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Dynamic recrystallization behavior of GH4169G alloy during hot compressive deformation
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作者 Dan Jia Wenru Sun +1 位作者 Dongsheng Xu Fang Liu 《材料科学技术学报:英文版》 SCIE EI CAS CSCD 2019年第9期1851-1859,共9页
The microstructure evolutions and nucleation mechanisms of GH4169G alloy were studied by optical microscope, electron backscatter diffraction (EBSD) and transmission electron microscope (TEM). The hot compression test... The microstructure evolutions and nucleation mechanisms of GH4169G alloy were studied by optical microscope, electron backscatter diffraction (EBSD) and transmission electron microscope (TEM). The hot compression tests were performed different imposed reductions in the range of true strain from 0.12 to 1.2 at the temperatures of 930 °-1050 ° with strain rates of 0.01 s^-1-l s^-1. It is found that cumulative and local misorientation increase firstly and then decrease when the strain is increased due to the progress of dynamic recrystallization (DRX). The low angle boundaries (LAGBs) rapidly develop to high angle boundaries (HAGBs) at relatively high deformation temperature or the low strain rate. There are three DRX mechanisms observed for GH4169 G alloy during hot deformation. Discontinuous dynamic recrystallization (DDRX) as the dominant mechanism for GH4169 G alloy is characterized by typical necklace structures and bulged-original boundaries. Besides, different deformation bands with dislocation cells formed in deformed matrix at low temperature and large strain, which indicates that continuous dynamic recrystallization (CDRX) contributed to the DRX process. The twin boundaries lost their coherent characteristics and provide sites for nucleation, which also accelerates the nucleation of DRX. 展开更多
关键词 GH4169G ALLOY DYNAMIC RECRYSTALLIZATION NUCLEATION mechanism
具有高浸出稳定性臭葱石的合成、原位包覆及表征 预览
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作者 柯平超 刘志宏 《中国有色金属学报:英文版》 SCIE EI CAS CSCD 2019年第4期876-892,共17页
为了提高臭葱石的稳定性,本文作者提出一种合成并原位包覆臭葱石的方法。在Fe(Ⅱ)-As(V)-H2O体系、90℃和pH1.5的条件下持续通入氧气合成多面体状和山梅状臭葱石颗粒。当初始Fe(Ⅱ)/As(Ⅴ)摩尔比超过1:1时,在合成过程中,一种含硫酸根的... 为了提高臭葱石的稳定性,本文作者提出一种合成并原位包覆臭葱石的方法。在Fe(Ⅱ)-As(V)-H2O体系、90℃和pH1.5的条件下持续通入氧气合成多面体状和山梅状臭葱石颗粒。当初始Fe(Ⅱ)/As(Ⅴ)摩尔比超过1:1时,在合成过程中,一种含硫酸根的铁的氧化物或氢氧化物包覆层包覆在臭葱石颗粒表面。为了检测这些合成样品的浸出稳定性,用TCLP毒性浸出方法对样品在pH4.93进行60h的浸出实验。此外,用多种不同pH5.40~10.88浸出溶液对样品进行30~40d的浸出实验。浸出结果表明,该包覆层能有效延缓臭葱石中砷的释放;TCLP结果显示,其被包覆后砷的浸出浓度低至0.12mg/L,长周期浸出实验显示砷的浸出浓度低于0.5mg/L。 展开更多
关键词 臭葱石 固砷 形核 原位包覆 稳定性
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A theoretical study of step edge geometry on sapphire(0001) and its effect on ZnO nucleation
