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991.
Several polymer‐layered silicate (clay) nanocomposites (PLSNs) were analyzed by transmission electron microscopy (TEM) and wide‐angle X‐ray diffraction (XRD) in an effort to characterize the nanoscale dispersion of the layered silicate. The PLSNs investigated included thermoset (cyanate esters) and thermoplastic polymers (polystyrene, nylon 6, and polypropylene‐g‐maleic anhydride). The results of this study reveal that the overall nanoscale dispersion of the clay in the polymer is best described by TEM, especially when mixed morphologies are present. XRD is useful for the measurement of d‐spacings in intercalated systems but cannot always observe low clay loadings (<5%) or be used as a method to identify an exfoliated nanocomposite where no XRD peaks are present (constituting a negative result). Most importantly, the study showed that XRD is not a stand‐alone technique, and it should be used in conjunction with TEM. Our studies suggest that new definitions, or a clarification of existing definitions, are needed to properly describe the diversity of PLSN nanostructures seen in various materials. Published 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1329–1338, 2003  相似文献   
992.
A partial phase diagram for the system Na3AlF6-Li3AlF6 was constructed from DTA and X-ray diffraction measurements. A region of solid solution extends from Na3AlF6 to the limiting composition Na2LiAlF6. At compositions between Na1.5Li1.5AlF6 and NaLi2AlF6 a cubic phase resembling the mineral cryolithionite is stable over a narrow range of temperatures, which shifts progressively to higher temperatures with increasing lithium content. A single phase can be quenched from samples annealed within this range except near the ideal cryolithionite composition (Na1.5Li1.5AlF6) where the upper temperature limit is too low to permit recombination of two solid phases to cryolithionite even with prolonged annealing. Cryolithionite precipitated from aqueous solution, a sample of the mineral, and the solid solutions containing from 53 to 65 mole % Li3AlF6 have identical powder patterns except for differences of lattice constants. Solid solubility of Na3AlF6 in Li3AlF6 reaches 30 mole % at the eutectic temperature.  相似文献   
993.
Optical inspection is a potentially powerful and practical tool to collect information on polymer blend morphology for on-line quality and process control. This paper describes two approaches for the characterization of polymer blend materials by multiple light scattering. A quantitative evaluation of spectral turbidimetry (scattering of transmitted light) is presented and an adaptation of this technique for monitoring particle size, independent of the volume fraction is demonstrated. Such a procedure is applicable to materials in film form. A different approach is presented for the analysis of nearly spherical particles in optically thick samples: the diffuse reflection pattern surrounding the position of incidence of a focused light beam on the surface of the turbid medium is scanned by a single side imaging system. A spectral pseudo-transmittance signal processing technique provides particle size information again independent of the volume fraction: Both techniques have been tested using well characterized polystyrene microspheres suspended in water as well as poly(methyl) (methacrylate)/polystyrene polymer blends.  相似文献   
994.
995.
Moderate or intense low oxygen dilution(MILD)combustion plays a significant role in the mitigation of combustion-generated pollutants and greenhouse gases whilst meeting thermal efficiency needs.However,due to the lack of the fundamental knowledge on this combustion,there is a misconception that MILD combustion should be established by high preheating of the air,which has limited its application.Our research and development on this combustion has been performed for several years. We have found that the requ...  相似文献   
996.
Calcium-sodium selectivity data for a number of carboxylic acid resins were obtained under constant solution conditions with the object of determining the effects of variations in resin structure. As weakly acidic resin ionization is pH dependant, plots of selectivity versus fraction ionized were obtained from measurements over a range of pH values.Calcium retention was found to be favoured by higher levels of resin ionization, greater degrees of crosslinking, by deliberate building in of chelating residues, and in commercial resins by acrylic over methacrylic acid types. In experimental composite resins comprising micro particles of active material embedded in an inert matrix, no difference in behavior of the two acid types was discernible, but the methacrylic variety is preferred for low calcium retention because of its more weakly acidic nature. The enhanced performance of a snake-cage acidic resin containing polyether and of a copolymer system containing ether groups in this regard was attributed to their greater swelling tendencies, arising from the incorporation of hydrophilic groups. In another copolymer system, however, the presence of amide groups was found to approximately halve the high affinity of acrylic acid resins for calcium, in particles which had normal swelling properties, and a reasonable high exchange capacity of 8.4 meq/g.  相似文献   
997.
