Artículos SCI

Abstract

We devise a unique heteronanostructure array to overcome a persistent issue of simultaneously utilizing the surface-enhanced Raman scattering, inexpensive, Earth-abundant materials, large surface areas, and multifunctionality to demonstrate near single-molecule detection. Room-temperature plasma-enhanced chemical vapor deposition and thermal evaporation provide high-density arrays of vertical TiO2 nanotubes decorated with Ag nanoparticles. The role of the TiO2 nanotubes is 3-fold: (i) providing a high surface area for the homogeneous distribution of supported Ag nanoparticles, (ii) increasing the water contact angle to achieve superhydrophobic limits, and (iii) enhancing the Raman signal by synergizing the localized electromagnetic field enhancement (Ag plasmons) and charge transfer chemical enhancement mechanisms (amorphous TiO2) and by increasing the light scattering because of the formation of vertically aligned nanoarchitectures. As a result, we reach a Raman enhancement factor of up to 9.4 × 107, satisfying the key practical device requirements. The enhancement mechanism is optimized through the interplay of the optimum microstructure, nanotube/shell thickness, Ag nanoparticles size distribution, and density. Vertically aligned amorphous TiO2 nanotubes decorated with Ag nanoparticles with a mean diameter of 10–12 nm provide enough sensitivity for near-instant concentration analysis with an ultralow few-molecule detection limit of 10–12 M (Rh6G in water) and the possibility to scale up device fabrication.

Noviembre, 2020 · DOI: 10.1021/acsami.0c14087

Abstract

We explore joining Si-Al-C-O fiber-bonded ceramics to Cu-clad-Mo using an Ag-Ti-Cu brazing alloy. A temperature of 900 degrees C and times in the range of 10-20 min are required to obtain sound joints irrespectively of the fiber orientation. The reaction layer is 1-2 mu m thick and free of pores and defects. The thermal conductivity of the joined samples is well described considering that the metal and the ceramic are in series for thermal resistance. This implies that the joint is highly conductive and forms an almost perfect 

Octubre, 2020 · DOI: 10.1016/j.matlet.2020.128203

Abstract

Organomica, C8-2-Mica, was obtained from a high charged synthetic mica, Na-2-Mica, by cation exchange reaction with octylammonium cations and these were used to host other bulky guest species such as polyhydroxy aluminium cations, Al(13)20. The hydrolization of 3-mercaptopropyltrimethoxysilane (MPTMS) allowed the covalent attachment with hydroxyl groups of the oligomeric cation, providing thiol groups that create specific adsorption sites, Al(13)20/SH. The structure of the adsorbents was analysed by XRD and Infrared spectroscopy and these were tested as an adsorbent for the removal of zinc and herbicide MCPA from aqueous solutions. C8-2-Mica was the best adsorbent for MCPA and thiol groups favoured the adsorption of Zn2+. Moreover, Al(13)20/SH showed excellent adsorptive properties for the simultaneous adsorption of MCPA and Zn2+.

Octubre, 2020 · DOI: 10.1016/j.clay.2020.105749

Abstract

Current studies on ammonia synthesis by means of atmospheric pressure plasmas respond to the urgent need of developing less environmentally aggressive processes than the conventional Haber-Bosch catalytic reaction. Herein, we systematically study the plasma synthesis of ammonia and the much less investigated reverse reaction (decomposition of ammonia into nitrogen and hydrogen). Besides analyzing the efficiency of both processes in a packed-bed plasma reactor, we apply an isotope-exchange approach (using D-2 instead of H-2) to study the reaction mechanisms. Isotope labeling has been rarely applied to investigate atmospheric plasma reactions, and we demonstrate that this methodology may provide unique information about intermediate reactions that, consuming energy and diminishing the process efficiency, do not effectively contribute to the overall synthesis/decomposition of ammonia. In addition, the same methodology has demonstrated the active participation of the interelectrode material surface in the plasma-activated synthesis/decomposition of ammonia. These results about the involvement of surface reactions in packed-bed plasma processes, complemented with data obtained by optical emission spectroscopy analysis of the plasma phase, have evidenced the occurrence of inefficient intermediate reaction mechanisms that limit the efficiency and shown that the rate-limiting step for the ammonia synthesis and decomposition reactions are the formation of NH* species in the plasma phase and the electron impact dissociation of the molecule, respectively.

