Preparation and characterization of carbon nanotubes/aluminum matrix composites

2024Al matrix composite reinforced with 1 wt.% carbon nanotubes (CNTs) was fabricated by cold isostatic pressing, followed hot extrusion techniques. The microstructure characteristics and the distribution of carbon nanotubes in the aluminum matrix were investigated. The mechanical properties of the composite were measured at room temperature. Experimental results showed that CNTs were distributed homogeneously in the composite, and the interfaces of Al–CNTs bonded well. The grain size of the matrix was as fine as 200 nm, and with a small amount of CNTs additions, the elastic modulus and the tensile strength were enhanced markedly over those of the 2024Al matrix fabricated under the same process. The reasons for the increments could be due to the extraordinary mechanical properties of CNTs, the bridging and pulling out role of CNTs in the Al matrix composite.     

以铝为支撑体的一种新型阳极氧化铝膜的制备与表征

阳极氧化铝膜在分离方面有许多优点如均一的孔径、高的热力学稳定性、独特的孔结构等,作为无机膜有较好的商业应用价值,但膜的脆性问题一直是公认的难题.用一次阳极氧化铝膜的铝面做阳极在盐酸中电解后,再在磷酸中扩孔,制得了两面贯通以大孔铝为支撑体的阳极氧化铝膜.研究了扩孔时间对膜的纯水通量、平均孔径、截留率的影响.结果表明,膜的平均孔径为65.5~119.2 nm;膜的孔径分布窄,孔隙率为28.6%~32.7%;随着扩孔时间的增加,膜的平均孔径、纯水通量均增大,而膜对聚乙二醇20 000的截留率减小;当扩孔时间为30min时,对聚乙二醇20 000截留率达到了26.5%;膜的纯水通量随着时间的增加而减小;膜的脆性问题在一定程度上得以改善.     

Thermomechanical characterization of a membrane deformable mirror

A membrane deformable mirror has been investigated for its potential use in high-energy laser systems. Experiments were performed in which the deformable mirror was heated with a 1 kW incandescent lamp and the thermal profile, the wavefront aberrations, and the mechanical displacement of the membrane were measured. A finite element model was also developed. The wavefront characterization experiments showed that the wavefront degraded with heating. Above a temperature of 35 degrees C, the wavefront characterization experiments indicated a dramatic increase in the high-order wavefront modes before the optical beam became immeasurable in the sensors. The mechanical displacement data of the membrane mirror showed that during heating, the membrane initially deflected towards the heat source and then deflected away from the heat source. Finite element analysis (FEA) predicted a similar displacement behavior as shown by the mechanical displacement data but over a shorter time scale and a larger magnitude. The mechanical displacement data also showed that the magnitude of membrane displacement increased with the experiments that involved higher temperatures. Above a temperature of 35 degrees C, the displacement data showed that random deflections as a function of time developed and that the magnitude of these deflections increased with increased temperature. We concluded that convection, not captured in the FEA, likely played a dominant role in mirror deformation at temperatures above 35 degrees C.     

Preparation and characterization of aluminum doped zinc oxide (AZO) nanorods

Aluminum doped Zinc Oxide (AZO) nanorods with 1at.% aluminum content were prepared by Sol-gel spin coating technique. The structural and topographical properties are studied using X-Ray Diffraction (XRD) technique and Atomic Force Microscopy (AFM), respectively. Higher intensity Zinc Oxide (ZnO) peak (002) is observed in 1at.% aluminum doped nanorod with 50 s spin coated sample underwent 300°C of annealing temperature. Morphologic, compositional and crystallographic information of the samples are predicted using Transmission Electron Microscopy (TEM), the 600 nm long nanorod with an aspect ratio of 10 is obtained for 20 s and 50 s spin coating time.     

Preparation and characterization of morph-genetic aluminum nitride/carbon composites from filter paper

Morph-genetic aluminum nitride/carbon composites with cablelike structure were prepared from filter paper template through the surface sol-gel process and carbothermal nitridation reaction. The resulting materials have a hierarchical structure originating from the morphology of cellulose paper. The aluminum nitride/carbon composites have the core-shell microstructure, the core is graphitic carbon, and the shell is aluminum nitride nanocoating formed by carbothermal nitridation reduction of alumina with the interfacial carbon in nitrogen atmosphere. Scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and transmission electron microscope were employed to characterize the structural morphology and phase compositions of the final products.     

