Solid Hydride Research Articles

Production of hydrogen from chemical hydrides via hydrolysis with steam

The objective of this work is to develop a method of producing H 2 for use in hand-portable fuel cells eliminating the bulkiness and high pressures associated with storage tanks. Water, either as liquid or vapor, will react with solid hydrides such as NaBH 4 to produce pure hydrogen. However, a number of limitations are inherent in the liquid–solid reaction. The insoluble hydrolysis products are extremely basic and high pH inhibits the reaction. A large excess of acid must be added to the mixture in order to force the reaction to completion, but is detrimental to the equipment. Furthermore, the liquid–solid reaction is inefficient on a weight basis because a large excess of the water-acid mixture must be used to obtain acceptable yields of hydrogen. Exploiting the vapor–solid reaction overcomes some of these limitations. An isothermal semi-batch reactor was constructed to test the concept. In each experiment the reactor was loaded with one gram of hydride and ambient pressure steam was metered through the reactor. A GC analysis of the product gas detected only hydrogen and water. The yield of hydrogen was measured and compared to the theoretical yield. The pH of the condensed, unreacted steam was tested and the percentage of excess water used was measured. A statistical analysis was conducted on the results in order to determine interactions between the parameters of flow rate and temperature. For some hydrides, nearly 100% yield of hydrogen was obtained without addition of any acid. Hydrogen yield depended strongly on temperature and, to a lesser extent, on flow rate of steam. The results and thermodynamic analysis suggest a conceptual hydrogen generation system in which the exothermic hydrolysis reaction is linked to an endothermic dehydriding reaction for the purpose of producing additional hydrogen.

All-electron calculations with plane waves in solid lithium hydride

All-electron calculations with plane waves in solid lithium hydride

All‐electron calculations with plane waves in solid lithium hydride

All‐electron calculations with plane waves in solid lithium hydride

On the design of liquid metal divertors

The divertor technology has become the focus of concern for prospective steady state tokamak reactors. The imposed heat flux and particle flux conditions cast doubt on the feasibility of any solid surface divertor. The aim of this work is to evaluate the existing concepts of liquid metal divertors from the physics, engineering, and safety points of view. Lithium metal is found to relatively suffer from a large tritium inventory that may develop in the form of solid hydride LiH, in addition to the fire hazard potential. Gallium does not form hydride within the temperature range of interest and is inactive with oxygen, therefore it is considered a more favorable metal. The flowing film and pool type divertors are found to suffer from the possible blistering erosion and resulting plasma contamination. The self-cooled liquid metal film divertor suffers also from a linear MHD instability, in addition to complicating factors such as the variation of the liquid metal electric property, dynamics of halo current, and the possible incompatibility with the insulator coating. The liquid gallium droplet curtain divertor appears to be the most feasible and roust, but its high temperature vapor is corrosive to most structural materials.

A Nickel Metal Hydride Battery for Electric Vehicles

Widespread use of electric vehicles can have significant impact on urban air quality, national energy independence, and international balance of trade. An efficient battery is the key technological element to the development of practical electric vehicles. The science and technology of a nickel metal hydride battery, which stores hydrogen in the solid hydride phase and has high energy density, high power, long life, tolerance to abuse, a wide range of operating temperature, quick-charge capability, and totally sealed maintenance-free operation, is described. A broad range of multi-element metal hydride materials that use structural and compositional disorder on several scales of length has been engineered for use as the negative electrode in this battery. The battery operates at ambient temperature, is made of nontoxic materials, and is recyclable. Demonstration of the manufacturing technology has been achieved.

A Feasibility Assessment of Liquid Metal Divertors

AbstractThe divertor technology has become the focus of concern for prospective steady state tokamak reactors. The imposed heat flux and particle flux conditions cast doubt on the feasibility of any solid surface divertor. The aim of this work is to evaluate the feasibility of the existing concepts of liquid metal divertors from both the physics and engineering points of view. It is found that lithium is not a favorable liquid metal due to the large tritium inventory that may develop in the form of solid hydride LiH. Gallium, on the other hand, does not form hydride within the temperature range of interest, and hence is considered a favorable material. Slowly flowing thin film and pool type divertors are found to be undesirable owing to the possible blistering erosion and resulting plasma contamination. The popular concept of self-cooled liquid metal film divertor suffers mainly from the linear MHD instability, in addition to other complicating factors such as the variation of the liquid metal electric pr...

