CARBON STRUCTURES AND Mg-BASED MATERIALS FOR GAS SORPTION

Hydrogen is an alternative energy carrier for both mobile and stationary applications, which can effectively alleviate greenhouse gas emissions and reduce dependence on fossil fuels. The other promising approach in reducing greenhouse gas emissions is carbon capture. Mgbased materials have been considered as a promising hydrogen storage system due to their high hydrogen capacity (up to 7.6 wt.%), high abundance, low cost and lightweight. Different carbon structures have also drawn considerable interests for hydrogen storage and carbon capture. In this research, the nanostructured carbon was produced in a cold plasma reactor designed in-house as additives for improving hydrogen storage properties of Mg-based materials and CO2 storage of MgO. The effects of the plasma reactor’s flow rate, temperature and power were evaluated for the formation of the carbon structures. TEM shows that the carbon consists of spherical particles of 40.8±8.7 nm in diameter and graphene sheets. Further thermal treatment of the plasma carbon was carried out to enhance the surface area. The treatment conditions were optimized through response surface methodology (RSM). The effects of the treatment temperature, time and pressure on BET surface area and yield were studied. The predicted BET surface area and yield by RSM were found to agree with the experimental values. The optimum treatment conditions for the plasma carbon (PC) were found to be: temperature = 950°C and time = 120 min, pressure = 100 kPaCO2 gas flow. The optimized PC was mixed as an additive with 20h-milled MgH2/TiC for improvement of hydrogen storage properties. RSM optimized the mixing time and the content of PC in the (MgH2/TiC + PC) composite. The results demonstrated that both mixing time and the content of plasma carbon (PC) significantly affected the hydrogen storage properties. The effects of the PC, activated carbon (AC) and carbon nanotubes (CNTs) on hydrogen storage properties of MgH2/TiC were studied. PC, AC and CNTs showed positive effects on reducing hydrogen desorption temperature and improving the adsorption kinetics of the 20h-milled MgH2/TiC. PC shows the best effect due to its unique structure. The mechanism of the effects of the three carbon structures on hydrogen storage was discussed. ABSTRACT II The optimized PC was also mixed with MgO, both by ball milling and chemical coprecipitation methods to form porous carbon supported MgO for CO2 storage and separation. The results indicated that the chemically synthesized MgO+PC calcined at 800 °C (referred to as MgO/PC-800) showed the most promising CO2 storage capacity up to 6.16 mmol/g at 25 °C and 1500 kPa CO2 pressure. The introduction of PC improves the CO2 adsorption capacity of the chemical synthesized MgO due to improved surface area. The dual-site Langmuir (DSL) model was employed to predict adsorption equilibria of CO2/H2 gas mixtures, which well simulated the behaviors of pure CO2 adsorption and H2 adsorption, and can be used to predict the binary CO2/H2 gas mixture separation

Development of magnesium-based multilayer PVD coatings for hydrogen storage applications

On the long list of solid-state hydrogen storage materials, magnesium hydride stands out for its relatively high hydrogen storage capacity of 7.7 wt%, combined with the low cost and abundance of magnesium. For practical applications however, issues such as the slow kinetics and the high stability of magnesium hydride must be resolved in order to reduce the potential operating temperatures of a magnesium-based solid-state hydrogen storage system. Catalysis has been widely used to improve the hydrogen storage kinetics and thin film techniques have been used to explore novel structures and combinations of materials in order to improve both the kinetics and thermodynamics of hydrogen storage in magnesium. The original contribution to knowledge of this work lies in the study and understanding of the evolution of a range of novel thin film multilayer coatings and the effect of the structure, structural evolution and materials on the hydrogen storage properties of these materials, each consisting of 150 layers of magnesium, < 20 nm thick, separated by < 3 nm thick layers of a nickel-rich, iron-based transition metal mix, chromium and vanadium. The samples, as well as a non-catalysed control sample, were produced by means of magnetron-assisted physical vapour deposition and delaminated from the substrate for volumetric, gravimetric and calorimetric hydrogen cycling measurements. The coatings were analysed both before and after hydrogen cycling to understand the structural evolution of the coatings from highly structured thin film multilayers to flaky thin film particles containing finely distributed nano-crystalline catalyst particles. The formation of the intermetallic Mg2Ni in one of the samples was found to be beneficial for the hydrogenation kinetics, whilst the dehydrogenation kinetics were found to be affected mostly by the nano-crystalline transition metal phases that formed in the catalysed samples during hydrogen cycling. This resulted in hydrogenation and dehydrogenation of magnesium hydride in less than 4 and 13 minutes at 250°C with activation energies as low as 60.6 ± 2.5 kJ mol-1

