Dielectric Response of Adhesive Joints to Water Absorption

Dielectric measurements have been used to infer the average moisture content of aluminum adhesive joints bonded with three commercial epoxy adhesives. Measurements were made on both aluminum-adhesive-aluminum joints and aluminum-adhesive specimens in order to assess the influence of moisture diffusion gradients. Similar experiments were also performed with foil electrodes embedded in the bondline. For average water concentrations less than approximately 2%, there existed a linear relationship between the permittivity and the average moisture level which was independent of the spatial nonuniformity produced by water diffusion. At higher moisture levels, the dielectric response varied considerably from one adhesive to another, but, in general, could be approximated as a linear dependence on the average moisture concentration. The dielectric response was recoverable upon drying.     

High Resolution Optical Interference Measurements of Changes in Bond-Line Thickness—A Review

A novel moire optical interference method, originally developed¹ to measure the swelling displacement normal to the plane of a simple butt joint during water uptake at the joint edge, was subsequently used to investigate the unexpected occurrence of shrinkage and, at the same time, swelling during exposure to organic solvents. In later experiments, synergistic displacement fields generated during simultaneous exposure to water and organic solvents were studied. The same method has also been used to investigate the origin of adhesion failures at copper plated-through holes in thermally cycled multi-layer circuit boards.

The method employs a thin glass cover slip as one adherend. Changes in bondline thickness flex the cover slip thereby changing the gap between the latter and a nearby optical flat. By using monochromatic light to illuminate the specimen, interference between incident and reflected light is achieved. The small displacements of individual fringes associated with changes in gap size are used to generate moire patterns which bear a 1:1 relationship to the local changes in bondline thickness. Application of thin plate elasticity theory to the flexing of the cover slip yields the stress acting normal to the joint. The magnitude of this normal stress is strongly inhomogeneous, oscillating in sign and reaching compressive values as high as 50MNm^-2 for water uptake by a simple butt joint, and exceeding the yield strength of oxygen-free high conductivity copper (1MNm^-2) for the thermal expansion that accompanies simulated soldering of a multi-layer circuit board.

Attention is drawn to the high resolution achievable with the method. Changes in bond-line thickness of the order of Δ/10, where Δ is the wavelength of the light giving rise to the interference pattern, are readily resolved. It is pointed out that the method may well be sufficiently sensitive to detect the effects of different physical properties (thermal conductivity, specific heat capacity) of adherend surface on the nature of the cured adhesive and hence on the mechanical behaviour of the bond-line.     

Blistering of Glass-Epoxy Amine Adhesive Joints in Water Vapour at High Pressure. An Indication of Interfacial Crumpling

When joints are made between solids, the surfaces of which are soluble in water, with an epoxy-amine adhesive, blistering is observed in water vapour at high temperature and pressure. The occurrence of these blisters follows the cavitation theory in elastomers. Microscopic observation of the blisters suggest that they come from initial smaller ones which are homogeneously spread along the interface (not air bubbles or defects) and grow under the osmotic pressure developed by water condensation in the initial “sucker” and by surface dissolution. These observations led us to suggest that the solid/adhesive interface crumples during hardening of the adhesive and that many small suckers exist along the interface. This leads to a new model for the loss of adherence of epoxy-metal joints kept in high humidities.     

金属胶接接头劈裂破坏的模型分析

对金属胶接接头劈裂强度测试方法和影响劈裂强度的主要因素的作用进行了分析与讨论。本文提出了金属胶接接头劈裂破坏模型，对完善劈裂强度测试方法提出了改进意见．     

Blistering of Glass-Epoxy Amine Adhesive Joints in Water Vapour at High Pressure. An Indication of Interfacial Crumpling

When joints are made between solids, the surfaces of which are soluble in water, with an epoxy-amine adhesive, blistering is observed in water vapour at high temperature and pressure. The occurrence of these blisters follows the cavitation theory in elastomers. Microscopic observation of the blisters suggest that they come from initial smaller ones which are homogeneously spread along the interface (not air bubbles or defects) and grow under the osmotic pressure developed by water condensation in the initial “sucker” and by surface dissolution. These observations led us to suggest that the solid/adhesive interface crumples during hardening of the adhesive and that many small suckers exist along the interface. This leads to a new model for the loss of adherence of epoxy-metal joints kept in high humidities.     

