Microstructure and properties of Si-TaSi2 eutectic in situ composite for field emission

The Si-TaSi2 eutectic in situ composite for field emission is prepared by electron beam floating zone melting (EBFZM) technique on the basis of Czochralski (CZ) crystal growth technique. The directional solidification microstructure and the field emission properties of the Si-TaSi2 eutectic in situ composite prepared by two kinds of crystal growth techniques have been systematically tested and compared. Researches demonstrated that the solidification microstructure of EBFZM can be fined obviously be-cause of the relatively high solidification rate and very high temperature gradient, i.e. both the diameter and inter-rod spacing of the TaSi2 fibers prepared by EBFZM technique were decreased, and the density and the volume fraction of the TaSi2 fibers prepared by EBFZM technique were increased in comparison with that of the TaSi2 fibers prepared by CZ method. Therefore the field emission property of the Si-TaSi2 eutectic in situ composite prepared by EBFZM can be improved greatly, which exhibits better field emission uniformity and straighter F-N curve.     

Atomic force microscope study of WC-10Co cemented carbide sintered from nanocrystalline composite powders

In order to compare the spark plasma sintering (SPS) process plus hot isostatic press (HIP) with vacuum sintering plus HIP, an investigation was carried out on the topography, microstructure and gain size distribution of nanocrystalline WC-l0Co composite powder and the sintered specimens prepared by SPS plus HIP and by vacuum sintering plus HIP by means of atomic force microscopy (AFM). The mechanical properties of the sintered specimens were also investigated. It is very easy to find cobalt lakes in the specimen prepared by vacuum sintering plus HIP process. But the microstructure of the specimen prepared by SPS plus HIP is more homogeneous, and the grain size is smaller than that prepared by vacuum sintering plus HIP. The WC-10Co ultrafine cemented carbide consolidated by SPS plus HIP can reach a relative density of 99.4%, and the transverse rupture strength (TRS) is higher than 3540 MPa, the Rockwell A hardness (HRA) is higher than 92.8, the average grain size is smaller than 300 nm, and the WC-10Co ultrafine cemented carbide with excellent properties is achieved. The specimen prepared by SPS with HIP has better properties and microstructure than that prepared by vacuum sintering with HIP.     

Influence of deposition time on the morphology and optical properties of SiO<Subscript>2</Subscript>-ZnO composite photonic crystals

SiO2 photonic crystal were successfully prepared by vertical deposition and then used as a template to fabricate SiO2-ZnO composite photonic crystals on ITO substrates by electrodeposition and subsequent calcination. A number of different deposition times were used. The morphologies of the silica opals and SiO2-ZnO composite photonic crystals were investigated by scanning electron microscopy. It was found that ZnO particles grew randomly on the surfaces of the silica spheres when the deposition time was short. As the deposition time was increased, the ZnO particles grew evenly on the surfaces of the silica spheres so that the interstitial space of the silica template was filled with ZnO particles. Reflectance spectra of the SiO2-ZnO composite crystals revealed that all of the fabricated photonic crystals exhibit a photonic band gap in the normal direction.     

Microstructure and corrosion resistance of Fe/Mo composite amorphous coatings prepared by air plasma spraying

Fe/Mo composite coatings were prepared by air plasma spraying (APS) using Fe-based and Mo-based amorphous and nanocrystalline mixed powders. Microstructural studies show that the composite coatings present a layered structure with low porosity due to adding the self-bonded Mo-based alloy. Corrosion behaviors of the composite coatings, the Fe-based coatings and the Mo-based coatings were investigated by electrochemical measurements and salt spray tests. Electrochemical results show that the composite coatings exhibit a lower polarization current density and higher corrosion potentials than the Fe-based coating when tested in 3.5wt% NaCl solutions, indicating superior corrosion resistance compared with the Fe-based coating. Also with the increase in addition of the Mo-based alloy, a raised corrosion resistance, inferred by an increase in corrosion potential and a decrease in polarization current density, can be found. The results of salt spray tests again show that the corrosion resistance is enhanced by adding the Mo-based alloy, which helps to reduce the porosity of the composite coatings and enhance the stability of the passive films.     