Kinetic and mechanistic studies of the gas-phase thermolysis of hexaborane(12), and of its cothermolysis with other binary boranes and with CO, BH3·CO and H2

The kinetics of thermal decomposition of hexaborane(12) have been studied by a mass-spectrometric technique in the pressure range 1–10 mmHg and temperature range 60–127 °C. In conditioned Pyrex vessels B6H12 decomposes in a homogeneous, first-order, gas-phase process which affords B5H9 and B2H6 in a molar ratio of 2:1 as the main volatile products. In marked contrast with the known thermolyses of other small boranes, only minor amounts of non-volatile solid hydride are produced. The Arrhenius activation energy (81.3 ± 2.6 kJ mol–1) and the unusually low pre-exponential factor (3.1 × 108 s–1) are very similar to those associated with decomposition of the structurally related B5H11, consistent with a mechanism involving elimination of {BH3} as the rate-determining step in both cases. Small amounts of B6H10 and H2 are also produced, in what is believed to be a competing but minor reaction channel involving the direct elimination of dihydrogen from B6H12. Detailed comparisons of the initial rates of consumption of B6H12 in its thermolysis alone and in the presence of either CO or BH3·CO suggest a mechanism in which the B2H6 arises from direct association of two {BH3} groups, and not from the interaction of {BH3} with a second molecule of B6H12. Separate cothermolysis reactions with H2, B2H6, B4H10, B5H9, B5H11 and B6H10 indicate that there is no direct reaction between the B6H12 molecule and any of these binary boranes under the conditions used, implying that B6H12 itself is not an intermediate in the stepwise build-up to B10H14.

ChemInform Abstract: A Kinetic Study of the Gas‐Phase Thermolysis of Pentaborane(11)

Abstractis performed in the temp. range 40‐150 °C by a mass‐spectrometric technique.

A kinetic study of the gas-phase thermolysis of pentaborane(11)

The kinetics of thermal decomposition of pentaborane(11) have been investigated by a mass-spectrometric technique in the pressure range 1.75–10.50 mmHg and temperature range 40–150 °C. In conditioned Pyrex vessels the reaction was shown to occur by a homogeneous gas-phase process according to the first-order initial-rate law –d[B5H11]/dt= 1.3 × 107 exp(–72 600/RT)[B5H11]. The main volatile products are H2 and B2H6, the latter appearing at the rate of ca. 0.5 mol per mol of B5H11 consumed. Pentaborane(9) is also produced, at less than half the rate of B2H6, together with even smaller amounts of hexaboranes and B10H14, and traces of B4H10; some 40–45% of the boron is converted into involatile solid hydride BHx, where x varies from ca. 2.0 at 40 °C to ca. 1.1. at 150 °C. No obvious dependence on temperature was detected in the overall distribution of boron between volatiles and solid, but the production of B5H9 was favoured at higher temperatures. Mechanistic implications of these results are discussed.

A kinetic study of the gas-phase thermolysis of tetraborane(10)

The kinetics of thermal decomposition of tetraborane(10) have been investigated by a mass spectrometric technique in the pressure range 0.86–38.69 mmHg and temperature range 40.3–77.9 °C (313.4–351.0 K). The initial rate of consumption of B4H10 follows the first-order rate equation –d[B4H10]/dt= 6.4 × 1011 exp(–99 400/RT)[B4H10], with no evidence for the -order dependence claimed in the most recent literature. In the initial homogeneous gas-phase reaction, B5H11is produced with an order slightly greater than unity, and at a rate of 0.4–0.5 mole per mole of B4H10 consumed; hydrogen is also produced, with first-order kinetics, together with non-volatile solid hydride. Significant induction periods are observed in the build-up of species other than B5H11(i.e. B2H6, B6H12, and B10H14), indicating that they are the result of reactions subsequent to those involved in the initial stages. The initial reaction is interpreted in terms of the three-step mechanism, (1a), (2), and (3), in which (1a) is rate-limiting. A possible fourth step (5) may be an additional minor reaction favoured at low pressures. B4H10⇌{B4H8}+ H2(1a), {B4H8}+ B4H10→ B5H11+{B3H7}(2), {B3H7}+{B3H7}→{‘B6H14 – 2m’}(polymerizes)+mH2(3), {B4H8}+{B4H8}→{‘B8H16 – 2n’}(polymerizes)+nH2(5)

