Properties of fine-grained graphites based on two-component fillers

The effect of the nature of two-component fillers on the physical and mechanical properties of finegrained graphites was studied using highly oriented needle coke and nearly isotropic synthetic graphite as components of fillers. Each filler was prepared in the form of coarse (-120 µm) and fine (-10 µm) powders. Different mixtures of these components were used in producing graphite samples, which were then characterized by density, thermal expansion, compressive strength, and modulus of elasticity measurements. The results demonstrate that the thermal expansion, compressive strength, and modulus of elasticity of the graphites thus prepared depend on the microtexture, size, and shape of the filler particles.Translated from Neorganicheskie Materialy, Vol. 40, No. 12, 2004, pp. 1448–1454.Original Russian Text Copyright © 2004 by Samoilov.     

Composition, Structure, and Thermal Expansion of Ca3Fe4S3O6 and CaFeSO

The iron calcium oxysulfides Ca₃Fe₄S₃O₆ and CaFeSO are synthesized by reacting mixtures of CaO and FeS in an inert atmosphere. Their elemental compositions and lattice parameters are determined by x-ray microanalysis and x-ray diffraction. From the temperature-dependent lattice parameters of the oxysulfides (measured up to 1020 K), their thermal expansion coefficients are evaluated.     

Relaxor Behavior of Ge-Doped TlInS2

The dielectric and pyroelectric properties of Ge-doped (0.1 mol %) TlInS₂ crystals are studied. The results demonstrate that TlInS₂ is a ferroelectric relaxor. The experimental data are used to evaluate, using the Vogel–Fulcher relation, the activation energy (0.045 eV), preexponential factor (f ₀ = 2 × 10¹³ Hz), and the dipole-freezing temperature (T _F = 142 K) and to determine the temperature range of the stable relaxor (nanodomain) state and the temperature of the transition to the ferroelectric (macrodomain) state, accompanied by an anomaly in the temperature-dependent pyroelectric coefficient.     

Assessing the Efficiency of Chemical and Mineral Admixtures in Early Cement Hydration

A procedure is proposed for evaluating the efficiency of chemical and mineral admixtures in early cement hydration with the use of calorimetric data and with allowance made for the selective effect of admixtures on the hardening process. The concepts of admixture efficiency and admixture–cement compatibility are formulated and are shown to be of practical importance. The proposed approach is substantiated using thermokinetic results on the effects of various admixtures on the hydration of different cements, and the underlying mechanisms are discussed.     

A direct stiffness analysis of a composite beam with partial interaction

The use of the conventional semi-analytical stiffness method in finite element analysis, in which interpolation polynomials are used to develop the stiffness relationships, leads to problems of curvature locking when beam-type elements are developed for composite members with partial interaction between the materials of which it is comprised. The curvature locking phenomenon that occurs for composite steel–concrete members is quite well reported, and the general approach to minimizing the undesirable ramifications of curvature locking has been to use higher-order polynomials with increasing numbers of internal nodes. This paper presents an alternate formulation based on a direct stiffness approach rather than starting from pre-defined interpolation polynomials, and which does not possess the undesirable locking characteristics. The formulation is based on a more general approach for a bi-material composite flexural member, whose constituent materials are joined by elastic shear connection so as to provide partial interaction. The stiffness relationships are derived, and these are applied to a simply supported and a continuous steel–concrete composite beam to demonstrate the efficacy of the method, and in particular its ability to model accurately both very flexible and very stiff shear connection that causes difficulties when implemented in competitive semi-analytical algorithms. Copyright © 2004 John Wiley & Sons, Ltd.     

A Theoretical Framework for Core Material Properties Identification in Cellular Solids using Novelty Detection

Abstract:  This paper presents a novelty detection-based technique to identify core material properties of honeycombs and cellular structures. A numerical model (finite element) representing full scale and/or reduced size of the cellular solid is used to generate transmissibilities between topological homologous points at cells in different locations. In order to make the procedure robust against noise, these transmissibilities are artificially corrupted. This step is representative of a series of experimentally obtained measurements which automatically return information relating to the size and shape of data noise along with the mean measurement. The next stage, both in this paper and in the proposal for the experimental approach, is to generate several further sets of transmissibilities from the finite element model; the only difference being that the core material properties are altered from the original values. A novelty detection framework is then adopted to find a similarity measure between each of these 'test' transmissibilities and the original set thereby identifying the material properties. Although this work is concerned with identifying only one material property, the methodology extends to identifying several properties.     

Electrosprayed and selenized Cu/In metal particle films

Nano-particulate copper and indium metal layers of 1-2 μm have been deposited by non-vacuum techniques such as doctor blade, screen printing and electrospray using alcoholic suspension pastes. Electrospray showed a high efficiency of material usage and yielded the most uniform morphology. The metal precursor layers were subjected to a thermal treatment (500-600 °C) in selenium vapor to convert the porous metal layers into CuInSe₂ compound layers. The chemical conversion, investigated by X-ray diffraction, showed the presence of the In₂O₃ impurity phase in the precursor as well as in the selenized layers.     

Accuracy Investigations of Boundary Element Methods for the Solution of Laplace Equations

Boundary element methods (BEMs) are approved methods for an efficient numerical solution of problems, which are based on a Laplace equation. Here, the solution of electrostatic field problems, steady current flow field problems, and magnetostatic field problems is considered. Focus of this paper is on investigations of accuracy of direct formulations, which are based on Green's theorem. Different types of coupling of computational domains are examined with respect to accuracy and convergence behavior of iterative solvers of the linear system of equations. Furthermore, the influence of singular and nearly singular integrals and the influence of matrix compression techniques to the accuracy of the solution are observed     

Preparation and properties of heavy-metal halide glasses

We have studied the effect of In³⁺, Pb²⁺, Gd³⁺, and Cl (heavier ions) substitutions for Al³⁺, Ba²⁺, La³⁺, and F^? on the crystallization stability and UV/IR optical properties of HBLAN fluorohafnatc glasses (HfF₄-BaF₂-LaF₃-AlF₃-NaF system). We obtained stable glasses containing InF₃ and BaCl₂ instead of AlF₃ and BaF₂, respectively, and offering increased IR transmission. The presence of CCl₄ in the process atmosphere and the removal of oxygen-containing impurities via directional solidification are shown to have an advantageous effect on the optical quality of the glasses. The fluoride-chloride glasses are capable of accommodating about 1.5 times higher levels of rare-earth activators in comparison with their fluoride analogs.     

Analysis of operating conditions of ground-fault protection schemes for generator stator winding

This paper presents results of simulation studies of the influence of methods of grounding the stator winding of the unit-connected generator neutral on the operating conditions of a 100-percent ground-fault protection excited by the third-harmonic voltage ratio in the generator neutral and at its terminals. The analysis was performed for a generator with the neutral grounded through a ground-fault neutralizer, a third-harmonic stop filter, a resistor, and a capacitive voltage divider. The influence of the parameters of the particular elements of the grounding circuits on the voltage-feeding measuring element of the protection was determined. The capacitance to ground of the generator breakers was taken into account. The simulations were run for 1110-MVA unit-connected generator at ground faults along the whole length of the generator stator winding. It has been found that the method of grounding the generator neutral and the parameter of the grounding elements significantly influences the operating conditions of this protection. It is shown that through the proper selection of these parameters, the ground-fault protection of whole stator winding, counting from the generator neutral to the terminals is ensured.