SiGe/SiHBT异质界面与pn结界面的相对位移的影响

从模拟和实验两方面研究了SiGe/Si HBT发射结中pn结界面和SiGe/Si界面的相对位置对器件的电流增益和频率特性的影响.发现两界面偏离时器件性能会变差.尤其是当pn结位于SiGe/Si界面之前仅几十?就足以产生相当高的电子寄生势垒,严重恶化器件的性能.据此分析了基区B杂质的偏析和外扩对器件的影响以及SiGe/Si隔离层的作用.     

偏晶合金液-液相分离机制和均质偏晶合金的制备方法

本文介绍了偏晶合金液－液分离机制的研制现状及偏晶合金形核特点,在此基础上,分析了影响钤昔日 合金液－液相分离的诸多因素和机制,并系统介绍了制备均质偏晶合金的各种方法。指出：景杰等是合金液－淮相分离的诸因素的作用过程及均质偏晶合金的制备和应用,将是该领域今后研究的重点。     

微量元素在Ni基合金凝固过程中分配行为的模拟

以多元合金系在凝固过程中组元的液固界面平衡方程,即组元在液固相中的化学位相等为基础建立了一个反映多元系凝固偏析的简易模型,利用它对多元合金系凝固初期的特征进行了定性描述,并对某些微量元素在Ｎｉ基合金凝固过程中的分配行为进行了计算模拟,得到的结果与实验结果较好地相符,从定性说明和计算模拟的角度,方便地确定出对Ｎｉ基合金凝固偏析起决定性作用的微量元素 。     

Mo—La2O3阴极La2O3表面富集研究

采用俄歇电子能谱法研究了 Mo- L a2 O3阴极材料中 L a2 O3向表面的富集过程。结果表明 ,在高温下 ,L a2 O3以 L a3+ ,O2 - 离子的形式分别向表面扩散 ,然后在表面上重新结合成分子。在 112 3 K～ 142 3 K范围内 ,L a3+ ,O2 -离子的扩散系数分别为 :DL a=3.6 70 3× 10 - 1 6 exp (- 1.0 16 39× 10 5 / RT) m2 / s;DO=1.5 12 2× 10 - 1 6 exp (- 8.130 6 6× 10 4/ RT) m2 / s     

Observation of yttrium oxide segregation in a ZrO2-SiO2 glass-ceramic at nanometer dimensions

Dopant segregation at grain boundaries (GBs) in ceramics has been widely reported, while whether similar segregation behavior occurs in glass-ceramics remains unknown. The distribution of dopant in glass-ceramics may be totally different due to the existence of glass phase. This study examines the distribution of Y³⁺ ions in a ZrO₂-SiO₂ glass-ceramic. Two samples were prepared by hot pressing, yttrium oxide-doped, and undoped 65 mol% ZrO₂-35 mol% SiO₂ nanocrystalline glass-ceramics (NCGCs). The NCGCs had the same microstructure, that is, ZrO₂ nanoparticles (NPs) embedded in an amorphous SiO₂ matrix. XRD results showed that the undoped NCGC was composed of 20.9 wt% (weight percentage) monoclinic ZrO₂ (m-ZrO₂) and 79.1 wt% tetragonal ZrO₂ (t-ZrO₂), while the yttrium oxide-doped NCGC was composed of 9.6 wt% m-ZrO₂ and 90.4 wt% t-ZrO₂. X-ray energy-dispersive spectrometry (EDS) results in scanning electron transmission microscopy (STEM) mode demonstrated that Y³⁺ ions segregated both on the surface of ZrO₂ NPs and within the thin intergranular glass film (with a thickness of approximately 7 Å) between ZrO₂ NPs in the yttrium oxide-doped NCGC. Interestingly, no obvious Y signals were detected in the amorphous SiO₂ matrix. Density functional theory calculation results showed that Y³⁺ ions had a strong segregation tendency in the GB area and the segregation of Y³⁺ ions increased the work of separation of GB layer. These findings provide new understanding of the segregation behavior of dopant in glass-ceramics, which may offer useful guidance for other researchers to tailor the properties of glass-ceramics through GB engineering.     

