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51.
This paper investigates the ability of a shear wave reflection (WR) method to monitor microstructural changes of Portland cement mortar during hydration. The wave reflection method measures the reflection loss of shear waves at an interface between a steel plate and mortar. Mortars with water/cement ratios of 0.35, 0.5 and 0.6 were tested at isothermal curing conditions of 25 °C. The numerical model HYMOSTRUC3D was used to simulate the evolution of microstructural properties of the cement paste phase of the tested mortars. The parameters obtained from the simulations were the volume fraction of the total and connected solid phase and the specific contact area of the hydrated cement particles. The investigations have shown that the wave reflection measurements are governed primarily by the degree of the inter-particle bonding of the cement particles as calculated from the specific contact area of a simulated microstructure. 相似文献
52.
Tests have been made with over 300 dyed or pigmented materials exposed to mercury-tungsten or mercury lamps. The colorations were of a wide range of hue and light-fastness properties (1 to 8 and above) and in several depths on different substrates. The mercury-tungsten fluorescent lamp (500 W) gave results identical with those obtained with daylight or xenon arclight for 75% of the very varied selection of 174 patterns examined, and 25 % were within one-half of a grade, except for five which differed by one grade. When the blue standards are faded in this lamp (at 45% r.h.), they have an average interval factor of about 2.1. The required times of exposure are similar to those for the xenon arclight. The equipment required is extremely simple, and its initial and operating costs are considerably lower than those of methods hitherto used for testing in artificial light. The equipment can readily be used on the laboratory bench and is suitable for routine testing of the light fastness of any coloured material. In addition to the control of humidity, temperature control is possible, though this is not usually necessary. The mercury-vapour lamp (400 W) has also been similarly examined, using 138 patterns. It is not recommended for general use but is valuable for routine sorting tests of materials of very high fastness (BS grading above 7). The blue standard patterns fade, under exposure to these lamps, in the same sequence and with similar interval spacings, as in daylight or xenon light. 相似文献
53.
Influence of Distributed Particle Size on the Determination of the Parabolic Rate Constant for Oxidation by the Powder Method 总被引:1,自引:0,他引:1
The established analysis for the study of oxidation using powder specimens is based on the assumption of monosized particles. The experiments, however, are conducted on powders with a distributed particle size. Here we present a statistical approach for the calculation of the rate constant for oxidation. The results of the analysis are applied to new data on oxidation studies of dense powders of silicon carbonitride amorphous ceramics. The monosized model requires a wide range of values for the rate constant to fit the short term and the long-term data, leading to considerable ambiguity in the estimate of the parabolic rate constant, k p , for oxidation. In contrast the statistical model fits over the entire range of data, yielding a much more reliable value for k p . For example, the monosized approach gave a value in the range 19.7 × 10−18 < k p < 2.7 × 10−18 m2 /s. In contrast, the statistical model yields a specific value of 4.5 × 10−18 m2 /s. 相似文献
54.
A mathematical model of fluid flow and mass transfer in a packed bed was derived and used to evaluate the liquid phase axial dispersion and mass transfer coefficients under high pressure conditions. The least-squares method was used to evaluate the rate parameters from experimental breakthrough curves, and the agreement between the concentration curves predicted from rate parameters and those measured experimentally was good. Experiments were performed at 20 and 200°C with water as a solvent and nonporous soda-lime glass beads as packing. Although the axial dispersion coefficient was independent of temperature and pressure, the mass transport parameters were found to be pressure dependent. 相似文献
55.
A detailed study of the structure-property relationships for nanocomposites prepared using melt processing techniques from a sodium ionomer of poly(ethylene-co-methacrylic acid) and a series of organoclays is reported. Transmission electron microscopy, X-ray scattering, stress-strain behavior, and Izod impact analysis were used to evaluate the nanocomposite morphology and physical properties. Four distinct surfactant structural effects lead to improved levels of exfoliation and higher stiffness for these nanocomposites: higher number of alkyl tails on the amine rather than one, longer alkyl tails instead of shorter ones, use of 2-hydroxy-ethyl groups as opposed to methyl groups on the ammonium ion, and an excess amount of the amine surfactant on the clay instead of an equivalent amount. These trends are opposite of what has been seen in nylon 6 based nanocomposites but are similar to those observed in nanocomposites formed from LDPE and LLDPE. Although some organoclays were exfoliated better than others, none of the ionomer-based nanocomposites exhibited exfoliation levels as great as those seen in nylon 6 nanocomposites; nevertheless, these nanocomposites offer promising improvements in performance and may be particularly interesting for barrier applications. 相似文献
56.
