Brown pigments based on perovskite structure of BiFeO3−δ

Light brown inorganic pigments based on BiFeO₃ doped by Sr²⁺ cations were prepared by a conventional solid-state reaction at high temperature. This study is focused on the synthesis of Bi_1?x Sr _x FeO_3?δ powders in a range of substitution (x = 0–0.35; with step size 0.05). The main role of strontium is to overcome the defects that come to exist during the evaporation of Bi over material preparation. The substitution of trivalent bismuth ions by divalent strontium ions results in oxygen deficiency in the lattice, which was proved by both thermogravimetric analysis and elemental analysis. The substitution has a positive effect on the thermal stability of samples. The thermal stability of BiFeO₃ is 1046 K, whereas the substitution of 20 mol% of Bi³⁺ by Sr²⁺ ions shifted it to 1403 K and powder with composition Bi_0.65Sr_0.35FeO_3?δ has a thermal stability that is higher than 1434 K. An increasing range of substitution is connected with the change in the pigment color from reddish-brown to orange-brown and back to reddish-brown. The Bi_0.85Sr_0.15FeO_3?δ pigment prepared by calcination at 1273 K offers the most interesting color properties (L* = 45.57; a* = 20.38; b* = 26.23).

     

Determination of phosphorus traces in platinum alloys by two-phase isotope exchange

The method of ZEMAN and KRATZER for the determination of phosphorus traces by means of two-phase isotope exchange was modified for the determination of phosphorus in pure platinum or pure platinum alloys. It was found that Pt, Rh, Ag, and As do not interfere with the determination. Among the elements usually present in platinum metal or platinum alloys, only gold interferes. It was removed by extraction from 7M HCl by MIBK and AmOAc. Hydrochloric acid also interferes but it can be removed by evaporation. The analytical procedure is given for the solution obtained by pressure decomposition of the sample (0.5 g) in a steel bomb with PTFE inlay. It is possible to determine >2 ppm P (approximate error −10%). Using a calibration dependence instead of the well known equation for isotope exchange, the content of P in the standard solution labelled with³²P need not be known.     

Über die Struktur und die Eigenschaften synthetischer Montmorillonite

Zusammenfassung Natürlich vorkommende Montmorillonite sind als Objekt von Strukturuntersuchungen wenig geeignet, da deren Zusammensetzung sehr veränderlich ist. Es wurden daher hydrothermal Mg- und Na-Montmorillonite dargestellt, deren chemischer Aufbau innerhalb weiter Grenzen variiert werden konnte. An solchen definierten Montmorilloniten wurden die Austauschkapazitäten, die Röntgenstruktur, das thermische Verhalten und die Menge des tetraedrisch koordinierten Aluminiums bestimmt. Die experimentell erhaltenen Resultate stimmen mit der nachC. S. Ross undS. B. Hendricks berechnetenHofmann-Endell-Wilm-Struktur der Montmorillonite gut überein.Mit 13 Abbildungen.In gekürzter Form vorgetragen anläßlich des XIII. Internat. Kongresses für Chemie in Stockholm, 1953.     

V2-dependence of centrifugal constants of H2O molecules in the Morse oscillator model

It is shown in this paper that the centrifugal constantsC ^l (t) calculated in the Morse, oscillator model for the sequence from the operator H _red ^(t) , which is used in processing the rotational levels of the H₂O molecule, are linked by recurrence relations, which enables H _z ^(t) –H _z ^(O) to be given in closed form.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 56–58, October, 1982.     

Using BBGKY hierarchies to study the effect of the local field on the rate of radiative relaxation of quantum systems in a dielectric medium

We consider a model of atomic radiators in a dielectric medium and its optical characteristics. In the framework of the microscopic approach and the Bogolyubov-Born-Green-Kirkwood-Yvon method, we obtain a chain of coupled equations for reduced density matrices and correlation operators of atomic particles and modes of a quantized field. We derive a closed system of equations describing the evolution of radiators in the model medium under the action of external radiation. We calculate the effective spontaneous relaxation rate in the presence of the local field produced by the medium. For the first time, we demonstrate the relation between micro and macro approaches to the solution of the problem involving a change in the spontaneous radiation rate in the medium.     

Two-dimensional random walk and loop factor in helix-coil transition theory of DNA

Theory of helix-coil transition in double-stranded homopolypeptides is considered. The theory develops an approach, which takes into account fundamental properties of the system (loop formation under complementary binding). Calculations are done in the framework of random walk theory. Partition function of the system is obtained in terms of arbitrary and first returns. It is shown that the loop factor of the theory has a power law behavior depending on the length of the chain.