共查询到19条相似文献,搜索用时 468 毫秒
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CuX/bpy催化体系中甲基丙烯酸甲酯的原子转移自由基聚合 总被引:14,自引:2,他引:12
讨论了以α-溴代丙酸乙酯(EPN-Br)为引发剂、卤化亚铜(CuX)/联二吡啶(bpy)为催化剂,80℃下,甲基丙烯酸甲酯(MMA)地不同溶剂中的原子转移自由基聚合(ATRP)反应。通过对催化剂CuBr或CuCl及几种溶剂的考察,发现在80℃下EPN-Br/CuBr/bpy能有效控制丙烯酸甲酯(MA)的本体ATRP反应,但并不能很好地控制MMA在EAc中的聚合反应为一可控聚合过程,引发效率为0.8 相似文献
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铜在HOPG上电沉积过程的现场ECSTM研究 总被引:3,自引:1,他引:3
用自制的电化学扫描隧道显微镜(ECSTM)现场研究Cu在HOPG上的电沉积过程.结果表明Cu在HOPG上的电沉积为三维成核的过程.当电位较低或Cu2+离子浓度较低时,铜在本体金属生长主要沿着台阶方向.过电位较高时,铜的成核数目增加,沉积层的晶粒有所细化.同时,非现场ECSTM比较研究表明,STM针尖对针尖局部区域的电沉积起屏蔽作用,针尖所在区域Cu的沉积速度比其它区域明显减小 相似文献
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Cu—Nd(Ce,La)—Al合金及Raney Cu—Nd(Ce,La)催化剂的XRD研究 总被引:1,自引:0,他引:1
采用XRD表征手段对不同稀土元素不同组成的Cu-Al-M(M=Nd,Ce和La)合金及其碱抽提产物RaneyCu-M催化剂的体相结构进行了表征,发现所有Cu-Al-M合金均形成有二元CuAl2和三元CuMAl8的两种晶相,随着稀土元素含量的增中,三元Cu,MAl8晶相逐渐增多。而且其中的Al难于CuAl2中的Al的抽提,RaneyCu-M催化剂中只存在金属铜的晶相,未形成Cu-M晶相,而一随着Al 相似文献
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Eu2+在多相体系中的发光 总被引:3,自引:1,他引:2
研究了基质结构与离子半径的形成关系和Eu2+在同时形成的多相体系中的发光现象.在MMgAl10O17体系中,当M离子半径小于0.10nm时,体系形成多相共存.首次观察到在磁铅矿、尖晶石和α-Al2O3三相同时共存体系中,Eu2+优先占据离子半径和电荷与之匹配的磁铅矿中的Ca2+离子格位,不进入尖晶石和α-Al2O3晶相中的Mg2+、Al3+离子格位,仅产生Eu2+的d→f跃迁宽带发射,且观察不到Eu3+的特征光谱;在尖晶石和α-Al2O3两相同时共存体系中,Eu2+可进入尖晶石和α-Al2O3晶相中的Mg2+、Al3+离子格位,分别产生Eu2+的d→f和f→f跃迁发射,同时还观察到相当强的Eu3+的特征光谱;在α-Al2O3单一相中,Eu2+产生f→f跃迁发射,并观察到明显的Eu3+的特征光谱,在α-Al2O3与γ-Al2O3同时存在的混合相中,Eu2+的f→f跃迁发射消失,产生新的d→f跃迁宽带发射 相似文献
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采用分子动力学模拟方法对液态NiAl凝固过程进行了研究,考察了不同冷却速度下液态NiAl结构变化特点,原子间相互作用势采用F-S多体势,结构分析采用键取向序和对分析技术.计算结果表明,冷却速度对液态NiAl结构转变有重要影响,在不同的冷却速度下, NiAl凝固过程出现了明显不同,冷速为4×1013和4×1012 K/s时, NiAl快速凝固为无序的非晶体结构;而在较慢的8×1011 K/s冷速下, NiAl凝固为晶态结构.给出了不同冷却速度下液态NiAl结构转变的微观信息. 相似文献
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耐蚀合金Au3 Cu高温冷却过程中能量及结构转变的分子动力学模拟 总被引:1,自引:0,他引:1
张长桥 《化学物理学报(中文版)》2001,14(6)
用分子动力学模拟方法对液态Au3Cu冷却过程进行了研究,考察了不同冷却速度下Au3Cu结构变化特点,原子间相互作用势采用F-S多体势,结构分析采用键取向序和对分析技术.计算结果表明,冷却速度对液态Au3Cu能量及结构转变有重要影响,给出了不同冷却速度下液态Au3Cu结构转变的微观信息. 相似文献
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用水热同晶置换法合成了杂原子磷酸铝分子筛Me-VPI-5(Me=Mg,Ti,Sn,Si).通过水相离子交换法掺杂稀土离子,考察了高温和高压下的相变行为.讨论了相变过程对稀土离子光谱的影响.随着温度升高,Eu(Ⅲ)Mg-VPI-5先转变为Eu(Ⅲ)-AlPO4-8,然后又转变成致密的磷石英相.压力对Eu(Ⅲ)光谱结构具有显著影响.随着压力增加,Eu(Ⅲ)光谱结构发生规律性变化. 相似文献
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金属Cu熔化结晶过程的分子动力学模拟 总被引:3,自引:0,他引:3
采用常温、常压分子动力学模拟技术,研究了在周期性边界条件下,由864个Cu原子构成的模型系统的熔化、结晶过程。原子间相互作用势采用EAM势。模拟结果表明:在连续升温过程中,金属Cu在1520 K熔化;以不同的冷速进行冷却,在较慢冷却条件下,液态Cu在1010 K结晶;当冷速较快时,液态Cu形成非晶态。分析了升降温过程中熔体偶分布函数、原子体积、能量、MSD随温度的变化特征。 相似文献
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采用F-S多体势对液态合金Al3Ni和Ni3Al在不同冷却速度下的微观结构及其转变机制进行了分子动力学模拟,得到了不同冷速下各温度的双体分布函数;采用HA键型指数法对其结构进行了分析,结果表明: Al3Ni在两种冷速下均以非晶的形式出现,只是慢冷时体系的有序度略有升高;而Ni3Al的结构及能量转变受冷速影响较大,快冷时形成非晶,而慢冷时出现明显结晶;同样冷速下Al含量较少的Ni3Al体系的有序度高,更易形成晶体,晶体的形成过程中有能量突变. 相似文献