Preparation and oxidation characteristics of ZrC-ZrB2 composite powders with different proportions

ZrC and ZrB2 are both typical ultra-high temperature ceramics,which can be used in the hyperthermal environment.In this study,a method for preparing ultrafine ZrC-ZrB2 composite powder was provided,by using the raw materials of nano ZrO2,carbon black,B4C,and metallic Ca.It is worth pointing out that ZrC-ZrB2 composite powder with any proportion of ZrC to ZrB2 could be synthesized by this method.Firstly,a mixture of ZrC and C was prepared by carbothermal reduction of ZrO2.By adjusting the addition amount of B4C,ZrC was boronized by B4C to generate ZrC-ZrB2 composite powder with different compositions.Using this method,five composite powders with different molar ratios of ZrC and ZrB2(100ZrC,75ZrC-25ZrB2,50ZrC-50ZrB2,25ZrC-75ZrB2,and 100ZrB2)were prepared.When the temperature of boronization and decarburization process was 1473 K,the particle size of product was only tens of nanometres.Finally,the oxidation charac-teristics of different composite powders were investigated through oxidation experiments.The oxidation resistance of ZrC-ZrB2 composite powder continued to increase as the content of ZrB2 increased.     

Polysaccharide separation mechanism in polysulfone-Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> magnetic composite membranes

Polysulfone (PSF)-Fe3O4 composite membranes were prepared by the phase-inversion process and their polysaccharide separation mechanism was explored using chondroitin sulfate (CS) and dextran. The mechanism was analyzed from constraints on the magnetic field and geometric deformation. It was found that variations in dextran rejection from 58% to 46% were mainly influenced by the geometric deformation of the composite membrane, while the magnetic field had a significant influence on variations in CS rejection from 82% to 35%. The results indicate that it is possible to continuously separate different types of polysaccharide with a composite membrane by adjusting the external magnetic field.     

Surface chemical structure of titania-silica nanocomposite powder

Titania-silica （TS） nanocomposite powder with three different composite structures, containing 10-30 mol% SiO2 in each structure, have been prepared by sol-gel processes. The surface characteristics of these titania-silica samples have been investigated by X-ray photo-emission spectroscopy （XPS） and high resolution transmission electron microscopy （HRTEM）. The study for all TS oxides annealed at 773 and 1173 K showed： an abnormal surface enrichment in Si increased with increasing annealing temperature; the Ti^3＋, Ti^2＋, Si^3＋ and Si^2＋ oxides coexisted with Ti^4＋ and Si^4＋ oxides, and the contents of these Ti/Si suboxides increased with increasing SiO2 content and annealing temperature; there was a layer rich in O on the topmost surface and the excess O could be attributed to the chem-adsorption of H2O; different composite structures could lead to different contents of Ti/Si suboxides. These results indicated that the surface of TS oxide powder derived by sol-gel process was a double layer with enriched O first and then SiOx/TiOy（x, y〈2）. Ti/Si suboxides could result from the thermal diffusion of Ti^4＋ and Si^4＋, which might be induced by the strong interaction between Ti^4＋ and Si^4＋.     

Fabrication and densification enhancement of SiC-particulate-reinforced copper matrix composites prepared via the sinter-forging process

The fabrication of copper (Cu) and copper matrix silicon carbide (Cu/SiC_p) particulate composites via the sinter-forging process was investigated. Sintering and sinter-forging processes were performed under an inert Ar atmosphere. The influence of sinter-forging time, temperature, and compressive stress on the relative density and hardness of the prepared samples was systematically investigated and subsequently compared with that of the samples prepared by the conventional sintering process. The relative density and hardness of the composites were enhanced when they were prepared by the sinter-forging process. The relative density values of all Cu/SiC_p composite samples were observed to decrease with the increase in SiC content.     

