Short and long term particle release from surfaces under the influence of gas flow

Preliminary measurement of particle reentrainment from 5 mm i.d. and 3 m long stainless steel tubes show two distinct regimes of concentration decay with time.

In the regime (t < few minutes) the concentration n(t) is proportional to t^−a with a > 1 being a function of flow rate and particle size. The ST regime appears to correspond to particle release by shear flow in the region where F = (adhesion force)/(removal force) 1.

The concentration decay is described by the desorption model of Wen and Kasper, where n(t) is proportional to (1/t) exp (−t/T). The LT regime appears to include the release of relatively strongly adhering particles where F > 1 up to about F = 5 or 6 (Wen and Kasper, 1989) which is classically forbidden and explained only in the model Reeks et al. (1988).     

Effect of long term humid aging on plastics

The warm humidity resistance of more than thirty plastic formulations has been evaluated in a program which aged specimens for periods ranging from 10 months to 3 years. Both thermoset and thermoplastic products were included in this study. All of these materials can be used in high humidity at moderate temperatures for short periods of time except where water absorption lowers the glass transition temperature enough to cause distortion. Several of these commercial products exhibit good long term resistance to humidity at temperatures approaching 100°C. However, some are degraded by long term exposure to warm humidity. This hydrolysis effect can result in useful lifetimes which are considerably shorter than would be expected from projections which are based on conventional dry oven aging tests. This broad data base provides a basis for selecting plastics for use in warm, humid environments.     

Short term isothermal aging of epoxy resin and epoxy-carbon fiber composites

Short term isothermal aging of a neat epoxy resin and one ply epoxy-carbon fiber composite has been performed. The glass transition temperature, T_g of the neat epoxy resin aged at 204°C increased with aging time. The weight loss of the neat epoxy resin due to aging increased with aging temperature and aging time. The weight loss of the epoxy–carbon fiber composite during aging was slightly less than that of the neat resin. SEM microscopy showed the presence of voids and pores on the surface of the composite due to loss of low molecular weight volatiles. The amount and the size of the voids formed during aging increased with aging temperature and time.     

The short and long term performance of polymers in different environments

The behaviour of polymeric solids in contact with different environments is considered. A thermodynamic viewpoint is adopted and worked out in terms of chemical reactions, physical processes and the interaction between the two. It is shown that chemical attack alone does not normally cause serious loss of physical properties, but that a combination of chemical and physical (or physico-chemical) interactions between polymer and environment can lead to rapid deterioration. An understanding of these processes, and their synergistic effects, is essential in designing against environmental failure.     

Short term flexural creep behavior of wood-fiber/polypropylene composites

Short term flexural creep tests were conducted to investigate the creep behavior of wood-fiber polypropylene composites. Three experimental parameters were selected: the addition of a wetting agent, temperature, and wood-fiber concentration. All creep curves are presented in terms of relative creep as a percentage of instantaneous (initial) strain. The creep power law model was used to accurately fit the creep data. The addition of a wetting agent greatly reduced the creep at high stress, but had little effect at a lower stress level. The extent of relative creep increased with increasing temperature. It was found that the slope of the power law model was directly proportional to the temperature. The addition of wood-fibers into pure polymer greatly improved the creep resistance of the matrix polymer. The relative creep of the composites decreased with an increase in wood-fiber concentration. However, the composite showed relatively large creep compared with that of solid wood. It was found that both the time exponent and slope of the power law model were inversely related to wood-fiber concentration. The flexural modulus of the composites also had an inverse relationship with the time exponent.     

国内离子膜电解法与金属阳极隔膜电解法烧碱将在相当长的时期内共存

关于选择烧碱生产工艺的问题,作者阐述了如下观点:离子膜法是电解法烧碱生产工艺的发展方向,金属阳极隔膜法最终将被离子膜法取代;但由于历史、投资、设备更新、经济效益、市场需求等方面的原因,国内金属阳极隔膜法和离子膜法电解工艺将在今后相当长的一段时期内共存.     

The effect of annealing on the short and long term behavior of PEEK

Summary Short and long-term tensile tests have been done on injection-moulded poly-ether-etherketone (PEEK) in order to assess the effect of annealing on its mechanical behavior. In addition to the behavior reported before, namely increases in yield and drawing stress, the annealed specimens exhibit a distinct work hardening behavior in the beginning of the drawing phase at temperatures between 80°C and 160°C. Subsequent creep tests show that the annealing treatment also influences greatly the long-term static properties of PEEK with creep rates after annealing being considerably below those recorded on the standard injection.DSC thermograms of the samples annealed for more than 20 minutes exhibit similar curves as those reported before, two endothermic peaks: a major peak at 340°C and a minor one at 260°C which is 10 K higher than the annealing temperature.The experimental results support that a type of secondary crystallites grow in the material by the annealing treatment. The existance of those secondary crystallites enhances the mechanical properties of PEEK.     

