Composite material comprising a magnesium alloy and method of preparation thereof

Abstract

A particulate composite comprising, based on the weight of the composite: from 86 to 94 wt. % of magnesium (Mg) alloy; from 3 to 7 wt. % of titanium (Ti); and, from 3 to 7 wt. % of multiwalled carbon nanotubes (MWCNT). The Mg alloy includes, based on the weight of the alloy: from 5.5 to 6.5 wt. % of aluminum (Al); from 0.1 to 0.5 wt. % of manganese (Mn); from 0.1 to 1.0 wt. % of the combination of zinc (Zn) with at least one of copper (Cu), iron (Fe), nickel (Ni), and silicon (Si); and, a balance of Mg and inevitable impurities. The particulate composite has a median volume particle size (Dv50) of from 10 to 35 micrometers (μm) and a surface area of from 1 to 60 m2 / g, as determined by Brunauer-Emmet-Teller (BET) analysis. The particulate composite may further have a measured H2 absorption capacity of from 4.5 to 6.2 wt. %, based on the weight of the composite.

Description

STATEMENT OF PRIOR DISCLOSURE BY INVENTOR

[0001] Aspects of the present disclosure are described in Abbas et al. “Microstructural characterization of AM60-TixNby nanocomposite powders processed by high-energy ball milling”, Materials Chemistry and Physics, Volume 313, Feb. 1, 2024, 128718, incorporated herein by reference in its entirety.STATEMENT OF ACKNOWLEDGEMENT

[0002] Support provided by King Fahd University of Petroleum and Minerals (KFUPM) under Grant No. ER221007 is gratefully acknowledged.BACKGROUNDTechnical Field

[0003] The present disclosure is directed to a particulate composite, more particularly, to a particulate composite which has utility for hydrogen absorption and which comprises a magnesium alloy.Description of Related Art

[0004] The ‘background’ description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present invention.

[0005] The energy economy is the foundation for human society's progress, and it is currently heavily dependent on fossil fuels. The polluting and depleting nature of fossil fuels has driven the search for alternative green energy sources. The improvement of urban air quality and the creation of new industrially and technologically sustainable energy sources are necessary for future sustainable energy supply.

[0006] Due to its affordability and status as a green energy fuel, hydrogen has been viewed as a potential energy carrier for a sustainable energy future. Hydrogen may be stored and used for electricity generation via fuel cells and internal combustion engines. Hydrogen has a high energy density (120 megajoules per kilograms (MJ / kg)) that is more than double that of conventional fuels and is also non-toxic. However, there are considered to be manufacturing, storage, and application hurdles which must be overcome to make hydrogen energy practicable in industry. Hydrogen storage technology, in particular, is considered a bottleneck which prevents hydrogen energy from being widely used.

[0007] Hydrogen can be stored in a plethora of forms, of which particular mention may be made of compressed gas, cryogenic liquid, and chemically bound solid-state materials. The first two of these hydrogen storage forms present numerous disadvantages, including the need to mitigate for leakage, the requirement for high-pressure or low temperatures and low efficiency. Thus focus has shifted to developing solid storage materials which may bind hydrogen at high density or, more particularly, at sufficiently high density to be viable for secondary energy applications, like secondary batteries and fuel cells.

[0008] Metal-based hydrides for solid-state hydrogen storage have shown promise given their large gravimetric capacity which is achieved in a relatively safe, effective, compact, and often reversible way. Sodium borohydride (NaBH4), for example, is stable, non-flammable and non-toxic: NaBH4 further contains two moles of hydrogen (H2) and that hydrogen constitutes 10.8 wt. % of the compound. Broadly, hydrogen storage in metal hydrides provides greater density without the disadvantage of cryogenic conditions. However, to date, no metal-based hydride has satisfied the requirements of low mass density, high-volume density, rapid de / hydration, increased decrepitation resistance, the ability to release H2 at lower temperatures, and, importantly, low acquisition and fabrication costs.

[0009] Nonetheless, solid-state hydrogen storage may be achievable using inexpensive magnesium (Mg)-based alloys with special thermodynamic and physical characteristics. Mg-based alloys have a low specific gravity of 1.74 gram per cubic centimeter (g / cm3), a higher discharge capacity, and are naturally abundant. The theoretical hydrogen capacity of pure Mg is 7.6 weight percent (wt. %) in the form of MgH2. However, its high dehydration temperature and weak oxidation resistance have rendered pure Mg as unsuitable for practical use as a hydrogen storage material. The slow kinetics and high thermal stability of MgH2 make it difficult to use in practical applications due to the requisite high operating temperatures.

[0010] By alloying Mg with the right additives, or by creating intermetallic compounds with distinct crystal structures from the parent metal, one may increase hydrogen absorption capacity, improve de / hydrogenation kinetics, and lower operating temperatures.

[0011] Research and development efforts are thus being directed toward increasing the hydrogen absorption capacity of magnesium at lower temperatures and to enhancing the absorption / desorption kinetics thereof. Recent initiatives include microstructure refinement, increased specific surface area, and catalyst addition. It has been observed that catalysis plays a significant role in influencing the hydrogenation properties of Mg alloys. Common catalytic agents for hydriding and dehydriding are transition metals, metal oxides, non-metals (carbon), and compounds. Catalytic effects of the transition metals Ti, V, Fe, and Mn, combined with magnesium using a 20-hour (h) ball milling procedure, have been studied, with results suggesting that the addition of vanadium promotes the fastest absorption / desorption kinetics and the lowest activation energy in comparison to MgH2. [See: G. Liang, J. Huot, S. Boily, A. van Neste, R. Schulz, Catalytic effect of transition metals on hydrogen sorption in nanocrystalline ball milled MgH2 Tm (Tm=Ti, V, Mn, Fe and Ni) systems, Journal of Alloys and Compounds. 292 (1999) 247-252.]. A further study has assessed nanocrystalline compounds based on Mg which include trace amounts, including V, Ti, and Nb [See: Rizo-Acosta, Pavel, Fermin Cuevas, and Michel Latroche. “Hydrides of early transition metals as catalysts and grain growth inhibitors for enhanced reversible hydrogen storage in nanostructured magnesium.” Journal of Materials Chemistry A 7, no. 40 (2019): 23064-23075.]. The addition of transition metals (Fe, Co, Ni, and Cu) nanoparticles into MgH2, using ball milling, has also been investigated [See: N. Hanada, T. Ichikawa, H. Fujii, Catalytic Effect of Nanoparticle 3d-Transition Metals on Hydrogen Storage Properties in Magnesium Hydride MgH2 Prepared by Mechanical Milling, The Journal of Physical Chemistry B. 109 (2005) 7188-7194.]. Further, the use of AZ91 and AZ60 Mg alloys for hydrogenation, after equal-channel angular pressing (ECAP), has been studied [See: A. M. Jorge Jr., E. Prokofiev, M. R. M. Triques, V. Roche, W. J. Botta, C. S. Kiminami, G. I. Raab, R. Z. Valiev, T. G. Langdon, Effect of cold rolling on the structure and hydrogen properties of AZ91 and AM60D magnesium alloys processed by ECAP, International Journal of Hydrogen Energy. 42 (2017) 21822-21831.].

[0012] Several transition metals have been used in Mg to enhance hydrogenation characteristics: for instance, Ni nanoparticles have demonstrated catalytic properties in reducing the activation energy of hydrogenation; Ti addition has been found to enhance hydrogenation, achieving up to 6.18 wt. % hydrogen absorption; and, binary (TiMn2, TiAl and TiFe) and ternary (TiVMn, TiMnCr and TiFeCr) compounds based on Ti have catalyzed Mg hydrogenation. Previous studies have shown that dehydrogenation properties followed the order: Mg—Ti>Mg-Nb>Mg-Ni>Mg-V>Mg—Co>Mg-Mo [See: J. Cui, J. Liu, H. Wang, L. Ouyang, D. Sun, M. Zhu, X. Yao, Mg-TM (TM: Ti, Nb, V, Co, Mo or Ni) core-shell like nanostructures: synthesis, hydrogen storage performance and catalytic mechanism, J. Mater. Chem. A. 2 (2014) 9645-9655.].

