Influences of the solid load on the microstructure and compressive behavior of Fe2O3 scaffolds manufactured by freeze-casting using stearic acid as dispersant agent

Porous materials manufactured by freeze-casting are demonstrating potential application as oxygen carriers for the production and purification of hydrogen, or anode material for lithium-ion batteries. However, to obtain the required pore morphology and sufficient mechanical strength, the suspension processing parameters must be controlled. Fe2O3 nanoparticles/camphene suspensions were fabricated using stearic acid as the dispersant agent showing a low-viscosity (130 mPa⋅s) with a high solid volume fraction (0.3). Suspensions show a shear-thinning behavior according to the Sisko model and a maximum packing fraction of 0.569 estimated from a zero porosity sample. A modified Krieger and Dougherty model was introduced to incorporate the influence of the particleaspect ratio. The Fe2O3 scaffolds manufactured by freeze-casting shown a gradient pore size along the freezing direction, which was diminished with the solid volume fraction, the compression strength was improved with the pore size reduction and fitted according to the minimum solid area model.Universidad de Sevilla PIF II.2AAgencia Estatal de Investigación (AEI) MAT2016-76713-

Microestructura y propiedades mecánicas de SiC bimórfico a partir de madera de jara

Se ha sintetizado SiC biomórfico mediante infiltración reactiva de silicio fundido en preformas de carbón obtenidas por medio de pirólisis de ramas de jara, de diámetro típico 5 mm. Debido a la especial microestructura de esta madera, el producto final es un tubo de SiC de densidad 2.40g/cm3 (25% de la sección) relleno de carbón sin reaccionar. Se realizaron ensayos de resistencia a rotura a velocidad de compresión constante de 5 mm/min para temperaturas entre 1150 y 1350ºC, obteniéndose tensiones de rotura entre 600 y 1000 MPa y deformaciones a rotura menores del 2%. Los resultados promedio presentan un buen acuerdo con la extrapolación de los obtenidos para SiC biomórfico con densidades menores, y los de carburo de silicio formado por reacción (RF-SiC) de densidades mayores

Development of a TiNbTaMoZr-Based High Entropy Alloy with Low Young´s Modulus by Mechanical Alloying Route

In this work, an equiatomic TiNbTaMoZr-based high-entropy alloy (HEA) has been developed by a powder metallurgy route, which consists of a process of combined one-step low-temperature mechanical milling starting from the transition metals as raw materials and a subsequent pressureless sintering. In this way, the optimized synthesized specimen, after 10 h of milling time, showed two di erent body-centered cubic (bcc) TiNbTaMoZr alloys, which, after sintering at 1450 C, 1 h of dwell time and a heating and cooling rate of 5 C min1, it remained formed as two bcc TiNbTaMoZr-based HEAs. This material, with micrometric and equiaxed particles, and with homogeneously distributed phases, presented a Young’s modulus that was significantly higher (5.8 GPa) and lower (62.1 GPa) than that of the usual commercially pure (cp) Ti and Ti6Al4V alloy used for bone-replacement implants. It also presented similar values to those of the HEAs developed for the same purpose. These interesting properties would enable this TiNbTaMoZr-based HEA to be used as a potential biomaterial for bulk or porous bone implants with high hardness and low Young´s modulus, thereby preventing the appearance of stress-shielding phenomena

BiOX (X = I or Cl?) modified Na-K2Ti6O13 nanostructured materials for efficient degradation of Tetracycline, Acid Black 1 dye and microbial disinfection in wastewater under Blue LED

This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)Photocatalysis process has emerged as a prompt method for wastewater treatment and microbial disinfection. The development of visible light active (VLA) photocatalysts, especially Blue LED active (BLA) is a challenge task for the current research scenario towards pollutants degradation and real wastewater treatment. Here, we have developed a material which is highly active under Blue LED. BiOX (X = I or Cl) modified Na-K2Ti6O13 with two concentrations of BiOX was fabricated and effectively utilized for Acid Black 1 (AB 1) dye and tetracycline (TCN) degradations under Blue LED. The TCN degradation was also performed under white LED and direct solar light for comparison, and found that Na-K2Ti6O13/BiOX composite was very efficient in Blue LED and white LED than direct solar irradiation. The higher activity of Na-K2Ti6O13/BiOX in Blue LED confirmed by Blue light absorption of Na-K2Ti6O13/BiOX via DRS measurements. The bare Na-K2Ti6O13 is almost no active (≈10 %) under Blue LED, while Na-K2Ti6O13/BiOX showed 99 % degradation under the same condition for AB 1 degradation. The stability of the Na-K2Ti6O13/BiOX was tested against AB 1 dye degradation with multiple runs. The degradation intermediates of AB 1 and TCN were analysed by GC–MS, and suitable degradation pathways were proposed. The Na-K2Ti6O13/BiOX was tested real wastewater treatment via microbial disinfection under Blue LED. The prepared composite could be effectivity used for piolet or industrial scale level effluent treatment

