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Liquid metallic hydrogen, in a fully dissociated state, is predicted at certain densities to pass from dirty to clean and from type II to type I superconducting behavior as temperature is lowered.
Liquid metallic hydrogen, in a fully dissociated state, is predicted at certain densities to pass from dirty to clean and from type II to type I superconducting behavior as temperature is lowered. Previously announced in STAR as N82-29374
Pure metallic hydrogen is predicted to have a specific impulse (Isp) of 1700 seconds, but the reaction temperature is too high for current engine materials. Diluting metallic hydrogen with liquid hydrogen can reduce the reaction temperature to levels compatible with current material limits and still provide an Isp greater than 900 s. Metallic hydrogen has not yet been produced on earth, but experimental techniques exist that may change this situation. This paper will provide a brief description of metallic hydrogen and the status of experiments that may soon produce detectable quantities of this material in the lab. Also provided are some characteristics for diluted metallic hydrogen engines and launch vehicles.
The heat transfer between a metal-hydrogen secondary battery and a hydrogen-storing metal hydride was studied. Temperature profiles of the endothermic metal hydrides and the metal-hydrogen battery were obtained during discharging of the batteries assuming an adiabatic system. Two hydride materials were considered in two physical arrangements within the battery system. In one case the hydride is positioned in a thin annular region about the battery stack; in the other the hydride is held in a tube down the center of the stack. The results show that for a typical 20 ampere-hour battery system with lanthanum pentanickel hydride as the hydrogen reservoir the system could perform successfully.
A proposed liquid ground state of metallic hydrogen at zero temperature is explored and a variational upper bound to the ground state energy is calculated. The possibility that the metallic hydrogen is a liquid around the metastable point (rs = 1.64) cannot be ruled out. This conclusion crucially hinges on the contribution to the energy arising from the third order in the electron-proton interaction which is shown here to be more significant in the liquid phase than in crystals.
The objective of this research is to produce metallic hydrogen in the laboratory using an innovative approach, and to study its metastability properties. Current theoretical and experimental considerations expect that extremely high pressures of order 4-6 megabar are required to transform molecular hydrogen to the metallic phase. When metallic hydrogen is produced in the laboratory it will be extremely important to determine if it is metastable at modest temperatures, i.e. remains metallic when the pressure is released. Then it could be used as the most powerful chemical rocket fuel that exists and revolutionize rocketry, allowing single-stage rockets to enter orbit and chemically fueled rockets to explore our solar system.
Upper bounds for the ground-state energies of liquid and solid phases of metallic hydrogen and metallic deuterium have been calculated with variational methods and Monte Carlo techniques. At four densities (0.8, 1.2, 1.36, and 1.488) crystalline phases are clearly preferred in the sense that the energy difference, when compared to the liquid, is in excess of the errors inherent in the numerical procedures. At a fifth density (1.6), the energy differences between solid and liquid phases are smaller than these errors.
The physical attributes of some of the more physically distinct ordered states of metallic hydrogen and metallic deuterium at T = 0 and nearby are discussed. The likelihood of superconductivity in both is considered with respect to the usual coupling via the density fluctuations of the ions.
When hydrogen is subjected to enough pressure the atoms will be pressed into close enough proximity that each electron is no longer bound to a single proton. The research objectives is to find whether metallic hydrogen can be produced and once produced will the metallic hydrogen be metastable and remain in the metallic form when the pressure is released.
A calculation is presented of the total energy of metallic hydrogen for a family of face-centered tetragonal lattices carried out within the self-consistent phonon approximation. The energy of proton motion is large and proper inclusion of proton dynamics alters the structural dependence of the total energy, causing isotropic lattices to become favored. For the dynamic lattice the structural dependence of terms of third and higher order in the electron-proton interaction is greatly reduced from static lattice equivalents.
The thermostatic properties of a high-symmetry phase of metallic hydrogen with atomic sphere radius between 0.1 and 1.5 bohr are studied, with special emphasis accorded to electronic screening and quantum proton motion. The electron-proton and proton-proton interactions receive a perturbation treatment based on the Singwi dielectric function, while the proton motion is handled by self-consistent harmonic approximation. Quantum behavior is found to be less pronounced than expected, and nuclear magnetism is absent. The phonon spectrum is, however, affected by screening and large proton motion. The zero-point vibrational energy and the superconducting critical temperature are below previous estimates. The crystalline-defect formation energies are a few times the Debye energy, which implies that defects contribute significantly to melting at the lower particle densities.
