Grafting polymerization of l-lactide on the surface of hydroxyapatite nano-crystals

A novel method of grafting ring-opening polymerization of l-lactide (LLA) onto the surface of hydroxyapatite nano-particles (n-HAP) was developed. PLLA was directly connected onto the HAP surface through a chemical linkage. The PLLA-g-HAP particles could be stably dispersed in organic solvent such as chloroform for several weeks. The n-HAP particles still retained the original dimension and shape after the grafting of PLLA. Compared with the ³¹P MAS-NMR spectrum of pure HAP powders, there appeared a downfield displacement of 1.2 ppm in the spectrum of PLLA-g-HAP. Fourier transformation infrared (FT-IR) spectra further confirmed the existence of PLLA on the surface of PLLA-g-HAP. The amount of grafted polymer determined by thermal gravimetric analysis (TGA) was about 6% in weight. The tensile strength and elongation at break of the PLLA/PLLA-g-HAP composite containing 8 wt% of PLLA-g-HAP were 55 MPa and about 10-13%, respectively, while those of the PLLA/n-HAP composites were 40 MPa and 3-5%, respectively.     

Tribocorrosion Behavior and Degradation Mechanism of 316L Stainless Steel in Alkaline Solution: Effect of Tribo-Film

Tribocorrosion behavior and degradation mechanism of 316L stainless steel (SS) in alkaline solution were studied. The SS was worn in 0.1 mol/L NaOH solution with di? erent potentials to investigate the synergism between wear and corrosion. The SS showed larger material loss at a cathodic potential of - 0.8 V and lower material loss at anodic potential when compared with that under pure wear condition. This was inverse when compared with that in other corrosive media,such as H ₂ SO     

X-ray diffraction and microstructural studies on hydrothermally synthesized cubic barium titanate from TiO2-Ba(OH)2-H2O system

In our earlier studies synthesis of pure barium titanate (BT) from TiO₂-Ba(OH)₂-NH₃ system was reported. This work describes a novel route for preparing cubic barium titanate from TiO₂-Ba(OH)₂-H₂O system without addition of any mineraliser. The experimental parameters varied were: reaction time (half-an-hour to 3 h), reaction temperature (80 to 150 °C) and [Ba/Ti] ratio (0.92 to 1.64). The progress of reaction for formation of BT was monitored by analyzing the X-ray diffraction data obtained under different processing conditions. Mono-phasic barium titanate powder having a mean crystallite diameter (MCD) of 26 nm along (101) plane was formed when the reaction was carried out for 3 h at 150 °C. The estimated strains on the planes of the BT nano-crystals were found to be negligible. The microstructure of pure BT showed the particles to be of single crystallite nature with average size matching with the MCD value calculated from the XRD data.     

One-step synthesis of hematite (α-Fe2O3) nano-particles by direct thermal-decomposition of maghemite

In this research work, α-Fe₂O₃ nano-particles were prepared by direct thermal-decomposition of γ-Fe₂O₃. Precursor powders (γ-Fe₂O₃) were synthesized by wet chemical method at room temperature and then, the precursors were subsequently calcined in air for 1 h at 500 °C. Samples were characterized by thermal gravimetric analysis (TGA), X-ray diffraction (XRD), energy dispersive spectra (EDS), infrared spectrum (IR) and transmission electron microscopy (TEM), respectively. The XRD, EDS, and IR results indicated that the synthesized α-Fe₂O₃ particles were pure. The TEM image showed that the α-Fe₂O₃ nano-particles were spherical and 18 ± 2 nm in size. Magnetic properties have been detected by a vibrating sample magnetometer (VSM) at room temperature. The γ-Fe₂O₃ and α-Fe₂O₃ nano-particles exhibited a super-paramagnetic and weak ferromagnetic behavior at room temperature, respectively. Using the present method, hematite nano-particles can be produced without expensive organic solvent and complicated equipment.     

纳米SiO2抑制PVC中增塑剂DOP迁移的研究

实验通过添加纳米粒子SiO2,研究抑制软质聚氯乙烯(PVC)中增塑剂邻苯二甲酸二辛脂(DOP)迁移规律,评价PVC样品溶剂抽出率,对挥发损失率、拉伸性能和邵氏硬度的测定分析,得出以下结论:纳米粒子SiO2可以抑制软质PVC中DOP的迁移。用正己烷浸泡PVC样品,随浸泡时间的延长,溶剂抽出率增大;随着添加的纳米SiO2含量的增加,样品的溶剂抽出率降低。在浸泡24h后,添加5份纳米SiO2样品PVC的溶剂抽出率为18.9%,比对照(25.6%)降低了26.2%。添加少量的纳米SiO2并没有使样品的挥发损失率明显降低,添加1~5份不同量的纳米SiO2的样品的挥发损失率均比不添加纳米SiO2的对照样品低。随着无机纳米粒子含量的增加,样品的拉伸强度和断裂伸长率反而降低,硬度有所增加。      

