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  • Correlation between electrical and mechanical properties in La1-xSrxGa1-yMgyO3-d ceramics used as electrolytes for solid oxide fuel cells

     Morales Comas, Miguel; Roa Rovira, Joan Josep; Pérez Falcón, José Manuel; Moure Arroyo, Alberto; Tartaj, Jesus; Espiell Álvarez, Ferran; Segarra Rubi, Merce
    Journal of power sources
    Date of publication: 2014
    Journal article

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    The relation between the electrical and the mechanical properties in Sr and Mg doped LaGaO3 ceramics, which can be used as electrolyte for solid oxide fuel cells, was investigated in terms of hardness and ionic conductivity. For this purpose, ceramic materials corresponding to the compositions of La1 xSrxGa1yMgyO3d (LSGM), with x ¼ 0.1 and y ¼ 0.2, and x ¼ 0.15 and y ¼ 0.2, were prepared. LSGM powders synthesized by the ethylene glycol complex solution method were shaped into disks by isostatic pressing method. The variation in the microstructure of samples was achieved by varying the sintering temperature between 1300 and 1450 C. While the effect of the different microstructures on the electrical properties of the LSGM electrolytes was determined by impedance spectroscopy, the influence of the hardness was extracted by instrumented indentation technique. The results showed a linear correlation between the hardness and total ionic conductivity within the temperature range of 500-660 C, thus indicating that both properties were strongly influenced on the relative density and purity of the samples. It has a potential practical implication: by measuring the LSGM hardness at room temperature, one can achieve an approach to the ionic conductivity within the studied temperature range.

    The relation between the electrical and the mechanical properties in Sr and Mg doped LaGaO3 ceramics, which can be used as electrolyte for solid oxide fuel cells, was investigated in terms of hardness and ionic conductivity. For this purpose, ceramic materials corresponding to the compositions of La1−xSrxGa1−yMgyO3−δ (LSGM), with x = 0.1 and y = 0.2, and x = 0.15 and y = 0.2, were prepared. LSGM powders synthesized by the ethylene glycol complex solution method were shaped into disks by isostatic pressing method. The variation in the microstructure of samples was achieved by varying the sintering temperature between 1300 and 1450 °C. While the effect of the different microstructures on the electrical properties of the LSGM electrolytes was determined by impedance spectroscopy, the influence of the hardness was extracted by instrumented indentation technique. The results showed a linear correlation between the hardness and total ionic conductivity within the temperature range of 500–660 °C, thus indicating that both properties were strongly influenced on the relative density and purity of the samples. It has a potential practical implication: by measuring the LSGM hardness at room temperature, one can achieve an approach to the ionic conductivity within the studied temperature range.

  • Hardness of FRHC-Cu Determined by Statistical Analysis

     Roa Rovira, Joan Josep; Martínez, Mónica; Rayón Encinas, Emilio; Ferrer, N; Espiell Álvarez, Ferran; Segarra Rubi, Merce
    Journal of materials engineering and performance
    Date of publication: 2014-02
    Journal article

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    A statistical indentation method has been employed to study the hardness value of fire-refined high conductivity copper, using nanoindentation technique. The Joslin and Oliver approach was used with the aim to separate the hardness (H) influence of copper matrix, from that of inclusions and grain boundaries. This approach relies on a large array of imprints (around 400 indentations), performed at 150 nm of indentation depth. A statistical study using a cumulative distribution function fit and Gaussian simulated distributions, exhibits that H for each phase can be extracted when the indentation depth is much lower than the size of the secondary phases. It is found that the thermal treatment produces a hardness increase, due to the partly re-dissolution of the inclusions (mainly Pb and Sn) in the matrix.

  • Deformation mechanisms induced under high cycle fatigue tests in a metastable austenitic stainless steel

     Roa Rovira, Joan Josep; Fargas Ribas, Gemma; Jimenez Pique, Emilio; Mateo Garcia, Antonio Manuel
    Materials science and engineering A. Structural materials properties microstructure and processing
    Date of publication: 2014
    Journal article

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    Advancedtechniqueswereusedtostudythedeformationmechanismsinducedbyfatiguetestsina metastableausteniticstainlesssteelAISI301LN.ObservationsbyAtomicForceMicroscopywerecarriedout tostudytheevolutionofapre-existingmartensiteplateletatincreasingnumberofcycles.Thesub-superficial deformationmechanismsoftheausteniticgrainswerestudiedconsideringthecross-sectionmicrostructure obtainedbyFocusedIonBeamandanalysedbyScanningElectronMicroscopyandTransmissionElectron Microscopy.Theresultsrevealednodeformationsurroundingthepre-existingmartensiticplateletduring fatiguetests,onlythegrowthonheightwasobserved.Martensiteformationwasassociatedwithshearbands on austenite,mainlyinthe{111}plane,andwiththeactivationoftheotherintersectingaustenite{111}<110> slipsystem.Furthermore,transmissionelectron microscopyresultsshowedthatthenucleationof e- martensitefollowsatwostagesphasetransformation(¿fcc-ehcp-a0 bcc).