Octubre, 2020 · DOI: 10.1021/acssuschemeng.0c04461

Abstract

Successful 3D printing by material extrusion of functional parts for new devices requires high quality filaments. Uniform homogeneity and good dispersion of particles embedded in filaments typically takes several cycles of extrusion or well-prepared feedstock by injection molding, industrial kneaders or twin-screw compounding. These methods need specific production devices that are not available in many laboratories non-specialized in polymer research, such as those working on different material science and technology topics that try to connect with additive manufacturing. Therefore, laboratory studies are usually limited to compositions and filler concentrations provided by commercial companies. Here, we present an original laboratory scale methodology to custom-prepare the feedstock for extruding magnetic composite filaments for fused filament fabrication (FFF), which is attainable by a desktop single-screw extruder. It consists in encapsulating the fillers in custom made capsules that are used as feedstock and reach the melting area of the extruder maintaining the same concentration of fillers. Results have shown that our approach can create smooth and continuous composite filaments with good homogeneity and printability with fine level of dimensional control. We further show the good dispersion of the particles in the composite filament using X-Ray Tomography, which enabled a 3D reconstruction of the spacial distribution of the embedded magnetic particles. The major advantage of this new way of preparing the composite feedstock is that it avoids the hassle of multiple extrusion runs and industrial machinery, yet providing uniform filaments of well controlled filler concentration, which is predictable and reproducible. The proposed methodology is suitable for different polymer matrices and applicable to other functional particle types, not just limited to magnetic ones. This opens an avenue for further laboratory scale development of novel functional composite filaments, useful for any community. This democratization of complex filament preparation, including consumers preparing their own desired uniform novel filaments, will facilitate to unify efforts nearing 3D printing of new functional devices.

Septiembre, 2020 · DOI: 10.1016/j.mtcomm.2020.101049

Abstract

The structural behavior of some cutin monomers, when deposited on mica support, was extensively investigated by our research group. However, other events, such as esterification reaction (ER), are still a way to explore. In this paper, we explore possible ER that could occur when these monomers adsorb on support. Although classical molecular dynamics simulations are not able to capture reactive effects, here, we show that they become valuable strategies to analyze the initial structural configurations to predict the most favorable reaction routes. Thus, when depositing aleuritic acid (ALE), it is observed that the loss of capacity to form self-assembled (SA) systems favors different routes to occur ER. In pure ALE bilayers systems, an ER is given exclusively through the -COOH and primary -OH groups. In pure ALE monolayers systems, the ER does not happen when the system is self-assembled. However, for disorganized systems, it is able to occur by two possible routes: -COOH and primary -OH (route 1) and -COOH and secondary -OH (route 2). When palmitic acid (PAL) is added in small quantities, ALE SAMs can now form an ER. In this case, ER occurs mostly through the -COOH and secondary -OH groups. However, when the presence of PAL is dominant, ER can occur with either of both possibilities, that is, routes 1 and 2.

Septiembre, 2020 · DOI: 10.1007/s00894-020-04544-9

Abstract

Mg2SiO4-MgAl2O4 eutectic ceramics have been fabricated by means of the laser floating zone (LFZ) technique. The microstructure has revealed as an unusual one at lower growth rate, composed of broken lamellae of MgAl2O4 distributed randomly along one matrix, composed of Mg2SiO4. At higher growth rates, a cell structure with intra-cell lamella structure is dominant. Contrary to most eutectic systems, hardness is not dependent upon the inter-spacing, but it does depend on one characteristic length of lamellae: their perimeter. One simple model based upon the dislocation is proposed, which successfully accounts for such extraordinary hardness law. Accordingly, Mg2SiO4-MgAl2O4 eutectic ceramics fabricated at 50 mm/h growth rate with the smallest MgAl2O4 lamella perimeter favorably showed more elevated hardness (13.4 GPa from Vickers indentation and 15.3 GPa from nanoindentation) and strength (430 MPa) than those found in the monolithic Mg2SiO4 matrix.

Septiembre, 2020 · DOI: 10.1016/j.jeurceramsoc.2020.05.015

Abstract

A series of monometallic and bimetallic palladium gold catalyst were prepared and studied for the formic acid dehydrogenation reaction. Different Pd/Au compositions were employed (PdxAu100-x, where x = 25; 50 and 75) and their impact on alloy structure, particle size and dispersion was evaluated. Active phase composition and reaction parameters such as temperature, formic acid concentration or formate/formic acid ratio were adjusted to obtain active and selective catalyst for hydrogen production. An important particle size effect was observed and related to Pd/Au composition for all bimetallic catalysts. 

