Macrokinetics of thermal explosion in a niobium—aluminum system. I. Basic macrokinetic stages

The basic macrokinetic stages of a gas-free thermal explosion in an Nb-Al system with different stoichiometric ratios of the reagents are determined using scanning differential calorimetry, electron metallography, and microanalysis. Chemical interaction begins when aluminum melts (993 K) and proceeds slowly up to a temperature of 1020-1040 K, at which dramatic self-heating and acceleration of the reaction (thermal explosion) occur. Migration of the melt from the center of the sample to the surface layers and growth of droplets on the sample surface are observed at the stage of slow reaction, and the drops penetrate again into the sample at the stage of thermal explosion. The phases NbAl₃ and Nb₂Al are formed in the thermal explosion regardless of the initial stoichiometry of the composition; the differences are manifested only in the ratio of these phases and in the amount of residual (nonreacted) niobium. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 2, pp. 40–44, March–April, 2000. This work was supported by the Russian Foundation for Fundamental Research (Grant No. 98-03-32137a).     

Dynamics of thermal conditions of molds in molding glass articles

It is proposed to introduce the concept of thermal stability in molds in the course of molding glass articles and a formula for calculating the stability coefficient, which will make it possible to model production conditions taking into account variations in the ambient temperature and molding duration. Translated from Steklo i Keramika, No. 5, pp. 6–7, May, 2000.     

Ceramic tiles containing diopside and clay raw materials from Khakassia

A local variety of diopside rock is investigated with a view to using it in ceramic-tile mixtures. Specifics of sintering and phase formation of ceramics are determined for the combination of diopside rock and local clays from Khakassia. A diagram is developed for choosing a tile mixture composition with the required degree of sintering. Properties of various-purpose tiles of optimum compositions are described. Translated from Steklo i Keramika, No. 3, pp. 13–16, March, 2000.     

Pinoresinol and 1-acetoxypinoresinol, two new phenolic compounds identified in olive oil

Polyphenols of olive oil show autoprotective, sensory, and nutritional-therapeutic effects. Two new phenolic compounds have been isolated from virgin olive oils by preparative high-performance liquid chromatography and their structures established on the basis of their mass spectra and nuclear magnetic resonance spectral data. The compounds identified are the lignans pinoresinol and 1-acetoxypinoresinol. Both have been found in all the commercial virgin olive oils analyzed. Pinoresinol concentration was rather similar in all the oils. In contrast, 1-acetoxypinoresinol concentration was higher in oils of the Arbequina and Empeltre cultivars than in Picual or Picudo cultivars. Pinoresinol and 1-acetoxypinoresinol may represent the major phenolic compounds in some Arbequina and Empeltre oils. Lignans possess biological and pharmacological properties and, therefore, the two new compounds identified in olive oils may contribute to the reported beneficial effects which are attributed to polyphenols on human health of a diet rich in olive oil.     

Exact solutions of nonlinear heat- and mass-transfer equations

The method of generalized separation of variables for solving nonlinear steady and unsteady heat- and mass-transfer equations is outlined. New exact solutions of one-, two-, and three-dimensional heat equations are obtained. Anisotropic media with a nonlinear heat source of general form are considered for the case in which the main thermal diffusivities show a power or an exponential dependence on the spatial coordinates. Equations with a logarithmic heat source are analyzed in detail. The results obtained are applied to the problem of thermal explosion in an anisotropic medium.     

Further Improvement in Mechanical Properties of Highly Anisotropic Silicon Nitride Ceramics

Si₃N₄ceramics were fabricated by tape casting of a raw-powder slurry seeded with three types of rodlike β-Si₃N₄particles. The effects of seed size on the microstructure and mechanical properties of the sintered specimens were investigated. All the seeded and tape-cast silicon nitrides presented an anisotropic microstructure, where the elongated grains grown from seeds were preferentially oriented parallel to the casting direction. The orientation degree of these grains, f ₀, was affected by seed size, and small-seed addition led to the highest f ₀value. This material exhibited high bending strength (∼1.4 GPa) and high fracture toughness (∼12 MPa^.m^1/2) in the direction normal to the grain alignment, which were attributed to the highly anisotropic and fine microstructure.     

Properties of vapor-deposited borophosphorosilicate glass layers employed in technology of silicon integrated circuits

The data of investigations on the physicochemical and electrophysical properties of borophosphosilicate glass layers deposited from mixtures of tetraethoxysilane and esters of boric and phosphoric acids in an oxygen-ozone medium (temperature, 400–440°C; atmospheric and subatmospheric pressures) have been generalized. The empirical relationships are obtained for determining the boundaries of the optimum dopant concentration region when the glass is used as a reflow interlayer dielectric in integrated circuit technology. The assumption is made that the structure of borophosphosilicate glass layers is formed by a porous network involving dopant clusters.     

Specific features of magnetic order in a multiferroic compound CuCrO<Subscript>2</Subscript> determined using NMR and NQR data for <Superscript>63, 65</Superscript>Cu nuclei

Results of studying the paramagnetic and ordered phases of a CuCrO₂ single crystal using nuclear magnetic and nuclear quadrupole resonances on ^63,65Cu nuclei are presented. The measurements have been carried out in wide ranges of temperature (T = 4.2–300 K) and magnetic-field strength (Н = 0–94 kOe), with the magnetic fields being directed along a and c axes of the crystal. The components of the electric-field gradient tensor and the magnetic-shift tensor (K _a,c) have been determined. The temperature dependences K _a(H || a) and K _c(H || c) for the paramagnetic phase are described by the Curie–Weiss law and reproduce the behavior of the magnetic susceptibility (χ_a,c). The hyperfine field on a copper nucleus has been determined, which is equal to h _hf ^a,c = 33 kOe/μB. Below the temperature Т _N = 23.6 K, nuclear magnetic resonance and nuclear quadrupole resonance spectra for ^63,65Cu nuclei have been recorded typical of helical magnetic structures, which are incommensurable with the lattice period.     

Influence of the Size and Structural Factors on the Magnetism of Multilayer Films Based on 3<Emphasis Type="Italic">d</Emphasis> and 4<Emphasis Type="Italic">f</Emphasis> Metals

This work has presented some data on the layer structuring of films of 3d and 4f metals and their alloys, which have potential for practical use in magnetic sensors. The decrease in the thickness of magnetic layers with this structuring entails natural worsening of the crystallinity and leads to a degradation of magnetic ordering. However, the manifestation of these tendencies depends to a great extent on the conditions of preparation, the composition, and the sequence of the deposition of the contacting layers in the multilayer structures. The combination of these factors makes it possible to realize an optimum composition and optimum structural states of the films, which in a number of cases lead to the appearance of new combinations of functional properties.