Nanoparticle synthesis and the addition of group IV elements for the destabilisation of magnesium hydride

This thesis explores hydrogen storage in magnesium for the goal of producing clean energy. Si nanoparticles were synthesised, then mixed with MgH2 to improve desorption. MgH2 and Si mixtures were desorbed and compared with the synthesised nano-silicon kinetics. Mg2Si nanoparticles were synthesised and high pressure hydrogenation attempted. Finally, the addition of Si, Ge and Sn to Mg-based hydrides led to the successful destabilisation of MgH2 and NaMgH3 resulting in improved hydrogen release at lower temperatures

Preparation and characterization of Mg-based hydrogen storage materials

Nowadays, the use of portable electronic devices is increasing tremendously. The continuous rise in the amount of built-in functionality, e.g in mobile phones, makes the power consumption of these devices ever higher. This puts very high demands on the portable energy source that is used for a particular application with regard to the operating time of the equipment, cycle life etc. On a larger scale, the availability of energy is also becoming an increasingly important issue. Traditional energy sources such as fossil fuels are not infinitely available and the resulting emissions are environmentally unfriendly. The use of hydrogen produced in a sustainable manner, such as from solar or wind power, has been proposed as an alternative, environmentally friendly, energy carrier. Stored hydrogen can be used in two forms; as a gas in e.g. PEM fuel cells or electrochemically in rechargeable Nickel-MetalHydride (NiMH) batteries, which can be used in portable electronic devices or in Hybrid Electric Vehicles (HEVs). At present, a number of different technologies to store gaseous hydrogen are under intense investigation. It can be stored under very high pressures in containers, as a liquid at cryogenic temperatures, physisorbed on large surface area materials such as activated carbons and Metal-Organic-Frameworks or in the form of reversible metal hydrides (MHs). For a hydrogen storage technology to be viable, it must store at least 6 wt.% of hydrogen as stated in the U.S. Department of Energy (DoE) target for 2010. The present-day AB5 type storage materials that are used as the negative electrode in NiMH batteries can store only 1.2 wt.%, which makes them unsuitable for use in fuel cell applications. Therefore, materials that can store a substantially higher amount of hydrogen, both as a gas and electrochemically, are intensively being investigated. Magnesium-based alloys have been identified as a promising class of materials, as the capacity of pure MgH2 is 7.6 wt.% Electrochemistry is used as the main tool to investigate the hydrogen storage properties of the alloys. The basic principles of electrochemistry are discussed in Chapter 2. The electrochemical hydrogen storage reactions as well as a numerous different measurement techniques such as constant-current (CC) measurements, galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS) and the experimental electrochemical setup are described. The preparative methods used to synthesize the Mgbased alloys and hydrides by casting and ball-milling are also discussed in Chapter 2. The remainder of this chapter is devoted to theoretical introductions on X-ray Diffraction (XRD), Nuclear Magnetic Resonance (NMR) and Density Functional Theory (DFT) calculations. XRD, as well as neutron diffraction, is extensively used to study the crystallographic properties of the alloys and hydrides. NMR gives insight into the direct chemical environment of the hydrogen atoms on nearest-neighbor level and in this way complements the information obtained from diffraction measurements. Using DFT, it is possible to predict hydrogenation enthalpies of metals and alloys and to compare the relative stabilities of different crystallographic modifications of the hydride. XRD, NMR and DFT are introduced to a level that is sufficient to understand how the results presented in subsequent chapters are obtained and how the conclusions drawn from those results are reached. Chapter 3 is an overview of the state-of-the-art in hydrogen storage materials. Some general properties of metal hydrides as well as a number of interesting application areas are highlighted in this chapter. Four classes of hydrogen storage materials are discussed, complex hydrides, nitride-based materials, interstitial metal hydrides and Mg-based alloys. The complex hydrides, in particular the borohydrides, have very high hydrogen storage capacities. Summary___________________________________________________________________ 140 Limiting factors for their practical application are the rather extreme conditions, several tens of bars hydrogen pressure and high temperatures, required for their rehydrogenation. For NaAlH4, use of Ti as a catalyst has lead to significant improvements in this respect, but this material has a reversible capacity of only 5.5 wt.