[0013] Whilst a few composites have therefore been developed in the past for hydrogen storage, each of them suffers from certain drawbacks hindering their adoption. Accordingly, one objective of the present disclosure is to explore a novel Mg alloy particulate composite for hydrogen absorption.SUMMARY

[0014] In an exemplary embodiment, a particulate composite is described. The particulate composite comprises from about 86 to about 94 weight percent (wt. %) of a magnesium (Mg) alloy, from about 3 to about 7 wt. % of titanium (Ti), and from about 3 to about 7 wt. % of multiwalled carbon nanotubes (MWCNT), based on the weight of the composite. The Mg alloy comprises from about 5.5 to about 6.5 wt. % of aluminium (Al), from about 0.1 to about 0.5 wt. % of manganese (Mn), from about 0.1 to about 1.0 wt. % of the combination of zinc (Zn) with at least one element selected from the group consisting of copper (Cu), iron (Fe), nickel (Ni), and silicon (Si), and a balance consisting of magnesium and inevitable impurities, based on the weight of the alloy. The particulate composite has a median volume particle size (Dv50) of from about 10 to about 35 micrometers (μm), as determined by Scanning Electron Microscopy, and a surface area of from about 1 to about 60 meter squared per gram (m2 / g), as determined by Brunauer-Emmet-Teller (BET) analysis.

[0015] In some embodiments, the particulate composite comprises from about 88 to about 92 wt. % of the Mg alloy, from about 4 to about 6 wt. % of Ti, and from about 4 to about 6 wt. % of MWCNT, based on the weight of the composite.

[0016] In some embodiments, the Mg alloy includes from about 5.5 to about 6.5 wt. % of Al, from about 0.2 to about 0.5 wt. % of Mn, from about 0.3 to about 0.9 wt. % of the combination of Zn with at least one element selected from the group consisting of Cu, Fe, Ni and Si, and a balance consisting of Mg and inevitable impurities, based on the weight of the alloy.

[0017] In some embodiments, the particulate composite has a median volume particle size (Dv50) of from about 15 to about 30 μm, as determined by Scanning Electron Microscopy.

[0018] In some embodiments, the particulate composite has a surface area of from about 5 to about 50 m2 / g, as determined by BET analysis.

[0019] In some embodiments, the particulate composite has a H2 absorption capacity of from about 4.5 to about 6.2 wt. %, based on the weight of the composite and as determined by volumetric analysis at a temperature of about 375 degrees Celsius (° C.) and a hydrogen (H2) pressure of about 3.5 megapascals (MPa).

[0020] In some embodiments, the particulate composite has a H2 absorption capacity of from about 5.0 to about 5.5 wt. %, based on the weight of the composite and as determined by volumetric analysis at a temperature of about 375° C. and an H2 pressure of about 3.5 MPa.

[0021] In some embodiments, at least a fraction of the MWCNTs in the particulate composite are present in agglomerated clusters.

[0022] In some embodiments, a method of preparing the composite is described. The method comprises: attriting the Mg alloy in a high energy ball mill (HEBM) having an inert atmosphere and including milling balls; and, adding Ti powder and MWCNTs to the attrited Mg alloy and further attriting the obtained mixture in the HEBM in the inert atmosphere for a sufficient duration to form the particulate composite having a median volume particle size (Dv50) of from about 10 to about 35 μm and a surface area of from about 1 to about 60 m2 / g.

[0023] In some embodiments, the atmosphere of the high energy ball mill (HEBM) includes argon (Ar).

[0024] In some embodiments, the high energy ball mill (HEBM) is operated at from about 150 to about 1500 rotations per minute (rpm) during attrition.

[0025] In some embodiments, the high energy ball mill (HEBM) is operated at a milling ball-to-powder ratio by weight (BPR) of from about 10:1 to about 20:1.

[0026] In some embodiments, the milling balls include tungsten carbide.

[0027] In some embodiments, a method for chemisorbing H2 from a gas stream is described. The method includes flowing the gas stream over the particulate composite.

[0028] In some embodiments, the gas stream has a temperature of from about 200 to about 400° C.

[0029] In some embodiments, the gas stream has a pressure of from about 2 to about 5 MPa.

[0030] In some embodiments, a hydrogenated particulate composite material is obtained according to the aforementioned method.

[0031] In some embodiments, the hydrogenated particulate composite comprises from about 4.5 to about 6.2 wt. % of H2, based on the weight of the composite, as determined by volumetric analysis.

[0032] In some embodiments, the hydrogenated particulate composite comprises from about 5.0 to about 5.5 wt. % of H2, based on the weight of the composite, determined by volumetric analysis.

[0033] In some embodiments, in the hydrogenated particulate composite: i) a fraction of the particles comprises a metallic oxide layer; ii) a fraction of the particles comprises a metallic hydroxide layer, or, iii) both i) and ii) are applicable.

[0034] The foregoing general description of the illustrative embodiments and the following detailed description thereof are merely exemplary aspects of the teachings of this disclosure, and are not restrictive.BRIEF DESCRIPTION OF THE DRAWINGS

[0035] A more complete appreciation of this disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

[0036] FIG. 1 is a method flowchart of preparing a particulate composite, according to certain embodiments.

[0037] FIG. 2 shows the X-ray diffraction (XRD) patterns of an AM60 magnesium (Mg) alloy, of certain additives, and of a ball-milled AM60 with multiwalled carbon nanotubes (MWCNTs) and titanium (Ti) additives, according to certain embodiments.

[0038] FIG. 3A shows a scanning electron microscopy (SEM) image of a mechanically filed commercial AM60 magnesium alloy before high energy ball milling (HEBM), according to certain embodiments.

[0039] FIG. 3B shows a scanning electron microscopy (SEM) image of AM60 after high energy ball milling (HEBM) for 20 hours (h), according to certain embodiments.

[0040] FIG. 3C shows a scanning electron microscopy (SEM) image of AM60 with an additive of 5 weight percentage (wt. %) Ti (AM60-Ti) after high energy ball milling (HEBM), according to certain embodiments.

[0041] FIG. 3D shows a scanning electron microscopy (SEM) image of AM60 with an additive of 5 wt. % MWCNTs (AM60-MWCNT) after high energy ball milling (HEBM), according to certain embodiments.

[0042] FIG. 3E shows a scanning electron microscopy (SEM) image of AM60 with an additive of 5 wt. % Ti+5 wt. % MWCNT (AM60-Ti-CNTs) after high energy ball milling (HEBM), according to certain embodiments.

[0043] FIG. 4 shows a nitrogen (N2) absorption-desorption isotherms of ball-milled AM60 with CNTs and Ti additives, according to certain embodiments.

[0044] FIG. 5 shows the hydrogen absorption (wt. %) of AM60, ball milled AM60 (AM60-BM), AM60-Ti, AM60-CNT, and AM60-Ti-CNT samples, according to certain embodiments.

[0045] FIG. 6A shows a scanning electron microscopy (SEM) image of an AM60 sample after hydrogenation, according to certain embodiments.

[0046] FIG. 6B shows a scanning electron microscopy (SEM) image of a ball milled AM60 after hydrogenation, according to certain embodiments.

[0047] FIG. 7A shows a SEM-energy-dispersive X-ray (EDS) map of AM60-Ti sample, according to certain embodiments.

[0048] FIG. 7B shows a SEM-energy-dispersive X-ray (EDS) map of AM60-CNT sample, according to certain embodiments.

[0049] FIG. 7C shows a SEM-energy-dispersive X-ray (EDS) map of AM60-Ti-CNT sample, according to certain embodiments.

