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水合醋酸铈直接热分解制备超细氧化铈及其抛光性能 总被引:3,自引:0,他引:3
Ultra fine ceria was prepared by calcining hydrate cerium acetate. The effects of pyrolysis temperature on the particle size, morphology, specific surface area and loose packing density of ceria were investigated, and the removal rate of optical glasses polishing by ceria was determined. The results show that with the increase of pyrolysis temperature, the loose deposit density and crystallinity increases and the specific surface area decreases, however, the particle size decreases firstly and then increases, the minimum medium particle size D50 is 0.47 μm at pyrolysis temperature of 1 000 ℃. The SEM images of ceria prepared by the decomposition at 800 ℃ or at 1 100 ℃ show porous powders or quasi-sphere small particles with loosely agglomeration, respectively. It was found that the removal rate varied with pyrolysis temperature in preparation of ceria and the property of glass polished. The removal rate for three kinds of glasses was in the order of ZF7> F1> K9, and the maximum value appeared at around 1 000 ℃ for ZF7 and F1, and at around 1 100 ℃ for K9. 相似文献
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Park等曾报道全氟丙烯与三氯化铝在50-60℃下反应,分离出一系列取代反应产物,并阐明其分子中氟氯基团与三氯化铝反应时的稳定性次序。Haszeldine等做了2,3-二溴全氟丙烯在三溴化铝存在下的重排反应,并提出了相应的重排机理。本工作以CFCl_2CF_2CF=CF_2(1)为原料与三氯化铝反应,通过试验找到在极温和反应条件下(三氯化铝与1的摩尔比为0.5,10℃下反应3h)获得几乎定量的重排产物CF_3CF_2CF=CCl_2(3),这一反应可用在三氯化铝催化下,1分子内烯丙位氟原子在分子内完成两次1,3-转移,从而使双键发生连续的烯丙型转移来解释. 相似文献
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在数学发现活动中,类比推理在提出猜想、确定研究方向、提供解题思路等方面发挥着重大作用.著名数学家、教育家波利亚说过:"在尝试去解一道题时,如果我们能成功地想到一道更为简单的类比题目,那么可以说我们是幸运的." 相似文献
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In order to investigate synthetic route of polyperfluorotriazine elastomer, 2-trifluoromethyl4,6-bis(4′-iodo-2′-oxahexafluorobutyl)-1,3,5-triazine (1), a novel triazine monomer, was synthesized from 5-iodo-3-oxa-octafluoropentanesulfonyl fluoride (2) in eight-steps. 2 was reduced by potassium sulfite to the sulfinate (3), which was treated with hydriodic acid to yield 5-iodo-3oxa-hexafluoropentanoic acid (4). Compound 4 was transformed to 5-iodo-3-oxa-hexafluoropentanenitrile (7) through the corresponding ester 5 and amide 6. The desired product 1 was prepared by acylation-cyclodehydration of the imidoylamidine 9, obtained by condensation of the nitrile 7 with the amidine 8.The various methods for the esterification of perfluorocarboxylic acid were studied and a possible mechanism for the transformation of perfluorosulfinate to the corresponding perfluorocarboxylic acid by hydriodic acid was proposed.Crude 1 contained compounds 6, 11, 13, as impurities which were removed by low temperature crystallization followed by filtration through a short alumina column. The monomer 1 was polymerized by UV-irradiation in the presence of Hg with or without solvent. Polyperfluorooxaalkyl triazine 17 thus obtained showed good thermal stability. In the main chain of the polymer there was no weak unit of the uncyclized ring. Polymer 17 had an average molecular weight of ca. 1.33—2.0×10~4 (D. P.=27—42) and the temperature of 10% weight loss in nitrogen was 340℃. 相似文献
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We discuss a new concept in lightning location system (LLS). Specitically,it is anoptimum method of lightning signal strength and a parameterization method of the site gaincurve estimation in LLS. Site gain correction curves for all DFs for 1989 were found byusing the data observed in an LLS of three direction finders (DFs) in Beijing region. Theresult shows that the curves, as a function of measured bearing, only include the one- andtwo-cycle sinusoidal components. It also indicates that the larger the site errors which DFhas, the larger the amplitude of the site gain curve. In this LLS, the ranges of site gainare 0.9--1.2, 0.85--1.05, 0.9--1.1 for DF1, DF2 and DF3 respectively. For discussion, we suggested a model for site gains due to dipole radiation. This modelcan be used to reasonably explain the characteristics of structure of site gain curves. 相似文献