%, which is not high enough for application in fuel-cell powered vehicles. Li3N can, potentially, store more than 10 wt.% hydrogen. However, the temperatures required for desorption are too high due to the low equilibrium gas pressure of this material. Addition of Mg was found to increase the equilibrium pressure by more than an order of magnitude and it is therefore likely that the properties of these materials can be tuned towards accessible working pressures at ambient temperatures. Of the interstitial hydrides, four different classes of Transition Metal based alloys are described. The AB5 and AB2-type materials as well as superlattice alloys and Vanadium-based solid solutions are reviewed based on their crystallographic properties, hydrogen storage capacity and the optimization of their composition for application as solid-gas or electrochemical hydrogen storage media. The AB5-type materials, where A is a Rare-Earth metal or a mixture of RE metals and B is a (mixture of) transition metal(s) are widely applied nowadays in rechargeable NiMH batteries. These materials have a hexagonal CaCu5-type structure, which is retained upon hydrogenation. The initial shortcomings of the original LaNi5 compound, an equilibrium pressure substantially above 1 bar and a large discrete lattice expansion, leading to progressive pulverization and corrosion of the material, were successfully solved by substitution of part of the Ni by Co, Mn and Al. The capacity of these alloys is rather low; only 1.2 wt.% of hydrogen can be stored, which is not sufficient with respect to the DoE targets. The AB2-type alloys, where A is Zr or Ti and B a mixture of other transition metals, have also been intensively studied for electrochemical applications. These materials can have a cubic (C15) or a hexagonal (C14) structure, depending on the overall composition, which is retained upon hydrogen loading, similar to the AB5-type alloys. Although their intrinsic capacity is substantially higher than that of AB5-type alloys, up to 1.96 and 2.8 wt.% for ZrCr2 and ZrV2, respectively, optimization of the corrosion resistance and activation behavior reduces the capacity to ~350 mAh/g (1.3 wt.%). The superlattice alloys have AB3-4 stoichiometry and consist of a periodic stacking of AB5 and AB2 structureunits. The gravimetric capacity is increased with respect to the AB5 and AB2-type alloys by substituting part of the Rare-Earth metals (A-site) for lightweight Mg. For the composition Mm0.83Mg0.17Ni3.1Al0.2 a 10% higher capacity compared to AB5 alloys has been reported for commercial AA-size batteries. The Vanadium-based solid solution alloys have the highest intrinsic storage capacity (~4 wt.%) of all the Transition Metal based systems and very interesting crystallographic properties. As the hydrogen content is increased, these alloys transform from a body-centered-cubic (bcc) to a face-centered-cubic (fcc) structure, sometimes via an intermediate tetragonal phase, depending on the exact composition. The total volume expansion often exceeds 35%, which is much higher than for the AB5 and AB2 type materials. The most favorable properties to date were reported for (Ti0.355V0.645)0.86Fe0.14, which has a reversible capacity of 2.3 wt.% at 100oC and can be fully charged with hydrogen gas within 40 s at room-temperature. Although significant improvements in storage capacity have been achieved, the V-based materials have almost twice the capacity of AB5 alloys, the capacity needs to be more than doubled once again to reach the DoE target of 6 wt.%. MgH2 has a very high storage capacity of 7.6 wt.%, but suffers from extremely slow (de)sorption kinetics. Hydrogen diffusion through rutile-structured MgH2 is extremely slow and hydrogenation of Mg particles is effectively blocked once a closed layer of hydride has been formed at the surface. An inverse relation between the final hydrogenated fraction and the initial hydrogenation rate is consistently found throughout the literature, even for nanocrystalline/nanoparticulate Mg produced by ball-milling. Addition of catalysts does not entirely solve this problem either, although more than 7 wt.