T6热处理对触变锻造加低过热铸造制备的A356和A380铝合金的影响（英文）

研究T6热处理对触变锻造A356和A380铝合金的影响。采用低过热铸造(LSC)技术制备用于触变锻造的样品。为了获得等轴晶粒并防止枝晶生长,将样品在高于液相温度20°C时进行浇铸,将浇铸坯料再加热不同时间(20~80 min)后进行触变锻造,变形量为50%,再将触变锻造后的A356和A380铝合金样品进行T6热处理。用光学显微镜、能量弥散X射线谱仪、扫描电镜和布氏硬度仪对经触变锻造、固溶处理和时效处理后样品的显微组织和硬度变化进行检测。结果表明,T6热处理后合金的显微组织更均匀,并分别在A356和A380坯料中形成了新的析出相Mg_2Si和Al_2Cu。相应地,经过人工时效后,样品的硬度大幅度提高,A356铝合金的硬度达到HB 93,A380铝合金的硬度达到HB 120。     

Deriving Ligand Orientation in Weak Protein–Ligand Complexes by DEEP-STD NMR Spectroscopy in the Absence of Protein Chemical-Shift Assignment

Differential epitope mapping saturation transfer difference (DEEP-STD) NMR spectroscopy is a recently developed powerful approach for elucidating the structure and pharmacophore of weak protein–ligand interactions, as it reports key information on the orientation of the ligand and the architecture of the binding pocket. 1 The method relies on selective saturation of protein residues in the binding site and the generation of a differential epitope map by observing the ligand, which depicts the nature of the protein residues making contact with the ligand in the bound state. Selective saturation requires knowledge of the chemical-shift assignment of the protein residues, which can be obtained either experimentally by NMR spectroscopy or predicted from 3D structures. Herein, we propose a simple experimental procedure to expand the DEEP-STD NMR methodology to protein–ligand cases in which the spectral assignment of the protein is not available. This is achieved by experimentally identifying the chemical shifts of the residues present in binding hot-spots on the surface of the receptor protein by using 2D NMR experiments combined with a paramagnetic probe.     

Chiral recognition of proteins having L-histidine residues on the surface with lanthanide ion complex incorporated-molecularly imprinted fluorescent nanoparticles

In this study, lanthanide ion complex incorporated molecularly imprinted fluorescent nanoparticles were synthesized. A combination of three novel approaches was applied for the purpose. First, lanthanide ions [Terbium(III)] were complexed with N-methacryloyl-L-histidine (MAH), polymerizable derivative of L-histidine amino acid, in order to incorporate the complex directly into the polymeric backbone. At the second stage, L-histidine molecules imprinted nanoparticles were utilized instead of whole protein imprinting in order to avoid whole drawbacks such as fragility, complexity, denaturation tendency, and conformation dependency. At the third stage following the first two steps mentioned above, imprinted L-histidine was coordinated with cupric ions [Cu(II)] to conduct the study under mild conditions. Then, molecularly imprinted fluorescent nanoparticles synthesized were used for L-histidine adsorption from aqueous solution to optimize conditions for adsorption and fluorimetric detection. Finally, usability of nanoparticles was investigated for chiral biorecognition using stereoisomer, D-histidine, racemic mixture, D,L-histidine, proteins with surface L-histidine residue, lysozyme, cytochrome C, or without ribonuclease A. The results revealed that the proposed polymerization strategy could make significant contribution to the solution of chronic problems of fluorescent component introduction into polymers. Additionally, the fluorescent nanoparticles reported here could be used for selective separation and fluorescent monitoring purposes.     

Microstructural and Tribological Characterization of Stainless Steel–Reinforced Aluminum Matrix Bimetal Composites Produced at Various Mold Burnout Temperatures

This study aims to identify the optimal burnout temperature (BT) of a plaster mold that was used in bimetal composite production. To achieve this goal, the mold was gradually heated up to 600, 650, 700, and 750?°C prior to melt infiltration casting. Molten A356 aluminum alloy was cast into mold at 730?°C for each casting process. Fifty percent porous 304 stainless steel (SS) preforms, obtained by assembling recycled SS shavings, were placed in a mold and infiltrated by A356 alloy until solidification was completed. The produced bimetal composites were subjected to a ball-on-disc tribometer with loads of 5, 10, and 15 N for 100 m sliding distance using an Al₂O₃ ball as a counterpart. θ-Fe₄Al₁₃ and η-Fe₂Al₅ phases were formed at A356 Al–304 SS interfaces for all samples. Wear rates increased with increasing load and decreased with increasing BT, except at 750?°C. At this temperature, interfacial phases with excessively increased layer thickness, hardness, and brittleness were fragmentized during the test, and these cracked particles decreased wear resistance by participating in the wear process. The most suitable BT of the mold was found to be 700?°C, considering the microstructure and wear results of bimetal composites.     

Investigation of spherisation in microstructures of aluminium casting alloys for thixoforging process

Thixoforging combined with low superheat casting (LSC) is a promising shaping process for aluminium casting alloys. LSC process is based on rapid solidification of an alloy which cast with low pouring temperature. With this method, a feedstock material is produced with non-dendritic microstructure that ready for spherisation in reheating sequence of further semi-solid process. Al-Si alloys are still castable even at low temperatures due to their excellent fluidities. This study subjects to present spherisation of A356 and A380 alloy billets cast with LSC process that provides appropriate beginning material with relatively high sphericity. Obtained billet parts were reheated for different times at a semi-solid state temperature. Some of these billets were directly quenched for observing the effects of reheating and the others were thixoforged. With sufficient reheating time, deformation of thixoforging process did not significantly affect on the spherical microstructure. Unnecessarily long reheating period caused excessive grain growth. A356 alloy had higher spherisation tendency than A380 alloy under similar process conditions.     

