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81.
J.A. ColladoM.A.G. Aranda A. CabezaP. Olivera-Pastor S. Bruque 《Journal of solid state chemistry》2002,167(1):80-85
The La2W2−xMoxO9 series has been synthesized by the ceramic method. An alternative synthesis using microwave radiation is also reported. La2W2O9 has two polymorphs and the low-temperature phase (α) transforms to the high-temperature form (β) at 1077°C. The influence of the W/Mo substitution in this phase transition has been investigated by DTA. The β structure for x≥0.7 compositions can be prepared as single phase at any cooling rate. The β phase for 0.3≤x≤0.7 compounds can be prepared as single phase by quenching, whereas a mixture of α and β phases is obtained by slow cooling. The W/Mo ratio in both coexisting phases is different with the β-phase having a higher Mo content. The x=0.1 and 0.2 compounds have been prepared as mixtures of phases. The room temperature structure of β-La2W1.7Mo0.3O9 has been analyzed by the Rietveld method in P213 space group. The final R-factors were RWP=9.0% and RF=5.6% with a structure similar to that of β-La2Mo2O9. Finally, the thermal expansion of both types of structures has been determined from a thermodiffractometric study. The thermal expansion coefficients were 2.9×10−6 and 9.7×10−6°C−1 for α-La2W2O9 and β-La2W1.2Mo0.8O9, respectively. 相似文献
82.
TheBeckInannrearrangement,theacid-mediatedisomerizationofoximestoamides,wasfirstdiscoveredinl886l.Asoneoftheoldestandmostfamiliartransformationsinorganicchemistry,ithasbeenwidelystudiedandagreatvarietyofmethodstoconductthistfansformationhavebeenreported'.However,mostofthesemethodswerecarriedoutbyusingalargeamountofsolventswithlongreactiontime.Whatismore,thepriorpreparationofthecorrespondingketoximesisusuallyrequired,whichmakestheseprocessesinconvenientandlessattractive.Bytakingadvantageofboth… 相似文献
83.
Shyh-Horng Chiou 《中国化学会会志》1989,36(5):435-442
A rapid peptide-bond hydrolysis by means of microwave irradiation is introduced for the facile preparation of protein hydrolysates used for amino acid analysis. The optimal hydrolysis condition has been determined using several enzymes with known amino acid compositions. The effects of hydrolysis time on the recovery of various labile and hydrophobic amino acids are also exemplified in the microwave heating of standard amino acids. The method has been applied to the complete amino acid analysis with a single nonvolatile solvent of methanesulfonic acid with good recovery of tryptophan and half-cystine. It provides a radical expedition of protein and peptide hydrolysis via commercial microwave ovens and specially-designed Teflon-Pyrex tubes, circumventing the tedious procedures using vacuum-sealed pyrex lubes heating at 110°C for more than 24 h. This novel type of microwave chemistry associated with rapid peptide-bond cleavage is of great potential in the automation of the complete process of amino acid analysis starting from the preparation of protein hydrolysates. 相似文献
84.
Dolores Bellido-Milla Anabel Oñate-Jaén Jose M. Palacios-Santander Dolores Palacios-Tejero María P. Hernández-Artiga 《Mikrochimica acta》2004,144(1-3):183-190
Many standard and official sample digestion procedures for trace metal determination are carried out in open vessels on hot plates. A new procedure for the determination of trace metals by flame atomic absorption spectrometry or inductively coupled plasmaatomic emission spectrometry in beer samples was developed to be performed in closed reactors assisted by microwaves. The results are compared with the ones obtained by other procedures by means of the analysis of the variance. The differences between the procedures are attributed to residual organic matter. Voltammetry, absorption molecular spectrophotometry and high pressure liquid chromatography with a photodiode array detector are used to study the nature of these residues. Nitrobenzoic acids, phenolic acids and other organic compounds are often present after digestion. The results obtained are related to the precision in metal determination by atomic spectrometry. The need for elaboration of certified reference materials for trace metals in beer is suggested. 相似文献
85.
微波萃取花生壳天然黄色素及其稳定性研究 总被引:19,自引:0,他引:19
对福建产花生壳进行了微波萃取天然黄色素及其稳定性的研究 .研究表明微波萃取的工艺条件是 :以pH =3,体积分数 70 %的乙醇水溶液作提取剂 ,原料与提取剂配比为 1g∶5mL ,微波辐射功率为 12 0W ,辐射时间2 4 0s.对该色素稳定性研究结果表明 ,该色素为水溶性色素 ,属黄酮类色素 ,适用pH值范围比较宽 ,尤其碱性状态效果最佳 ,对光、热稳定性好 ,大多数食品添加剂对色素稳定性影响不大 ,对氧化剂H2 O2 的耐受能力较差 ,对还原剂Na2 SO3 的耐受能力强 相似文献
86.
Xue Yuan HU Xue Sen FAN Xin Ying ZHANG Gui Rong QU Yan Zhen LI School of Chemical Environmental Sciences Henan Key Laboratory for Environmental Pollution Control Henan Normal University Xinxiang Chongqing University of Medical Sciences Chongqing 《中国化学快报》2005,(7)
Construction of tetrahydropyran rings has attracted a great deal of interests in organic synthesis in recent years1, since tetrahydropyran moiety constitutes a structural unit in a number of natural products2. In addition, tetrahydropyran derivatives possess wide range of biological activities and pharmacological properties, such as anticancer activity3 and antihypersensitivity4. Many methods for the preparation of such compounds have already been developed5. Among them, condensation of α, β… 相似文献
87.
88.
以LiOH·H2O,Al2O3和Co3O4为原料,微波加热合成Li离子电池正极材料LiAlxCo(1-x)O2.通过XRD测试表征了不同Al加入量时合成产物的晶体结构,确定当x≤0.4时,产物为单一相层状结构.计算了不同x时LiAlxCo(1-x)O2的晶胞参数,随着x的增大,a值减小,c值增大.对合成LiAlxCo(1-x)O2样品进行DSC—TGA测试,结果表明,当x不同时,合成样品的热稳定性不同.SEM测试表明,合成晶体粒度较均匀,粒径在5μm左右.电化学测试表明,LiAl0.2Co0.8O2的电化学性能最好,首次循环放电容量为127mAh/g,多次循环容量损失率小于LiCoO2. 相似文献
89.
90.
A. Fendler M. P. Villanueva E. Gimenez J. M. Lagarón 《Cellulose (London, England)》2007,14(5):427-438
The present work presents and discusses the interrelation between composition, morphology, thermal history, mechanical and
barrier properties to oxygen and limonene of composites of HDPE/MA-PE/cellulose fibers of significant interest in, among others,
food packaging applications. From the overall results, it was observed that increasing the loading of purified alpha-cellulose
fibers in the polyethylene matrix beyond 10 wt.% led to a decrease in the permeability coefficient of d-limonene, effect which was found to be primarily related to a decrease in the overall solubility of this strongly plasticizing
aroma component. On the other hand, the oxygen permeability was found to decrease to a significant extend with increasing
fiber content beyond 5 wt.%, but this effect was more strongly ascribed to a significant decrease in the diffusion coefficient.
Therefore, the fibers are thought to generate a more tortuous path for the non-interacting gas molecules to travel across
the composites thickness, even when tested at high relative humidity conditions. Optimum fiber loading levels in terms of
overall property balance were found to be around 20 wt.%. 相似文献