% of hydrogen can be stored in a ball-milled mixture of Mg, Zr and Mn. Mg-RE (RE = Gd, La, Y) thin films undergo drastic changes in their optical properties as a function of hydrogen content. The films are reflective in the as-deposited state, highly absorbing (black) at intermediate hydrogen content and transparent when fully loaded with hydrogen. The films can be very rapidly switched between these optical states up to quite high Mg content of more than 70 at.%. Although a phase segregation model has been used to explain the occurrence of the black state, the experimental findings on a bulk Mg0.50Y0.50 alloy and ball-milled Mg0.65Y0.35 hydrides indicate the formation of a cubic, ternary hydride. Because Sc is directly above La and Y in the periodic table, Mg-Sc alloys can be expected to show the same improvements in (de)sorption rates as the Mg-RE and Mg-Y systems. Moreover, because Sc is much lighter than Y and La, Mg-Sc alloys will have the highest gravimetric capacity. In view of the results on Mg-Y bulk alloys and thin films, the Mg-Sc system presented an interesting case for a comparative study between bulk materials and thin films and the results are described in Chapter 4. The main aim of this work was to determine whether the electrochemical, crystallographic and thermodynamic properties of thin films give a good indication of the behavior of bulk materials. If this is indeed the case, then thin films can be used to quickly search for promising new compositions, as the preparation technique (e-beam deposition) is not restricted to thermodynamically stable alloys. The trends in the electrochemical capacity, the equilibrium hydrogen pressure and the crystallographic structure are shown to be virtually identical between the two systems. With increasing Mg/Sc ratio, the reversible capacity first increases to a maximum of 1795 mAh/g (6.7 wt.%) for thin films and 1495 mAh/g (5.6 wt.%) for bulk materials at a composition Mg0.80Sc0.20. These values are very close to the theoretically expected ones based on the absorption of 3 H/Sc and 2 H/Mg and desorption of 2 H/Mg and approximately 1 H/Sc. For higher Mg content, the rate capability as well as the total capacity decreases sharply. This is ascribed to a change in crystal structure from the fluorite structure of ScH2 to the rutile structure of MgH2. The presence of large empty octahedral interstices in the fluorite structure facilitates much more rapid hydrogen motion compared to the rutile structure. The plateau pressure determined by GITT measurements, is only very weakly dependent on the Mg/Sc ratio in the compositional range between 85 and 65 at.% Mg and almost equal to that of pure Mg at 10-6-10-7 bar. The concentration boundaries of the plateau region are approximately 2 and 1 H/M. Only for a Mg0.50Sc0.50Pd0.024 bulk material, the equilibrium pressure at the beginning of the plateau region was lowered by more than 1 order of magnitude, similar to what was observed for the Mg0.50Y0.50 alloy. Impedance spectroscopy reveals that the surface kinetics of the thin films are completely dominated by the Pd topcoat. The dependence of the charge transfer rate on the hydrogen content is identical to that of a single Pd layer if the exchange current density is plotted as a function of the equilibrium potential. At low hydrogen concentrations, the overall kinetic response of the thin films is dominated by the transfer of hydrogen from the Pd layer to the MgSc phase. For a bulk Mg0.65Sc0.35 alloy ball-milled with Pd, the same behavior was found although the transfer of hydrogen across the Pd/MgSc interface never comes to dominate the kinetic response. Formation of the fcc structure of ScH2 upon hydrogenation is confirmed by ex-situ XRD measurements for Mg0.65Sc0.35 and Mg0.75Sc0.25 bulk materials. Partial desorption of a hydrogenated Mg0.65Sc0.35 alloy showed coexistence of 2 fcc structures at H/M ratios between 1 and 2. This shows that the metal host structure is retained upon crossing the plateau region, the same as for AB5 and AB2 type alloys. Although the strong preferential orientation of the Summary___________________________________________________________________ 142 thin films puts severe limitations on the crystallographic information that can be obtained, their behavior seems strongly similar to