Begoña Ferrari - Academia.edu (original) (raw)

Papers by Begoña Ferrari

Materials, 2021

Colloidal processing techniques, based on the suspension of powders in a liquid, are very versati... more Colloidal processing techniques, based on the suspension of powders in a liquid, are very versatile techniques to fabricate porous structures. They can provide customized pores, shapes and surfaces through the control of operational parameters, being the base of the alternative additive manufacture processes. In this work disperse and stable titanium aqueous slurries has been formulated in order to process porous materials by the incorporation of methylcellulose (MC) as a gelation agent and ammonium bicarbonate as an expansive porogen. After casting the slurries and heating at mild temperatures (60–80 °C) the methylcellulose gels and traps the gas bubbles generated by the ammonium bicarbonate decomposition to finally obtain stiff porous green structures. Using an experimental design method, the influence of the temperature as well as the concentration of gelation agent and porogen on the viscosity, apparent density and pore size distribution is analyzed by a second-order polynomial ...

Materials Science and Engineering: B

Boletin De La Sociedad Espanola De Ceramica Y Vidrio, 1997

El avance en aplicaciones estructurales, asi como en sistemas expuestos a condiciones agresivas q... more El avance en aplicaciones estructurales, asi como en sistemas expuestos a condiciones agresivas que hacen necesario reducir la corrosion, ha hecho evolucionar el diseno de materiales laminados y recubrimientos ceramicos sobre metal, potenciando el estudio de tecnicas de procesamiento que permitan su fabricacion. Tal es el caso de la tecnica de deposicion electroforetica, que se revela como una prometedora ruta para este tipo de aplicaciones. En el presente trabajo se estudian las condiciones de electrodeposicion de AI2O3 sobre un sustrato metalico, como es el Zn, que se ha elegido por ser un material sujeto a fuertes reacciones de oxidacion y corrosion que lo hacen un caso extremo de estudio. Considerando las condiciones de estabilidad de la suspension acuosa de AI2O3, en terminos de viscosidad, potencial zeta y conductividad, se ha estudiado la influencia de los parametros electricos en el crecimiento del deposito. Para ello, se han realizado ensayos a intensidad de corriente const...

Use of porous titanium (Ti) and Ti alloys in orthopedic implants or in light structures requires ... more Use of porous titanium (Ti) and Ti alloys in orthopedic implants or in light structures requires processing routes that could generate an as-much-as possible control in the pores amount, shape, size and connectivity. In this work, a colloidal approach to the processing of Ti porous structures by the inside foaming of a porogen into a gelled high solid content aqueous suspension of Ti powders, is presented. The prepared slurries contained different amounts of Methyl Cellulose (MC) as gelling agent (8, 10 and 12 g/L) and ammonium bicarbonate (BA) as porogen (15, 20, 25 wt. %). The gel-casted samples were heated at mild temperatures ranging (60, 70 and 80 °C) to promote the gelation and produce, at the same time, the porosity by the thermal decomposition of the ammonium bicarbonate. Different structures are obtained depending on the combination of the study variables

Boletin De La Sociedad Espanola De Ceramica Y Vidrio, 2009

Se describen los parametros de procesamiento mas adecuados para obtener laminados constituidos po... more Se describen los parametros de procesamiento mas adecuados para obtener laminados constituidos por capas finas de alumina-titanato de aluminio deflectoras de grietas alternadas con capas gruesas de alumina resistentes a las cargas. Estas ultimas se han fabricado a partir de laminas obtenidas por colaje en cinta y presintetizadas. Las estructuras con capacidad para la deflexion de las grietas se conformaron mediante una combinacion de deposicion electroforetica e inmersion. Se han establecido las condiciones optimas para que las capas obtenidas por inmersion actuen como capas reactivas durante la sinterizacion, sin que desaparezca la estructura EPD durante la sinterizacion ni se produzca el agrietamiento durante el secado y la manipulacion de la estructura. El comportamiento mecanico de las estructuras laminadas obtenidas se analizo mediante ensayos de flexion en tres puntos, con la carga aplicada en la direccion perpendicular a la superficie de las capas, y observaciones fractografi...

