Processing of In Situ Aluminium Matrix Composites by Micropyretic Reactive Sintering

In situ aluminium matrix composites were processed by the micropyretic reactions between the host aluminium matrix and powder containing nanodimensional Fe₂O₃ crystallites used as the precursor compound. Differential Scanning Calorimetric (DSC), studies have shown, use of nanosized Fe₂O₃ crystallites has decreased the initiation temperature of the in situ micropyretic reaction and the desirable reinforcements; iron-aluminide and alumina are formed during sintering. Microstructural features of the composite consist of well-dispersed reinforcements in the host Al matrix with size less than 1 µm. Wear tests performed on the composite samples have revealed coefficient of friction and wear volume can be reduced significantly by incorporating 20 vol% reinforcement.     

Synthesis of C_f/TiAl_3 Composite by Infiltration-In Situ Reaction

Infiltration-in situ reaction synthesis of Cf /TiAl3 composite was investigated. The as-cast material was obtained by titanium particles, carbon fibers and pure aluminum. Titanium particles and carbon fibers were mixed and pressed to form a preform firstly, and then molten pure aluminum was pressed into the preform, subsequently, cooled rapidly. In situ reaction samples were obtained by heating the as-cast material from 600 to 1000 °C for 1 h. The microstructural evolution of in situ reaction samples was an...     

Interface Structure of Ag/SnO_2 Nanocomposite Fabricated by Reactive Synthesis

The electric contact material of Ag/SnO2 composite was achieved by reactive synthesis method. The compositions and microstructure of Ag/SnO2 composite were analyzed and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution electron microscopy (HRTEM). The structural feature was typical of the particle reinforced composites. The HRTEM images revealed that the observed Ag/SnO2 interface was absence of the precipitated phase and the lattice contrast across the interf...     

氧化镁真空碳热还原法炼镁的工艺研究

采用物料失重率、金属Mg还原率、X射线衍射(XRD)与扫描电子显微镜(SEM)等手段与方法,研究了真空条件下氧化镁碳热还原温度、物料造球成型压力、物料配比、碳热还原保温时间以及催化剂对氧化镁碳热还原法炼镁工艺的影响。研究结果表明,在30~100 Pa时,碳热还原温度高于1553 K,控制物料压块压力为8 MPa,此时物料失重率最大,最有利于氧化镁的还原。随着焦煤还原剂与氧化镁摩尔比以及碳热还原时间的增加,碳热还原反应速率加大,还原率提高,但是变化效果不明显,加入氟盐CaF2后,物料失重率明显提高,添加CaF2的质量超过物料总质量的3%时,物料失重率超过95%,还原率也相应大幅提高。因此,选择适当的焦煤还原剂与氧化镁摩尔比值以及碳热还原时间,添加超过3%CaF2,将有利于该法炼镁过程的顺利进行与金属Mg还原率的提高。此研究为真空碳热法从氧化镁中提取金属Mg工艺提供了很好的实验依据。     

Interface Structure of Ag/SnO2 Nanocomposite Fabricated by Reactive Synthesis

The electric contact material of Ag/SnO₂ composite was achieved by reactive synthesis method. The com-positions and microstructure of Ag/SnO₂ composite were analyzed and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution electron microscopy (HRTEM). The structural feature was typical of the particle reinforced composites. The HRTEM images revealed that the observed Ag/SnO₂ interface was absence of the precipitated phase and the lattice contrast across the interface was clear and sharp. The average particle size of SnO₂ in composite was near 50 nm and it was well dispersed in spherical shape. The thermodynamic mechanism of reactive synthesis method was also discussed. The electronic density distribution analysis of the interface showed the charges of Ag atoms transmitted to O atoms and the conductivity of the material was also affected. No extra compounds expected such as Ag_xO_y formed at interface. The distribution of electrons was of inequality near the interface which explained why the mechanical property of the metal/ceramic materials was improved but the machining property declined.     

微波烧结原位合成TiC增强钛复合材料的性能

以纳米管(MWCNTs)和纯钛为原料,用微波烧结法原位合成TiC增强钛基复合材料,研究了这种材料的组织和性能并探讨了TiC增强相的生成机理.结果 表明,微波烧结时MWCNTs与Ti原位生成TiC增强相.MWCNTs的添加量(质量分数,下同)低于1％时TiC呈现颗粒状且分布均匀,Ti基体致密;MWCNTs的添加量高于1....     

