Evaluation of microhardness,fracture toughness and residual stress in a thermal barrier coating system: A modified Vickers indentation technique

The evolution of microhardness, fracture toughness and residual stress of an air plasma-sprayed thermal barrier coating system under thermal cycles was investigated by a modified Vickers indentation instrument coupled with three kinds of indentation models. The results show that fracture toughness on the top coating surface after thermal cycles changes from 0.64 to 3.67 MPa m^1/2, and the corresponding residual stress near the indented region varies from − 36.8 to − 243 MPa. For the interface region of coating and bond coat, fracture toughness in the coating close to interface ranges from 0.11 to 0.81 MPa m^1/2, and residual stress varies from − 5 to − 30 MPa, which are consistent with available data. For the lateral region of coating, fracture toughness and residual stress display strong gradient characteristics along the thickness direction due to the special layered structure.     

Selective deposition on block copolymer film by thermal evaporation of silver

Selective deposition of Ag onto nanostructured block copolymer film template of poly(ethylene oxide) and poly(methacrylate) with azobenzene mesogen (PEO-b-PMA(Az)) has been done by thermal evaporation technique. A hexagonally arranged pattern or ordered strip structure of the PEO nanocylinders dispersed in the PMA(Az) matrix appears on the pure copolymer film surface after thermal annealing at 140 °C or 110 °C, respectively. Atomic force microscopy confirms that the deposited Ag atoms prefer to wet PMA(Az) matrix domains on the film surface, and finally aggregate into discrete nanoparticles in both cases. An ordered porous metallic layer is created on the hexagonally patterned copolymer template surface due to the preferential interaction of Ag toward the PMA(Az) phase. Alternatively, ordered array of metallic chains is formed on the template featured with strip structure. While the nominal layer thickness of the deposited Ag is 50 nm, the ordered metallic nanostructure disappears, indicating the host copolymer template cannot guide the spatial distribution of the deposited metal any more.     

影响铸铁热疲劳抗力的因素

在热交变应力的作用下，热疲劳是铸铁工件的主要失效形式之一。本文综述了影响铸铁热疲劳抗力的诸因素。     

超临界CO2萃取烟草中烟碱

为研究超临界CO2萃取烟草中烟碱的工艺条件,利用实验室超临界萃取装置对烟草中烟碱进行了提取,考察了萃取压力、萃取温度、夹带剂乙醇的浓度、萃取时间等因素对烟碱提取率的影响,并就各个工艺参数对萃取率的影响机理和原因进行了分析与讨论。结果表明:在本研究范围内,最佳萃取工艺条件为:萃取压力30 MPa,萃取温度50℃,夹带剂乙醇浓度75%～80%,夹带剂流量为0.5 mL.min-1时,萃取时间为2～2.5 h。     

高半纤维素浆粕制备Lyocell纤维的研究

采用半纤维素质量分数21%的高半纤维素浆粕在N-甲基吗琳-N-氧化物(NMMO)水溶液中制备Lyocell纤维,并与半纤维素质量分数为10%的高α-纤维素浆粕的可纺性进行了对比。结果表明:高半纤维素浆粕在溶剂NMMO·H_2O中更易溶解,其过滤性能和可纺性能好,可在较高浆粕浓度下纺丝,制备成Lyo- cell纤维的产率高,且能提高Lyocell纤维的力学性能。高半纤维素浆液的稳定性能略低,在溶剂回收中需要消耗较多的双氧水进行氧化回收溶剂NMMO。     

控制气相PE流化床高度对装置运行周期的影响

分析了聚合过程中控制流化床床高对聚合物粒径,催化剂聚合产率和装置运行周期的影响.增加流化床床高,有利于聚合物粉料对反应器上部扩大段的冲刷,有效减少了粉料堵塞循环回路和反应器结块的发生几率,提高了聚合反应器运行周期.     

