic conductor surrounded by the polymer (particles isolated), aggregates of particles ionic conductor surrounded by the polymer (aggregates isolated), and aggregates driver ion particles ranging from one end of the composite material to the other end (aggregates extended). Only the latter allow the conduct of Li + ions as a model percolativo. The threshold for percolation (30% by volume of LiSn2 (PO4) 3) is higher than expected (17%) for a random distribution of particles. This is because in the process of aggregation of particles are formed aggregates isolated before connecting with each other to give rise to widespread aggregates. To explain the dependence of the ionic conductivity depending on the frequency has been developed a model that takes into account the microstructure of the composites. This model has allowed us to determine the intrinsic ionic conductivity of LiSn2 (PO4) 3 and is applicable to other drivers ionic hardly sinterizables. The dc conductivity of the composite material is dominated by the grain boundary conductivity. This conductivity is far below the intrinsic conductivity of LiSn2 (PO4) 3, which has prevented us from using these composite materials as solid electrolytes in a lithium battery. Depending on the method of processing which is used for composite materials cathode, the particles remain isolated PVDF (physical method) or form a network within the composite material (chemical method). In the first case, the composite material is fragile and the second is ductile. In both cases, the electronic conductivity of the composite material varies with the contents of NC as a model percolativo, with a percolation threshold of 3% in volume, lower than expected for a distribution random (17%). This is because the particles NC, which are typically smaller than those of LiMn2O4 surround the latter. We have found that the specific capacity of LiMn2O4 as cathode (4V) varies with the contents of NC Like the electrical conductivity of the composite material, ie both magnitudes are interrelated and their values depend on the composition of the composite material. It has been determined the composition of composite material that has the highest capacity. It has improved composite cathode active material improving. To increase the speed of integration, have been synthesized spinel composition LiNiyMn2-yO4 (0 and 0.5) with the nano particle size. This has been achieved by a method of combustion that is fast and cheap and using sugar as fuel. The samples have a very homogeneous particle size, which grows with temperature, and only slightly to the composition and = 0.5. The ability (5V) and ciclabilidad of the sample LiNi0.5Mn1.5O4 obtained by the combustion method has been compared with a sample of the same composition obtained by solid state reaction. 8 The cicl 34c ability of the sample obtained by combustion is slightly lower than that of the ceramic sample, but the ability of the former is clearly superior to the second, especially for high current densities.

Author: RASTELLINI FERNANDO GABRIEL.
Year: 2005.
University: POLITÉCNICA DE CATALUÑA [www.upc.edu].
Place of defense: C.Internacional de Mètodes Numèrics en Enginyeria.
Place of preparation: EDIFICI C1 Campus NORD.

Summary: The mechanical response of composite materials depends on the behavior of materials and components for its micro-estructura. To improve and optimize the design of structural components of composite materials, the industry requires software tools that adequately reproduce the behavior of these materials even in the non-linear range. It is therefore very important research and development of numerical models for compounds that take into account the structure and morphology of the material in an appropriate and efficient, besides being a need for a graphical environment specifically for this type of problem to facilitate entry data code calculation and then support display the desired results. The main objective of this dissertation is the development, formulation and implementation computer, a numerical model for the treatment of non-linearity constituting laminated reinforced with fibers, in the context of the mechanics of the continuum. This formulation raises combine the simple behavior of materials (homogeneous) with the objective of obtaining the mechanical response of composite material (heterogeneous). To that end, he proposed the proper management of the constitutive models (homogeneous), currently available, each of the component materials; exploiting this way the great advances achieved in the field of modeling constituent materials simple, and allowing the transfer of all this technology to the field of composite materials. Taking into account the internal structure of the composite material, is developing a strategy for decoupling and interaction of these stages of a novel way. This methodology, called âcomposición of comportamientosâ, designed to take into account many local phenomena of degradation taking place in stages components such as plasticity, injury, fatigue, etc.. In a manner coupled, which is also new in this kind of approach. It develops the algorithm proposed resolution model that creates a quadratic convergence, both local and global problems of nonlinear to be implemented as a model in establishing a code of finite elements, providing fast and accurate analysis of structures of composite materials in many engineering applications. The simulation of the laminate is achieved through a combination of the proposed model with a laminate theory applied at each point of integration. Used items 3D solid isoparamétricos for discretizar thick laminated structures; while studying for laminar structures of small thickness, develops a foil laminate layered composite material, based on a foil simpler. Validation of the model shows compliance with the closure equations (balance of tensions and strains of compatibility between components), both in the direction of the fibers (behavior in parallel) and orthogonal directions (behavior in series). Furthermore, it illustrates several envelopes of failure to foil / laminates generated with the proposed model and compares them with other global failure criteria for compounds and experimental results available in the literature. The applicability of the model is demonstrated by numerical simulations performed on more complex geometries to shape 8 the respu 3c4 this mechanical parts industry. The numerical results contrasted with the pilot indicates the ability of the proposed model to describe the non-linear behavior of fiber-reinforced laminates in different directions under multiaxial loading conditions both static and cyclic.

