Bogdan Baranowski

Absorption and desorption of hydrogen in manganese and manganese-nickel alloys in high pressure conditions. Formation of manganese hydride☆

Abstract Extensive work has been carried out to obtain a stoichiometric manganese hydride using a high pressure hydrogen technique. Because of difficulties in obtaining the hydride at room temperature, the procedure previously applied to investigate the possibility of the formation of platinum, iron, and rhodium hydrides has been used. A series of NiMn alloys, starting from the pure nickel, which forms a hydride under well-defined thermodynamic conditions, has been investigated at 298 K with regard to the conditions of the alloy hydride formation. The miscibility gap in hydrogen-alloy systems at 298 K occurred only in alloys up to about 18 at.% manganese; at higher manganese contents the hydrogen was present only in the form of solid solution. The standard free energies of formation have clearly indicated the possibility of the formation of a pure manganese hydride under hydrogen pressures of 103−104 bar. A non-stoichiometric manganese hydride has been obtained at 577 K and under about 8 kbar: X-ray analysis indicated a h.c.p. arrangement of metal atoms in the hydride unit cell and with lattice parameters: a = 2.692 A ± 0.002, c = 4.361 A ± 0.002 . Mass-spectrometric analysis of hydrogen concentration gave a H/Mn atomic ratio of 0.82.

The influence of hydrogen absorption on the electrical resistance and thermopower of some PdSibased metallic glasses

Abstract The electrical resistance and thermopower of amorphous Pd 83 Si 17 , Pd 79 X 4 Si 17 and Pd 73 X 10 Si 17 ( X = Ag , Co , Cr , Cu , Fe , Ni ) were measured as functions of the hydrogen pressure in the range 1 bar–20 kbar. The electrical resistance of some of these alloys was measured as a function of the deuterium pressure in the range 1 bar–0.8 kbar. A distinct isotope effect was found. In most cases the absolute thermoelectric power is a linear function of the logarithm of hydrogen fugacity and thus is a linear function of the chemical potential of gaseous hydrogen. The electrical resistance exhibits a non-linear dependence on the chemical potential of hydrogen or deuterium in all cases. No discontinuities were observed in either property in the total pressure range. Hysteresis was observed during absorption and desorption, with increasing values at higher pressures. This suggests local restructuring in the glassy matrix as a result of the presence of hydrogen atoms. No evidence of saturation behaviour was obtained. All the measurements were carried out at 25 °C.

Investigation of some metal-hydrogen systems in the high pressure region

Abstract The advantages and possible applications of the high pressure technique in investigations of metal-hydrogen systems are briefly discussed. Recent results obtained in metallic glasses, Ni-Cr alloy hydrides and pure aluminium are reviewed. The activation volume for hydrogen (deuterium) diffusion in palladium hydrides (deutendes) with high hydrogen (deuterium) concentrations is evaluated.

Electrochemical formation of nickel hydride in alkaline solutions

The electrochemical formation of nickel hydride in alkaline solutions is discussed and compared with known results in acid solutions and investigations in high pressure electrolysis. It is supposed that probably surface or subsurface hydrides are formed in alkaline solutions, instead of the bulk, three-dimensional hydride. The importance of electrochemical investigations in this respect is stressed, but a warning is expressed for overinterpretations of the equivalence between the overvoltage and the effective thermodynamic activity on the electrode surfaces considered.

Pressure dependence of phase transitions in CsHSO4 studied with differential scanning calorimetry

The pressure dependence of three solid-solid and solid-liquid phase transitions in CsHSO4 has been investigated with differential scanning calorimetry at pressures up to 0.9 GPa with gaseous argon as the pressure-transmitting medium. The transitions that at ambient pressure occur at 333 K and 375 K seem to coincide at a pressure of about 0.15 MPa and probably exhibit above 0.1 GPa a solid-solid critical point. The ΔV value of the phase transition that occurs at 333 K (at ambient pressure) is calculated from the measured ΔH values and the constant dT/dp slope and is compared with rontgenographic determinations. The phase transition that occurs at 415 K (at ambient pressure) exhibits a linear temperature increase up to about 0.55 GPa and a flat maximum at about 0.6 GPa. The melting curve was determined up to 0.7 GPa and is described by Simons equation.

