The study of diffusion of media in the organic coating films by BAW admittance analysis

The permeation of water and corrosive species in coating films is very important for the corrosion protection by organic coatings. As a new method for the study of diffusion of media in coating films, bulk acoustic wave (BAW) admittance analysis has been proposed in this article. Real-time information on the change of the film mass, mechanic property of the layer, and the permeation process of the media can be provided simultaneously by the parameters of BAW admittance analysis, f_s (series resonant frequency), ΔL₁ (inductance variance), R₁ (resistance), Q (quality factor), and C_s (film capacitance). The diffusion behavior of media and the corresponding film stability can be described by the following parameters: D (diffusion coefficient), P (permeation coefficient), S (the solubility of media), and SC (the swelling coefficient of the coating layer). © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2283–2290, 1998     

体声波／生物传感器用于人尿中葡萄糖的酶法分析

在氧存在下,氧化酶催化反应的产物之一为H2O2。酸性条件下,H2O2与KI反应生成单质碘。本文将高选择性的酶技术与灵敏的体声波／生物传感技术有机结合,基于镀银电极对I2的特性吸附,建立了一种简便的酶法分析体系。以葡萄糖氧化酶为模型,完成了人尿中葡萄糖含量的分析。本文还进一步讨论了各种实验条件及某些影响因素。在最佳条件下以3倍信噪比计算得葡萄糖的检测下限为36ng,检测范围为0．2～20μg,相对偏差为2．4％,结果令人满意。     

Effects of the Langatate crystal quality on the resonance frequency stability of bulk acoustic wave resonators

ABSTRACT

In the time and frequency domain, we need ultrastable crystal resonators embedded in Ultra Stable Oscillators (USO), working at 10?MHz and exhibiting excellent short-term stabilities. Up to now, the quartz crystal fulfils its function. But, Langatate La₃Ga_5.5Ta_0.5O₁₄ (LGT) piezoelectric crystal seems to allow better performances with high quality material. The applications of this domain require high-quality material with reproducible properties. The LGT crystal is grown by the Czochralski method. Its physical and chemical properties and specificities of this growth process induce defects. They can react as ionic and electronic charge carriers and generate conductive losses. To assess the quality of the LGT crystal, we recorded the UV–VIS and IR transmission spectra and measured the electrical resistivity. At least, Y-cut resonators have been designed and manufactured to study the quality of the 10 MHz resonance, particularly its Q-factor, directly linked to the stability of the USO. We studied the effect of air annealing on the resonance frequency quality.     

The investigation on the curing process of polysulfide sealant by in situ dielectric analysis

In this work, in situ dielectric analysis (DEA) was employed for the first time to the best of our knowledge, to monitor the curing process of polysulfide (PSF) sealant using manganese dioxide (MnO₂) as the curing agent, where the gel point and ending point were determined. The obtained results were verified by rheological tests of dynamic mechanical analysis and tensile strength tests. It showed a significant difference between this curing process and those of usual thermosetting materials. The influences of the pH value of the samples and curing temperature were investigated and discussed in detail. Also, activation energies of the curing reaction of the samples with different pH values were calculated. The results proved DEA as a reliable and useful method for in situ monitoring PSF–MnO₂ curing process. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

紫外光固化法制备漆酚/石墨复合导电涂料的研究

以漆酚为基体,石墨为导电填料,利用紫外光固化法制备漆酚/石墨复合导电涂料,讨论了涂膜中石墨的含量以及固化方式等对漆膜导电性能的影响,并测试了漆膜的常规物理机械性能。结果表明,在紫外光辐照下,漆酚/石墨混合物涂膜可快速固化。当石墨含量达到25%(wt%)时,漆膜的表面电阻率为442Ω.cm,硬度为6H,附着力2级,冲击强度为45kg.cm。     

Dynamic mechanical analysis study of the curing of phenol‐formaldehyde novolac resins

The curing reaction of typical commercial phenol‐formaldehyde novolac resins with hexamethylentetraamine (HMTA) was followed by dynamic mechanical analysis. The evolution of the rheological parameters, such as storage modulus G′, loss modulus G″, and tanδ (G″/G′), as a function of time, for samples of the phenolic resins on cloth, was recorded. The curing reaction, leading to the formation of a crosslinked structure, is described by a third‐order phenomenological equation. This equation takes into account a self‐acceleration effect, as a consequence not only of the chemical reaction of crosslinking after the gel point but of phase segregation as well. This rheokinetic model of the curing of phenolic novolac resins permits the determination of the numerical values of the kinetic equation constants. The influence of the composition, structure, and physical treatment on the curing kinetics of the novolac resins is evaluated. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1902–1913, 2001     

