A large‐scale double‐stage‐screw 3D printer for fused deposition of plastic pellets

Fused deposition molding (FDM) is the most popular technology in the fields of three‐dimensional printing, but it is hard to use a variety of plastic materials due to the limitation of filament form of material. Using plastic pellets as printing materials gives advantages in cost, processing speed, and available materials. In this work, a large‐scale double‐screw FDM three‐dimensional printer based on plastic pellets has been designed. It is capable of printing large plastic products at a low cost and high speed. Using ABS + 10%GF as printing material, this work is first focused on the effects of the pressure and speed of the metering screw on the flowrate of melt. The equation for the relationship of these three parameters was established as well. Based on this equation, the effects of melt flow, printing speed, and layer thickness on the width of fused filament were investigated with experiments. Furthermore, the effects of printing spacing between fused filaments on surface accuracy and bonding strength were also explored. By printing models, it was revealed that the designed printer is able to print products with plastic pellets. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45147.     

Investigations into the impact of the substrates with ultra thin seed layers deposited by atomic layer deposition on ZnO Nanowire Arrays

ABSTRACT: The impact of various substrates and ZnO ultra thin seed layers prepared by atomic layer deposition on the geometric morphology of subsequent ZnO nanowire arrays (NWs) fabricated by the hydrothermal method was investigated. The investigated substrates included B-doped ZnO films, Indium Tin Oxide films, single crystal silicon (111), and glass sheets. Scanning electron microscopy and X-ray diffraction measurements revealed that the geometry and aligment of the NWs were controlled by surface topography of the substrates and thickness of the ZnO seed layers, respectively. According to atomic force microscopy data, we suggest that the substrate, fluctuate amplitude and fluctuate frequency of roughness on ZnO seed layers have a great impact on the alignment of the resulting NWs, wherease the influence of the seed layers' texture was negligible. Transmission Electron Microscopy and Photoluminescence spectroscopy showed that crystal defects were influenced greatly by substrates instead of seed layers.     

Mechanically activated catalyst mixing for high-yield boron nitride nanotube growth

ABSTRACT: Boron nitride nanotubes (BNNTs) have many fascinating properties and a wide range of applications. An improved ball milling method has been developed for high-yield BNNT synthesis, in which metal nitrate, such as Fe(NO3)3, and amorphous boron powder are milled together to prepare a more effective precursor. The heating of the precursor in nitrogen-containing gas produces a high density of BNNTs with controlled structures. The chemical bonding and structure of the synthesized BNNTs are precisely probed by near-edge X-ray absorption fine structure spectroscopy. The higher efficiency of the precursor containing milling-activated catalyst is revealed by thermogravimetric analyses. Detailed X-ray diffraction and X-ray photoelectron spectroscopy investigations disclose that during ball milling the Fe(NO3)3 decomposes to Fe which greatly accelerates the nitriding reaction and therefore increases the yield of BNNTs. This improved synthesis method brings the large-scale production and application of BNNTs one step closer.     

Can misfit dislocations be located above the interface of InAs/GaAs (001) epitaxial quantum dots?

ABSTRACT: InAs/GaAs(001) quantum dots grown by droplet epitaxy were investigated using electron microscopy. Misfit dislocations in relaxed InAs/GaAs(001) islands were found to be located approximately 2 nm above the crystalline sample surface, which provides an impression that the misfit dislocations did not form at the island/substrate interface. However, detailed microscopy data analysis indicates that the observation is in fact an artefact caused by the surface oxidation of the material that resulted in substrate surface moving down about 2 nm. As such, caution is needed in explaining the observed interfacial structure.     

SnO2 nanorod arrays: low temperature growth, surface modification and field emission properties

SnO(2) nanorod arrays have been deposited on 4 inch SiO(2)/Si and Si wafers and stainless steel substrates by plasma-enhanced chemical vapor deposition without any high temperature treatment or additional catalysis. The SnO(2) nanorods grow up from seed nanocrystals along the [110] preferential direction by a self-catalyzed vapor-solid growth mechanism. The surface of the SnO(2) nanorods was modified by ZnO, Pt and Ni nanocrystals. After surface modification, the field emission properties of the SnO(2) nanorod arrays are improved. The Ni nanocrystal with sharp tips and edges act as additional field emission sites to SnO(2) nanorods and thus the Ni/SnO(2)/SiO(2)/Si outperforms other samples due to the synergistic effects of good conductivity and hierarchical sharp apexes. The field enhancement factor of the Ni/SnO(2)/SiO(2)/Si increased around 3 times while the turn-on field of 8.0 V μm(-1) is about one third of the SnO(2)/SiO(2)/Si device.     

