Kinetics of Lead Sulfide Precipitation from Citrate Solutions of Thiourea

The kinetics of lead sulfide precipitation with thiourea from alkaline solutions at 30, 40, and 50°C under conditions of spontaneous nucleation of the solid phase in the solution bulk was studied.     

Study of wind characteristics at heights of 200 to 800 meters using a decimeter sodar

The results of the experiment carried out in July–August 1997 using a two-position sodar are reported. Different types of intensity and spectrum variations of scattered acoustic signals have been obtained. The possibilities of using the sodar for the study of atmospheric turbulence and search of signals caused by “Fresnel” scattering from “plane” irregularities are discussed. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 7, pp. 841–848, July, 1998.     

Kinetics of Cadmium Sulfide Precipitation from Aqueous Thiourea Solutions

Kinetics of cadmium sulfide precipitation with thiourea from solutions of cadmium(II) ammine complexes under conditions of spontaneous nucleation of the solid phase in the bulk of solution was studied.     

Synthesis and some physicochemical properties of the carbazine acid silyl esters

Structure of the dimethylcarbazine acid trimethylsilyl ether and pyrolysis of its derivative, the trimethylsilyl ester of N,N-dimethyl-N′-trimethylsilylcarbazine acid, were studied by the metods of X-ray diffraction and gas chromatography/mass spectrometry. The presence of the bifurcated hydrogen bonds between the trimethylsilyl dimethylcarbazinate molecules was detected. It was revealed why impossible to obtain dimethylaminoisocyanate even by the low-temperature pyrolysis.     

Molecular dynamics simulation of surface segregation in a (110) B2-NiAl thin film

Surface segregation in (110) B2-NiAl film approximately 3 nm thick is investigated by using molecular dynamics simulation with a reliable embedded-atom potential. The simulation is performed for the stoichiometric composition at a temperature of 1500 K, just below the melting temperature of the film model. It is found that the (110) surface is structurally stable but develops adatoms, vacancies and antisites. The coverage of an adatom layer is estimated to be ～0.07 ML (monatomic layers) and it contains on average ～95% of Al atoms. The top (surface) and second (subsurface) layers of the (110) surface is the most enriched in Ni relative to the bulk composition. These layers contain on average ～51% of Ni atoms. The Ni fraction in the third and forth layers of the film is estimated as ～50.5%. The deeper layers have essentially the bulk composition. Vacancies in the film model are found only on the Ni sublattice. The vacancy concentration on the Ni sublattice in the top layer is ～7.5%. The second layer almost does not contain vacancies. The next layers have essentially the constant bulk vacancy composition which can be estimated as ～1.3-1.4%.     

Mass spectrometric study of the overheated vapor over lanthanide dipivaloylmethanates Ln(thd)<Subscript>3</Subscript> (Ln = Nd,Er, Yb,Lu)

A mass spectrometric study of the overheated vapor over neodymium, erbium, ytterbium, and lutetium dipivaloylmethanates has been carried out. The mass spectra of these compounds depend significantly on the degree of overheating. This fact can be interpreted in terms of the variation of the concentration and chemical composition of metal-containing molecular species with vapor temperature. As the vapor temperature is raised from 200 to 700°C, the intensity of the molecular ion [M(thd)₃]⁺ decreases relative to the [M(thd)₂]⁺ ion intensity by approximately one order of magnitude for M = Er, Yb, and Lu and by two orders of magnitude for M = Nd. This finding is evidence in favor of the thermal decomposition of the lanthanide tris(dipivaloylmethanates) occurring via a two-step mechanism initially yielding the M(thd)₂ radical.     

Tautomeric and conformational properties of dibenzoylmethane,C<Subscript>6</Subscript>H<Subscript>5</Subscript>–C(O)–CH<Subscript>2</Subscript>–C(O)–C<Subscript>6</Subscript>H<Subscript>5</Subscript>: gas-phase electron diffraction and quantum chemical study

Tautomeric and structural properties of dibenzoylmethane, C₆H₅–C(O)–CH₂–C(O)–C₆H₅, have been investigated by gas-phase electron diffraction (GED) and quantum chemical calculations (B3LYP and MP2 approximation with different basis sets up to cc-pVTZ). Analysis of GED intensities resulted in the presence of 100(5)% enol tautomer at 380(5) K. The enol ring possesses C _S symmetry with a strongly asymmetric hydrogen bond. The two phenyl rings are rotated with respect to the enol ring by 15.1(5.0) and 12.1(5.8)°. The experimental geometric parameters are reproduced very closely by the B3LYP/cc-pVTZ method.     

Experimental Ro-Vibrational Line Intensities for the v1 + v2 and v2 + v3 Bands of the D234S Molecule

Russian Physics Journal - The study of the absolute line intensities in the high-resolution spectrum of the D234S molecule in the range of 2300–2900 cm–1 has been carried out for the...     

Analysis of interdiffusion via isolated vacancies in strongly ionic crystals

In this paper, we analyse chemical interdiffusion in strongly ionic crystals for diffusion couples AY _m –BY _m , where A and B have the same charge numbers. We employ the exact sum rule given by Moleko and Allnatt relating the phenomenological coefficients for diffusion in the multicomponent random alloy via the agency of monovacancies. It is shown that the ratio of the intrinsic diffusivities can be expressed very simply in terms of the atom–vacancy exchange frequencies without correlation terms. For the case of an immobile anion sublattice and making use of a highly accurate diffusion kinetics theory due to Moleko et al., it is shown that the interdiffusivity is principally proportional only to the off-diagonal phenomenological coefficient relating the two cations.     

Interdiffusion in strongly ionic insulating compounds: The Nernst–Planck equation

In strongly ionic insulating materials, the Nernst–Planck Equation relates the interdiffusion coefficient of the cations (having the same charge) with the corresponding tracer diffusivities and the thermodynamic factor. In this paper, we explore the Nernst–Planck Equation for ionic ternary (quasi-binary) and ionic quaternary (quasi-ternary) systems using the diffusion kinetics formalisms of Darken [Trans. Am. Inst. Min. (Metall.) Eng. 175 184 (1948)], Manning [Phys. Rev. B 4 1111 (1971)] and Moleko, Allnatt and Allnatt [Phil. Mag. A 59 141 (1989)]. It is shown that for the binary system, the Darken and Manning formalisms both give the usual form of the Nernst–Planck Equation. However, the almost exact Moleko, Allnatt and Allnatt formalism (for randomly mixed systems) provides an additional correction factor analogous to the vacancy-wind factor in the well-known Darken–Manning Equation used in binary alloy systems. Nernst–Planck-type equations are also derived for strongly ionic insulating ternary systems and are found to behave similar to the binary case.