[0050] FIG. 8 shows XRD patterns of AM60, AM60-BM, AM60-Ti, AM60-CNT, and AM60-Ti-CNT samples after hydrogenation, according to certain embodiments.DETAILED DESCRIPTION

[0051] When describing the present disclosure, the terms used are to be construed in accordance with the following definitions, unless a context dictates otherwise.

[0052] Embodiments of the present invention will now be described more fully hereinafter with reference to the accompanying drawings wherever applicable, in that some, but not all, embodiments of the disclosure are shown.

[0053] As used herein, the words ‘a,’‘an’ and the like generally carry a meaning of ‘one or more,’ unless stated otherwise.

[0054] Furthermore, the terms ‘approximately,’‘approximate,’‘about,’ and similar terms generally refer to ranges that include the identified value within a margin of 20%, 10%, or preferably 5%, and any values therebetween.

[0055] When amounts, concentrations, dimensions and other parameters are expressed in the form of a range, a preferable range, an upper limit value, a lower limit value or preferable upper and limit values, it should be understood that any ranges obtainable by combining any upper limit or preferable value with any lower limit or preferable value are also specifically disclosed, irrespective of whether the obtained ranges are clearly mentioned in the context.

[0056] A weight percent of a component, unless specifically stated to the contrary, is based on the total weight of the formulation or composition in which the component is included. For example, if a particular element or component in a composition or article is said to have 5 wt. %, it is understood that this percentage is in relation to a total compositional percentage of 100%.

[0057] The use of the terms ‘include,’‘includes’, ‘including,’‘have,’‘has,’ or ‘having’ should be generally understood as open-ended and non-limiting unless specifically stated otherwise.

[0058] As used herein, the term ‘compound’ refers to a chemical entity, regardless of its phase-solid, liquid, or gaseous—as well as its state-crude mixture, purified, or isolated.

[0059] As used herein, the term ‘particle’ refers to a small object that acts as a whole unit with regard to its transport and properties.

[0060] Unless otherwise stated, the term “particle size” refers to the largest axis of the particle. In the case of a generally spherical particle, the largest axis is the diameter.

[0061] The term “median volume particle size” (Dv50), as used herein, refers to a particle size corresponding to 50% of the volume of the sampled particles being greater than and 50% of the volume of the sampled particles being smaller than the recited Dv50 value. Particle size is determined herein by Scanning Electron Microscopy (SEM).

[0062] As used herein, ‘nanoparticles (NPs)’ refers to particles having a particle size of 1 nanometer (nm) to 500 nm within the scope of the present invention. It is envisaged, for example, that nanoparticles of the present composite that are fibrous, acicular, spherical, ellipsoidal, cylindrical, bead-like, cubic or platelet-like may be present alone or in combination. Moreover, it is envisaged that agglomerates of nanoparticles having the same or different morphologies may be present in the nanocomposite.

[0063] The term ‘grain’ is used herein in accordance with its standard crystallographic definition as a single, individual crystal within a polycrystalline material, wherein all atoms are arranged in a consistent crystal structure. Within a polycrystalline material, the interface between two neighboring grains is referenced as the ‘grain boundary’.

[0064] As used herein, the term ‘room temperature’ refers to a temperature range of 25 degrees Celsius (° C.)±3° C. in the present disclosure.

[0065] As used herein, the term ‘particulate composite’ refers to a material created by embedding a first material into a matrix material, usually a polymer, metal, or ceramic, to improve qualities such as strength, stiffness, or thermal resistance.

[0066] As used herein, the term “alloy” refers to a substance composed of two or more metals or of a metal and a non-metal which have been intimately united, usually by being fused together and dissolved in each other when molten. The terms “magnesium alloy” or “Mg alloy” denotes an alloy of which magnesium (Mg) is the major constituent component. As regards magnesium alloys of the present disclosure magnesium (Mg) will generally comprise at least about 90 wt. % or at least about 92 wt. % of the alloy.

[0067] The term “inevitable impurities” encompasses all metallic or non-metallic elements which are present in the magnesium alloy as a consequence of the production process thereof but which were not deliberately added in that process. Impurities are present, at most, in only trace amounts which will have no (adverse) effect on the desired properties of the magnesium alloy. An impurity may, in certain circumstances, be present in an amount which is not measurable by techniques generally used in the art. The amount of impurities in toto should typically be less than 0.1 wt. % or even less than 0.05 wt. %, based on the weight of the magnesium alloy.

[0068] The term “carbon nanotube” as used herein refers to carbon fullerene, a synthetic graphite, which typically has a molecular weight of greater than 840 g / mole. The term is intended to encompass roped carbon nanotubes, single-walled carbon nanotubes (SWCNT) and multiple walled carbon nanotubes (MWCNT). Single walled carbon nanotubes-having a wall consisting of only one graphene layer-typically have diameters of from 1 to 5 nm; multi-walled carbon nanotubes typically have diameters of from 5 to 200 nm. It is further envisaged that carbon nanotubes having utility herein may be opened or chopped. And still further, the present disclosure does not preclude the use of carbon nanotubes which have been chemically modified through, for example, doping with thionyl chloride (SOCl2).

[0069] As used herein, the term ‘attrition’ as used herein includes fragmentation, abrasion or wearing down of a material or substance caused by continual friction, abrasion, or impact. In impact particle attrition, the kinetic energy from the high-speed collisions is converted to thermal energy and / or may provide enough energy for fracture, specifically in inelastic collisions. A primary variable in this process is the velocity of impact, although other variables including hardness of both particles and impact surface, angle of impact, resilience of both particles and surface, particle size and shape, pressure and shear stresses may be important. The term “milling” as used herein refers to mechanical ways to break larger particulate components into smaller sizes, such as nano-sized particles. The milling is carried in a milling chamber by media that exert shear forces to break the larger sized particles into smaller sized particles. A stirring device of some form can then be used to agitate the grinding media, thereby causing the solid particles of the mixture to be ground. Alternatively, the grinding media can be set in motion by either applying planetary, tumbling or vibratory motion to the milling chamber, or subjecting magnetic grinding media that has been charged to the milling chamber to an alternating or fluctuating magnetic field.

[0070] The present disclosure references the use of ball mills, wherein the type of grinding media charged to the milling chamber grinding media charged to the milling chamber comprises spherically shaped media milling beads. Spherically shaped grinding media may be preferred on account of its mechanical stability and the absence of edges or features which may be attrited.

[0071] As used herein, the term ‘high energy ball milling (HEBM)’ refers to a powdered milling process that can facilitate alloying on an atomic level. As such, the process utilizes substantially larger impact energies than other conventional powdered milling techniques, such as planetary milling or attritor milling, wherein, due to the physical design of the equipment, the energy given to the powder is less. Conventionally, in high energy ball mills, ball velocities of the magnitude of meters per second may be achieved. Independently of, or additional to this velocity being attained, the kinetic energy of the balls at impact in a high energy ball mill should be greater than about 30 mJ. The main milling mechanism of high energy ball milling is the competition between the generation of crystalline defects, due to plastic deformation, and its thermally activated recover.

[0072] As used herein, the term ‘volumetric analysis’ refers to a technique for determining the concentration of a material in a solution by measuring the amount of reagent required to react with it.

[0073] The term “chemisorption” may also be referred to as chemical absorption. The term encompasses absorption in which the forces involved are valence forces of the same kind as those operating in the formation of chemical compounds. Chemisorption is characterized by chemical specificity.

[0074] The term “hydrogenation” references the chemical reaction of a substance with molecular hydrogen.

[0075] The present disclosure is intended to include all hydration states of a given compound or formula, unless otherwise noted or when heating a material.

[0076] In addition, the present disclosure is intended to include all isotopes of atoms occurring in the present compounds and complexes. Isotopes include those atoms having the same atomic number but different mass numbers. By way of general example, and without limitation, isotopes of hydrogen include deuterium and tritium, and isotopes of carbon include 13C and 14C. Isotopes of oxygen include 16O, 17O, and 18O. Isotopically-labeled compounds of the disclosure may generally be prepared by conventional techniques known to those skilled in the art or by processes analogous to those described herein, using an appropriate isotopically-labeled reagent in place of the non-labeled reagent otherwise employed.