Search for “cold-fusion” in some MeD systems at high pressures of gaseous deuterium

Abstract Metallic palladium and nickel were treated with gaseous deuterium at 298 K to pressures of 3.1 GPa and 1.0 GPa respectively. The high concentrated deuterides did not exhibit, at long time equilibrium as well as in dynamic conditions, evidence of neutron emission nor evolution of heat due to possible “cold fusion”. The volume concentrations of deuterium definitely exceeded those achieved by electrolytic charging. Electrical resistance measurements of palladium deuteride up to 3.1 GPa of gaseous deuterium indicated a further uptake of deuterium above the estimated stoichiometry of octahedral vacancies. A partial filling up of tetrahedral vacancies probably takes place. Electrolytic charging in high pressures of gaseous deuterium did not improve the negative observations above. Thus the observations of Fleischmann and Pons are not confirmed at higher volume concentrations of deuterium in the palladium and nickel lattice as well in equilibrium as in dynamic conditions (phase transitions, high pressure electrolysis).

Electrical resistance of some alkaline earth metal hydrides and alkali metal aluminium hydrides and borohydrides under high pressure

Abstract The electrical resistances of alkaline earth metal hydrides (CaH2, SrH2 and BaH2) and alkali metal aluminium hydrides and borohydrides (LiBH4, NaBH4, RbBH4 and LiAlH4) were measured to 16 kHz in a Bridgman anvil device at room temperature at pressures up to 140 kbar using pressed powdered samples. A more or less continuous decrease in the electrical resistance as a function of pressure was observed in all alkaline earth hydrides. A similar behaviour is exhibited by LiAlH4. Contrary to this behaviour, the alkali metal borohydrides show a minimum in the electrical resistance in the low pressure range and a further increase at higher pressures. The steepness of this increase in LiBH4 and NaBH4 suggests a phase transition in the pressure range between 20 and 30 kbar.

Pressure dependence of high temperature phase transitions in solid CsH2PO4 and RbH2PO4

Temperatures and enthalpies of phase transitions have been determined by differential scanning calorimetry (DSC) for CsH2PO4 and RbH2PO4 in the pressure range up to 1 GPa and 0.75 GPa, respectively. For temperatures between ambient and 400 K the cesium salt has two monoclinic phases at normal pressure, while the rubidium salt has one tetragonal and two monoclinic phases. For both salts the transition between monoclinic phases is reversible, although very sluggish for cooling. Adsorbed water has an influence on the reversibility of the transition between tetragonal and monoclinic RbH2PO4. For CsH2PO4 the transition temperature is 380 ± 2 K at normal pressure and about 440 K at 1 GPa, and the transition enthalpy decreases when the pressure is increased. For RbH2PO4 the temperature of the structural transition increases from 352 ± 3 K at normal pressure to about 370 K at 0.75 GPa, while the enthalpy decreases. The transition between monoclinic phases (380 ± 3 K at normal pressure) appears to have a tricritical point at about 0.15 GPa and 374 K, where, the enthalpy approaches zero while the gradient dT/dp has a sharp change. An alternative interpretation would be a triple point, but this is excluded since no evidence of a similar behaviour is noticed for the transition line of the lower transition. A brief comparison is made of the results for the two dihydrogen phosphates with what is reported in the literature concerning RbD2PO4.

High pressure X-ray diffraction study of copper hydride at room temperature

Abstract High pressure X-ray studies on CuH up to 23 GPa have been performed at room temperature using a gasketed diamond anvil cell. The experimental data on the molar volume of CuH as a function of pressure have been fitted to Murnaghans equation of state giving a bulk modulus: B0 = 72.5±2 GPa and B0 = 2.7 ± 0.3. By comparison with the equation of state for pure copper the effective additive volume of hydrogen has been evaluated as a function of pressure. It decreases from 3.2 cm3/mol H, at ambient pressure reaching a flattening value of 1.7cm3hol H at about 60 GPa. This suggests a continuous transition of CuH from ionic or covalent character at normal pressure to metallic hydride behavior at high pressure

Hydride Formation at high Hydrogen Pressure

The transition from low concentrated solutions of hydrogen in metals to hydride phases is treated from the point of view of the thermodynamic stability condition. The necessity for an increase of the hydrogen concentration in the metallic matrix is exposed. The available methods for creation of active hydrogen are reviewed. The simplicity of various kinetic procedures is outlined. The preference of the high pressure equilibrium method is clearly demonstrated. Recently used high pressure devices are shortly described whereby the limitations and difficulties are discussed. Properties possible to be directly investigated “in situ” conditions are enumerated. Examples of hydrides requiring high pressure of gaseous hydrogen for formation under equilibrium conditions are given. Transition metals like nickel, chromium, cobalt, manganese, molybdenium and rhodium as well as their alloys are mentioned. Some secondary properties possible to be measured are described. Conclusions and further perspectives of the high pressure technique are discussed.