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Wei Yunhe Zhang Changqiao Ma Xiaolong Zhang Guoyu Hou Qi Wang Hongchen Sun Yuansheng 《化学物理学报(中文版)》2004,17(4):443-448
During the hot-dip process of Cu on the surface of the steel,it involves the solidification from liquid to coating. The cooling rate has great influence on the microstructure and the performance. By means of constanttemperature,constant-pressure molecular dynamics simulation technique,the solidification process of the liquid model system made of 500 Cu particles has been studied with the period boundary condition. With the pairs analysis technology and the bond orientational order method,the difference of the structure and energy of the liquid Cu model system between different cooling velocities has been compared. The significant information of microcosmic structural transformation in the solidification process of liquid Cu system has been obtained. The calculation results show that the Finnis-Sinclair(FS)potential works very well in the solidification process of Cu. Cooling slowly the crystal copper layer can be obtained. Cooling quickly the amorphous copper layer can be obtained. 相似文献
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用分子动力学方法和EAM模型势对液态金属Ni原子系统在不同冷却速率下凝固过程中微观结构的演变进行了模拟研究.结果表明, 冷却速率对微结构演变有决定性影响, 当冷速为1.0×1014和 4.0×1013 K•s-1时, 系统将形成以1551、1541和1431三种键型为主的非晶态结构. 当冷速为2.0×1013和 1.0×1012 K•s-1时, 系统将形成不同的晶态结构;前者形成以1421、1422二种键型为主的 fcc 与hcp结构共存的晶态结构;后者形成以1421键型为主的fcc 结构占绝对优势的晶态结构, 其结晶起始温度Tc分别为1073 K和1173 K.同时发现, 原子的平均配位数(最近邻数)对温度和冷速的变化相当敏感, 且其突变点正好与结晶转变温度Tc相对应, 这将为液态金属结晶转变过程的研究提供一条新途径. 相似文献
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L. M. Ramenskaya E. P. Grishina N. O. Kudryakova 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2018,92(1):24-28
Thermochemical properties of the 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ionic liquid [EMim]NTf2 containing moisture absorbed from the atmosphere (0.242 wt %) are investigated. The phase behavior and thermal stability relative to salt dried in vacuum are studied by means of thermogravimetry and differential scanning calorimetry at different heating and cooling rates. The glass transition, crystallization, and melting temperatures, the enthalpies of phase transitions, and the changes in heat capacity during the formation of glass are determined. It is established that the absorbed water crystallizes at a temperature of around ?40.6°C and has virtually no effect on the thermal stability and phase behavior of the salt. Rapid cooling results in the ionic liquid transitioning into the glass state at ?91.7 °C and the formation of three mesophases with different melting temperatures; one crystalline modification that melts at a temperature of ?19.3°C forms upon slow cooling. 相似文献
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Silva MA Rino JP Monteil A Ribeiro SJ Messaddeq Y 《The Journal of chemical physics》2004,121(15):7413-7420