[0077] Aspects of the present disclosure are directed to a particulate composite of commercial AM60 magnesium (Mg) alloy catalyzed with titanium (Ti) and multiwalled carbon nanotubes (MWCNT) additives, with microstructural modifications made by high energy ball milling (HEBM). The HEBM reduced particle size, increased the surface area, and improved the hydrogen absorption and storage capacity of AM60 Mg alloy.

[0078] A particulate composite is described. The particulate composite comprises from about 86 to about 94 wt. %, for example from about 87 to about 93 wt. %, from about 88 to about 92 wt. %, or from about 89 to about 91 wt. % of a Mg alloy. The particulate composite further comprises: from about 3 to about 7 wt. %, for example from about 4 to about 6 wt. %, or about 4.5 to about 5.5 wt. % of Ti; and, from about 3 to about 7 wt. %, for example from about 4 to about 6 wt. %, or from about 4.5 to about 5.5 wt. % of MWCNT, based on the weight of the composite.

[0079] In some embodiments, the particulate composite comprises, based on the weight of the composite: from about 88 to about 92 wt. %, for example from about 88.5 to about 91.5 wt. %, from about 89 to about 91 wt. %, from about 89.5 to about 90.5 wt. %, or about 90 wt. % of the Mg alloy; from about 4 to about 6 wt. % for example from about 4.5 to about 5.5 wt. %, or about 5 wt. % of Ti; and, from about 4-6 wt. %, for example from about 4.5 to about 5.5 wt. %, or about 5 wt. % of MWCNT.

[0080] The Mg alloy of the particulate composite comprises, based on the weight of the alloy: from about 5.5 to about 6.5 wt. %, for example from about 5.75 to about 6.25 wt. %, or about 6 wt. % of aluminum (Al); from about 0.1 to about 0.5 wt. %, for example from about 0.2 to about 0.4 wt. %, or about 0.3 wt. % of manganese (Mn); from about 0.1 to about 1.0 wt. %, for example from about 0.2 to about 0.9 wt. %, from about 0.3 to about 0.8 wt. %, from about 0.4 to about 0.7 wt. %, or from about 0.5 to about 0.6 wt. % of the combination of zinc (Zn) with at least one element selected from copper (Cu), iron (Fe), nickel (Ni), and silicon (Si); and, a balance consisting of Mg and inevitable impurities.

[0081] In some embodiments, the Mg alloy comprises, based on the weight of the alloy: from about 5.5 to about 6.5 wt. %, for example from about 5.75-6.25 wt. %, or about 6 wt. % of Al; from about 0.2 to about-0.5 wt. %, for example from about 0.3 to about 0.4 wt. %, or about 0.35 wt. % of Mn; from about 0.3 to about 0.9 wt. %, for example from about 0.4 to about 0.8 wt. %, from about 0.5 to about 0.7 wt. %, or about 0.6 wt. % of the combination of Zn with at least one element selected from the group consisting of Cu, Fe, Ni and Si; and, a balance consisting of Mg and inevitable impurities.

[0082] In some embodiments, the particulate composite has a median volume particle size (Dv50) of from about 10 to about 35 micrometers (μm), for example from about 11 to about 34 μm, from about 12 to about 33 μm, from about 13 to about 32 μm, from about 14 to about 31 μm, from about 15 to about 30 μm, from about 16 to about 29 μm, from about 17 to about 28 μm, from about 18 to about 27 μm, from about 19 to about 26 μm, from about 20 to about 25 μm, from about 21 to about 24 μm, of from about 22 to about 23 μm, as determined by Scanning Electron Microscopy.

[0083] In some embodiments, the particulate composite has a median volume particle size (Dv50) of from about 15-30 μm, for example from about 16 to about 29 μm, from about 17 to about 28 μm, from about 18 to about 27 μm, from about 19 to about 26 μm, from about 20 to about 25 μm, from about 21 to about 24 μm, or from about 22 to about 23 μm, as determined by Scanning Electron Microscopy.

[0084] In some embodiments, the particulate composite has a surface area, as determined by Brunauer-Emmet-Teller (BET) analysis, of from about 1 to about 60 meter square per gram (m2 / g), for example from about 1 to about 55 m2 / g, from about 5 to about 55 m2 / g, from about 5 to about 50 m2 / g, from about 10 to about 50 m2 / g, from about 15 to about 50 m2 / g, from about 20 to about 50 m2 / g, from about 25 to about 50 m2 / g, from about 30 to about 50 m2 / g, from about 35 to about 50 m2 / g or from about 40 to about 50 m2 / g.

[0085] In some embodiments, the particulate composite has a surface area of from about 30 to about 50 m2 / g, for example from about 36 to about 50 m2 / g, from about 42 to about 50 m2 / g, from about 42 to about 48 m2 / g or from about 44 to about 46 m2 / g, as determined by BET analysis.

[0086] In some embodiments, at least a fraction of the MWCNTs in the particulate composite are present in agglomerated clusters. As used herein, the term ‘agglomerated clusters’ refers to a clustered particulate matter made up of fundamental particles that have been grouped together in a certain manner to create clusters.

[0087] FIG. 1 illustrates a flow chart of a method 50 of preparing the composite. The order in which the method 50 is described is not intended to be construed as a limitation, and any number of the described method steps can be combined in any order to implement the method 50. Additionally, individual steps may be removed or skipped from the method 50 without departing from the spirit and scope of the present disclosure.

[0088] At step 52, the method 50 includes attriting the Mg alloy in a HEBM having an inert atmosphere and including milling balls. Ball milling helps reduce alloy particle size by repeated collisions and friction, resulting in the desired material qualities. This technique often refines the alloy's structure and can improve its performance in specific applications. In some embodiments, the inert atmosphere can be provided nitrogen (N2), helium (He), and argon (Ar). In a preferred embodiment, the atmosphere of the HEBM includes Ar.

[0089] In some embodiments, the milling balls include tungsten carbide. Tungsten carbide milling balls aid in the efficient breakdown and refinement of Mg alloys, providing endurance and wear resistance during the milling process, resulting in improved particle size reduction and material characteristics. In alternate embodiments, the milling balls may be made of stainless steel, ceramic, or agate.

[0090] In some embodiments, the HEBM is operated at from about 150 to about 1500 rotations per minute (rpm), for example from about 200 to about 1400 rpm, preferably from about 300 to about 1300 rpm, from about 400 to about 1200 rpm, from about 500 to about 1100 rpm, from about 600 to about 1000 rpm, from about 700 to about 900 rpm, or about 800 rpm during attrition. In an exemplary embodiment, the HEBM is operated at about 300 rpm during attrition. In some embodiments, the HEBM is operated at a milling ball-to-powder ratio by weight (BPR) of from about 10:1 to about 20:1, for example from about 11:1 to about 19:1, from about 12:1 to about 18:1, from about 13:1 to about 17:1, from about 14:1 to about 16:1, or about 15:1. In an exemplary embodiment, the HEBM is operated at a milling BPR ratio by weight of about 12:1.

[0091] In an embodiment of the method, the particulate magnesium alloy is initially provided as chips or filings obtained from a bulk solid form of the alloy. Prior to ball milling at step 52, such chips or filings may have an irregular array of flake or platelet type particles, as illustrated in FIG. 3A appended hereto. A fraction of those particles may also possess a lamellar structure: lamellar particles having up to 30 lamellae are observable in FIG. 3A.

[0092] The action of high energy ball milling at step 52 of FIG. 1 alters the morphology of the particles of magnesium alloy. As depicted in FIG. 3B appended hereto, particles of a granular morphology may be formed. The depicted granules, having particle sizes of from about 1 to about 50 μm, show limited agglomeration and a sphericity of at least about 0.3. Moreover, there is some regularity in the packing of the particles and thereby some regularity in the interstitial pores disposed between the particles.