    Advanced techniques were used to study the deformation mechanisms induced by fatigue tests in a metastable austenitic stainless steel AISI 301LN. Observations by Atomic Force Microscopy were carried out to study the evolution of a pre-existing martensite platelet at increasing number of cycles. The sub-superficial deformation mechanisms of the austenitic grains were studied considering the cross-section microstructure obtained by Focused Ion Beam and analysed by Scanning Electron Microscopy and Transmission Electron Microscopy. The results revealed no deformation surrounding the pre-existing martensitic platelet during fatigue tests, only the growth on height was observed. Martensite formation was associated with shear bands on austenite, mainly in the {111} plane, and with the activation of the other intersecting austenite {111}〈110〉 slip system. Furthermore, transmission electron microscopy results showed that the nucleation of ε-martensite follows a two stages phase transformation (γfcc→εhcp→α'bcc).

  • Structural and mechanical characterization of graphite foam/phase change material composites

     Canseco, Vladimir; Anguy, Yannick; Roa Rovira, Joan Josep; Palomo, Elena
    Carbon
    Date of publication: 2014-08-01
    Journal article

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    We consider graphite/phase change material (PCM) composites for energy storage by latent heat in the context of power generation by solar concentration technologies. Based on X-ray computerized tomography 3D data, we calculate the cell-size distribution of polycrystalline highly ordered mesophase pitch-based graphitic foams (KFoam (R)) and semi-crystalline coal-based graphite foams (CFoam (R)). Compressive experiments show that the elastic modulus and strength are higher in the z-direction (foaming direction) than in the xy-plane. The elastic modulus E-z is found linearly related to the mean cell size d, while no simple relation is found between E-xy and d. This supports that mechanical properties of graphite foams do not relate to the same geometrical characteristics depending whether the z-direction or the xy-plane direction is considered. After infiltrating the KFoam and CFoam host porous media with a molten PCM (sodium nitrate or a binary mixture of hydroxides), the response of the composite materials to compression tests is shown to be dependent upon a complex network of cracks all through the PCM, the occurrence of which is explained by the process whereby the PCM crystallizes within the host graphite foam and by the contrast between the thermo-mechanical properties of the PCM and those of the graphite. (C) 2014 Elsevier Ltd. All rights reserved.

    We consider graphite/phase change material (PCM) composites for energy storage by latent heat in the context of power generation by solar concentration technologies. Based on X-ray computerized tomography 3D data, we calculate the cell-size distribution of polycrystalline highly ordered mesophase pitch-based graphitic foams (KFoam ) and semi-crystalline coalbased graphite foams (CFoam ). Compressive experiments show that the elastic modulus and strength are higher in the z-direction (foaming direction) than in the xy-plane. The elastic modulus Ez is found linearly related to the mean cell size d, while no simple relation is found between Exy and d. This supports that mechanical properties of graphite foams do not relate to the same geometrical characteristics depending whether the z-direction or the xy-plane direction is considered. After infiltrating the KFoam and CFoam host porous media with a molten PCM (sodium nitrate or a binary mixture of hydroxides), the response of the composite materials to compression tests is shown to be dependent upon a complex network of cracks all through the PCM, the occurrence of which is explained by the process whereby the PCM crystallizes within the host graphite foam and by the contrast between the thermo-mechanical properties of the PCM and those of the graphite.

  • Anisotropía plástica y mecanismos de deformación activados mediante nanoindentación en granos de WC

     Roa Rovira, Joan Josep; Verge, C.; Jimenez Pique, Emilio; Tarrago Cifre, Jose Maria; Llanes Pitarch, Luis Miguel
    Congreso Nacional de Materiales
    Presentation's date: 2014-06-19
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    Fatigue crack growth behavior of WC-Co and WC-CoNi cemented carbides  Open access

     Tarrago Cifre, Jose Maria; Roa Rovira, Joan Josep; Valle, Vladimir; Jessica, Marshall; Mateo Garcia, Antonio Manuel; Llanes Pitarch, Luis Miguel
    Encuentro del Grupo Español de Fractura
    Presentation's date: 2014-04-02
    Presentation of work at congresses

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    En este trabajo se investigó el crecimiento de grietas por fatiga para diversas calidades de metal duro en función de la microestructura y el cociente de carga aplicada (R). De esta forma, se evaluó la influencia de la naturaleza química y el contenido del ligante (Co and 76wt%Co-24wt%Ni), así como del tamaño de grano de la fase cerámica, en el umbral (Kth) y en la cinética de la propagación de grietas por fatiga. Los resultados experimentales indican que las calidades con carburos gruesos presentan un mayor Kth que aquellas con un tamaño de grano medio. Esta mejora se asocia con la operatividad del mecanismo de deflexión de grieta. Los resultados señalan que los carburos cementados con base CoNi exhiben una dureza algo inferior que las calidades con base cobalto, pero a su vez presentan valores de tenacidad ligeramente superiores. Por otro lado, la resistencia a la flexión y la sensibilidad a la fatiga no se ven afectadas por la naturaleza química del ligante para los materiales estudiados. Finalmente, se realizó una inspección detallada de la interacción grieta-microestructura, mediante el uso de técnicas de microscopía electrónica de barrido y de difracción de electrones retrodispersados, con el objetivo tanto de evaluar la tortuosidad de la grieta como de discernir los micromecanismos de fatiga en la fase ligante.