Septiembre, 2020 · DOI: 10.1016/j.ijhydene.2020.06.076

Abstract

A conventional Pt/CeO2/Al(2)O(3)catalyst physically mixed with an ionic conductor (Mo- or Eu-doped ZrO2) was tested at high space velocity (20,000 h(-1)and 80 L h(-1)g(cat)(-1)) under model conditions (only with CO and H2O) and industrial conditions, with a realistic feed. The promoted system with the ionic conductor physically mixed showed better catalytic activity associated with better water dissociation and mobility, considered as a rate-determining step. The water activation was assessed by operando diffuse reflectance infrared fourier transformed spectroscopy (DRIFTS) studies under reaction conditions and the Mo-containing ionic conductor exhibited the presence of both dissociated (3724 cm(-1)) and physisorbed (5239 cm(-1)) water on the Eu-doped ZrO(2)solid solution, which supports the appearance of proton conductivity by Grotthuss mechanism. Moreover, the band at 3633 cm(-1)ascribed to hydrated Mo oxide, which increases with the temperature, explains the increase of catalytic activity when the physical mixture was used in a water gas shift (WGS) reaction.

Agosto, 2020 · DOI: 10.3390/catal10080841

Abstract

A model for high-temperature plasticity of polycrystals controlled by disclination dipoles is proposed that predict a parabolic dependence of the strain rate versus the applied stress. The presence of a precise stationary disclination density explains the origin of plasticity without microstructural invariance, commonly known as superplasticity. The disclination mechanism is universal, although other processes, such as dislocation glide, are superposed to this one in many systems such as metals or metallic alloys. While, in ceramics it is likely to be the only operative mechanism. Activation of disclination dipoles is a necessary condition for plasticity and sufficient one for superplastic yielding. 

Agosto, 2020 · DOI: 10.1016/j.scriptamat.2020.03.049

Abstract

A bimetallic CuPd/TiO2 system has been prepared by a two-step synthesis and was used for a methanol steam photoreforming reaction. By sequential deposition, palladium is deposited over copper nanoclusters through a galvanic replacement process. Hydrogen production by steam reforming from methanol was achieved by both thermo-photocatalytic and photocatalytic processes. It appears that H-2 production on the bimetallic system is notably higher than the Pd monometallic reference. Moreover this difference in the catalytic performance could be related to the higher CO evolution observed for the monometallic Pd-1.0 TiO2 system which is partially inhibited in the bimetallic catalyst. In addition, an important thermal effect can be envisaged in all cases. Nevertheless, this improved effect in the thermo-photocatalytic process is accompanied by a remarkable CO evolution and SMSI effect (important strong metal-support interactions) that hindered the efficiency as temperature increases. On this basis, optimal operational conditions for H-2 production are obtained for thermo-photocatalytic reforming at 100 degrees C, for which the synergetic effect is higher with lower CO production (H-2/CO=4)

Agosto, 2020 · DOI: 10.1002/cptc.202000010

Abstract

The commercial deployment of calcium-looping (CaL)-based technologies relies on the availability of nontoxic, widely available and cheap CaCO3 rich materials. Biomineralized CaCO3 from waste amply fulfills the aforementioned requirements. In the present work, we study the performance of eggshell and snail shell from food waste as CaO precursors for CaL applications. The results obtained suggest the feasible use of these waste materials. The multicyclic conversion exhibited by biomineralized CaCO3 was comparable to that demonstrated by limestone, which is a commonly proposed material for CaL applications. In addition, the temperature needed to completely calcine biomineralized CaCO3 in short residence times is lower than that required to fully calcine limestone. This would mitigate the energy cost of the technology.

