CaH2 Research Articles

Mechanochemical Synthesis, Characterization and Reactivity of a Room Temperature Stable Calcium Electride.

A new calcium-based Room temperature Stable Electride (RoSE), K[{Ca[N(Mes)(SiMe3)]3(e-)}2K3] (2), is successfully synthesized from the reaction of a calcium tris-amide, [Ca{N(Mes)(SiMe3)}3K] (1) (Mes = 2,4,6-trimethylphenyl), with potassium under mechanochemical treatment. The dimeric structure of K[{Ca[N(Mes)(SiMe3)]3(e-)}2K3] is calculated using ab initio random structure searching (AIRSS) methods. This shows the existence of highly localized anionic electrons (e-) and suggests poor electrical conductance, as confirmed via electroconductivity measurements. The two anionic electrons in 2 are strongly antiferromagnetically coupled, thus in agreement with the largely diamagnetic response from magnetometry. Reaction of 2 with pyridine affords 4,4'-bipyridine, while reaction with benzene gives C-H activation and formation of a calcium hydride complex, [K(η6-C6H6)4][{Ca[N(Mes)(SiMe3)](H)}2K3] (3). Computational DFT analysis reveals the crucial role played by the ligand framework in the stabilization of this new Ca-hydride complex.

Type-I clathrate calcium hydride and its hydrogen-vacancy structures at high pressure

Type-I clathrate calcium hydride and its hydrogen-vacancy structures at high pressure

Fabrication of powder high-entropy TiZrHfNbTa alloy by calcium-hydride method: Synthesis kinetics and structure evolution

High-entropy alloys are currently considered as prospective hydrogen storage materials and getters, which can be utilized to create a high vacuum in specialized devices. To provide high sorption properties, it is crucial to use highly porous materials or powders that makes powder metallurgy an attractive and suitable method. In the current work, a powder high-entropy alloy TiZrHfNbTa was obtained by reducing transition metal oxides with calcium hydride. The mechanism and features of the calcium-hydride synthesis of the high-entropy alloy have been studied. Phase composition has shown to be dependent on holding time at a temperature of 1200 °C. The powder’s structure comprises four BCC solutions based on Nb, Ta, TiZrHf, and TiZrHfNb, when holding time is up to two hours. Prolonged holding leads to more homogeneous structure, and the final product possesses two BCC phases: Ti0.21Zr0.24Hf0.24Nb0.25Ta0.06 (BCC-I: ∼75 wt%) and Ti0.15Zr0.05Hf0.08Nb0.10Ta0.62 (BCC-II: ∼25 wt%). The analysis of BCC-I formation kinetics with the aid of the Avrami equation has shown that a quite prolonged time of around 48 hours is necessary to achieve a single-phase structure of the powder due to the presence of tantalum, which impedes homogenization. Parameter n in the Avrami equation has been determined to be 0.361.

Reaction of a Bulky β‐Diketiminato Magnesium Hydride with CO2 Yielding a Polynuclear Magnesium Cage Compound

The reaction of a sterically shielded Mg hydride complex, bearing a bulky β‐diketiminato (BDI) ligand, with CO2 leads to the formation of polynuclear complexes. CO2 not only inserts into the metal hydride bond yielding formate ions, but also adds onto the γ‐C of the BDI ligand. This reactivity gives rise to the formation of tri‐ and tetranuclear structures in THF, leading to a hexameric structure associated with a change in the coordination mode of the BDI ligand at 60 °C in THF within four days. The hexameric complex was isolated in high reproducible yield from the solution and characterized by X‐ray diffraction analysis. The reaction affording the hexameric complex was shown to be completed within 1 h at room temperature in toluene. Similar reactions of CO2 with a BDI calcium hydride complex proceeds less cleanly and a pure product could not be isolated.

Bioactive Calcium Hydride-Driving "Triple" Hydrogen/Alkaline/Calcium Therapy for Efficient Treatment of Osteomyelitis.

