Vol 42, No 3 (2016)

The cluster self-assembly of an icosahedral structure of intermetallic compound Sc₁₈B₂₃₈ (Pbam, oP514, V = 4078.8 Å3) is modeled. The cluster-precursor of the crystalline structure of Sc₁₈B₂₃₈ contains 156 boron atoms and consists of 13 icosahedra of (B₁₂)₁₃, as in the previously studied borides of YB₆₆. On the surface of the cluster-precursor (B₁₂)₁₃, ten Sc atoms are located in the form of ring. The space between the clusters of (B₁₂)₁₃ is filled by additional extra-icosahedra of B₁₂. The symmetry and topological codes of the selfassembly processes of the crystal structure are completely reconstructed from S₃⁰ nanoclusters-precursors in the following form: primary chain S₃¹ → microlayer S₃² → microframe S₃³. The topological type of a basic 2D grid, characterizing the packing of clusters-precursors of (B₁₂)₁₃, as in the structure of YB₆₆, corresponds to a square 2D grid 4.4.4.4. with the cluster coordination number CN = 4. The difference in the self-assembly mechanism of Sc₁₈B₂₃₈ and YB66 is established in the formation stage from nanoclusters-precursors of (B₁₂)₁₃ of the primary chain S₃¹ with an index of the complementary binding of 7 and 8, respectively. Reduction of the complementary binding degree in Sc₁₈B₂₃₈ occurs as a result of blocking by two Sc atoms of the B₁₂ icosahedron, and, respectively, the absence of the B–B bond with the neighboring cluster-precursor, which leads to an increase in the size of voids in a 2D-microlayer of S₃². The distances between the centers of clustersprecursors of (B₁₂)₁₃ from neighboring chains in a 2D-microlayer of S₃² determine the values of the modules of the largest translation vectors a = 17.415 Å and b = 16.158 Å. Microframe S₃³ is formed upon the packing (without shear) of bilayer micropacks, consisting of a primary (basic) 2D microlayer and the secondary layer from Sc extra-atoms, related to the atoms of B and nine-vertex polyhedra of B₉, formed on its surface. The distances between the centers of clusters-precursors of (B₁₂)₁₃ from neighboring packs determine the values of the modulus of the translation vector c = 14.495 Å.

The features of the volumetric nucleation of crystals in glass obtained by melting furnace slags with the additive of SiO₂, chromium sesquioxide Cr₂O₃, are studied by the methods of differential thermal and Xray phase analysis and optical microscopy. Upon the introduction of Cr₂O₃ as the catalytic additive, two phases are sequentially formed in the glass: magnesiochromite (MgO · Cr₂O₃) and diopside (CaO · MgO · 2SiO₂). The characteristics of homogeneous and heterogeneous crystallization are determined: the stationary nucleation rate, nonstationary nucleation time, crystal growth rate, and their temperature dependences are obtained. Practical recommendations on the use of the obtained glass are given.

CdS nanoparticles of an average diameter of ~2.7 nm have been synthesized in silicate glass by two stage heat treatment. As was demonstrated using the methods of spectrophotometry and luminescence in the ultraviolet and visible optical ranges, semiconductor phase nuclei were formed at the first stage of thermal treatment, and they grew at the second stage. The image of the spatial distribution of CdS nanoparticles in the glass network has been obtained by computer simulation. The calculated pair distribution function revealed that the average distance between nanoparticles was ~15 nm, which appears sufficient to isolate them from each other in the dielectric matrix and to ensure reliable confinement of electrons inside each nanoparticle.

The concept of the alkaline activity of glass powder used as additives to Portland cement was introduced in Part I of the paper [1] and the technique for its experimental determination was developed. However, in some cases, there is a need for rapid assessment of the alkaline activity of complex additives containing a mixture of glass powder, microsilica, slag, etc. Therefore, the calculation method for determining the alkaline activity of glass powder is required.

Changes in the intensity of evaporation and the composition of condensing oxides are experimentally studied upon diluting corium by iron(III) oxide and Portland cement. It is found that the formation rate of aerosols over the melt is reduced upon diluting the corium by the studied sacrificial material by almost an order of magnitude up to 0.5 g/(cm² s). In the reducing atmosphere, the form of the particles of the aerosols is octahedral and in an oxidizing atmosphere it is spherical.

Two compositions of heat-resistant electrical insulating organosilicatephosphate coatings are developed with the use of debased aluminophosphate Al₂(HPO₄)₃ · 2.5H₂O in the composition. The coating has resistance of 600 and 700°C and thermal shock resistance from the maximum allowable to–60°C. Electrical insulating and various physical and mechanical properties of the coatings are determined.

The model representations of the formation of the internal fields at the grain boundaries in polycrystalline lead zirconate titanate (PZT) films are discussed. According to the model proposed, the local distortion of the stoichiometric composition of the PZT films caused by the segregation of the oxygen and lead ions from the bulk PZT grains towards their boundaries during high-temperature annealing gives rise to electrical double layers near the grain boundaries and fixes the polarization in these areas. As a result, the ferroelectric polarization that can be switched by the electric field in polycrystalline PZT films decreases.

Kinetics of the cationic ring opening polymerization of octamethylcyclotetrasiloxane (D₄) in bulk initiated by solid superacid was studied. The optimalizing experimental conditions were based on preliminary experiments. Higher temperature was beneficial to equilibrium conversion while stirring intensity beyond a certain level displayed no obvious effect on the rate of the reaction. A kinetic model was elicited and kinetic parameters were obtained through optimization. The calculated activation energies were 32.6 and 34.1 kJ mol^–1 for D4 and all other annuluses (D_x), respectively.

The electrokinetic properties of the particles of microporous borosilicate glass powder containing the magnetite phase in its composition on the background of an indifferent electrolyte (NaCl) have been studied. It is found that the modification of two-phase sodium borosilicate glass with iron oxide leads to a shift in the position of the isoelectric point from pH 0.5 for alkali borosilicate (ABS) porous glass (PG) to pH 4.1 ± 0.1 for iron-containing ABS PG. The observed changes in the behavior of modified PG open up new prospects for their practical application.