    En este trabajo se investigó el crecimiento de grietas por fatiga para diversas calidades de metal duro en función de la microestructura y el cociente de carga aplicada (R). De esta forma, se evaluó la influencia de la naturaleza química y el contenido del ligante (Co and 76wt%Co-24wt%Ni), así como del tamaño de grano de la fase cerámica, en el umbral (Kth) y en la cinética de la propagación de grietas por fatiga. Los resultados experimentales indican que las calidades con carburos gruesos presentan un mayor Kth que aquellas con un tamaño de grano medio. Esta mejora se asocia con la operatividad del mecanismo de deflexión de grieta. Los resultados señalan que los carburos cementados con base CoNi exhiben una dureza algo inferior que las calidades con base cobalto, pero a su vez presentan valores de tenacidad ligeramente superiores. Por otro lado, la resistencia a la flexión y la sensibilidad a la fatiga no se ven afectadas por la naturaleza química del ligante para los materiales estudiados. Finalmente, se realizó una inspección detallada de la interacción grieta-microestructura, mediante el uso de técnicas de microscopía electrónica de barrido y de difracción de electrones retrodispersados, con el objetivo tanto de evaluar la tortuosidad de la grieta como de discernir los micromecanismos de fatiga en la fase ligante.

  • Zero-resistance state and magnetic irreversibility in melt-textured YBaCuO probed by pulsed magnetic fields

     Teixeira Dias, Fábio; Vieira, Valdemar das Neves; da Silva, Douglas Langie; Wolff-Fabris, Frederik; Kampert, Erik; Roa Rovira, Joan Josep; Paiva Gouvêa, Cristol de
    Encontro Nacional de Física da Matéria Condensada
    Presentation's date: 2014
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    Paramagnetic meissner effect and strong time dependence at high fields in melt-textured high-Tc superconductors  Open access

     Paiva Gouvêa, Cristol de; Teixeira Dias, Fábio; Vieira, Valdemar das Neves; da Silva, Douglas Langie; Schaf, Jacob; Wolff-Fabris, Frederik; Roa Rovira, Joan Josep
    Journal of the Korean Physical Society
    Date of publication: 2013-05
    Journal article

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    In this work we report on systematic field-cooled magnetization experiments in melt-textured YBa2Cu3O7-d samples containing Y211 precipitates. Magnetic fields up to 14 T were applied either parallel or perpendicular to the ab planes and a strong paramagnetic response related to the superconducting state was observed. This effect is known as paramagnetic Meissner effect (PME). The magnitude of the PME increases when the field is augmented. This effect shows a strong paramagnetic relaxation, such that the paramagnetic moment increases as a function of the time. The pinning by the Y211 particles plays a crucial role in the explanation of this effect and our results suggest that the pinning capacity can produce a strong flux compression into the sample, originating the PME and the strong time dependence.

    In this work we report on systematic field-cooled magnetization experiments in melt-textured YBa 2 Cu 3 O 7 − δ samples containing Y211 precipitates. Magnetic fields up to 14 T were applied either parallel or perpendicular to the ab planes and a strong paramagnetic response related to the superconducting state was observed. This effect is known as paramagnetic Meissner effect (PME). The magnitude of the PME increases when the field is augmented. This effect shows a strong paramagnetic relaxation, such that the paramagnetic moment increases as a function of the time. The pinning by the Y211 particles plays a crucial role in the explanation of this effect and our results suggest that the pinning capacity can produce a strong flux compression into the sample, originating the PME and the strong time dependence

  • Depth-sensing indentation applied to polymers: A comparison between standard methods of analysis in relation to the nature of the materials

     Giró Paloma, Jessica; Roa Rovira, Joan Josep; Díez Pascual, Ana Maria; Rayón Encinas, Emilio; Flores Aguilar-Amat, Araceli; Martínez López, Monica; Chimenos Ribera, Josep Maria; Fernández Renna, Ana Ines
    European polymer journal
    Date of publication: 2013
    Journal article

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    Mechanical data (hardness and elastic modulus) from instrumented indentation testing are often extracted assuming linear elasticity in the initial portion of the unloading. The method is nowadays widely accepted as a convenient tool to interpret depth-sensing data, however it is a matter of controversy when applied to polymer materials due to their timedependent behavior. More recently, Loubet and co-workers applied continuous stiffness measurements (CSM), consisting of superimposing a small oscillation to the quasi-static component of loading, to the study of the mechanical properties of polymers and proposed a new model to account for the apparent increase in the contact area detected at the first stages of contact. The present work offers a comparative study between the Loubet¿s model using CSM and the procedure yielding a single reading from the onset of unloading. A wide range of thermoplastic polymer materials including glassy and semicrystalline polymers have been investigated. The most important equations employed for each method are summarized and the advantages and disadvantages of employing one procedure or the other are discussed. The differences found between the results obtained from both approaches are discussed in relation to the nature of the polymer material. A comparison between mechanical data extracted from indentation measurements and from classical dynamic mechanical analysis is offered.

    Mechanical data (hardness and elastic modulus) from instrumented indentation testing are often extracted assuming linear elasticity in the initial portion of the unloading. The method is nowadays widely accepted as a convenient tool to interpret depth-sensing data, however it is a matter of controversy when applied to polymer materials due to their time- dependent behavior. More recently, Loubet and co-workers applied continuous stiffness measurements (CSM), consisting of superimposing a small oscillation to the quasi-static component of loading, to the study of the mechanical properties of polymers and proposed a new model to account for the apparent increase in the contact area detected at the first stages of contact. The present work offers a comparative study between the Loubet’s model using CSM and the procedure yielding a single reading from the onset of unloading. A wide range of thermoplastic polymer materials including glassy and semicrystalline polymers have been investigated. The most important equations employed for each method are sum- marized and the advantages and disadvantages of employing one procedure or the other are discussed. The differences found between the results obtained from both approaches are discussed in relation to the nature of the polymer material. A comparison between mechanical data extracted from indentation measurements and from classical dynamic mechanical analysis is offered.