原位金属基复合材料的制备原理及工艺

简述了原位自生增强体金属基复合材料的制备原理及工艺。基于热力学和动力学原理，讨论了自生增强体的形成机制，展望了这种新型复合材料的工业应用前景。     

原位增强镁基复合材料研究进展与原位反应体系热力学

本文综述了原位镁基复合材料制备方法的研究进展 ,并对原位镁基复合材料的可能的原位反应体系进行热力学分析     

聚电解质复合膜中原位合成纳米结构氧化铁中空微球并用于释氧光阳极

利用层层静电自组装技术,将PSS-Fe3+复合物与聚二烯丙基二甲基氯化铵(PDADMAC,Po-ly(diallyldimethylammonium)Chloride)交替吸附在三聚氰胺甲醛树脂(MF)微球外.以聚电解质复合层作为纳米反应器,原位合成了氧化铁纳米颗粒;高温热处理可将中心的MF微球去除,生成中空纳米结构的铁氧化物微球.TEM说明,中空微球具有单分散性;XRD说明纳米颗粒是α-Fe2O3,壁的孔径约为7nm.在紫外灯开启和关闭时,由该氧化铁微球修饰的释氧光阳极会引起光电流的即时变化,显示该中空α-Fe2O3微球组成的薄膜具有灵敏的光电催化活性.     

Sintering of copper nanopowders under hydrogen: an in situ X-ray diffraction analysis

The reduction by hydrogen gas of the cuprite layer on copper nanocrystals and the subsequent sintering of the nano-particles were studied using in-situ X-ray diffraction and dilatometry. Spherical nanocrystals produced by evaporation and condensation have an average size of 35 nm, exhibiting a large surface curvature. Each nanoparticle is coated with a 3.5 nm layer of Cu₂O, which is rough and disordered, as revealed by high-resolution electron microscopy. Reduction by hydrogen of this curved cuprite layer occurs at 363 K, which is ≈65 K lower than is observed on a layer supported by micrometer-sized or bulk copper with a flat surface. The reduction process and its effect on the sintering of nanopowders are analysed and discussed.     

用变温红外研究聚乳酸嵌段共聚物生成过程中的化学反应

本文采用熔融缩聚法合成一定分子量的聚乳酸(PLA),采用聚己内酯多元醇(PCL)的聚氨酯预聚体进行共聚反应,以制得PLA-PCL嵌段共聚物.采用变温红外研究了PLA预聚体与PCL预聚体的反应活性,并研究了共聚产物的分子量.结果表明,PLA预聚体与PCL预聚体具有很高的反应活性,共聚后PLA的分子量有大幅度提高.     

钒钛铁精矿碳热还原制备Fe-Ti(C,N)复合材料

以钒钛铁精矿和煤粉为原料,通过碳热还原法制备Fe-Ti(C,N)复合材料。采用正交实验研究了还原温度、碳氧比、还原时间和MgO添加量对还原产物的物相组成和碳氮化钛中C/N比的影响。对还原产物进行了X射线衍射分析,结果表明,还原温度对还原产物中碳氮化钛的C/N比的影响程度较大,而MgO的添加不利于碳氮化钛的形成。还原温度为1450℃、还原时间为40min、碳氧比为1.4时,还原产物的C/N比达到较大值。     

Controlling the Formation of Nanocavities in Kirkendall Nanoobjects through Sequential Thermal Ex Situ Oxidation and In Situ Reduction Reactions

Controlling the porosity, the shape, and the morphology of Kirkendall hollow nanostructures is the key factor to tune the properties of these tailor‐made nanomaterials which allow in turn broadening their applications. It is shown that by applying a continuous oxidation to copper nanowires following a temperature ramp protocol, one can synthesize cuprous oxide nanotubes containing periodic copper nanoparticles. A further oxidation of such nanoobjects allows obtaining cupric oxide nanotubes with a bamboo‐like structure. On the other hand, by applying a sequential oxidation and reduction reactions to copper nanowires, one can synthesize hollow nanoobjects with complex shapes and morphologies that cannot be obtained using the Kirkendall effect alone, such as necklace‐like cuprous oxide nanotubes, periodic solid copper nanoparticles or hollow cuprous oxide nanospheres interconnected with single crystal cuprous oxide nanorods, and aligned and periodic hollow nanospheres embedded in a cuprous oxide nanotube. The strategy demonstrated in this study opens new avenues for the engineering of hollow nanostructures with potential applications in gas sensing, catalysis, and energy storage.     

