同步冷却技术在微波辅助有机合成中的应用

同步冷却技术作为微波化学领域的一项新技术,可以使某些有机反应速度加快,产率提高,选择性变好,因此同步冷却条件下的微波辅助有机合成成为研究的热点之一。从具有同步冷却的微波反应装置、同步冷却条件下微波辅助有机合成的反应特点、同步冷却技术在低温微波化学中的应用和该技术在研究"微波的非热效应"中的应用4个方面进行综述,总结并展望了它在微波化学中的发展前景。     

快速热处理对电子辐照直拉硅中氧沉淀的影响

对n型[111]晶向直拉硅样品进行电子辐照,然后分别在不同温度和降温速率下快速热处理(rapid thermal process,RTP),再在1100℃下进行常规一步退火。研究了RTP温度和降温速率对硅样品内氧沉淀的变化及样品表面清洁区形成的影响。结果表明:经过RTP再经高温一步退火后,硅晶体内形成了密度较高的氧化诱生层错以及完整的位错环,样品表面形成了一定宽度的清洁区;清洁区的宽度随RTP温度及降温速率的升高而变窄。当RTP温度达到1280℃时,样品中的层错和位错环明显减少,此时当RTP降温速率增加至150℃/s时,大部分层错消失,样品中出现了大量的点状腐蚀坑。     

微波辐射合成1,3-二苯基-4-甲酰基吡唑

在微波辐射下,以苯肼和苯乙酮为原料,经脱水和Vislmeier环合反应,简便、高效地合成1,3-二苯基-4-甲酰基吡唑,并对微波辐射下的原料配比、反应温度和辐射时间等反应条件进行优化。     

CuFe_2O_4光催化剂在模拟太阳光下对大肠杆菌杀灭作用的研究

采用溶胶-凝胶法制备了纳米CuFe2O4光催化剂,并通过TEM,XRD和UV-visDRS对其进行表征,表明样品是由粒径约为80nm的粒子组成,晶体结构均匀,具有良好的可见光吸收性能。以大肠杆菌为研究对象,考察了光催化剂在模拟太阳光照射下的杀菌性能。结果表明:CuFe2O4光催化剂杀菌性能随着焙烧温度的不同而变化,当焙烧温度为700℃时,杀菌效果最佳,光照60m in后,细菌的存活率仅为5.6%,而在相同条件下使用催化剂避光和不用催化剂光照时细菌存活率分别为94.4%和87.4%,说明该催化剂本身无毒性,是一种在可见光下有优良杀菌性能的光催化剂。     

微波辐射下单质碘催化合成苯甲醛乙二醇缩醛

微波辐射下以单质碘为催化剂无溶剂合成了苯甲醛乙二醇缩醛,试验了微波辐射功率、微波辐射时间、原料配比、催化剂用量对产率的影响,最佳条件为:辐射功率为259W,反应时间为6.0min,苯甲醛与乙二醇的物质的量比为1∶1.8,单质碘用量为2.5%,产率可达86.7%。     

波长和气氛对激光诱导硅表面微结构的影响

为了研究特定气氛下激光辐照对单晶硅表面微结构的影响,采用红外(基频波长1064nm)和紫外(3次谐波波长355nm)YAG纳秒激光脉冲连续辐照方法,分别在SF6、空气、N2和真空环境下对硅表面微结构进行了实验研究。得到红外纳秒激光在SF6和空气中形成的微结构较真空和N2下有更高的纵横比;紫外纳秒激光在SF6和真空中产生的锥形结构比N2和空气中要更为显著,但SF6中形成的微结构上有絮状物的结果。结果表明,激光波长和环境气氛对微结构的形成起着决定性作用,且激光辅助化学刻蚀的效率不同。该结果对深入研究纳秒激光在特定气氛下诱导硅表面微结构是有帮助的。     