Environmental, technological and cost advantages make aqueous electrophoretic deposition (EPD) fe... more Environmental, technological and cost advantages make aqueous electrophoretic deposition (EPD) feasible for manufacturing advanced ceramic parts or coatings.

Polymers

The properties of polylactic acid (PLA) filaments have not yet been analysed in detail, and they ... more The properties of polylactic acid (PLA) filaments have not yet been analysed in detail, and they are strongly affected by the extrusion process used in some additive manufacturing systems. Here we present the mechanical, thermal, physical, and fractographical properties of an extruded filament (not the bulk material or scaffolds), the basic building block of any PLA structure printed via material extrusion. This research aims to create a reference point for the modelisation of additively manufactured structures via extrusion processes, as the main building block is characterised in detail for a deep understanding. Furthermore, we investigated the natural ageing (up to one year), the effect of the printing (extruding) temperature (180 and 190 °C), and the effect of the crosshead speed during the tensile tests (10−1 to 102 mm/min) to provide a deeper analysis of the material. The results showed that the material extruded at 190 °C performed better than the material extruded at 180 °C....

Catalysts

The performance of an immobilized photocatalyst has been successfully improved by colloidal proce... more The performance of an immobilized photocatalyst has been successfully improved by colloidal processing of a heterostructure composed by TiO2 nanoparticles and lignocellulose nanofibers (LCNFs) obtained from biomass residues. The incorporation of 4 wt.% of biotemplate to the formulation increased the degradation rate and reduced the operating time to remove the 100% of methyl orange of a liquid solution. The reaction rate constant (k = 0.29–0.45 h−1) of the prepared photocatalytic coatings (using commercial particles and templates obtained from natural-derived resources) are competitive with other pure TiO2 materials (no composites), which were prepared through more complex methodologies. The optimization stages of deposition and sintering processes allowed us to obtain homogeneous and crack-free microstructures with controlled thickness and mass values ranging from 3 to 12 µm and 0.9 to 5.6 mg, respectively. The variation of the microstructures was achieved by varying the amount of ...

Polymers

Among several ions playing a vital role in the body, Sr2+ and Mg2+ are involved in the mechanism ... more Among several ions playing a vital role in the body, Sr2+ and Mg2+ are involved in the mechanism of bone formation, making them especially useful for bone tissue engineering applications. Recently, polylactic acid (PLA)/Mg composites have emerged as a promising family of biomaterials due to their inherent biocompatibility and biodegradability properties. In these composites, polymer and bio-metal have a synergetic effect—while the PLA inhibits the Mg fast reactivity, Mg provides bioactivity to the inert polymer buffering the medium pH during degradation. Meanwhile, the typical form of administrating Sr2+ to patients is through the medication strontium ranelate (SrR), which increases the bone mineral density. Following this interesting research line, a new group of composites, which integrates Mg particles and SrR charged onto halloysite nanotubes (HNT) in a polymeric matrix, was proposed. PLA/Mg/SrR–HNT composites have been processed following a colloidal route, obtaining homogenous...

