Probing the Nucleation and Growth Kinetics of Bismuth Nanoparticles via In-situ Transmission Electron Microscopy

The nucleation and growth mechanism of nanoparticles is an important theory,which can guide the preparation of nanomaterials.However,it is still lacking in direct observation on the details of the evolution of intermediate state structure during nucleation and growth.In this work,the evolution process of bismuth nanoparticles induced by electron beam was revealed by in-situ transmission electron microscopy(TEM)at atomic scale.The experimental results demonstrate that the size,stable surface and crystallographic defect have important influences on the growth of Bi nanoparticles.Two non-classical growth paths including single crystal growth and polycrystalline combined growth,as well as,corresponding layer-by-layer growth mechanism along{012}stable crystal plane of Bi nanoparticles with dodecahedron structure were revealed by in-situ TEM directly.These results provide important guidance and a new approach for in-depth understanding of the nucleation and growth kinetics of nanoparticles.

Visualization of atomic scale reaction dynamics of supported nanocatalysts during oxidation and ammonia synthesis using in-situ environmental(scanning) transmission electron microscopy

Reaction dynamics in gases at operating temperatures at the atomic level are the basis of heterogeneous gas-solid catalyst reactions and are crucial to the catalyst function.Supported noble metal nanocatalysts such as platinum are of interest in fuel cells and as diesel oxidation catalysts for pollution control,and practical ruthenium nanocatalysts are explored for ammonia synthesis.Graphite and graphitic carbons are of interest as supports for the nanocatalysts.Despite considerable literature on the catalytic processes on graphite and graphitic supports,reaction dynamics of the nanocatalysts on the supports in different reactive gas environments and operating temperatures at the single atom level are not well understood.Here we present real time in-situ observations and analyses of reaction dynamics of Pt in oxidation,and practical Ru nanocatalysts in ammonia synthesis,on graphite and related supports under controlled reaction environments using a novel in-situ environmental(scanning) transmission electron microscope with single atom resolution.By recording snapshots of the reaction dynamics,the behaviour of the catalysts is imaged.The images reveal single metal atoms,clusters of a few atoms on the graphitic supports and the support function.These all play key roles in the mobility,sintering and growth of the catalysts.The experimental findings provide new structural insights into atomic scale reaction dynamics,morphology and stability of the nanocatalysts.

Interface charges boosted ultrafast lithiation in Li_4Ti_5O_12 revealed by in-situ electron holography

It is still a great challenge at present to combine the high rate capability of the electrochemical capacitor with the high electrochemical capacity feature of rechargeable battery in energy storage and transport devices. By studying the lithiation mechanism of Li_4Ti_5O_12 （LTO） using in-situ electron holography, we find that double charge layers are formed at the interface of the insulating Li_4Ti_5O_12 （Li_4） phase and the semiconducting Li_7Ti_5O_12 （Li_7） phase, and can greatly boost the lithiation kinetics. The electron wave phase of the LTO particle is found to gradually shrink with the interface movement, leaving a positive electric field from Li_7 to Li_4 phase. Once the capacitive interface charges are formed, the lithiation of the core/shell particle could be established within 10 s. The ultrafast kinetics is attributed to the built-in interface potential and the mixed Ti3＋/Ti4＋ sites at the interface that could be maximally lowering the thermodynamic barrier for Li ion migration.

High-resolution electron microscopy for heterogeneous catalysis research

Heterogeneous catalysts are the most important catalysts in industrial reactions. Nanocatalysts, with size ranging from hundreds of nanometers to the atomic scale, possess activities that are closely connected to their structural characteristics such as particle size, surface morphology, and three-dimensional topography. Recently, the development of advanced analytical transmission electron microscopy（TEM） techniques, especially quantitative high-angle annular darkfield（HAADF） imaging and high-energy resolution spectroscopy analysis in scanning transmission electron microscopy（STEM） at the atomic scale, strengthens the power of（S）TEM in analyzing the structural/chemical information of heterogeneous catalysts. Three-dimensional reconstruction from two-dimensional projected images and the real-time recording of structural evolution during catalytic reactions using in-situ（S）TEM methods further broaden the scope of（S）TEM observation. The atomic-scale structural information obtained from high-resolution（S）TEM has proven to be of significance for better understanding and designing of new catalysts with enhanced performance.

