Pure Alkali Metal Research Articles

Evidence for an alkali-like conduction band in alkali graphite intercalation compounds

The valence bands of pure graphite and several alkali graphite intercalation compounds (AGIC's) were studied by UPS ( hv = 21.2 eV). The most significant observation is an intensity peak at the Fermi energy E F in the intecalation compounds. This peak is mainly due to alkali-like s-states. The density of states at E F is enhanced by a factor of 30 compared to pure graphite. The alkali-like conduction bands in the first stage AGIC's are similar to those of pure alkali metals.

A new catalytic determination of ultratrace amounts of iron with p-anisidine and n, n-dimethylaniline

A new sensitive catalytic method for the determination of iron(II) and iron(III) is proposed. p-Anisidine reacts with N, N-dimethylaniline to form N-( p-methoxyphenyl)- N', N'-dimethyl- p-phenylenediamine (MDP). In the presence of hydrogen peroxide, iron(III) catalyzes the oxidation of MDP to a blue compound (λ max= 735 nm). Iron(II) is also determined, being oxidized by hydrogen peroxide. Working curves are linear in the approximate range 6–20 ng Fe ml -1; as little as 10 -7 M iron can be determined easily. The method is applicable to the analysis of pure ammonium and alkali metal salts containing 10 -4–10 -5% iron.

Modes for transmission of microwaves through alkali metals at cryogenic temperatures

We present experimental results for three different modes of magnetic-field-dependent microwave transmission through thin foils of pure alkali metals at cryogenic temperatures. The first of these modes occurs when the magnetic field is parallel to the surface, and results in propagation windows above the field for cyclotron resonance ${H}_{c}$ and its subharmonics. The mode is identified as the transmission analog of cyclotron waves as observed in reflection. The data are compared with extensive computer simulations in an effort to deduce values for the coefficients of the momentum part of the Landau correlation function. Results are presented for Na, K, and Rb, and compared with other values. The second mode contains two series, each characterized by a rapid oscillatory dependence of the transmitted field on the angle between the applied dc magnetic field and the sample surface. They occur when the dc field is much greater than ${H}_{c}$. We identify one of these series with a model dependent upon the simple time of flight for electrons along the field lines. The other appears to be more complicated and we suggest warrants theoretical attention. The third mode, for the dc field normal to the sample, is identified as the Gantmakher-Kaner oscillations at microwave frequencies. Attention is focused on the behavior of this mode near ${H}_{c}$ and for fields much greater than ${H}_{c}$. The signal-to-noise ratio available experimentally for observation of all of the modes discussed is very high. Consequently it is suggested that if any electronic properties of interest of the alkali metals can be theoretically identified with an observed mode, they could be further measured and analyzed.

The Calcium Anode in Molten Nitrate Electrolytes

The electrochemical behavior of the calcium anode in molten nitrates was determined using constant current methods. Investigations were made in both and at 350°C and in (60‐40 mole percent) over a temperature range of 250°–400°C. Differential scanning calorimetry studies were also made on calcium in many nitrate mixtures. No exothermic reactions were detected for calcium in any pure alkali metal nitrate melt; however, chemical reactions were apparent for many calcium‐molten nitrate systems which contained added halide salts. The rate of the calcium electrode reaction is determined largely by the passivating oxide film formed on calcium in molten nitrates. The addition of halides that promote breaks in the film can greatly improve both the electrode kinetics and the open‐circuit potential. With sufficient breakdown of the passivating layer, high current densities can be obtained for the calcium anode with very little polarization. The effectiveness of the added halides in reducing polarization generally decreased in the order . The experimental results can be explained by a passivating layer model involving specific adsorption of anions at the interface.

Ionic product and enthalpy of ionization of water from electromotive force measurements

New e.m.f. data have been obtained for the cell: Pt, H2|MOH,NX|AgX|Ag at 25°C where M, N = Li, Na, K, Cs and X = Cl, Br, from which the ionic product (Kw) of water can be obtained (pKw= 14.004). Application of a theory of mixed electrolyte solutions to the results enables the variation of the apparent ionic product (K′w) with ionic strength and cation to be expressed in terms of the properties of the pure alkali metal halide and hydroxide solutions at the same total ionic strength. The conditions M = Li, N = K, X = Cl were selected for a study over the temperature range 0–60°C and from these measurements the enthalpy of ionization of water was calculated (ΔH°= 13430 ± 5 cal mol–1). The use of mixed cations in the cell minimises the variation of apparent ionic product with ionic strength, thereby reducing the uncertainty in the extrapolation to zero ionic strength felt previously to be the principal contributing factor leading to the discrepancy between calorimetric and e.m.f. derived values for the ionization enthalpy of water.

The temperature dependence of theg-shifts of conduction electrons in pure and impure alkali metals

Theg-shifts of conduction electrons in pure and impure alkali metals have been calculated by taking the average over the Fermi surface along the [100], [110] and [111] directions. The conduction-electron wave functions are approximated by taking orthogonalized plane waves orthogonal to the core states and are the irreducible representations in the double group. The calculatedg-shift for Li is —6.7·10−5 which is in satisfactory agreement with the experimental result (—6.1±0.2)·10−5. The temperature dependence of theg-shift is obtained when the integration over theK-vector involves the Fermi-Dirac distribution. Theg value for Li shifts only about 0.3% from a temperature of 4°K to 500°K. The wave functions for the impure alkali metals are obtained by Bardeen expansion to second order around the center of the Brillouin zone.