Author: MENDOZA RESENDEZ RAQUEL.
Year: 2005.
University: COMPLUTENSE DE MADRID [www.ucm.es].
Place of defense: CIENCIAS FÍSICAS.
Place of preparation: FACULTAD DE CIENCIAS FÍSICAS.

Summary: In this research have been prepared particles of iron oxide (hematite) monodispersas with morphology acicular and different axial relations. The technique used has been a salt hydrolysis of iron (III) assisted by temperature. The mechanism of formation of these particles is an aggregation of primary particles (2-3mm). Through the technique heterocoagulación particles aciculares Haematite were uniformly coated with different additives (cobalt, aluminum, yttrium). We have analyzed the effect of each of these additives in their structural and magnetic properties. The particles hametites and hematite coated particles have been reduced to metallic iron (pure) and hierro-aditivo in an atmosphere of hydrogen to 400Â º C, evaluating the effect of the flow of hydrogen, temperature and time reduction, the magnetic properties of different metal particles are determined primarily by the anisotropia of form and microstructure. The results indicate that are hard magnetic materials with high coercitividades (1200 Oe) and imanación saturation 160 emu / g. It has analyzed the possible mechanism of investment dela imanación of these systems, determined an investment incoherent. The experimental results are in accordance with the best model chains areas.

Author: GARCÍA HERNÁNDEZ KARIN LILIANA.
Year: 2005.
University: COMPLUTENSE DE MADRID [www.ucm.es].
Place of defense: FACULTAD DE CIENCIAS FÍSICAS.
Place of preparation: INSTITUTO DE CIENCIA DE MATERIALES DE MADRID CSIC.

Summary: It has studied the origins of the coercive field fluctuations observed experimentally in microhilos magnetostrictive. It has been successfully extended the thermal activation model to describe the process of reversing the imanación. The temperature dependence of the width of the distribution of the investment field, which presents a comprotamiento unusual compared with the experimental data presented thus far, has been resolved in terms of the model termoactivación. It has been regarded as the potential anchor of a single domain wall and its dependence with the field applied to conduct the evaluation of the experimental data and the adjustment to the theory of thermal activation. We have identified two mechanisms to coercitividad anchor of the samples studied a magnetoelástico far-reaching structural and other relaxation considered short-sighted. Moreover, it has studied the speed of propagation of a single domain wall in a microhilo amorphous ferromagnetic in the presence of a homogeneous magnetic field. The parameters that promote or hinder his movement of the wall has been studied as a function of the temperature. The quantitative analysis of the parameters obtained and the characteristics of the wall, has introduced a damping mechanism, introduced just before so theoretical, time-dependent and dominant at low temperatures.

Author: TIRADO MARTIN JOSE MARIA.
Year: 2006.
University: CASTILLA-LA MANCHA [www.uclm.es].
Place of defense: E.T.S.INGENIEROS INDUSTRIALES.
Place of preparation: ESCUELA TECNICA SUPERIOR DE INGENIEROS INDUSTRIALES.

