G. Mamantov

Reversible deposition of metals on solid electrodes by voltammetry with linearly varying potential

Abstract It has been shown by extending the treatment of Berzins and Delahay that for the reversible deposition of metals on solid electrodes by voltammetry with linearly varying potential, the plot of log (ip — i)vs. E approaches linearity over the approximate current range 0.5–0.9-ip the slope, being 2.2 nF/RT. The experimental data for the reduction of Ag(I) in i M KNO3 at silver and pyrolytic graphite electrodes, the reduction of Fe(II) in molten LiF—BeF2 (66-34 mole%) and LiF—NaF—KF (46.5-11.5-42 mole%) at 500°, and Ni(II) in LiF—NaF—KF (46.5-11.5-42 mole%) at pyrolytic graphite electrodes, agreed satisfactorily with the theory.

Raman spectra of aluminum fluoride containing melts and the ionic equilibrium in molten cryolite type mixtures

The structure of molten aluminum fluoride−alkali fluoride mixtures has been investigated by Raman spectroscopy at 700−900°C using a captive liquid windowless cell. Changes in spectra with temperature and melt composition reflect an equilibrium between the species AlF4− and AlF63−. Complete spectrum of the AlF63− was obtained confirming an octahedral coordination; the frequencies of the ν1, ν2, and ν5 vibrations were found to be 555, 390, and 345 cm−1, respectively. A strong cation effect on the bandwidth of the AlF63− ν1 band was observed when the cation is changed from Li+ to Cs+. This effect is believed to be due to a restriction of the rotational mobility of the anion in the presence of a smaller cation. Quantitative analysis of the intensity ratios of the AlF4− and AlF63− ν1 bands as a function of the composition of the melt permits the calculation of the stoichiometric dissociation constant K = XAlF4−XF−2/XAlF63−. An average value of 3±1×10−2 (concentration scale in mole fractions) was found at 780°C...

Photochemical transformation of pyrene and benzo(a)pyrene vapor-deposited on eight coal stack ashes

The photochemical decomposition of pyrene and benzo(a)pyrene, as adsorbates deposited from the vapor phase, has been examined on eight coal stack ashes of diverse origin and properties. Similar studies using alumina, silica gel, controlled-porosity glass, and graphite adsorbents also have been performed. Phototransformation of the adsorbates proceeds more slowly on any of the ash substrates than on alumina, silica, or glass surfaces. Those ashes relatively high in carbon and/or iron content are especially effective at suppressing photodegradation of adsorbed pyrene or benzo(a)pyrene. This relationship appears, at least in part, to be associated with the relatively dark colors of those ashes. The apparent acidity of ash surfaces does not appear to be related to the rate of phototransformation of adsorbed polycyclic aromatic hydrocarbons. 40 references, 1 figure, 5 tables.

Film formation on pyrolytic graphite electrodes

It has been shown that electrochemical or chemical oxidation with a strong oxidant, such as Ce(IV), results in the formation of a film on the surface of pyrolytic graphite. The film produced anodically differs electrochemically from the film produced chemically, although in both cases reduction of the film is observed at ≈ +.5 V vs. the saturated calomel electrode. The reduction of the film apparently proceeds irreversibly. Attempts to study the film by high voltage electron diffraction were unsuccessful. The nature of the film has not been determined.

Analytical Applications of Matrix Isolation Fourier Transform Infrared Spectroscopy

A review of analytical applications of matrix isolation Fourier transform infrared spectroscopy is presented. The characteristics of matrix isolation spectroscopy are discussed along with practical techniques for obtaining analytically useful results. A few studies relating to matrix isolation used in conjunction with Raman and conventional IR spectroscopy are reviewed. The majority of analytical applications of matrix isolation vibrational spectroscopy has entailed the use of FT-IR techniques. Qualitative and quantitative results from a number of sample types are presented. The coupling of matrix isolation vibrational spectroscopy with chromatographic separations is reviewed.

Chlorine–Fluorine System at Low Temperatures: Characterization of the ClF2 Radical

Near‐ultraviolet photolysis of matrix (N2 or Ar)‐isolated chlorine trifluoride (ClF3) or mixtures of chlorine monofluoride (ClF) and fluorine at 16°K results in the production of a new infrared absorption at ∼u2009575 cm−1. This band is assigned to the asymmetric stretching vibration of the chlorine difluoride (ClF2) free radical on the basis of the chemistry of the system, temperature dependence of the band intensity, and results of isotopic labeling. Much weaker bands, assigned to the symmetric stretching vibration and to the bending motion, are observed at 536 and 242 cm−1, respectively. The apex angle and force constants are calculated from the data.

A Simple Raman Cell and Furnace Usable at Temperatures Higher than 1000° for Corrosive Melts

The two basic requirements for a sample container suitable for obtaining Raman spectra of corrosive melts are that the cell be optically transparent and inert to chemical attack by the melt. Several cell designs have been proposed in the past few years based on uv-visible spectroscopy experience. Two designs have been used for molten fluorides: a windowless cell in which the liquid level is maintained by its surface tension and a graphite cell with diamond windows to resist the attack by molten fluorides.

Practical Aspects of Rapid Scanning Fourier Transform Time-Resolved Infrared Spectroscopy:

The results of experiments designed to study the infrared spectra of transient species produced by ultraviolet photolysis of acetaldehyde are reported and analyzed. Spectra obtained in similar work [A. W. Mantz, Appl. Opt. 17, 1347 (1978)] are critically reinterpreted. The evidence presented demonstrates that insufficient attention has been given to the necessary stringent control of experimental conditions. The consequences of poor control are described and a qualitative explanation is offered. This paper discusses, in particular, the production of spectral artifacts consisting of displaced (not folded) bands and their previous erroneous assignments. Other practical aspects of time resolved Fourier transform spectroscopy with a rapid scanning Michelson interferometer are outlined.

E.M.F. measurements on the nickel-nickel(II) couple in molten fluorides*†

Summary E.m.f. measurements on the concentration cells Ni/Ni(II) ( a 1 =constant) ‖ BN sheath ‖ Ni(II) ( a 2 )|Ni in molten LiF−NaF−KF (42.0−11.5−46.5 mole%) and LiF−BeF 2 −ZrF 4 (65.6−29.4−5.0 mole%) at ∼500° result in linear plots of e.m.f. vs . log X 2 (the mole fraction of Ni(II) in the bulk of the melt), and the slopes predicted from the Nernst equation. The measured e.m.f. values are stable. The Ni/Ni(II) couple, contained in a boron nitride sheath, is a useful reference electrode for fluoride melts.

Raman spectra of Al2O3 solutions in molten cryolite and other aluminum fluoride containing melts

Abstract Our experiments show that oxide concentrations as low as 2 mole % can be detected in aluminum fluoride melts by Raman spectroscopy. All new bands observed associated with the oxide were below 600 cm −1 (530, 460, 310, and 185 cm −1 ). The exact nature of the oxide species present in the melts has not been determined but species involving nonbridging Alue5f8O bonds have been eliminated from consideration in concentrated Al 2 O 3 solutions in aluminum fluoride containing melts.