高效液相色谱直接光学拆分手性农药(英文)

Enantiomer separation is one of the most important prerequisites for the investigation of environmental enantioselective behavior for chiral pesticides.The enantiomeric separation of three chiral pesticides,indoxacarb,lambda-cyhalothrin,and simeconazole,were studied on cellulose tris-(3,5-dimethylphenyl-carbamate)-coated chiral stationary phase(CDMPC-CSP) using high-performance liquid chromatography under normal phase condition.The effects of chromatographic conditions,such as the mobile phase composition including the concentration and type of alcohol modifiers in hexane,flow rate and column temperature,on enantiomer separation were examined.The thermodynamical mechanism of enantioseparation and chiral recognition mechanism were discussed.Better separation were achieved using 20% n-propanol for indoxacarb,2% iso-butanol for lambda-cyhalothrin,and 20% iso-propanol for simeconazole as modifiers in hexane at 25℃ with the selectivity factor(a) of 1.69,1.82 and 1.70,respectively.The resolution factor(Rs) decreased as the flow rate increased from 0.4 to 1.1 ml·min-1.The retention factor(k’) and selectivity factor for the enantiomers of analytes decreased as temperature increased.The lna-1/T plots for racemic chiral pesticides were linear in the range of 15-35℃ in hexane/iso-propanol and the chiral separation was controlled by enthalpy.Hydrogen bonding,π-π and dipole-dipole interactions between enantiomers and CDMPC-CSP play an important role in chiral identification,and the fitting of the asymmetric portion of solutes in a chiral cavity or channel of the CSP is also important.     

微波法制备高吸水性树脂的溶胀性能研究

以2-丙烯酰胺-2-甲基丙磺酸(AMPS)和丙烯酸(AA)为单体,N,N′-亚甲基双丙烯酰胺为交联剂,在不加引发剂的情况下采用微波聚合法合成了丙烯酸-2-丙烯酰胺-2-甲基丙磺酸二元共聚高吸水性树脂。研究了交联剂用量、中和度等因素对产物性能的影响,并对溶胀动力学进行了初步探讨。     

The Deformation of the Adherends in an Adhesive Joint Undergoing Water Uptake

Beam and elasticity theory have been applied to the deformation observed to occur when a model adhesive joint is exposed to water. The adhesive joint is comprised of a thin microscope cover slip/adhesive layer/rigid substrate sandwich.

The presence of damped normal displacement waves in the cover slip, predicted to exist in the joint in regions of negligible water concentration, has been confirmed by measurements on photographs of interference patterns generated with an optical interferometer.

A “theory assisted” fit for the normal displacement has led to an improved fourth derivative, and this has enabled a better estimate to be made for the distribution of normal swelling stress.     

用光学拆分法制备左旋薄荷脑

<正> 薄荷脑是一种重要的香料和医药原料。天然薄荷脑是从薄荷油中提取的左旋薄荷醇结晶。它具有清凉、镇痛、止痒、杀菌作用,在日用化妆品、清凉饮料、卷烟、医药等方面早已得到广泛的应用。由于天然薄荷脑的生产易受天时影响,产量时有波动,故国外对利用石油化工原料来合成薄荷脑的研究工作颇为重视。但是合成的薄荷脑大都为消旋体,其药用疗效和凉味均不及天然的主旋体,还不能与左旋薄荷脑媲美。虽然,近些年来有报导可以利用立体     

The Effect of PEEK Fibres and Powder on Joints Made with a High Temperature Adhesive

High temperature adhesives typically exhibit low levels of peel strength since they tend to be more brittle than typical toughened adhesives used for lower temperature applications. It was found that incorporating thermoplastic fibres or powder into the bondline of a joint made with a high temperature epoxy-based adhesive resulted in significant improvements in peel strength. Poly(ether ether ketone) (PEEK) fibres and powder were incorporated into the adhesive resin and used in aluminium joints. These were tested in peel and single lap shear using a range of fibre lengths, orientations and volume fractions. It was seen that large increases in peel strength could be achieved but that lap shear strength was degraded with most types of modification. However, some modifications resulted in significant increases in peel strength with limited decrease in lap shear strength. These improved properties have been achieved using physical modifications rather than chemical alteration of the resin.     

高固含量水乳型塑─木复合胶的研制

研究高固含量塑-木复合胶粘剂的制备与性能,讨论了主要原材料对产品性能的影响,介绍了该胶粘剂的应用。     

高固含量水乳型塑─木复合胶的研制

研究高固含量塑-木复合胶粘剂的制备与性能,讨论了主要原材料对产品性能的影响,介绍了该胶粘剂的应用。     

Inverting High Spectral Resolution Aerosol Optical Depth to Determine the Size Distribution of Atmospheric Aerosol

Measurements of aerosol optical depth are presented in the spectral interval 0.40–1.10 μm, which includes the most transparent region of the solar spectrum and the near infrared. The measurements were obtained by a grating spectrometer with a resolution ≈ 0.5 nm during the 1994 summer season at a mountain site (about 850 m above sea level) in the South of Italy. Spectral regions free from gas absorption features have been singled out and used to retrieve the aerosol columnar size distribution. Inversions have been performed by using the Phillips-Twomey inversion method along with a χ² criterion which allows one to choose a suitable value for the regularization parameter. The result of the inversions are presented in the particle radius range 0.1 ÷ 3 μm and indicate the presence of a bimodal aerosol with the second mode radius at about 1.0 μm undergoing transformations which are well correlated with relative humidity.     

