排序方式: 共有29条查询结果,搜索用时 31 毫秒
1.
2.
3.
The aim of this study is to shed more light on the formation of mullite and the kinetics of mullitization from sol-gel synthesized precursors. Tetraethylorthosilicate (TEOS) and aluminum nitrate nonahydrate (ANN) were used, as a source of silica and alumina, respectively, for the synthesis of homogenous mullite precursor powder. The mullitization process was characterized by thermogravimetry (TG), differential thermal analysis (DTA), thermodilatometric analysis (TDA), and x-ray powder diffraction (XRD) techniques. It was found that mullite started to crystalize at temperatures of 1050, 1200, and 1241 °C as determined by XRD, DTA, and TDA, respectively?. Mullite crystallization kinetics was thoroughly investigated under isothermal and non-isothermal conditions using DTA. The activation energy for mullite formation was calculated, for different crystallization fractions, following the Freidman, Kissinger, Boswell, and Ozawa methods. The average values were found to be 1282.92, 1324.30, 1336.93, and 1283.09 kJ/mol, respectively. The kinetic parameters and the crystallization mechanism were determined and the results were compared with those available in the literature. The Sestak Berggren SB(m,n) model was found to be the most suitable for the determination of mullite crystallization mechanism. The calculated average values of the Gibbs free energy (ΔG#), enthalpy (ΔH#), and entropy (ΔS#) for mullite formation, at different heating rates, were 433.98 kJ/mol, 1294.20 kJ/mol, and 566.23 J/mol.K, respectively. 相似文献
4.
We analyze in detail an almost optimal algorithm for generating an exponentially distributed variate. The algorithm is due to Knuth and Yao and relies on a method which goes back to J. von Neumann. It is shown here that it can generate k bits of an exponentially distributed variate using an average of about k + 5.67974692 coin flippings. This solves a problem left open by Knuth and Yao. 相似文献
5.
Reference electrodes for room temperature ionic liquid (RTIL) applications were constructed that have a known and reproducible potential versus the ferrocene/ferrocenium couple. They are based on reference electrodes of the first kind, Ag/Ag+ couple type, or of the second kind, based on Ag/AgCl in M+Cl?. The former uses AgNO3 salt and the latter tetrabutylammonium chloride, Bu4NCl, dissolved in acetonitrile which are then introduced to the ionic liquid of choice for a final concentration of 0.1 M. The reference electrodes can be easily and reproducibly constructed. An ionic contact of these reference systems with the test electrolyte was made using an asbestos fiber liquid junction. The internal compartment of the reference system was filled with the same ionic liquid as used for the electrochemical experiment. The performance of these reference electrodes was tested in selected ionic liquids using the ferrocene/ferrocenium redox couple. The stability, reproducibility, and temperature behavior of the two reference systems have been characterized in the following ionic liquids: 1‐butyl‐3‐methylimidazolium tetrafluoroborate (BMIBF4), 1‐butyl‐3‐methylimidazolium bis(trifluoromethanesulfonyl)imide (BMI(CF3SO2)2N), and 1‐butyl‐3‐methylimidazolium hexafluorophosphate (BMIPF6). It has been found that the formal potentials of the examined reference systems are stable over several days. There is a linear relationship for the temperature studied in the range from 25 to 60 °C. 相似文献
6.