Surface and Coatings Technology

Abstract PLA/Mg composites have been successfully proposed as biodegradable and fully bioabsorbab... more Abstract PLA/Mg composites have been successfully proposed as biodegradable and fully bioabsorbable materials for bone repair. The present work claims the benefits of Mg particles modification throughout the adsorption of surface modifiers in the in vitro biodegradation behavior of PLA/Mg composites. Additionally, the mixture of PLA with Mg particles in a colloidal suspension replaces the thermal-melting extrusion mixing, preventing the drawbacks associated to the thermal degradation of the polymer during processing. To fulfill this requirement it is necessary to improve the interaction particle-liquid medium for the hydrophilic surface of Mg particles and the organic solvent of PLA, which will provide the maximum dispersion of the Mg in the composite. In this sense, surfaces of Mg particles were modified by the adsorption of two different stabilizers, a surfactant as cetyltrimethylammonium bromide (CTAB) and a polyelectrolyte as polyethylenimine (PEI). The colloidal and chemical stability of Mg was studied in terms of Mg2+ dissolution, zeta-potential and rheology. A chemically stable suspension of modified Mg particles was mixed with the PLA solution in THF, and the mixture was used as feedstock to prepare films by tape casting. The characterization of the composites shows that particle surface modification determines Mg corrosion and hence governs the composite biodegradation.

Chemical Engineering Research and Design

Abstract In this study, the viscosifiers for diesel oil drilling fluid were prepared using Tunisi... more Abstract In this study, the viscosifiers for diesel oil drilling fluid were prepared using Tunisian clay modified with cationic surfactant for five concentration levels from 0.5 to 4.0 times the cationic exchange of purified clay (CEC). The organo-modified clay samples were characterized by X-ray diffraction (XRD), Infrared spectroscopy (FTIR), scanning electron micrography (SEM) and specific surface area (BET model). Oil–clays suspensions were investigated using polarized light optical microscopy (PLOM) and double cone rheometer. The influence of surfactant concentration on rheological properties of suspensions is related to the different microstructures development which depend on surfactant arrangement in the interlayer of clay. The results showed the growth of yield stress and consistency coefficient as the surfactant concentration is increased and the best behaviors were observed for the 3.0 CEC concentration. This sample was tested for two weight percents (5 and 10 wt%), the higher Herschel Bulkley parameters (τ0 = 3.6 Pa, K = 0.397 and n = 0.85) were found for the organoclay at 10 wt%. The latest sample has the high thixotropy loop area so can be used as viscosity enhancer for the oil drilling fluid.

Colloids and Surfaces B: Biointerfaces

New biocompatible and bioabsorbable materials are currently being developed for bone regeneration... more New biocompatible and bioabsorbable materials are currently being developed for bone regeneration. These serve as scaffolding for controlled drug release and prevent bacterial infections. Films of polylactic acid (PLA) polymers that are Mg-reinforced have demonstrated they have suitable properties and bioactive behavior for promoting the osseointegration process. However little attention has been paid to studying whether the degradation process can alter the adhesive physical properties of the biodegradable film and whether this can modify the biofilm formation capacity of pathogens. Moreover, considering that the concentration of Mg and other corrosion products may not be constant during the degradation process, the question that arises is whether these changes can have negative consequences in terms of the bacterial colonization of surfaces. Bacteria are able to react differently to the same compound, depending on its concentration in the medium and can even become stronger when threatened. In this context, physical surface parameters such as hydrophobicity, surface tension and zeta potential of PLA films reinforced with 10% Mg have been determined before and after degradation, as well as the biofilm formation capacity of Staphylococcus epidermidis. The addition of Mg to the films makes them less hydrophobic and the degradation also reduces the hydrophobicity and increases the negative charge of the surface, especially over long periods of time. Early biofilm formation at 8 h is consistent with the physical properties of the films, where we can observe a reduction in the bacterial biofilm formation. However, after 24 h of incubation, the biofilm formation increases significantly on the PLA/Mg films with respect to PLA control. The explosive release of Mg ions and other corrosion products within the first hours were not enough to prevent a greater biofilm formation after this initial time. Consequently, the Mg addition to the polymer matrix had a bacteriostatic effect but not a bactericidal one. Future works should aim to optimize the design and biofunctionality of these promising bioabsorbable composites for a degradation period suitable for the intended application.

