Materials Science Forum Vol. 941

Abstract: Al and Al12Si matrix composites reinforced with synthetic diamond particles have been developed by using conventional powder metallurgy and emerging additive manufacturing techniques, i.e. vacuum hot pressing (VHP) and selective laser melting (SLM), respectively. Relative density and interface structure have been evaluated to relate to measured thermal conductivity (TC) of the composite. Despite very different physical and metallurgical mechanisms (VHP vs. SLM), the diamond/Al interface can be tailored allowing to form a ‘clean’ and tightly-adhered interface at the micrometer scale in both cases. This so-called diffusion-bonded interface is the most favorable for enhancing overall TC which demonstrates the potential of SLM for processing multifunctional Al matrix composites. However, how to realize full densification and simultaneously maintain such an interface structure during SLM remains a key technical problem to figure out.

Abstract: Lack of industrially available materials for additive manufacturing (AM) of metallic materials along with the promises of materials with improved or unique properties provides a strong drive for developing new process/material combinations. As powder bed technologies for metallic materials are relatively new to the market, and to some extent are only maturing, developers of new process/material combinations have certain challenges to overcome. Firstly, basic knowledge on the behavior of materials (even those well established for other applications) under extreme conditions of melting/solidification with beam-based AM methods is far from being adequate. Secondly, manufacturing of the equipment is up to date driven by industrial application, thus optimization of the AM machines for small test batches of powders is still belongs to research and development projects. Also, majority of the powder manufacturers are primarily driven by the market development, and even they are well aware of the demands imposed by the powder bed AM machines, availability of small test batches of adequate powders may be problematic or at least quite costly for the R&D oriented users. Present paper describes the experiences in developing new materials for EBM A2 machine by Arcam EBM, modified for operating with powder batches of 100-200 ml and less. In particular it discusses achievements and challenges of working with powders from different materials with specifications far beyond the range suggested by machine manufacturer. Also it discusses the possibility of using blended rather than pre-alloyed powders for achieving both composite-like and alloyed materials in the same part by steering electron beam energy deposition strategy.

Abstract: Additive manufacturing (AM) and three-dimensional printing (3DP) technologies are being developed for use in manufacturing. In this study, a new AM technology, laser stereo-lithography, that enables to fabricate ceramic components in a single process is developed. This method is demonstrated with alumina under various laser conditions.

Abstract: Hydrogen storage is one of the most important industrial applications of titanium hydride (TiH₂). A critical issue is the hydrogen release rate that strongly depends on the surface structure of TiH₂ particles. This work reports the results of an experimental campaign carried out on TiH₂ powders submitted to heat treatments in air at different temperatures and treatment times. After each heat treatment the TiH₂ powders were examined by X-ray diffraction (XRD) and the results evidenced that the surface layer consists of TiO₂ and Ti₂O. Titanium oxide formation has been monitored by XRD at high temperature. Hydrogen release during heating of oxidized powders was investigated through temperature programmed desorption (TPD). Residual hydrogen in TiH₂ depends on the specific treatment: higher temperature and soaking time of the treatment, lower its content.

Abstract: Layered double hydroxides (LDHs) are anionic clays composed by host layers of positively charged metal hydroxide, in which anions are intercalated to neutralize the charge of the positive layers. Because of the positive charge of the structure and because of their properties of anion exchanges, different anions can be intercalated into the structure. In recent years the ionic conductivity of LDHs was studied for use as the anode material in lithium-ion batteries or PVA/LDH hybrid membranes for fuel cells. However, such studies have reported very low values of the electrical conductivity that is less than 10-3 S cm-1 near room temperature. However, the ion conductivities of LDHs depends on the intercalated anion species and may be affected by difference in the synthesis condition. Moreover, the anion conductivity increases with increasing interlayer distance and as more water is adsorbed by LDH. Within this framework, we have intercalated two ionic liquids, tetramethylammonium hydroxide (TMAH) and 1-buthyl-3-methylimidazolium hydrogen sulfate (Bmim-HSO4) in the interlamellar space with the purpose of increasing the ionic conductivity and decreasing the dependence from the water content. LDH was prepared using the co-precipitation method with controlled pH. The introduction of IL was performed by the intercalation methods. The increase of conductivity was around an order of magnitude in the case of Bmim-HSO4. The LDH-IL can be an interesting material to prepare composite membranes for electrochemical applications.

