A new type of mesoporous silica has been prepared which showed 780 m2/g of BET surface area and 0.6 ml/g of primary mesopores narrowly distributed around 4.2 nm. More importantly however, is that it showed short-range zeolite crystallinity as demonstrated by FTIR and XRD analysis, and hydrophobicity as demonstrated by water and n-hexane adsorption.
This material was synthesized via a dual-template, three-step hydrothermal–flocculation–steaming synthesis procedure developed by us recently. Briefly, MFI nanoprecursors (NPs) were first prepared by a low-temperature hydrothermal step using TPAOH as template for zeolite structure, and then flocculated using a surfactant that served as the template for the mesopores. The collected NPs are mesoporous silica exhibiting short-range MFI domains when directly calcined. However, the steaming step promoted the crystallization of the NPs and created uniform mesopores. It was found that almost every detail in these procedures affected the properties of the final product. The most important variables, however, were identified as the duration the flocculants were kept in contact with the liquid phase, and the humidity under which the steaming was conducted. By properly adjusting the procedures, the said mesoporous silica, as well as nanocrystals having high external surface area, could be produced at will. 相似文献
Scanning probe microscopy (SPM) is in a period of rapid development. It shows great promise for characterizing coating surfaces. This paper describes modification of an SPM so that it can be used to mar the surfaces of coatings under controlled conditions and to characterize the mars. Mar resistance of coatings is analyzed in terms of a ‘three response, two mechanism model.' The three responses (fracture, elastic, and plastic) can be measured quantitatively using the SPM. Of the three responses, only two (fracture and plastic deformation) are marring mechanisms – elastic deformations recover instantaneously. In some cases mars resulting from plastic deformation may recover slowly with time or with immersion in water; this phenomenon is attributed to viscoelastic creep. Microhardness is also measured with the modified SPM. Some thermoset coatings appear to be substantially harder near their surfaces than in the mass of material, and such materials may respond quite differently to stress applied at different levels near the surface. This finding has important implications for all coating properties that are strongly influenced by the surface. A quantity called ‘micro mar resistance' is defined. It may be useful for comparing different coatings under specified conditions of marring. However, there can be no single quantity that expresses ‘mar resistance' of a coating under all conditions. 相似文献
Bisphenol-A polycarbonate (PC) has been incorporated into epoxy resin cured with 4,4-diaminodiphenyl sulphone (DDS) and 4,4'-diaminodiphenyl methane (DDM). IR spectra reveal that transesterification and transamidation occur between the carbonate group of PC and the hydroxyl group of cured epoxy resin for the DDM-cured system, and that only transesterification occurs for the DDS-cured system. Scanning electron micrographs (SEM) show no evidence of phase separation in these cured systems, which is an indication of full miscibility between the bisphenol-A monomers and PC-oligomers with the copolymer network. The mechanical strength and glass transition temperature (Tg) fluctuate with PC content, whereas the flexural modulus shows a steadily increasing tendency. 相似文献
This article investigates the basic combustion parameters including start of the ignition timing, burn duration, cycle-to-cycle variation, and carbon monoxide (CO), unburned hydrocarbon (UHC), and nitric oxide (NOx) emissions of homogeneous charge compression ignition (HCCI) engines fueled with primary reference fuels (PRFs) and their mixtures. Two primary reference fuels, n-heptane and iso-octane, and their blends with RON25, RON50, RON75, and RON90 were evaluated. The experimental results show that, in the first-stage combustion, the start of ignition retards, the maximum heat release rate decreases, and the pressure rising and the temperature rising during the first-stage combustion decrease with the increase of the research octane number (RON). Furthermore, the cumulative heat release in the first-stage combustion is strongly dependent on the concentration of n-heptane in the mixture. The start of ignition of the second-stage combustion is linear with the start of ignition of the first-stage. The combustion duration of the second-stage combustion decreases with the increase of the equivalence ration and the decrease of the octane number. The cycle-to-cycle variation improved with the decrease of the octane number. 相似文献