Tracking lithiation with transmission electron microscopy

Li-ion batteries(LIBs)have dominated energy-storage techniques for portable electronic devices and electric cars,and are expanding their territory into the large-scale energy storage.The energy storage of LIBs is realized by the reversible shuttle of lithium ions between electrodes.It is essential to track the lithium diffusion and obtain a profound insight into the lithiation mechanism during the work cycle of LIBs.Transmission electron microscopy(TEM)is a powerful tool for the structural characterization,which can provide the information about the lithiation at the atomic scale.In this review,we summarize the research frontiers of TEM applications on LIBs.We introduce the techniques for the direct observation of Li species in LIB-related materials.Especially,the application of cryo-TEM is highlighted.Moreover,in-situ TEM technique is further discussed since it shows great advantages in studying the dynamical structure changes of LIBs.The perspectives and strategies in this review offer feasible guidance for researchers to further improve the performance of LIBs.

Revealing structural degradation in layered structure oxides cathode of lithium ion batteries via in-situ transmission electron microscopy

Transition metal oxides with layered structure have been widely used as cathode materials for lithium-ion batteries(LIBs)which have relatively high energy density,large capacity and long life.However,in the long-term electrochemical cycle,the inevitable degradation of performance of LIBs due to structural degradation in cathodes severely restricts their large-scale practical applications.Understanding the underlying mechanism of structural degradation is the most critical scientific problem.Recently,in situ transmission electron microscopy(TEM)has become a useful tool to study the structural and compositional evolutions at atomic scale in electrochemical reactions,which provided a unique and in-depth understanding of the structural degradation.In this review,we discuss the recent advances in the in situ TEM,focusing on its role in revealing the structural degradation mechanisms in the four key places:(1)the interface between the cathodes and electrolyte;(2)the cathode surface;(3)the particle interior and(4)those induced by thermal effect.The insight gained by the in-situ TEM which is still developing at its fast pace is unique and expected to provide guidance for designing better layered cathode materials.

In-situ formation of Al-CaB_6 composites with low resistivity

In this work, in-situ CaB6 reinforced aluminum matrix composites were fabricated, and the microstructure, resistivity, microhardness and coefficient of thermal expansion (CTE) of Al-CaB6 composites were studied. It is found that CaB6 compounds can be formed by reducing reaction occurred in the Al melt: . CaB6 exhibits a hexahedron morphology and distributes uniformly in the Al alloy matrix. The resistivity of Al-CaB6 composites is 3.02*10-8 Ω·m, which is close to that of pure Al and lower than that of 6063Al/Ga composites. The average microhardness of Al-CaB6 composites can reach 1270 MPa, 259.8% higher than that of pure Al. Compared to pure Al, the CTE of Al-CaB6 composites is much lower.

原位加热电镜技术研究WO_(3)-BiVO_(4)非晶复合薄膜退火相变过程

本文利用原位加热电镜技术和高分辨透射电镜研究了WO_(3)-BiVO_(4)非晶复合薄膜原位退火相变过程。退火过程中,薄膜中的Bi元素逐渐挥发,由于电镜中的高真空缺氧环境,加热到600℃时,形成的结晶相大部分为立方W相,少量的WO_(x)(0<x≤3)、VO_(x)(0<x≤25)和BixVOy(0<x≤1,0<y≤4)氧化物晶相,完全不同于利用脉冲激光沉积方法在充足氧气气氛和600℃条件下生长退火后形成的WO_(3)纳米柱嵌入BiVO_(4)基质中的垂直异质外延结晶复合薄膜。因此,退火气氛和样品的受热方式对薄膜的结晶相变过程有很大影响。

时效温度和Ag对Al-Zn-Mg合金力学性能与微观结构的影响

本文研究了在不同时效温度条件下Ag对Al-Zn-Mg铝合金力学性能与微观结构的影响。结果表明,随着时效温度的提升,Ag对合金硬度的影响增大,合金晶界无析出带宽度明显减小。时效温度为120℃时,含Ag和不含Ag的Al-Zn-Mg铝合金均以η系列相析出为主,但含Ag合金的晶内析出相分布更为细小弥散,尺寸减小的同时径厚比增大。当时效温度升高至160℃和180℃,Ag对合金峰值硬度的提升作用显著增加。此时,Al-Zn-Mg合金主要强化相由η系列相转变为T系列相,同时尺寸明显增大,而含Ag合金中主要强化相类型与120℃时相同,仍然为η系列相,且尺寸并未明显增大。

Electron force-induced dislocations annihilation and regeneration of a superalloy through electrical in-situ transmission electron microscopy observations

What effect does electric current do on dislocation evolution of metals keeps being a confusing question to be answered and proved. To this end, the dislocation evolution of a superalloy with electric current was directly observed by electrical in-situ transmission electron microscopy in this work. Dislocations annihilation at first and then regeneration was found for the first time, which directly proves the existence of electron force during the electrically-assisted manufacturing. Dislocations regeneration would be driven by the electron force and the resistance softening by the local Joule heating effect. Resultantly,a base could be provided for future electrically-assisted research.

