Heterogeneous nucleation of metals and colloids on templates - a comparative study

设想研究胶体体系和金属合金在不同结构模板上的异相成核。模板的结构在结晶学和晶格位置的中间距离上发生了变化，所用的胶体体系是由盐溶液中的带电粒子组成的。通过改变表面电荷密度和/或盐浓度来调节胶体之间的相互作用势。将应用具有简单体心立方和面心立方结构表面的熔融二氧化硅模板。为此，将采用连续制备技术制备悬浮液，该技术允许精确控制相互作用参数。模板将被固定在平流室中，并用显微镜和光散射进行研究。测量将在低至中等亚稳状态下进行。在亚稳性较高的情况下，采用了超小角X射线散射。研究的重点是模板的动力学、形态变化和相行为与模板结构和取向的关系，以及金属与不同结构模板接触时的结晶情况。Fe-Ni金属熔体通过无容器电磁悬浮进行过冷，通过不同结构的形核触发器在预先选定的过冷温度下接触过冷熔滴，从外部刺激晶化。这些变化对相形成的异质形核的形核势垒以及由此产生的微观组织的形成的影响将被研究。

It is envisaged to investigate heterogeneous nucleation of colloidal systems and metallic alloys on differently structured templates. The structure of the template is changed in crystallography and intermediate distance of lattice sites.The colloidal systems used are consisting of charged particles in a salty solution. By changing the surface charge density and/or the salt concentration the interaction potential between the colloids is tuned. Fused silica templates with simple bcc and fcc structured surfaces will be applied. For this the suspensions will be prepared with a continuous preparation technique which allows for the precise control of interaction parameters. Templates will be fixed in flat flow cells and investigated with microscopy and light scattering. Measurement will be carried out at low to moderate metastability. At higher metastability ultra small angle x-ray scattering is applied. Investigations will focus on the kinetics, the morphological changes and phase behaviour in dependence on structure and orientations of the templates.Also crystallization of metals in contact with templates of different structures is studied. Metallic melts of Fe-Ni are undercooled by containerless electromagnetic levitation and crystallization is externally stimulated by touching the undercooled melt drop at preselected undercooling temperature by different structured nucleation trigger. The effect of these changes on the nucleation barrier of heterogeneous nucleation of phase formation as well as the resulting microstructure formation will be investigated.