扩散渗析-电渗析回收赖氨酸离子交换废液中的盐

为缓解电渗析膜污染,提高电渗析性能,采用阴膜扩散渗析对待脱盐的赖氨酸离子交换废液进行净化处理,对扩散渗析回收的(NH4)2SO4溶液进行电渗析脱盐浓缩。结果表明,当扩散渗析流量为5.6 L/h时,扩散渗析的扩散系数达2.24?10?7 cm2/s,离子交换废液中(NH4)2SO4透过率约为30%,可截留90.1% Mg2+和94.5%有机氮、80.3%蛋白、86.0%总糖、79.3%化学需氧量(COD);与直接电渗析赖氨酸离子交换废液相比,对扩散渗析回收的(NH4)2SO4溶液进行电渗析脱盐浓缩,SO42?膜通量、电流效率分别提高了55.7%和18.3%,操作时间、单位膜通量能耗分别降低了26.1%和42.3%。用扩散渗析净化赖氨酸离子交换废液可有效缓解后续电渗析的膜污染,提高电渗析性能。     

Monitoring the curing processes of epoxy oligomers with partially substituted polyethoxymetallosiloxanes by IR spectroscopy and thermomechanical analysis

In this work, the curing of «ED-20» epoxy resin with partially siloxy-substituted aluminum, iron, and zirconium siloxanes that we obtained previously was studied. The initial content of a metallosiloxane in the compositions was 5–50 wt% with respect to the resin. In all the cases, thermal curing was used to obtain a series of samples in the form of solid homogeneous materials. The fact of the epoxy ring opening in the resin was confirmed by IR spectroscopy. The catalytic properties of the metal atom in a metallosiloxane were found to affect the curing process. The samples demonstrate rather a high resistance to thermooxidative destruction, and in most cases, their glass transition temperatures are lower than those obtained upon standard curing of «ED-20» resin with triethylenetetramine. Partially siloxy-substituted metalloalkoxysiloxanes can be efficient agents for curing and formation of a hybrid material based on epoxy resins.     

The study of the proton diffusion process in the porous MnO2 electrode

The proton diffusion coefficients in an electrolytic manganese dioxide (EMD) electrode at various stages of the constant current discharge have been determined by means of AC impedance technique. The finite diffusion model was applied in the numerical fitting. The crystallite size of EMD was estimated from (1 1 0), (1 2 1) and (0 2 1) diffraction peaks with both Scherrer equation and Warren-Averbach theory. X-ray diffraction (XRD) peak broadening caused by instrument, crystallite size and microstrain was separated. The crystallite size of ramsdellite was assumed to be the proton diffusion length.     

板材粗糙度对水性3C1B工艺所得涂层短波的影响及改善方法探讨

为了改善采用超高泳透力电泳漆与水性3C1B工艺所得涂层的短波,讨论了电泳粗糙度和板材粗糙度对涂层橘皮的影响.除了控制板材粗糙度小于1.00μm,还可以通过打磨电泳层、调整中涂与清漆膜厚等措施来解决该问题.     

Numerical analysis on particle coating by the pulsed plasma process

The a-Si thin-film growth on particles in the rotating pulsed SiH₄ plasma process was analyzed numerically. The evolutions of chemical concentrations (SiH₄, SiH_x, and polymerized negative ions) in the pulsed plasmas have been shown during the plasma-on and -off. During plasma-on, SiH₄ is consumed by the electron impact dissociative reactions, but, during plasma-off, the disappearance reaction of SiH₄ stops because the electrons disappear in the plasma reactor. During plasma-on, SiH_x and are generated quickly by a fast dissociative reaction of SiH₄, but, during plasma-off, SiH_x disappears rapidly by a reaction with hydrogen and also by the deposition onto the reactor wall and particles, and is consumed quickly by fast neutralization reactions with the negative ions. The negative ions are polymerized by the reactions with SiH₄ during plasma-on, but, disappear by neutralization reactions during plasma-off. The growth rate of the film thickness profile depends on the SiH_x concentration because the particles grow with the SiH_x deposition. As the plasma-on time increases or as the plasma-off time decreases, the thin film thickness on the particles increases more quickly with faster SiH_x deposition onto them. A fraction of the particles falling down in the gas phase (W_FP) increases as the rotation speed of the plasma reactor increases. As W_FP increases, as the particle concentration decreases, or as the particle diameter decreases, the film thickness on the particles increases more quickly because the flux of SiH_x toward the particles increases.The pulsed plasma process can efficiently reduce the growth of polymerized negative ions and particles, both of which are not good for high-quality thin films. We showed that the high-quality thin films on the particles can be prepared successfully by deposition of low mass chemical precursors by pulsed plasma processes.     