In-situ transmission electron microscopy observation of the evolution of dislocation loops and gas bubbles in tungsten during H2+and He+dual-beam irradiation

Dislocation loop and gas bubble evolution in tungsten were in-situ investigated under 30 keV H_(2)^(+)and He^(+)dual-beam irra-diation at 973 K and 1173 K.The average size and number density of dislocation loops and gas bubbles were obtained as a function of irradiation dose.The quantitative calculation and analysis of the migration distance of 1/2<111>loops at low irradiation dose indicated that the main mechanism of the formation of<100>loops should be attributed to the high-density helium cluster inducement mechanism,instead of the 1/2<111>loop reaction mechanism.H2+and He+dual-beam irradiation induced the formation of<100>loops and 1/2<111>loops,while increasing the irradiation temperature would increase<100>loop percentage.The percentage of<100>loops was approximately 18.6%at 973 K and increased to 22.9%at 1173 K.The loop reaction between two 1/2<111>loops to form a large-sized 1/2<111>loop was in-situ observed,which induced not only the decrease of the number of 1/2<111>loops but also the significant increase of their sizes.The<100>loops impeded the movement of dislocation line and tended to escape from it instead of being absorbed.With the increase of irradiation dose,the yield strength increment(Δ_(σloop))caused by the change of loop size and density increased first and then decreased slightly,while the yield strength increment(Δ_(σbubble))caused by the change of bubble size and density always increased.Meanwhile,within the current irradiation dose range,Δ_(σloop)was much larger thanΔ_(σbubble).

冷热交变花岗岩的力学与损伤特性研究

为研究冷热交变岩石的力学性能和损伤演变规律,对冷热交变后的花岗岩进行单轴压缩试验和巴西劈裂试验,利用声发射监测和电镜扫描技术分析花岗岩加载过程中的声发射信号特征和试样破坏后的微观形态特征。结果表明,在不同冷热交变次数下,花岗岩的抗压强度与抗拉强度都明显降低,且两者呈显著的线性关系。在单轴压缩条件下,花岗岩的破坏模式以轴向劈裂破坏和剪切破坏为主;在巴西劈裂条件下,随着热处理温度的升高,花岗岩的破坏表现为径向破坏、径向弧形破坏和沿弱结构平面的混合破坏。两种实验条件下试样破坏过程中的声发射计数变化与应力−应变曲线变化基本一致。归一化累积声发射计数可以较好地反映试样加载过程中的损伤演变特征。试样的初始损伤随着温度和冷热交变次数的增加而增加,导致花岗岩在加载过程中的损伤率持续增长。此外,基于力学参数定义了三个损伤变量,其中基于抗拉强度的损伤变量对冷热交变次数最为敏感。

In-situ imaging electrocatalysis in a solid-state Li-O_(2) battery with CuSe nanosheets as air cathode

The development of highly efficient catalysts in the cathodes of rechargeable Li-O_(2) batteries is a considerable challenge.To enhance the electrochemical performance of the Li-O_(2) battery,it is essential to choose a suitable catalyst material.Copper selenide(CuSe)is considered as a more promising cathode catalyst material for Li-O_(2) battery due to its better conductivity and rich electrochemical active sites.However,its electrochemical reaction and fundamental catalytic mechanism remain unclear till now.Herein,in-situ environmental transmission electron microscopy technique was used to study the catalysis mechanism of the CuSe nanosheets in Li-O_(2) batteries during discharge and charge processes.It is found that Li_(2)O was formed and decomposed around the ultrafine-grained Cu during the discharge and charge processes,respectively,demonstrating excellent cycling.This indicate that the freshly formed ultrafine-grained Cu in the conversion reaction catalyzed the latter four-electron-transfer oxygen reduction reaction,leading to the formation of Li_(2)O.Our study provides important understanding of the electrochemistry of the LiO_(2) nanobatteries,which will aid the development of high-performance Li-O_(2) batteries for energy storage applications.

硫磺回收装置废热锅炉泄露原因分析及预防措施

废热锅炉作为硫磺回收装置关键设备,其运行稳定对装置长周期运行至关重要。该文针对炉管内漏,从腐蚀状况、锅炉水质、扫描电镜检测等方面对废锅炉管腐蚀泄漏进行原因探究,同时分析废热锅炉日常管理,解决了Clans单元停工期间无法通过常规方式点炉吹硫、开工期间烟气二氧化硫排放不合规的问题,并提出严格控制除氧水中溶解氧含量、定期更换废热锅炉等预防废热锅炉腐蚀泄漏的措施,对装置稳定运行有重要意义。

