The initial stage of salt passivation of metals

A theoretical model of the nucleation of a passivating salt layer on the surface S of an anode-dissolving metal was developed. The layer is considered a new phase formed by the mechanism of heterogeneous nucleation, which serves as a related substrate for subsequent growth of the passivating layer. According to experiments, the surface S of real metals is inhomogeneous, that is, anode current density fluctuates on S. It is assumed that, at large current fluctuations, localized regions with volume ΔV _ϕ appear, in which the C _M and C _A concentrations of the M ^z+ and A ⁿ⁻ ions are increased. At fairly large current fluctuations, these concentrations can reach saturation. For this reason, the ΔV _ϕ regions are treated as mother phases, in which A _a M _m salt nuclei are formed with a certain probability. The formation of such ΔV _ϕ volumes and the kinetics of formation of nuclei in them, from which a passivating layer with a finite thickness is formed, are considered.     

Nitropyrazoles

A method of preparation of 5-amino-3,4-dinitropyrazole (1) from 3(5)-methyl-5(3)-nitro- and 3(5)-methyl-4,5(3)-dinitropyrazoles was developed, the key step of which was the Hofmann rearrengement of nitro- and dinitropyrazolecarboxamides. The protonation of 5-amino- 3,4-dinitropyrazole was studied by spectral methods (UV spectroscopy, NMR spectroscopy). In spite of low basicity of the amino group, compound 1 undergoes N-arylation, N-nitration, and annulation reactions with formation of dinitropyrazolo[5,1-a]pyrimidine derivatives and hitherto unknown dinitroimidazo[1,2-b]pyrazole derivatives. Diazotization of 1 leads to 5-diazo-3,4-dinitropyrazole (19), which exists in the form of the internal salt. Some reactions of this compound were studied and the formation of the corresponding 5-halogeno(azido)- 3,4-dinitropyrazoles under the action of the halide and azide ion was shown. Dinitropyrazolo- [5,1-c][1,2,4]triazine and 7-hydroxydinitro-4,7-dihydropyrazolo[5,1-c][1,2,4]triazine deriva- tives were obtained by the action of active methylene compounds on the betaine 19.     

Piezoelectric effect in ferroelectric liquid crystal: A review

The data in the literature and our results of studying the piezoelectric effect in ferroelectric liquid crystals are analyzed. The existing theories of this effect in liquid crystals are discussed. The parametric transformations of electromechanical oscillations in ferroelectric liquid crystals are considered.     

The role of the covalent interaction in the formation of the electronic structure of Au- and Cu-intercalated graphene on Ni(111)

A study is reported of the role played by covalent interaction in the coupling of graphene formed on Ni(111) to the Ni substrate and after intercalation of Au and Cu monolayers underneath the graphene. Covalent interaction of the graphene π states with d states of the underlying metal (Ni, Au, Cu) has been shown to bring about noticeable distortion of the dispersion relations of the graphene electronic π states in the region of crossing with d states, which can be described in terms of avoided-crossing effects and formation of bonding and antibonding d-π states. The overall graphene coupling to a substrate is mediated by the energy and occupation of the hybridized states involved. Because graphene formed directly on the Ni(111) surface has only bonding-type occupied states, the coupling to the substrate is very strong. Interaction with intercalated Au and Cu layers makes occupation of states of the antibonding and bonding types comparable, which translates into a weak resultant overall coupling of graphene to the substrate. As a result, after intercalation of Au atoms, the electronic structure becomes similar to that of quasi-free-standing graphene, with linear dispersion of π states at the K point of the Brillouin zone and the Dirac point localized close to the Fermi level. Intercalation of Cu atoms under the graphene monolayer results, besides generation of covalent interaction, in a slight charge transport, with a partial occupation of the previously unoccupied π* states and the Dirac point shifted by 0.35 eV toward increasing binding energy.     

Behavior of antiferromagnetic MnCoSi in a magnetic field under pressure

Experimental data on magnetization of the antiferromagnetic (AFM) polycrystalline samples in the temperature range of 20-300 K, for pressures of 2 kbar and in magnetic field of 300 kOe, are presented in the paper. In the fields of 250 kOe, the magnetization curve demonstrates a jump explained by exchange-interaction sign change. In the region of 50-70 kOe, on the differential susceptibility versus magnetic field curve, there is a break of the 2nd order corresponding to the anomalous behavior of the magnetization. The obtained results were processed on the basis of the phenomenological Landau theory. It is shown that the ferromagnetic vector occurrence is forced during the formation of AFM spiral structure. The behavior of thermodynamic potential factors has been determined. Three more anomalies have been revealed and explained by a jump-like magnetization change of the Co-subsystem.     

Hardy-type inequalities on the cones of monotone functions

We establish necessary and sufficient conditions for various Hardy-type inequalities on the cones of monotone functions.     

Properties of epoxy polymers cured with polyoxypropylene diamine

The results of investigations of epoxy polymers cured with polyoxypropylene diamine D-230 depending on the molecular weight of epoxide oligomer, the content of the curing agent, active diluents, and plasticizers are presented. It is shown that epoxy polymers cured with polyoxypropylene diamine are characterized by a rather high complex of physicomechanical and adhesion properties.     

(4+2) Dimerization of imides of arylmaleic acids in the presence of the 3,5-dimethyl-1H-pyrazole and 2,6-lutidine

Imides of arylmaleic acids in the presence of 3,5-dimethyl-1H-pyrazole underwent (4+2) dimerization under heating in chlorobenzene within 24 h to afford 1,2,3,3a,3b,4,5,6,6a,10b-decahydrobenzo[e]pyrrolo[3,4-g]isoindole-1,3,4,6-tetraones in good yields. It was established that during the heating of imides of arylmaleic acid in 2,6-lutidine at 100 °C the (4+2) dimerization products containing a lutidine fragment are obtained.