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作者 Ping Yang Li-Xin Zhang 《物理学前沿:英文版》 SCIE CSCD 2019年第2期105-112,共8页
Step-edge-induced nucleation plays a key role in controlling the growth of novel nanostructures and low-dimensional mat erials. However, it is difficult to experimentally determine the step edge structures of complex ... Step-edge-induced nucleation plays a key role in controlling the growth of novel nanostructures and low-dimensional mat erials. However, it is difficult to experimentally determine the step edge structures of complex metal oxides. In this work, we present a detailed theoretical study of the stability of stoichiometTic steps on sapphire(OOOl). Based on first-principles calculations and excess charge computation by Finnis1 approach, a pair of non-polar step edges are determined to be the most stable. By studying the adsorption characteristics of ZnO and combining previous works, we successfully explained how growth temperature and deposition rate affect the in-plane orientation of ZnO grown on sapphire(OOOl). The knowledge on the step edge structures and nucleation patterns would benefit the study on step-edge-guided nanostruc ture grow th. 展开更多
关键词 stepped SAPPHIRE surface FIRST-PRINCIPLES EXCESS charge step-edge-induced NUCLEATION
An overview on nucleation theories and models
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作者 Marcos Flavio de Campos Jose Adilson de Castro 《中国稀土学报:英文版》 SCIE EI CAS CSCD 2019年第10期1015-1022,共8页
Several different models for coercivity are discussed. There are two main situations: i) nanocrystalline magnets, with grain size bellow the single domain particle size, and ii) magnets with grain size above single do... Several different models for coercivity are discussed. There are two main situations: i) nanocrystalline magnets, with grain size bellow the single domain particle size, and ii) magnets with grain size above single domain particle size. The described theories and models are general, and can be applied in either NdFeB magnets, SmFeCoCuZr or strontium ferrite magnets. The spring effect observed in isotropic nanocrystalline magnets can be explained with the Stoner-Wohlfarth model. Modifications of the StonerWohlfarth model are necessary to take into account the effect of interaction between grains. When the grain size is above the single domain size, energy considerations show that nucleation should occur at the surface of grains. Nucleation is interpreted as a two-step process, where domain wall displacement occurs for grain size above single domain size, after a nucleus is first formed. The effect of grain size on the coercive field is discussed. 展开更多
