Structural and spectroscopic characterization of A nanosized sulfated TiO2 filler and of nanocomposite nafion membranes

A large number of nano-sized oxides have been studied in the literature as fillers for polymeric membranes, such as Nafion®. Superacidic sulfated oxides have been proposed and characterized. Once incorporated into polymer matrices, their beneficial effect on peculiar membrane properties has been demonstrated. The alteration of physical-chemical properties of composite membranes has roots in the intermolecular interaction between the inorganic filler surface groups and the polymer chains. In the attempt to tackle this fundamental issue, here we discuss, by a multi-technique approach, the properties of a nanosized sulfated titania material as a candidate filler for Nafion membranes. The results of a systematic study carried out by synchrotron X-ray diffraction, transmission electron microscopy, thermogravimetry, Raman and infrared spectroscopies are presented and discussed to get novel insights about the structural features, molecular properties, and morphological characteristics of sulphated TiO2 nanopowders and composite Nafion membranes containing different amount of sulfated TiO2 nanoparticles (2%, 5%, 7% w/w

Different approaches to obtain functionalized alumina as additive in polymer electrolyte membranes

A series of sulfated aluminum oxides (S-Al2O3), investigated as an electrolyte additive in Nafon membranes, was synthesized via three diferent methods: (i) sol–gel sulfation starting from an aluminum alkoxide precursor, (ii) room temperature sulfation of fumed aluminum oxide, and (iii) hydrothermal sulfation of fumed aluminum oxide. Through the characterization of the synthesized S-Al2O3 by means of X-ray difraction (XRD), thermogravimetric analysis (TGA), and infrared (IR) spectroscopy, a higher sulfation rate was found to be achieved via a hydrothermal sulfation, and the coordination state of sulfate groups was identifed as monodentate. By using this hydrothermally synthesized S-l2O3 as additive, a composite Nafon-based membrane was realized and compared to plain Nafon, by means of thermal analyses and fuel cell tests. Although higher hydration degree was found for the undoped membrane by diferential scanning calorimetry (DSC), improved retention of fuel cell performance upon the increase of operation temperature was observed by using the composite electrolyte, confrming the stabilizing efect of the acidic inorganic additive

Functionalized Al2O3 particles as additives in proton-conducting polymer electrolyte membranes for fuel cell applications

This study reports on the synthesis and characterization of sulfated Al2O3 and of composite membranes, prepared by dispersing the functionalized oxide in Nafion, acting as electrolytes in proton-exchange membrane fuel cells. Different synthetic routes were explored to obtain nanometric alumina particles with sulfate groups. Structural and morphological characteristics of the inorganic compounds and the nature of the bond of the sulfates with the oxide were investigated by x-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, N2 adsorption and thermal gravimetric analysis. Key properties of the hybrid membranes were elucidated in terms of thermal characteristics, water uptake and ionic exchange capacity. Functionality of the nanocomposite membranes, compared with plain Nafion, was tested in hydrogen-fed fuel cells. Polarization and power density curves and in-situ electrochemical impedance spectroscopy were accomplished to evaluate the effect of temperature on the cell performance. It is shown that well-addressed variations in the synthetic routes are able to determine different morphologies and dimensions of the particles and different degrees of functionalization. The incorporation of alumina in Nafion changes the characteristics of the membrane, with special regard towards hydration. In-situ fuel cell electrochemical tests reveal improved electrode-composite membrane interface properties as the working temperature of the cell increases

Heat treatment effect on microstructure evolution of two Si steels manufactured by laser powder bed fusion

Additive manufacturing technology represents a valid alternative for the production of ferromagnetic components in Si steels (FeSi) with high Si content. In this work the effect of heat treatments on microstructural evolution of two steels with standard (3.0 wt.% - FeSi3) and high (6.5 wt.% - FeSi6.5) Si content manufactured by Laser Powder Bed Fusion (L-PBF) was investigated. Four different temperatures ranging from 900 °C up to 1150 °C (soaking time of 1 h) were tested for each steel.In as-built condition, all the grains of FeSi3 are columnar with the [100] direction parallel to the building direction (BD) whereas in the case of FeSi6.5 there is a mix of columnar and equiaxed grains. The average grain size of FeSi6.5 (11.3 ± 0.6 μm) is about one order of magnitude lower than that of FeSi3 (103.1 ± 5.2 μm). EBSD analysis revealed that there is a prevalence of low-angle boundaries (LABs) in FeSi3 and of high-angle boundaries (HABs) in FeSi6.5. The different initial microstructure affects the response to heat treatments of the two alloys: grain size and shape of FeSi3 do not remarkably change, on the contrary significant grain growth takes place in FeSi6.5 without a weakening of the [100] texture. No brittle ordered phases were detected in as-built and heat treated samples of both materials. The results indicate that heat treatments at high temperature can be exploited to improve the magnetic characteristics of printed FeSi6.5 and reach similar properties of commercial steels

