Effect of pulsed current on the microstructure evolution of Cu–Sn intermetallic compounds

The dissolution behaviour between Cu and Sn during spark plasma sintering (SPS) was investigated with emphasis on the intrinsic effect of the applied pulsed current. Metallographic analyses revealed that the phase formation of Cu–Sn intermetallics was significantly influenced by the applied pulsed current as a series of phase evolutions along the sintering temperature occurred: Cu₆Sn₅?+?Sn?→?Cu₆Sn₅?+?Cu₃Sn?→?Cu₃Sn. The evolution of Cu–Sn intermetallic compounds (IMCs) was analysed by considering the accelerated atomic diffusion and the increased flux of Cu into the IMCs with a pulsed current, which can provide new insights into the basic understanding of the SPS process and promote the development of rapid forming process of IMCs joints for applications at higher temperatures.     

Study of 3D-quantitative structure–activity relationship on a set of 1,2,4-triazole compounds

In this article, 3D-quantitative structure–activity relationship on a set of 1,2,4-triazole compounds is studied. A set of 16 derivatives of triazole that have different biological activities to wheat black rust as inhibitors are characterized by molecular mechanics. The analysis result by PLS agrees with the study of 2D-QSAR, and it offers useful 3-dimensional information for designing high activity compounds.     

Effects of heat treatments on the serrated flow in a Ni–Co–Cr-base superalloy

Serrated flow in a Ni–Co–Cr-base superalloy was studied in three microstructural conditions (SUB, SUBA, and SUPER) from 25 to 750 °C by tensile test at initial strain rates ranging from 8 × 10⁻⁵ to 3 × 10⁻³ s⁻¹. The results showed that the SUB and SUBA samples had fine grain size of about 9 μm, whereas the SUPER samples had coarse grain size of about 600 μm. The tertiary γ′ fraction was about 0 in the SUB, 5% in the SUBA, and 15% in the SUPER samples, respectively. The types and temperature ranges of serration were different in the alloy with SUB, SUBA, and SUPER microstructures. It is proposed that the tertiary γ′ fraction and size had great effects on the serrated flow of the alloy with different microstructures.     

Effect of casting and homogenizing treatment conditions on the formation of Al–Fe–Si intermetallic compounds in 6063 Al–Mg–Si alloys

The effect of casting and homogenizing treatment conditions on the formation of several Al–Fe–Si intermetallic compounds in 6063 aluminum alloy was investigated using X-ray diffraction and transmission electron microscopy (TEM). The four kinds of alloys containing 0.1 to 0.5 mass% Fe were melted and then cooled at three different cooling rates ranging from 0.06 to 50 K/s, following the homogenization at 858 K for 54 ks and 2400 ks. The Al–Fe–Si compound particles were extracted from the alloy ingots using the thermal phenol method. The as-cast 0.1 mass% Fe ingot obtained at the casting cooling rate of 0.06 K/s had a largest amount of the phase among the ingots investigated. When this ingot was homogenized at 858 K for 54 ks and 2400 ks, the amount of the phase decreased, while that of the phase increased. On the other hand, the as-cast 0.5 mass% Fe ingot obtained at the casting cooling rate of 50 K/s had the largest amount of the phase among the ingots investigated. When this ingot was homogenized at 858 K for 54 ks, a large amount of the phase remained. However, the homogenization at 858 K for 2400 ks resulted in the transformation of the phase to the phase. The main phase in the as-cast 0.2 mass% Fe ingot obtained at the casting cooling rate of 5 K/s, close to the industrial cooling rates, was the phase. The phase gradually decreased, and the relative amounts of the and phases increased during homogenization at 858 K for 54 ks. Furthermore, almost all of the Al–Fe–Si intermetallic compounds were transformed into the phase in the ingots homogenized at 858 K for 2400 ks.     

Influence of the silica matrix on the formation of α-alumina in a mullite–alumina composite from a diphasic precursor

In mullite–alumina composite precursors, interaction between the silica matrix and the fine -alumina texture strongly influences the precursor phase transformation, the nucleation and the crystal geometry both of the mullite and of the -alumina. The mullite–alumina composite precursor calcined at 1000 °C has a layered structure probably derived from the layered texture of the -alumina. The phase transition of this layered texture is retarded by the presence of the silica matrix and a metastable mullite phase is formed before nucleation of -alumina. By leaching away the silica matrix, the remaining layered texture is readily transformed into very fine, thin -alumina platelets by calcination at 1000 °C. This seems to be one reason for the appearance of elongated mullite grains in a pure mullite matrix and the platelet shaped -alumina grains in the mullite–alumina composite prepared from diphasic precursors. © 1998 Chapman & Hall     

Effects of various poisoning compounds on the activity and stereospecificity of heterogeneous Ziegler–Natta catalyst

Abstract

A TiCl₄/ethylbenzoate/MgCl₂ Ziegler–Natta catalyst was pretreated with chemically different poisoning compounds to investigate their effects on the catalyst activity and stereospecificity for propylene polymerization. The poisoning power on the activity was in the order of methanol > acetone > ethyl acetate. A kinetic analysis using the stopped-flow method revealed that addition of the poisoning materials decreased the activity through the reduction of the number of active sites, whereas the catalyst isospecificity was hardly affected by these materials.     

Effects of various poisoning compounds on the activity and stereospecificity of heterogeneous Ziegler–Natta catalyst

A TiCl₄/ethylbenzoate/MgCl₂ Ziegler–Natta catalyst was pretreated with chemically different poisoning compounds to investigate their effects on the catalyst activity and stereospecificity for propylene polymerization. The poisoning power on the activity was in the order of methanol > acetone > ethyl acetate. A kinetic analysis using the stopped-flow method revealed that addition of the poisoning materials decreased the activity through the reduction of the number of active sites, whereas the catalyst isospecificity was hardly affected by these materials.     

