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 strengthening methods on the properties of Cu–Ti–B alloys

A copper alloy of Cu–1.9?wt-%Ti–0.7?wt-%B was fabricated by vacuum induction melting and casting followed by cold working and annealing. Four strengthening methods has been involved during the preparation of the alloy, and the combined action of these methods results in the alloy with the tensile strength of 530?±?24?MPa and the electrical conductivity (EC) of 48.0?±?2.1% International Annealed Copper Standard. The specific contribution (or deterioration) of different strengthening methods to hardness and EC was quantitatively evaluated. With regard to combined properties of Cu–Ti–B alloys, age hardening and forming TiB₂ particles are two effective methods to improve hardness and to maintain EC at a relatively high level simultaneously, but solid solution strengthening and work hardening are two inferior strengthening methods.     

Effect of thermal processing on the microstructure and composition of Cu–Sb–Se compounds

We report on the effects of thermal processing on the microstructure and composition of a system with overall stoichiometry of 3Cu:1Sb:3Se with the aim of producing single-phase Cu₃SbSe₃. It was found that slow cooling from the melt produced a multiphase material consisting of Cu₂Se and CuSbSe₂, but devoid of Cu₃SbSe₃. Cooling rapidly from the melt resulted in three-phase microstructures consisting of Cu₂Se, CuSbSe₂, and Cu₃SbSe₃. Subsequent annealing of the three-phase material between 325 and 400 °C shifted the composition toward nearly pure Cu₃SbSe₃—the target compound of this work. The kinetics of the transformation into Cu₃SbSe₃ was successfully described using a modified Avrami model which suggests that diffusion is the rate-controlling step. Values of Young’s modulus and hardness, obtained by nanoindentation, are reported for Cu₂Se, CuSbSe₂, and Cu₃SbSe₃.     

Effects of temperature and dispersants on the phases and morphology of Ag–Cu nanoparticles

Ultrafine Ag–Cu nanoparticles (NPs) have been synthesized by a rapid one-step reduction within only 10 min. Effects of temperature and dispersants on the phases and morphology of Ag–Cu NPs were investigated. Results showed that citric acid exhibited an advantageous nature to avoid the formation of Cu₂O and form uniform morphology over PVP. The average particle size of the Ag–Cu NPs synthesized simply in ice-cubes bath could be controlled in 8.6 nm about a quarter of that synthesized at room temperature. The synthesized Ag–Cu NPs presented alloy states near the eutectic composition of 72:28. Due to the lower Ostwald ripening rate and citric acid protection, smaller Ag–Cu NPs were achieved in ice-cube bath. Results also showed that the ultrafine Ag–Cu NPs could be expected to sinter at about 330 °C which was much lower than the eutectic temperature (779 °C) of bulk Ag–Cu alloy. The ultrafine Ag–Cu NPs could be applied as potential die attach materials for SiC power devices.     

Effects of Ti addition on the microstructures and mechanical properties of the Al–Mn–Mg–RE alloy

The effects of higher Ti addition (near peritectic point) on microstructures and mechanical properties of a designed Al–Mn–Mg–RE alloy were investigated by optical microscopy, scanning electron microscopy, energy dispersive spectroscopy and tensile tests, respectively. The results show that the addition of Ti refined grains evidently, meliorated the morphology and distribution of iron-rich phase, and hence improved the mechanical properties of the Al–Mn–Mg–RE alloy. The fracture mechanisms changed from brittle fracture to ductile fracture after extruding. The addition of Ti refined the constituent particles and resulted in deeper and more homogenized dimples of the tensile fracture surfaces.     

Effects of yttrium and zinc addition on the microstructure and mechanical properties of Mg–Y–Zn alloys

The effects of the yttrium and zinc additions on microstructure and mechanical properties of Mg–Y–Zn alloys were investigated. It was found that the addition of yttrium increases the eutectic temperature of Mg–Y–Zn alloys greatly. The addition of yttrium can also greatly increase the dynamic recrystallization (DRX) temperature of Mg–Y–Zn alloys. The volume fraction of DRX grains in Mg₉₇Y₂Zn₁ alloy is larger than that in Mg₉₆Y₃Zn₁ alloy but smaller than that in Mg_95.5Y₃Zn_1.5 alloy due to the effects of yttrium and zinc addition. The long period stacking (LPS) structures of 18R and 14H were observed in Mg–Y–Zn alloys. The increase in the yttrium content results in increase in strength and decrease in elongation in Mg–Y–Zn alloys. The increase in both yttrium and zinc contents results in increase in both strength and elongation in Mg–Y–Zn alloys. The high strengths of the alloys were thought due to the strengthening by the grain refinement, solid solution strengthening, strain strengthening, high density of plane faults of the LPS structures, and distribution of fine Mg₂₄Y₅ phase.     

