Publication: Electrodeposición de materiales compuestos aplicados a termoactuadores
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2009
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2009
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Abstract
El fin del presente proyecto es encontrar materiales con los que se consiga una elevada expansión en un rango de temperaturas muy pequeño para su posible uso en el campo de los termoactuadores. El estudio se ha centrado en las propiedades térmicas y mecánicas de los materiales. Con respecto al coeficiente de expansión térmica, se esperaba obtener un incremento en el caso de los materiales composites obtenidos respecto a los metales puros ya que las partículas poseen valores de coeficiente de expansión térmica superiores. En el caso del poliestireno varía entre 90·10-6 y 150·10-6 ºC-1, mientras que en el cobre y en el níquel puros se encuentra en 16.5·10-6 y 13.4·10-6 ºC-1 a temperatura ambiente respectivamente. Se esperaba obtener mayor expansión en el caso de los recubrimientos de cobre al tener unos valores menores de módulo elástico que el níquel (115 GPa en el cobre y 207 GPa en el níquel) y límite elástico (de 18 a 69 GPa para el cobre electrodepositado y de 35 a 107 GPa para el níquel electrodepositado).1 Se han estudiado las propiedades mecánicas y térmicas de materiales composites formados por la matriz metálica (de cobre o níquel) y partículas dispersas en ella (poliestireno sólido o microcápsulas con agua en su interior). Dicho análisis se ha centrado especialmente en la expansión térmica, obtenida gracias al cambio de fase de las partículas dispersas y en la variación del módulo elástico o de Young de las distintas muestras. Se ha aplicado diversos tests a las muestras para el estudio de las propiedades anteriormente citadas: calorimetría diferencial de barrido y termodilatometría, descritas en profundidad en el capítulo 3. Para poder llevar a cabo el test de termodilatometría, es necesario que las muestras tengan una geometría específica. En nuestro caso, se emplearon cilindros huecos preparados por electrodeposición mediante el uso de un ánodo paralelo y un cátodo rotatorio de forma también cilíndrica en un baño de electrolito con agitación forzada. El proceso completo se explica en el capítulo 2. __________________________________________________________________________
The aim of this Master Thesis is to analyse the thermal and mechanical properties of composite materials made up of a metal matrix (nickel and copper) and polymer particles finely and homogeneously embedded on it (solid polystyrene and microcapsules containing water). The main focus of study will be the expansion behaviour arising from the phase change of the particles embedded in the metal matrix in a small temperature range and its relationship to the change in the elastic modulus. It is expected that the resultant thermal expansion coefficient rises because of the higher values of these particles embedded on the metal matrix. In the case of PS particles, the thermal expansion coefficient varies from 90·10-6 to 150·10-6 ºC-1 whereas for copper and nickel at room temperature is 16.5·10-6 and 13.4·10-6 respectively. The thermal expansion obtained is expected to be higher in the copper coatings as it has lower elastic modulus, 115 GPa for copper and 207 GPa for nickel, and lower yield strength, varying from 18 to 69 MPa in the case of electrodeposited copper and from 35 to 107 MPa for electrodeposited nickel.1 This expansion behaviour under thermal loads, with a sharp rise in a small temperature range, will be responsible for their applicability in fields such as thermo actuators. Each material separately does not have such adequate properties for being used as thermo actuators. On the one hand, metals have a high thermal conductivity coefficient (398 W/mK and 90 W/mk for copper and nickel respectively) but a low thermal storage capacity (386 J/kgK and 443 J/kgK for copper and nickel respectively) so they suffer thermal fatigue when heating cycles are applied reducing their life time due to the thermal stresses. On the other hand, the particles used have a poor thermal conductivity (0.13 W/mK for PS) and therefore their response to temperature changes is slowly performed. The particles have a high thermal storage capacity (1170 J/kgK and 4180 J/kgK for PS and water respectively) and therefore they will absorb part of the thermal stresses avoiding the premature degradation of the samples. In order to analyse the properties above mentioned, some tests must be carried out such as differential scanning calorimetry (DSC) and thermal dilatometry, which will be explained in detail in chapter 4. In order to perform thermal dilatometry, cylindrical samples are required. They were prepared by electrocodeposition by using parallel anode and rotating cylinder cathode (RCC). Agitation was applied during experiments. The complete process will be explained in chapter 3.
The aim of this Master Thesis is to analyse the thermal and mechanical properties of composite materials made up of a metal matrix (nickel and copper) and polymer particles finely and homogeneously embedded on it (solid polystyrene and microcapsules containing water). The main focus of study will be the expansion behaviour arising from the phase change of the particles embedded in the metal matrix in a small temperature range and its relationship to the change in the elastic modulus. It is expected that the resultant thermal expansion coefficient rises because of the higher values of these particles embedded on the metal matrix. In the case of PS particles, the thermal expansion coefficient varies from 90·10-6 to 150·10-6 ºC-1 whereas for copper and nickel at room temperature is 16.5·10-6 and 13.4·10-6 respectively. The thermal expansion obtained is expected to be higher in the copper coatings as it has lower elastic modulus, 115 GPa for copper and 207 GPa for nickel, and lower yield strength, varying from 18 to 69 MPa in the case of electrodeposited copper and from 35 to 107 MPa for electrodeposited nickel.1 This expansion behaviour under thermal loads, with a sharp rise in a small temperature range, will be responsible for their applicability in fields such as thermo actuators. Each material separately does not have such adequate properties for being used as thermo actuators. On the one hand, metals have a high thermal conductivity coefficient (398 W/mK and 90 W/mk for copper and nickel respectively) but a low thermal storage capacity (386 J/kgK and 443 J/kgK for copper and nickel respectively) so they suffer thermal fatigue when heating cycles are applied reducing their life time due to the thermal stresses. On the other hand, the particles used have a poor thermal conductivity (0.13 W/mK for PS) and therefore their response to temperature changes is slowly performed. The particles have a high thermal storage capacity (1170 J/kgK and 4180 J/kgK for PS and water respectively) and therefore they will absorb part of the thermal stresses avoiding the premature degradation of the samples. In order to analyse the properties above mentioned, some tests must be carried out such as differential scanning calorimetry (DSC) and thermal dilatometry, which will be explained in detail in chapter 4. In order to perform thermal dilatometry, cylindrical samples are required. They were prepared by electrocodeposition by using parallel anode and rotating cylinder cathode (RCC). Agitation was applied during experiments. The complete process will be explained in chapter 3.
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Keywords
Materiales compuestos, Propiedades térmicas, Termoactuadores, Propiedades mecánicas, Termodinámica