关键词 COERCIVITY NUCLEATION GRAIN size Spring effect ND-FE-B PERMANENT MAGNET
结霜初期无液核形成时的抑霜研究 被引量:1
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作者 李丽艳 刘中良 +1 位作者 赵玲倩 李艳霞 《工程热物理学报》 EI CAS CSCD 北大核心 2019年第1期198-203,共6页
通过系统地总结计算各种不溶表面上的成核能障,分析比较了冰晶在球面、平面和凹弧面上成核的难易。其中以球面上成核较难,凹弧面上成核较容易。异质核半径与新相核临界半径的比值大于10后,球面和凹弧面上成核都相当于平面上成核。想通... 通过系统地总结计算各种不溶表面上的成核能障,分析比较了冰晶在球面、平面和凹弧面上成核的难易。其中以球面上成核较难,凹弧面上成核较容易。异质核半径与新相核临界半径的比值大于10后,球面和凹弧面上成核都相当于平面上成核。想通过异质核表面形式来显著地影响新相成核,异质核半径与新相核临界半径的比值应在小于1的范围内。通过实验对比在结霜初期无液核生成时超疏水表面和普通表面上的结霜发现,此时超疏水表面不再具有延迟结霜的效果。 展开更多
关键词 结霜 成核 疏水表面
A novel analytical model for hysteresis loops of exchange-coupled hard-soft magnets
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作者 Jing Zou Laichuan Shen +5 位作者 Lei Qiu Youhua Feng Chan Luo Xue Liang Li Zhao Guoping Zhao 《中国稀土学报:英文版》 SCIE EI CAS CSCD 2019年第10期1034-1039,共6页
Hard/soft permanent magnets have attracted a lot of attention because of their rich magnetic properties and their potential for realizing giant energy products. However, energy products obtained by scientists in exper... Hard/soft permanent magnets have attracted a lot of attention because of their rich magnetic properties and their potential for realizing giant energy products. However, energy products obtained by scientists in experiments are much smaller than the theoretical values, which has been studied by various analytical and numerical methods. The famous Stoner-Wohlfarth model(S-W model) is too simple to give the hysteresis loops whereas the intensively used variational method is too complicated to reveal the underlying mechanism in a simple form. The analytical model proposed in this paper maintains a balance between simplicity and precision, where the spins in the soft layer rotate fast and coherently with the applied field while those in the hard layer response to the applied field much slower but also coherent. An exchange coupling is provided to maintain the exchange spring which drags the spins in the hard layer to follow those in the soft layer. Similar to the more sophisticated model, the calculated hysteresis loops display three typical magnetic phases, i.e., the rigid composite magnet, the exchange spring and decoupled magnet, whereas the simple SW model can only give one single phase, i.e., the rigid composite one. In addition to the hysteresis loop, the energy product and the nucleation fields have been calculated and compared with those calculated by other methods, which justifies our model.Careful comparisons show that our calculations are in good agreement with the experimental results and other theoretical results, especially for the important coercivity value and the related mechanism. 展开更多
