Conventional oven drying (COD) and supercritical drying (SCD) methods were applied to the preparation of Mn-substituted hexaaluminate (BaMnA111O19-α) catalysts. The effect of drying methods on phase composition, specific surface area, pore structure, reduction behavior of Mn^3 ions, and combus-tion activity of the samples was investigated. The homogenous mixing of the components in the sol-gel process could be maintained by SCD, and the hexaaluminate phase was almost the only phase of the resulting materials after calcination. H2-TPR revealed that the Mn^3 ions in the sample obtained by SCD were easier to be reduced than that by COD. Moreover, the samples obtained by SCD have higher surface area, narrower pore size distribution, and higher combustion activity than those obtained by COD. 相似文献
Characterizing the physical properties of individual nanostructures is challenging because of the difficulty in manipulating the objects of sizes from nanometers to micrometers. Most nanomeasurements have been carried using scanning probe microscopy. In this article, we demonstrate that transmission electron microscopy can be a powerful tool for quantitative measurements of the mechanical and electrical properties of a single nanostructure. Dual-mode resonance of an oxide nanobelt has been observed, and its bending modulus has been measured. An in situ technique was demonstrated for measuring the work function at the tip of a carbon nanotube. The ballistic quantum conductance of a multiwalled carbon nanotube was observed at room temperature using the setup in TEM. It is concluded that in situ measurement by directly linking structure with property is a future direction of electron microscopy. 相似文献
The alkylation of DNA by antitumor agents such as mechlorethamine hydrochloride (mustargen), thiophosphoramide (TSPA), mitomycin
c (MMC), bleomycin-A5 and dacarbazine (DTIC) can be detected with quartz crystal resonators (QCR). In the course of alkylation, the resonator frequency
change in polyethylene glycol (PEG)-DNA solutions follows the cross-linking of DNA and the cleavage of the sugarphosphate
backbone of DNA. It is at least partly attributed to the viscosity change of the PEG-DNA solution and possibly to some extent
to the change of mass adsorbed on the QCR surface due to cross-linking and cleavage. Experimental results are consistent with
that expected from theory.
Received: 15 April 1996 / Revised: 3 July 1996 / Accepted: 9 July 1996 相似文献
Abstract— 1-Aryl-2-methyl-4,5-dihydropyrrol-3-carboxylic acid ethyl ester (a cyclic enamine) was observed to dehydrogenate to give 1-aryl-2-methyl-pyrrol-3-carboxylic acid ethyl ester upon irradiation in the presence of oxygen and in the presence or absence of meso -tetraphenylporphine (TPP). N -Aryl cyclic amines were shown to be singlet oxygen sensitizers. 相似文献
The thermal reaction of HNCO has been studied in a static cell at temperatures between 873 and 1220 K and a constant pressure of 800 torr under highly diluted conditions. The reaction was measurable above 1000 K by FTIR spectrometry. The products detected include CO, CO2, HCN, NH3, and the unreacted HNCO. In this moderate temperature regime, the rates of product formation and HNCO decay cannot be accounted for by a previously established high-temperature mechanism, assuming HNCO → NH + CO (1) as the initiation process. Instead, a new bimolecular reaction, 2HNCO → CO2 + HNCNH (2), has been invoked to interpret the disappearance of HNCO as well as the formation of various products, most importantly CO2. The concentration profiles of all measured species can be quantitatively modeled, throughout the temperature range analyzed, by varying k2 using a modified mechanism. The kinetically modeled values of k2 can be effectively represented by This result agrees closely with that computed with the conventional transition-state theory using the TST parameters predicted by the BAC-MP4 method: The bimolecular reaction takes place via a stable 4-membered ring intermediate which is isoelectronic with diketene; viz. 相似文献