Julio, 2020 · DOI: 10.1021/acs.iecr.9b05997

Abstract

The hexagonal and monoclinic phases of CePO4 have been demonstrated to be excellent catalytic supports for Pt-based water-gas shift (WGS) catalysts. Consequently, the elucidation of the WGS reaction mechanism in these materials constitutes a fundamental aspect in order to explain their catalytic behavior. Because the observed WGS reaction path is closely related to the absence or presence of oxygen vacancies in the support, the study of the oxygen mobility in these solids constitutes a key factor for the understanding of the structure of the materials and its influence on the reaction mechanism. In this study, the oxygen mobility in CePO4 supports and the corresponding Pt catalysts has been evaluated by means of isotopic exchange experiments using O-18(2) and (CO2)-O-18 as probe molecules. Results demonstrate that the evaluated solids present a low exchange activity when O-18(2) is used, indicating the absence of oxygen vacancies in these solids, thus suggesting a poor influence of the WGS redox mechanism. On the contrary, a high oxygen exchange activity is observed using (CO2)-O-18, demonstrating that the exchange in these materials takes place through the formation of carbonate-like intermediates, thus suggesting the associative mechanism of the WGS reaction as the preferred path in these solids. Operando diffuse reflectance infrared spectroscopy experiments under WGS reaction conditions confirm these results, proving that the WGS reaction in the studied materials takes place through a formate-mediated associative mechanism.

Julio, 2020 · DOI: 10.1021/acs.jpcc.0c03649

Abstract

The present recommendations have been developed by the Kinetics Committee of the International Confederation for Thermal Analysis and Calorimetry (ICTAC). The recommendations provide guidance on kinetic analysis of multi-step processes as measured by thermal analysis methods such as thermogravimetry (TGA) and differential scanning calorimetry (DSC). Ways of detecting the multi-step kinetics are discussed first. Then, four different approaches to evaluation of kinetic parameters (the activation energy, the pre-exponential factor, and the reaction model) for individual steps are considered. The approaches considered include multi-step model-fitting as well as distributed reactivity, isoconversional, and deconvolution analyses. For each approach practical advice is offered on its effective usage. Due attention is also paid to the typical problems encountered and to the ways of resolving them. The objective of these recommendations is to help a non-expert with efficiently performing multi-step kinetic analysis and interpreting its results.

Julio, 2020 · DOI: 10.1016/j.tca.2020.178597

Abstract

In the current study, synthesis and detailed characterization of cellulose biochars as a waste biomass model component and vine shoot biochars as a real waste biomass catalyst was performed. Although initially biochars exhibit poor textural properties, a simple activation process can make them much more suitable as a catalyst supports. A combination of physical (CO2) and chemical activation (ZnCl2) was evaluated. The characterization results indicated that the surface area and pore volume of the biochars have increased significantly by chemical activation treatment with ZnCl2. A series of metal catalysts (Pd, Au and Ru) supported on biochars was prepared and characterized. The prepared materials represent a set of noble metal catalysts supported on biochars with different textural and surface properties, which can be used to evaluate the catalytic role of the active phase and carbon support nature in catalytic reactions of interest, such as hydrodeoxygenation, described in the part II.

Julio, 2020 · DOI: 10.1016/j.apcatb.2019.118423

Abstract

In this work, the synthesis of graphene-like nanosheets (GNS) by an electrochemical exfoliation method, their microstructural characterization and their performance as fillers in a ceramic matrix composite have been assessed. To fabricate the composites, 3 mol % yttria tetragonal zirconia (3YTZP) powders with 1 vol % GNS were processed by planetary ball milling in tert-butanol to enhance the GNS distribution throughout the matrix, and densified by spark plasma sintering (SPS). According to a thorough Raman analysis and SEM observations, the electrochemically exfoliated GNS possessed less than 10 graphene layers and a lateral size lower than 1 mu m. However, they contained amorphous carbon and vacancy-like defects. In contrast the GNS in the sintered composite exhibited enhanced quality with a lower number of defects, and they were wavy, semi-transparent and with very low thickness. The obtained nanocomposite was fully dense with a homogeneous distribution of GNS into the matrix. The Vickers hardness of the nanocomposite showed similar values to those of a monolithic 3YTZP ceramic sintered in the same conditions, and to the reported ones for a 3YTZP composite with the same content of commercial graphene nanosheets.