that of bulk materials. Overall, thin films seem to give a very good indication of the behavior of a bulk material regarding the storage capacity, thermodynamic properties and crystal structure and are therefore considered suitable as a model system. In Chapter 5, the properties of MgSc alloys and hydrides are studied in more detail using Neutron Diffraction, NMR and DFT calculations. Contrary to X-ray diffraction, neutron diffraction enables direct determination of the positions of the hydrogen (deuterium) atoms. For a fully charged Mg0.65Sc0.35 alloy, simultaneous occupation of tetrahedral and octahedral sites was found at a D/M ratio of 2.25. Partial solid-gas desorption showed a single fcc phase down to a D/M ratio of 1.69. At 1.21 D/M, coexistence of two fcc phases was found, in accordance with the XRD results presented in Chapter 4. However, the concentration boundaries of the plateau region are, at 1.55 and 0.85 D/M, found to be substantially different from those derived from the GITT measurements. In-situ neutron diffraction measurements in a specially designed electrochemical cell yielded crystallographic information on the first hydrogen loading. Remerkably, no evidence of a two-phase coexistence region was found during charging. During discharge, the material’s behavior was identical to what was found in the solid-gas experiments. The hydrogen motion rates were quantified by determining NMR relaxation times as a function of temperature. Diffusional motion of hydrogen was found to be seven orders of magnitude higher in cubic ScH2 compared to rutile MgH2. For the ternary Mg0.65Sc0.35H2.20 hydride, the hydrogen motion rate is increased by a further two orders of magnitude, although it is still far below that of LaNi5H6. These measurements provided quantitative evidence for the improved hydrogen transport properties in cubic hydrides compared to rutile MgH2, which was already inferred from the electrochemical experiments in Chapter 4. NMR spectroscopy showed clear evidence of clustering of the metal atoms and thus of partial phase segregation. So-called TRAPDOR measurements, which involve simultaneous excitation of the deuterium and scandium atoms, were used to determine the amount of Datoms with pure Mg coordination. Based on a statistically random distribution of the metal atoms in a hydrided (deuterated) Mg0.65Sc0.35 alloy, 17% of the D-atoms is expected to have Mg4 coordination. However, about 50% of the D-atoms was insensitive to Sc-irradiation, which means the material has a tendency to segregate into the binary hydrides. This is an intriguing result because diffraction measurements did not give any evidence for phase separation, but instead showed only one type of long-range order. From 2-D Exchange measurements, the deuterium atoms were found to exchange between all NMR-distinct sites. Full randomization took place within 100 ms. The fluorite-to-rutile transition point, as derived from the electrochemical measurements, is exactly reproduced by DFT calculations at 80 at.% Mg. Around the transition point, a significant shift of the hydrogen atoms away from the tetrahedral positions is found, which should be detectable by neutron diffraction. At 1 H/M, the sphalerite structure that is commonly found in ionic solids was found to be the most unstable. Instead, the hydrogen atoms are found to cluster together as close as possible for any H/M ratio lower than 2. These results, together with the NMR measurements, show that MgSc hydrides indeed tend to segregate into the binary hydrides, although the tendency is not very strong for bulk materials, as even after repeated exposure to elevated temperatures during slid-gas desorption, diffraction still showed a coherent fcc structure. Chapter 6 describes the synthesis and characterization of metastable Mg-Ti alloys and hydrides by mechanical alloying. Sc is a very expensive element (&gt; 10 USD/g) and a suitable, cheaper substitute had to be found. Because the cubic crystal structure had been found to be very important in obtaining favorable (de)sorption kinetics, suitable candidates were sought among elements that form a cubic dihydride. Previous studies on thin films had already shown that Ti is a promising alternative to Sc, and a reversible capacity of 6.5 wt.% had been reached for Mg0.80Ti0.20. Unfortunately, Mg and Ti are immiscible in thermodynamic equilibrium, although bulk Mg-Ti hydrides have been synthesized using ultra-high pressure ‘anvil-cell’ techniques. The solid solubility of Ti in Mg can be extended by mechnical alloying, while retaining the hexagonal-close-packed (hcp) structure of Mg and Ti. A solute level of 12.5 at.