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    Influence of laser cutting on the fatigue limit of two high strength steels  Open access

     Mateo Garcia, Antonio Manuel; Fargas Ribas, Gemma; Calvo Muñoz, Jessica; Roa Rovira, Joan Josep
    International Conference on Low Cycle Fatigue
    Presentation's date: 2013-09-11
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    Laser cutting is widely used in the metal industry, particularly when components of high strength steels sheets are produced. On the other hand, the roughness of cut - edges produced by laser differs from that obt ained by other methods, such as mechanical blank ing, and this fact influence s the fatigue performance. Moreover, thermal effects are another factor to consider. In the present investigation, specimens of two grades of high strength austenitic steels were cut by laser and tested in the high cycle fatigue regime to determine their corresponding fatigue limits. One of the steels was a metastable stainless grade (AISI 301LN) whereas the other corresponded to the TWIP family (TWIP17Mn). Load control fatigue te sting was conducted at a stress ratio R of 0.1 and using the stair - case methodology. A series of fatigue specimens were tested without polishing the cut - edges and other s eries after a careful polishing, in order to assess the influence of the cut - edges con dition. R esults indicate a significant influence of the edges roughness, more marked for the AISI 301LN than for the TWIP steel. In the latter material, the presence of nitrides induced a premature fatigue crack nucleation

    Laser cutting is widely used in the metal industry, particularly when components of high strength steels sheets are produced. On the other hand, the roughness of cut - edges produced by laser differs from that obt ained by other methods, such as mechanical blank ing, and this fact influence s the fatigue performance. Moreover, thermal effects are another factor to consider. In the present investigation, specimens of two grades of high strength austenitic steels were cut by laser and tested in the high cycle fatigue regime to determine their corresponding fatigue limits. One of the steels was a metastable stainless grade (AISI 301LN) whereas the other corresponded to the TWIP family (TWIP17Mn). Load control fatigue te sting was conducted at a stress ratio R of 0.1 and using the stair - case methodology. A series of fatigue specimens were tested without polishing the cut - edges and other s eries after a careful polishing, in order to assess the influence of the cut - edges con dition. R esults indicate a significant influence of the edges roughness, more marked for the AISI 301LN than for the TWIP steel. In the latter material, the presence of nitrides induced a premature fatigue crack nucleation

  • Influencia de los tratamientos térmicos en la respuesta a fatiga de un acero TWIP

     Salán Ballesteros, Mª Núria; Calvo Muñoz, Jessica; Mateo Garcia, Antonio Manuel; Roa Rovira, Joan Josep; Fargas Ribas, Gemma; Sixto Rué, Guillem
    Congreso Nacional de Tratamientos Térmicos y de Superficie
    Presentation's date: 2013-04-23
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    Los Aceros TWIP ( T W inning Induced Plasticity ) se caracterizan por la combinación de excelente resistencia mecánica y elevados niveles de ductilidad, siendo muy valorados en la industria automovilística para la elaboración de componentes estructurales. La particular respuesta mec ánica de estos aceros se debe a su composición química, en la que destaca e l alto contenido en Mn (generalmente superior al 1 5 % ) , que garantizan una microestructura austenítica muy propensa al maclado como principal mecanismo de deformación. En este estudio se pretende analizar el efecto del tamaño de grano, modificado mediante tratamientos térmicos de recristalización ( a temperaturas comprendidas entre 1000 y 1200 ºC), en los valores de dureza, en la respuesta a tracción y también en el comportamiento a fatiga de alto número de ciclos de un acero TWIP. La caracterización microestructural del acero, tanto en las condiciones de partida ( as received ) como tras los tratamientos térmicos, se ha efectuado mediante diferentes técnicas de microscopía : óptica, electrónica de barrido (SEM), de fuerza atómica (AFM) y de haz de iones focalizado s (FIB

  • Effect of shot peening on a metastable austenitic stainless steel

     Mateo Garcia, Antonio Manuel; Fargas Ribas, Gemma; Roa Rovira, Joan Josep; Jimenez Pique, Emilio
    European and Exhibition Congress on Advanced Materials and Processes
    Presentation's date: 2013-09-09
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  • Estudio de las propiedades mecánicas mediante nanoindentación y de la adhesión interfacial de una SOFC basada en un electrolito de Galato de Lantano Dopado

     Morales Comas, Miguel; Roa Rovira, Joan Josep; Pérez-Falcón, J. M.; Tartaj, Jesus; Segarra Rubi, Merce
    Reunión Nacional de Electrocerámica
    Presentation's date: 2013
    Presentation of work at congresses

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  • Mechanical characterization of heterostructured zirconia electrolytes using instrumented indentation technique

     Morales Comas, Miguel; Roa Rovira, Joan Josep; Figueiredo, F. M.; Frade, J. R.; Segarra Rubi, Merce
    European and Exhibition Congress on Advanced Materials and Processes
    Presentation's date: 2013-09
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  • Processing and characterization of LSGM electrolytes for intermediate temperatures SOFCs