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 strain rate and temperature on the stress–strain response of solder alloys

To ensure reliable design of soldered interconnections as electronic devices become smaller, requires greater knowledge and understanding of the relevant mechanical behavior of solder alloys than are presently available. The present paper reports the findings of an investigation into the monotonic tensile properties of bulk samples of three solder alloys; a lead–tin eutectic and two lead-free solders (tin–3.5 copper and a tin–3.5 silver alloy). Temperatures between–10 and 75°C and strain rates between 10^–1 and 10^–3 s^–1 have been studied. Both temperature and strain rate may have a substantial effect on strength, producing changes well in excess of 100%. Strength is reduced by lowering strain rate and increasing temperature, and Sn–37 Pb is usually most sensitive to the latter. Expressions for strain and strain rate hardening have been developed. The Sn–0.5 Cu alloy is usually the weakest and most ductile. Sn–37 Pb is strongest at room temperature but with increasing temperature and lower strain rates it becomes inferior to Sn–3.5 Ag. Ductility changes with temperature and strain rate for all three alloys are generally small with inconsistent trends. The role of such data in stress analysis and modeling is considered and the paramount importance of employing data for conditions appropriate to service, is emphasized.     

Effects of added kaolinite on the strength and porosity of freeze-cast kaolinite–silica nanocomposites

This paper examines the effects of kaolinite on the mechanical strength and porosity of freeze-cast kaolinite–silica composites. Measurement of the equibiaxial flexural strength shows that, after sintering at 1250 °C for 1 h, a ceramic containing 10 vol% kaolinite and 8 vol% silica has a strength that is 52 times greater than a ceramic containing only 18 vol% silica and 2.5 times greater than one containing only 18 vol% kaolinite, yet while also being 69 % porous (i.e., the porosity after sintering). It is proposed that this greater strength arises from three mechanisms. First, the kaolinite and silica particles bond together to form a connected network in which the much larger kaolinite platelets distribute the applied stress over a larger region of the sample (this increased strength is even seen in the freeze-cast green bodies before sintering). Second, X-ray diffraction measurements indicate that upon sintering at 1250 °C, new phases are formed when both silica and kaolinite are present, which we postulate contribute greatly to the strength of the composite. Third, the pore walls in samples containing both kaolinite and silica are much more continuous and unbroken than in samples containing only kaolinite.     

Effects of solution treatment on the microstructure and mechanical properties of Al–Cu–Mg–Ag alloy

The effects of solution treatment on the microstructure and mechanical properties of Al–Cu–Mg–Ag alloy were studied by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), differential scanning calorimeter (DSC), transmission electron microscopy (TEM) and tensile test, respectively. The results show that the mechanical property increases and then decreases with increasing the solution temperature. And the residual phases are dissolved into the matrix gradually, the number fraction of the precipitation and the size of recrystallized grains increase. Compared to the solution temperature, the solution holding time has less effect on the microstructure and the mechanical properties of Al–Cu–Mg–Ag alloy. The overburnt temperature of Al–Cu–Mg–Ag alloy is 525 °C. The yield strength and the elongation get the best when the alloy is solution treated at 515 °C for 1.5 h, is 504 MPa and 12.2% respectively. The fracture mechanism of the samples is ductile fracture.     

Effects of Zr and B on the structure and tensile properties of Al–20%Mg alloy

In current research, the effects of different Zr and B contents on the structure and tensile properties of Al–20%Mg alloy have been investigated by using Al–15Zr and Al–8B master alloys. Optical and scanning electron microscopy (SEM) were utilized to study the microstructures and fracture surfaces. Microstructural analysis of the cast alloy showed dendrites of primary α-phase within the eutectic matrix which consists of β-Al₃Mg₂ intermetallic and α-solid solution. After tensile testing, the optimum amounts for both Zr and B were found to be 0.5 wt.%. Ultimate tensile strength (UTS) value of the unrefined alloy increased from 168 MPa to 243 MPa and 236 MPa by adding 0.5% Zr and 0.5%B, respectively. The main mechanism for UTS enhancement was found to be due to the refinement of grains and also altering large dendrites of Al(α)-phase to finer structure. The study of fracture faces revealed that B/Zr addition changes the mode of fracture from brittle to rather ductile.     