% Ti in Mg had been reached in the past, but the resulting alloy was only studied at elevated temperatures and decomposed into MgH2 and TiH2. By milling Mg and Ti powders together with up to 4 wt.% of stearic acid as a process-control agent, a mixture of 65 at.% Mg and 35 at.% Ti can be completely reacted to form 2 fcc structured compounds with different lattice constants. The phase with a = 4.25 Å was identified as pure Ti, which is apparently transformed from hcp to fcc. This behavior was known from studies on high-energy ball milling of pure Ti. The second phase has a = 4.40-4.42 Å and is a cubic solid solution of Ti in Mg. At higher Mg content, some unreacted Mg always remained at the end of the milling process. A Mg0.85Ti0.15 powder mixture can be processed without addition of stearic acid. In this case, dissolution of a few at.% of Ti in Mg is also observed, besides the formation of cubic compounds. When using Mg ribbon instead of powder, a hcp solid solution of Ti in Mg is formed with only trace amounts of the cubic MgTi phase. It is concluded that oxygen impurities, more abundant in a powder which has a much higher specific suface area compared to a ribbon, induce the transformation from hexagonal to cubic. From the shift in the lattice parameters, a Ti-content of 10 at.% could be determined. This is, however, much lower than the 25-35 at.% Ti that the mixtures nominally contained and in the compositional range where a rutile structure is formed upon hydrogenation. The addition of 5-10 at.% of Ni powder does not drastically change the outcome of the milling process. The same two fcc phases are formed when Mg and Ti powders are used and the values of the lattice constants give no indication that Ni is dissolving in either of the fcc phases. It is therefore most likely than the Ni forms an amorphous secondary Mg-Ni-Ti phase, which has also been intensively investigated by others as a hydrogen storage medium. When Ni is added to a hexagonal Mg(Ti) solid solution, a shift of the Mg reflections is observed in the XRD patterns in the direction of pure Mg. This means that Ti is ‘leaking’ back out of the Mg to form a secondary phase. Formation of a nanocrystalline supersaturated solid solution of Ti in Ni is indeed observed. The hydrogen storage capacity of the binary hexagonal compounds is much larger than that of their cubic counterparts. The hcp solid solutions absorb up to 975 mAh/g (3.7 wt.%) whereas the cubic compounds reach no more than 500 mAh/g. The influence on the discharge capacity is much smaller, reaching 420 mAh/g for the cubic vs. 550 mAh/g for the hexagonal compounds. The addition of Ni has a very favorable influence on the electrochemical properties for both the cubic and hexagonal materials. The discharge capacity increases to 520 mAh/g for the cubic compounds and to 837 mAh/g for the hexagonal solid solution. Moreover, 85% of the total capacity extracted at a current density of 10 mA/g can be extracted at 50 mA/g for the ternary cubic mixture compared to only 50% for the binary compound. For the hexagonal solid solutions, a similar improvement is observed from less than 30% for the binary to more than 50% for the ternary mixture. Neutron diffraction and NMR on a deuterated cubic Mg0.65Ti0.35 mixture showed complete decomposition into the binary deuterides at 175oC and 75 bars of pressure. Remarkably, 2-D Exchange NMR did show that deuterium atoms exchange between Mg and Ti environments, despite the extremely poor transport properties of rutile MgD2 and that a large part of the deuterium atoms in a Ti environment are very tightly bound and isolated. The fluorite-to-rutile transition point derived from studies on MgxTi1-x thin films is exactly reproduced by DFT calculations at x = 0.80, the same as for MgSc. In conclusion, the research work described in this thesis clearly shows that the crystal structure of the hydride plays a very dominant role in determining the hydrogen storage properties of Mg-based alloys. Sc and Ti are proved to be suitable alloying elements to induce a transformation from a rutile to a much more favorable cubic structure. The high price of Sc makes Ti the preferred choice. Although much progress has been made in synthesizing metastable Mg-Ti bulk materials, their properties need to be improved further be