     Morales Comas, Miguel; Roa Rovira, Joan Josep; Pérez Falcón, José Manuel; Moure Arroyo, Alberto; Tartaj, Jesus; Segarra Rubi, Merce
    Iberian Symposium on Hydrogen, Fuel Cells and Advanced Batteries
    Presentation's date: 2013-06-27
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  • Effect of shot peening on a metastable austenitic steel

     Fargas Ribas, Gemma; Roa Rovira, Joan Josep; Jimenez Pique, Emilio; Mateo Garcia, Antonio Manuel
    European and Exhibition Congress on Advanced Materials and Processes
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  • Contact damage and fracture mechanisms of multilayered TiN/CrN coatings at micro- and nano-length scales

     Roa Rovira, Joan Josep; Jimenez Pique, Emilio; Tarrago Cifre, Jose Maria; Martínez, R.; Rodríguez, R.; Llanes Pitarch, Luis Miguel
    An International Workshop on the Mechanical Behavior of Nanoscale Multilayers
    Presentation's date: 2013-10-01
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  • Study by AFM and EBSD of plastic deformation mechanisms induced by nanoindentation in a hardmetal binder-like cobalt alloy

     Roa Rovira, Joan Josep; Jimenez Pique, Emilio; Tarrago Cifre, Jose Maria; Zivcec, Maria; Broeckmann, C.; Llanes Pitarch, Luis Miguel
    Conference on Nanomechanical Testing in Materials Research and Development
    Presentation's date: 2013-10-10
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  • TEM and AFM study of the elementary deformation mechanisms induced by nanoindentation in the MAX phase Ti3AlC2

     Tromas, Christophe; Joulain, Anne; Thilly, Ludovic; Jimenez Pique, Emilio; Roa Rovira, Joan Josep
    Conference on Nanomechanical Testing in Materials Research and Development
    Presentation's date: 2013-10-07
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  • Nanoindentation measurements in plan view and cross section in a nitrided maraging steel: relation between hardness and nitrogen concentration

     Roa Rovira, Joan Josep; Tromas, Christophe; Pichon, Luc
    International Workshop on Plasma-Based Ion Implantation and Deposition
    Presentation's date: 2013
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  • Mechanical characterization at nanometric scale for heterogeneous graphite-salt phase change materials with a statistical approach

     Canseco, Vladimir; Roa Rovira, Joan Josep; Rayón Encinas, Emilio; Fernández, Ana Inés; Palomo, Elena
    Ceramics international
    Date of publication: 2012-01-04
    Journal article

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    A statistical indentation analysis of a series of phase change graphite–salt composite materials for latent heat thermal energy storage applications was investigated using instrumented indentation technique with the aim of isolate the mechanical influence of each phase. This method employs the instrumented indentation technique to extract the in situ hardness and Young's modulus properties of individual components without the need to observe the residual imprints for heterogeneous materials. This approach relies on a large array of imprints (around 1000 indentations performed at 200 nm of indentation depth) and the statistical analysis of the resulting data. A statistical study by a Cumulative Distribution Function fit and Gaussian simulated distributions showed that the mechanical properties for each compound can be isolated when the indentation depth is much lower than the size of the secondary phases.

    Instrumented indentation technique; Statistical method; Heterogeneous materials; Hardness; Young's modulus; Phase change materials

  • Corrosion induced degradation of textured YBCO under operation in high humidity conditions

     Roa Rovira, Joan Josep; Jimenez Pique, Emilio; Díaz, Jordi A.; Morales, Manuel; Calleja Lázaro, Albert; Segarra Rubi, Merce
    Surface and coatings technology
    Date of publication: 2012-05-25
    Journal article

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    The early stages of aggressive degradation at 85% of humidity for 24 h of single crystals of YBa2Cu3O7 − δ textured by Bridgman technique have been analyzed by means of atomic force microscopy, X-ray photoelectron spectroscopy, nanoindentation and focused ion beam. The results show that the initial formation of barium hydroxide and the non-superconducting green phase, Y2BaCuO5, induces the surface degradation and the loss of the mechanical properties as a consequence of the mechanical transformation after the degradation process due to an embrittlement of the superficial layer.

  • Performance and short-term stability of single chamber SOFCs based on La0.9Sr0.1Ga0.8Mg0.2O3-d electrolyte

     Morales Comas, Miguel; Roa Rovira, Joan Josep; Tartaj, Jesus; Segarra Rubi, Merce
    Journal of power sources
    Date of publication: 2012-10-15
    Journal article

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    In the present work, the performance of La0.9Sr0.1Ga0.8Mg0.2O3 (LSGM) electrolyte-supported SOFCs was evaluated under single-chamber conditions. For this purpose, two single cells, one with and the other without Sm0.2Ce0.8O3−δ (SDC) buffer layer between anode and electrolyte, were studied in order to determine and compare the performance and short-term stability of cells under single-chamber conditions. The reactivity of the Ni-SDC anode with SDC (for the cell with buffer layer) and the LSGM electrolyte (for the cell without buffer layer) were studied by X-ray diffraction. The reaction between Ni and LSGM during anode sintering and cell operation leads to a substantial loss in the cell performance when no buffer layer is present. As a result, maximum power densities of 246 and 132 mW cm−2 were obtained for the buffered and non-buffered cells respectively, at 800 °C, under optimized gas composition (CH4/O2 = 1.2) and a total flow rate of 400 ml min−1. After 55 h operating at 750 °C and 6 thermal cycles, the performances of both cells were decreased around 25–30 mW cm−2.

