M. Sherif El-Eskandarany

In-situ catalyzation approach for enhancing the hydrogenation/dehydrogenation kinetics of MgH2 powders with Ni particles

One practical solution for utilizing hydrogen in vehicles with proton-exchange fuel cells membranes is storing hydrogen in metal hydrides nanocrystalline powders. According to its high hydrogen capacity and low cost of production, magnesium hydride (MgH2) is a desired hydrogen storage system. Its slow hydrogenation/dehydrogenation kinetics and high thermal stability are the major barriers restricting its usage in real applications. Amongst the several methods used for enhancing the kinetics behaviors of MgH2 powders, mechanically milling the powders with one or more catalyst species has shown obvious advantages. Here we are proposing a new approach for gradual doping MgH2 powders with Ni particles upon ball milling the powders with Ni-balls milling media. This proposed is-situ method showed mutually beneficial for overcoming the agglomeration of catalysts and the formation of undesired Mg2NiH4 phase. Moreover, the decomposition temperature and the corresponding activation energy showed low values of 218 °C and 75 kJ/mol, respectively. The hydrogenation/dehydrogenation kinetics examined at 275 °C of the powders milled for 25 h took place within 2.5 min and 8 min, respectively. These powders containing 5.5 wt.% Ni performed 100-continuous cycle-life time of hydrogen charging/discharging at 275 °C within 56 h without failure or degradation.

Metallic glassy Zr70Ni20Pd10 powders for improving the hydrogenation/dehydrogenation behavior of MgH2

Because of its low density, storage of hydrogen in the gaseous and liquids states possess technical and economic challenges. One practical solution for utilizing hydrogen in vehicles with proton-exchange fuel cells membranes is storing hydrogen in metal hydrides. Magnesium hydride (MgH2) remains the best hydrogen storage material due to its high hydrogen capacity and low cost of production. Due to its high activation energy and poor hydrogen sorption/desorption kinetics at moderate temperatures, the pure form of MgH2 is usually mechanically treated by high-energy ball mills and catalyzed with different types of catalysts. These steps are necessary for destabilizing MgH2 to enhance its kinetics behaviors. In the present work, we used a small mole fractions (5 wt.%) of metallic glassy of Zr70Ni20Pd10 powders as a new enhancement agent to improve its hydrogenation/dehydrogenation behaviors of MgH2. This short-range ordered material led to lower the decomposition temperature of MgH2 and its activation energy by about 121 °C and 51 kJ/mol, respectively. Complete hydrogenation/dehydrogenation processes were successfully achieved to charge/discharge about 6 wt.%H2 at 100 °C/200 °C within 1.18 min/3.8 min, respectively. In addition, this new nanocomposite system shows high performance of achieving continuous 100 hydrogen charging/discharging cycles without degradation.

The history and necessity of mechanical alloying

It is well established that melting and casting techniques, using of fine inert particles or so-called filamentary reinforcements with high temperature strengths combined with soft conventional matrix metals can produce composites which outperform superalloys. In mid-1966, attention was turned to the ball-milling process that had been used to make metal powders for wetting studies as a means of making the alloy itself by powder metallurgy. The reason was attributed to the capability of this process to coat hard phases (e.g., WC or ZrO2) with a soft phase (Co or Ni). This choice is attributed to the fact that the ball-milling process could be employed to coat hard phases, such as tungsten carbide or zirconium oxide with soft phases such as cobalt or nickel. These key ideas led to the concept of establishing a kneading action which would refine the internal structure of powders while maintaining their overall particle size at a relatively coarse level, preventing pyrophoricity.

Contamination Effects on Improving the Hydrogenation/Dehydrogenation Kinetics of Binary Magnesium Hydride/Titanium Carbide Systems Prepared by Reactive Ball Milling

Ultrafine MgH2 nanocrystalline powders were prepared by reactive ball milling of elemental Mg powders after 200 h of high-energy ball milling under a hydrogen gas pressure of 50 bar. The as-prepared metal hydride powders were contaminated with 2.2 wt. % of FeCr-stainless steel that was introduced to the powders upon using stainless steel milling tools made of the same alloy. The as-synthesized MgH2 was doped with previously prepared TiC nanopowders, which were contaminated with 2.4 wt. % FeCr (materials of the milling media), and then ball milled under hydrogen gas atmosphere for 50 h. The results related to the morphological examinations of the fabricated nanocomposite powders beyond the micro-and nano-levels showed excellent distributions of 5.2 wt. % TiC/4.6 wt. % FeCr dispersoids embedded into the fine host matrix of MgH2 powders. The as-fabricated nanocomposite MgH2/5.2 wt. % TiC/4.6 wt. % FeCr powders possessed superior hydrogenation/dehydrogenation characteristics, suggested by the low value of the activation energy (97.74 kJ/mol), and the short time required for achieving a complete absorption (6.6 min) and desorption (8.4 min) of 5.51 wt. % H2 at a moderate temperature of 275 °C under a hydrogen gas pressure ranging from 100 mbar to 8 bar. van’t Hoff approach was used to calculate the enthalpy (∆H) and entropy (∆S) of hydrogenation for MgH2, which was found to be −72.74 kJ/mol and 112.79 J/mol H2/K, respectively. Moreover, van’t Hoff method was employed to calculate the ΔH and ΔS of dehydrogenation, which was found to be 76.76 kJ/mol and 119.15 J/mol H2/K, respectively. This new nanocomposite system possessed excellent absorption/desorption cyclability of 696 complete cycles, achieved in a cyclic-life-time of 682 h.