CO_2激光辐照对PZT-4陶瓷压电性能的影响

常温常压下,采用CO2激光辐照带有电极的PZT-4陶瓷片,当激光辐照时间分别为2、5和10 s时,在适当的激光功率密度下可使其压电应变常数d33从380 pC/N下降为零。系统地研究了激光功率密度和激光辐照时间对PZT-4陶瓷压电性能影响的规律。XRD、拉曼光谱和退火实验结果表明:CO2激光辐照使d33下降为零的原因是由于激光热效应导致PZT-4陶瓷的电畴排列失序,极化状态消失;而激光辐照未使其物相发生变化。     

Isothermal solid‐state transformation kinetics applied to Pd/Cu alloy membrane fabrication

In this work, time‐resolved, in situ high‐temperature X‐ray diffraction was used to study the solid‐state transformation kinetics of the formation of the fcc Pd/Cu alloy from Pd/Cu bilayers for the purpose of fabricating sulfur‐tolerant Pd/Cu membranes for H₂ separation. Thin layers of Pd and Cu (total ～15 wt % Cu) were deposited on porous stainless steel with the electroless deposition method and annealed in H₂ at 500, 550, and 600°C. The kinetics of the annealing process was successfully described by the Avrami nucleation and growth model, showing that the annealing process was diffusion controlled and one dimensional. The activation energy for the solid‐state transformation was 175 kJ/mol, which was similar to the activation energy of Pd‐Cu bulk interdiffusion. Furthermore, the Avrami model was able to successfully describe the changes in permeance and activation energy observed in Pd/Cu alloy membranes during characterization as they were annealed at high temperatures. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Crystal structure and electrochemical performance of Li3V2(PO4)3 synthesized by optimized microwave solid-state synthesis route

To investigate the crystal structure and electrochemical performance of samples synthesized under different microwave solid-state synthesis condition, a series of Li₃V₂(PO₄)₃ samples has been synthesized at five different temperatures for 3-5 min and at 750 °C for various time. The as-synthesized Li₃V₂(PO₄)₃ samples are characterized and studied by ICP-AES analysis, X-ray diffraction (XRD), Rietveld analysis, scanning and transmission electron microcopy (SEM and TEM). At relatively lower temperature (650 °C) and very short reaction time (3 min), pure phase of Li₃V₂(PO₄)₃ could be synthesized in microwave irradiation field. The crystal structure and Li atomic fractional coordinate present a significant deviation upon the change of microwave irradiation temperature and time. Relatively, the diffusion ability of lithium cations and the electrochemical performance are affected. Under the proper reaction temperature and time, the carbon-free samples MW750C5m and MW850C3m show the best specific discharge capacity 126.4 and 132 mAh g⁻¹ at the voltage range of 3.0-4.3 V, near the reversible cycling of two lithium ions per Li₃V₂(PO₄)₃ formula unit (133 mAh g⁻¹). At the voltage range of 3-4.8 V, the sample MW750C5m presents the best initial specific charge capacity of 197 mAh g⁻¹, equivalent to the reversible cycling of three lithium ions per Li₃V₂(PO₄)₃ formula unit (197 mAh g⁻¹). The initial discharge capacity, the samples MW750C5m and MW850C3m present high specific discharge capacity 183.4 and 175.7 mAh g⁻¹, respectively. The relationship among microwave irradiation condition, crystal structure, lithium atomic fractional coordinates and the electrochemical performance have been discussed in detail.     

Hydrolytic Depolymerization of PET in a Microwave Reactor

Recycling of PET was examined using hydrolytic depolymerization in an alkaline solution under microwave irradiation. The reaction was carried out in a sealed microwave reactor in which the pressure and temperature were controlled and recorded. The main products were the monomers TPA and EG. The effect of reaction temperature, time, amount of PET and alkaline concentration on the degree of PET depolymerization and TPA recovery was investigated. Microwave irradiation was found to reduce the time needed to achieve a specific degradation of PET significantly, with almost complete depolymerization occurring in 30 min at 180 °C and only 46 W of microwave power. Using a phase transfer catalyst (TOMAB) resulted in the same amount of unreacted PET but at significantly lower depolymerization temperatures.