  • Oxygenation kinetics of YBCO-TSMG samples using Nanoindentation technique

     Roa Rovira, Joan Josep; T Dias, Fabio; Martinez, Monica; Padilla, Josep Antonio; Segarra, M.
    Journal of the european ceramic society
    Date of publication: 2012-02-14
    Journal article

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    Since hardness is a quantitative measure of bulk mechanical properties, it can be used to examine the kinetics of crack propagation inside YBa2Cu3O7−δ (YBCO or Y-123) ceramics. YBCO samples with a tetragonal phase were oxygenated at a range of temperatures (from 250 °C to 750 °C) for different times. For each oxygenation temperature and time, hardness was measured by the nanoindentation technique, to study the defects (macro-/microcracks and porosity) produced along the c-axis. These defects were visualized by optical microscopy. The main purpose of this study was to establish the oxygenation kinetics for YBCO samples, which were textured by the top-seeded melt growth technique. We studied the evolution of hardness perpendicular to the ab-plane, as measured by the nanoindentation technique at a maximum penetration depth of 150 nm. The results indicate that the nanoindentation technique can be used successfully to monitor oxygenation and to establish the kinetics of the process.

  • Contact mechanics at nanometric scale using nanoindentation technique for brittle and ductile materials

     Roa Rovira, Joan Josep; Rayón Encinas, Emilio; Morales Comas, Miguel; Segarra, M.
    Recent patents on nanatechnology
    Date of publication: 2012-06-12
    Journal article

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  • Electrical and mechanical characterization by instrumented indentation technique of La0.85Sr0.15Ga0.8Mg0.2O3-d electrolytes for SOFCs

     Morales Comas, Miguel; Roa Rovira, Joan Josep; Pérez Falcón, José Manuel; Moure Arroyo, Alberto; Tartaj, Jesús; Segarra, Mercè
    Journal of the european ceramic society
    Date of publication: 2012-11-15
    Journal article

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    La0.85Sr0.15Ga0.8Mg0.2O3−δ pellets obtained by the polymeric organic complex solution method, isostatic pressing and sintering at 1350 °C have been electrical and mechanically studied. Electrical measurements evidenced reasonable ionic conductivities (0.01 S cm−1 at 800 °C), which were comparable to those reported for the La1−xSrxGa1−yMgyO3−δ prepared by other synthesis methods. On the other hand, the mechanical properties (elastic modulus, E and hardness, H) have been determined at micro/nanometric scale using the instrumented indentation technique. While E did not vary significantly with the increasing indentation depth (h), H values strongly decreased with the indentation depth up to 500 nm. For h > 500 nm, both mechanical properties remained almost constant, thus obtaining E = 271 ± 6 GPa and H = 13.2 ± 0.4 GPa. Finally, the residual imprints and fracture mechanisms have been observed by atomic force microscopy (AFM).

  • Nanoindentation of Bridgman YBCO samples

     Roa Rovira, Joan Josep; Konstantopoulou, Dimitra; Jimenez Pique, Emilio; Martín, V.; Segarra Rubi, Merce; Pastor, J.Y.
    Ceramics international
    Date of publication: 2012-04
    Journal article

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    n this study, the mechanical properties of YBa2Cu3O7−x, obtained by the Bridgman technique, were examined using a Berkovich tip indenter on the basal plane (0 0 1). Intrinsic hardness was measured by nanoindentation tests and corrected using the Nix and Gao model for this material. Furthermore, Vickers hardness tests were performed, in order to determine the possible size effect on these measurements. The results showed an underestimation of the hardness value when the tests were performed with large loads. Moreover, the elastic modulus of the Bridgman samples was 128 ± 5 GPa. Different residual imprints were visualised by atomic force microscopy and a focused ion beam, in order to observe superficial and internal fracturing. Mechanical properties presented a considerable reduction at the interface. This effect could be attributed to internal stress generated during the texturing process. In order to corroborate this hypothesis, an observation using transmission electron microscopy was performed.

  • Processing of graded anode-supported micro-tubular SOFCs based on samaria-doped ceria via gel-casting and spray-coating

     Morales Comas, Miguel; Navarro, M. E.; Garcia Capdevila, Xavier; Roa Rovira, Joan Josep; Segarra, M.
    Ceramics international
    Date of publication: 2012-07-11
    Journal article

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    A simple gel-casting method was successfully combined with the spray-coating technique to manufacture graded anode-supported micro-tubular solid oxide fuel cells (MT-SOFCs) based on samaria-doped ceria (SDC) as an electrolyte. Micro-tubular anodes were shaped by a gel-casting method based on a new and simple forming technique that operates as a syringe. The aqueous slurry formulation of the NiO–SDC substrate using agarose as a gelling agent, and the effect of spray-coating parameters used to deposit the anode functional layers (AFLs) and electrolyte were investigated. Furthermore, pre-sintering temperature of anode substrates was systematically studied to avoid the anode–electrolyte delamination and obtain a dense electrolyte without cracks, after co-sintering process at 1450 °C. Despite the high shrinkage of substrate (∼70%), an anode porosity of ∼37% was achieved. MT-SOFCs with ∼2.5 mm of outer diameter, 370 μm thick substrate, 20 μm thick AFLs and 15 μm thick electrolyte were successfully obtained. The use of AFLs with 30:70 and 50:50 wt% NiO–SDC allowed to obtain a continuous gradation of composition and porosity in the anode–electrolyte interface.