Effects of trace Er addition on the microstructure and mechanical properties of Mg–Zn–Zr alloy

The effects of trace Er addition on the microstructure in Mg–9Zn–0.6Zr alloy during casting, homogenization, pre-heating, and hot extrusion processes were examined. The mechanical properties of alloys with and without Er were compared. The results showed that Er exhibited a lower solubility in solid magnesium and formed thermally stable Er- and Zn-bearing compounds. The Er-bearing alloy exhibited a considerably improved deformability, as well as a fine and uniform microstructure. Moreover, dynamic precipitation of fine MgZn₂ particles with a modified spherical morphology occurred during hot extrusion, resulting in a tensile yield strength of 313 MPa and a high elongation to failure value of 22%. Further aging of the Er-bearing alloy led to an increment of another 30 MPa in yield strength. In addition, Er markedly increased the thermal stability of the alloy structure.     

Effects of short- and long-term thermal exposures on the stability of a Ni–Co–Cr–Si alloy

Long-term thermal stability is often needed for high temperature alloys used in a variety of industrial applications for extended operating lifetimes. In this paper, the effects of thermal exposures or aging on the mechanical properties and microstructure of a Ni–Co–Cr–Si alloy (HAYNES® HR-160® alloy) were studied. It includes both short- and long-term elevated temperature exposures ranging from 649 °C to 1093 °C (1200–2000 F) for duration of 6 min (0.1 h) to 6 years (50,000 h). The residual room temperature (RT) tensile and Charpy-V impact toughness properties were evaluated and correlated to microstructural changes as well as to fracture surfaces of the tensile tested samples. It was found that the RT ductility and impact toughness of the HR-160 alloy decreased continuously with time. A significant percentage of reduction in the ductility occurred in the initial 1000 h of exposure and the subsequent exposure led only to a minimal loss of ductility and impact toughness values. The concomitant microstructural changes were studied using optical metallography, SEM/EDS and X-ray diffraction of extracted residues. The results presented in this paper demonstrated that the HR-160 alloy exhibits good thermal stability characterized by >16% RT elongation after 50,000 h exposures at 649 °C, 760 °C, and 871 °C.     

Effects of stress-aging on the microstructure and properties of an aging forming Al–Cu–Mg–Ag alloy

The effects of stress-aging on the microstructure and properties of Al–Cu–Mg–Ag alloy were studied by hardness test, electric resistivity test, optical microscopy and transmission electron microscopy. The results show that the application of external stress during aging did not change the grain morphology of Al–Cu–Mg–Ag alloy, but resulted in great changes of the precipitations. The precipitation of θ^′ phases was promoted while that of Ω phases was restrained and the initial hardening rate of the alloy decreased. This might originate from the large amounts of dislocations during stress-aging that provided sites facilitating heterogeneous nucleation of θ^′ phases. This was verified by the phenomenon that the density of θ^′ phases increased while that of Ω phases decreased and the peak hardness was reduced when Al–Cu–Mg–Ag alloy was cold deformed with 6% stretch prior to aging.     

Effects of carbon and chromium on the solidification structure and properties of ferrite–austenite duplex heat-resistant alloy

In order to design a new kind of low-cost high-temperature ferrite–austenite duplex alloy, the effects of carbon and chromium on the alloy solidification structure and properties have been investigated with orthogonal experiments. The addition of carbon promotes strongly the formation of austenite and that of carbides in the alloy solidification structure and refines the alloy grains. With the increase of carbon content, the alloy high temperature strength and oxidation resistance at 1250°C improves at first, but then begins to deteriorate greatly when the carbon content exceeds 0.15%. The addition of chromium facilitates the formation of ferrite in the alloy solidification structure. As the chromium content increases, the alloy rupture strength at 1250°C initially is enhanced, but then reduces rapidly, while the alloy oxidation resistance improves continuously.     

Effects of sintering aids on the densification of Mo–Si–B alloys

The effects of seven sintering aids (0.5?at.% Ni, Co, Fe, Cr, Zr, Nb, and Pd) on the densification of Mo–Si–B alloys of six different compositions (Mo, Mo–0.2Si, Mo–0.2Si–0.02B, Mo–2.5Si–2.5B, Mo–7Si–5B, and Mo–8.9Si–7.7B?at.%) are systematically investigated. It was found that Ni, Co, and Fe are effective in enhancing densification of Mo–Si–B alloys, and Ni is the most effective sintering aid. This study supports a previously proposed hypothesis that activated sintering results from enhanced mass transport in the sintering-aid-induced quasi-liquid intergranular films (a type of grain boundary complexion). The relative effectiveness of these sintering aids can be rationalized by analyzing several key thermodynamic parameters that control the stability of premelting-like grain boundary complexions. Future studies are needed to develop interfacial thermodynamic models and methods for computing “grain boundary complexion (phase) diagrams” for multicomponent systems, which can be a useful component for the “Materials Genome” project that will enable better predictions of the activated sintering and other materials phenomena.     