Osteomyelitis with high mortality and disability rates is a common clinical disease caused by a bacterial infection that is difficult to cure. Considering the stubborn nature and depth of tissue infection, rapid and effective treatments for osteomyelitis remain an enormous challenge. Calcium hydride (CaH2), as efficient hydrogen/alkaline/calcium donors, is employed for combined osteomyelitis therapy. CaH2 reacts with water to sufficiently generate a strong alkali environment with hydroxide anions (OH-) to inhibit bacterial proliferation and induce bacterial death. The released calcium ions (Ca2+) induce calcium overload to kill bacteria first and then serves as calcium source to promote new bone formation. Another byproduct, hydrogen enhances the bacterial membrane permeability and scavenges excess reactive oxygen species (ROS). After incubation with bacteria, CaH2 significantly increases the permeability of the bacterial membrane, therefore increasing the entry of OH- and Ca2+ into bacterial cells, thereby leading to significant bacterial death. After being applied to S. aureus-infected mouse tibia osteomyelitis, CaH2 materials efficiently kill bacteria, relieve local inflammation, and promote new bone formation in a short time. Overall, bioactive metal hydride-associated "triple" hydrogen/alkaline/calcium therapy provides a new idea for the treatment of deep-site bacterial infection, which is beneficial for relieving the pressure caused by antibiotic-resistant bacteria.

Aluminum hydrolysis for hydrogen generation enhanced by sodium hydride

Aluminum is the most abundant and promising material for hydrolytic hydrogen generation. It can be easily transported and stored. However, the oxide protective layer around Al limits its hydrolytic activity and hinders practical applications. To solve this problem, NaH is introduced to form the core-shell structure of Al-based NaH solid fuel powder by a simple hand mixing method in an open lab environment. The new core-shell structure of Al-based NaH solid fuel powder showed the best hydrolytic performance among Al-based materials and produced 98 % hydrogen yield at a 1 to 0.9 M ratio of NaH and Al in water. The hydrolytic activity consists of NaH hydrolytic splitting and Al hydrolysis. XRD and SEM analysis confirmed that NaH is the key to supporting complete Al hydrolysis and attaining maximum yield as compared to calcium hydride. Our research endorsed the practical implementation of inexpensive and transportable hydrolytic hydrogen generation materials and offered a new idea for the design of hydrolytic hydrogen generation materials for further development.

Hydrogenation features of TiZrHfNbTa high-entropy alloy produced by calcium-hydride synthesis

A high-entropy alloy TiZrHfNbTa has been synthesized by a method of the mutual reduction of the higher oxides of corresponding metals with calcium hydride. The alloy structure was characterized and hydrogen absorption properties were studied. The alloy of overall equiatomic composition TiZrHfNbTa consists of two BCC phases with unit cell parameters of 3.419 and 3.328 Å. The distribution of the elements was established as follows: Ti0.21Zr0.24Hf0.24Nb0.25Ta0.06 (BCC-I) and Ti0.15Zr0.05Hf0.10Nb0.08Ta0.62 (BCC-II). The hydrogenation behavior of the alloy under different conditions was thoroughly studied. It was shown that complete hydrogenation resulted in the formation of FCC-type (H/M → 2) and BCT-type hydrides (H/M → 1) from BCC-I and BCC-II, respectively. Under low hydrogen pressure (< 212.8 Torr), BCC-I absorbed up to 0.33 at. H/M within a solid solution without changing the structural type. According the kinetic analysis, this process can be described as a second order reaction with activation energy of 102 kJ/mol. The BCC-I-based solid solution is capable of retaining hydrogen in a deep vacuum at a temperature of 430 °C. The fast kinetics of hydrogen absorption and high thermal stability allow us to suggest the studied two-phase TiZrHfNbTa alloy as a promising getter for vacuum devices.

Synthesis of core–shell silicon–carbon nanocomposites via in-situ molten salt-based reduction of rice husks: A promising approach for the manufacture of lithium-ion battery anodes