Effects of polymeric curing agent modified with silazanes on the mechanical properties of silicone rubber

Polymeric curing agent modified with hexamethyldisilazane (PCA‐D), or with hexamethylcyclotrisilazane (PCA‐T), was used to improve the mechanical properties of hydroxyl‐teminated polydimethylsiloxane (PDMS) rubber. The structure and the gel time of PCA were characterized by ²⁹Si NMR and shear viscosity measurement, respectively. The PCA modified with silazanes was more stable in storage than that without treatment (PCA‐0). Chemical bonds were formed during the reaction of silazanes and PCA according to ²⁹Si NMR results. The crosslink density (γ_e) and the mechanical properties of PCA/PDMS rubber were determined by swelling equilibrium and stress–strain tests. It was found that PCA treated with both silazanes could better enhance the mechanical properties of PCA/PDMS rubber compared with PCA‐0. PCA‐T/PDMS rubber, with additional crosslinks, was the best among the three types of PCA/PDMS rubber on the mechanical properties. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

High yield synthesis of diverse well‐defined end‐functionalized polymers by combination of anionic polymerization and “click” chemistry

Well‐defined poly(methyl methacrylate) (M_n = 3630 g mol^?1, PDI = 1.06) with a primary benzylic bromide prepared using anionic polymerization was successfully transformed into diverse end‐functionalities (ω‐carboxyl, ω‐hydroxy, ω‐methyl‐vinyl, ω‐trimethylsilane, and ω‐glycidyl‐ether) via “click” reaction. The bromine end‐terminated poly(methyl methacrylate) was first substituted by an azide function and sequentially was reacted with various functional alkynes (propiolic acid, propargyl alcohol, 2‐methyl‐1‐buten‐3‐yne, propargyl trimethylsilane, and propargyl glycidylether). In all the cases, ¹H‐NMR, ¹³C NMR, FT‐IR, and GPC measurements show qualitative and quantitative transformation of the chain‐end poly(methyl methacrylate) into the desired functionalities with high conversion (above 99%). © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Nucleation mechanism and morphology of polystyrene/Fe3O4 latex particles via miniemulsion polymerization using AIBN as initiator

In this study, oil‐based magnetic Fe₃O₄ nanoparticles were first synthesized by a coprecipitation method followed by a surface modification using lauric acid. Polystyrene/Fe₃O₄ composite particles were then prepared via miniemulsion polymerization method using styrene as monomer, 2,2′‐azobisisobutyronitrile (AIBN) as initiator, sodium dodecyl sulfate (SDS) as surfactant, hexadecane (HD) or sorbitan monolaurate (Span20®) as costabilizer in the presence of Fe₃O₄ nanoparticles. The effects of Fe₃O₄ content, costabilizer, homogenization energy during ultrasonication, and surfactant concentration on the polymerization kinetics (e.g., conversion), nucleation mechanism, and morphology (e.g., size distributions of droplets and latex) of composite particles were investigated. The results showed that at high homogenization energy, an optimum amount of SDS and hydrophobic costabilizer was needed to obtain composite particles nucleated predominately by droplet nucleation mechanism. The morphology of the composite particles can be well controlled by the homogenization energy and the hydrophobicity of the costabilizer. The magnetic composite particles can be made by locating Fe₃O₄ inside the latex particles or forming a shell layer on their PS core surface depending on the aforementioned polymerization conditions. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis of antimicrobial silver nanoparticles on silk fibers via γ‐radiation

Antimicrobial silver nanoparticles (NPs) were successfully synthesized on the surface of silk fibers via γ‐ray irradiation. The products were characterized with scanning electron microscope (SEM), energy dispersion spectrum, and X‐ray diffraction. The results revealed that the silver particles with a diameter of less than 20 nm were immobilized and well dispersed on the surface of silk fibers. The antimicrobial capability against the gram positive bacterium Staphylococcus aureus and the washing stability of the silk fibers produced with different conditions were tested and found to be excellent. The silk fibers treated with 1 mM solution and 10 kGy γ‐radiation showed 96% antimicrobial activity and still kept above 85% antibacterial activity after 10 washing cycles. Moreover, a mechanism for the formation of silver NPs on silk fibers under γ‐radiation was generally discussed. The resulting silk fibers coated with silver NPs can be useful as functional fabrics in a range of applications. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009