Effects of the porcelain-fused-to-metal firing process on the surface and corrosion of two Co–Cr dental alloys

The aim of this study was to evaluate the effects of a simulated porcelain-fused-to-metal (PFM) firing process on the surface, corrosion behavior, and cell culture response of two cobalt–chromium (Co–Cr) dental alloys. Two Co–Cr dental alloys were tested—a high and a low molybdenum (Mo)-containing alloys. Before PFM firing, as-cast alloy specimens were examined for their microstructure, surface composition, and hardness. Corrosion behavior was evaluated using electrochemical impedance spectroscopy tests. Mouse 3T3 fibroblasts were exposed indirectly to specimens and MTT cell proliferation assays were performed after 3 and 6 days. The cell culture medium exposed to specimens was analyzed for metal ion release. After firing, similar alloy specimens were examined for the same properties. The tests showed that the PFM firing changed both alloys’ microstructures and hardness values. After PFM firing, the corrosion resistance of the low Mo-containing Co–Cr alloy decreased statistically, which corresponded with a reduction of Cr and oxygen levels in the surface oxides via X-ray photoelectron spectroscopy. Also, the MTT assay of this alloy decreased significantly corresponding with an obvious increase of Co release after the firing. For the high Mo-containing Co–Cr alloy, the surface composition, corrosion resistance, and cell culture response were not significantly changed after PFM firing. The results suggested that the corrosion resistance and biocompatibility of the low Mo-containing Co–Cr alloy decreased after PFM firing, whereas the firing process had little effect on the same properties of the high Mo-containing Co–Cr alloy.     

Effects of interphase strength on the damage modes and mechanical behaviour of metal–matrix composites

A numerical version of the generalized self-consistent method previously developed by the authors is combined with the Gurson model to undertake a parametric investigation of the damage mechanisms and their relations with the macroscopic tensile properties of SiC reinforced aluminium, for three different interphase strengths. The results show that the interphase strength is a governing factor for damage propagation in the composite. Thus, transformation of the failure mechanism from reinforcement fracture to void nucleation and growth can be achieved by reducing the interphase bond strength, although the strengthening effects on the composite decrease unfavourably.     

Effects of equal channel angular pressing on the strength and toughness of Al–Cu alloys

Tensile and impact tests were performed on Al–0.63 wt%Cu and Al–3.9 wt%Cu alloys subjected to equal channel angular pressing (ECAP) with different number of passes. Besides the tensile properties, data about the static toughness and the impact toughness were obtained. The strength and the toughness of the Al–Cu alloys were ameliorated and upgraded to a high level collectively. In addition, fracture surface observations show that the fracture behavior of the Al–Cu alloys changes from brittle mode to ductile mode after multi-pass ECAP.     

Effects of nano-kaolinite clay on the freeze–thaw resistance of concrete

This paper investigates the effects of nano-kaolinite clay (NKC) on the freezing and thawing (F–T) behavior of concrete. In our experiments, we substituted NKC for 0%, 1%, 3%, and 5% of mixtures of ordinary Portland, cement, by weight. The blended concrete was prepared using w/c ratio as 0.5. A rapid freeze–thaw Cabinet was then used to measure the resistance of ordinary Portland cement concrete, as opposed to the concrete/NKC mixture, to examine deterioration caused by repeated F–T actions. We regularly measured the properties of the concrete specimens, including the pore structure, mass, electrical resistivity, chloride diffusion coefficient, compressive strength and dynamic modulus of elasticity. A computed tomography scan test evaluated the porosity characteristics of the concrete. This paper also applied scanning electron microscopy and X-ray diffraction tests in order to investigate the micro morphology and chemical element distributions inside of the concrete. The experimental results and visual comparisons revealed that the introduction of NKC improves the F–T resistivity values, as compared to the control concrete. The samples with 5% NKC exhibited the highest compressive strength, chloride diffusion resistivity, relative dynamic modulus of elasticity, and the most electrical resistivity after 125 F–T cycles. We designated the anti-freezing durability coefficient (DF) as the index to assess the F–T resistivity of concrete. The following research discusses the relationship between the concrete’s DF and the number of F–T cycles, compressive strength, chloride diffusion coefficient, and the electrical resistivity of the concrete samples.