Junio, 2020 · DOI: 10.3390/ma13112656

Abstract

Mixed-halide perovskites represent a particularly relevant case within the family of lead-halide perovskites. Beyond their technological relevance for a variety of optoelectronic devices, photoinduced structural changes characteristic of this type of material lead to extreme photophysical changes that are currently the subject of intense debate. Herein we show that the conspicuous photoinduced phase segregation characteristic of these materials is primarily the result of the local and metastable rearrangement of the iodide sublattice. A local photophysical study comprising spectrally resolved laser scanning confocal microscopy is employed to find a correlation between the defect density and the dynamics of photoinduced changes, which extend far from the illuminated region. We observe that iodide-rich regions evolve much faster from highly defective regions. Also, by altering the material composition, we find evidence for the interplay between the iodide-related defect distribution and the intra- and interdomain migration dynamics giving rise to the complexity of this process.

Junio, 2020 · DOI: 10.1021/acs.jpclett.0c01127

Abstract

Catalytic hydrodeoxygenation (HDO) is a fundamental and promising route for bio-oil upgrading to produce petroleum-like hydrocarbon fuels or chemical building blocks. One of the main challenges of this technology is the demand of high-pressure H-2, which poses high costs and safety concerns. Accordingly, developing cost-effective routes for biomass or bio-oil upgrading without the supply of commercial H-2 is essential to implement the HDO at commercial scale. This article critically reviewed the very recent studies relating to the novel strategies for upgrading the biofeedstocks with 'green' H-2 generated from renewable sources. More precisely, catalytic transfer hydro-genation/hydrogenolysis, combined reforming and HDO, combined metal hydrolysis and HDO, water-assisted in-situ HDO and nonthermal plasma technology and self-supported hydrogenolysis are reviewed herein. Current challenges and research trends of each strategy are also proposed aiming to motivate further improvement of these novel routes to become competitive alternatives to conventional HDO technology.

Junio, 2020 · DOI: 10.1016/j.cogsc.2019.12.008

Abstract

Semiconductor photocatalysis is regarded as most privileged solution for energy conversion and environmental application. Recently, photocatalysis methods using bismuth-based photocatalysts, such as BiPO4, have been extensively investigated owing to their superior efficacy regarding organic pollutant degradation and their further mineralization into CO2 and H2O. It is well known that BiPO4 monoclinic phase exhibited better photocatalytic performance compared to Degussa (Evonik) P25 TiO2 in term of ultraviolet light driven organic pollutants degradation. However, its wide band gap, poor adsorptive performance and large size make BiPO4 less active under visible light irradiation. However, extensive research works have been conducted in the past with the aim of improving visible light driven BiPO4 activity by constructing a series of heterostructures, mainly coupled with π-conjugated architecture (e.g., conductive polymer, dye sensitization and carbonaceous materials). However, a critical review of modified BiPO4 systems using π-conjugated materials has not been published to date. Therefore, this current review article was designed with the aim of presenting a brief current state-of-the-art towards synthesis methods of BiPO4 in the first section, with an especial focuses onto its crystal-microstructure, optical and photocatalytic properties. Moreover, the most relevant strategies that have been employed to improve its photocatalytic activities are then addressed as the main part of this review. Finally, the last section presents ongoing challenges and perspectives for modified BiPO4 systems using π–conjugated materials

Junio, 2020 · DOI: 10.1016/j.cis.2020.102160

Abstract

The large area scalable fabrication of supported porous metal and metal oxide nanomaterials is acknowledged as one of the greatest challenges for their eventual implementation in on-device applications. In this work, we will present a comprehensive revision and the latest results regarding the pioneering use of commercially available metal phthalocyanines and porphyrins as solid precursors for the plasma-assisted deposition of porous metal and metal oxide films and three-dimensional nanostructures (hierarchical nanowires and nanotubes). The most advanced features of this method relay on its ample general character from the point of view of the porous material composition and microstructure, mild deposition and processing temperature and energy constrictions and, finally, its straightforward compatibility with the direct deposition of the porous nanomaterials on processable substrates and device-architectures. Thus, taking advantage of the variety in the composition of commercially available metal porphyrins and phthalocyanines, we present the development of metal and metal oxides layers including Pt, CuO, Fe2O3, TiO2, and ZnO with morphologies ranging from nanoparticles to nanocolumnar films. In addition, we combine this method with the fabrication by low-pressure vapor transport of single-crystalline organic nanowires for the formation of hierarchical hybrid organic@metal/metal-oxide and @metal/metal-oxide nanotubes. We carry out a thorough characterization of the films and nanowires using SEM, TEM, FIB 3D, and electron tomography. The latest two techniques are revealed as critical for the elucidation of the inner porosity of the layers.