Coatings

A simple, low cost and transferable colloidal processing method and the subsequent heat treatment... more A simple, low cost and transferable colloidal processing method and the subsequent heat treatment has been optimized to prepare binder-free electrodes for their application in supercapacitors. NiO/Ni core-shell hybrid nanostructures have been synthetized by heterogeneous precipitation of metallic Ni nanospheres onto NiO nanoplatelets as seed surfaces. The electrophoretic deposition (EPD) has been used to shape the electroactive material onto 3D substrates such as Ni foams. The method has allowed us to control the growth and the homogeneity of the NiO/Ni coatings. The presence of metallic Nickel in the microstructure and the optimization of the thermal treatment have brought several improvements in the electrochemical response due to the connectivity of the final microstructure. The highest specific capacitance value has been obtained using a thermal treatment of 325 • C during 1 h in Argon. At this temperature, necks formed among ceramic-metallic nanoparticles preserve the structural integrity of the microstructure avoiding the employment of binders to enhance their connectivity. Thus, a compromise between porosity and connectivity should be established to improve electrochemical performance.

Advanced Engineering Materials

A preceramic polymer, is mixed with TiH2 particles in different amounts and a MAX phase (Ti3SiC2)... more A preceramic polymer, is mixed with TiH2 particles in different amounts and a MAX phase (Ti3SiC2) are produced by heating in inert atmosphere. Composites produced by mixing the reactive mixture with an excess of TiH2 powder, lead to Ti/Ti3SiC2/TiC bulk composites possessing greatly increased wear resistance and increased hardness in comparison to pure Ti. An emulsion-based colloidal processing and foaming technique is implemented together to produce cellular Ti composite foams containing TiC and Ti3SiC2 ceramic phases. The addition of methylcellulose enabled to suitably control the viscosity of the aqueous TiH2 slurry and to produce stable foams with homogeneous morphology.

International Journal of Refractory Metals and Hard Materials

Ti(C,N) based cermets are currently used in high speed cutting tools industry due to its high the... more Ti(C,N) based cermets are currently used in high speed cutting tools industry due to its high thermal stability. In previous works, Fe was proposed as metal matrix, however the use of iron as continuous matrix strongly affects the processing due to the low wetting capability of molten Fe with the reinforcement phase, Ti(C,N). To solve this problem, the use of alloys such as FeNi has been proposed, where Ni improves the wettability between the ce ramic and the metal phases. This work proposes a bottom up approach to build the cermet microstructure through the synthesis of metal nanoparticles (NPs) on the surface of Ti(C,N) micrometric particles, creating Ti(C,N) Ni core shell structures. For that purpose, the in situ synthesis of Ni NPs through the chemical reduction of a Ni precursor onto the surface of micrometric Ti(C,N) particles, previously stabilized in an aqueous suspen sion, was proposed. Core shell structures were characterized by X Ray Diffraction (XRD), scanning electron mi croscopy (SEM), field emission scanning electron microscopy (FE SEM), scanning transmission electron microscopy (STEM), high resolution scanning electron microscopy (HRTEM), energy dispersive X Ray spectros copy (EDX) and Raman Spectroscopy.

Electrochimica Acta

Abstract Different polyelectrolyte multilayers of Polyethilenimine (PEI) and Polyacrylic Acid (PA... more Abstract Different polyelectrolyte multilayers of Polyethilenimine (PEI) and Polyacrylic Acid (PAA) have been assembled onto β-Ni(OH) 2 nanoplatelets using a simple one-pot route by means of consecutive adsorption (Layer by layer method, LbL). The increase of the number of the layers, from 1 to 5, has been varied to tune the microstructure of supercapacitor electrodes and try to improve their physical properties (specific surface, porosity, etc.) which would increase the specific capacitance in the final device. For this, three stabilized suspensions, prepared with modified nanoplatelets with 1, 3 and 5 layers, were shaped by Electrophoretic Deposition (EPD) onto Ni foils and Ni foam. The effect of the LbL on the final microstructure of the ceramic semiconductor material was evaluated in terms of pseudocapacitance.