[0093] At step 54 of FIG. 1, the method 50 includes adding Ti powder and MWCNTs to the attrited Mg alloy and further attriting the obtained mixture in the HEBM in the inert atmosphere for a sufficient duration to form the particulate composite having: a median volume particle size (Dv50) of from about 10 to about 35 μm; and, a surface area of from about 1 to about 60 m2 / g. Exemplary values of the median volume particle size (Dv50) and the surface area, as measured by gas absorption analysis, are provided above.

[0094] The action of high energy ball milling (HEBM) the magnesium alloy with titanium and multi-walled carbon nanotubes introduces some heterogeneity into the particle size distribution of the composite. As illustrated in FIG. 3E appended hereto, the composite comprises agglomerated MWCNT and also plate-like particles which may be obtained by the fragmentation of the granular particles of magnesium alloy provided to the high energy ball mill. The agglomerates of MWCNT are porous, the pores thereof providing surface area for the absorption of gases and titanium.

[0095] In another aspect of the present disclosure, a method for chemisorbing hydrogen (H2) from a gas stream is described. The method comprises flowing the gas stream over the particulate composite. The composite reacts with hydrogen and forms a stable chemical bond. In some embodiments, the gas stream has a temperature of from about 200 to about 400° C., for example from about 210 to about 390° C., from about 220 to about 380° C., from about 230 to about 370° C., from about 240 to about 360° C., from about 250 to about 350° C., from about 260 to about 340° C., from about 270 to about 330° C., from about 280 to about 320° C., or from about 290 to about 310° C. In some embodiments, the gas stream has a pressure of from about 2 to about 5 MPa, preferably from about 2.5 to about 4.5 MPa, and more preferably from about 3 to about 4 MPa.

[0096] In some embodiments, the particulate composite has a H2 absorption capacity of from about 4.5 to about 6.2 wt. %, for example from about 4.6 to about 6.1 wt. %, from about 4.7 to about 6.0 wt. %, from about 4.8 to about 5.9 wt. %, from about 4.9 to about 5.8 wt. %, or from about 5.0 to about 5.7 wt. %, based on the weight of the composite and as determined by volumetric analysis at a temperature of about 375° C. and a H2 pressure of about 3.5 megapascals (MPa). In some embodiments, the particulate composite has a H2 absorption capacity of from about 5.0 to about 5.5 wt. %, from about 5.1 to about 5.4 wt. %, or from about 5.2 to about 5.3 wt. %, based on the weight of the composite and as determined by volumetric analysis at a temperature of about 375° C. and an H2 pressure of about 3.5 MPa.

[0097] In some embodiments, a hydrogenated particulate composite material is obtained according to the aforementioned method. In some embodiments, the hydrogenated particulate composite includes from about 4.5 to about 6.2 wt. %, for example from about 4.6 to about 6.1 wt. %, from about 4.7 to about 6.0 wt. %, from about 4.8 to about 5.9 wt. %, from about 4.9 to about 5.8 wt. %, or from about 5.0 to about 5.7 wt. %, of H2, based on the weight of the composite, as determined by volumetric analysis. In some embodiments, the hydrogenated particulate composite includes from about 5.0 to about 5.5 wt. %, preferably from about 5.1 to about 5.4 wt. %, and more preferably from about 5.2 to about 5.3 wt. %, of H2, based on the weight of the composite, as determined by volumetric analysis.

[0098] In some embodiments, in the hydrogenated particulate composite: i) a fraction of the particles have a metallic oxide layer; ii) a fraction of the particles have a metallic hydroxide layer, or, iii) both i) and ii) are applicable. Exemplary metallic oxide layers include, but are not limited to, titanium dioxide (TiO2), zinc oxide (ZnO), iron oxide (Fe2O3), copper oxide (CuO), nickel oxide (NiO), and manganese oxides (MnxOy). Exemplary metallic hydroxide layers include, but are not limited to, aluminum hydroxide (Al(OH)3), iron hydroxide (Fe(OH)3), copper hydroxide (Cu(OH)2), magnesium hydroxide (Mg(OH)2), and nickel hydroxide (Ni(OH)2).EXAMPLES

[0099] The following examples demonstrate a particulate composite for hydrogen absorption. The examples are provided solely for illustration and are not to be construed as limitations of the present disclosure, as many variations thereof are possible without departing from the spirit and scope of the present disclosure.Example 1: Materials

[0100] The starting material was a commercial AM60 magnesium (Mg) alloy bought from Jiangsu Huyi Metal Materials Co. Ltd. The alloy has the composition Mg6.35 Al0.45 Mn0.15Zn with trace quantities of iron (Fe) and silicon (Si). Titanium (Ti) powder (325 micrometers (μm) mesh size, 99.5% purity) was purchased from Alfa Aesar's, and MWCNT was obtained from Sigma-Aldrich and was used as a catalyst.Example 2: Materials Processing

[0101] Mechanical chipping was used to make a powder from the commercial AM60 Mg alloy. The AM60 chips were then processed using high energy ball milling (HEBM) in an inert atmosphere of argon (Ar) using a planetary Micro Mill PULVERISETTE 7 premium line machine for 20 hours. The ball mill was operated at a milling ball-to-powder ratio by weight (BPR) of 12:1, a speed of 300 rotations per minute (rpm). Tungsten carbide vails and tungsten carbide balls of 10 millimeters (mm) diameter were used as the attrition media.

[0102] Samples of the ball-milled AM60 Mg alloy were then independently ball-milled for 3 hours with the following additives, for which the given percentage weight is based on the total weight of the composition: i) 5 wt. % MWCNT; ii) 5 wt. % Ti; and, iii) both 5 wt. % MWCNT and 5 wt. % Ti. The materials will be labeled: AM60 (mechanically filed commercial AM60); AM60-BM (AM60 HEBM for 20 hours); AM60-Ti (AM60 with additive of 5 wt. % Ti); AM60-CNT (AM60 with additive of 5 wt. % MWCNT); and, AM60-Ti-CNT (AM60 with additives of 5 wt. % Ti+5 wt. % MWCNT).Example 3: Characterizations

[0103] The materials' phases, crystallite sizes, particle sizes, and powder morphologies were evaluated using X-ray diffraction (XRD) (AXSD8 Bruker) and SEM (SEM: JEOL JSM-6460), respectively.

[0104] XRD analysis—employing a scan rate of 2 degrees per minute (° / min), 2θ in a range from 19 degrees (°) to 80°, and Cu Kα radiation (1.544°)—was performed on the Ti additive, the MWCNT addition and the aforementioned milled and catalyzed samples. The Scherrer equation was employed to ascertain the crystallite size, utilizing the full width at half maximum (FWHM) and 2θ position.

[0105] The surface area of each material was determined by measuring N2 sorption isotherms at 77 Kelvin (K) using a Quantachrome Autosorb iQ3 BET Surface Area Analyzer. Before the measurement, the samples were exposed to degassing at a temperature of 150° C. for 4 hours to eliminate any molecules that may have been absorbed.Example 4: Hydrogen Absorption Measurements

[0106] Using a commercial Sievert's apparatus, the volumetric approach was used to measure hydrogen absorption. An about 0.2 g sample of the material was placed inside the chamber. Activation was carried out at 400° C. with 4 megapascals (MPa) of hydrogen for 90 minutes (min). The hydrogenation process was studied at 375° C. with a hydrogen pressure of 3.5 MPa. The effects of HEBM and different additives on the hydrogenation properties of AM alloy were investigated. The LAB-View software was used to control the entire hydrogenation apparatus. Following the hydrogen absorption test, XRD and scanning electron microscopy (SEM) were used to further evaluate the hydrogenated materials.Results and Discussion

[0107] The XRD analysis of monolithic AM60 and AM60-Ti / CNTs composites before hydrogenation is presented in FIG. 2. It can be observed that the principal phase in the processed samples is α-Mg, and no diffraction peaks for secondary phases are present in XRD due to trace amounts of aluminum (Al) and manganese (Mn) elements. All samples exhibit similar diffraction peaks, indicating that the crystal structure remains unchanged. The XRD analysis revealed that ball milling and additives have broadened and shortened the α-Mg peaks, indicating the formation of fine crystallites and enhanced micro stresses.