Junio, 2020 · DOI: 10.3389/fchem.2020.00520

Abstract

This study pretends to evaluate and understand the effect of moisture presence during CO2/CH4 separation on small-pore SAPO-34 molecular sieves. Two SAPO-34 samples with different physicochemical properties (composition, crystal size and texture) were prepared by hydrothermal synthesis using either one or a mixture of two templates. Transient operando DRIFTS-MS measurements revealed that the sample's hydrophobic character is associated to the presence of Si islands, which enhanced sample's moisture tolerance during repetitive adsorption/desorption cycles. This knowledge is fundamental to achieve the rational design of efficient SAPO-34 membranes under realistic conditions.

Mayo, 2020 · DOI: 10.1016/j.micromeso.2020.110071

Abstract

Optical properties of polycrystalline molybdenum are determined from ultraviolet up to extreme ultraviolet by reflection electron energy loss spectroscopy (REELS). Calculations are performed within the dielectric response theory by means of the quantitative analysis of electron energy losses at surfaces QUEELS-epsilon (k, omega)-REELS software [Surf. Interface Anal. 36, 824 (2004)] that allows the simulation of inelastic scattering cross sections, using a parametric energy loss function describing the optical response of the material. From this energy loss function, the real and imaginary parts of the dielectric function, the refractive index, and the extinction coefficient are deduced and compared with previously published results.

Mayo, 2020 · DOI: 10.1364/AO.391014

Abstract

Semi-transparent perovskite solar cells have the competitive edge of being employed for building integrated photovoltaics due to their esthetic benefits as light harvesting windows/facades. Perovskites have received considerable attention in recent years as a thin film photovoltaic alternative, that can also be tweaked for its transparency, evolving from potentially high bandgaps that are suited for semi-transparent solar cell fabrication. Due to the existing trade of between the efficiency and transparency of a perovskite solar cell, tuning the band gap can address this by making a bridge between the aforementioned parameters. We report our findings on the use of a wide-bandgap perovskite MAPbBr₃, with a rational energetic level hole transport materials based on polycyclic aromatic hydrocarbon molecules that can be a promising alternative class of p-type material. In the present work, DBP (Dibenzo{[f,f′]-4,4′,7,7′-tetraphenyl}diindeno[1,2,3-cd :1′,2′,3′-lm]perylene was evaluated with high bandgap as well as with mixed (FAPbI₃)_0.85(MAPbBr₃)_0.15 perovskites for the fabrication of solar cell. DBP-based solar cells yielded competitive power conversion efficiencies as compared with classical HTMs.

Mayo, 2020 · DOI: 10.1007/s42247-020-00098-x

Abstract

The properties of ZnO based materials for ethanol detection have been studied. Cu doped samples obtained from different precursors have been investigated. ZnO and ZnS have been used as host and Cu and CuO as dopant sources.

The sensing measurements have been mostly performed at room temperature. To monitor the effect of the presence of gas, resistivity and photoluminescence experiments with and without sensing gas have been carried out. The sensing behaviour is affected by the nature of the precursors used. For ZnO:Cu and ZnO:CuO series, a higher sensitivity is obtained at the lower gas concentrations, the better response is obtained for the sample ZnO:Cu with wt.1% of metallic copper. Strong segregation effects observed in these samples could be deleterious for the sensing properties. In the series ZnS:CuO, no segregation is observed, however the sensing behaviour is erratic and attributed to the reduction of Cu ions to the metallic state.

Abril, 2020 · DOI: 10.1016/j.ceramint.2019.12.068

Abstract

A thermogravimetric instrument that works at high pressure of different gases has been designed and assembled. The instrument has been devised to work in a temperature range from room temperature to 1000 degrees C in various controlled pressures of selected gas up to 15 bar, and under conventional rising temperature and constant rate thermal analysis (CRTA) modes. CRTA method allows an intelligent control of the reaction temperature using a feedback system that monitors the mass gain or mass loss of the sample in such a way that the reaction rate is maintained constant all over the process at a preselected value. CRTA method provides a significant advantage for studying processes under high pressure as it reduces heat and mass transfer phenomena that are very relevant under these high-pressure experimental conditions. The thermal oxidation of Ni at 8 bar of pure oxygen has been used for testing the performance of the instrument under both linear heating rate and CRTA conditions.