The Electrical Conductivity of Solid Lithium Hydride Doped with Sulphur

The Electrical Conductivity of Solid Lithium Hydride Doped with Sulphur

Thermal conductivity of magnesium-nickel hydride powder beds in a hydrogen atmosphere

A non-stationary hot-wire method was applied to measure the thermal conductivity of Mg, Mg/10wt%Ni and Mg 2Ni hydride powder beds in high temperature and pressure hydrogen atmospheres up to 200°C and 40 atm for three levels of bulk density for each sample. The effective conductivity values obtained were nearly equal for the former two, but was lower for the latter. Using Yagi and Kunii's model on the thermal conductivity of powder bed in stationary gas atmospheres, the conductivity of solid hydrides was estimated from the experimental effective conductivity values. These are ∼3 kcal mh −1°C for Mg and Mg/10wt%Ni hydrides and ∼ 1 kcal mh −1°C for Mg 2Ni hydride.

Decarbonylation of 2-germaacetic acid in aqueous solutions

In dilute aqueous acid solutions (0.05 to 0.5 M H/sup +/), 2-germaacetic acid decomposes to form carbon monoxide, an orange-yellow solid of approximate composition GeH/sub 0/./sub 6/, and small amounts of germane. The rate law for the reaction is -d(GeH/sub 3/COOH)/dt = k(H/sup +/)(GeH/sub 3/COOH); k = (5.59 +- 0.14) x 10/sup -4/M/sup -1/s/sup -1/ at 22.5/sup 0/C and ionic strength 1.0 M. From rate measurements in the temperature interval 0 to 39.5/sup 0/C, the activation energy was determined to be 16.9 kcal/mol. When the reaction is carried out in strongly acidic solutions (e.g., greater than 6 M HCl, greater than 4 M H/sub 2/SO/sub 4/, or greater than 6 M HClO/sub 4/), carbon monoxide is evolved quantitatively, but no solid hydride or germane forms. The resulting solution contains the GeH/sub 3//sup +/ group, probably stabilized in the form of the germyloxonium ion, GeH/sub 3/OH/sub 2//sup +/. The data implicate GeH/sub 2/ as an intermediate of the reaction in dilute acid solutions. 2 figures, 2 tables.

Stress-corrosion cracking in plastic solids including the role of hydrogen

Abstract Small changes in surface environments can change the energy needed to create a surface shear step. Increases in this energy tend to shift a delicate balance between glide and cleavage initiation at a crack tip. By inhibiting plastic deformation this causes an increased tendency for cleavage. Thus a material that is ductile in a vacuum can become quite brittle in the presence of certain surface-active environments, particularly atomic hydrogen. The quantitative criterion for deciding whether flow or cleavage will prevail is the ratio of the appropriate glide plane's surface energy to the cleavage plane's surface energy. A survey of the strengths of the interactions between hydrogen and metals has been made. Throughout the periodic table strong diatomic interactions occur. At solid surfaces the interactions remain strong although they are somewhat weaker than for diatoms. In solid hydrides they tend to be much weaker or non-existent. Thus the strength of the interaction depends on the metal-metal d...

Les proprietés electrochimiques de l'hydrure de lithium solide

The electrical conductivity of solid lithium hydride was measured. The electromotive forces of cells (Li)/LiH/H2p were determined at pressurep equal tol or to the equilibrium pressure of lithium hydride at the resp. temperatures. From the results it seems that lithium hydride, under the conditions where its conductivity is essentially ionic, may be used as a solid electrolyte for measurements of thermodynamic data of other less stable hydrides.