关键词 PERMANENT MAGNETS Analytical model HYSTERESIS LOOPS NUCLEATION fields Rare earths
用于锂金属负极的轻质、高掺氮量碳纳米纤维基三维集流体
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作者 吴浩良 张云博 +5 位作者 邓亚茜 黄志佳 张琛 贺艳兵 吕伟 杨全红 《中国科学:材料科学(英文版)》 CSCD 2019年第1期87-94,共8页
锂金属是未来二次电池实现高能量密度化的关键负极材料,然而,如何实现锂金属的均匀和无枝晶沉积是目前制约其实际应用的关键问题.本论文采用静电纺丝技术及高温碳化方法制备了一种轻质、高掺氮量(9.5at%)的三维碳纳米纤维集流体.该集流... 锂金属是未来二次电池实现高能量密度化的关键负极材料,然而,如何实现锂金属的均匀和无枝晶沉积是目前制约其实际应用的关键问题.本论文采用静电纺丝技术及高温碳化方法制备了一种轻质、高掺氮量(9.5at%)的三维碳纳米纤维集流体.该集流体较低的密度能提升基于整个电池的能量密度,而且高掺氮量使其具备亲锂的特性,从而有效降低锂离子在其表面的初始形核过电位,得到均匀的金属锂种子层,实现后续金属锂的均匀沉积.这种三维结构有效抑制了锂枝晶的产生,降低了电池的极化,金属锂沉积,脱除测试中其库伦效率在循环250圈后仍可保持在98%以上.将其沉积金属锂后与LiFePO4组装全电池,电池极化降低,在循环300圈后容量保持率可达82.4%,表现出很好的应用前景. 展开更多
关键词 碳纳米纤维 三维结构 负极材料 碳化方法 锂金属 集流体 氮量 轻质
氢化钛-石油焦制备Al-Ti-C-Ce母合金显微组织及其凝固机制研究
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作者 贺永东 杨啸雨 +3 位作者 郭锋 李鹏 张媛庆 豆银丽 《稀有金属》 EI CAS CSCD 北大核心 2019年第7期733-738,共6页
采用X射线衍射(XRD)、扫描电子显微镜(SEM)、能谱仪(EDS)等现代检测分析方法,研究了由TiH2-石油焦-铝铈合金与铝液制备的不同Ce含量的Al-Ti-C-Ce母合金的显微组织,结果表明:Al-Ti-C-Ce母合金由α(Al),(TiC),(TiAl3),(Ti2Al20Ce)相组成;A... 采用X射线衍射(XRD)、扫描电子显微镜(SEM)、能谱仪(EDS)等现代检测分析方法,研究了由TiH2-石油焦-铝铈合金与铝液制备的不同Ce含量的Al-Ti-C-Ce母合金的显微组织,结果表明:Al-Ti-C-Ce母合金由α(Al),(TiC),(TiAl3),(Ti2Al20Ce)相组成;Al-Ti-C-Ce母合金铸样晶界为连续的共晶组织,晶内分布着大量的粗大第二相组织,晶界共晶和晶内第二相中均含有Ti2Al20Ce相。部分大颗粒第二相组织为复合结构,复合晶粒内部存在颜色较深的α(Al)+Ti2Al20Ce+(TiC)的包晶组织。线分析结果表明:第二相粒子中,元素C的分布相对均匀,粒子内部C, Al含量相对较低, Ti, Ce含量相对较高, Ce的分布显著高于粒子外部区域;具有复合结构的第二相中所包含的粒子区域, Ti, C含量极高,而Al, Ce含量较低。合金在凝固过程中, TiC粒子作为晶核优先析出, TiAl3相通过TiC粒子形核,并与游离的Ti, Ce发生包晶反应生成Ti2Al20Ce相,多余Ce原子会与晶界处的TiC, TiAl3的复合粒子反应生成TiC, Ti2Al20Ce复合粒子。含Ti, C, Ce的复合粒子作为领先相优先析出,细化Al-Ti-C-Ce母合金晶粒。 展开更多
关键词 Al-Ti-C-Ce母合金 显微组织 复合粒子 形核 凝固机制
飞机冷板液滴相变实验研究 预览
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作者 孙金绢 田建辉 彭润玲 《低温工程》 CAS CSCD 北大核心 2019年第4期26-30,共5页
利用模拟风洞、显微镜、高速摄像机及各种传感器等设备设计搭建了实验平台,对不同工况下飞机冷板上液滴冻结形成进行了实验研究。研究结果显示过冷液滴成核的过程非常短暂仅持续几十毫秒,在相变完成后液滴体积会膨胀并形成乳状凸起,较... 利用模拟风洞、显微镜、高速摄像机及各种传感器等设备设计搭建了实验平台,对不同工况下飞机冷板上液滴冻结形成进行了实验研究。研究结果显示过冷液滴成核的过程非常短暂仅持续几十毫秒,在相变完成后液滴体积会膨胀并形成乳状凸起,较低的冷板温度与较高的相对湿度会缩短液滴冻结时间,增加液滴体积将使冻结时间呈现先增加后减小的趋势,增加空气流速将使冻结时间呈现先减少后增大的趋势。 展开更多
关键词 液滴冻结 成核 过冷度 飞机积冰
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水合物浆液非牛顿特性与黏度模型研究进展 预览
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作者 陈玉川 史博会 +5 位作者 李文庆 黄芳飞 吕晓方 柳扬 吴海浩 宫敬 《化工进展》 EI CAS CSCD 北大核心 2019年第6期2682-2696,共15页
水合物浆液的黏度及非牛顿特性是水合物流动安全保障的重要参数,其研究对于水合物风险控制技术以及深水油气管线输送的安全预警具有重要的意义。本文介绍了用于水合物生成、黏度及非牛顿特性研究的流变仪类型以及在流变仪内进行水合物... 水合物浆液的黏度及非牛顿特性是水合物流动安全保障的重要参数,其研究对于水合物风险控制技术以及深水油气管线输送的安全预警具有重要的意义。本文介绍了用于水合物生成、黏度及非牛顿特性研究的流变仪类型以及在流变仪内进行水合物生成的实验材料;总结了水合物生成影响因素对水合物生成过程中黏度的影响规律,梳理分析了水合物浆液黏度定量表征模型;从剪切稀释性、触变性、屈服特性以及黏弹性4个方面总结了水合物浆液非牛顿特性的研究成果。总体而言,水合物浆液黏度及非牛顿特性研究存在较强的体系依赖性,构建的水合物浆液黏度模型所考虑的因素各异、普适性不高。最后,本文给出了今后在流变仪内开展水合物实验及模型研究的方向和建议:水合物微观结构参数和浆液流变参数的耦合研究;综合考虑水合物浆液非牛顿特性的黏度预测模型;水合物浆液黏度及非牛顿特性和水合物堵管理论的结合。 展开更多
