Microstructure and properties of alumina-silicon carbide nanocomposites fabricated by pressureless sintering and post hot-isostatic pressing

Al2O3/5%SiC nanocomposites were fabricated by pressureless sintering using MgO as a sintering aid and then post hot-isostatic pressed (HIP), which can subsequently break through the disadvantage of hot-pressing process. The MgO additive was able to promote the densification of the composites, but could not induce the grain growth of Al2O3 matrix due to the grain growth inhibition by nano-sized SiC particles. After HIP treatment, Al2O3/SiC nanocomposites achieved full densification and homogeneous distribution of nano-sized SiC particles. Moreover, the fracture morphology of HIP treated specimens was identical with that of the hot-pressed Al2O3/SiC nanocomposites showing complete transgranular fracture. Consequently, high fracture strength of 1 GPa was achieved for the Al2O3/5%SiC nanocomposites by pressureless sintering and post HIP process.     

Characteristic evaluation of Al2O3/CNTs hybrid materials for micro-electrical discharge machining

The characteristic evaluation of aluminum oxide (Al₂O₃)/carbon nanotubes (CNTs) hybrid composites for micro-electrical discharge machining (EDM) was described. Alumina matrix composites reinforced with CNTs were fabricated by a catalytic chemical vapor deposition method. Al₂O₃ composites with different CNT concentrations were synthesized. The electrical characteristic of Al₂O₃/CNTs composites was examined. These composites were machined by the EDM process according to the various EDM parameters, and the characteristics of machining were analyzed using field emission scanning electron microscope (FESEM). The electrical conductivity has a increasing tendency as the CNTs content is increased and has a critical point at 5% Al₂O₃ (volume fraction). In the machining accuracy, many tangles of CNT in Al₂O₃/CNTs composites cause violent spark. Thus, it causes the poor dimensional accuracy and circularity. The results show that conductivity of the materials and homogeneous distribution of CNTs in the matrix are important factors for micro-EDM of Al₂O₃/CNTs hybrid composites.     

Portable nano probe for micro/nano mechanical scratching and measuring

A nano probe system which can measure precise micro parts or optical parts in nanometer range resolution and scratch contact force in mN scale was demonstrated. The nano probe was originally designed for on-machine measuring applications and one kind of contact type measuring probes was designed for miniaturized or microfactory system. It ideally should be of small size and able to measure surface topography in nanometer scale. A commercial capacitive displacement sensor was proposed. It was a new concept in nano probe systems which can measure the displacement of shaft driven by the variation of surface topography. The nano probe mainly consisted of three parts: a capacitive displacement sensor, a porous type air slide and a contact probe part with various tip radiuses. The porous type air slide assured the shaft slided smoothly with controllable normal force in mN scale and had high positioning accuracy. The probe part which was directly in contact with target surface, can be applied to micro/nanoscale scratching as well as the measurement of sample topography by a simple tip change.     

纳米铝晶粒生长的抑制方法(英文)

对纳米铝、铝合金和铝基化合物的晶粒生长行为进行了比较。首先,采用球磨粉末的烧结方法制备纳米铝。然后,添加能在晶界形成热稳定二次相和阻碍晶界运动的元素,如Mn、Zr和混合稀土元素,形成纳米铝合金。最后,因为多壁碳纳米管有望在晶界处抑制晶粒生长,因此,制备含有多壁碳纳米管的纳米铝复合材料。将3种样品在550 oC,5 d下进行退火处理,比较了退火时间对样品维氏硬度的影响。结果表明,采用多壁碳纳米管阻碍纳米铝晶粒生长的方法最为有效。     

Mechanical properties of CNT reinforced hybrid functionally graded materials for bioimplants

The hybrid functionally graded materials (FGM) of hydroxyapatite (HA), stainless steel 316L (SS316L) and carbon nanotubes (CNT) were synthesized for biomedical implants. Three different types of FGM were produced by the combination of SS316L and CNT to reinforce HA in discrete layers of FGM. In the first type of FGM, concentration of SS316L was varied from 10% to 40% (mass fraction) with an increment of 10% to reinforce micro HA. In the second type of FGM, 0.5% (mass fraction) functionalized CNT was added by maintaining the rest of composition as that of the first type of FGM. In the third type of FGM, mixture of micro and nano HA (mass ratio1:1) was used, keeping rest of composition similar to the second type of FGM. All types of FGM were subjected to uniaxial compaction and sintered by pressureless sintering technique at similar compaction and sintering parameters. The results show that the densification is enhanced with the addition of CNT and nanocrystalline HA in the FGM. Hardness and fracture toughness increase in both FGM reinforced with CNT, but the increase of the hardness and fracture toughness are more pronounced in FGM with micro and nanocrystalline HA.     

Purification and Characterization of β-amylase from Bacillus polymyxa No. 26-1

An extracellular β-amylase, which was easily adsorbable onto raw corn starch, was purified 22.5-fold from a new isolate of Bacillus polymyxa No 26–1 with a M_r of 53 kDa and pI of 9.1. The optimum temperature was 45°C and pH 5.5 for raw corn starch. Thermal stability at 40°C and pH stability at 5.0–8.5 were shown. The degradation ofraw starch by β-amylase was greatly stimulated by pullulanase addition. Scanning electron micrographs revealed that starch granule degradation by the enzyme alone occured at the equatorial grooves of lecticular granules. Corn starch granules hydrolyzed by β-amylase had large holes on granule surfaces.     

Comparative studies on the binding site of anesthetics to GABA a receptors using <i>in silico</i> docking methods

Background: Although the GABAA receptor (GABAAR) has been proposed as the main action site for sevoflurane, isoflurane, halothane, enflurane, propofol, and benzodiazepines (BZDs), binding of these anesthetics with high-resolution structures of the GABAAR have been rarely examined by comparative docking analyses. Moreover, various combinations of ligands on more GABAARs with various subtypes need to be analyzed to understand the elaborate action mechanism of GABAARs better because some GABAA ligands showed specificity toward the distinct subtypes of the GABAAR. Methods: We performed in silico docking analysis to compare the binding modes of sevoflurane, isoflurane, halothane, enflurane, propofol, and BZDs to the GABAAR based on one of the most recently provided 3D structures. We performed the docking analysis and the affinity-based ranking of the binding sites. Results: Our docking studies revealed that isoflurane, halothane, and enflurane docked in an extracellular domain (ECD) on GABAARs, in contrast to sevoflurane. Conclusion: Our results supported a multi-site mechanism for the allosteric modulation of propofol. Propofol was bound to the pore or favored various subsites in the transmembrane domain (TMD). Our result confirmed that different chemically related BZD ligands interact via distinct binding modes rather than by using a common binding mode, as previously suggested.