Materials, 2021

Colloidal processing techniques, based on the suspension of powders in a liquid, are very versati... more Colloidal processing techniques, based on the suspension of powders in a liquid, are very versatile techniques to fabricate porous structures. They can provide customized pores, shapes and surfaces through the control of operational parameters, being the base of the alternative additive manufacture processes. In this work disperse and stable titanium aqueous slurries has been formulated in order to process porous materials by the incorporation of methylcellulose (MC) as a gelation agent and ammonium bicarbonate as an expansive porogen. After casting the slurries and heating at mild temperatures (60–80 °C) the methylcellulose gels and traps the gas bubbles generated by the ammonium bicarbonate decomposition to finally obtain stiff porous green structures. Using an experimental design method, the influence of the temperature as well as the concentration of gelation agent and porogen on the viscosity, apparent density and pore size distribution is analyzed by a second-order polynomial ...

Materials Science and Engineering: B

Boletin De La Sociedad Espanola De Ceramica Y Vidrio, 1997

El avance en aplicaciones estructurales, asi como en sistemas expuestos a condiciones agresivas q... more El avance en aplicaciones estructurales, asi como en sistemas expuestos a condiciones agresivas que hacen necesario reducir la corrosion, ha hecho evolucionar el diseno de materiales laminados y recubrimientos ceramicos sobre metal, potenciando el estudio de tecnicas de procesamiento que permitan su fabricacion. Tal es el caso de la tecnica de deposicion electroforetica, que se revela como una prometedora ruta para este tipo de aplicaciones. En el presente trabajo se estudian las condiciones de electrodeposicion de AI2O3 sobre un sustrato metalico, como es el Zn, que se ha elegido por ser un material sujeto a fuertes reacciones de oxidacion y corrosion que lo hacen un caso extremo de estudio. Considerando las condiciones de estabilidad de la suspension acuosa de AI2O3, en terminos de viscosidad, potencial zeta y conductividad, se ha estudiado la influencia de los parametros electricos en el crecimiento del deposito. Para ello, se han realizado ensayos a intensidad de corriente const...

Use of porous titanium (Ti) and Ti alloys in orthopedic implants or in light structures requires ... more Use of porous titanium (Ti) and Ti alloys in orthopedic implants or in light structures requires processing routes that could generate an as-much-as possible control in the pores amount, shape, size and connectivity. In this work, a colloidal approach to the processing of Ti porous structures by the inside foaming of a porogen into a gelled high solid content aqueous suspension of Ti powders, is presented. The prepared slurries contained different amounts of Methyl Cellulose (MC) as gelling agent (8, 10 and 12 g/L) and ammonium bicarbonate (BA) as porogen (15, 20, 25 wt. %). The gel-casted samples were heated at mild temperatures ranging (60, 70 and 80 °C) to promote the gelation and produce, at the same time, the porosity by the thermal decomposition of the ammonium bicarbonate. Different structures are obtained depending on the combination of the study variables

Boletin De La Sociedad Espanola De Ceramica Y Vidrio, 2009

Se describen los parametros de procesamiento mas adecuados para obtener laminados constituidos po... more Se describen los parametros de procesamiento mas adecuados para obtener laminados constituidos por capas finas de alumina-titanato de aluminio deflectoras de grietas alternadas con capas gruesas de alumina resistentes a las cargas. Estas ultimas se han fabricado a partir de laminas obtenidas por colaje en cinta y presintetizadas. Las estructuras con capacidad para la deflexion de las grietas se conformaron mediante una combinacion de deposicion electroforetica e inmersion. Se han establecido las condiciones optimas para que las capas obtenidas por inmersion actuen como capas reactivas durante la sinterizacion, sin que desaparezca la estructura EPD durante la sinterizacion ni se produzca el agrietamiento durante el secado y la manipulacion de la estructura. El comportamiento mecanico de las estructuras laminadas obtenidas se analizo mediante ensayos de flexion en tres puntos, con la carga aplicada en la direccion perpendicular a la superficie de las capas, y observaciones fractografi...

