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The formation of non-stoichiometric cubic perovskite solid solutions based on BaZn1/3 Nb2/3 O3 (BZN) was examined along 10 different directions in the BaO–ZnO–Nb2 O5 ternary system. Limited ranges of non-stoichiometry were observed along several pseudo-binaries and the BZN structure can accommodate a variety of different types of defects. Although the deviations from stoichiometry are quite small, typically ∼1 mole%, they induce large changes in the extent and stability of the 1:2 B-site ordering, the sintering and microstructure, and the dielectric loss properties. The highest Q × f s (∼110 000 at 8 GHz) in the system, which coincide with the highest degree of order, were located in two regions along the BZN–Ba5 Nb4 O15 and BZN–BaNb2 O6 lines. The results of this study provide an explanation for the large variations in crystal structure and Q × f s previously reported for BZN and other related systems (e.g., Ba(Zn1/3 Ta2/3 )O3 ), and demonstrate that non-stoichiometric starting compositions provide a route to the highest Q values. 相似文献
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The clay is treated with a reducing agent and an acid so as to obtain a clay containing various metal components with a variable‐valence state. Then, the clay is coprecipitated with natural rubber (NR) latex to prepare a vulcanized NR/clay composite. The degradation process of the NR/clay composite under hot air condition was studied dynamically by using a Fourier transform infrared spectrometer attaching an in situ sample cell and was also investigated using the TGA method. The test result obtained from the infrared spectrometry indicated that under low decomposition temperature, the decomposition products of the test samples mainly are ethylene, low molecular olefinic hydrocarbon, and carbonyl compounds. As the decomposition temperature rises, the low molecular olefinic hydrocarbon content decreases, the olefine with longer chain is formed, and a lot of alkane decomposition products are formed at the same time. When the content of the metal components with a variable‐valence state in clay such as Cu, Mn, Co, and Fe increases, the oxidation products containing the carbonyl group, the olefinic hydrocarbon, and CO2 in the decomposition product of the test sample also increase. The TGA result clearly shows a shoulder peak that appears by the side of the main peak on the DTG curve of NR/clay composite. With the increase in the content of metal components with variable‐valence state in clay, the initial degradation temperature of the test sample (T0), the degradation peak temperature (Tp1), and the final degradation temperature (Tf1) in first‐stage reaction, as well as the degradation peak temperature (Tp2) and the last final degradation temperature (Tf) in second‐stage reaction of all the test samples more or less shift to the direction of low temperature; besides, the activation energy (E) of the reaction of the test samples more or less decreases. This means that the metal components with variable‐valence state promote the oxidative degradation of the clay–rubber masterbatch. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3809–3815, 2006 相似文献
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微波辐射对甲苯磺酸催化合成乙酸环己酯 总被引:15,自引:0,他引:15
以冰醋酸和环己醇为原料 ,环已烷为带水剂 ,对甲苯磺酸作催化剂 ,采用微波辐射技术 ,在常压下直接合成乙酸环己酯。最适宜反应条件为 :n(环己醇 )∶n(乙酸 ) =1 5∶1 0 ,对甲苯磺酸用量 0 2 0 g ,带水剂用量 5mL ,微波功率 5 95W ,辐射时间 15min ,产率达 97%以上 相似文献