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181.
催化动力学光度法测定痕量锰(Ⅱ) 总被引:11,自引:0,他引:11
研究了在Na2HPO4-NaOH介质中,Mn(Ⅱ)催化高碘酸钾氧化镁试剂1[4-(对硝基苯偶氮)间苯二酚]的反应及其动力学条件,建立了一种高灵敏、高选择性测定痕量Mn(Ⅱ)的新方法。可测0.01-2.5μg/25mL范围的锰(Ⅱ),方法的检测限为6.43×10^-11gm/mL。 相似文献
182.
183.
纳米尺寸团簇NinZrn(n=3~5)的几何结构与成键规律研究 总被引:3,自引:0,他引:3
根据化学键理论与拓扑原理,设计了团簇NinZrn(n=3-5)的可能几何构型,并用从头算方法进行构型优化,结果表明,由NiZr组成的团簇原子间的Zr-Zr和Zr-Ni键明显较强,而Ni-Ni的成键较弱,并发与NinZrn(n=3-5)团簇电子性质与有机烯烃分子等瓣相似,原子之间的成键按照强弱相间的规则分布。 相似文献
184.
Ti基IrO2+Ta2O5阳极在H2SO4溶液中的电解时效行为 总被引:5,自引:0,他引:5
研究了450 ℃制备所得Ti/70%IrO2 30%Ta2O5(摩尔分数)高寿命阳极在H2SO4溶液电解过程中电极的物理、化学及电化学性能的时效行为.结果发现,整个电解过程可分为“活化”、“稳定”及“失效”三个阶段.在“活化”及“稳定”区内主要发生电极表面活性氧化物的溶解,涂层中IrO2金红石相的(110)、(101)晶面择优取向随电解时间延长而减弱,而(002)晶面择优增强.但是在“失效区”内,各晶面的择优程度却不随电解时间的变化而变化,这表明在“失效区”内氧化物的损失机制发生了变化.电化学阻抗谱测试表明,电极的析氧电化学反应电阻随电解时间的延长发生缓慢而连续的上升,而整个电极的物理阻抗在“失效区”内却发生突升现象.X射线衍射分析(XRD)表明,随电解时间的延长TiO2金红石相的衍射强度增大,达“失效区”时衍射强度发生突升.根据实验现象特别是“失效区”内阳极的时效行为提出高寿命Ti基氧化物涂层阳极的失效机制. 相似文献
185.
186.
Photocycloadditionof(4-methyl-7-coumarinyl)OxyaceticAcidPropanediolDiesterandX-rayCrystalStructureofProductDuDa-Ming;WangYong... 相似文献
187.
Preparation of poly(propylene carbonate)/organo-vermiculite nanocomposites via direct melt intercalation 总被引:2,自引:0,他引:2
Intercalated nanocomposites comprised of poly(propylene carbonate) (PPC) and organo-vermiculite (OVMT) was first prepared via direct melt compounding of the alkali-vermiculite intercalated host with PPC in a twin rotary mixer. The dispersion and morphologies of OVMT within PPC were investigated by X-ray diffraction and transmission electron microscopic techniques. The results revealed the formation of intercalated-exfoliated vermiculite sheets in the PPC matrix. Because of the thermally sensitive nature of PPC, thermal degradation occurred during the melt compounding. The degradation led to a deterioration of the mechanical properties of the nanocomposites. Tensile test showed that the yield strength and modulus of the nanocomposites decrease with increasing vermiculite content. The degradation mechanism was discussed according to the results of GPC and TGA measurements. 相似文献
188.
Yong Hong Wang Ting Fang Tian Xing Qin Liu Guang Yao Meng 《Journal of membrane science》2006,280(1-2):261-269
The high-quality tubular titania MF membranes are successfully prepared by dip-coating techniques and systematically investigated with regard to their corrosive resistances. The experiments show that dispersants PAA and anatase powder were preferably employed to prepare desired suspensions with solid loading 10–15 wt.% and that suspensions properties significantly affect the final membranes quality. The titania MF membranes with pure water permeability 742.42 l m−2 h−1 bar−1 and 0.1 μm pore diameter have been obtained using the prepared suspensions. The corrosion resistance of titania membranes exhibits that the anatase layers are more stable than the alumina supports in boiling corrosive medium and that the poor quality titania MF membranes become more deteriorated due to its top layer pore blockages and fouling layer formation, which provides a wide range of practical application fields in very hash environments with reliable data supports. 相似文献
189.
Understanding effect of wall structure on the hydrothermal stability of mesostructured silica SBA-15
Zhang F Yan Y Yang H Meng Y Yu C Tu B Zhao D 《The journal of physical chemistry. B》2005,109(18):8723-8732
Mesostructured silica SBA-15 materials with different structural parameters, such as pore size, pore volume, and wall thickness, etc., were prepared by varying the postsynthesis hydrothermal treatment temperature and adding inorganic salts. The hydrothermal stabilities of these materials in steam (100% water vapor) were systematically investigated using a variety of techniques including powder X-ray diffraction, transmission electron microscopy, nitrogen sorption, and (29)Si solid-state NMR. The effect of the pore size, microporosity or mesoporosity, and wall thickness on the stability was discussed. The results show that all of the SBA-15 materials have a good hydrothermal stability under steam of 600 degrees C for at least 24 h. N(2) sorption measurements show that the Brumauer-Emmett-Teller surface area of SBA-15 materials is decreased by about 62% after treatment under steam at 600 degrees C for 24 h. The materials with thicker walls and more micropores show relatively better hydrothermal stability in steam of 600 degrees C. Interestingly, we found that the microporosity of the mesostructured silica SBA-15 is a very important factor for the hydrothermal stability. To the materials with more micropores, the recombination of Si-O-Si bonds during the high-temperature steam treatment may not cause direct destruction to the wall structure. As a result, SBA-15 materials with more micropores show better stability in pure steam of 600 degrees C. Nevertheless, these materials are easily destroyed in steam of 800 degrees C for 6 h. Two methods to effectively improve the hydrothermal stability are introduced here: one is a high-temperature treatment, and another is a carbon-propping thermal treatment. Thermal treatment at 900 degrees C can enhance the polymerization degree of Si-O-Si bonds and effectively improve the hydrothermal stability of these SBA-15 materials in 800 degrees C steam for 12 h. But, this approach will cause very serious shrinkage of the mesopores, resulting in smaller pore diameter and low surface area. A carbon-propping thermal treating method was employed to enhance the polymerization of Si-O-Si bonds and minimize the serious shrinkage of mesopores at the same time. It was demonstrated to be an effective method that can greatly improve the hydrothermal stability of SBA-15 materials in 800 degrees C steam for 12 h. Furthermore, the SBA-15 materials obtained by using the carbon-propping method possess larger pores and higher surface area after the steam treatment at 800 degrees C compared to the materials from the direct thermal treatment method after the steam treatment. 相似文献
190.
The chemical reactions and kinetics of the catalytic coupling reaction of carbon monoxide to diethyl oxalate were studied in the presence of hydrogen over a supported palladium catalyst in the gaseous phase at the typical coupling reaction conditions. The experiments were performed in a continuous flow fixed-bed reactor. The results indicated that hydrogen only reacts with ethyl nitrite to form ethanol, and kinetic studies revealed that the rate-determining step is the surface reaction of adsorbed hydrogen and the ethoxy radical (EtO-). A kinetic model is proposed and a comparison of the observed and calculated conversions showed that the rate expressions are of rather high confidence. 相似文献