Environmental, technological and cost advantages make aqueous electrophoretic deposition (EPD) fe... more Environmental, technological and cost advantages make aqueous electrophoretic deposition (EPD) feasible for manufacturing advanced ceramic parts or coatings.

Polymers

The properties of polylactic acid (PLA) filaments have not yet been analysed in detail, and they ... more The properties of polylactic acid (PLA) filaments have not yet been analysed in detail, and they are strongly affected by the extrusion process used in some additive manufacturing systems. Here we present the mechanical, thermal, physical, and fractographical properties of an extruded filament (not the bulk material or scaffolds), the basic building block of any PLA structure printed via material extrusion. This research aims to create a reference point for the modelisation of additively manufactured structures via extrusion processes, as the main building block is characterised in detail for a deep understanding. Furthermore, we investigated the natural ageing (up to one year), the effect of the printing (extruding) temperature (180 and 190 °C), and the effect of the crosshead speed during the tensile tests (10−1 to 102 mm/min) to provide a deeper analysis of the material. The results showed that the material extruded at 190 °C performed better than the material extruded at 180 °C....

Catalysts

The performance of an immobilized photocatalyst has been successfully improved by colloidal proce... more The performance of an immobilized photocatalyst has been successfully improved by colloidal processing of a heterostructure composed by TiO2 nanoparticles and lignocellulose nanofibers (LCNFs) obtained from biomass residues. The incorporation of 4 wt.% of biotemplate to the formulation increased the degradation rate and reduced the operating time to remove the 100% of methyl orange of a liquid solution. The reaction rate constant (k = 0.29–0.45 h−1) of the prepared photocatalytic coatings (using commercial particles and templates obtained from natural-derived resources) are competitive with other pure TiO2 materials (no composites), which were prepared through more complex methodologies. The optimization stages of deposition and sintering processes allowed us to obtain homogeneous and crack-free microstructures with controlled thickness and mass values ranging from 3 to 12 µm and 0.9 to 5.6 mg, respectively. The variation of the microstructures was achieved by varying the amount of ...

Polymers

Among several ions playing a vital role in the body, Sr2+ and Mg2+ are involved in the mechanism ... more Among several ions playing a vital role in the body, Sr2+ and Mg2+ are involved in the mechanism of bone formation, making them especially useful for bone tissue engineering applications. Recently, polylactic acid (PLA)/Mg composites have emerged as a promising family of biomaterials due to their inherent biocompatibility and biodegradability properties. In these composites, polymer and bio-metal have a synergetic effect—while the PLA inhibits the Mg fast reactivity, Mg provides bioactivity to the inert polymer buffering the medium pH during degradation. Meanwhile, the typical form of administrating Sr2+ to patients is through the medication strontium ranelate (SrR), which increases the bone mineral density. Following this interesting research line, a new group of composites, which integrates Mg particles and SrR charged onto halloysite nanotubes (HNT) in a polymeric matrix, was proposed. PLA/Mg/SrR–HNT composites have been processed following a colloidal route, obtaining homogenous...