Critical Filler Concentration in Sulfated Titania-Added Nafion™ Membranes for Fuel Cell Applications

In this communication we present a detailed study of Nafion™ composite membranes containing different amounts of nanosized sulfated titania particles, synthesized through an optimized one-step synthesis procedure. Functional membrane properties, such as ionic exchange capacity and water uptake (WU) ability will be described and discussed, together with thermal analysis, atomic force microscopy and Raman spectroscopy data. Also electrochemical properties such as proton conductivity and performances in hydrogen fuel cells will be presented. It has been demonstrated that a critical concentration of filler particles can boost the fuel cell performance at low humidification, exhibiting a significant improvement of the maximum power and current density delivered under 30% low-relative humidity (RH) and 70 °C with respect to bare Nafion™-based systems

An NMR study on the molecular dynamic and exchange effects in composite nafion/sulfated titania membranes for PEMFCs

Sulfated titania nanoparticles were evaluated as inorganic additives in composite Nafion based membranes, to be considered as advanced electrolyte in proton exchange membrane (PEM) fuel cells (FCs). Three different filler loadings respect to the polymer were comparatively investigated to elucidate the effect of the inorganic particles on membrane peculiar properties and finally establish the most effective electrolyte composition. Water dynamics were investigated by NMR spectroscopy, including pulsed-field-gradient diffusion and 1H spectral analyses conducted as a function of temperature (20-130 °C), and by water content measurements, providing a general description of the water management inside the systems and of the effects of the fillers. Due to its strong acidity and hydrophilicity, sulfated titania was found to improve both the water retention and diffusion in the composite membranes in respect to plain recast Nafion, in the whole range of investigated temperatures, with a significant impact in the region of high temperatures and very low water content. In this work, self-diffusion coefficients data were interpreted in terms of a simple “two sites” model involving exchange between relatively bound and mobile water sites to discuss the nature of water dynamics and the state(s) of the water (bound and free states) both inside composite and filler-free membranes, as well as its interaction with the hydrophilic polymer sites and particles surface. A quantitative analysis was elaborated to estimate the number of water molecules involved in the hydration shell of the hydrophilic groups of both polymer and filler, as function of the membrane water content. Despite the simplicity of this “bound/free water exchange” model, we obtain consistent values corresponding to about thirteen water molecules per sulfonic group

Multimodal and multiscale investigation for the optimization of AlSi10Mg components made by powder bed fusion-laser beam

Abstract In recent years, there has been a growing interest in the use of additive manufacturing (AM) to fabricate metallic components with tailored microstructures and improved mechanical properties. One of the most promising techniques for the aerospace industry is powder bed fusion-laser beam (PBF-LB). This technique enables the creation of complex shapes and structures with high accuracy and repeatability, which is especially important for the aerospace industry where components require high precision and reliability. However, the impact of the PBF-LB process on microstructural features, such as the grain size distribution and porosity, remains an important area of research since it influences mechanical properties and performance of materials. In this study, a multimodal and multiscale correlative microscopy approach is used to investigate the microstructure of AlSi10Mg components made by PBF-LB. The study found that the correlative microscopy approach involving X-ray images with visual, chemical, and diffraction information coming from optical microscopy (OM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) is highly effective in reaching a more comprehensive understanding of the relationship between the fabrication process and the effective microstructure of PBF-LB fabricated components enabling the optimization of their performance for a wide range of applications

Influence of Vanadium Micro-Alloying on the Microstructure of Structural High Strength Steels Welded Joints

The inter-critically reheated grain coarsened heat affected zone (IC GC HAZ) has been reported as one of the most brittle section of high-strength low-alloy (HSLA) steels welds. The presence of micro-alloying elements in HSLA steels induces the formation of microstructural constituents, capable to improve the mechanical performance of welded joints. Following double welding thermal cycle, with second peak temperature in the range between Ac1 and Ac3, the IC GC HAZ undergoes a strong loss of toughness and fatigue resistance, mainly caused by the formation of residual austenite (RA). The present study aims to investigate the behavior of IC GC HAZ of a S355 steel grade, with the addition of different vanadium contents. The influence of vanadium micro-alloying on the microstructural variation, RA fraction formation and precipitation state of samples subjected to thermal cycles experienced during double-pass welding was reported. Double-pass welding thermal cycles were reproduced by heat treatment using a dilatometer at five different maximum temperatures of the secondary peak in the inter-critical area, from 720 °C to 790 °C. Although after the heat treatment it appears that the addition of V favors the formation of residual austenite, the amount of residual austenite formed is not significant for inducing detrimental effects (from the EBSD analysis the values are always less than 0.6%). Moreover, the precipitation state for the variant with 0.1 wt.% of V (high content) showed the presence of vanadium rich precipitates with size smaller than 60 nm of which, more than 50% are smaller than 15 nm