Abril, 2020 · DOI: 10.1007/s10973-020-09644-5

Abstract

Long bone defects still represent a major clinical challenge in orthopedics, with the inherent loss of function considerably impairing the quality of life of the affected patients. Thus, the purpose of this study was to assess the safety and potential of bone regeneration offered by a load‐bearing scaffold characterized by unique hierarchical architecture and high strength, with active surface facilitating new bone penetration and osseointegration in critical size bone defects. The results of this study showed the potential of bio‐ceramization processes applied to vegetable hierarchical structures for the production of new wood‐derived bone scaffolds, further improved by surface functionalization, with good biological and mechanical properties leading to successful treatment of critical size bone defects in the sheep model. Future studies are needed to evaluate if these scaffolds prototypes, as either biomaterial alone or in combination with augmentation strategies, may represent an optimal solution to enhance bone regeneration in humans.

Abril, 2020 · DOI: 10.1002/jbm.b.34414

Abstract

Mineral trioxide aggregate (MTA) is considered a bioactive endodontic material, which promotes natural mineralization at the material-tooth tissue interface. MTA Repair HP stands out because of the short setting time and the quick and effective bioactive response in vitro. The bioactivity, depens on material composition and microstructure. This work is devoted to analyze MTA Repair HP microstructural features, of both the powder precursor and set material, to get insights into the material physicochemical parameters-functionality performance relationships. Transmission electron microscopy (TEM), and field emission gun scanning electron microscopy (FEG-SEM) coupled with energy-dispersive X-ray (EDX) analyses were performed. X-ray diffraction (XRD) measurements were carried out at different times to investigate setting process. Bioactivity evaluation in vitro was carried out by soaking the processed cement disk in simulated body fluid (SBF). The presented results point out those MTA Repair HP precursor material characteristics of tricalcium silicate particles of nanometric size and high aspect ratio, which provide an elevated surface area and maximized components dispersion of calcium silicate and very reactive calcium aluminate. The MTA Repair HP precursor powder nanostructure and formulation, allows a hydration process comprising silicate hydrate structures, which are very effective to achieve both fast setting and efficient bioactive response.

Abril, 2020 · DOI: 10.3390/ma13071641

Abstract

Enhancement of the main physicochemical properties of a natural bentonite was carried out by means of modifications using surfactant, reflux, microwave treatment and, subsequently, the incorporation of AlZr and AlCe species. The evolution of the main changes in each modification stage was evaluated by means of X-ray diffraction, N-2 sortometry, scanning microscopy (SEM), NH3-TPD, NH3-DRIFTS and CO adsorption at low temperature. For the evaluation of the catalytic behavior, the dehydration-dehydrogenation reactions of 2-propanol and hydro-conversion of decane were used; both of which generate, in addition, information regarding the acidic properties of the materials. The correlation of the number, type and acid strength with the catalytic behavior, allowed establishing the effect produced by both the delamination method and the nature of the incorporated cation. This generated tools that allow controlling the physicochemical properties, and more specifically, the enhancement of the acidity of new supports based on this type of natural clay mineral.

Marzo, 2020 · DOI: 10.1016/j.materresbull.2019.110728

Abstract

The calcium looping process, based on the reversible reaction between CaCO3 and CaO, is recently attracting a great deal of interest as a promising thermochemical energy storage system to be integrated in Concentrated Solar Power plants (CaL-CSP). The main drawbacks of the system are the incomplete conversion of CaO and its sintering-induced deactivation. In this work, the influence of particle size in these deactivation mechanisms has been assessed by performing experimental multicycle tests using standard limestone particles of well-defined and narrow particle size distributions. The results indicate that CaO multicycle conversion benefits from the use of small particles mainly when the calcination is carried out in helium at low temperature. Yet, the enhancement is only significant for particles below 15 μm. On the other hand, the strong sintering induced by calcining in CO2 at high temperatures makes particle size much less relevant for the multicycle performance. Finally, SEM imaging reveals that the mechanism responsible for the loss of activity is mainly pore-plugging when calcination is performed in helium, whereas extensive loss of surface area due to sintering is responsible for the deactivation when calcination is carried out in CO2 at high temperature.

Marzo, 2020 · DOI: 10.1016/j.jare.2019.10.008