Investigation of hydrogen sorption in magnesium-based sputtered thin films

Hydrogen sorption into Mg-based thin films prepared by magnetron sputtering was investigated. The hydrogen storage properties and thin films’ physical properties were investigated in the experiments. Mg thin films were prepared in a Closed Field Unbalanced Magnetron Sputter Ion Plating (CFUBMSIP) system. This system has advantage for homogenous and uniform coatings which is better than conventional coating system. The sputtering parameters are shown to have a significant influence on the microstructure and intrinsic film growth stress in Mg thin films. The intrinsic stress can be examined by X-Ray Diffraction (XRD) during hydrogen absorption, in plane tensile stress of Mg thin films grows due to crystallite coalescence. The surface roughness and buckling appearance were characterized by Confocal microscopy and Profilometry. Surface roughness has the relationship with the Mg thickness. During hydrogen absorption, high stress accumulates leading to more buckling. While, more buckling indicates high thin film surface roughness. The effect of Mg layer thickness (lower than 1000 nm) was investigated. Mg thickness can influence the hydrogen sorption behavior. Thinner Mg layers can have a lower hydrogen absorption temperature comparing with thicker films. Film thickness has the effect on Mg grain boundary diffusion which is dominated by trans-granular diffusion. Different film thickness has different Mg grain boundary diffusion rate. As Pd alloys with Mg at high temperatures, a Ti interlayer can be used to prevent inter-diffusion between Pd and Mg. SEM microscopy was tried to find the grain boundary between Mg and Pd. Si substrate was tried considering weight and volume of glass substrate. Thermodynamics was influenced during hydrogen sorption process with Si substrate. Mg based thin films were sputtered onto glass substrates. The overall hydrogen storage uptake was reduced due to the volume of glass. Thus, a silicon substrate was used, which has a lower volume and weight comparing to the glass substrate. Hydrogen storage capacity will be modified. In addition, different substrates can influence the adhesion energy between the Mg layer and the substrate. The films growth mode and microstructure are factors which can ultimately influence the thermodynamics of the Mg thin films. Buckling is shown during hydrogen sorption process, which can accumulate stresses. The interface shear stress of Mg thin films can be measured. High stress accumulates with more buckling at the surface. The hydrogenation conditions are relevant with the interface shear stress. Mg thickness, hydrogenation times and hydrogenation temperature are the main hydrogenation conditions. For example, the interface shear stress is around 1.75 GPa of sample Pd (60 nm)-Mg (150 nm) glass substrate after hydrogenation 72h at room temperature. While at the same conditions, sample Pd (60 nm)-Mg (800 nm) glass substrate has the interface shear stress lower than 1 GPa. The interface shear stress is influenced by hydrogenation conditions which may be useful for mechanical hydrogen sensors. The electrical resistance of Mg based thin film can be measured using two probes and four probes technique. The four probe technique gave more accurate results. 2A 25sccm condition has the lowest electrical resistance among the measuring samples which is around 2Ω. Finally, a Mg/Y based multilayer system was investigated. Mg/Y based multilayer appears to provide a new method towards MgH2 destabilization by accommodating of lattice mismatch between strained FCC Mg/Y interfaces. There is no alloying phase formation between Y and Mg under high temperature He atmosphere

The Thirteenth Annual Conference YUCOMAT 2011: Programme and the Book of Abstracts

The First Conference on materials science and engineering, including physics, physical chemistry, condensed matter chemistry, and technology in general, was held in September 1995, in Herceg Novi. An initiative to establish Yugoslav Materials Research Society was born at the conference and, similar to other MR societies in the world, the programme was made and objectives determined. The Yugoslav Materials Research Society (Yu-MRS), a nongovernment and non-profit scientific association, was founded in 1997 to promote multidisciplinary goal-oriented research in materials science and engineering. The main task and objective of the Society has been to encourage creativity in materials research and engineering to reach a harmonic coordination between achievements in this field in our country and analogous activities in the world with an aim to include our country into global international projects. Until 2003, Conferences were held every second year and then they grew into Annual Conferences that were traditionally held in Herceg Novi in September of every year. In 2007 Yu-MRS formed two new MRS: MRS-Serbia (official successor of Yu-MRS) and MRS-Montenegro (in founding). In 2008, MRS – Serbia became a member of FEMS (Federation of European Materials Societies)