Silicon (Si) has gained substantial interest as a potential component of lithium-ion battery (LIB) anodes due to its high theoretical specific capacity. However, conventional methods for producing Si for anodes involve expensive metal reductants and stringent reducing environments. This paper describes the development of a calcium hydride (CaH2)–aluminum chloride (AlCl3) reduction system that was used for the in-situ low-temperature synthesis of a core–shell structured silicon–carbon (Si–C) material from rice husks (RHs), and the material was denoted RHs-Si@C. Moreover, as an LIB anode, RHs-Si@C exhibited exceptional cycling performance, exemplified by 90.63 % capacity retention at 5 A g−1 over 2000 cycles. Furthermore, the CaH2–AlCl3 reduction system was employed to produce Si nanoparticles (Si NPs) from RHs (R-SiO2, where SiO2 is silica) and from commercial silica (C-SiO2). The R-SiO2-derived Si NPs exhibited a higher residual silicon oxides (SiOx) content than the C-SiO2-derived Si NPs. This was advantageous, as there was sufficient SiOx in the R-SiO2-derived Si NPs to mitigate the volumetric expansion typically associated with Si NPs, resulting in enhanced cycling performance. Impressively, Si NPs were fabricated on a kilogram scale from C-SiO2 in a yield of 82 %, underscoring the scalability of the low-temperature reduction technique.

Evolution of the Composition and Morphology of Ti–18 Zr–15 Nb Alloy Powder during Calcium Hydride Synthesis

Evolution of the Composition and Morphology of Ti–18 Zr–15 Nb Alloy Powder during Calcium Hydride Synthesis

Fabrication of Refractory Intermetallic Cr2Ta by Reducing Metal Oxides with Calcium Hydride

Fabrication of Refractory Intermetallic Cr2Ta by Reducing Metal Oxides with Calcium Hydride

Effect of Gamma Heating on Heat Pipe–Cooled, Calcium Hydride–Moderated Core

A novel microreactor, called MoveluXTM, was previously proposed that utilizes heat pipes as the primary heat transfer device and calcium hydride as the moderator. In this core design, the moderator temperature is the critical core operation limit because at high temperatures above 800°C, the hydrogen dissociates from the calcium hydride. The core temperature distribution, therefore, was previously evaluated. However, this evaluation did not consider gamma heating in the core and assumed that power was produced only in the fuel region. By contrast, the moderator region has a power density under realistic conditions due to gamma heating. Thus, the present work considers gamma heating in the core power distribution calculation and evaluates the impact on the moderator temperature. The power density of gamma heating was 1/10th that of the fuel region and around 1/100th that of the core thermal power. This increased the temperature of the moderator by 10 K from the case without considering gamma heating. In addition, this temperature distribution difference did not have an impact on the core criticality. In conclusion, considering the gamma heating, concerns regarding the core design are not suggested.

Calcium hydride with aluminium for thermochemical energy storage applications

Addition of aluminium to calcium hydride delivers excellent operating conditions for utilisation as a thermal energy storage material.

Using oral molecular hydrogen supplements to combat microinflammation in humans: a pilot observational study.

Background: Persistent inflammation over time can cause gradual harm to the body. Molecular hydrogen has the potential to specifically counteract reactive oxygen species (ROS), reduce disease severity, and enhance overall health. Investigations of the anti-inflammatory and antioxidant properties of oral solid hydrogen capsules (OSHCs) are currently limited, prompting our examination of the beneficial effects of OSHCs. Subsequently, we conducted a clinical study to assess the impact of OSHCs supplementation on individuals with chronic inflammation. Materials and methods: Initially, we evaluated the oxidative reduction potential (ORP) properties of the OSHCs solution by comparing it to hydrogen-rich water (HRW) and calcium hydride (CaH2) treated water. In our outpatient department, stable patients with chronic illnesses who were treated with varying doses of OSHCs were randomized into low-, medium-, and high-dose groups for 4 weeks. Primary outcomes included changes in the serum erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) concentrations after four weeks of OSHCs consumption. Secondary outcomes included changes in the Brief Fatigue Inventory-Taiwan (BFI-T) fatigue scale, Control Status Scale for Diabetes (CSSD70) scores, and Disease Activity Score 28 (DAS28). Results: Compared to HRW and CaH2, OSHCs demonstrated a prolonged reduction in ORP for 60 minutes in vitro and enabled a regulated release of hydrogen over 24 hours. A total of 30 participants, with 10 in each dosage (low/medium/high) group, completed the study. The average ESR120 significantly decreased from the first week to the fourth week, with a noticeable dose effect (low-dose group, p = 0.494; high-dose group, p = 0.016). Overall, the average CRP concentration showed a distinct decreasing trend after four weeks of OSHCs administration (w0 vs. w4, p = 0.077). The average DAS28 score demonstrated a significant decrease following OSHCs treatment. Furthermore, there were improvements in the BFI-T and CSSD70 scores. Conclusion: OSHCs supplementation may exert anti-inflammatory and antioxidant effects on individuals with chronic inflammation. However, further clinical studies could be investigated to explore the potential therapeutic effects of OSHCs.