World consumption of PVC was around 25 MM MT (55 billion pounds) in year 2001, second only to that of low density polyethylene. Only 10% of the PVC produced is classified as specialty PVC resins, while the other 90% is referred to as general purpose (GP) commodity resins. This paper tries to define what specialty PVC resins are, how they are produced, and their markets, applications, fabrication processes, and compounding as compared to those of GP resins. 相似文献
57.
Raina Aman Qazi Mohammad Saleem Khan Luqman Ali Shah Rizwan Ullah Ayesha Kausar Rozina Khattak 《Polymer-Plastics Technology and Engineering》2020,59(9):928-951
ABSTRACTFabrication of electronic materials from nanocomposite of biopolyesters reinforced with carbon nanotubes can be regarded as the effective alternative for conventional nanocomposites consisting of non-biodegradable polymers. Commercial availability of biopolyester-based nanocomposites is limited because of their high cost compared to other polymers, but the factor of their compostable nature is worthless for environmental protection. Such nanocomposites have potential applications in biodegradable sensors, EMI materials, etc. In this review, the current progress of biopolyester/CNTs nanocomposites in the field of biodegradable electronics is reviewed and also the impact of CNTs dispersion on electrical, thermal and mechanical properties of eco composites is stipulated. 相似文献
58.
J. S. Abichandani J. H. Wieland Y. T. Shah D. C. Cronauer 《American Institute of Chemical Engineers》1984,30(2):295-303
The liquefaction kinetics of Powhatan No.5 mine coal (Pittsburgh Seam) in the presence of SRC-II recycle solvent at short contact times (<10 min) and temperature and pressure ranges of 573–723 K and 10.3–13.8 MPa is examined in a well-mixed reactor. In the initial stages of liquefaction, while overall coal conversion (tetrahydrofuran solubles) increases with temperature, oil (pentane solubles) is lost with an increase in temperature. An increase in solvent-to-coal ratio results in an increase of conversion. The initial coal particle size distribution, total pressure, and nature of gas phase (nitrogen or hydrogen) have no significant effect on the production of any of the product of liquefaction for contact times up to 10 min. A lumped kinetic model is presented to describe the product distribution. 相似文献
59.
Supported 12-tungstophosphoricacid (12-TPA) and 12-tunstosilicicacid (12-TSA) were used as heterogeneous catalysts for liquid-phase
tert-butylation of m-cresol, an industrial important reaction. Alkylation reactions have been carried out with supported 12-TPA by varying different
parameters such as % loading of 12-tungstophosphoricacid onto support, mole ratio of alcohol to m-cresol, reaction temperature, amount of the catalyst, reaction time and calcination temperature to optimize the conditions.
To see the effect of the acidity on the reaction, the same reaction was studied over supported 12-TSA. Both the catalysts
give 100% selectivity for o-isomer with different % conversion. The difference in catalyst performance of both the catalyst
was correlated with the value of total acidity as well as Bronsted acidity. 相似文献
60.
Awdhoot V. Kerkar Sebastian Joseph Yatish T. Shah 《Chemical Engineering Communications》1987,54(1):225-239
The reactor systems used for the Fischer-Tropsch synthesis, fixed bed, fluidized bed and slurry bed, are compared on the basis of space time yield (STY) and level of conversion obtainable under the same set of feed and operating conditions. The slurry bed and fluidized bed reactor were compared on the basis of a first order reaction model. The performance of these two reactors was found to be comparable at low values of WHSV, but at higher values of WHSV, the fluidized bed reactor gave higher conversions and STY. A power law kinetic expression was used to compare the performance of the slurry bed and fixed bed reactors. Higher conversions and STY were obtained from the fixed bed with varying WHSV. This may be due to the omission of the intra and inter phase mass transfer resistances in the modelling of the fixed bed reactor. 相似文献