Low-valent Ions Research Articles

Stimulation of rare metals dismutation reactions in chloride melts by F-ion

Transition elements of IV and V groups have tendency to form the low-valent ions in chioride melts which determines the instability of redox equilibria in these media used for inogranic synthesis and rare metals electrodeposition. We have estabiished that injection of a stronger ligand, e.g. fluoride-ion, into chloride melts containing Ti, Zr, Hf, Nb, Ta in a divalent state is stimulating the dismutation reaction: mMe n+→-nMe m+ + Me (where m>n) at the expense of formation of stable fluoride complexes. The stoichiometry of substitution reaction when chlorine is being substituted by fluorine in ion shells of transition metal central atoms, have been determined by linear-sweep voltametry and amperometric titration methods: 3Me Cl 2 + 12F − = 2Me F 3− 6 + Me + 6Cl − (for Ti). 2Me Cl 2 + 6F − = Me F 2− 6 + Me + 4Cl − (for Zr, Hf, Nb). 5Me Cl 2 + 14F − = 2Me F 2− 7 + 3Me + 10Cl − (for Ta) Formation of the high oxidation state fluoride complexes in the chloride-fluoride melt is typicai for zirconium, hafnium and tantalum as the low- and medium-valtent complexes in these cases are not thermodynamicalIy stabie. The situation is inverse to titanium and niobium. The equilibrium of dismutation reactions is shifted to the right.

EPR study of osmium species derived from Os 3(CO) 12 clusters supported on CeO 2 and ThO 2

High-valence osmium ions (Os 5+ or Os 7+) were stabilized on CeO 2 and ThO 2, when the initially impregnated cluster Os 3(CO) 12 was decomposed under oxidizing conditions. This is in contrast to the formation of low-valence ions (Os 1+ and Os 3+) on Al 2O 3. The presence of osmium on CeO 2 and ThO 2 presumably modified their redox properties and created new centers for O 2 − radical anion localization.

Optical study of hydrogen diffusion in yttrium iron garnet

Hydrogen diffusion in magnetic garnets is of interest in connection with both H+ ion implantation in bubble films and the proposed application to high-temperature chemical sensors. We have investigated hydrogen diffusion in several pure and doped YIG samples, using optical absorption and magnetic circular dichroism as probes. Differently from the previously reported cases of F− ions and oxygen vacancies, H+ ions are found to diffuse in YIG not obeying the classical diffusion equation. At constant temperature, simple exponential time behaviors are observed, and the time constants are much shorter for inward than for outward diffusion. These facts indicate that a major role is played by surface effects. H+ diffusion in YIG is accompanied by neither additional absorption nor dichroism at wavelengths λ>1.1 μm, so that charge compensation must involve centers of very different character, and more strongly bound, than Fe2+ induced by tetravalent ion dopings. In Ca2+- and Pb2+-doped YIG, besides the absorption peak due to the OH− stretching, a broad peak at λ=3.6 μm is found, similar to that previously reported for YIG(Na): the interaction of the OH− group with dodecahedral low valence ions is thus apparent. For T≤100 K, additional absorption structures arise at λ=3.15 μm indicating the formation of new equilibrium states for the H+ ion.

Effect of strong metal–support interaction in the case of nickel supported on a silica surface containing titanium ions

The properties (Ni + Ti)–SiO2 catalysts, obtained by anchoring Ni(π-C3H5)2 on silica modified by low-valent titanium ions, were shown to be similar to those of Ni-TiO2 in the hydrogenation of CO; this result is evidence of the direct interaction of metallic nickel particles with low-valent ions of titanium, resulting from the phenomenon of ‘strong metal–support interaction.’

Surface conductance of silica in electrolyte solutions

Three kinds of silica samples were prepared by treating Aerosil at different temperatures, being used for the measurements of electrokinetic potential by means of streaming potential method and for those of surface conductance in solutions of various kinds of electrolytes. The results obtained indicate that both the surface conductance and surface charge density are strongly affected in a similar way by the type of electrolyte used, being larger in a solution containing higher valent ions than in a solution containing lower valent ions. Furthermore, the experimental values of surface conductance were exceedingly higher than the calculated ones by applying Bikerman's theory. These facts give evidence that the surface conductance is caused by ion transfer not only in the diffuse double layer but also in the fixed double layer. It was also found that the surface roughness is responsible for the values of electrokinetic potential, but has no effect on the surface conductance.

Surface conductance of metal oxides in electrolyte solutions

Three kinds of metal oxides, Al 2O 3, Cr 2O 3 and Fe 2O 3, all of which have the same crystal form, were used in powder form for the investigation of surface conductance in electrolyte solutions. The results obtained demonstrate that the surface conductance is remarkably affected by the type of electrolyte used, being larger in a solution containing polyvalent ions than in a solution containing lower valent ions. The surface charge density calculated by introducing the ζ potential data into the Gouy—Chapman equation changes with the type of electrolyte similarly to the surface conductance. This suggests that the surface conductance originates from ion transfer not only in the diffuse double layer but also in the Stern layer. The activation energy of surface conductance is larger with larger adsorbed ions, and smaller with smaller adsorbed ions, compared to that of bulk conductance.

Changes in b Dimension of Na–Montmorillonite with Interlayer Swelling

THE purpose of this letter is to point out an alternative explanation for the results published under this title by Low et al.1. Briefly, they found that when montmorillonite saturated in sodium is swollen in water, the lateral (b) dimension of the silicate layer increases as a function of water content, even at water thicknesses of 400 A or more. They ascribe these changes to strong (epitaxial) interaction between montmorillonite and water “which modifies their respective structures”. We propose that there is a solubility equilibrium between some component of the silicate layer (probably octahedral aluminium) and the interlayer water and that an increase in water content of the clay suspension favours further solution of this component. It is well known that substitution of octahedral Al3+ by lower-valent ions results in an increase in b (ref. 2) and also that such substitution occurs rapidly in the presence of hydrogen ion3,4. (Other possible mechanisms for changing the composition of the silicate layer have been considered in another context by Low himself3—slight hydrolysis of an Al-bentonite, or chemisorption of H+ into the silicate lattice.)

Seebeck Coefficient of Semiconducting Oxide Glasses

The Seebeck coefficient, α, of semiconducting glasses based on vanadium pentoxide can be calculated from a knowledge of the concentration ratio of the high and low valence ions. The concentration of vanadium ions in the glass and long-range order apparently have no effect on α. Semiconducting glasses based on iron oxide, however, are not amenable to the simple treatment presently developed.

Recombination of oxygen atoms on oxide surfaces. Part 3.—Catalytic activities of doped oxides

The recombination of oxygen atoms has been studied on the surfaces of pure and doped Fe2O3, NiO and ZnO at 300°K. Increasing p-typeness achieved by doping with lower valent ions, led in all cases to some increase in the recombination rate. Increasing n-typeness, caused by doping with higher valent ions, also produced an increase in activity relative to that of the pure parent oxide, which was most marked for Cr-doped NiO. A simple electrostatic approach was shown to account qualitatively for these observations.