长期搁置碳钢管的化学清洗及预膜处理工艺介绍

介绍了长期搁置碳钢管的化学清洗,以及在总Fe含量较高的水环境中的钝化预膜处理工艺。该工艺的实施取得了良好的化学清洗和钝化预膜效果,控制了碳钢管的腐蚀趋势;同时节约了用水、降低了清洗成本。     

技术创新 管理细化 实现装置长周期运行

结合本装置已连续运行 90 0多天的实际经验 ,从技术创新和管理细化两个方面探讨了如何保证老装置的长周期运行     

On the nonlinear characterization of the long term behavior of polymeric materials

In the linear viscoelastic range the long term behavior of viscoelastic materials—such as polymers—can be described by using exponential series with a limited number of terms for the approximation of the relaxation modulus or of the creep compliance. This procedure can be extended to the nonlinear viscoelastic range by multiplying the linear parameters of the material by certain nonlinearity factors, which depend upon the level of the applied loading. Application of this method to stress relaxation data of several polymers has shown that nonlinearity factors can be approximated as linear functions of the applied constant strain. From creep tests, on the other hand, one can observe that the immediate strain response to the suddenly applied stress is linear elastic even in the nonlinear viscoelastic range of the investigated polymer. The computation of the linear viscoelastic material parameters as well as of the nonlinearity factors is conducted numerically by using least squares techniques. Good agreement between computed results and experimental data can be observed in the presented examples.     

Short term essential fatty acid deficiency in rats. Influence of dietary carbohydrates

The effects of long term (8–14 wk) essential fatty acid (EFA)-deprived diets in rats are well documented. In the present study, we compared, in weanling rats, the effect of a short term (two wk) hydrogenated coconut oil, EFA-deprived, diet (D) with that of a corn oil, EFA-adequate, diet (A), using either sucrose (SU) or starch (ST) as carbohydrate. After two wk, rats fed the sucrose/hydrogenated coconut oil diet developed some characteristic features of EFA deprivation: slower growth rate, decreases in linoleic and arachidonic acid of plasma phospholipids and an increase in n−9 eicosatrienoic acid of plasma phospholipids. When rats ate the starch/hydrogenated coconut oil diet, there was a similar decrease in linoleic acid of plasma phospholipids, but only a small effect on growth rate and no change in the arachidonic acid content of plasma phospholipids. EFA deprivation and sucrose had opposite effects on plasma triglyceride (TG) levels: deprivation induced a decrease, whereas the sucrose induced an increase in very low density lipoprotein (VLDL) triglycerides. The observed decrease in plasma triglyceride during EFA deporivation might result from an activation of lipoprotein lipase during the early stages of deprivation.     

电解槽长期停车期间离子膜的保护及开车时注意事项

介绍电解槽长期停车期间的处理方案及离子膜的保护措施,指出电解槽长期停车后再开车过程中的注意事项,给出电解槽停车前后的各项数据对比。     

Application of time-temperature superposition principle to long term engineering properties of plastic materials

Time-temperature equivalence was used to predict the long term engineering behavior of highly crystalline ethylene-butene copolymers. The long term behavior (greater than 1000 hrs.) was accurately predicted from tests of short duration (30 hrs.). This time-temperature principle was applied to stress-relaxation and creep at stresses, strains and temperatures normally encountered in engineering practices. It was also used to solve a design problem involving the creep deformation of metal plastic laminates. Long term tests were performed to confirm the predicted results. This technique was not applicable to rubber modified polystyrene because of an unexpected transition at 88°F.     

化工区公共管廊危险品物流管道实施在线腐蚀检测与长期监测的深讨——MsS长距离超声导波检测与长期监测技术

某化工区公共管廊的危险品物流管道和受压管线近300多公里,介质多变,如氯化氢、苯、丙烯、丁烷等,分布在区内近十条道路上,面积大、区域广、联系难度大、关联性强、聚集度高、危险性大。使用常规无损检测手段根本无法解决问题,因而急需寻找一种快速在线检测危险品物流管道腐蚀状态,并对其腐蚀状态可进行长期监测的技术,以确保其长期正常安全运行。MsS长距离导波技术正是满足危险品物流管道腐蚀在线检测与长期状态监测的有效手段。     

Studies of long term administration of aflatoxin to rats as a natural food contaminant