Doxorubicin loaded silica nanorattles actively seek tumors with improved anti-tumor effects

Silica nanorattles (SNs) have proven to be promising vehicles for drug delivery. In order to further enhance efficacy and minimize adverse effects, active targeted delivery to tumors is necessary. In this work, SNs modified with a tumor specific targeting ligand, folic acid (FA), was used as carrier of doxorubicin (DOX) (DOX-FA-SNs). Drug loading, cytotoxicity and cellular uptake of DOX-FA-SNs in vitro in human cervical carcinoma cells (HeLa cells) were evaluated. DOX-FA-SNs showed a higher cytotoxicity in human cervical carcinoma cells (HeLa cells) than DOX loaded carboxyl (-COOH) and poly(ethylene glycol) (PEG) modified SNs (DOX-COOH-SNs and DOX-PEG-SNs, respectively). However, DOX-FA-SNs showed lower cytotoxicity in folate receptor negative normal mouse fibroblast cells (L929 cells) compared with free DOX. In vivo tumor-targeted fluorescence imaging indicated specific tumor targeting and uptake of FA-SNs in nude mice bearing subcutaneous HeLa cell-derived xenograft tumors. In vivo anti-tumor experiments demonstrated that DOX-FA-SNs (10 mg kg(-1) of DOX) significantly regressed the tumor growth and reduced toxicity compared with free DOX. These results have great significance in developing and optimizing SNs as effective intracellular delivery and specific tumor targeting vehicles.     

Phase formation of REBa2Cu3O7−δ (RE: Y0.5Gd0.5, Y0.5Nd0.5, Nd0.5Gd0.5) superconductors from nanopowders synthesised via co-precipitation

Phase formation of REBa₂Cu₃O_7−δ (RE: Y_0.5Gd_0.5, Y_0.5Nd_0.5, Nd_0.5Gd_0.5) superconductors synthesised via co-precipitation (COP) method were investigated by thermogravimetric analysis (TGA), differential thermal analysis (DTA) and X-ray diffraction (XRD) analysis. All samples showed identical thermal decomposition behaviour from the thermogram in which 5 major weight losses were observed. However, XRD of the samples at different heat treatment temperatures showed different diffraction patterns indicating different thermolytic processes. Meanwhile, transmission electron microscopy and surface area analysis revealed that the powders obtained from COP have particle sizes ranging from 7 to 12 nm with relatively large surface area. Molar ratios of prepared samples obtained were near to the theoretical values as confirmed by elemental analyses using X-ray fluorescence (XRF). The T_C(R=0) for sintered YGd, YNd and NdGd were 87 K, 86 K and 90 K, respectively. Surface morphological study via scanning electron microscope showed the structures of samples were dense and non porous.     

Fenton试剂对剩余污泥脱水性能的改善

研究了利用Fenton试剂调理城市污水处理厂剩余污泥,通过测定污泥毛细吸水时间(CST)、污泥比阻(SRF)和泥饼含水率来表征污泥脱水性能的变化,分别考察了污泥初始pH、H2O2投加量、H2O2/Fe2+、反应温度和反应时间对污泥调理效果的影响。综合考虑,确定Fenton调理污泥的最佳条件为:pH=3、抽滤脱水和离心脱水H2O2最佳投加量分别为3 g/L和9 g/L、H2O2/Fe2(+质量比)最佳范围为8～12、反应温度50℃、反应时间60 min。对污泥离心上清液中胞外聚合物(EPS)含量的研究表明,Fenton调理后污泥上清液中蛋白质和多糖含量有大幅升高,说明Fenton试剂能有效氧化破解EPS,从而提高污泥的絮凝性,改善污泥的脱水性能。Fenton氧化后污泥颗粒粒径变小,比表面积增大。