铝合金表面三嗪二硫醇和硅烷纳米复合薄膜的制备及表征

通过电化学方法,在铝合金表面制备6-N,N-二丁基胺-1,3,5-三嗪-2,4-二硫醉单盐(DBN)的纳米聚合薄膜(PDB),然后采用自组装技术对铝合金表面PDB膜进行十六烷基三甲氧基硅烷化处理,形成疏水性的高分子纳米复合薄膜(CPDB).通过循环伏安法解释了DBN在铝合金表面的反应及PDB的生长过程,同时分析了CPD...     

Preparation of aluminum sulfide

Three methods are described for the preparation of α-Al₂S₃. These are the direct sulfidation of Al, chemical vapor transport and a new AlI₃ flux growth method.     

Preparation and characterization of a quaternized chitosan

A novel method was developed to obtain N-(2-hydroxy)-propyl-3-trimethylammonium chitosan chloride (HTCC) using glycidyl trimethyl ammonium chloride (GTMAC) and chitosan in a homogeneous system. The factors affecting the degree of substitution (DS) of HTCC, including the amount of perchloric acid, the reaction temperature, and the reaction time, were especially investigated. Under optimal conditions (i.e., with 2.0, 1.9, and 15 g of chitosan, perchloric acid, and GTMAC, respectively), chitosan was pre-reacted with GTMAC at 60 °C, and then the reaction was continued at 80 °C for 8 h. The as-produced HTCC had a DS of 86.9%. Its structure was characterized by Fourier transform infrared spectroscopy and nuclear magnetic resonance. Moreover, it had a good solubility in water within a wide pH range. Besides, the composite was formed from HTCC loaded on bentonite surface.     

Damage characterization and modeling of a 7075-T651 aluminum plate

In this paper, the damage-induced anisotropy arising from material microstructure heterogeneities at two different length scales was characterized and modeled for a wrought aluminum alloy. Experiments were performed on a 7075-T651 aluminum alloy plate using sub-standard tensile specimens in three different orientations with respect to the rolling direction. Scanning electron microscopy was employed to characterize the stereology of the final damage state in terms of cracked and or debonded particles. A physically motivated internal state variable continuum model was used to predict fracture by incorporating material microstructural features. The continuum model showed good comparisons to the experimental data by capturing the damage-induced anisotropic material response. Estimations of the mechanical stress–strain response, material damage histories, and final failure were numerically calculated and experimentally validated thus demonstrating that the final failure state was strongly dependent on the constituent particle morphology.     

Preparation and characterization of a titanium bonding porcelain

The titanium bonding porcelain was synthesized through normal melting-derived route using borate–silicate system. The porcelain was characterized by thermal expansion, X-ray diffraction, scanning electron microscope and cytotoxicity tests. The results of X-ray diffraction showed that the main phase of the bonding porcelain was SnO₂. The SnO₂ microcrystals precipitated from the glass matrix when the SnO₂ content was increased. The thermal expansion coefficient of bonding porcelains decreased with the increasing concentration of SiO₂. The thermal expansion coefficient of bonding porcelains first decreased slightly with the increasing of B₂O₃ concentration (from 0 wt% to 10 wt%) and then increased to about 9.4 × 10^? 6/°C(from 10 wt% to 12 wt%). As an intermediate, B₂O₃ can act as both network formers and modifiers, depending on the relationship between the concentration of basic oxides and intermediates. The Vickers hardness of bonding porcelains increased with the increase of SnO₂ concentration. When SnO₂ concentration was 6 wt%, only Si and Sn elements attended the reaction between titanium and porcelain and mainly adhesive fracture was found at Ti-porcelain interface. When SnO₂ concentration was 12 wt%, failure of the titanium–porcelain predominantly occurred in the bonding porcelain and mainly cohesive fracture was found at Ti-porcelain interface. The methyl thiazolyl tetrazolium assay results demonstrated that the cytotoxicity of the titanium porcelain was ranked as 0.     

