Effect of NiS addition on nitridation of alumina to aluminum nitride using polymeric carbon nitride as a nitridation reagent

We investigated the effect of adding nickel(II) sulfide (NiS) on nitridation of alumina (Al₂O₃) to aluminum nitride (AlN) using polymeric carbon nitride (PCN), which was synthesized by polymerization of dicyandiamide at 500 °C. The product powders obtained from nitridation of a mixture of δ-Al₂O₃ and NiS powders (mole ratio of 1:0.01) at various reaction temperatures were characterized by powder X-ray diffraction, ²⁷Al magic-angle spinning nuclear magnetic resonance, and Raman spectroscopy. δ-Al₂O₃ began to convert to AlN at 900 °C and completely converted to AlN at 1300 °C. The as-synthesized sample powders contained nitrogen-doped carbon microtubes (N-doped CMTs) with a length of several tens of mm and thickness of ca. 3 µm. The addition of NiS to δ-Al₂O₃ resulted in the enhancement of the amount of N-doped CMTs and nitridation rate, which might be due to the catalytic action of Ni particles on the thermal decomposition of vaporized PCN. The change in Raman spectra with reaction temperatures indicated that the crystallinity of N-doped CMTs was increased by calcining at higher reaction temperatures.     

Cr3+-Yb3+-Er3+共掺杂NaYF4微管的制备及上转换发光

利用水热法制备了Cr~(3+)-Yb~(3+)-Er~(3+)共掺杂的NaYF_4微管。在980nm的红外激光激发下,微管产生了强的可见上转换荧光。相比于Yb~(3+)-Er~(3+)共掺NaYF4微棒,微管的绿光和红光强度分别提高30倍及20倍。上转换荧光增强的原因被归结为Cr~(3+)掺入引起稀土离子周围晶体场对称性的减弱。对微管的生长过程及上转换发光机制进行了分析。     

EXPERIMENTAL STUDY ON FLOW CHARACTERISTICS OF LIQUID IN CIRCULAR MICROTUBES

Glass, silicon, and stainless steel microtubes with diameters of 79.9–166.3 μm, 100.25–205.3 μm, and 128.76–179.8 μm, respectively, were employed to study the characteristics of frictional resistance for deionized water flow in microtubes. Glass and silicon microtubes can be treated as smooth ones, whereas stainless steel microtubes with 3%–4% relative roughness has to be treated as coarse ones. It can be concluded from experimental results that for fully-developed water flow in smooth glass and silicon microtubes, the product of Darcy friction factor f and Reynolds number Re remains approximately 64, which is consistent with the results in macrotubes. While the value of f ˙ Re for water flow in rough stainless steel microtubes is 15%–37% higher than 64, it is distinctly different from the conventional conclusion that relative roughness below 5% has no effect on the flow resistance for incompressible fluid flow in macrotubes.     

Template synthesis and magnetic response of polyaniline/Fe3O4 composite microtubes

Template synthesis technique was employed to prepare magnetic polyaniline (PANI)/Fe₃O₄ composite microtubes using anodic aluminum oxide (AAO) membrane as template. Magnetic microtubes were obtained through in situ polymerization of aniline in the presence of Fe₃O₄ nanoparticles in the microchannels of template. A tubular structure was formed once when aniline was preferentially adsorbed and polymerized on the surface of channels wall. Electron microscope images demonstrated that the shape and size of guest (PANI/Fe₃O₄ composite microtubes) were strictly depended on those of the host (template channels). Magnetic force microscopy images showed that the PANI/Fe₃O₄ composite microtubes possessed reasonable magnetism and the magnetism distribution of microtubes was regular as distribution of template channels. Moreover, the magnetic response and oriented arrangement of PANI/Fe₃O₄ microtubes were fulfilled in the magnetic field. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Core–Sheath Wet Electrospinning of Nanoporous Polycaprolactone Microtubes to Mimic Fenestrated Capillaries

Formation of capillary vessel structures in scaffolds is critical for engineering various tissues and organs. Various biofabrication techniques are developed in recent years to create scaffolds integrated with perfusion channels. However, rapid fabrication of artificial capillary vessels (<10 µm) still remains challenging. In this study, a novel electrospinning approach is developed to fabricate nanoporous polycaprolactone microtubes as potential functional capillaries. The results show that ambient environment parameters and solution properties affect the pore formation and tube morphology. Porous microbeads, helical fibers, and microtubes were fabricated under different processing conditions. The optimal tubular structure is obtained with consistent viscosities between the core and the sheath solutions. The biomimetic nanoporous microtubes hold great potential for vascularization in tissue engineering.