Errors in measuring the directivity of a field by the method of a reference field in the range of 25–400 MHZ

Conclusions The cited data on error components in measuring the field-strength lead to the conclusions that the reference field (provided that the distances are measured with an error of ±2%) can be determined with an error of 6%, at frequencies up to 150 MHz, and of ±7% in the range from 150 to 400 MHz. The error in determining the resulting field-strength is smaller for small angles of elevation, since the beam reflected from the ground has a substantial effect on the value of the field.     

Influence of strain rate on the temperature rise of specimens in static tests of a titanium alloy in the 293–4.2 K range

The influence of two strain rates, 1.10^–1 and 2.10^–2 sec^–1, on the temperature rise of specimens of -titanium alloys in static tests in the 290- 4.2 K range is investigated. It is established that at room temperature conditions (290 K) the temperature rise of the specimens is nonuniform over the length and is 14 K, in liquid nitrogen (77 K) it is more than 0.5 K, and in liquid helium (4.2 K) the temperature depends upon the strain rate and reaches 46 K. It is shown that the temperature rise of the specimens in liquid helium in strain at a rate of 2.10^–2 sec^–1 reduces the tensile strength but does not influence the yield strength of the material.Translated from Problemy Prochnosti, No. 12, pp. 70–78, December, 1992.     

Conference proceedings as a matter of bibliometric studies: the Academy of International Business 2006–2008

This study does a bibliometric analysis based on keywords of conference proceedings. Scientometric investigations of conference proceedings are a new and innovative, not very common approach. The studies and papers presented may be interpreted as early indicators of scientific development. The Academy of International Business (AIB) was chosen for being the leading organization for studies in international business with contributions covering a 3-year period (2006–2008). The study presents the general structure of current scholarly interest in international business studies, clusters the keywords and reflects details on the focused research areas of the papers analyzed. The bibliometric analysis indicates three clusters: the core, the semi-periphery and the periphery. The five most occurring keywords were found to be multinational enterprise, emerging markets, foreign direct investment, internationalization and knowledge management in descending order. The analyses focus on concepts building the core (in total ten keywords), the semi-periphery which is coined by performance and related topics (60 keywords) and the periphery of the studies with governance and specific facets of it (199 keywords).     

The Effect of Impurities on the Evolution of the Melting Front Analyzed in a Two-Dimensional Representation for the Eutectic Pt–C

The paper discusses the effect of two-front melting on the liquidus temperature of the eutectic Pt–C and the eutectic temperature of the system in its pure state. This influence factor has not been considered thus far in the uncertainty budget associated with the assignment of thermodynamic temperatures to the eutectics Co–C (1597.15 K), Pt–C (2011.05 K), and Re–C (2747.35 K), selected in the European Metrology Research Programme project Implementing the New Kelvin. For Pt–C, simulation of the effect of two-front melting on the melting process has been done before in a 1D analytical model, and this formed the starting point to the present study. In this study the melting process is analyzed by means of a 2D axisymmetrical finite-volume model. In the model, freezing and melting are considered for an impure ingot and for a pure ingot. As to the impure ingot, the impurity concentrations are the concentrations met in current practice of the realization of the high-temperature reference fixed point, but formulated in terms of an effective concentration and associated effective distribution coefficient \(k< 1\) , related to a Scheil fit to the melting curve at given melting conditions as measured for the eutectic Pt–C. Heat injection rates for melting varied from 15 000 W \({\cdot }\) m \(^{-2}\) down to 3000 W \({\cdot }\)  m \(^{-2}\) . In any case for the impure system, two melting fronts are showing up. For the pure system, only one melting front is generated, traveling from the outside of the ingot toward its inside.     

Cesium-137 of Chernobyl origin in lake–river systems of Eastern Fennoscandia: 30 years after the accident

Contamination of waters of lake–river systems after many-year migration of ¹³⁷Cs in water bodies was studied. In lakes with the ¹³⁷Cs fallout density lower than 8 kBq m^–2, the radionuclide concentrations in water after 24–29 years did not exceed 2–3 Bq m^–3, and at a fallout level of 37 kBq m^–2 it was in the range 11–34 Bq m^–3. The natural half-clearance time Т of lake waters from ¹³⁷Cs was 6–7 years at the exposure of up to 20 years. The ¹³⁷Cs migration in the lake–river systems that occurred during ~30 years did not lead to structural changes in the water contamination: The initially low ¹³⁷Cs level in lake waters did not become high, and vice versa. Among rivers feeding Lake Ladoga, the ¹³⁷Cs level in the Vuoksa River is ~3 times higher than in waters of the Volkhov and Svir rivers. During the period 1988–2015, 21.3 TBq of ¹³⁷Cs was supplied to Lake Ladoga with Vuoksa waters. The Vuoksa source from the Saima lake system with increased contamination with ¹³⁷Cs of Chernobyl origin leads to long-term supply of this radionuclide to Lake Ladoga.     

The irradiation effect of a Nd–YAG pulsed laser on the CeO2 target in the liquid

The irradiation of an Nd–YAG pulsed laser on the CeO₂ target in water was investigated. The reaction products depend mainly on the energy density of the Nd–YAG laser. The CeO₂ nanoparticles with sizes of 20–80 nm were formed in water, while the energy density was larger than 32 kJ/cm². The nanocrystalline films with grain sizes of 50–150 nm were formed on the target with the energy density of 20–25 kJ/cm². Finally, the amorphous films were formed with the energy density of 6–15 kJ/cm². The formation mechanisms of the nanoparticles and the films were discussed according to the triple-point phase diagram of CeO₂.