Ball milling as a powerful nanotechnological tool for fabrication of nanomaterials

According to the real and potential applications of nanocrystalline materials and nanoparticles, these new materials that present the backbone of nanotechnology have been receiving great attention since the mid-1970s. The top-down approach, using high-energy ball milling, is considered to be the most powerful and simplest technique for preparing industrial scale nanocrystalline powders. In this chapter, the mechanism of the formation of nanocrystalline materials by ball-milling technique is explained and few examples are also presented. In the present chapter, we will focus on the applications of spark plasma sintering method for fabrication of bulk nanocrystalline materials using the ball-milled powders as feedstock powders.

Synthetic nanocomposite MgH 2 /5 wt. % TiMn 2 powders for solid-hydrogen storage tank integrated with PEM fuel cell

Storing hydrogen gas into cylinders under high pressure of 350 bar is not safe and still needs many intensive studies dedic ated for tank’s manufacturing. Liquid hydrogen faces also severe practical difficulties due to its very low density, leading to larger fuel tanks three times larger than traditional gasoline tank. Moreover, converting hydrogen gas into liquid phase is not an economic process since it consumes high energy needed to cool down the gas temperature to −252.8 °C. One practical solution is storing hydrogen gas in metal lattice such as Mg powder and its nanocomposites in the form of MgH2. There are two major issues should be solved first. One related to MgH2 in which its inherent poor hydrogenation/dehydrogenation kinetics and high thermal stability must be improved. Secondly, related to providing a safe tank. Here we have succeeded to prepare a new binary system of MgH2/5 wt. % TiMn2 nanocomposite powder that show excellent hydrogenation/dehydrogenation behavior at relatively low temperature (250 °C) with long cycle-life-time (1400 h). Moreover, a simple hydrogen storage tank filled with our synthetic nanocomposite powders was designed and tested in electrical charging a battery of a cell phone device at 180 °C through a commercial fuel cell.

8 – Mechanically Induced Solid-State Amorphization

The field of glassy metals or metallic glass has seen enormous development during recent years. For the uninitiated, the notion of a metallic glass may be rather unusual, since one would primarily associate glass with transparent and insulating window material. However, the term glass is nowadays almost unanimously used for an amorphous substance which is obtained by cooling the corresponding melt. Metallic glasses are new substances with exciting properties which are of interest not only for basic solid-state physics, but also for metallurgy, surface chemistry, and technology. Metallic glasses have properties which are quite different from solid metals making them promising candidates for technical applications.

Utilization of mechanically alloyed powders for surface protective coating

Surface engineering is focused on the design and modifications of the bulk materials’ surfaces (substrates) to provide specific physical, chemical, and engineering properties that were not inherently present in the original bulk materials. Improving the wear-, oxidation-, and corrosion-resistances, friction coefficients, bio-inertness, electronic properties, and thermal insulations are some of those properties that can be successfully enhanced with surface treatments. Improving the surface properties can be achieved by metallurgical, mechanical, or chemical approaches. Coating, which is simply defined as a single or multilayered materials deposited artificially on the surface of bulk object (substrate) made of another material, is a well-known process used in part to obtaining some required technical or decorative properties or to protect the material from expected chemical and physical interactions with its surrounded environment. Coatings are widely used in automotive systems, boiler components, and power generation equipment, chemical process equipment, aircraft engines, pulp and paper processing equipment, bridges, rollers and concrete reinforcements, orthopedics and dental, land-based and marine turbines, and ships.

Controlling the powder milling process

Powder milling process, using ball or rod mills, aim to produce a high-quality end-product that can be composites and nanocomposites, and nanocrystalline powder particles of intermetallic compounds, amorphous, hydrides, nitrides, silicates, etc. Powder milling process has been continuously improving by introducing numerous innovative types of ball mills in order to improve the quality and homogeneity of the end-products and to increase the productivity. This chapter discusses the factors affecting the mechanical alloying, mechanical disordering, and mechanical milling processes and their effects on the quality of the desired end-products. Moreover, we will present some typical examples that show the effect of these factors on the physical and chemical properties of the milled powders.

Mechanically induced gas-solid reaction for synthesizing of hydrogen storage metal hydrides

Owing to the dramatic global environmental changes associated with man-made carbon dioxide emissions and the huge consumption of the limited resources of fossil fuels, developing alternate and renewable energy sources is important for a sustainable future. In the background, there is a growing concern about the environmental pollution caused by combustion engines and additional problems associated with large-scale mining, transportation, processing, and usage of fossil fuels. The increase in threats from global warming due to the consumption of fossil fuels requires of us to adopt new strategies to harness the inexhaustible sources of energy. Hydrogen is an energy carrier which holds tremendous promise as a new renewable and clean energy option. It is a convenient, safe, versatile fuel source that can be easily converted to a desired form of energy without releasing harmful emissions. Thus, hydrogen has been considered as the ideal candidate as an energy carrier for both mobile and stationary applications.