Model of crystallization of a melt containing nonsoluble particles

A mathematical model of the electron beam hardening of carbon steels irradiated with a relativistic electron beam is proposed which takes into account the change in crystallization conditions as a result of ingress of inert particles into the melt. The model is based on an analogy with the two-phase zone theory. The problem is solved numerically.     

Effect of Mechanochemical Activation on the Catalytic Properties of Zinc Oxide

The reasons for changes in catalytic activity as a function of the time of mechanochemical activation in a planetary mill were studied with the use of a set of physicochemical techniques. The dependence of the specific rate of CO oxidation on the time of mechanochemical activation exhibited an extremal character. Small-angle interblock boundaries, disordered dislocations, and shear defects were formed in the sample with maximum activity because of mechanochemical activation. The linear dependence of the specific rate of CO oxidation on the value of microstresses suggested that the above defects were responsible for an increase in the catalytic activity. It is likely that oxygen atoms situated at the sites of the outcrop of defects on the surface served as elementary active centers.     

Kinetics of bleaching of rice straw and husk with potassium peroxoborate

The kinetics of bleaching with potassium peroxoborate of waste from rice production (straw and husk), untreated and treated with water, acid, and sodium hydroxide, was studied.     

Synthesis of aluminum oxides from the products of the rapid thermal decomposition of hydrargillite in a centrifugal flash reactor: II. Structural and textural properties of aluminum hydroxide and oxide obtained from the product of the centrifugal thermal activation of hydrargillite (CTA product)

The basic properties of aluminum hydroxide compounds, namely, the flash product and the centrifugal thermal activation (CTA) product both before and after heat treatment at 400–1100°C are considered. The hydration conditions for obtaining 100% pseudoboehmite from the CTA product are determined. The structure, morphology, and texture of pseudoboehmite aluminum hydroxide synthesized from the CTA product and of the aluminum oxides obtained from this hydroxide in the temperature range 600–1100°C are described.     

High-temperature studies of La1−x SrxFeO3−δ solid solutions using synchrotron radiation

A series of La_1?x Sr_xFeO_3?δ samples with a perovskite structure were investigated by high-temperature X-ray analysis using synchrotron radiation. In this series, one can observe a morphotropic phase transition (0.3 ? x ? 0.4) from the orthorhombic (0 ? x < 0.3) to cubic (0.4 < x ? 0.75) modification. The samples from the morphotropic transition region (MTR) at room temperature have a highly disordered microblock structure related to their phase heterogeneity; according to high-temperature X-ray analysis data, this is the result of particle stratification of the high-temperature homogeneous solid solution formed at the temperature of the synthesis (1200°C) in the course of cooling.     

Four-Center Nodes: Supramolecular Synthons Based on Cyclic Halogen Bonding

The isocyanide trans-[PdBr₂(CNC₆H₄-4-X′)₂] (X′=Br, I) and nitrile trans-[PtX₂(NCC₆H₄-4-X′)₂] (X/X′=Cl/Cl, Cl/Br, Br/Cl, Br/Br) complexes exhibit similar structural motif in the solid state, which is determined by hitherto unreported four-center nodes formed by cyclic halogen bonding. Each node is built up by four Type II C−X′⋅⋅⋅X−M halogen-bonding contacts and include one Type I M−X⋅⋅⋅X−M interaction, thus giving the rhombic-like structure. These nodes serve as supramolecular synthons to form 2D layers or double chains of molecules linked by a halogen bond. Results of DFT calculations indicate that all contacts within the nodes are typical noncovalent interactions with the estimated strengths in the range 0.6–2.9 kcal mol⁻¹.     

Formation of Mesopores in USY Zeolites: A Case Revisited

Steaming of NH₄Y zeolite at 723 K and 873 K is accompanied by the formation of extra‐framework amorphous aluminosilicate and silica gel in addition to earlier observed extra‐framework aluminum species. Their occurrence is directly associated with the formation of mesopores. Bulk (intracrystalline) mesopores occur inside the crystallite nuclei and surface (intercrystalline) mesopores are located nearby the crystallite surface. Corrosion of the zeolite framework results in a loss of crystallinity and, consequently, decreased catalytic activity of the USY catalysts synthesized. Analysis of the reasons of mesopore formation may help to reduce these disadvantages.     

Adsorption of staphylococcus on carbon-mineral sorbents

Adsorption of staphylococcus on spherical carbon-mineral sorbents (SCMS) and on some other home-made hemosorbents based on active coals has been studied.

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Physicochemical and Catalytic Properties of La1 – xCaxFeO3 – 0.5x Perovskites Prepared Using Mechanochemical Activation

The phase composition of La_{1 – x} Ca _x FeO_{3 – 0.5x} perovskites synthesized from preactivated oxides was studied by powder X-ray diffraction analysis and differential dissolution. The system does not form a continuous series of homogeneous solid solutions. No intermediate samples from this series are monophasic. It was found that the synthesis under nonequilibrium conditions (mechanical activation + calcination at 900° for 4 h) resulted in nonequilibrium microheterogeneous solid solutions with degrees of calcium substitution for lanthanum of no higher than 0.5. A longer calcination (for 16 h) or an increase in the calcination temperature of solutions up to 1100 ° decreased the calcium content of the samples down to x 0.2 because of the formation of a brownmillerite phase. The catalytic activity of the test samples in the oxidation of CO changed nonmonotonically with x, and it was maximum at x = 0.5–0.6, which correlates with the maximum density of interphase boundaries in these samples.     

Structural Arrangement of Fe–Sb–O Catalysts

In iron–antimony catalysts containing excess antimony oxide and consisting of a mixture of FeSbO₄ and -Sb₂O₄ phases, the structure of iron antimonate changes compared to the catalyst with an equimolar composition, which is the pure FeSbO₄ phase. In the presence of excess antimony oxide in the near-surface layer of iron antimonate, extended defects with a structure of crystallographic shift are formed. These accumulate overstoichiometric antimony. Such a structural change is associated with changes in the acid–base properties and the surface oxygen binding strength.