The effect of feeding aflatoxin, as a natural food contaminant, to rats over long periods of time was studied using multigeneration and longevity tests. The test animals in the multigeneration study consisted of three groups of rats fed diets containing 0, 1 and 10 ppb of aflatoxin (predominantly B₁) continued over four generations, with animals of the first and fourth generation fed the diets for 104 weeks. These diets were in proper nutritional balance and included 35% ground roasted peanut products; the ration with 0 ppb aflatoxin excluded the peanuts usually discarded; the one with 1 ppb had the roasted discards returned, while the ration with 10 ppb included the discards in amount 10 times that which had been initially removed. Another longevity study was also performed in which rats were fed diets containing aflatoxin at a level of 80 ppb. In this case, the test peanuts, also fed as a simulated peanut butter at 35% concentration, consisted entirely of roasted peanut discards. Control diets provided no peanut components. Animals fed the low levels of aflatoxin grew as well and actually had a higher percentage survival at 104 weeks than did the animals on the control, aflatoxinfree diets. Organ weights, liver total lipid and cholesterol levels were comparable in all groups. Pathological abnormalities, e.g., hemorrhagic and opaque spots and mottling in some of the livers, were attributed to the aging process since the abnormalities appeared in the control as well as the experimental groups. In the animals fed the aflatoxin at 80 ppb, which has been reported by several investigators to produce well-defined hepatomas in rats, there was liver involvement and some biochemical changes occurred that were not noted in the controls. However, no hepatomas were observed in these animals even after 21 months on this diet. The liver lesions, indicative of a toxic effect, have not been associated with the development of hepatomas. It is possible that some components of the diet used in these experiments may have protected the animal against hepatoma formation. Our studies indicate that there may be a tolerance for aflatoxin as judged by results in one species of rats when whole ground roasted peanuts provide the natural contaminant. Presented in part at the AOCS Meeting, New York, October 1968.     

Nitrate distribution and accumulation in an Ustochrept soil profile in a long term fertilizer experiment

Distribution and accumulation of NO₃—N, down to 210 cm depth, in the soil profile of a long term fertilizer experiment were studied after 16 cycles of cropping (maize-wheat-fodder cowpea). The application of fertilizer N without P and K or in combination with only P resulted in higher NO₃—N concentration in the soil profile than the application of N with P and K. With an annual application of 320 kg N ha^–1 alone, a peak in NO₃—N accumulation occurred at 135 cm soil depth. However, with the application of NPK, no peak in NO₃—N distribution was discernible and its content at most of the sampling depths was either less than or equal to N and NP treatments. The annual application of 10 tons farm yard manure (FYM) per ha along with NPK resulted in a relatively lower NO₃—N content in the sub soil. The amount of NO₃—N accumulation in the soil profile decreased as the cumulative N uptake by the crops increased. Application of fertilizer amounts greater than that of the recommended (100% NPK) resulted in low percent N recoveries in crops and greater NO₃—N accumulation in the soil profile.     

An accelerated method for establishing the long term performance of polyethylene gas pipe materials

It was demonstrated in a previous investigation that both horizontal and vertical shifting is required to produce master curves for the relaxation moduli from elevated temperature data for polyethylene gas pipe materials. In this study, the shift functions obtained from these stress relaxation tests are applied to an assortment of elevated temperature time-dependent failure data for a variety of medium and high density polyethylenes. In all cases the data are successfully shifted to produce coherent master curves within the intrinsic scatter of the original data sets. The implication is that these horizontal and vertical shift functions are, for all practical purposes, universal for polyethylene gas pipe materials. This finding provides the basis for interpreting elevated temperature test data for polyethylene pipe materials so that a substantial savings in cost and time may be achieved in assessing the performance, structural integrity, and life expectancy of piping systems made from these materials.     

Effects of soy proteins containing trypsin inhibitors in long term feeding studies in rats

Pancreatic hypertrophy that occurs in rats fed raw soy flour containing about 1200 mg tripsin inhibitor (TI)/100 g diet was reversed by switching the rats to control diets or to diets containing 30% toasted defatted soy flour. No pancreatic hypertrophy occurs in rats fed commercial, edible grade soy flours, concentrate or isolate from time of weaning to adulthood (ca. 300 days). TI content of the soy diets ranged from 178–420 mg/100 g. Except for pancreas enlargement in rats fed raw soy flour, gross and microscopic examination of pancreata revealed no abnormalities. The gross appearance of heart, kidney, spleen, and liver was normal. Soy flour, protein concentrate, and protein isolate in a formulated corn-soy diet provided optimum growth and maintained body weight only if supplemented with vitamin B-12 in long term feeding studies with rats. In the absence of such supplementation, rats fed soy diets initially grew at a rate equal to or greater than those fed a comparable corn-casein control diet; but, with continued feeding for ca. 300 days, body weight of rats fed the casein control was significantly greater than that of the soy flour-fed rats. Those fed soy isolate ceased to grow; and rats fed soy concentrate lost weight. No significant differences were found in organ weights between groups fed soy products and casein, except for increased kidney, liver, and testes weights relative to body weight with the group fed soy concentrate. Supplementation of the soy diets with vitamin B₁₂ stimulated growth to the greatest extent, calcium pantothenate or riboflavin had an intermediate effect, other vitamins had little or no effect; whereas a complete mineral mix was detrimental. Supplementation of the soy diets with vitamin B₁₂ stimulated growth to the greatest extent, calcium pantothenate or roboflavin had an intermediate effect, other vitamins had little or no effect; whereas a complete mineral mix was detrimental. Supplementation of the control diet was without effect. The dietary protein level in these diets was 20%, with casein or soy protein representing 75% of total protein. When fed continuously to rats from weaning to adulthood, properly processed soy protein products, when balanced with essential nutrients, can provide growth comparable to corn-casein diets.