Photoelectrochemical properties of sol–gel synthesized titanium dioxide nano-particles using different acids: X-ray photoelectron spectroscopy reveals the induced effect of hydrolysis precursor

Properties such as crystalline structure (X-ray diffraction – XRD), surface chemistry–electronic states (X-ray photoelectron spectroscopy – XPS), morphology and particle size-distribution (Transmission Electron Microscopy – TEM), electronic structure-band-gap (UV–vis spectroscopy) and surface area (BET-nitrogen physisorption) were analyzed for titanium dioxide (TiO₂)-semiconductor-surfaces synthesized by sol–gel route using nitric, acetic and phosphoric acids as hydrolysis precursors. According to XRD analysis, it was established that anatase phase has been obtained with a particle size linked to the acid of hydrolysis employed (i.e. dissociation constant), as also demonstrated by TEM and area BET. On the other hand, using XPS, a shift toward lower binding energies was observed from TiO₂ obtained using HNO₃ promoting some structural modification and the reduction in the band-gap, inducing a better faradic current-performance by decreasing charge-transfer resistance during polarization and at induced-generated photocurrent using UV-light.     

纳米颗粒材料的制备及其组装

较系统地介绍了纳米颗粒材料制备的一般方法及其特点,对纳米颗粒材料的组装研究现状作了介绍,并展望了纳米颗粒晶的应用前景。     

聚丙烯/四氧化三铁纳米复合材料的制备、表征及磁性能研究

采用固态高速搅拌预混-熔融密炼过程制备了磁性聚丙烯(PP)/四氧化三铁(Fe3O4)纳米复合材料,并分别利用扫描电镜(SEM)、X射线衍射(XRD)、示差扫描量热仪(DSC)、热失重分析仪(TGA)和振动样品磁强计(VSM)对获得的复合材料的形貌、结构及磁性能进行了表征。结果显示:Fe3O4纳米粒子质量分数为5%时在聚合物基体中分散良好,基本呈单颗粒分散;随着Fe3O4含量的增加,粒子在PP基体中团聚程度加剧。Fe3O4和PP在复合材料中保持了各自的晶相结构,但是Fe3O4的加入降低了PP的结晶程度。同时,Fe3O4的加入提高了PP的热稳定性。振动样品磁强计(VSM)的结果表明:复合材料的饱和磁化强度(Ms)随Fe3O4含量的增加而增加,并呈线性的依赖关系;矫顽力(Hc)和剩余磁化强度(Mr)均很小,所制得的磁性纳米复合材料近似呈超顺磁性;该研究为磁性高分子纳米复合材料的制备提供了一种简单易行,Fe3O4纳米粒子在聚合物基体中良好分散,并且可以大批量生产磁性纳米复合材料的方法,并可能促进PP/Fe3O4纳米复合材料在电磁屏蔽和微波吸收等领域的应用。     

Metallic nano-particles for trapping light

We study metallic nano-particles for light trapping by investigating the optical absorption efficiency of the hydrogenated amorphous silicon thin film with and without metallic nano-particles on its top. The size and shape of these nano-particles are investigated as to their roles of light trapping: scattering light to the absorption medium and converting light to surface plasmons. The optical absorption enhancement in the red light region (e.g., 650nm) due to the light trapping of the metallic nano-particles is observed when a layer of metallic nano-particle array has certain structures. The investigation of the light with incident angles shows the importance of the coupling efficiency of light to surface plasmons in the metallic nano-particle light trapping.

PACS

73.20.Mf, 42.25.s, 88.40.hj     

Effect of fluid–particle-interactions on dispersing nano-particles in epoxy resins using stirred-media-mills and three-roll-mills

Fibre reinforced composites are indispensable in the field of modern lightweight structures, such as used in aerospace, automotive industry or in wind power plants. Those materials provide high weight savings and increase the efficiency of a structure significantly. Therefore, various efforts are made to continuously improve the quality of the matrix and the fibres. By embedding nano-particles into the epoxy matrix, the mechanical properties as well as the electrical and thermal characteristics can significantly be improved [1]. In most cases these nano-sized particles are produced as dry powders not as single primary particles but rather as particle collectives consisting out of several primary particles. For the application in reinforced composites the particles must be suspended in epoxy resin as separately dispersed primary particles or in a certain aggregate size. Generally, the influencing parameters to break up the aggregates in a dispersion process can be divided into the stress mechanism, the intensity and the frequency of the dispersing machine itself, the properties of the dispersed particles (e.g. the particle–particle interactions) the properties of the homogenous phase and the particle–resin-interactions. Besides the effect of the chosen dispersing machine the optimization of the dispersing process was investigated by applying modified particle surfaces and varying the fluid properties. The results show that the surface properties of the particles must fit to the epoxy resin properties and the attractive forces between the primary particles must be reduced or the stabilization improved, respectively. An indication for an improved stabilization and adjustment of the particles surface properties to the fluid properties can be obtained by measurements of the contact angle and the rheological properties. Generally, an increase of viscosity and mass fraction of the product leads to a higher energetic efficiency of the dispersion process in the stirred media mill and three-roll-mill.