[0108] Carbon nanotubes (CNT) peaks in AM60-CNT composites indicate that regular crystalline structure is maintained. This is expected in that the regular crystalline structure of CNTs is damaged and changed to amorphous carbon when ball milled is conducted for significantly longer periods-such as at least 15 hours—at high energy. The intentional milling for 3 hours only serves to preserve the morphology of CNTs, ensuring that the maximum surface area of elemental carbon is accessible for hydrogenation properties. The small peak intensities of CNTs and Ti in composites may probably be due to the lower weight fraction of these additives in Mg alloy. The increase in peak broadness and shortening in peaks indicate enhancements in lattice defects and lattice strains induced at higher milling times.

[0109] The SEM micrographs of all samples prior to hydrogenation are presented in FIG. 3A-3E. FIG. 3A shows a SEM image of mechanically filed commercial AM60 before HEBM. The powder was prepared from the AM60 rod by mechanical filing, and the particles are elongated chips. The tortured chips range from 110 micrometers (μm) to 225 μm. FIG. 3B shows a SEM image of AM60 after HEBM for 20 hours. The milling of the tortured chips was carried out under an inert atmosphere of Argon gas. The ball milling has reduced the particle size, and substantially spherical-shaped particles are produced with a median volume particle size (Dv50) of 27.7 μm.

[0110] The SEM analysis revealed limited agglomeration of the AM60 alloy after 20 hour of ball milling. It is clear that particle size is homogeneously distributed and small particles are dispersed among the large particles. The particles are more similar in size and morphology than filed powder.

[0111] FIG. 3C shows a SEM image of AM60 with an additive of 5 wt. % Ti (AM60-Ti) after HEBM (3 hours). A decrease in in the median volume particle size (Dv50) to 20.3 μm is observed after Ti addition and a substantially homogeneous distribution is retained.

[0112] FIG. 3D shows a SEM image of AM60 with an additive of 5 wt. % multiwalled carbon nanotubes (MWCNT) (AM60-MWCNT) after HEBM (3 hours). No substantial change in the morphology of large particles has been observed after this CNT addition. However, it is noted that some smaller particles have become more elongated and cylindrical, and some agglomerated thereof into bigger particles is evident. The median volume particle size (Dv50) in this case was measured as 23.5 μm with non-homogeneously distributed large particles among the small, elongated particles. The intrinsic property of agglomeration of CNTs makes it difficult to achieve a homogenous and uniform distribution. The entangled and agglomerated CNTs are more clearly visible in the enlarged section. The low-energy ball milling was performed purposefully to maintain the morphology of CNTs so that maximum surface area should be available for hydrogenation characteristics.

[0113] FIG. 3E shows a SEM image of AM60 with additive of 5 wt. % Ti+5 wt. % MWCNT (AM60-Ti-CNTs) after HEBM. The addition of Ti has significantly enhanced the agglomeration of CNTs with Mg alloy. The CNTs are present in clusters; no secondary phases have been observed. It is considered that through this change in morphology, the ball milling of CNTs with Ti may produce a more effective surface area for hydrogen penetration. The porous structure of the agglomerated CNTs may help trap titanium and hydrogen. Further, the rough surfaces and fragmented particles which are produced due to continuous fracture during high energy ball milling may present an enhanced surface area which can effectively improve the de / hydrogenation behavior of Mg-CNTs / Ti composites.

[0114] Before the hydrogenation test, the surface area of the materials was determined using N2 sorption isotherms (FIG. 4), and the measured hydrogen absorption capacity and Brunauer-Emmet-Teller (BET) surface area were correlated. Table 1 herein below reports the BET surface area of the samples. Table 1 further reports the external surface area, micropore area and micropore volume as determined in accordance with the statistical thickness model of de Boer and wherein a micropore is defined as a pore having a diameter of less than 2 nm.TABLE 1Surface area and Pore Characteristics for AM60 with CNTs and Ti AdditivesBETExternalAveragesurfacesurfaceMicroporeMicroporeTotal poreporeareaareaareaVolumevolume1diameterSample[m2 g−1][m2 g−1][m2 g−1][m3 g−1][m3 g−1][Å]AM6000000.00165.2AM60-BM00000.00633.7AM60-Ti22000.00225.3AM60-CNT3410240.0120.0213.1AM60-Ti-4513320.0160.0313.4CNT1Calculated at P / P0 = 0.9

[0115] To further understand the effect of HEBM and additives on hydrogen storage capacity, the hydrogen absorption curves of several AM60 samples were investigated at 375° C. FIG. 5 shows hydrogen absorption of AM60, ball milled AM60 (AM60-BM), AM60-Ti, AM60-CNT, and AM60-Ti-CNT samples. The corresponding results have been summarized in Table 2.TABLE 2Measured Hydrogen Absorption capacity, SBET (BET surface area),and Theoretical Capacity for AM60 with CNTs and Ti additives.MedianMeasuredVolumeAbsorptionTheoreticalParticleCapacity afterAbsorptionSize, Dv5090 minutesCapacitiestaSample(μm)(wt. %)(wt. %)(s)AM60 167 ± 571.57.07—AM60-BM27.7 ± 154.07.075400AM60-Ti20.3 ± 114.56.433820AM60-CNT23.7 ± 126.26.872416AM60-Ti-CNT  22 ± 115.36.222920

[0116] Theoretical hydrogen absorption capacity can be determined by applying Eq. (1), and the resulting values are presented in Table 2.TC⁢ (%)⁢xMH⁢2(xMH⁢2+y⁢M⁢M⁢g+zMAl+jMMn+lMZn+k⁢M⁢A⁢d⁢d+… .)*
100(1)

[0117] In this equation, TC represents the theoretical hydrogen capacity (wt. %), MH2 is the molecular weight of hydrogen, and MMg, MAl, MMn, and MZn are the molecular weight of Mg, Al, Mn, and Zn, respectively. Madd is the molecular weight of additives. x, y, z, l and k are the corresponding weight fractions in the reaction.

[0118] The time(s) it takes to achieve a hydrogen absorption of 4 wt. % is used as a benchmark for comparison of the materials and is symbolized by the symbol ta. The required time (ta) of absorbing 4 wt. % H2 is 5400, 3820, 2416, and 2920 seconds(s) corresponding to AM60-BM, AM60-Ti, AM60-CNT, and AM60-Ti-CNT samples, respectively. The lowest time was for the AM60-CNT composite, which confirmed an improvement in the hydrogen kinetics of AM60 catalyzed with CNT.