The vitrification and devitrification features of lead fluoride are investigated by means of molecular dynamic simulations. The influence of heating rate on the devitrification temperature as well as the dependence of the glass properties on its thermal history, i.e., the cooling rate employed, is identified. As expected, different glasses are obtained when the cooling rates differ. Diffusion coefficient analysis during heating of glass and crystal, indicates that the presence of defects on the glassy matrix favors the transition processes from the ionic to a superionic state, with high mobility of fluorine atoms, responsible for the high anionic conduction of lead fluoride. Nonisothermal and isothermal devitrification processes are simulated in glasses obtained at different cooling rates and structural organizations occurring during the heat treatments are clearly observed. When a fast cooling rate is employed during the glass formation, the devitrification of a single crystal (limited by the cell dimensions) is observed, while the glass obtained with slower cooling rate, allowing relaxations and organization of various regions on the glass bulk during the cooling process, devitrifies in more than one crystalline plane. 相似文献
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Van den Brande J. Weuts Ilse Verreck G. Peeters J. Brewster M. Van den Mooter G. 《Journal of Thermal Analysis and Calorimetry》2004,77(2):523-530
Thermal analysis was performed on the anti-HIV agent loviride in order to test its suitability to be processed using hot-melt
extrusion. Temperature characteristic parameters of crystallization were determined to quantify the stability of amorphous
loviride. The present study has shown that cooling and heating loviride at different rates influenced its thermal stability.
At high cooling rates melted loviride did not crystallize during cooling, and formed a glass that recrystallized during reheating.
Very low cooling rates resulted in significant decomposition of the drug. The glass transition temperature was found to increase
as a function of increasing heating rates and the activation energy for the transition from the glassy to the super-cooled
liquid state was relatively high, indicating good stability of the glass.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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用差示扫描量热法(DSC)研究聚乳酸(PLA)从熔体及玻璃态为初始条件下的非等温结晶行为,采用Ozawa方程、Mo法、Khanna法和Kissinger法对结晶动力学参数进行计算处理。 实验结果表明,这几种方法均适合处理PLA的非等温结晶过程,而Khanna法提出的结晶速率系数(CRC)能够方便地评价PLA相对结晶速率的大小。 PLA从玻璃态升温结晶比从熔体降温结晶容易得多,升温过程有利于晶核生成,而降温有利于晶体生长。 升温结晶时,升温速率2.0 ℃/min时,结晶焓(ΔHc)达到最大为27.1 J/g。 从熔体等速降温过程中,随着冷却速率的降低ΔHc单调增加,冷却速率为0.25 ℃/min时ΔHc增加到28.3 J/g。 在较低温度下从玻璃态结晶,主要表现为异相成核的二维生长方式。 在较高的温度下从玻璃态升温结晶及从熔体冷却结晶时,以均相成核的三维生长方式结晶为主。 与升温过程相比,冷却不利于晶核的生成,所以导致冷却过程总体ΔHc偏低,扩散活化能偏大。 相似文献