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991.
《The Journal of Adhesion》2007,83(1):1-14
The durability of epoxy-aluminium joints that use a homopolymerised epoxy resin was studied, and the effects of relative humidity, temperature, and salt concentration were analysed. The adhesive properties were measured by lap-shear tests, and the water uptake of the epoxy resin was determined by gravimetric measurements. Ageing and degradation effects on the epoxy resin and on the aluminium substrates were also analysed.
The homopolymerised epoxy resin absorbs little water (1.5 wt%) because of its nonpolar network structure. The water uptake is enhanced by increasing relative humidity and temperature; however, the joint strength remains constant because of epoxy plasticization. A saline environment is damaging to the adhesive joints, because of metal corrosion, but was not significantly harmful to the epoxy resin, because of a lower diffusion coefficient of salt water. The Tg decrease of the epoxy adhesive due to water absorption depends only on the amount of absorbed water and is independent of the hydrothermal ageing conditions. 相似文献
The homopolymerised epoxy resin absorbs little water (1.5 wt%) because of its nonpolar network structure. The water uptake is enhanced by increasing relative humidity and temperature; however, the joint strength remains constant because of epoxy plasticization. A saline environment is damaging to the adhesive joints, because of metal corrosion, but was not significantly harmful to the epoxy resin, because of a lower diffusion coefficient of salt water. The Tg decrease of the epoxy adhesive due to water absorption depends only on the amount of absorbed water and is independent of the hydrothermal ageing conditions. 相似文献
992.
The two types of high-sulphur coals Mequinenza and Illinois No. 6, in the initial form and subjected to potassium/liquid ammonia reduction, were analysed by atmospheric pressure-temperature programmed reduction (AP-TPR) method. It has been shown that preliminary demineralisation was beneficial for AP-TPR measurements because of the removal of calcium compounds. The reduction of sulphides and disulphides in the potassium/liquid ammonia system was found to lead to formation of aromatic and aliphatic thiols. The presence of the latter is better manifested in the AP-TPR kinetograms when the measurements are performed in the presence of a special reducing mixture. It has been shown that the coal reduction in the potassium/liquid ammonia system apart from transformations of non-thiophene sulphur groups also leads to breaking up of the C-S bonds in some thiophene systems. 相似文献
993.
Dongjin Seo 《Polymer》2005,46(17):6482-6493
Foam reaction injection molding (FRIM) is one of the most popular and useful processes for producing polyurethane foam with a complex geometry. A theoretical model which includes chemical reactions, foaming, and mold filling was developed to analyze FRIM. Energy balance equation was derived by considering polyurethane reaction, water-isocyanate reaction, and evaporation of physical blowing agents. Density and viscosity model was proposed for the bubble suspension, which was assumed to be a homogeneous phase. Based on the theoretical model, three-dimensional numerical simulation for mold filling of the polyurethane foam was carried out to predict flow field, flow front advancement, and density distribution during mold filling. Mold filling of a refrigerator cavity was investigated numerically. The density and thermal conductivity of the foam in the flow front was higher than those in the initially filled region. 相似文献
994.
Abstract. Several models have been proposed in recent years for analysing spatial data and also, to some extent, spatio‐temporal data. One of the important problems, namely the choice of an appropriate model for describing real data sets, remains unsolved. Here we consider the analysis of spatio‐temporal processes from which observations over space and time are available. We propose statistical tests for discriminating between space–time autoregressive processes and multivariate autoregressive processes. The sampling properties of the proposed tests are considered. We illustrate the methods with a real example. We use the above tests to find the best model to describe spatio‐temporal variations of hourly carbon monoxide measurements at four locations in London in January 2004. 相似文献
995.
K. Mengel 《Nutrient Cycling in Agroecosystems》1991,28(3):251-262
Excess nitrogen fertilizer rates are an environmental hazard. To avoid excess rates, the level of available nitrogen in the soil must be known and considered for assessing the nitrogen fertilizer rate. In arable soils nitrate and exchangeable ammonium in the rooting depth of a crop are directly available to plant roots. These two nitrogen forms are recovered with the Nmin method and they are considered in assessing the nitrogen fertilizer rate for arable crops.Besides nitrate and ammonium recovered by the Nmin method from soil samples taken in early spring, a considerable amount of organic soil nitrogen may be mineralized during the growth period and contribute to crop nutrition. The nitrogen mineralization potential can be determined in incubation tests. The absolute quantities of mineralized nitrogen thus obtained, however, are much higher than the mineralization rates under field conditions. It is for this reason that incubation tests have not obtained a major importance for assessing nitrogen fertilizer rates.With the electro-ultrafiltration (EUF) method nitrate, ammonium, and a minor portion of organic soil nitrogen are extracted from a soil suspension. There is experimental evidence that this organic nitrogen (=Norg) is easily mineralizable. Based on field experiments with cereals and maize formulae were established by which the nitrogen fertilizer rate can be calculated. In these formulae nitrate, ammonium and organic nitrogen extracted by EUF are considered.Advantages and drawbacks of the Nmin method and EUF method are discussed. 相似文献
996.
A. N. Gent 《The Journal of Adhesion》1987,23(2):115-122
Three new methods are discussed for measuring the work Ga, required to detach unit area of an adhering material from a substrate. The first is a simple modification of the Outwater double-torsion test for long rectangular plates, bonded together. This method is suitable for evaluating aluminum-epoxy bonds, for example, or the transverse strength of fibrous composites. The second is a pull-off test for long strips adhering to a rigid surface. It seems suitable for adhesive tapes and laminates. The third is a reconsideration of the “blister” test for films and coatings, in which a circular debond at the interface is made to grow by internal pressure. The relation obtained between pull-off force F for a strip, or blow-off pressure P for a layer, takes the unusual form:
F4 (or P4) ∞ KG3a
where K is the tensile stiffness of the detaching layer. This dependence arises from the non-linear (cubic) relation between load or pressure and deflection in these configurations. Nevertheless, the product Fθ, where θ is the angle of detachment of a strip, or Py, where y is the height of a “blister”, give direct measures of the strength of adhesion Ga, independent of the stiffness of the adhering material and of the extent of detachment. 相似文献
F4 (or P4) ∞ KG3a
where K is the tensile stiffness of the detaching layer. This dependence arises from the non-linear (cubic) relation between load or pressure and deflection in these configurations. Nevertheless, the product Fθ, where θ is the angle of detachment of a strip, or Py, where y is the height of a “blister”, give direct measures of the strength of adhesion Ga, independent of the stiffness of the adhering material and of the extent of detachment. 相似文献
997.
论述一种用透射谱包络线法计算非晶薄膜的折射率、消光系数和光学带隙的方法。通过正交实验确定除压强之外的工艺参数,研究压强的改变对薄膜主要光学常数的影响,运用最小二乘法、内插值法在matlab编程基础上,拟合出光学常数曲线,借由观察曲线的特点,分析在低工作气压下,气压的改变对光学常数的影响。 相似文献
998.
999.
开发新型工程现场快速检测砌块含水率方法,与传统的烘箱干燥方法进行比较,开展了工程现场试验,研究了在上海地区自然干燥环境条件下不同砌块墙面、朝向、砌块深度等对砌块含水率变化的影响。研究表明,该方法测试结果可信、操作方便,可用于现场快速检测。 相似文献
1000.
以高密度条件下航天发射试验为对象,对发射试验风险因素进行了系统分析,在此基础上,构建了风险评估指标体系,并针对高密度条件下航天发射试验主要风险,从人力资源风险、设备资源风险和进度风险等方面提出了具体应对措施,对航天发射试验风险管理具有一定的现实意义。 相似文献