C60与金刚石薄膜成核关系的研究

采用热丝化学气相沉积法在覆盖C60膜的硅基片上沉积金刚石膜,研究了金刚石膜的成核与生长.实验结果表明,金刚石的成核密度可达1×106Cm-2,利用这种方法可实现衬底无损淀积金刚石膜.C60之所以能够促进金刚石成核,我们认为主要与C60分子本身独特的结构及H原子的激活作用有关.同时,高温下C60分解后残留的石墨等碳碎片以及C原子与衬底Si反应生成的SiC都可作为金刚石的成核位.     

NUMERICAL SIMULATION OF THE FORMATION OF NANOPARTICLES IN AN IMPINGING TWIN-JET

The Large Eddy Simulation (LES) method has been used to solve the fluid momentum equations coupled with a convection-diffusion equation to study the formation of pollutant nanoparticles in a vehicular exhaust with impinging twin-jet. The functions of the space (S) between the two jets and the distance (H) from the exit of nozzle to the impingement plane are evaluated according to the distributions of pollutant nanoparticles. The results show that the nucleation produces a large number of nanoparticles, and gas-to-nanoparticle conversion mostly takes place in the interface region of the two jets, the circumambience of the jets, and region near the plane. The maximal particle size and maximal number concentration produced by both nucleation and coagulation appear around the region of free jet and the region near the plane, respectively. The significant differences for various spaces between the two jets are the number concentration and size distributions in the interface region of the two jets. For the case with larger space, more nanoparticles are produced by nucleation and coagulation. The more the distance from the exit of nozzle to the impingement plane, the lower is the number concentration and the fewer the particles distribute near the plane. Increasing the distance from nozzle to plane is beneficial to the reduction of nanoparticle formation.     

无皂苯丙乳液的粒径与成核机理

研究了甲基丙烯酸甲酯(MMA)-丙烯酸丁酯(BA)-苯乙烯(St)-甲基丙烯酸(MAA)四元无皂乳液聚合体系中各种因素对单体转化率、乳胶粒大小及分布的影响,并对其成核机理进行了分析。结果表明,在引发剂用量一定的条件下,引发剂的加入方式对单体转化率和乳胶粒的单分散性均有很大的影响;引发剂含量增大,聚合温度升高,单体转化率先升高后趋稳定,乳胶粒粒径和分散度先减小后增大;反应性乳化剂量增大,乳胶粒粒径和分散度均逐渐减小。在所研究的条件下,含有反应性乳化剂的无皂苯丙乳液聚合体系以均相成核为主。     

超音速喷嘴涡流管气体分离性能的数值模拟与实验

 建立了超音速喷嘴涡流管的简化几何模型,利用描述两相双组分超音速冷凝流动的 Eulerian 双流体三维湍流模型,以含湿空气为介质对装置内部的自发凝结过程进行数值模拟。设计制造相应的装置,建立实验平台,对装置的含湿气体分离性能进行实验研究。通过模拟和实验2种手段研究了影响超音速喷嘴涡流管气体分离性能的参数及其影响规律。结果表明,气流在喷嘴内部达到超音速流动,使得水蒸气自发凝结成液滴,为混合气体分离提供了先决条件;热端管内气体自旋产生的离心加速度可以达到重力加速度的6×10⁵倍,为气、液分离提供了必要条件;降低进出口压力之比和冷流率,增大入口相对湿度和长径比可以提高装置的气体分离性能,安装阻涡器对性能有不利影响。因此,采用超音速喷嘴涡流管实现混合气体中重组分的脱除是可行的。     

Synthesis of Millimeter‐Scale Transition Metal Dichalcogenides Single Crystals

The emergence of semiconducting transition metal dichalcogenide (TMD) atomic layers has opened up unprecedented opportunities in atomically thin electronics. Yet the scalable growth of TMD layers with large grain sizes and uniformity has remained very challenging. Here is reported a simple, scalable chemical vapor deposition approach for the growth of MoSe₂ layers is reported, in which the nucleation density can be reduced from 10⁵ to 25 nuclei cm^?2, leading to millimeter‐scale MoSe₂ single crystals as well as continuous macrocrystalline films with millimeter size grains. The selective growth of monolayers and multilayered MoSe₂ films with well‐defined stacking orientation can also be controlled via tuning the growth temperature. In addition, periodic defects, such as nanoscale triangular holes, can be engineered into these layers by controlling the growth conditions. The low density of grain boundaries in the films results in high average mobilities, around ≈42 cm² V^?1 s^?1, for back‐gated MoSe₂ transistors. This generic synthesis approach is also demonstrated for other TMD layers such as millimeter‐scale WSe₂ single crystals.     

生物质复合材板坯内部孔隙形成的模拟与实验分析

应用计算机模拟的方法研究了生物质复合材板坯内部孔隙的形成.通过对板坯内孔隙体积比率与加工参数包括原料的几何形状、材料的公称密度之间的关系的考察结果表明,由模型得到的数据与由实验得到的数据的结果趋向一致.研究中通过在板材热压实验中测量板坯中心部位的温度和气体压力变化来说明孔隙对热和质传输的影响,实验和分析的结果也验证了该模型和模拟的方法对于研究生物质复合材板坯内孔隙具有一定的有效性.     

绝热剪切带内微孔洞演化规律研究

为深入了解绝热剪切带内微孔洞的演化规律,进而揭示高应变率加载条件下绝热剪切破坏的特殊规律,本文对D35钢进行了约束爆破实验,爆破后回收圆筒的微观观察表明,绝热剪切破坏要经过绝热剪切带内微孔洞形核、长大和相互联接形成裂纹等一系列演化过程.在Guduru P等人的测试结果和Li Shaofan等人数值仿真结果基础上,通过简化(剪切带内的温度分布为由剪切带中心向边缘线性降低,并最终降至与基体温度相同; 微孔洞的形核、长大受温度控制,长大速度随温度呈指数规律降低)对Timothy S P和Hutchings I M的模型进行了修正,修正后的模型可以定量的描述绝热剪切带内微孔洞的演化直至破坏的全过程,模型的描述与微观分析获得的实验结果有较好的一致性.     

HFCVD法合成金刚石的初期生长过程

用XL30FEG扫描电镜对热丝化学气相沉积 (HFCVD)法合成的金刚石颗粒的初期生长过程进行了研究。结果表明 ,金刚石在 p -Si(10 0 )基片上的初始形核密度很高 ,可达 10 10 /cm2 ;在随后的颗粒长大过程中 ,颗粒快速长大 ,颗粒密度急剧减少 ;颗粒的长大速率随其尺寸的增大而减小 ,最后趋于一稳定值     

无铅时代的来临

介绍了铅的危害与焊接中的问题,希望能给一些同业者带来帮助。     

不同成核效果成核剂的应用与研究进展

成核调节剂按其对成核的影响分为成核促进剂和成核抑制剂,介绍了这两类成核剂的特性、研究现状及其对结晶过程及晶体产品质量的影响,且对溶液结晶中的成核剂作用机理进行了简要的论述,旨在使研究者对成核调节剂及成核作用机理有更深的理解,为晶体成核的研究提供理论指导.