Kattakgoundar Govindaraj Sudha Saheb Ali Gopalu Karunakaran Mariyappan Kowsalya Evgeny Kolesnikov Mohan Prasanna Rajeshkumar 《应用有机金属化学》2020,34(4):e5511
The tunable ZnO nanorods (NRs) are produced due to the phytochemicals present in Cycas pschannae leaves which act as reducing and stabilizing agents. The confirmations of the ZnO NRs were validated using different characterization techniques: X-ray diffraction, Fourier transform infrared spectroscopy, Brunauer, Emmett and Teller (BET), scanning electron microscopy–Energy Dispersive X-Ray Analysis (EDX), UV–visible spectroscopy, Raman spectroscopy, and transmission electron microscopy. The ZnO NRs show unique surface area and low particle size. Photocatalytic activity was measured and found to be 50.75% at low concentrations and 78.33% at high concentrations. The antioxidant activity of the ZnO NRs also showed promising results for their use in free radical scavenging. In vitro toxicity studies using zebrafish embryos was performed to evaluate the toxic nature of it and the obtained result confirmed its non-toxic nature. In addition, ZnO anticancer potential was verified using the A549 lung cancer cell line. Cytotoxic assessments of ZnO NRs were performed via 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT), 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT), and neutral red uptake assays to examine the cell death cycle on the A549 lung cancer cell. Dose-dependent apoptosis and necrosis were confirmed by Lactate dehydrogenase (LDH) assay. It was also confirmed that ZnO NRs induce Reactive oxygen species (ROS) and apoptosis inside cancer (A549) cells via different intrinsic gene expression. Thus, based on this research it is evident that an effective ecofriendly, nontoxic potential anticancer drug can be synthesized using C. pschannae leaf extract. 相似文献
7.
Molecular Diversity - In this research, a new multilayered magnetized bio-nanocomposite has been prepared. At first, the amino acid-based ionic liquid was obtained from L-histidine and... 相似文献
8.
P.Z.?Saheb S.?Asokan Email author K.A.?Gowda 《Applied Physics A: Materials Science & Processing》2003,77(5):665-668
Samples of bulk Ge20Te80-xPbx(2x8) glasses have been prepared by melt quenching and their electrical switching behavior has been investigated as a function of lead content and sample thickness. The samples are found to exhibit a threshold type of switching. The switching voltages are found to decrease with increase in lead content and they show an anomaly at the composition x=5 and a minimum at the composition x=7.5 respectively. The samples are found to withstand about 28 switching cycles, before latching permanently to the ON state. PACS 61.43.Dq; 61.43.Fs; 72.20.Ht; 72.80.Ng; 73.61.Jc;
84.32.Dd; 85.30.Fg 相似文献
9.
This work explores the application of digitalimage-processing techniques to the measurement of large plastic strains. Two
sample problems have been selected, namely the uniform tensile deformation of aluminum-sheet metal strips and the post-necking
deformation of copper circular rods. Images of these gridded metallic test pleces were captured, digitized and analyzed in
a fully computerized way to evaluate strain distributions, anisotropic parameters and plastic stress-strain flow curves. For
post-necked test pieces, Bridgman stress correction has been easily applied by defining the neck profile contour from the
automated processing of digitized images. Results compare satisfactorily with those based on displacements measured by conventional
microscopy. The presented technique, with added improvements, can consititute a viable one for accurate and fully computerized
measurement of large deformations. 相似文献
10.
Highly Ordered Mesoporous Tungsten Oxides with a Large Pore Size and Crystalline Framework for H2S Sensing
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Yuhui Li Wei Luo Nan Qin Dr. Junping Dong Jing Wei Wei Li Shanshan Feng Junchen Chen Prof. Dr. Jiaqiang Xu Dr. Ahmed A. Elzatahry Dr. Mahir H. Es‐Saheb Prof. Dr. Yonghui Deng Prof. Dr. Dongyuan Zhao 《Angewandte Chemie (International ed. in English)》2014,53(34):9035-9040
An ordered mesoporous WO3 material with a highly crystalline framework was synthesized by using amphiphilic poly(ethylene oxide)‐b‐polystyrene (PEO‐b‐PS) diblock copolymers as a structure‐directing agent through a solvent‐evaporation‐induced self‐assembly method combined with a simple template‐carbonization strategy. The obtained mesoporous WO3 materials have a large uniform mesopore size (ca. 10.9 nm) and a high surface area (ca. 121 m2 g?1). The mesoporous WO3‐based H2S gas sensor shows an excellent performance for H2S sensing at low concentration (0.25 ppm) with fast response (2 s) and recovery (38 s). The high mesoporosity and continuous crystalline framework are responsible for the excellent performance in H2S sensing. 相似文献