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    Magnetical response and mechanical properties of second generation of HTSC, YBCO materials  Open access

     Roa Rovira, Joan Josep; Dias, F.T.; Segarra, M.
    Date of publication: 2012-05-15
    Book chapter

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  • Friction, hardness and elastic modulus determined by AFM-FS and nanoindentation techniques for advanced ceramic materials

     Oncins Marco, Gerard; Roa Rovira, Joan Josep; Rayón Encinas, Emilio; Díaz, Jordi; Morales Comas, Miguel; Segarra, M.; Sanz Carrasco, Fausto
    Date of publication: 2012
    Book chapter

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  • Hardness and elastic modulus gradients in a nitride maraging steel: Nanoindentation measurements in plan view and cross section

     Roa Rovira, Joan Josep; Tromas, Christophe; Pichon, Luc
    CSM Instruments Users Meeting
    Presentation's date: 2012-10-24
    Presentation of work at congresses

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  • Effect of lattive anisotropy on plasticity mechanisms in Ti2AlN studied by in situ compression of micro-pillars under synchrotron micro-beam

     Roa Rovira, Joan Josep; Thilly, Ludovic; Guitton, A.; Villechaise, P.; Tromas, Christophe; Joulain, Anne; Marichal, C.; Van Petegem, S.; Van Swygenhoven, H.
    European Inter-Regional Conference on Ceramics
    Presentation's date: 2012-09-13
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  • Estudio de las propiedades eléctricas y mecánicas, mediante la técnica de Nanoindentación, de electrolitos de La0.9Sr0.1Ga0.8Mg0.2o3-d utilizados en pilas SOFCs

     Morales Comas, Miguel; Roa Rovira, Joan Josep; Moure Arroyo, Alberto; Pérez Falcón, José Manuel; Tartaj, Jesus; Segarra, M.
    Congreso Nacional de Materiales
    Presentation's date: 2012-05-30
    Presentation of work at congresses

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  • Estudio comparativo a escala nanométrica de materiales poliméricos mediante el método de Loubet y el de Oliver y Pharr

     Giró-Paloma, J.; Roa Rovira, Joan Josep; Rayón Encinas, Emilio; Martínez, M.; Chimenos Ribera, Josep Maria; Fernández, A.I.
    Congreso Nacional de Materiales
    Presentation's date: 2012-05-31
    Presentation of work at congresses

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  • Enhanced pinning properties and the zero-resistance state in melt-textured high Tc superconductors probed by pulsed magnetic fields

     Dias, F.T.; Vieira, Valdemar das Neves; da Silva, Douglas Langie; Nunes, S.E.; Wolff-Fabris, Frederik; Kampert, E.; Schaf, Jacob; Roa Rovira, Joan Josep
    International Conference on Magnetism with Strongly Correlated Electron Systems
    Presentation's date: 2012-07-13
    Presentation of work at congresses

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  • Electrical and mechanical characterization of La0.85Sr0.15Ga0.80Mg0.20O3-d electrolyte for SOFCs using nanoindentation technique

     Morales Comas, Miguel; Roa Rovira, Joan Josep; Moure Arroyo, Alberto; Tartaj, Jesús; Segarra, M.
    European SOFC Forum
    Presentation's date: 2012-06-27
    Presentation of work at congresses

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  • Possible correlations between magnetic irreversibility and zero resistance in YBCO samples

     Nunes, S.E.; Dias, F.T.; da Silva, Douglas Langie; Vieira, Valdemar das Neves; Schaf, Jacob; Roa Rovira, Joan Josep; Wolff-Fabris, Frederik
    National Meeting on Condensed Matter Physics
    Presentation's date: 2012-05-14
    Presentation of work at congresses

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  • Estudio comparativo de materiales polimércios mediante el método de loubet y el de Oliver & Pharr a escala nanometrica

     Martínez, Mónica; Giró, Jéssica; Roa Rovira, Joan Josep; Rayón Encinas, Emilio; Chimenos Ribera, Josep Maria; Fernández, Anna Inés
    Congreso Nacional de Materiales
    Presentation's date: 2012-05-30
    Presentation of work at congresses

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  • Grain boundary motion in MAX phase materials activated by nanoindentation

     Tromas, Christophe; Roa Rovira, Joan Josep; Villechaise, P.; Guitton, A.; Thilly, Ludovic; Joulain, Anne
    CSM Instruments Users Meeting
    Presentation's date: 2012-10-23
    Presentation of work at congresses

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  • Étude des mécanismes de déformation à température ambiante de la phase MAX Ti2AlN - Compression sous pression de confinement et compression in-sit couplée à la diffraction neutronique

     Guitton, A.; Joulain, Anne; Thilly, Ludovic; Tromas, Christophe; Roa Rovira, Joan Josep; Van Swygenhoven, H.; Van Petegem, S.
    Colloque Plasticité
    Presentation's date: 2012-04-11
    Presentation of work at congresses

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  • Electrical and mechanical characterization of SOFC electrolytes based on Sr and Mg-doped Lanthanum Gallate using Nanoindentation technique