关键词 水合物 成核 黏度 非牛顿特性 定量表征
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Direct Comparison of Crystal Nucleation Activity of PCL on Patterned Substrates
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作者 Rui Xin Chun-Yue Hou +1 位作者 Shou-Ke Yan Ji-Chun Liu 《高分子科学:英文版》 SCIE CAS CSCD 2019年第7期693-699,共7页
A sample containing different regions with poly(ε-caprolactone)(PCL), oriented polyethylene (PE), and oriented isotactic polypropylene (iPP) films in contact with glass slide has been prepared to be observed in the s... A sample containing different regions with poly(ε-caprolactone)(PCL), oriented polyethylene (PE), and oriented isotactic polypropylene (iPP) films in contact with glass slide has been prepared to be observed in the same view field in an optical microscope and the crystallization of PCL in different regions during cooling from 80 °C down to room temperature at a rate of 1 °C·min^-1 was studied. The results showed that the crystallization of PCL started first at the PE surface and then at the iPP surface, while its bulk crystallization occured much later. This indicates that though both PE and iPP are active in nucleating PCL, the nucleation ability of PE is stronger than that of iPP. This was due to a better lattice matching between PCL and PE than that between PCL and iPP. Moreover, since lattice matching existed between every (hk0) lattice planes of both PCL and PE but only between the (100)PCL and (010)iPP lattice planes, the uniaxial orientation feature of the used PE and iPP films resulted in the existence of much more active nucleation sites of PCL on PE than on iPP. This led to the fact that the nucleation density of PCL at PE surface was so high that the crystallization of PCL at PE surface took place in a way like the film developing process with PCL microcrystallites happened everywhere with crystallization proceeding simultaneously. On the other hand, even though iPP also enhanced the nucleation density of PCL evidently, the crystallization of PCL at iPP surface included still a nucleation and crystal growth processes similar to that of its bulk crystallization. 展开更多
关键词 Poly(ε-caprolactone) POLYPROPYLENE Polyethylene EPITAXY HETEROGENEOUS NUCLEATION
Exploring the synthesis conditions to control the morphology of gold-iron oxide heterostructures
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作者 Pablo Tancredi Luelc Souza da Costa +6 位作者 Sebastian Calderon Oscar Moscoso-Londono Leandro M. Socolovsky Paulo J. Ferreira Diego Muraca Daniela Zanchet Marcelo Knobel 《纳米研究:英文版》 SCIE EI CAS CSCD 2019年第8期1781-1788,共8页