Surface and Coatings Technology

Abstract PLA/Mg composites have been successfully proposed as biodegradable and fully bioabsorbab... more Abstract PLA/Mg composites have been successfully proposed as biodegradable and fully bioabsorbable materials for bone repair. The present work claims the benefits of Mg particles modification throughout the adsorption of surface modifiers in the in vitro biodegradation behavior of PLA/Mg composites. Additionally, the mixture of PLA with Mg particles in a colloidal suspension replaces the thermal-melting extrusion mixing, preventing the drawbacks associated to the thermal degradation of the polymer during processing. To fulfill this requirement it is necessary to improve the interaction particle-liquid medium for the hydrophilic surface of Mg particles and the organic solvent of PLA, which will provide the maximum dispersion of the Mg in the composite. In this sense, surfaces of Mg particles were modified by the adsorption of two different stabilizers, a surfactant as cetyltrimethylammonium bromide (CTAB) and a polyelectrolyte as polyethylenimine (PEI). The colloidal and chemical stability of Mg was studied in terms of Mg2+ dissolution, zeta-potential and rheology. A chemically stable suspension of modified Mg particles was mixed with the PLA solution in THF, and the mixture was used as feedstock to prepare films by tape casting. The characterization of the composites shows that particle surface modification determines Mg corrosion and hence governs the composite biodegradation.

Chemical Engineering Research and Design

Abstract In this study, the viscosifiers for diesel oil drilling fluid were prepared using Tunisi... more Abstract In this study, the viscosifiers for diesel oil drilling fluid were prepared using Tunisian clay modified with cationic surfactant for five concentration levels from 0.5 to 4.0 times the cationic exchange of purified clay (CEC). The organo-modified clay samples were characterized by X-ray diffraction (XRD), Infrared spectroscopy (FTIR), scanning electron micrography (SEM) and specific surface area (BET model). Oil–clays suspensions were investigated using polarized light optical microscopy (PLOM) and double cone rheometer. The influence of surfactant concentration on rheological properties of suspensions is related to the different microstructures development which depend on surfactant arrangement in the interlayer of clay. The results showed the growth of yield stress and consistency coefficient as the surfactant concentration is increased and the best behaviors were observed for the 3.0 CEC concentration. This sample was tested for two weight percents (5 and 10 wt%), the higher Herschel Bulkley parameters (τ0 = 3.6 Pa, K = 0.397 and n = 0.85) were found for the organoclay at 10 wt%. The latest sample has the high thixotropy loop area so can be used as viscosity enhancer for the oil drilling fluid.

Colloids and Surfaces B: Biointerfaces

New biocompatible and bioabsorbable materials are currently being developed for bone regeneration... more New biocompatible and bioabsorbable materials are currently being developed for bone regeneration. These serve as scaffolding for controlled drug release and prevent bacterial infections. Films of polylactic acid (PLA) polymers that are Mg-reinforced have demonstrated they have suitable properties and bioactive behavior for promoting the osseointegration process. However little attention has been paid to studying whether the degradation process can alter the adhesive physical properties of the biodegradable film and whether this can modify the biofilm formation capacity of pathogens. Moreover, considering that the concentration of Mg and other corrosion products may not be constant during the degradation process, the question that arises is whether these changes can have negative consequences in terms of the bacterial colonization of surfaces. Bacteria are able to react differently to the same compound, depending on its concentration in the medium and can even become stronger when threatened. In this context, physical surface parameters such as hydrophobicity, surface tension and zeta potential of PLA films reinforced with 10% Mg have been determined before and after degradation, as well as the biofilm formation capacity of Staphylococcus epidermidis. The addition of Mg to the films makes them less hydrophobic and the degradation also reduces the hydrophobicity and increases the negative charge of the surface, especially over long periods of time. Early biofilm formation at 8 h is consistent with the physical properties of the films, where we can observe a reduction in the bacterial biofilm formation. However, after 24 h of incubation, the biofilm formation increases significantly on the PLA/Mg films with respect to PLA control. The explosive release of Mg ions and other corrosion products within the first hours were not enough to prevent a greater biofilm formation after this initial time. Consequently, the Mg addition to the polymer matrix had a bacteriostatic effect but not a bactericidal one. Future works should aim to optimize the design and biofunctionality of these promising bioabsorbable composites for a degradation period suitable for the intended application.