Release of the antiaggregation pheromone, verbenone, at 3.8 mg/ day from a concentrated source within a multiple-funnel trap completely inhibited response by the mountain pine beetle (MPB),Dendroctonus ponderosae Hopkins, to attractive semiochemical lures. When aerial applications were simulated and verbenone was released at the same rate from beads lying in a 2×2-m area on the forest floor 15–35 cm below a trap, the response of the MPB was inhibited by only 50%. This reduced inhibition may be explained in part by the photoisomerism of verbenone. When exposed to full sunlight on two occasions, the times required for 50% of verbenone vapors to be converted to chrysanthenone were 75 and 100 min, respectively. Trap and tree-baiting experiments indicated no biological activity of chrysanthenone. Rapid photoisomerization could reduce the concentration of verbenone below biologically active levels and would allow the MPB to colonize trees close to already occupied hosts, contributing to the characteristic clumped distribution of MPB attack. The rate of verbenone photoisomerization may vary according to geographic location, stand elevation and density, and should be considered before verbenone is applied to control the MPB and other bark beetles.  相似文献   
998.
The precision and accuracy of the Iatroscan method was evaluated by comparing the results obtained with established phosphorus and gas chromatographic techniques. A complete lipid class analysis of rat heart lipids was chosen in order to evaluate the performance of the Iatroscan method for biological samples which contained both neutral lipids and phospholipids. A partial scan and repeat development with chloroform/methanol/water (68.5∶29∶2.5) was introduced to achieve consistently good separations of the phospholipids on the Chromarods in the Iatroscan method. The results showed that the precision of the Iatroscan method for some lipid classes was comparable to that of phosphorus or gas chromatographic techniques, while for other lipid classes it was lower. Compared to the data obtained using the phosphorus method, the Iatroscan data were generally similar, while the gas chromatographic method generally gave lower values. These findings, together with the advantages of time required for analysis, size of sample, and universality of detection, suggest that the Iatroscan is a valuable complementary method for complex lipid analyses.  相似文献   
999.
Electrical conductivity of concrete containing silica fume   总被引:15,自引:0,他引:15  
The influence of silica fume on concrete properties represents an important technical research. In general, silica fume tends to improve both mechanical characteristics and durability of concrete. Thus the electrical properties of concrete containing silica fume can be studied to clarify its physical performance during hydration. The electrical conductivity of neat cement, mortar and concrete pastes was measured during setting and hardening. The ordinary Portland cement was partially replaced by different amounts of silica fume by weight. The changes in the electrical conductivity were reported during setting and hardening after gauging with water. The results of this study showed that the electrical conductivity can be used as an indication for the setting characteristics as well as the structural changes of the hardened pastes made with and without silica fume.  相似文献   
1000.
Ultramicroscopy studies have been made of micelle formation by two poly(styrene)-poly(isoprene) block copolymers in organic solvents (N,N-dimethylacetamide and n-decane respectively) and a poly(l-glutamic acid)-poly(l-leucine) block copolymer in an aqueous solution of 0.2M NaCl at pH = 4.0. The technique provides a method of determining the number-average translational diffusion coefficient) D?n, of association colloids and leads, via the Stokes-Einstein relation, to a measure of the number-average of the reciprocal hydrodynamic radius (RD?1)n for spherical particles. Particles having a radius less than approximately 30 nm were too small to be detected by the technique.The ultramicroscopy results were compared with data obtained by laser light scattering photon correlation spectroscopy which provides a measure of the z-average translational diffusion coefficient. D?z. An additional comparison was made by carrying out measurements on two well-characterized poly(styrene/divinyl benzene) latices.  相似文献   
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