Nonequilibrium Grain Boundary Segregation of Phosphorus in Ni-Cr-Fe Superalloy

 In virtue of Auger electron spectroscopy, the grain-boundary concentrations of phosphorus in Ni-Cr-Fe superalloy after solution-treated at 1180℃ for 45 min are measured, the results show that a peak of phosphorus concentration occurs at about 180 min during isothermal ageing at 500℃, and a maximum concentration of phosphorus appears also at about 500℃ for all specimens aged for 20 min at temperatures of 200,400,500,700 and 800℃. The results are analysed with the laws of non-equilibrium grain-boundary segregation. It is found from the analysis that peaks are relative to critical time for non-equilibrium grain-boundary segregation of phosphorus.     

连铸板坯中心线偏析的预测

从生产经验和文献可知,结晶过程中产生的凝固收缩会导致中心线偏析,很多情况下,在热轧产品的中心也会发现结晶过程中产生的微细缩孔。从这方面讲,板坯凝固过程中形成缩孔簇的尺寸大小,以及形成这种缩孔的条件是首要的,在全面分析统计数据的基础上,对此进行了讨论,得出一个重要结论:当固液比率达到一定的值后,在此部位的铸坯中心只有糊状物,实际上没有更多的液体可以补充。建立了数学模型,用于计算板坯中心部位的流动速度和方向以及预测的疏松。计算表明,在给定的成分和冷却条件下,中心线偏析主要受支承辊的设置、形变和偏心度的影响,同时支承辊之间铸坯的鼓肚也是重要影响因素之一。     

Tuning the surface structure and phase structure of PtCu3 nanoparticle for highly efficient electrocatalysts

Significantly improving the catalytic activity and durability of platinum (Pt) based electrocatalysts is crucial for commercial application of fuel cells by tuning structure of Pt alloy nanoparticles. Here, we report a method of tuning structure of PtCu₃ alloy nanoparticle by annealing in different atmospheres. The detailed analyses showed that evolution of surface structure and phase structure of PtCu₃ alloy nanoparticles heat-treated in N₂ atmosphere and N₂/H₂ mixed atmosphere are mainly as follows: (1) when heat-treated in N₂, the crystal phase of PtCu₃ has undergone a transformation from disordered PtCu₃ alloy to ordered PtCu₃ alloy and then to disordered PtCu₃ alloy with the increase of holding time from 30 min to 90 min; (2) when heat-treated in H₂/N₂, a Pt-rich surface is formed on the Pt–Cu nanoparticles due to Pt segregation induced by H₂ adsorption. Electrochemical measurements demonstrated that both PtCu₃/C_-N2 electrocatalysts prepared in N₂ and PtCu₃/C_-N2/H2 electrocatalysts prepared in H₂/N₂ exhibit enhanced mass activities toward the oxygen reduction reaction (ORR) relative to Pt/C electrocatalyst in acidic media. In particular, when the holding time is 90 min, the obtained PtCu₃/C_-N2/H2 electrocatalysts with Pt-rich surface showed highest mass activity of 435 mA/mg_Pt (at 0.9 V vs. RHE), which is four times greater than that of Pt/C catalyst (20 wt.% Pt, 115 mA/mg_Pt). This study provides a promising method for the reasonable design and preparation of low cost and high performance Pt-based electrocatalysts.     

82B盘条异常组织研究

研究82B盘条的异常组织,针对马氏体及网状渗碳体问题,以直径12.5 mm的82B盘条为研究对象,采用光学显微镜和扫描电镜分析马氏体的形成原因:(1)C,Mn,Cr等元素的偏析,形成局部马氏体或心部马氏体;(2)轧制控冷工艺不当,冷速过快所致.提出消除或减轻82B盘条异常组织的建议:合理调整炼钢电磁搅拌位置以减小铸坯成...