Measurement of Absorption and Velocity of Ultrasound in Liquid Alkali Metals

Ultrasonic absorption and velocity measurements have been made in pure liquid alkali metals at temperatures from their melting points to 250°C. Measured absorptions have been found to exceed the computed classical values by 10%–25%. Sound velocities decrease linearly with increasing temperature. The distilled liquid metals were transferred to the measurement apparatus under vacuum (better than 10−4 Torr) and measurements were made under a high-purity argon cover gas. No significant reaction with the cover gas was observed. No bonding agent was needed between the transducer and the clean liquid surface. [This work was supported by the Office of Naval Research.]

Vibrational Spectra and Structures of Ionic Liquids. II. The Pure Alkali Metal Nitrates

Attenuated total reflection infrared spectroscopy has been used together with thin-film transmission measurements to obtain detailed spectra for the molten nitrates of lithium, sodium, and potassium in the 250–4000-cm−1 range. The techniques, which yield spectra approaching the ultimate in resolution and precision possible for salt melts, permit the detection of several features which, when combined with Raman data, definitely rule out a melt structure dominated by either ion pairs or simple 1:1 complexes. Rather, systems wherein important factors include both cation distortion of the nitrate symmetry (site effect) and vibrational coupling of neighboring anions (correlation field effect) are definitely suggested. Thus, an assignment based on a perturbed orthorhombic lattice structure is presented which accounts very satisfactorily for all observed features. Order in the melts seems to be slightly greater in LiNO3 than for the other salts.

Status report on MHD electrical power generation–IAEA/ENEA International Liaison Group on MHD Electrical power generation

The present status of commercial large-scale MHD electrical power generation is reviewed in the light of information presented at the Third International Symposium on MHD Electrical Power Generation (Salzburg, 1966) and of subsequent developments. Research and development activities, and the state of evaluation of engineering and economic factors are assessed in respect of open-cycle MHD power plant, closed-cycle MHD power plant, and the associated electromagnet.The MHD power generator is attractive in that energy is extracted directly from that of the flow of working fluid. The generator itself is of simple static construction, thus permitting high maximum cycle temperature, high specific power output and potentially much larger unit size than may ultimately be achievable with turbomachinety. In principle, these features should offer increased thermal efficiency and reduced capital cost compared with conventional plant.In the ‘open-cycle’ MHD system electrical energy is extracted directly from the flow of a plasma formed by the seeded products of combustion of a hydrocarbon fuel. The ‘closed-cycle’ MHD system similarly employs a working fluid which may be a seeded inert gas (helium, neon, argon) or a pure alkali metal. Operation may be based on the gas turbine or Brayton cycle, or incorporate steam plant (for the lower range of temperature) based on the condensing or Rankine cycle. In the case of the open-cycle MHD system, installations are being constructed or already operating successfully with hundreds of MW thermal input and tens of MW electrical output, and substantial effort has been devoted to other aspects of the plant. It is concluded that a pilot-scale power station is technically feasible but that the economics of MHD steam plant are not fully established.Research and development towards the closed-cycle MHD system is at an earlier stage, and there are fundamental aspects of plasma behaviour relating to instabilities and the feasibility of utilizing magnetically-induced non-equilibrium ionization which have to be resolved. Engineering and economic evaluation of system concepts requires attention. Closed-cycle systems operated on a condensing or Rankine cycle with liquid-metal MHD generators are also at an early stage of development. There is as yet insufficient information on the performance of various liquid acceleration schemes and MHD generators to allow assessment for commercial plant, although for special applications (e.g. space vehicle power systems) the concept is attractive.Superconducting electromagnets are technically and economically necessary for MHD power systems which, in almost all respects, derive benefit from operation at higher magnetic fields. Field levels of 5 – 7 T are attainable at present, and there are good prospects for further development to large size and higher fields.

Ground-State Energy of an Electron Gas in a Lattice of Positive Ions—Cohesive Energy of Alkali Metals and Alloys

Our previous calculations for the ground-state energy of a high-density electron gas in a lattice of positive point ions are extended to lattices of real ions with a core of bound electrons. The core effect on the electron gas is taken into account by the method of pseudopotentials put forward by Cohen and Heine. Both cases of lattices covered with one species and two species of ions are discussed. The present model should give a rough picture of metals and alloys and was subsequently applied to alkali metals for which rather simple pseudopotentials have been proposed by Cohen. Numerical results obtained for the cohesion energy of the electron gas and the lattice of ions agree fairly well with the data of pure alkali metals. The heats of mixing of alkali metals have also been calculated with this model: They are very small and agree roughly with the order of magnitude of the experimental data.

Mass Spectrometric Study of Positive-Ion Emission from Iron Oxide Catalysts Containing Alkali Metals

Samples of iron oxide catalysts containing small amounts of added alkali-metal oxides were mounted in the ionization chamber of a mass spectrometer equipped with a grid. The evaporation products obtained under various conditions were investigated. Alkali atom emission, the intensity of which decayed rapidly, and alkali ion emission were measured. The ratio of potassium ion emission to sodium ion emission from samples containing the two alkalis decreased markedly with heating time. The magnitude of the experimentally derived apparent work functions for evaporation of the alkali ions from the iron oxide catalysts agreed with those computed for the evaporation of the same ions from pure alkali metals.

Solubility of alkali metal carboxylates in hydrocarbons

The solubility of alkali metal, mainly lithium, carboxylates in n-heptane, isooctane, or benzene has been investigated. Regardless of structure variations the solubility of pure aliphatic or alicyclic alkali metal carboxylates was found to be below 10 −4 mole/l. at 27.0°C. It is shown that erroneously high results can be obtained by ( a) the presence of trace amounts of impurities, ( b) incomplete separation of the liquid and solid phases, or ( c) the instability of the colloidal dispersion. The solubility of alkali metal naphthenates or arylstearates is related to the fact that they are mixtures. The exceedingly low solubility of pure alkali metal carboxylates is explained by their inability to form stable micelles in hydrocarbon media.