N. B. Mikheev

Morphological Memory of Dispersed Solid Phases

A formalism of the morphological memory of disperse systems was formulated. Using CsI as an example, it was established that a dispersed solid phase formed by vapor condensation stores information on the nucleation, growth, and aggregation of its particles for a long time. Therefore, the determination of distribution functions of properties and the texture of particles at the end of the condensation allows us to qualitatively describe the genesis of the phase. Basic equations and conditions relating properties of crystals of the dispersed phase, which are necessary for the extraction of information on the genesis from data on final distribution functions of crystal states, were considered.

Physicochemical properties of uranium in lower oxidation states

Data on the properties of U in lower oxidation states, published between 1988 to 2005, are summarized. In this period, the interest in the chemistry of trivalent and bivalent uranium, especially in its coordination and organometallic chemistry, considerably increased. Possible applications of trivalent uranium are outlined.

Lanthanides and actinides among other groups of elements of the periodic table

The extent to which actinides (An) are similar to other elements of the periodic table is discussed. Actinides show certain similarity with transition metals in trends in variation of the stability of the highest and lowest oxidation states with increasing atomic number. Similarity between elements of the first half of the lanthanide (Ln) family and those of the second half of the An family is demonstrated. In the lowest oxidation states, An and Ln are analogs of alkali and alkaline-earth elements, and in the tetravalent state they start to exhibit noticeable similarity with d elements. The formation of Pu(VIII) is suggested on the basis of essentially similar volatility of oxides ot Os and Ru with that of Pu. Of particular interest are bivalent An and Ln ions with one d electron. Being analogs of bivalent elements, they form various types of clusters.

Lower Oxidation States of f Elements: III. Properties of Low-Valence Lanthanide and Actinide Compounds in the Solid State and in Various Solvents

Properties of low-valence f-element compounds in the solid state and in protic, aprotic, and mixed solvents are discussed, including the solubility of low-valence f-element compounds, hydration of Ln2+ and An2+, and their complexation in aqueous and organic solutions with various anions (I−, Br−, Cl−, ClO4−, BF4−, BPh4− and polycyclic crown ethers.

Lower Oxidation States of f Elements: I. Preparation and Identification of Actinides and Lanthanides in Lower Oxidation States

Studies on the title subject, published mainly in the second half of the XX century and made both with macroamounts of lanthanides (Ln) and actinides (An) and with micro- and ultramicroamounts of radionuclides of these elements, are considered. Procedures for preparing f elements in lower oxidation states in solutions, melts, and solid matrices and methods for identifying these states (electrochemistry, spectrometry, high-temperature extraction, cocrystallization, etc.) are discussed.

Metal-Containing Zeolites as Sorbents for Localization of Radioiodine and CsI Aerosols from Vapor-Air and Aqueous Phases

New sorbents for efficient sorption of radioiodine and radiocesium from the vapor-gas phase and aqueous solutions were prepared by treatment of Cu+- and Ag+-substituted NaX and NaA zeolites with acetylene in aqueous solution. The distribution factor Kd of radioiodine and radiocesium between the modified sorbents and aqueous solutions is higher than 103-104 ml g-1. Decontamination factor of the vapor-gas phase with respect to radioiodine and 137CsI aerosols exceeds 102-103 and 103, respectively. The sorption properties of the modified sorbents in both aqueous solutions and the vapor-gas phase are better than those of the initial sorbents. However, localization of radioiodine from the vapor-gas phase with the Cu+-containing sorbents is less efficient than with the Ag+-containing zeolites. At the same time, in aqueous solutions the sorption capacity of the Cu+-containing sorbents for radioiodine is appreciably higher than that of the Ag+-containing sorbents. The sorption properties of the modified sorbents were studied as influenced by various factors. Paracomplexes of univalent copper and silver with C2H2, H2O, and anions present in the solution are probably formed during modification of the metal-containing zeolites. The dependence of Kd of radioiodine on the metal concentration in the sorbent, the free pore volume of the sorbent, and the anion nature was revealed.

Preservation of the charge of radioaerosols formed by condensation of supersaturated 137Cs131I vapor in the course of their bubbling through aqueous solution

Variation of the charge of radioaerosols formed by condensation of supersaturated 137Cs131I vapor, observed when the gas flow passes through an aqueous solution, was studied. The supersaturated 137Cs131I vapor was formed by evaporation of salt crystals from the metal surface heated to high temperatures owing to ohmic resistance. The radioactive aerosols preserve their charge even after bubbling through aqueous solutions, which allows using electric filters for localizing the aerosols.

The dynamics of solid substance formation in strongly supersaturated media

Proceeding from the idea of the isolation of a substance from a supersaturated medium as the nucleation, growth, and aggregation of substance particles, a kinetic equation for changes in the particle state distribution function corresponding to the experimental data was obtained. The equation satisfying the requirement of the conservation of the number of new phase particles was simplified to the Liouville, Fokker-Planck, Farkas, and Zel’dovich equations.

Basic and applied aspects of the chemistry of radioactive iodine in a gas medium

The results of studies in the field of gas-phase chemistry of radioactive iodine, published in the past 15 years, are systematized and analyzed. The prospects for applying these data to various fields of nuclear power engineering are assessed. Particular attention is given to localization of nanodispersed aerosols of radioactive iodine and its poorly sorbable organic compounds. The topicality of further studies in the field of radioactive iodine chemistry, aimed to solve problems related to accidents at nuclear power plants and plants for reprocessing of spent nuclear fuel, is demonstrated.

Cocrystallization processes in physicochemical studies of radioactive elements in various media

Cocrystallization processes widely occur in the nature and are used in chemical technology. In radiochemistry, they came into use since the end of XIX-beginning of XX century owing to studies by M. Curie, O. Hahn, V.G. Khlopin, and his disciples. They formulated the laws of isomorphous cocrystallization involving microamounts of radioactive elements. However, the formation of anomalous mixed crystals remained poorly understood. Major contribution to the development of this problem was made by A.N. Kirgintsev. Thanks to his studies and the subsequent studies made by other researchers, it became possible to make substantiated conclusions on the charges of ions of the cocrystallizing microcomponents. The use of cocrystallization processes allowed determination of the main physicochemical properties of actinides that are inaccessible in weighable amounts.