A Model for the Diffusion of Moisture in Adhesive Joints. Part II: Experimental

The concentration dependence and temperature dependence of the diffusion coefficient, as discussed in Part I, are validated with literature data on poly(styrene) and on poly(vinylacetate). The effect on diffusivity, of a uniaxial tensile stress state and of a biaxial tensile stress state, is measured with permeation tests on stretched poly(ethyleneterephthalate) (PET) films. The influence of semi-crystallinity is briefly discussed. Further, diffusivity measurements under a tensile stress state, under a compressive stress state, and under a pure shear stress state are performed on Ultem^® polyimide films, using a modified sorption technique. Good agreement between theoretical predictions and experiment is found. Finally, predictions by the solubility model discussed in Part I are compared with data on low density polyethylene and on Ultem polyimide.     

非达司他中间体的酶法拆分

(2S)-6-氟-3,4-二氢-4-氧代-2H-1-苯并吡喃-2-羧酸是合成非达司他(一种口服醛糖还原酶抑制剂)关键中间体。该研究使用脂肪酶Novozym 435,对(±)-6-氟-3,4-二氢-4-氧代-2H-1-苯并吡喃-2-羧酸甲酯进行拆分,并对拆分反应条件进行了优化,确定了拆分的最适反应条件:乙腈-水溶液为溶剂,V(水)∶V(乙腈)=1∶4,m(酶)∶m(底物)=1∶10,在pH=7.0,温度40℃,时间为6 h条件下,得到的(2S)-6-氟-3,4-二氢-4-氧代-2H-1-苯并吡喃-2-羧酸的总收率为32.5%,对映体过量值为92.1%,为非达司他的制备提供了一条可行途径。     

Determination of Water Diffusion Coefficients and Dynamics in Adhesive/Carbon Fiber-Reinforced Phenolic Resin Composite Joints

Energy-dispersive X-ray spectroscopy analysis (EDX) is an easy and exact method for determination of water diffusion coefficients and dynamics. Here we have calculated the water diffusion coefficients and dynamics in adhesive/carbon fiber-reinforced phenolic resin composite joints subjected to different surface treatments with both EDX and elemental analysis. The water diffusion coefficients and dynamics in the adhesive joints determined with EDX analysis are almost the same as those determined with elemental analysis. The durability of the adhesive joints with carbon fiber-reinforced phenolic resin composites subjected to silane coupling agent treatment is better than those subjected to sandpaper burnishing and chemical oxidation treatment.     

A Model for the Diffusion of Moisture in Adhesive Joints. Part III: Numerical Simulations

The coupling mechanisms between the diffusion process and the viscoelastic response of an adhesive are explained. A numerical scheme for fully-coupled solutions is proposed and implemented in a two-dimensional finite element code. A number of numerical simulations are presented in order to illustrate the importance of the following features: (1) the bulk viscoelastic behavior, (2) penetrant size, (3) physical aging, (4) the strain dependence of the diffusion coefficient, (5) the concentration dependence of the diffusion coefficient and (6) differential, swelling. The effect of moisture intrusion on the stress (strain) distribution across a butt joint is also presented.     

Effect of the Secondary Transition on the Behaviour of Epoxy Adhesive Joints at High Rates of Loading

The shear yield behaviour of a modified epoxy joint has been investigated over a wide range of strain rates (γ˙ = 10^–2 s^–1 – 10⁴s^–1) and at different temperatures (–30°C, 24°C, 60°C, 80°C).

Assuming that high polymers exhibit pure viscous yield, the sharp increase of the yield stress in the strain rate sensitivity at high strain rates is explained in terms of a difference in relaxation times at low strain rates and high strain rates (α and β). The Bauwens's approach, which is a modification of the Ree-Eyring theory, gives an acceptable fit to the data. The yield behaviour of the modified epoxy joint, above a critical strain rate γ˙_β(T), may be described by the sum of the partial stresses τ_α and τ_β required to free the different kinds of molecular motions implied in the deformation process.

A good correlation between high impact resistance and the presence of the β mechanical loss peak in the range of the explored strain rates is established.

At very low temperature (-30°C), the data do not accurately fit the Ree-Eyring equation, meaning a heterogeneous deformation process characterized by the formation of local adiabatic shear bands and a permanent evolution of the molecular structure.     

水煤浆装置氧泵因"晃电"跳停原因分析及对策

简单介绍了水煤浆装置空分氧泵变频器的电气控制原理.分析了氧泵变频器因系统"晃电"而导致空分高压液氧泵跳停的情况.通过采取一些有针对性的措施,确保空分氧泉稳定运行.     

氨基酰化酶固定化细胞光学拆分DL-丙氨酸

用具有氨基酰化酶基因的大肠杆菌工程菌构建固定化细胞,并对DL-丙氨酸进行酶拆分进行了实验研究。考察了温度、pH、底物浓度、金属离子和时间对酶促反应的影响。确定了氨基酰化酶固定化细胞光学拆分DL-丙氨酸中酶促反应的最佳工艺条件:pH=7.5,温度50℃,反应时间6h,Co2+离子浓度5×10-4mol/L,在该条件下,D-丙氨酸产率为87.2%,光学纯度为98.0%。