[0119] The un-milled AM60 presents a very small hydrogenation capacity and very small measured absorption capacity. Monolithic AM60 (milling: 0 hours) absorbs (1.48 wt. %) hydrogen after 90 minutes of absorption. The 20 hours of ball milling of AM60-BM has significantly reduced the particle size and enhanced the surface area, consequently increasing the hydrogen absorption capacity to (3.96 wt. %). These AM60 alloys are considered non-porous, and the ball milling induces lattice defects and reduces the particle size, enhancing the porosity between the particles, as observed in the N2 sorption isotherms with higher uptake at higher pressure (FIG. 4). The AM60-BM sample showed a surface area of 0.2384 m2 / g compared to 0.0278 m2 / g for un-milled AM60 sample (Table 1). The addition of 5 wt. % Ti improves the hydrogen absorption capacity to 4.35 wt. % after 90 min of the hydrogenation process and hydrogenation kinetics. AM60-Ti has achieved the 2.9 wt. % hydrogen absorption capacity in 12.5 min (FIG. 5). Adding Ti into the Mg enhanced the porosity of the materials for sample AM60-Ti compared to the parent ball-milled AM60. The addition of 5 wt. % Ti and 5 wt. % CNTs have almost similar hydrogenation kinetics for the first 30 minutes with the same hydrogenation capacity (3.37 wt. %) at 30 min. The hydrogen absorption capacity was increased to 5.3 wt. % after 90 minutes of hydrogenation. The significant improvement in hydrogen absorption capacity was due to the higher surface area provided by CNTs. AM60-CNT sample showed the highest surface area of 1.7155 m2 / g compared to other samples (Table 1). Incorporating the CNT into the alloys enhanced the microporosity of the composite with an increase in the BET surface area. The enhanced surface area of nanostructures may provide a greater number of sites for H-atom dissociation: it facilitates a rapid diffusion from the outer to the inner regions of the alloy materials. The addition of 5 wt. % CNTs enhanced the hydrogen absorption capacity to 6.2 wt. % after 90 minutes. However, it has reduced the hydrogenation kinetics relative to AM60-Ti and AM60-Ti-CNTs. Linear hydrogenation kinetics has been observed to have the highest hydrogen absorption capacity. The faster kinetics rates have been observed in AM60-Ti and AM60-Ti-CNTs. Hydrogen absorption kinetics is intimately related to particle size, which serves as a diffusion pathway for hydrogen.

[0120] The decreased particle size due to ball milling, catalytic effects Ti, and higher surface area provided by the CNTs has improved the hydrogen kinetics in AM60-Ti and AM60-Ti-CNTs. Moreover, dispersed CNTs as modification agents, have reduced the particle size and enhanced the defect density and grain nucleation during HEBM, which may provide a reason for the higher improved kinetics of AM60. The agglomeration of CNTs has negatively influenced the hydrogen kinetics, but overall, the hydrogen absorption capacity has improved significantly to 6.5 wt. %.

[0121] It is evident from the above discussion that adding CNTs and Ti catalysts improves plastic deformation, effectively improving hydrogen kinetics. Consequently, low hydrogen kinetics in AM60-5CNTs is due to the fracturing phenomenon during deformation under HEBM, despite agglomeration. Additionally, the addition of 5 wt. % CNTs have resulted in a large grain size through agglomeration, which causes the relatively poor hydrogen kinetics.

[0122] High energy ball milling (HEBM) provides a high energy input to the system, resulting in a high milling intensity that yields fine and homogenous nanocrystalline structures. This reduces grain size while improving the mechanical and physical properties of synthetic alloys. The high energy input of HEBM causes defects in the crystal lattice, such as vacancies and dislocations, which accelerate hydrogen absorption reactions and increase Mg alloys' hydrogen storage capacity.

[0123] HEBM further leads to particle size reduction, which increases grain boundary area. Grain boundaries can serve as locations where hydrides can form, and the movement of hydrogen along these grain borders is accelerated. With a decrease in grain size, the number of grain boundaries is increased. Consequently, the rate at which hydrogen is absorbed increases, allowing for more hydrogen to be absorbed during the same reaction time.

[0124] In concert with HEBM, the additions serve two main functions: they act as heterogeneous nucleation sites for grain refinement and as surface catalysts for decoupling hydrogen molecules. These functions are widely recognized for their ability to enhance the kinetics of hydrogenation in Mg-based materials. [See: X. Yao, C. Wu, A. Du, J. Zou, Z. Zhu, P. Wang, H. Cheng, S. Smith, G. Lu, J. Am. Chem. Soc. 129 (2007) 15650, the disclosure of which is herein incorporated by reference in its entirety.] H2 molecules can be easily dissociated on the Mg surface using effective catalytic processes. The characteristics of hydrogen absorption curves can be determined by the hydride layer initially formed on the surface. The layer may gradually become the limiting factor in the diffusion of H atoms during the hydrogen absorption reaction.

[0125] In general, the interaction between Mg and H2 consists of three steps: dissociating H2 into H atoms on the surface, diffusing H atoms, and forming MgH2 by mixing H with Mg atoms. It is worthwhile to analyze the needed energy for dissociating hydrogen molecules as a rate control factor. Increasing the milling time reduces the size of particles and grains. The increase in crystal defect density and surface state changes in the alloy improve hydrogen molecule absorption on the particle surface as well as gas diffusion capabilities.TABLE 3Comparison of Hydrogen Absorption Rates in CompositeMaterials with Related Literature.HydrogenTeststorage capacitytemperatureComposite material(wt. %)(° C.)ReferenceAM60-Ti4.35375This workAM60-CNT6.2375This workAM60-Ti-CNT5.3375This workMg-5 wt. % MWNTs5.89200Chen, D., L. Chen, S.Liu, C. X. Ma, D. M.Chen, and L. B. Wang.‘Microstructure andhydrogen storageproperty of Mg / MWNTscomposites.’JournalCompounds 372, no.1-2 (2004): 231-237 Mg-5 wt. % MWNTs6.08275Chen, D., L. Chen, S.Liu, C. X. Ma, D. M.Chen, and L. B. Wang.‘Microstructure andhydrogen storageproperty of Mg / MWNTscomposites.’JournalCompounds 372, no.1-2 (2004): 231-237 Mg—Al4.4300A. ANDREASEN,Hydrogenationproperties of Mg—Alalloys, Int J. Hydrog.Energy vol. 33 (24)(2008) 7489-7497 Mg—Al—Ti4.28360Y. Wang, S. Lü, Z.Zhou, W. Zhou, J.Guo, Z. Lan, Effect oftransition metal onthe hydrogen storageproperties of Mg—Alalloy, J. Mater. Sci.vol. 52 (5) (2017)2392-2399 AZ613.9375Mose, Matoke Peter,AZ61-Ni4.5375and Song-JengAZ61- Ni + Co5.13375Huang. ‘EnhancedHydrogen StorageCapacity andKinetics in AZ61Alloy with Nickel andCobalt Additives:Insights into ReactionMechanisms andActivationEnergy.’Journal of(2024): 173934 Mg—Ti / Graphene4.3300Ye, Wei, QianqianChi, Han Zhou, andPeng Gao. ‘Ball-milling preparationof titanium / graphenecomposites and itsenhanced hydrogenstorage ability.”Energy 43, no. 41(2018): 19164-19173. Mg + 2 wt. % CNTs5.6300Liu, Haizhen,Chenglin Lu,Xinchun Wang, LiXu, Xiantun Huang,Xinhua Wang, HuaNing, Zhiqiang Lan,and Jin Guo.“Combinations ofV2C and Ti3C2MXenes for boostingthe hydrogen storageperformances ofMgH2.”ACS AppliedInterfaces 13, no. 11(2021): 13235-13247. MgH2 + 10 G5250Shang, C. X., and Z.X. Guo. “Effect ofcarbon on hydrogendesorption andabsorption ofmechanically milledMgH2.”Journal ofPower Sources 129,no. 1 (2004): 73-80.  The disclosure of this document is herein incorporated by reference in its entirety

[0126] Table 3 displays a comparative analysis of Mg-based alloys with different additives reported in the literature. It demonstrates that AM60 Mg alloy with Ti and CNT additives shows potential for hydrogen storage. The enhanced absorption kinetics may be a direct consequence of the reduced grain size achieved by using CNTs during the milling process. CNTs may facilitate the rapid passage of H-atoms into Mg. Transition metals can form alloys that decrease the activation energy required for the hydrogenation of Mg. The catalytic events on the Mg surface facilitate the dissociation of H2 molecules. The process of combining Mg with transition metals, mainly through the creation of solid solutions, has created a method for hydrogen to move through the alloy. In addition, many alloyed metals cannot create a solid solution phase. Instead, the metal atoms combine with Mg atoms to form a distinct phase, leading to the accumulation of stress. The specific surface area of the alloy is increased, so widening the area where hydrogen and metal react and improving the alloy's kinetic and thermodynamic properties. Two explanations for the suitability of catalysts composed of metal and carbon-based materials for hydrogen storage may be presented: (1) carbon-based materials can improve the hydrogen storage kinetics of Mg metal by physically capturing hydrogen on their surface when the hydrogen is being absorbed, thereby allowing them to function as a hydrogen pump for the material; (2) the presence of expansion fractures in the Mg-based alloy while it absorbs hydrogen causes a steady decline in the alloy's capacity during the hydrogen absorption and desorption process, ultimately failing but the presence of carbon can reduce the expansion of the alloy and extend its durability during usage.