Numerical results for the phonon spectra of metallic hydrogen and other Coulomb systems in cubic lattices are presented. In second order in the electron-ion interaction, the behavior of the dielectric function of the interacting electron gas for arguments around the seond Fermi harmonic leads to drastic Kohn anomalies and even to imaginary phonon frequencies. Third-order band-structure corrections are also calculated. Properties of self-consistent phonons and the validity of the adiabatic approximation are discussed.
It is reported that the transition of condensed hydrogen from an insulating molecular crystal phase to a metallic liquid phase, at zero temperature and high pressure, appears possible. Liquid metallic hydrogen (LMH), comprising interpenetrating proton and electron fluids, would constitute a two-component Fermi liquid with both a very high component-mass ratio and long-range, species-dependent bare interactions. The low-temperature equilibrium properties of LMH are examined by means of a generalization to the case of two components of the phenomenological Landau Fermi-liquid theory, and the low-temperature specific heat, compressibility, thermal expansion coefficient and spin susceptibility are given. It is found that the specific heat and the thermal expansion coefficient are vastly greater in the liquid than in the corresponding solid, due to the presence of proton quasiparticle excitations in the liquid.
A theory is developed for the compressibility and transport properties of liquid metallic hydrogen, near to its melting point and under high pressure. The interionic force law is assumed to be of the screened Coulomb type, because hydrogen has no core electrons. The random phase approximation is used to obtain the structure factor S(k) of the system in terms of the Fourier transform of this force law. The long wavelenth limit of the structure factor S(o) is related to the compressibility, which is much lower than that of alkali metals at their melting points. The diffusion constant at the melting point is obtained in terms of the Debye frequency, using a frequency spectrum analogous with the phonon spectrum of a solid. A similar argument is used to obtain the combined shear and bulk viscosities, but these depend also on S(o). The transport coefficients are found to be about the same size as those of alkali metals at their melting points.
We study two possible types of pairing involving the protons of a proposed low-temperature liquid phase metallic hydrogen. Electron-proton pairing, which can result in an insulating phase, is investigated by using an approximate solution of an Eliashberg-type equation for the anomalous self-energy. A very low estimate of the transition temperature is obtained by including proton correlations in the effective interaction. For proton-proton pairing, we derive a new proton pair potential based on the Abrikosov wave function. This potential includes the electron-proton interaction to all orders and has a much larger well depth than is obtained with linear screening methods. This suggests the possibility of either a superfluid paired phase analogous to that in He-3, or alternatively a phase with true molecular pairing.
Hydrogen environment embrittlement causes failure of hydrogen storage vessels at and below design pressures of 5000 to 6000 psi. Investigation of thirty-five alloys determines their susceptibility to such embrittlement.
The application is studied of metallic H2 as a rocket propellant, which contains a specific energy of about 52 kcal/g in theory yielding a maximum specific impulse of 1700 s. With the convincing advantage of having a density 14 times that of conventional liquid H2/liquid O2 propellants, metallic H2 could satisfy the demands of advanced launch vehicle propulsion for the next millennium. Provided that there is an atomic metallic state of H2, and that this state is metastable at ambient pressure, which still is not proven, the results are given of the study of some important areas, which concern the production of metallic H2, the combustion, chamber cooling, and storage. The results show that the use of metallic H2 as rocket propellant could lead to revolutionary changes in space vehicle philosophy toward small size, small weight, and high performance single stage to orbit systems. The use of high metallic H2 mass fractions results in a dramatic reduction of required propellant volume, while gas temperatures in the combustion chamber exceed 5000 K. Furthermore, it follows, that H2 (liquid or slush) is the most favorable candidate as working fluid. Jet generated noise due to high exhaust velocities could be a problem.
Description of a split-sphere apparatus modified for use at low temperature and affording a possible method for compressing molecular hydrogen to a pressure in excess of 1 Mbar and for converting it to the metallic state. The construction costs of the apparatus are relatively low and the amount of liquid helium required for low-temperature operation is readily obtainable with modern liquefiers.