CO reduction by calcium and ytterbium hydride complexes with a bulky monodentate carbazolyl ligand.

The bulky monodentate carbazolyl ligand 1,8-bis(3,5-ditertbutylphenyl)-3,6-ditertbutylcarbazole (dtbpCbz) was employed in the synthesis of monomeric heteroleptic amido carbazolyl complexes of Ca and Yb. For both central metal atoms, dimeric hydride complexes [(dtbpCbz)Ca(benzene)H]2, [(dtbpCbz)Ca(THF)H]2, [(dtbpCbz)Yb(benzene)H]2 and [(dtbpCbz)Yb(THF)H]2 were obtained, which show remarkably poor solubility in organic solvents. The characteristic hydride 1H NMR resonance of [(dtbpCbz)Ca(benzene)H]2 was observed at 2.07 ppm, and for the first time, characteristic vibrational modes of the Ca2H2 and Yb2H2 moiety are discussed. Despite their poor solubility, the hydride complexes could be reacted with CO to yield the corresponding ethenediolate complexes.

Pathway to a molecular calcium methyl.

The dimeric β-diketiminato calcium hydride, [(BDI)CaH]2 (BDI = HC{(Me)CN-2,6-iPr2C6H3}2), reacts with ZnMe2 to afford the bimetallic calcium zincate complex, [(BDI)Ca(μ-CH3)2Zn(μ-H)]2, which subsequently undergoes an intramolecular reaction to effect the formation of [(BDI)CaMe]2, a notable omission from the homologous series of β-diketiminato alkylcalcium derivatives.

Variable Ca-Caryl Hapticity and its Consequences in Arylcalcium Dimers.

The dimeric β-diketiminato calcium hydride, [(Dipp BDI)CaH]2 (Dipp BDI = HC{(Me)CN-2,6-i-Pr2 C6 H3 }2 ), reacts with ortho-, meta- or para-tolyl mercuric compounds to afford hydridoarylcalcium compounds, [(Dipp BDI)2 Ca2 (μ-H)(μ-o-,m-,p-tolyl)], in which dimer propagation occurs either via μ2 -η1 -η1 or μ2 -η1 -η6 bridging between the calcium centers. In each case, the orientation and hapticity of the aryl units is dependent upon the position of the methyl substituent. While wholly organometallic meta- and para-tolyl dimers, [(Dipp BDI)Ca(m-tolyl)]2 and [(Dipp BDI)Ca(p-tolyl)]2 , can be prepared and are stable, the ortho-tolyl isomer is prone to isomerization to a calcium benzyl analog. Computational analysis of this latter process with density functional theory (DFT) highlights an unusual mechanism invoking the generation of an intermediate dicalcium species in which the group 2 centers are bridged by a toluene dianion formed by the formal attachment of the original hydride anion to the initially generated ortho-tolyl substituent. Use of a more sterically encumbered aryl substituent, {3,5-t-Bu2 C6 H3 }, facilitates the selective formation of [(Dipp BDI)Ca(μ-H)(μ-3,5-t-Bu2 C6 H3 )Ca(Dipp BDI)], which can be converted into the unsymmetrically-substituted σ-aryl calcium complexes, [(Dipp BDI)Ca(μ-Ph)(μ-3,5-t-Bu2 C6 H3 )Ca(Dipp BDI)] and [(Dipp BDI)Ca(μ-p-tolyl)(μ-3,5-t-Bu2 C6 H3 )Ca(Dipp BDI)] by reaction with the appropriate mercuric diaryl. Conversion of [(Dipp BDI)Ca(H)(Ph)Ca(Dipp BDI)] to afford [{{(Dipp BDI)Ca}2 (μ2 -Cl)}2 (C6 H5 -C6 H5 )], comprising a biphenyl dianion, is also reported. Although this latter transformation is serendipitous, AIM analysis highlights that, in a related manner to the ortho-tolyl to benzyl isomerization, the requisite C-C coupling may be facilitated in an "across dimer" fashion by the experimentally-observed polyhapto engagement of the aryl substituents with each calcium.