Gold-iron oxide nano-heterostructures with a clear and well-defined morphology were prepared via a seed-assisted method. The synthesis process and the events of heterogeneous nucleation during the decomposition of the... Gold-iron oxide nano-heterostructures with a clear and well-defined morphology were prepared via a seed-assisted method. The synthesis process and the events of heterogeneous nucleation during the decomposition of the iron precursor were carefully studied in order to understand the mechanism of the reaction and to tailor the architecture of the fabricated heterostructures. When employing Au seeds of 3 and 5 nm, nanoparticles with a dimer-like morphology were produced due to the occurrence of a single iron oxide nucleation event. Otherwise, multi-nucleation events could be favored by two mechanisms:(i) by the incorporation of a reducing agent and the slowing down of the heating protocol, leading to a core-shell system;(ii) by the increase of the Au seed size to 8 nm, leading to a flower-like system. Further increase of the Au seed size to 12 nm using similar synthesis conditions promotes the homogeneous nucleation and growth of the iron oxide phase, without formation of heterostructures. An in-depth study was performed on the gold-iron oxide heterostructures to confirm the epitaxial growth of the oxide domain over the Au seed and to analyze the elemental distribution of the components within the heterostructures. Finally, it was found that the modification of the plasmonic properties of the Au nanoparticles are strongly influenced by the architecture of the heterostructure, with a more pronounced damping effect for the systems produced after multi-nucleation events. 展开更多
关键词 nanoparticles gold-iron oxide HETEROSTRUCTURES HETEROGENEOUS NUCLEATION EPITAXIAL growth HR-microscopy
成核层生长工艺对紫外LED外延片性能的影响
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作者 孟锡俊 李建婷 《电子元器件与信息技术》 2019年第4期92-94,共3页
目前LED产品已经形成了成熟且稳定的产业,新兴的紫外LED的市场也随之发展迅速,使得越来越多的技术人员开始开发研究。本文通过对成核层工艺的研究,结合外延过程中的翘曲情况,得到了成核层生长工艺对紫外LED外延片性能的影响效果。
关键词 成核层 翘曲 紫外LED 一致性
微细硬质合金刀具沉积金刚石薄膜的形核研究 预览
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作者 孔维星 巩春志 田修波 《真空与低温》 2019年第3期170-177,共8页
形核是HFCVD金刚石薄膜沉积的重要阶段,对金刚石薄膜质量至关重要。为实现金刚石薄膜在微细硬质合金刀具表面的高质量形核,选取了形核过程中的几个核心参数:热丝功率(Pf)、碳氢比(X)以及形核气压(p),设计了三因素三水平正交实验,采用SE... 形核是HFCVD金刚石薄膜沉积的重要阶段,对金刚石薄膜质量至关重要。为实现金刚石薄膜在微细硬质合金刀具表面的高质量形核,选取了形核过程中的几个核心参数:热丝功率(Pf)、碳氢比(X)以及形核气压(p),设计了三因素三水平正交实验,采用SEM形貌分析、拉曼光谱分析以及EDS能谱分析等对形核尺寸、表面覆盖率和形核质量进行了研究。实验结果表明,热丝功率对形核尺寸和形核速率的影响最大,形核气压的影响最小,而对沉积质量影响较大的为热丝功率和形核气压,碳氢比的影响则最小。实验得到的最佳形核参数为:Pf=2000W,X=2.0%,p=1400Pa。 展开更多