Silk Fibroin Film Blended with Poly（ ethylene glycol-glycerin）

To improve the toughness of silk fibroin（ SF） films,poly（ ethylene glycol-glycerin）（ PEGG） was synthesized with ethylene glycol and epichlorohydrin. The SF / PEGG blend films were prepared by casting aqueous solution and their structures were characterized. The PEGG was in liquid state at room temperature so it will not be a single phrase at blend film. It crosslinked with SF and made it insolubility in water. The results of X-ray diffraction（ XRD） indicated that the crystallinity of the SF in the blend films decreased with the content of PEGG increasing. The tensile strength and elongation at break of blend films were measured using an instron tensile tester. The results showed that the tensile strength and elongation at break of blend films were high enough for application.After the blend films were stored at room temperature for 100 d,the crystallinity, the tensile strength and elongation at wet state increased. The blend films are superior to SF films in providing excellent flexibility and mechanical properties in both dry and wet states. Based on the fact that SF has good biocompatibility,the SF /PEGG blend film will offer new options in many different biomedical applications.     

Processing and characterization of Cf/SiC composites

Carbon fiber-reinforced SiC composites were prepared by precursor pyrolysis-hot pressing (PP-HP) and precursor impregnation-pyrolysis (PIP), respectively. The effect of fabrication methods on the microstructure and mechanical properties of the composites was investigated. It was found that the composite prepared by PP-HP exhibits a brittle fracture behavior, which is mainly ascribed to a strongly bonded fiber/matrix interface and the degradation of the fibers caused by a higher processing temperature. On the contrary, the composite prepared by PIP shows a tough fracture behavior, which could be rationalized on the basis of a weakly bonded fiber/matrix interface as well as a higher strength retention of the fibers. As a result, in comparison with the composite prepared by PP-HP, the composite prepared by PIP achieves better mechanical properties with a flexural strength of 573.4 MPa and a fracture toughness of 17.2 MPa·m1/2.     

BaSO4-PAM无机-高分子复合微球的制备研究

以聚丙烯酰胺(polyacrylamide,PAM)高分子微凝胶为模板,结合反胶束法制备了具有表面图案结构的硫酸钡-聚丙烯酰胺(BaSO4-PAM)无机-高分子复合微球材料.利用扫描电镜(SEM)和XRD对复合微球的形貌和无机沉积物BaSO4的晶型进行了表征.结果表明,BaSO4的沉积量、沉积反应速度等因素对复合微球的表面形貌都有显著影响;复合微球中BaSO4具有正交重晶石结构.实验所得BaSO4-PAM复合微球兼具高分子的柔性和无机物的刚性.     

基于微凝胶模板法制备新型P(AM-co-MAA)/Cu_2O复合微球的研究

采用反相乳液聚合法合成的P(AM-co-MAA)高分子微球为模板,经Cu(Ac)2溶液溶胀后,以抗坏血酸为还原剂,通过两相界面反应,制得新型P(AM-co-MAA)/Cu2O有机-无机复合微球材料.考察了抗坏血酸用量、Cu(Ac)2浓度、反应温度、NaOH用量等因素对复合微球形貌和组成的影响.利用扫描电子显微镜(SEM)、傅里叶红外分析仪(FT-IR)、热重分析仪(TG)、X射线衍射分析仪(XRD)对复合微球的表面形貌和组成进行了表征.实验表明,高分子的模板作用使得复合微球整体上呈现球状结构,微球大小主要决定于模板的尺寸.由于此复合微球不仅具有微米级材料容易分离的优点,而且同时兼有纳米级颗粒比表面积大的特点,因此,这类材料有望在构筑纳米反应器、负载催化剂以及制备杀菌材料等方面具有广阔的应用前景.     

微凝胶模板法制备表面图案化CuS有机-无机复合微球

采用反相悬浮聚合法合成了PNIPAM和P(NIPAM-co-MAA)微凝胶,以这2种微凝胶为模板,制得了具有表面图案化结构的PNIPAM/CuS和P(NIPAM-co-MAA)/CuS有机—无机复合微球。结果表明:复合微球的表面形貌取决于微凝胶模板的性质和金属无机物的相对沉积量。微凝胶模板法为制备具有复杂形貌的有机-无机复合微球材料提供了一种新的途径。     

磁性温敏复合微球的制备及磁场作用下的药物缓释行为

采用无皂乳液聚合的方法将Fe3O4与温敏性N-异丙基丙烯酰胺-丙烯酰胺共聚物[P(NIPAAm-co-Am)]复合,制备了具有核壳结构的磁性温敏复合微球,并研究了其在60kHz,6.5kA·m-1交变磁场作用下的磁热性能和药物缓释行为.结果表明,所制备的Fe3O4/P(NIPAAm-co-Am)复合微球具有良好的磁热性能,20min内即可使自身温度升高到温敏聚合物的最低临界溶解温度(LCST),约为42°C.复合微球在连续和间歇磁场作用下的药物释放行为显示,间歇性施加磁场能够延长药物的释放周期,而且能够有效增大药物的积累释放量.因具有良好的磁热和药物缓释性能,所制备的聚合物微球有望同步实现肿瘤热疗和化疗药物的可控释放.     