Hydroxylation-Depolymerization of Oxyphenylene-Based Super Engineering Plastics To Regenerate Arenols.

Super engineering plastics, high-performance thermoplastic resins, show high thermal stability and mechanical strength as well as chemical resistance. On the other hand, chemical recycling for these plastics has not been developed due to their stability. This study describes depolymerization of oxyphenylene super engineering plastics via carbon-oxygen main chain cleaving hydroxylation reaction with an alkali hydroxide nucleophile. This method is conducted with cesium hydroxide as a hydroxy source and calcium hydride as a dehydration agent in 1,3-dimethyl-2-imidazolidinone, which provides hydroxylated monomers effectively. In the case of polysulfone, both 4,4'-sulfonyldiphenol (bisphenol S) and 4,4'-(propane-2,2-diyl)diphenol (bisphenol A) were obtained in high yields. Other super engineering plastics such as polyethersulfone, polyphenylsulfone, and polyetheretherketone were also applicable to this depolymerization.

Reduction of Amides to Amines Catalyzed by Ca(CH2C6H4NMe2‐o)2(THF)2/HBpin

AbstractReduction of amides to amines is an attractive subject in organic synthesis. Ca(CH2C6H4NMe2‐o)2(THF)2, an easily accessible main‐group complex, on combination with pinacolborane (HBpin) could serve as a highly active catalyst system in the reduction of primary, secondary and tertiary amides into the corresponding amines. This protocol showed good tolerance for functional groups and heteroatoms, and the aimed products could be obtained in a gram‐scale. The active species in this transformation was supposed to be a calcium hydride.

Microwave-assisted chemical synthesis of SmCo5 magnetic particles with high coercivity

The hard-magnetic SmCo5-based materials with high coercivity have an enormous range of high-value-added technological applications. We reported the novel synthesis of SmCo5 particles with desired particle size by a microwave-assisted combustion process. The process consists of a combination of Sm-Co oxide precursor preparation by microwave-assisted combustion, and the following calcium hydride reduction-diffusion. The microwave-assisted combustion offers a time and energy-saving, and environmentally-friendly methodology to form the homogenous Sm-Co oxide precursor nanoparticles. This high-quality Sm-Co oxide precursor paves the way for achieving high coercivity in SmCo5 magnetic materials. A high coercivity up to 39.2 kOe was achieved in the aligned SmCo5 particles. These SmCo5 magnetic particles show promising prospects for high-performance permanent magnet applications and can be utilized for the development of exchange-coupled nanocomposite magnets with high energy density. This work also provides instructive information for designing and synthesizing rare-earth-based magnetic materials.

Thermodynamic and kinetic properties of calcium hydride

Calcium hydride has shown great potential as a hydrogen storage material and as a thermochemical energy storage material. To date, its high operating temperature (above 800 °C) has not only hindered its opportunity for technological application but also prevented detailed determination of its thermodynamics of hydrogen sorption. In addition, calcium metal suffers from high volatility, high corrosivity from Ca (and CaH2), slow kinetics of hydrogen sorption, and the solubility of Ca in CaH2. In this work, a literature review of the wide-ranging thermodynamic properties of CaH2 is provided along with a detailed experimental investigation into the thermodynamic properties of molten and solid CaH2. The thermodynamic values of hydrogen release from both molten and solid CaH2 were determined as ΔHdes (molten CaH2) = 216 ± 10 kJ mol−1.H2, ΔSdes (molten CaH2) = 177 ± 9 J K−1 mol−1.H2, which equates to a 1 bar hydrogen equilibrium temperature for molten CaH2 of 947 ± 65 °C. Similarly, in the solid-state: ΔHdes (solid CaH2) = 172 ± 12 kJ mol−1.H2, ΔSdes (solid CaH2) = 144 ± 10 J K−1 mol−1.H2. Moreover, the activation energy of hydrogen release from CaH2 was also calculated using DSC analysis as Ea = 203 ± 12 kJ mol−1. This study provides the first thermodynamics for the Ca–H system in over 60 years, providing more accurate data on this emerging energy storage material.