Frequency analysis of the acoustic emission signals from PZT ceramics during the application of AC fields

Frequency analysis of Acoustic Emission signals in the range of 100-1200 kHz obtained from PZT ceramics during the application of limited and continuous cycles of ac field was undertaken to understand the fatigue behaviour of these ceramics. In the limited cycles experimentation, lower fields yielded higher range of frequency components (200-900 kHz) and higher fields yielded lower range of frequency components (200-500 kHz) at differnt temperatures of 60° C and 160° C. During continuous application of ac field, the initial stages of application yielded higher frequency components (100-850 kHz) and with increasing time of application, the frequency components of acoustic emission signal shifted towards lower frequency (less than 400 kHz). Electrical discharge induced cracking, resulted in the emission of frequency components in the range of 100-275 kHz.     

The single fiber pull-out test analysis: influence of a compliant coating on the stresses at bonded interfaces

The mechanical properties at the fiber/matrix interface play a significant role in controlling the fracture resistance of fiber-reinforced composites. By coating the fiber with sizing and coupling agents, these interfacial properties can be modified. The aim of the present analysis was to examine the effects of the coating thickness and modulus on the stresses at the bonded interfaces between the fiber, coating, and matrix. Using the fiber pull-out test as the analytical model, the stresses are first obtained by minimizing the total complementary energy in the coated fiber/matrix composite. The analytical results show that the interfacial shear stress between the fiber and the coating is higher than that between the matrix and the coating. Also, a thin and compliant coating reduces substantially the peak interfacial shear stress but not the interfacial radial stress due to Poisson's effect on the fiber. Furthermore, the shear stress transfer from the fiber to the matrix across the coating layer is found to be more uniform. The implications of these findings are discussed.     

Three-dimensional analysis of the spatial distribution of iron oxide particles in a decorative coating by electron microscopic imaging

The three-dimensional (3D) spatial structure of an iron oxide containing alkyd paint specimen has been investigated by serial block-face scanning electron microscopy (SBFSEM). The resultant images of the 3D structure clearly present the spatial distribution of the iron oxide pigment particles in the coating film and reveal the extent of aggregation of the particles in the matrix material. More than one-half of the iron oxide particles (in volume) had aggregated to form clusters of considerable sizes that follow a Gaussian spacing distribution in the measured coating film. Over 80% of the clusters have dimensions between 1.5 μm and 3.5 μm; also, pores are evident at the centres of clusters whose sizes are larger than 2 μm. The work demonstrated here reveals a new approach to fully characterize the 3D spatial structure of coatings and to explore their correlations with the performance of the materials.     

Kinetic study by FTIR,TMA, and DSC of the curing of a mixture of DGEBA resin and γ‐butyrolactone catalyzed by ytterbium triflate

A mixture of diglycidylether of bisphenol A (DGEBA) and γ‐butyrolactone (γ‐BL) was cured in the presence of ytterbium triflate as a catalyst. The kinetics of the various elemental processes that occur in the curing process were studied by means of isothermal curing in the FTIR spectrometer. The kinetics of the contraction during the curing was also evaluated by TMA. In both cases, the kinetics was analyzed by means of isoconversional procedure and the kinetic model was determined with the so‐called compensation effect (isokinetic relationship). The isothermal kinetic analysis was compared with that obtained by dynamic curing in DSC. We found that all the reactive processes and the contraction follow a surface‐controlled reaction type of kinetic mechanism, R₃. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 381–393, 2004     

Synthesis of polyesters as binders for deinkable inks. V. Structural analysis of the polyesterification between o-phthalic anhydride and trimethylolpropane in bulk at 165°C by high resolution 13C and 1H nuclear magnetic resonance

Structural analysis of the polyesterification in bulk without external catalyst at 165°C between o-phthalic anhydride (P) and trimethylolpropane (1,1, 1-tri(hydroxymethyl)propane) (T) with a mole ratio ([−COOH]/[−OH])=0·70 has been carried out by high resolution ¹³C nuclear magnetic resonance (¹³C NMR) in DMSO-d₆ and CDCl₃ solutions and by ¹H nuclear magnetic resonance (¹H NMR) in CDCl₃ solution. The use of CDCl₃ as NMR solvent has allowed us to identify several signals, which have been assigned to trimethylolpropane monoesters with different esterification degree in the o-phthalate residue. Identically, we have detected signals assignable to chain-end monoesters in structures with different chain lengths. These monoesterified structures have also been confirmed by analysing, by the same procedures, samples modified by diazomethane addition to the samples in chloroformic solution. These modified samples have also been used to determine free acid groups as their methoxylic derivatives by ¹H NMR in CDCl₃ solution. The values compare very well with those obtained by ¹³C and ¹H NMR spectro-scopies in both solvents in some other regions of the spectra. It has been found that NMR allows quantitative determination as a function of the reaction time, of the conversion of acid P and alcohol T functions, as well as monoester and diester of P distributions and those of free, mono- di- and tri-esterified T. We have not observed any detectable signs of gelation. ©1997 SCI