Feedstock powders for reactive structural materials

Metals as fuels have higher energy density per unit mass or volume compared to any hydrocarbon. At the same time, metals are common structural materials. Exploring metals as reactive structural materials may combine their high energy density with attractive mechanical properties. Preparing such materials, however, is challenging. Requirements that need to be met for applications include density, strength, and stability enabling the component to sustain the structure during its desired operation; added requirements are the amount and rate of the energy release upon impact or shock. Powder technology and additive manufacturing are approaches considered for design of reactive structural materials. Respectively, feedstock powders are of critical importance. These feedstock powders must have the chemical composition ensuring, along with mechanical characteristics, a rapid initiation of the reactive material upon impact or shock, and high total energy release. They also must have the morphology suitable for processing. In this work, several powders designed to serve as feedstock for manufacturing reactive structural materials are prepared, tuned, and characterized. High-energy mechanical milling is the common manufacturing approach for such powders in this study. The materials include elemental metals, such as aluminum, with the narrowly sized spherical porous powder and magnesium, with custom powder coating. Composite powders combining metals and metalloids, e.g., boron-titanium and boron-zirconium, with different structures and morphologies are also prepared and characterized. Milling conditions are varied and it is shown that the structures, sizes, porosities, and shapes of the produced powder particles can be adjusted through such variation. The experimental work includes characterizing ignition and combustion of the prepared powders. Custom experiments employing an electrically heated wire are used with all prepared materials. Particle combustion experiments, quantifying the particle burn time and temperatures are performed with selected materials. Additionally, thermal analysis is used extensively in addition to electron microscopy and x-ray powder diffraction. Microcalorimetry in oxidizing gas serves to quantify stability of the selected materials. Nitrogen adsorption is used for many prepared powders to characterize their specific surface area and respective porosity. Prepared powders combine unique morphological properties making them amenable to additive manufacturing, in particular, with high reactivity and stability. It is expected that using them as feedstock will lead to design of a new generation of reactive structural materials

Nanomaterials by severe plastic deformation: review of historical developments and recent advances

International audienceSevere plastic deformation (SPD) is effective in producing bulk ultrafine-grained and nanostructured materials with large densities of lattice defects. This field, also known as NanoSPD, experienced a significant progress within the past two decades. Beside classic SPD methods such as high-pressure torsion, equal-channel angular pressing, accumulative roll-bonding, twist extrusion, and multi-directional forging, various continuous techniques were introduced to produce upscaled samples. Moreover, numerous alloys, glasses, semiconductors, ceramics, polymers, and their composites were processed. The SPD methods were used to synthesize new materials or to stabilize metastable phases with advanced mechanical and functional properties. High strength combined with high ductility, low/room-temperature superplasticity, creep resistance, hydrogen storage, photocatalytic hydrogen production, photocatalytic CO2 conversion, superconductivity, thermoelectric performance, radiation resistance, corrosion resistance, and biocompatibility are some highlighted properties of SPD-processed materials. This article reviews recent advances in the NanoSPD field and provides a brief history regarding its progress from the ancient times to modernity

The Thirteenth Annual Conference YUCOMAT 2011: Programme and the Book of Abstracts

The First Conference on materials science and engineering, including physics, physical chemistry, condensed matter chemistry, and technology in general, was held in September 1995, in Herceg Novi. An initiative to establish Yugoslav Materials Research Society was born at the conference and, similar to other MR societies in the world, the programme was made and objectives determined. The Yugoslav Materials Research Society (Yu-MRS), a nongovernment and non-profit scientific association, was founded in 1997 to promote multidisciplinary goal-oriented research in materials science and engineering. The main task and objective of the Society has been to encourage creativity in materials research and engineering to reach a harmonic coordination between achievements in this field in our country and analogous activities in the world with an aim to include our country into global international projects.\ud Until 2003, Conferences were held every second year and then they grew into Annual Conferences that were traditionally held in Herceg Novi in September of every year. In 2007 Yu-MRS formed two new MRS: MRS-Serbia (official successor of Yu-MRS) and MRS-Montenegro (in founding). In 2008, MRS – Serbia became a member of FEMS (Federation of European Materials Societies)

Programme and The Book of Abstracts / Twentieth Annual Conference YUCOMAT 2018, Herceg Novi, September 3-7, 2018

The First Conference on materials science and engineering, including physics, physical chemistry, condensed matter chemistry, and technology in general, was held in September 1995, in Herceg Novi. An initiative to establish Yugoslav Materials Research Society was born at the conference and, similar to other MR societies in the world, the programme was made and objectives determined. The Yugoslav Materials Research Society (Yu-MRS), a nongovernment and non-profit scientific association, was founded in 1997 to promote multidisciplinary goal-oriented research in materials science and engineering. The main task and objective of the Society has been to encourage creativity in materials research and engineering to reach a harmonic coordination between achievements in this field in our country and analogous activities in the world with an aim to include our country into global international projects. Until 2003, Conferences were held every second year and then they grew into Annual Conferences that were traditionally held in Herceg Novi in September of every year. In 2007 Yu-MRS formed two new MRS: MRS-Serbia (official successor of Yu-MRS) and MRS-Montenegro (in founding). In 2008, MRS – Serbia became a member of FEMS (Federation of European Materials Societies)