Abstract: Dry methane reforming (DRM) has recently received considerable attention as a perspective CO₂ utilization technology allowing the valorization natural gas and biogas. The commercialization of the DRM process depends on the use of more stable and active catalysts. The nickel-based catalysts are commonly used in the DRM reaction as they are effective in hydrogen production and nickel is a less expensive material compared to noble metals. However, Ni-based catalysts undergo fast deactivation. The stability of nickel catalysts in DRM reaction may be enhanced by introduction of supports or promoters with basic and/or redox properties. Thus, in this work, Ceria-Zirconia supports were modified by rare earth metals such as Lanthanum, Praseodymium and Yttrium in order to stabilize the raw materials and to promote the catalytic activity. Nickel was then impregnated on such supports and the modified catalysts were tested in dry methane reforming for syngas production since it was already reported that a promotion with nickel and yttrium lead to better activity in DRM catalytic tests over mesoporous materials. All promoted catalysts were characterized by the means of S_BET, XRD, TEM, H₂-TPR, CO₂-TPD in order to define the physical, textural and chemical properties. The influence of basicity on the catalytic activity was clearly evidenced. Moreover, the influence of Nickel loading was also studied. It was evidenced that an optimal Ni loading is needed in order to reach higher activity and stability in DRM.

Abstract: A holistic approach is required for the development of materials and systems for hydrogen storage, embracing all the different steps involved in a successful advance of the technology. The several engineering solutions presented in this work try to address the technical challenges in synthesis and application of solid-state hydrogen storage materials, mainly metal hydride based compounds. Moving from the synthesis of samples in lab-scale to the production of industrial sized batches a novel process development is required, including safety approaches (for hazardous powders), and methods to prevent the contamination of sensitive chemicals. The reduction of overall costs has to be addressed as well, considering new sources for raw materials and more cost-efficient catalysts. The properties of the material itself influence the performances of the hydride in a pilot storage tank, but the characteristics of the system itself are crucial to investigate the reaction limiting steps and overcome hindrances. For this, critical experiments using test tanks are needed, learning how to avoid issues as material segregation or temperature gradients, and optimizing the design in the aspects of geometry, hull material, and test station facilities. The following step is a useful integration of the hydrogen storage system into real applications, with other components like fuel cells or hydrogen generators: these challenging scenarios provide insights to design new experiments and allow stimulating demonstrations.

Abstract: Gas diffusion media (GDM) is an integral part of all gas diffusion electrodes because it facilitates both the transport of reactants to the electrocatalyst surface and the removal of reaction products from the system. Proper reactant/product distribution is critical for high power operation in polymer electrolyte fuel cells (PEMFCs) because oxygen transport and water rejection determine the maximum current density that can be obtained from PEMFCs. This paper will discuss NRL’s research on how GDM morphology influences cell performance in both closed-cathode fuel cell and open-cathode fuel cell designs. The comprehensive study linking the influence of compression on the GDM micro and macro structure morphology will be presented using micro X-ray computed tomography (μ-CT), scanning electron microscopy (SEM), N₂ Physisorption (BET) and traditional electrochemical characterization techniques (CV, Pol. Curves, etc.). Optimal GDM selection for the challenge of open-cathode operation will be presented and related to water retention through rational morphology selection. The relationship between high power performance and water transport will be elucidated and the goals for future GDM properties will be proposed for use in unmanned systems

Abstract: We present an efficient and simple approach for preparing superhydrophobic-superoleophilic polystyrene (PS) fibers via electrospinning. Bead-on-string fibers from a 5% PS solution and micro-sized fibers from a 20% PS solution were combined to achieve a surface having very high contact angle (about 160°) and low contact angle hysteresis. The presence of bead-on-string fibers increases the superhydrophobicity of the sorbent. The micro-sized PS fibers improve the mechanical properties of the electrospun mat through their elastic and flexible behavior. An evaluation of wettability at a low temperature (-10 oC) showed a delayed freezing time for water droplets on the superhydrophobic surface. Water droplets on a polished aluminum surface froze more quickly (about 6 seconds) than droplets on the fabricated superhydrophobic surface (about 500 seconds). Finally, the oil adsorption capacity of the developed superhydrophobic PS fibers, which have a porous surface structure, showed values of 69.1, 69.3 and 61.2 g/g for canola oil, olive oil and motor oil, respectively.

Abstract: Particulate matter (PM) is the air pollutant which has the most severe impact on health. Currently, around 90% of the population of European cities for which PM data exist is exposed to levels exceeding World Health Organization (WHO) air quality guidelines levels. To improve air quality in cities, the challenge is to develop an innovative material solution that can reduce the concentration of PM in the air. In this presentation new porous hybrid materials produced from sodium alginate and some by-products (silica fume, wood ash), are presented. The material porosity is obtained by thermal decomposition of sodium bicarbonate, made at low temperature (70-80°C). The structural and morphological characterization made by XRD, and SEM shows that the materials are porous organic-inorganic hybrid. The mechanical performances of the obtained materials are also investigated. On the basis of embodied energy and carbon footprint of materials primary production, the sustainability of the new obtained materials is evaluated and quantified. The different materials compositions are evaluated and compared in terms of mechanical strength and sustainability. The air particulate matter adsorption characteristics of the material are investigated by a laboratory room, to evaluate its adsorption capacity. Finally the versatility of the new material is also demonstrated in term of their design possibilities: these materials can be direct foamed, extruded, and also 3D printed, with several application advantages.