Coatings

A simple, low cost and transferable colloidal processing method and the subsequent heat treatment... more A simple, low cost and transferable colloidal processing method and the subsequent heat treatment has been optimized to prepare binder-free electrodes for their application in supercapacitors. NiO/Ni core-shell hybrid nanostructures have been synthetized by heterogeneous precipitation of metallic Ni nanospheres onto NiO nanoplatelets as seed surfaces. The electrophoretic deposition (EPD) has been used to shape the electroactive material onto 3D substrates such as Ni foams. The method has allowed us to control the growth and the homogeneity of the NiO/Ni coatings. The presence of metallic Nickel in the microstructure and the optimization of the thermal treatment have brought several improvements in the electrochemical response due to the connectivity of the final microstructure. The highest specific capacitance value has been obtained using a thermal treatment of 325 • C during 1 h in Argon. At this temperature, necks formed among ceramic-metallic nanoparticles preserve the structural integrity of the microstructure avoiding the employment of binders to enhance their connectivity. Thus, a compromise between porosity and connectivity should be established to improve electrochemical performance.

Advanced Engineering Materials

A preceramic polymer, is mixed with TiH2 particles in different amounts and a MAX phase (Ti3SiC2)... more A preceramic polymer, is mixed with TiH2 particles in different amounts and a MAX phase (Ti3SiC2) are produced by heating in inert atmosphere. Composites produced by mixing the reactive mixture with an excess of TiH2 powder, lead to Ti/Ti3SiC2/TiC bulk composites possessing greatly increased wear resistance and increased hardness in comparison to pure Ti. An emulsion-based colloidal processing and foaming technique is implemented together to produce cellular Ti composite foams containing TiC and Ti3SiC2 ceramic phases. The addition of methylcellulose enabled to suitably control the viscosity of the aqueous TiH2 slurry and to produce stable foams with homogeneous morphology.

International Journal of Refractory Metals and Hard Materials

Ti(C,N) based cermets are currently used in high speed cutting tools industry due to its high the... more Ti(C,N) based cermets are currently used in high speed cutting tools industry due to its high thermal stability. In previous works, Fe was proposed as metal matrix, however the use of iron as continuous matrix strongly affects the processing due to the low wetting capability of molten Fe with the reinforcement phase, Ti(C,N). To solve this problem, the use of alloys such as FeNi has been proposed, where Ni improves the wettability between the ce ramic and the metal phases. This work proposes a bottom up approach to build the cermet microstructure through the synthesis of metal nanoparticles (NPs) on the surface of Ti(C,N) micrometric particles, creating Ti(C,N) Ni core shell structures. For that purpose, the in situ synthesis of Ni NPs through the chemical reduction of a Ni precursor onto the surface of micrometric Ti(C,N) particles, previously stabilized in an aqueous suspen sion, was proposed. Core shell structures were characterized by X Ray Diffraction (XRD), scanning electron mi croscopy (SEM), field emission scanning electron microscopy (FE SEM), scanning transmission electron microscopy (STEM), high resolution scanning electron microscopy (HRTEM), energy dispersive X Ray spectros copy (EDX) and Raman Spectroscopy.

Electrochimica Acta

Abstract Different polyelectrolyte multilayers of Polyethilenimine (PEI) and Polyacrylic Acid (PA... more Abstract Different polyelectrolyte multilayers of Polyethilenimine (PEI) and Polyacrylic Acid (PAA) have been assembled onto β-Ni(OH) 2 nanoplatelets using a simple one-pot route by means of consecutive adsorption (Layer by layer method, LbL). The increase of the number of the layers, from 1 to 5, has been varied to tune the microstructure of supercapacitor electrodes and try to improve their physical properties (specific surface, porosity, etc.) which would increase the specific capacitance in the final device. For this, three stabilized suspensions, prepared with modified nanoplatelets with 1, 3 and 5 layers, were shaped by Electrophoretic Deposition (EPD) onto Ni foils and Ni foam. The effect of the LbL on the final microstructure of the ceramic semiconductor material was evaluated in terms of pseudocapacitance.