熔炼法原位合成TiB-Nd2O3-Ti复合材料的组织与力学性能

用熔炼法原位合成了TiB-Nd2O3-Ti复合材料。采用金相显微镜、扫描电镜、透射电镜等对其组织及性能进行了观察和分析。结果显示,原位合成的复合材料中,增强体为TiB与Nd2O3,它们均匀分布在Ti基体中,与基体之间没有发生显著的界面反应。原位合成复合材料的压缩屈服强度及其在500℃和600℃时的高温拉伸强度与基体Ti相比均有大幅度提高,其断裂机理与组织结构及变形温度有关。     

Oral Sustained Delivery of Theophylline and Cimetidine from In Situ Gelling Pectin Formulations in Rabbits

ABSTRACT

The aim of this study was to evaluate the potential of an in situ gelling pectin formulation as a vehicle for the oral sustained delivery of theophylline and cimetidine. In vitro studies demonstrated diffusion-controlled release of theophylline from 1, 1.5, and 2% w/v pectin gels. Release of this drug from 1.5% w/v pectin gels formed in situ in rabbit stomach was sustained over a period of 12 hours giving a theophylline bioavailability some seven fold higher than when administered from a commercial syrup. In contrast, interactions between cimetidine and pectin led to weak gelation of the pectin sols that prevented any meaningful determination of in vitro release characteristics. Similarly, in vivo release profiles from pectin formulations containing cimetidine were similar to that from a solution of this drug in buffer, indicative of weak gelation. Examination of the content of the rabbit stomach 5 hours after administration of 1.5% w/v pectin sols containing drug confirmed gel formation, but gels containing cimetidine were noticeably softer than those containing theophylline.     

Behavior analysis of silica in aluminum production by alumina carbothermic reduction-chlorination process in vacuum

In present work, the behavior of silica was investigated experimentally in the alumina carbothermic reduction process and chlorination process in the temperature range of 1173 K-1763 K. The phase of slags, surface morphology and composition of condensate were examined by means of XRD, SEM and EDS. The results showed that SiC was produced by SiO₂ and C in the temperature range of 1573 K-1673 K, while alumina transformed into corundum completely, then Al₄SiC₄ was produced by SiC and intermediates (Al₄C₃ and Al₄O₄C) obtained during carbothermic reduction of alumina at about 1763 K. In the chlorination process, the silicon-containing materials in the condensate were not found. Because SiO₂ consumed Al₃C₄ and Al₄O₄C, then the recovery rate of aluminum decreased. It was inferred that silica may be unfavourable for aluminum extracted from alumina by carbothermic reduction-chlorination process in vacuum.     

On the Synthesis of In Situ Ni-SiO2 Nanocomposites by Isothermal and Non Isothermal Reduction Technique

In situ Ni-SiO₂ nanocomposites were prepared from silica gels containing NiCl₂ and dextrose by isothermal and non isothermal reduction treatment. Analysis of the isothermal kinetic data indicates that contracting geometry and nucleation and growth type of mechanism remain operative in the 600-750°C and 800-950°C temperature range respectively. However, analysis of non isothermal kinetic data reveals that contracting geometry type of mechanism solely remains operative over the entire temperature range of 600-950°C. Transmission electron microscopic (TEM) studies reveals that the microstructural features of the nanocomposites are sensitive to reduction conditions.     

纳米银/PAMPS复合物的微波合成及表征

在不加还原剂的条件下,微波辐射双原位合成纳米银/2-丙烯酰胺基-2-甲基丙磺酸均聚物[PAMPS]复合材料。并通过UV-Vis、XRD、FTIR、TEM、XPS和TG等分析方法对其进行表征。结果表明:纳米银粒子具有面心立方结构,且较均匀地分散在聚合物基体中;微波辐射时间不影响纳米银粒子的形态;纳米银与基体PAMPS中的氮原子和羰基氧原子存在相互作用,而且对基体PAMPS的热学性能有很大影响。