关键词 微细硬质合金刀具 金刚石薄膜 形核 正交试验
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有机羧酸改性氧化铝纳米颗粒在聚丙烯中的成核效果研究 预览
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作者 蒋晓峰 赵世成 辛忠 《化工学报》 EI CAS CSCD 北大核心 2019年第10期4052-4061,共10页
利用正庚酸、硬脂酸、环己基甲酸和苯甲酸对氧化铝纳米粒子表面进行化学改性,研究了改性粒子表面的基团结构以及接枝量对其在聚丙烯(iPP)基体中成核效果的影响。结果表明:与直链烷基和环烷基羧酸相比,苯甲酸改性颗粒(BA-Al2O3)具有优异... 利用正庚酸、硬脂酸、环己基甲酸和苯甲酸对氧化铝纳米粒子表面进行化学改性,研究了改性粒子表面的基团结构以及接枝量对其在聚丙烯(iPP)基体中成核效果的影响。结果表明:与直链烷基和环烷基羧酸相比,苯甲酸改性颗粒(BA-Al2O3)具有优异的成核效果,当BA-Al2O3的添加量为0.1%(质量)时,成核聚丙烯的结晶温度和弯曲模量相对于纯iPP分别提高了9.4℃和21.9%。改性纳米颗粒BA-Al2O3的苯甲酸接枝量对复合材料的结晶温度和力学性能也有重要影响,接枝量小于1.3mmol/(gAl2O3)时,BA-Al2O3的成核效果随接枝量增加而显著增加;接枝量大于1.3mmol/(gAl2O3)时,成核效果略微增加。所以,通过调控改性颗粒的表面结构,可以有效提升iPP复合材料的结晶和力学性能。 展开更多
关键词 纳米粒子 合成 基团结构 接枝量 聚丙烯 复合材料 成核
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纳米C-S-H对水泥水化、硬化浆体孔结构及混凝土强度的影响
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作者 张朝阳 蔡熠 +1 位作者 孔祥明 郝挺宇 《硅酸盐学报》 EI CAS CSCD 北大核心 2019年第5期585-593,共9页
通过水化热测试、化学结合水含量测试、X射线衍射分析、压汞测试及强度测试研究了合成的纳米水化硅酸钙(n-C-S-H)对水泥水化过程、硬化水泥浆孔结构及混凝土强度的影响。结果表明:n-C-S-H显著加速了水泥早期水化,提升了水泥在12~24 h龄... 通过水化热测试、化学结合水含量测试、X射线衍射分析、压汞测试及强度测试研究了合成的纳米水化硅酸钙(n-C-S-H)对水泥水化过程、硬化水泥浆孔结构及混凝土强度的影响。结果表明:n-C-S-H显著加速了水泥早期水化,提升了水泥在12~24 h龄期的水化程度,从而显著提高混凝土12~24 h龄期的抗压强度,24 h以后对强度提升效果逐渐减小。3 d以后n-C-S-H对混凝土强度发展没有明显的促进作用,1.5%掺量下混凝土强度反而较空白样有所降低;加入n-C-S-H的硬化水泥浆在12 h~3 d龄期内相比空白水泥浆临界孔径降低,凝胶孔孔隙率提高,毛细孔孔隙率降低。n-C-S-H改变了C-S-H凝胶的生成方式,使其原本从水泥颗粒表面析出变为了从孔溶液中析出,显著减小了毛细孔孔隙率,同时增加了凝胶间孔的体积。这种多核生长的方式导致水化产物结构疏松,从而导致基体强度略微降低。因此,在相同水化程度时,掺有n-C-S-H的混凝土抗压强度略低于空白混凝土。 展开更多
关键词 纳米水化硅酸钙 水化 孔结构 强度 成核效应
高纯铝/尖晶石形核机理及形核界面研究
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作者 王双 《热加工工艺》 北大核心 2019年第12期125-128,共4页
通过调控温度和时间等化学反应动力学因素,研究了Al与MgAl2O4之间不发生化学反应的情况下MgAl2O4基板对Al的直接形核作用。分析了形核过冷度与保温温度和保温时间的关系。采用了X射线衍射、扫描电镜、EDX能谱分析、高分辨率透射电镜、T-... 通过调控温度和时间等化学反应动力学因素,研究了Al与MgAl2O4之间不发生化学反应的情况下MgAl2O4基板对Al的直接形核作用。分析了形核过冷度与保温温度和保温时间的关系。采用了X射线衍射、扫描电镜、EDX能谱分析、高分辨率透射电镜、T-EBSD等手段研究了Al/MgAl2O4形核界面。结果表明:在保温时间较短的情况下,Al可以在MgAl2O4上直接形核;但不同保温温度下,Al在MgAl2O4基板的凝固过程会使基板表面出现不同程度的应变,从而影响形核过冷度和Al形核的晶面择优取向。 展开更多
关键词 MGAL2O4 界面结构 晶粒细化 形核
非晶Ag晶化过程中不同类型晶核结构的识别与跟踪 预览
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作者 李媛 彭平 《物理学报》 SCIE EI CAS CSCD 北大核心 2019年第7期222-229,共8页
采用分子动力学模拟研究了非晶Ag的等温晶化过程,通过原子轨迹逆向追踪法分析了不同类型晶体团簇的结构遗传与组态演化.在团簇类型指数法的基础上,根据基本团簇种类与联结方式不同,提出了一种可区分fcc单晶、多晶与混晶团簇的分析方法.... 采用分子动力学模拟研究了非晶Ag的等温晶化过程,通过原子轨迹逆向追踪法分析了不同类型晶体团簇的结构遗传与组态演化.在团簇类型指数法的基础上,根据基本团簇种类与联结方式不同,提出了一种可区分fcc单晶、多晶与混晶团簇的分析方法.在非晶Ag等温晶化过程中,基于团簇结构的连续遗传性特征,发展了一种可区分fcc单晶、多晶与混晶晶胚与晶核的结构分析技术.结果发现:不论临界尺寸还是几何构型,不同类型的晶核结构都存在差异,其中fcc单晶临界尺寸最小,多晶次之,混晶最大;fcc单晶与多晶壳层原子中有少量hcp和bcc原子,而混晶壳层则全部为非晶类原子,并且fcc单晶、多晶与混晶的临界晶核都不是球型结构. 展开更多
