Experiments on mechanical consolidation of rapidly solidified (RS) powder of 6061 + 26 mass% Si alloy were performed using the oscillating-die extrusion method. The RS powder was wrapped in thin-wall 6061-alloy cup 35 mm in diameter and vacuum-compressed by means of 100 ton press. Bars 8 mm in diameter were extruded with cross-section reduction of λ = 19 without any preheating of the charge. Tubes with a diameter/wall thickness of 14 mm/1 mm and cross-section reduction of λ = 33 were also manufactured with success. TEM/STEM observations revealed a very fine structure of as-extruded material and bimodal distribution of quasi-spherical silicon particles. Statistical analysis revealed a silicon fine fraction of 0.1–0.7 μm and a coarse fraction 2.1–2.5 μm in diameter. Examination by means of TEM did not reveal any significant changes in the morphology of the silicon particles, even when a high extrusion ratio and the material annealing after deformation were used. Hot compression tests on as-extruded rods (λ = 19) and preliminary annealed samples were performed at a constant true strain rate of 5 × 10?3 s?1 within the temperature range of 293–823 K. High strength of the material and relatively high ductility of samples deformed by compression up to ?t ? 0.4 were observed. The maximum flow stress value for as-extruded material was reduced with deformation temperature from ~390 to ~3.5 MPa for 293 and 823 K, respectively. Annealing of the samples at 773 K/30 min was found to reduce the maximum flow stress by 30–40%. Tensile strengths of similar as-cast alloys and materials manufactured by means of other powder metallurgy methods were shown for the purpose of comparison. 相似文献
The effect of an uniform magnetic field with a flux density up to 1 T and different configurations relative to the electrode surface on the electrocrystallization of Fe on polycrystalline Au(1 1 1) from acidic sulphate electrolyte has been investigated. It was found, irrespective of the applied parameters, that the deposition proceeds through successive nucleation and growth steps. The first one related to 2D growth was followed by a second nucleation and 3D diffusion controlled growth. At potential of −1500 and −1550 mVMSE nucleation proceeds via a progressive mode, while at −1650 mVMSE it follows an instantaneous mode. A strong influence of the parallel-to-electrode magnetic field on the nucleation processes was found for the progressive mode, which leads to the increase of the growth rate and as a consequence to retardation of the nucleation rate of the 3D step. Additionally, in this configuration at a sufficiently high magnetic flux density a third nucleation step could be observed (3D), which was found to be also affected by a magnetic field. No effect of a perpendicular-to-electrode magnetic field on the nucleation has been observed. The effects of a magnetic field on the nucleation and growth processes are discussed with respect to the magnetohydrodynamic effect (MHD) and confirmed by rotating disc electrode (RDE) experiments. 相似文献
Introduction of hydrogen technology provided hot-rolling fabrication of thin strips from chips of VT1-0 titanium alloy without chip remelting. It is established that the plasticity of strips made from this alloy largely depends on the presence of excess dispersed particles in the structure. It is assumed that they are the sparingly soluble oxides formed during the destruction in the course of pressure treatment of the oxide film retained on the chip surface. After homogenization, which can be combined with vacuum annealing for hydrogen removal, the structure and mechanical properties of the strips obtained by hydrogen technology correspond to the characteristics of semifinished products fabricated by ingot technology. 相似文献
A simplified two-dimensional finite elements model was created for a polyvinyl alcohol (PVA) coated Bioglass® strut undergoing tensile stresses (loading mode I). The strengthening contributions due to the infiltration of coating into surface cracks and coating's stiffness were evaluated in terms of stress intensity factor KI and tensile stresses σyy in the proximity of the crack tip. The infiltration of the coating until the crack tip resulted as the most effective criterion for the struts strengthening. Bioglass® based scaffolds were dip coated into PVA and PVA/microfibrillated cellulose (MFC) aqueous solutions and tested in tensile load. Coated samples exhibited remarkably higher tensile strength than non-coated ones, which further raised with the increased amount of MFC. Contact angle θ and linear viscosity η measurements of PVA/MFC solutions showed that MFC caused a reduction in θ and a drastic increase in η, indicating that a balance between these two effects must be achieved. 相似文献
In the past few years, gallium‐68 has demonstrated significant potential as a radioisotope for positron emission tomography (PET), and the optimization of chelators for gallium coordination is a major goal in the development of radiopharmaceuticals. Methylaminotriazacyclononane trimethylphosphinate (MA‐NOTMP), a new C‐functionalized triazacyclononane derivative with phosphinate pendant arms, presents excellent coordination properties for 68Ga (low ligand concentration, labelling at low pH even at room temperature). A “ready‐to‐be‐grafted” bifunctional chelating agent (p‐NCS‐Bz‐MA‐NOTMP) was prepared to allow 68Ga labelling of sensitive biological vectors. Conjugation to a bombesin(7–14) derivative was performed, and preliminary in vitro experiments demonstrated the potential of MA‐NOTMP in the development of radiopharmaceuticals. This new chelator is therefore of major interest for labelling sensitive biomolecules, and further in vivo experiments will soon be performed. 相似文献
We report herein an efficient and mechanistically unique tandem chemoselective 1,2‐/1,4‐migration of the thio group in keto thioesters that provides substituted butenolides in moderate to excellent yields. Thus, α‐keto thioesters in the presence of stabilized phosphonate carbanions undergo tandem 1,2‐sulfur migration; whereas 1,4‐migration of the thio group has been achieved with the same thioesters after the treatment with Wittig reagents followed by BF3⋅OEt2‐catalyzed tandem reaction. The crossover experiments and the isolation of intermediates reveal a stepwise mechanism for both of these transformations.
The growth of InMnAs quantum dots by low pressure MOVPE technique on patterned (1 0 0) GaAs substrates was studied. The patterning in the form of ridges with sidewalls having (2 1 1) and (3 1 1) facets was prepared by wet chemical etching via a GaAs/AlAs sacrificial etching mask structure. AFM studies showed that the dots formation and distribution were very similar for both types of facets under study. InMnAs dot density on the (3 1 1) plane is about 5–7 times lower in comparison to that on the (1 0 0) planar substrate. The dots on sidewalls are larger in comparison to average dots formatted on planar GaAs (1 0 0) substrate. The lateral dimensions of these dots are in the interval 100–180 nm. In addition, dot distribution along the sidewall (from top to bottom) is not uniform. A higher dot concentration was observed close to the intersection of (3 1 1) facets with concave bottom part of the valleys between ridges. Finally, no dots were grown on the (1 0 0) plane created by self-faceting on the top of the triangular ridges. This is probably a consequence of the high quality of the (1 0 0) facet formed by lateral overgrowth. 相似文献
Conventional static mixers typically require high length to diameter ratios to be effective. This paper considers static mixers design to increase first appearance times in short, fat reactors. Three types are considered: conical baffles and annular baffles for tubular reactors and axial baffles for reactors with a rectangular cross-section. Relatively simple designs allow production increases (or reactor volume decreases) on the order of 20–50%. 相似文献