Summary: DEVICES BASED COMPOUNDS III-V, SPECIFIC THE GaN, PRESENT SERIES OF GAPS IN ITS PERFORMANCE, ASSIGNED TO VARIOUS FACTORS. THE STUDY OF THE SURFACE OF THE SAME IS A KEY PIECE FOR UNDERSTANDING OF THESE DEFICIENCIES, AND IS THROUGH THIS THESIS WHERE IS ATTEMPT TO GIVE SOME DEGREE OF LIGHT PROBLEMS APPEAR ON IT. IN THIS WORK IS ANALIZADA THE CHARACTERIZATION ELECTRIC IN DC AND LOW FREQUENCY OF SETS HIGH MOBILITY ELECTRONES (HEMT) AlGaN / GaN, DISCUTIENDO EFFECTS NOTED. SE IMPLEMENTA A MODEL FISICO BIDIMENSIONAL OF DEVICES MESFET OF GaN And HEMT OF AlGaN / GaN, ANALIZANDO And DISCUTIENDO THE PRESENCE OF STATIC AND DYNAMIC STATES IN THE AREAS OF DEVICES, REALIZANDO COMPARISON BETWEEN AN EXPERIMENTAL AND THEORETICAL RESULTS OBTAINED THROUGH THE TESTS LABORATORY

Author: GONZALEZ DE CABAÑES ANTONI.
Year: 2006.
University: POLITÉCNICA DE CATALUÑA [www.upc.edu].
Place of defense: SALA DE JUNTES DEL RECTORAT DE LA UPC.
Place of preparation: ETSEIB, PAVELLÓ E Campus SUD.

Summary: NiTi alloys presented a priori excellent properties of corrosion resistance [96 Ron], however, to be used in conjunction with other metals and half in common, may lead to serious problems of galvanic corrosion. Another problem with NiTi alloys is the release of Ni ions in the middle. These ions Neither can result in allergic reactions in the body, type cytotoxicity. Moreover can be reached at the destruction of groups of cells due to the migration of these ions. The PA is a polymer with excellent chemical resistance to aggressive chemicals, as well as a good barrier effect the release of ions. For this reason, which is to undertake a study of the properties of the polymer as a coating and will study the feasibility of PA11 as polymer used for the coating of metals in biomedical applications. Overall, as we increase the number of carbons in the drive for a constitutional repeating molecule PA we are getting a polymer with a lower melting temperature, and therefore with ease added as a coating for processing. We are also hampering the ease by which it Polyamides have to absorb moisture to be in touch with Foreshore and get a polymer to its more stable environment. To carry out this thesis, let's perform in a first phase, a study of the corrosion resistance of varying degrees of materials at its pure state, manufactured by different commercial firms and different chemical composition. The same tests will be conducted later with materials coated polyamide 11. There will also be analysis of the solution HANKS used in the trials potenciodinámicos to determine the degree of Ni ions released to the environment and therefore the effect that makes the polymer barrier to the migration of ions. In a second phase, a study of wear experienced in the coating of PA each of the alloys coated, using techniques Pin-on disk. This aspect is very important in applications such as orthodontics. It should be borne in mind that orthodontic wires are in constant contact with fastening devices or brackets, which friccionan and continuously wear material. In many other applications, such as cardiovascular stents or filters, it is also very important to conduct this type of study, because the materials used might be the same. The hardness of the layer lining PA alloy is also studied and characterized taking into account the thickness of the coating. The surface of a polymer, is a priori, for its elastic modulus, its hardness and texture, a touch more comfortable for contact with the human body that a metal alloy. It will also perform the necessary tests to determine how that affects the polymeric coating, the properties of shape memory alloy that is. These studies are based on tests and test thermodynamic tension. Likewise be obtained values of temperature processing, super-elasticidad and elasticity shape memory. In a third phase to assess the biocompatibility of coating PA and carried out studies on cell culture substrate PA, in addition to studies cytotoxicity. If we take into account the problems of NiTi alloys Reviewed and properties of the PA, opens a wide field of study, the coating NiTi alloys with a PA base of this thesis.