关键词 形核 分子动力学模拟 团簇 临界晶核
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SO2-NO2-NH3-H2O四元反应体系中气溶胶的生成特性 预览
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作者 萧嘉繁 刘鹤欣 +2 位作者 谭厚章 杜勇乐 王毅斌 《中国环境科学》 EI CAS CSCD 北大核心 2019年第7期2721-2729,共9页
通过烟雾箱实验,研究了SO 2-NO 2-NH 3-H2O四元反应体系在气-粒转化过程中新形成颗粒物数浓度与粒径分布的变化.研究发现,SO2-NO2-NH3-H2O四元反应体系具有显著的成核能力,且其成核强度大,持续时间短.当SO2、NO 2浓度为200mg/m^3,NH 3... 通过烟雾箱实验,研究了SO 2-NO 2-NH 3-H2O四元反应体系在气-粒转化过程中新形成颗粒物数浓度与粒径分布的变化.研究发现,SO2-NO2-NH3-H2O四元反应体系具有显著的成核能力,且其成核强度大,持续时间短.当SO2、NO 2浓度为200mg/m^3,NH 3浓度为12×10^-6时,反应体系的气溶胶总个数浓度在2min时达到峰值2.5×10^6cm^-3.缺少任一种气体均会使气溶胶成核强度下降.SO2、NO2及NH 3浓度分别为0的工况下气溶胶总个数浓度峰值分别下降了41.0%、83.6%及98.5%.在电厂污染气体排放浓度区间内,NO 2对气溶胶生成影响大于SO2.燃煤电厂控制NO x排放浓度对改善烟囱出口气溶胶数浓度更有效.在实验基础上,对颗粒物成核特性进行拟合,反应体系在气-粒转化过程中产生的新颗粒物总个数浓度及中值粒径与气态前体物浓度线性相关;采用布朗团聚模型对气溶胶成核后的团聚过程总个数浓度及粒径变化进行模拟计算,根据给定的燃煤电厂SO2、NO2、NH 3排放浓度,给出预测气溶胶颗粒成核速率、粒径分布及总个数浓度变化的方法. 展开更多
关键词 燃煤电厂 灰霾 气溶胶 烟雾箱 成核 团聚
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Effect of grain size on α-variant selection in a ZrTiAlV alloy
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作者 LI FeiTao QIU Xi +4 位作者 LIAO ZhongNi LUAN BaiFeng ZHANG XinYu LIU RiPing LIU Qing 《中国科学:技术科学英文版》 SCIE EI CAS CSCD 2019年第6期982-988,共7页
Local crystallographic orientation characteristics of grains with different sizes in a ZrTiAlValloy after interrupted cooling from βphase region are investigated by electron backscatter diffraction(EBSD) technique. A... Local crystallographic orientation characteristics of grains with different sizes in a ZrTiAlValloy after interrupted cooling from βphase region are investigated by electron backscatter diffraction(EBSD) technique. A statistical analysis of EBSD data shows that bigger parent β grains present weaker variant selection than smaller grains. The relevant influences are studied by comparing the nucleation behavior of grain boundary α(GBα) and succedent growth stage in varisized grains. In-depth analysis indicates that the deviation between pole of GBα and common pole of adjacent parent β grains is responsible for the smaller degree of variant selection inside the bigger parent β grains. The formation of more than one GBα type at the β/β grain boundary with common pole in bigger grains results in obstructing each other for these variants during the following growth stage, while only one type of GBα nucleate at the β/β grain boundary with common pole in smaller grains and it can freely grow into the interior of the grains, leading to stronger variant selection in smaller β grains. 展开更多
关键词 VARIANT SELECTION EBSD BURGERS ORIENTATION relationship NUCLEATION behavior
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