溶胶-凝胶法制备新型P（AM-CO-MAA）／SnO2复合微球

以反相悬浮聚合法制备得到的P（AM—CO—MAA）为模板,通过SnCl4的Sol—gel法制备得到新型P（AM—CO—MAA）／SnO2复合微球．通过扫描电子显微（SEM）、傅立叶红外分析（FTIR）、热重分析（TG）、X-射线衍射分析（XRD）和元素分析（EA）等一系列表征手段对复合微球的表面形貌和无机物组成进行了表征。     

吉格森油田柔性微凝胶深部调驱体系室内研究及现场应用——以淖尔区块为例

柔性微凝胶分散颗粒(微球)可用油田污水配制,具有耐温、耐盐、成本低廉等优点。针对吉格森油田各油组主力油层分布广、厚度大,所占储量比重大,地下原油物性一般,地层温度较高,地层水矿化度高(>90000mg/L)这一情况,开展了柔性微凝胶深部调驱在吉格森油田的适应性及现场应用情况分析。实验所选用的纳米级和微米级微球溶解性和热稳定性都较好,微米级微球更好。4种微球均具有一定的封堵性,其中2号微球颗粒的残余阻力系数较大,为3.09,其次为1号微球,其残余阻力系数为1.44。天然岩心的驱油实验结果表明柔性微凝胶驱具有较好的驱油效果,但是微球尺寸要在孔径的1/8～1/3,才能保证有效封堵。现场实际应用情况表明吉格森油田在各个区块所开展的柔性微凝胶深部调驱增产措施,在一定程度和阶段内取得了较好的控水稳油效果。     

CuS纳米晶光催化还原Cr(VI)的研究

合成了片状、球状、花状、管状的CuS,在可见光照射下,其光催化还原Cr(VI)研究的结果表明:CuS的比表面积越大,光催化还原活性越好,活性顺序为片状>管状>花状>球状.     

CuS纳米晶光催化还原Cr(VI)的研究

合成了片状、球状、花状、管状的Cu S,在可见光照射下,其光催化还原Cr(VI)研究的结果表明:Cu S的比表面积越大,光催化还原活性越好,活性顺序为片状>管状>花状>球状.     

表面图案化PNIPAM/SiO2复合微球的制备和表征

采用反相悬浮聚合法合成了聚N-异丙基丙烯酰胺（PNIPAM）高分子微凝胶,以PNIPAM为微反应器,利用四乙氧基正硅烷在氨水介质中的溶胶-凝胶反应,制得了具有表面图案化的核-壳型微米级PNIPAM/SiO2复合微球.并利用扫描电镜、红外光谱仪和热重分析等手段对复合微球进行了形貌和组分表征.     

Nanotribological behaviors of in situ nanoparticles doped molecular deposition films

The molecular deposition films of poly （diallyl dimethylammonium chloride） （PDDA） and poly （acrylicacid） （PAA） with Cu2＋ on quartz and glass substrates were prepared in laboratory first, then different bilayers films were dipped into fresh Na2S aqueous solution. As a result, CuS nanoparticles were fabricated in multilayer molecular deposition films in situ. The structure and nanotribological properties of the composite films were analyzed by ultraviolet-visible （UV-visible） spectroscopy, XPS and atomic force microscope （AFM）. It was found that the CuS nanoparticles were homogeneously distributed throughout the whole film. And these films had a much smaller friction force than their substrates and higher antiwear life than pristine PDDA/PAA molecular deposition films. The fluctuation and variation trend of the topography, hardness, and friction with the AFM indentation length were also investigated.