Dicyclopentadienyl complexes of titanium,niobium, and tungsten in the controlled synthesis of poly(methyl methacrylate)

Organometallic compounds Cp₂TiCl₂, (EtC₅H₄)₂NbCl₂, and (PrⁱC₅H₄)₂WCl₂ were assessed as additives that control polymer chain growth in the polymerization of methyl methacrylate. In the presence of compounds mentioned in amounts comparable with that of the initiator, a uniform process with no gel-effect occured and respective linear increase in the molecular weight of the polymer up to high degrees of the monomer conversion was observed.     

Preparation of isomeric 1,3- and 1,5- (o-phenylene)-hexamethylcyclotetrasiloxanes and investigation of their spectral characteristics

Workup of the mixture of products of pyrolysis of cyclotetrasiloxane (Me₂SiO)₂(MePhSiO)₂ yielded 1,3- (I) and 1,5-(o-phenylene)cyclosiloxane (II), the structures of which were established on the basis of data from their IR, PMR, and mass spectra.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 24–25, January, 1978.     

Specific features of the catalytic behavior of supported palladium nanoparticles in heterogeneous catalytic reactions

Specific features of the catalytic behavior of supported palladium nanoparticles were analyzed in terms of both the size of the particles and their interaction with the support. The influence of these factors on the activity and selectivity of palladium nanoparticles in carbon-carbon bond hydrogenolysis, hydrogenation of aromatic compounds, olefins, and acetylenes, hydrodechlorination, as well as complete oxidation of organic compounds was discussed. It was shown that the optimal nanoparticle size depends on the type of the reaction and also such factors as the nature of interaction between the nanoparticles and support, absorptivity of the substrates and catalytic reaction products, and electronic and crystal structure of the nanoparticles.     

Method for edge contour extraction of a scanning probe microscope image

A method for edge contour extraction of a scanning probe microscope image is proposed. This method is developed to process an image that has the large size irregularity and/or objects bound together. It is based on definition of the local minimum points of brightness data function and permits one to obtain the correct edge contour line. The advantages of the proposed method over traditional methods are demonstrated using model results. This method can be used to process different images.     

Effect of hydrogenation on the magnetic properties of the intermetallic compound Er2Fe14B with single-crystal and nanocrystalline structures

Hydrogenated single crystals Er₂Fe₁₄Bh _x with different hydrogen contents are grown and their magnetic properties are studied for the first time. It is established that both the Curie temperature and the temperature of the spin-reorientation phase transition increase with an increase in the hydrogen content. In the Er₂Fe₁₄B single crystal, the contributions of the rare-earth metal and iron sublattices to the magnetic anisotropy decrease upon hydrogenation. However, their compensation occurs at a temperature higher than that in the initial compound Er₂Fe₁₄B due to the enhancement of the Fe-Fe and R-Fe exchange interactions. The effect of hydrogenation on the magnetic characteristics of the Er₂Fe₁₄B compound with a nanocrystalline structure is investigated. It is revealed that the hydrogenation leads to an increase in the coercive force and the residual magnetization of these alloys.     

Magnetostriction and magnetization of the intermetallic compounds R Fe2 ? x Co x ( R = Tb, Dy, Er) with compensated magnetic anisotropy

The compounds Tb_0.35Dy_0.45Er_0.2Fe_{2 − x} Co _x (0 ≤ x ≤ 2) are synthesized in both polycrystalline and single-crystal states. The composition of the new multicomponent alloys with compensated magnetic anisotropy is calculated in the framework of the single-ion magnetic anisotropy model with allowance for the data on the temperature dependences of the magnetic anisotropy constants for RFe₂ single crystals. The synthesized compounds are characterized using metallographic, chemical, X-ray diffraction, and thermomagnetic methods. A combined analysis of the magnetic and magnetoelastic properties is also carried out. It is established that the high magnetostriction characteristics of the rare-earth intermetallic compounds Tb_0.35Dy_0.45Er_0.2Fe_{2 − x} Co _x with a structure of Laves phases are observed in the region of the spin-reorientational phase transition whose temperature can be varied by properly choosing the Co content. It is found that, in the room-temperature region, the magnetic susceptibility (dλ/dH) of the composition with x = 1.3 reaches levels in excess of the value of dλ/dH for terphenol D due to the compensation of magnetic anisotropy. Original Russian Text ? I.S. Tereshina, S.A. Nikitin, G.A. Politova, A.A. Opalenko, E.A. Tereshina, I.V. Telegina, 2009, published in Fizika Tverdogo Tela, 2009, Vol. 51, No. 1, pp. 85–90.     

Effect of hydrogenation on spin-reorientation phase transitions and magnetic anisotropy constants of RFe11Ti single crystals (R=Lu, Ho, and Er)

The magnetic anisotropy and spin-reorientation phase transitions in single crystals of the RFe₁₁Ti (R=Lu, Ho, and Er) compounds and their hydrides are investigated. Measurements are carried out on capacitance and torque magnetometers. The magnetic anisotropy constants K ₁ and K ₂ are determined by the mathematical processing of experimental magnetization curves in terms of the phenomenological theory of the anisotropic ferromagnet magnetization. It is demonstrated that the hydrogenation strongly affects the magnitude and the sign of magnetic anisotropy constants, as well as the spin-reorientation phase transitions. The hydrogenation of the HoFe₁₁Ti compound leads to the change in sign of the magnetic anisotropy constant K ₁. The inference is made that a change in the atomic volume and the axial ratio c/a cannot result in the observed effects. A change in the magnetic anisotropy constants upon hydrogenation is primarily due to the change in the interaction of the quadrupole moment of a 4f electron subshell of rare-earth ions with surrounding ions of the crystal lattice and also with valence and conduction electrons.     

Hydrolysis of Chloro(silyl)olefins in Neutral and Acidic Media

Action of water on chloro[chloro(alkoxy)silyl]olefins with various number of chlorines in the unsaturated moiety was studied in acidic and neutral media. Linear and cyclic oligosiloxanes with unsaturated chlorine-containing groups were obtained. Correlation between the hydrolytic stability of the Si-Csp ² bond and the structure of the starting chlorosilylolefin was explored.