Kinetics of the reaction of water vapour with crystalline lithium hydride

The kinetics of the reaction of water vapour with crystalline lithium hydride to produce hydrogen, and either lithium oxide or hydroxide, has been investigated over the temperature range 0–121°C. The chemical nature of the solid product is determined solely by the amount of water vapour added in any single dose; when this is only sufficient to react with a single surface layer of lithium hydride or less, the oxide is found almost exclusively but when there is sufficient water to react with several layers, only the hydroxide is formed. On introduction, water vapour is rapidly and almost completely removed from the gas phase by the solid hydride (and products) but the hydrogen-producing process continues for several hours by reaction of sorbed water with the hydride. Diffusion of sorbed water to the reaction interface is not rate-controlling. The kinetics of hydrogen production, irrespective of the chemical nature of the product, is adequately represented by 1//tlog (a//a–x)–Cx//t=D. The parameters C, D vary with temperature, and decrease independently as the product accumulates. To account for this latter variation, it is suggested that annealing and recrystallization processes occur in the oxide layers in the time-interval between successive additions of water vapour, and that these structural changes affect the adsorptive capacity of the layers for water. A quantitative development of these concepts has been given and values for rate constants and activation energies for the hydrogen-producing reaction, and also some relative heats of adsorption of water by the oxides have been evaluated. The formation of the hydroxide that takes place when larger doses of water vapours are employed is the result of rapid reaction of unreacted sorbed water with the freshly-formed oxide, which is always the initial product of reaction.

76. The thermal decomposition of 2-ethyldecaborane

The first page of this article is displayed as the abstract.

Electrical Storage and Hydrogen Transfer between Electrodes of Palladium and Palladium Alloys

ELECTRODES of palladium and palladium alloys can absorb large volumes of hydrogen. In general, the solid hydrides retain excellent electrical conductivity and are not severely embrittled or disrupted. For pure palladium, and for many alloys, the relationships between electrodo potential E (with respect to a hydrogen reference electrode in the same solution) and hydrogen content (written here. Fig. 1, as the ratio, H/Me, of hydrogen atoms to the total number of metal atoms) exhibit ‘plateau’ regions—over which α- and β-phase hydrides co-exist—where E is relatively invariant (Eα,β). Over such ‘plateau’ regions, hydrogen transfer should, in principle, occur at a constant rate when connexion is made between an alloy and palladium or between two alloys. However, polarization1 would be expected to occur rapidly if the diffusion of hydrogen within the electrodes were not sufficiently fast for the concentration of hydrogen at the surfaces to be continuously representative of the ranges of H/Me corresponding to the plateaux. The following experiments serve to illustrate what may be observed in practice.

A model for the rationalization of saline and metallic hydride formation

The exothermic, reversible formation of solid hydrides from the elements is rationalized on the basis of a model in which the hydride consists of hydrogen anions and metal cations, the latter likewise engaging in metal-metal bonding in the metallic hydrides. The lattice energy is evaluated as the sum of the Madelung energy and this metal-metal interaction energy. Two empirical methods of estimating the latter are suggested, one involving crystal field stabilization. The total lattice energy so calculated is compared semi-quantitatively with the sum of the endothermic factors in a Born-Haber cycle. The energy balance is favourable with few exceptions for hydrides known to form directly, and unfavourable for hydrides which evidently do not form directly from the elements.

The pyrolysis of diborane

AbstractThe pyrolysis of diborane has been studied in single‐ and multi‐pass flow systems to determine the optimum conditions for its conversion to pentaborane.In a single‐pass flow system the products consisted of tetraborane, dihydropentaborane (B5H11), pentaborane (B5H9), decaborane and undesirable non‐volatile solid hydrides. The most economical conversion of diborane to pentaborane was obtained under the following conditions: temperature 250°, flow rate 400 c.c./min. and ratio of diborane/hydrogen 1 : 5 when 15·1% of the diborane was converted into pentaborane, 4·4% to solid hydrides and 80% recovered.In multi‐stage reactors designed on the basis of single‐pass experiments, the best yield of pentaborane was obtained in a 12‐unit reactor operating at 240°, flow rate 400 c.c./min. and ratio diborane/hydrogen 1 : 5. Under these conditions 57·0% of the diborane was converted into pentaborane, 14·1% to solid hydrides and 29·0% was recovered unchanged.Rate expressions are developed for the disappearance of diborane and activation energies calculated.The mechanism of the formation of pentaborane and decaborane is discussed.