Preparation and characterization of a novel willemite bioceramic

Willemite (Zn₂SiO₄) ceramics were prepared by sintering the willemite green compacts. The effects of sintering temperature on the linear shrinkage, porosity and mechanical strength of the ceramics were examined. With the sintering temperature increased, the linear shrinkage of the ceramics increased and the porosity decreased. When sintered at 1,300°C, willemite ceramics showed mechanical properties of the same order of magnitude as values for human cortical bone, as measured by bending strength (91.2 ± 4.2 MPa) and Young’s modulus (37.5 ± 1.5 GPa). In addition, the adhesion and proliferation of rabbit bone marrow stromal cells (BMSCs) on willemite ceramics was investigated. The results showed that the ceramics supported cell adhesion and stimulated the proliferation. All these findings suggest that willemite ceramics possess suitable mechanical properties and favorable biocompatibility and might be a promising biomaterial for bone implant applications.     

Frequency-dependent graded reflectivity mirror: characterization and laser implementation

We present a theoretical and experimental investigation of a new family of variable reflectivity mirrors, based on frustrated total internal reflection and interference effects. These mirrors are sensitive to frequency in the sense that their transverse reflectivity distribution changes significantly as a function of the frequency of light. The mirror reported here shows total power reflectivity changes of 50% within 8.0 GHz. The mirror was tested as the output coupler of an unstable resonator in a Nd:YAG laser working in the free-running regime. This configuration was compared with the standard stable multimode resonator configuration. The beam divergence was reduced by more than 1 order of magnitude and the output power was reduced by only 10%. The laser resonator mode competition that is due to the frequency-dependent mirror reflectivity distribution is discussed.     

新型聚乳酸-聚酰亚胺嵌段共聚物的合成与表征

用氨基封端的PEG-800(ATPEG)与均苯四甲酸酐(PMDA)共聚得到一种新型的氨基封端的可溶性聚酰亚胺(PI)。氨基封端的PI在辛酸亚锡(Sn(Oct)2)的催化作用下引发丙交酯开环共聚,形成聚乳酸-聚酰亚胺(PLA-PI-PLA)嵌段共聚物。采用傅里叶变换红外光谱(FT-IR)、核磁氢谱(1H NMR)、凝胶渗透色谱(GPC)、水接触角等对PI和PLA-PI-PLA进行了表征。FT-IR、1H NMR、GPC的结果表明成功合成了PI及PLA-PI-PLA。水接触角结果显示PLA-PI-PLA相对于聚乳酸亲疏水性明显改善,同时PI主链上的酰亚胺环能在一定的条件下发生开环反应,可提供修饰聚乳酸材料的活性位点。     

凝胶注模成形法制备多孔铝及其性能研究

为了开发多孔铝制备新工艺与提高性能,采用凝胶注模法制备了形状较复杂的多孔铝。探讨了固相含量和烧结温度对多孔铝的密度、孔隙率、显微结构及力学性能的影响。结果表明,随固相含量的增加,烧结体密度随之增大,抗压缩性能提高;在不添加烧结助剂的条件下,680℃为最佳烧结温度。制得的多孔铝为开孔结构,孔隙率在34%～53%间可调,平均孔径3.82μm,抗压强度76.8MPa,比表面积0.12m2/g。     

用新工艺制备半固态铝合金浆料

用低过热度浇注和弱电磁搅拌工艺制备A356铝合金半固态浆料，研究了浇注温度、搅拌功率和搅拌时间对A356铝合金的半固态浆料的影响．结果表明，用该工艺可以制备出球状初生α—Al晶粒的半固态A356合金浆料．与单纯低过热度浇注的试样相比较，在弱电磁搅拌条件下，适当提高浇注温度亦可获得理想的球状A356合金浆料，也简化了实际浇注工艺的操作．低过热度浇注和弱电磁搅拌，加速了合金液向外传热和减小了其温度梯度，扩大了同时凝固的区域，细化了初生α—Al晶粒，造成的强迫流动，扩大了合金熔体的温度扰动和局部温度起伏，促使初生α—Al二次臂的熔断和球状初生α—Al晶粒的形成．     