L-histidine imprinted synthetic receptor for biochromatography applications

We have proposed novel surface-imprinted beads for selective separation of cytochrome c (cyt c) by N-methacryloyl-(L)-histidine-copper(II) [MAH-Cu(II)] as a new metal-chelating monomer via metal coordination interactions and histidine template. We have combined molecular imprinting with the ability of histidine to chelate metal ions to create ligand exchange beads suitable for the binding of cyt c (surface histidine exposed protein). The histidine imprinted beads were produced by suspension polymerization of MAH-Cu(II)-L-histidine and ethylene glycol dimethacrylate. After polymerization, the template (L-histidine) was removed from the beads using methanolic KOH, thus getting histidine imprinted metal-chelate beads. L-Histidine imprinted metal-chelate beads can be used several times without considerable loss of cyt c adsorption capacity. The association constant (Ka) for the specific interaction between the template imprinted polymer and the template (L-histidine) itself were determined by Scatchard plots using L-histidine imprinted beads and found as 58,300 M(-1). Finally, we have used these histidine imprinted beads for cyt c and ribonuclease A (surface histidine exposed proteins) and enantiometric separation of D- and L-histidine by FPLC.     

Relationship Between Nanoindentation and Wear Properties of Stainless Steel-Reinforced Aluminium Matrix Composite

304 Stainless steel (SS)-reinforced A356 aluminium matrix composites were manufactured by melt infiltration casting. Recycled SS shavings were pressed to obtain porous monoblock preform, and molten Al alloy was infiltrated into vacancies of the preform during casting process. Various preform preheating times (0–60 min) before casting were studied, and the effect of preheating time on relationship between nanoindentation and wear properties of produced composites was discussed. All casting operations were carried out at 730 °C. Fabricated composites were characterized by optical microscope, SEM, FEG-SEM, XRD, EDS, nanoindentation tester and ball-on-disc type tribometer with using Al₂O₃ ball as counterpart. θ-Fe₄Al₁₃ and η-Fe₂Al₅ phases were obtained at the interfaces, except for 60 min preheated sample. These reaction phases increased the hardness, compressive residual stress and consequently wear resistance. On the other hand, when the sample was not preheated or preheated excessively, interface bonding was weakened and crack propagation was occurred. Cracked particles from interfacial phases in these specimens participated wear process and caused increase in wear rate of manufactured composites.     

Adsorption of Ni2+ from aqueous solutions by novel polyethyleneimine‐attached poly(p‐chloromethylstyrene) beads

In this study Ni²⁺ adsorption properties of polyethyleneimine (PEI)‐attached poly(p‐chloromethylstyrene) (PCMS) beads were investigated. Spherical beads with an average size of 186 μm were obtained by the suspension polymerization of p‐chloromethylstyrene conducted in an aqueous dispersion medium. Owing to the reasonably rough character of the bead surface, PCMS beads had a specific surface area of 14.1 m²/g. PEI chains could be covalently attached onto the PCMS beads with equilibrium binding capacities up to 208 mg PEI/g beads, via a direct chemical reaction between the amine and chloro‐methyl groups. After PEI adsorption with 10% (w/w) initial PEI concentration, free amino content of PEI‐attached PCMS beads was determined as 0.91 mEq/g. PEI‐attached PCMS beads were utilized as adsorbents in the adsorption/desorption of Ni²⁺ ions from synthetic solutions. The adsorption process was fast; 90% of adsorption occurred within 90 min, and equilibrium was reached at around 2 h. Adsorption capacity was obtained to be 78.2 mg/g at a pH of about 6.0. The chelating beads can be easily regenerated by 0.1 M HNO₃ with higher effectiveness. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2467–2473, 2002     

Preconcentration of phosphate ion onto ion-imprinted polymer

In this study, selective separation and preconcentration of phosphate ions on the phosphate-imprinted chitosan-succinate beads have investigated. Chitosan-succinate, phosphate, epichlorohydrin were used as the complexing monomer, template and crosslinking agent, respectively. In the first step, chitosan was modified with succinic anhydrides and complex formation occurred between carboxylic acid functional groups and iron(III) ions. Secondly, Fe(III)-chitosan-succinate particles were reacted with phosphate ions. Afterwards, particles were crosslinked with epichlorohydrin and the template (phosphate ions) was removed using 1M KOH solution. Selective cavity for the phosphate ion was obtained in the phosphate-imprinted metal-chelate polymer. These phosphate-imprinted metal-chelate polymer was used in the adsorption-desorption process. The adsorption process was fast and equilibrium was reached around 30 min. The adsorption behaviour of this system was described approximately by the Langmuir equation. Percent extraction, distribution ratio and selectivity coefficients of phosphate and other ions using non-imprinted and phosphate-imprinted polymer were also determined and comparison of these data was reported.     

A Model for Molecular Weight Prediction in Acrylonitrile Polymerization

Poly ethylene terephthalate (PET)-based nanocomposites containing three differently modified clays were prepared by melt compounding. The influence of type of modified clay on surface properties of the resultant nanocomposite was investigated by various analytic techniques, namely, Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), contact angle measurement (CAM), scanning electron microscopy (SEM) and reflectance spectroscopy (RS). Any possible interaction between each nanoclay and PET at the surface was elucidated by Fourier transform infrared spectroscopy. Atomic force microscopy studies of the resultant nanocomposites showed increased in surface roughness compared to pure PET. Contact angle measurements on the resultant PET composites demonstrated that the wettability of such composites depends on hydrophilicity of the nanoclay particles. Scanning electron microscopy images illustrated poor interfacial interaction between PET and Na⁺ clay particles causing fracture type non-uniformity of PET/Na⁺ clay nanocomposite.