Aplicaciones del SiC biomórfico como reforzante estructural en hormigones refractarios

Una posible aplicación del SiC biomórfico (bioSiC) son los reforzante estructural en hormigones refractarios. En este caso se han fabricado piezas de bioSiC con forma de cilindros alargados, 3-4 mm de diámetro y 30-35 mm de longitud, mediante infiltración reactiva de Si líquido en piezas de carbón obtenidas por pirolización de madera de haya de calidad comercial. Hemos estudiado las características microestructurales y las propiedades mecánicas de los reforzantes, como paso previo al estudio de la aplicación mencionada, de la que se ofrece un avance en este trabajo. Para caracterizar la calidad del material y del proceso de fabricación, la microestructura de las piezas se ha estudiado mediante microscopía electrónica de barrido. Los reforzantes de bioSiC fueron ensayados a compresión uniaxial y flexión en cuatro puntos a temperatura ambiente y a alta temperatura (1250-1400ºC) para la determinación de sus propiedades mecánicas, y se realizaron estudios fractográficos en el segundo tipo de ensayos. Subsecuentemente, se prepararon ladrillos refractarios con un 3% en peso de reforzantes de bioSiC, que fueron curados a diferentes temperaturas (máx. 1600ºC). Estos ladrillos se han ensayado en compresión y flexión en tres puntos, a temperatura ambiente, comparándose los resultados con los obtenidos en ladrillos sin reforzantes y reforzados con agujas metálicas de calidad comercial (acero refractario 306 ó 310), con la misma formulación y condiciones de curado.This work is devoted to the study of the time and temperature dependence of the static grain growth in YTZP 4 mol %, with an average grain size within the submicrometric range ( > 0.1 µm). Also, the mechanical response in the temperature interval between 1200 ºC and 1500 ºC is analysed. The grain growth is controlled by the yttria segregation at the grain boundaries, which plays a key role in the cationic diffusion processes. Microstructural characterization of both as-received and deformed samples allows to conclude that plastic deformation is due to grain boundary sliding (GBS), with stress exponents increasing with the flow stress, but in all cases they are lower than n = 2

Microestructure and mechanical properties of biomorphic SiC obtained from eucalyptus

El desarrollo de materiales cerámicos con una estructura de tipo celular, similar a la del hueso o la madera, ha sido una cuestión que ha suscitado un gran interés en los últimos años. Su atractivo se debe al hecho de poseer una estructura porosa altamente interconectada de baja densidad, perfeccionada por la evolución. En el caso del SiC biomórfico (bio-SiC) el proceso de fabricación es sencillo: se piroliza una pieza de madera y a continuación se inyecta con silicio líquido, el material así obtenido es un compuesto Si/SiC en el que el SiC mimetiza la estructura de la madera original. En este trabajo se estudian las propiedades mecánicas del SiC biomórfico fabricado a partir de eucalipto (madera dura con una distribución bimodal de poros). Se ha estudiado el comportamiento mecánico del mismo (resistencia a compresión, resistencia a flexión, tenacidad de fractura y módulo de elasticidad) entre 25 y 1350 o C. Asimismo, se discute la relación entre el comportamiento mecánico del material y su microestructura.The development of cellular ceramics with a biological structure, like bones and wood, has been a matter of interest in recent years. A low density highly interconnected structure, perfected by evolution, rises as the principal advantage of these materials. In the case of biomimetic SiC (biomorphic SiC, or bioSiC), the fabrication process technique is quite simple: a piece of wood is pyrolysed and is infiltrated with molten silicon after, the final product is a composite Si/SiC, which replicates the wood anisotropic microstructure This work focus on the mechanical properties of bioSiC fabricated using eucalyptus wood as precursor (hard wood with a bimodal channel distribution). It has been studied the mechanical behavior of this bioSiC (compression strength, flexure strength, fracture toughness and elastic modulus) between 25 and 1350 o C. It is also discussed the relationship between mechanical behavior of the material and its microstructure