Preparation and characterization of a novel hyperbranched polyphosphate ester

Polyphosphate esters have received a great deal of attention due to their important application in biomaterials field. Hyperbranched structure of polymers may support unique properties, including low viscosity and perfect intrinsic property. We report here three generations of hyperbranched polyphosphate esters (HPPE-1, HPPE-2 and HPPE-3) synthesized from a dehydrochlorination reaction between 1,3,5-tris(2-hydroxyethyl)cyanuric acid (THEIC) and phosphorus oxychloride (POCl₃), and characterize their chemical structures by FT-IR, ¹H NMR, ¹³C NMR, ³¹P NMR and 2D NMR (¹H,¹H-COSY and ¹³C, ¹H-HSQC) techniques. Degrees of branching of HPPE-1, HPPE-2 and HPPE-3 are 0.90, 0.91 and 0.87 respectively from the calculation of their ¹³C NMR spectra. Molecular weights of HPPE-1, HPPE-2 and HPPE-3 are m/z 1530, 1768 and 2750 from their MALDI-TOF-MS spectra. Study on thermal degradation mechanism of the HPPE-2 by a 3D FT-IR/TG technology shows that there are two cracking processes of its molecular chains, including the thermal degradation of hydroxylethyl-ended groups, nitrogen heterocycle and –CH₂CH₂– groups of HPPE-2.     

亲水性高分子-陶瓷复合膜的制备与表征

采用均质的氧化铝支撑体和不同表面层孔径的非对称氧化铝支撑体直接接枝聚丙烯酸(PAA)制备亲水性PAA-Al2O3复合膜。对所制备出复合膜的红外光谱(IR)分析、光电子能谱(XPS)分析、扫描电子显微镜(SEM)分析和表面的水接触角分析表明,成功地制备出了PAA-Al2O3复合膜。在相同实验条件下对所制备的复合膜进行纯水和纯乙醇的通量实验以及质量分数95%乙醇的脱水分离试验表明,最适合用于制备PAA-Al2O3复合膜的陶瓷膜支撑体是孔径为2～3μm的均质氧化铝支撑体,用其制备的复合膜的分离因子为139.33,通量为0.61kg/(m2.h),可以达到分离效率高、通量较大的效果.     

Preparation and mechanical characterization of a PNIPA hydrogel composite

A poly (N-isopropylacrylamide) (PNIPA) hydrogel was synthesized by free radical polymerization and reinforced with a polyurethane foam to make a hydrogel composite. The temperature dependence of the elastic modulus of the PNIPA hydrogel and the composite due to volume phase transition was found using a uniaxial compression test, and the swelling property was investigated using an equilibrium swelling ratio experiment. The gel composite preserves the ability to undergo the volume phase transition and its elastic modulus has strong temperature dependence. The temperature dependence of the elastic modulus and swelling ratio of the gel composite were compared to the PNIPA hydrogel. Not surprisingly, the modulus and swelling ratio of the composite were less dramatic than in the gel.     

Preparation of aluminum nitride granules by a two-step heat treatment method

The sintered aluminum nitride granules were prepared in a continuous process through a two-step heat treatment at 1600?°C for 5?h and 1850?°C for 5?h using the spherical γ-alumina/phenol-resin precursor obtained by spray granulation as the starting material. In the first step of heat treatment, the alumina powders were nitrided to form porous aluminum nitride granules via a carbothermal reduction reaction and then were continuously heated in the second step of heat treatment to produce dense spherical aluminum nitride granules without using sintering aids. The obtained porous and sintered aluminum nitride granules were characterized by XRD, SEM and BET measurements and exhibited an average grain size of about 1 and 3?µm, respectively. Furthermore, the specific surface area of the obtained porous and sintered aluminum nitride granules dramatically decreased from 2.49 to 0.16?m²/g showing that the low-porosity, dense, polycrystalline aluminum nitride granules were successfully prepared.     

Structural characterization of a mechanically milled carbon nanotube/aluminum mixture

The structural evolution of carbon nanotubes (CNTs) during mechanical milling was investigated using SEM, TEM, XRD, XPS and Raman spectroscopy. The study showed that milling of the CNTs alone introduces defects but preserves the tubular structure. When milling the CNTs with aluminum (Al) powder in order to produce a composite, Raman spectroscopy has shown that most of the nanotubes are destroyed. During sintering of the CNT/Al milled mixture, the carbon atoms available from the destruction of the nanotubes react with the Al to form aluminum carbide (Al₄C₃). The effect of milling on the Al matrix was also studied.