     Morales Comas, Miguel; Roa Rovira, Joan Josep; Pérez Falcón, José Manuel; Moure Arroyo, Alberto; Tartaj, Jesús; Segarra, M.
    European Inter-Regional Conference on Ceramics
    Presentation's date: 2012-09-13
    Presentation of work at congresses

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  • Twin boundary motion in MAX phase materials activated by nanoindentation

     Tromas, Christophe; Roa Rovira, Joan Josep; Villechaise, P.; Guitton, A.; Thilly, Ludovic; Joulain, Anne
    International Conference on Fundamental Properties of Dislocations
    Presentation's date: 2012-08-29
    Presentation of work at congresses

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    Análise de Transiçao Resistiva e da irreversibilidade magnètica no superconductor YBACUO texturizado  Open access

     Nunes, S.E.; Dias, F.T.; Schaf, Jacob; Vieira, Valdemar das Neves; Roa Rovira, Joan Josep; Wolff-Fabris, Frederik
    Encontro de Pós-Graduçao UFPEL
    Presentation's date: 2012-10-30
    Presentation of work at congresses

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    Os supercondutores de alta temperatura crítica, em especial os granulares, apresentam uma transição resistiva que ocorre em duas etapas: a uma temperatura acima da temperatura crítica de transição Tc0, chamada de supercondutividade intragranular e a uma temperatura mais baixa onde ocorre a supercondutividade em toda a amostra, chamada de supercondutividade intergranular. Em Tc0 ocorre à ativação das ligações fracas e uma ordem de longo alcance é obtida, neste momento, a resistência elétrica é nula em toda amostra. Nos supercondutores de alta temperatura crítica, a linha de irreversibilidade magnética divide o estado misto do plano H-T em duas regiões: reversível e irreversível. Na região reversível todo o transporte elétrico sofre dissipação devido aos efeitos da dinâmica de fluxo magnético no supercondutor. Na região irreversível todo transporte de corrente elétrica é permitido. Em supercondutores granulares, as medidas de irreversibilidade magnética e resistividade nula não dependem das mesmas partes da amostra. Enquanto, a resistência elétrica depende de um arranjo de grãos que atravessam toda a amostra a irreversibilidade depende de clusters de grãos bem acoplados. Devido a isso, as medidas de resistência nula devem estar em pontos abaixo da linha de irreversibilidade magnética. O objetivo deste trabalho é analisar as medidas de transporte elétrico e magnetização e correlacionar às linhas de resistência nula e as linhas de irreversibilidade magnética, em diferentes orientações de campo-corrente, para uma amostra com a adição de 30% da fase Y211 (Y2BaCuO5) e comparar os dados obtidos com uma amostra na qual foram adicionados 17% desta mesma fase.

  • Paramagnetic meissner effect ad strong time dependence at high fields in melt-textured high Tc superconductors

     Paiva Gouvêa, Cristol de; Dias, F.T.; Vieira, Valdemar das Neves; da Silva, Douglas Langie; Kampert, E.; Schaf, Jacob; Wolff-Fabris, Frederik; Roa Rovira, Joan Josep
    International Conference on Magnetism with Strongly Correlated Electron Systems
    Presentation's date: 2012-07-13
    Presentation of work at congresses

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  • Possible correlations between magneic irreversibility and zero resistance in YBCO samples

     Nunes, S. E.; Dias, F.T.; Vieira, Valdemar das Neves; Schaf, Jacob; Roa Rovira, Joan Josep; Wolff-Fabris, Frederik; da Silva, Douglas Langie
    National Meeting on Condensed Matter Physics
    Presentation's date: 2012-05-15
    Presentation of work at congresses

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  • Microestructura y propiedades mecánicas de material masivo superconductor YBCO a 300 y 77K

     konstantopoulou, K.; Pastor, J.Y.; Roa Rovira, Joan Josep; Segarra, M.
    Encuentro del Grupo Español de Fractura
    Presentation's date: 2012-03-21
    Presentation of work at congresses

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  • Effect of lattice anisotropy on plastic mechanisms in Ti2AlN studied by in situ compression of micro-pillars

     Thilly, Ludovic; Roa Rovira, Joan Josep; Guitton, A.; Villechaise, P.; Tromas, Christophe; Joulain, Anne; Marichal, C.; Van Petegem, S.; Van Swygenhoven, H.
    International Conference and Exposition on Advanced Ceramics and Composites
    Presentation's date: 2012-01-25
    Presentation of work at congresses

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  • Microestructura y propiedades mecanicas del material masivo superconductor YBCO a 300 y 77 K

     Konstantopoulou, K.; Pastor, J.Y.; Roa Rovira, Joan Josep; Segarra, M.
    Encuentro del Grupo Español de Fractura
    Presentation's date: 2012-03-21
    Presentation of work at congresses

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  • Electrical and mechanical characterization of La0.85Sr0.15Ga0.8Mg0.2O3-d electrolyte for SOFCs using Nanoindentation technique

     Morales, M.; Roa Rovira, Joan Josep; Pérez Falcón, José Manuel; Moure Arroyo, Alberto; Tartaj, Jesús; Segarra, M.
    European Inter-Regional Conference on Ceramics
    Presentation's date: 2012-09-14
    Presentation of work at congresses

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  • Nanoindentation measurements on nitrided maraging steel - Report 1

     Roa Rovira, Joan Josep; Tromas, Christophe
    Date: 2012-03
    Report

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