Alumina doped Fe2O3 foams by freeze-casting for redox cycling applications

Hydrogen is the next energy vector for a decarbonization society but industrial production is still methane-based. The Steam Iron Process (SIP) could provide a carbon-free production and safety storage option. Here, we show that a Fe2O3-3 wt% of Al2O3 foams created by freeze-casting withstand 10 redox cycles at different temperatures with no reduction in performance or pore shrinking. The use of stearic acid as a dispersant agent/binder produces the porous structure enhancement of the foam and promotes the early reduction of the hematite phase during foam sintering. The Al2O3 incorporation was detected as a solid solution in the Fe2O3 phase at the particle surface. This result is relevant as correlated the positive values of the zeta potential observed. Freeze-casted foams could improve long-term redox performances combining a unique tailored interconnected pore structure with a specific chemical composition.Ministerio de Ciencia e Innovación – Agencia Estatal de Investigación – FEDER MAT2016-76713-PUniversidad de Sevilla PIF II.2

Development of highly efficient cost-effective CdS/Ag nanocomposite for removal of azo dyes under UV and solar light

This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)Water pollution by toxic dyes is an environmental problem that threatens human health. A green technology to solve this problem is the use of highly efficient photocatalysts under visible/solar light to degrade these organic molecules. However, develop affordable photocatalytic particles with high luminescence performance, enhanced stability, and low degradation is still a challenge. Here, it is reported the hydrothermal synthesis of an advanced and cost-effective nanocomposite based on a ceramic, cadmium sulphide, covered by silver nanoparticles (CdS/Ag), with outstanding photocatalytic efficiency for toxic dyes degradation under ultraviolet and direct solar light. The CdS/Ag nanocomposite completely degrade the Reactive Red 120 (RR 120), Acid Black 1 (AB 1) and Direct Blue 15 (DB 15) dyes in both light irradiations. Without scavenger, about 93% of degradation was observed at 75 min, remaining a high stability (more than 90%) after fourth degradation cycles

Green hydrogen production using doped Fe2O3 foams

This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).Hydrogen is the ideal energy vector to reduce our fossil-fuels dependency and diminish the climate change consequence. However, current production is still methane based. It is possible to produce hydrogen using bioethanol from the alcoholic fermentation of organic waste by chemical looping processes, but unfortunately current redox systems generate hydrogen with significant traces of CO. In the case of proton exchange membrane fuel cells (PEMFC), hydrogen must be highly purified to produce electricity. Here, high porosity interconnected Fe2O3 foams doped with 2 wt% Al2O3 were manufactured by the freeze-casting method, obtaining around 5.1 mmol H2 g1 sample of highly pure hydrogen (<10 ppm of CO) consuming only 3.42 mmol of ethanol on each redox cycles, with no deactivation. This result shows the possibility of using an abundant and inexpensive raw material as the iron oxide to scale-up the direct pure H2 production and facilitates its use in the automotive secto

Propiedades mecánicas de SiC biomórfico poroso

Se han estudiado carburos de silicio biomórficos (bioSiC) fabricados mediante infiltración reactiva de silicio líquido en una preforma de carbón de origen vegetal. Se obtiene así una cerámica porosa de SiC con silicio remanente en sus poros. Este silicio puede alterar considerablemente las propiedades mecánicas de los bioSiC. Este trabajo preliminar se centra en el estudio de las propiedades mecánicas de los bioSiC fabricados a partir de preformas de haya, eucalipto y pino, tras reacción con una disolución de HF y HNO3 que elimina ostensiblemente el silicio residual. Las propiedades mecánicas a altas temperaturas fueron estudiadas a partir de ensayos de compresión a velocidad de deformación constante. La caracterización microestructural del material resultante, antes y después de los ensayos mecánicos, fue realizada mediante Microscopía Electrónica de Barrido (MEB).Biomorphic SiC (bioSiC) materials fabricated by silicon infiltration of chescoal preforms have been studied. As a result of this process, a porous SiC ceramics with remnant silicon partially filling pores is obtained. This remnant silicon can considerably alter the mechanical properties of the bioSiC but it can be effectively removed by reaction with a mixture of HF and HNO3 producing a clean pororus bioSiC. In this work the comparison of the mechanical properties of bioSiC from preforms of beech, eucalyptus and pine, with and without remanent silicon is studied. High temperature mechanical properties were studied from deformation tests in compression at constant strain rate. Microstructural characterization of the samples, before and after the mechanical tests, was performed by scanning electron microscopy (SEM)