700MPa级低碳贝氏体钢的热处理工艺研究

采用扫描电镜、透射电镜等方法研究了不同回火温度对70 0MPa级贝氏体钢组织性能的影响。结果表明,回火温度对钢的屈服强度的影响明显,而对抗拉强度的影响较小。回火温度为6 0 0℃时的屈服强度比未热处理的增加1 2 7MPa ,同时随着回火温度的增加,屈强比提高。热处理前的贝氏体板条比热处理后的细小,热处理前的析出物主要是尺寸为4 0～6 0nm之间的(Nb ,Ti) (C ,N) ,热处理后的析出物主要是1 0nm以下的(Nb ,Ti) (C ,N)以及2 0～4 0nm的εCu。

热处理制度对2519铝合金晶间腐蚀性能的影响

通过拉伸测试、显微硬度测试、透射电镜 (TEM)及扫描电镜 (SEM)分析等手段研究了不同热处理制度对 2 5 19铝合金组织、力学性能及抗晶间腐蚀性能的影响。结果表明 ,与T6状态相比 ,2 5 19合金经T8处理后 ,合金的强度、硬度提高 ,合金峰值时效时间提前 ,但塑性降低 ,同时 ,晶内沉淀析出的θ′相数目增加、尺寸减小、分布均匀 ,沿晶界析出的θ′(θ)相数量减少 ,且不连续分布 ,无沉淀带变窄。T8处理提高了合金峰值时效态抗晶间腐蚀的能力。

固溶处理对高纯7055铝合金组织的影响

采用光学显微镜(OM)、扫描电镜(SEM)和X射线衍射谱仪研究了固溶处理对高纯7055铝合金组织的影响。结果表明:合金固溶时,粗大的初生AlZnMgCu相溶解缓慢,并逐渐球化;而初生AlZnMgCuFeTi相几乎不溶解。固溶温度越高(460-480℃),时间越长(0-240min),初生AlZnMgCu相溶解越多,再结晶越多,晶粒尺寸越大。再结晶主要于初始晶界上的粗大初生相上形核(PSN机制),并向弥散Al3Zr粒子少的变形晶粒内部长大。490℃固溶时,出现过烧组织,晶粒粗大。分级固溶较单级固溶可更好的控制合金组织,如460℃×120min+480℃×60min与480℃×180min相比,再结晶和晶粒尺寸小得多,但初生AlZnMgCu相溶解程度相差不大。

FGH96合金晶粒长大规律的研究

对FGH96合金在热处理过程中晶粒长大规律进行了系统的研究。结果表明 ,γ′相对晶粒长大有显著阻碍作用 ,在低于γ′相固溶温度 (1 1 0 9℃ )热处理时 ,大量未溶解的γ′相使得晶粒长大缓慢 ;在高于γ′相固溶温度以上时 ,合金为单相奥氏体组织 ,晶粒随温度的升高快速长大。晶粒长大动力学表明 :在高于γ′相固溶温度以上时 ,晶粒生长指数随着热处理温度的升高而增加 ;在热处理温度为 1 1 35℃和1 1 5 0℃下的晶粒长大激活能为 2 93 4kJ mol,晶粒长大机理为自扩散过程控制机理 ,并建立了相应的晶粒长大动力学方程。

不同均匀化制度对3003阴极箔比电容的影响

采用金相显微镜、扫描电镜(能谱)、透射电镜及比电容检测等方法研究了不同均匀化制度下0 0 5mm的30 0 3阴极箔腐蚀箔的表面腐蚀形貌和光箔的析出相形貌、大小以及体积分数及其对比电容的影响。结果表明:样品经6 2 0℃2 4h +水淬+5 0 0℃ 10h +空冷的双级均匀化后,析出相粒子尺寸细小,分布弥散,体积分数达6 5 % ,阴极箔腐蚀均匀,比电容可达5 30 μF cm2 ,而其他单级均匀化制度下,析出相较粗大且细小析出相相对较少,因而比电容比双级均匀化样品的低。实验结果同时表明,不同的均匀化制度对光箔的位错组态影响不明显,析出相的组态决定了比电容的高低和腐蚀形貌。

活性粉末混凝土的性能与微细观结构

研究了活性粉末混凝土(reactive powder concrete,RPC)的强度、动弹模量、气体渗透性、碳化以及长期热处理条件下的膨胀性等宏观性能.用压汞测孔仪、扫描电镜等现代微观手段分别研究了RPC的孔结构及微观形貌.分析了RPC的性能与微细观结构之间的相互关系,提出了相应的细观结构模型.结果表明:RPC具有非常低的孔隙率,其气体渗透系数比传统混凝土的低1～2个数量级.经过21 d热处理后,其试样长度基本不产生膨胀.RPC优异的宏观性能得益于其致密、均匀的内部微观结构.