[0127] FIG. 6A-6B shows SEM images of the AM60 sample and ball-milled AM60 after the hydrogenation test. FIG. 7A, FIG. 7B, and FIG. 7C shows SEM-energy-dispersive X-ray (EDS) maps of AM60-Ti, AM60-CNT, and AM60-Ti-CNT samples. FIG. 7C reveals a substantially uniform distribution of Ti and CNT in the AM60 matrix.

[0128] FIG. 8 shows XRD patterns of AM60, AM60-BM, AM60-Ti, AM60-CNT, and AM60-Ti-CNT samples after the hydrogenation test. The peaks represent the presence of Mg and magnesium hydride (MgH2), indicating that MgH2 was generated during the hydrogenation process. The hydrogenated sample patterns reveal strong peaks, indicating finely crystallized MgH2. The existence of non-hydrogenated Mg after the hydrogenation test, however, indicates that the maximal theoretical capacity has not been reached. The XRD peaks did not show any contribution from carbon-based phases, indicating that no chemical reaction has occurred between Mg and carbon additives, perhaps due to their low quantity. All samples with additives showed reduced Mg intensity in their X-ray diffractograms, indicating magnesium hydrogenation. After analyzing the measured and theoretical hydrogen capacities in Table 2, it is clear that the measured maximum hydrogen absorption capacities have not reached the theoretical values. The observed results of Table 2 are consistent with the XRD findings of FIG. 8. The failure to achieve the maximum theoretical hydrogen absorption capabilities may be due to two primary factors: irreversible hydrogen trapping; and, the formation of semi-permeable oxide and hydroxide layers on the surface of the composite particulates.

[0129] The present examples describe the hydrogen absorption characteristics of a MgAl0.055-0.065Mn0.001-0.005 alloy-specifically an AM60 alloy-which has been processed via HEBM and catalyzed with Ti and CNT additives. The phases and microstructure were analyzed using XRD and SEM. The hydrogenation process was measured using Sievert's equipment. The present examples show:

[0130] 1. The HEBM reduced particle size, increased the surface area, and improved the hydrogen absorption and storage capacity of the exemplary Mg alloy from 1.48 wt. % to 3.98 wt. %.

[0131] 2. Catalyzing AM60 with Ti and CNT additives enhances hydrogen absorption and storage capacity of the Mg alloy to 4.35 wt. % and 6.2 wt. %, respectively.

[0132] 3. Fast kinetics were observed in AM60-5Ti-5CNTs samples at the initial 12 minutes of hydrogenation, which was attributed to the synergistic enhancement achieved by the Ti and CNT integration and more accessible Mg sites for absorption.

[0133] 4. After hydrogenation, the existence of non-hydrogenated Mg in AM60-5Ti-5CNTs samples indicated that the maximal theoretical capacity was not reached.

[0134] Numerous modifications and variations of the present disclosure are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

Claims

1. A particulate composite comprising, based on the weight of the composite:from about 86 to about 94 weight percent (wt. %) of a magnesium (Mg) alloy;from about 3 to about 7 wt. % of titanium (Ti); and,from about 3 to about 7 wt. % of multiwalled carbon nanotubes (MWCNT),wherein the Mg alloy includes, based on the weight of the alloy:from about 5.5 to about 6.5 wt. % of aluminium (Al);from about 0.1 to about 0.5 wt. % of manganese (Mn);from about 0.1 to about 1.0 wt. % of the combination of zinc (Zn) with at least one element selected from the group consisting of copper (Cu), iron (Fe), nickel (Ni), and silicon (Si); and,a balance consisting of Mg and inevitable impurities,wherein the particulate composite has:a median volume particle size (Dv50) of from about 10 to about 35 micrometers (μm), as determined by Scanning Electron Microscopy; and,a surface area of from about 1 to about 60 meter square per gram (m2 / g), as determined by Brunauer-Emmet-Teller (BET) analysis.

2. The particulate composite according to claim 1 comprising, based on the weight of the composite:from about 88 to about 92 wt. % of the Mg alloy;from about 4 to about 6 wt. % of Ti; and,from about 4 to about 6 wt. % of MWCNT.

3. The particulate composite according to claim 1, wherein the Mg alloy comprises, based on the weight of the alloy:from about 5.5 to about 6.5 wt. % of Al;from about 0.2 to about 0.5 wt. % of Mn;from about 0.3 to about 0.9 wt. % of the combination of Zn with at least one element selected from the group consisting of Cu, Fe, Ni and Si; and,a balance consisting of Mg and inevitable impurities.

4. The particulate composite according to claim 1 having a median volume particle size (Dv50) of from about 15 to about 30 μm, as determined by Scanning Electron Microscopy.

5. The particulate composite according to claim 1 having a surface area of from about 5 to about 50 m2 / g, as determined by BET analysis.

6. The particulate composite according to claim 1 having a H2 absorption capacity of from about 4.5 to about 6.2 wt. %, based on the weight of the composite and as determined by volumetric analysis at a temperature of about 375 degrees Celsius (° C.) and a H2 pressure of about 3.5 megapascals (MPa).

7. The particulate composite according to claim 1 having a H2 absorption capacity of from about 5.0 to about 5.5 wt. %, based on the weight of the composite and as determined by volumetric analysis at a temperature of about 375° C. and an H2 pressure of about 3.5 MPa.

8. The particulate composite according to claim 1, wherein at least a fraction of the MWCNTs are present in agglomerated clusters.

9. A method of preparing the composite as defined in claim 1, the method comprising:attriting the Mg alloy in a high energy ball mill (HEBM) having an inert atmosphere and including milling balls; and,adding Ti powder and MWCNTs to the attrited Mg alloy and further attriting the obtained mixture in the HEBM in the inert atmosphere for a sufficient duration to form the particulate composite having a median volume particle size (Dv50) of from about 10 to about 35 μm and a surface area of from about 1 to about 60 m2 / g.

10. The method according to claim 9, wherein the atmosphere of the HEBM comprises argon (Ar).

11. The method according to claim 9, wherein the HEBM is operated at from about 150 to about 1500 rotations per minute (rpm) during attrition.

12. The method according to claim 9, wherein the HEBM is operated at a milling ball-to-powder ratio by weight (BPR) of from about 10:1 to about 20:1.

13. The method according to claim 9, wherein the milling balls comprise tungsten carbide.

14. A method for chemisorbing H2 from a gas stream comprising that element, the method comprising flowing the gas stream over the particulate composite as defined in claim 1.

15. The method according to claim 14, wherein the gas stream has a temperature of from about 200 to about 400° C.

16. The method according to claim 14, wherein the gas stream has a pressure of from about 2 to about 5 MPa.

17. A hydrogenated particulate composite material obtained according to the method defined in claim 14.

18. The hydrogenated particulate composite according to claim 17 including, based on the weight of the composite, from about 4.5 to about 6.2 wt. % of H2, as determined by volumetric analysis.

19. The hydrogenated particulate composite according to claim 17 comprising, based on the weight of the composite, from about 5.0 to about 5.5 wt. % of H2, as determined by volumetric analysis.

20. The hydrogenated particulate composite according to claim 17, wherein:i) a fraction of the particles comprises a metallic oxide layer;ii) a fraction of the particles comprises a metallic hydroxide layer; or,iii) both i) and ii) are applicable.

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