Packing-dependent viscous sintering of glass powder from wet deposition

在金属和陶瓷基材上喷涂、刷涂和浸渍玻璃粉末浆料是搪瓷和牙科陶瓷行业中最先进的涂层技术。影响绿色坯体和烧制的玻璃态涂层的结构的工艺参数主要是根据经验开发的。到目前为止，仍然缺少对控制粘性烧结的基本机制的知识驱动的理解。特别地，由于相对低的工艺温度、亚微米颗粒部分和非球形形状的锯齿状颗粒的粘附，不规则和不均匀填充的效果可以在很大程度上控制烧结。因此，该项目旨在更深入地了解控制烧结动力学的参数。一方面，这是通过探索绿色体的3D微观结构和使用X射线断层扫描（XCT）、X射线显微镜（XRM）和TEM断层扫描以分别可视化微米和亚微米范围内的局部颗粒接触的短时间烧制后的变化来解决的（两侧是Hg孔隙率测定法和BET分析以覆盖整体开孔孔隙率的发展）。为了可视化玻璃粉末系统的堆积结构，XCT和XRM似乎是选择的方法，因为这些非破坏性技术提供了所需长度尺度的局部和全局信息。另一方面，在烧结过程中的玻璃颗粒的致密化的数值建模使用离散的描述的收缩，占颗粒的局部致密化结构。将使用三项模型（用于颗粒重排、颈部形成和孔隙球化），并通过利用3D数据的几何参数进行直接实验验证。干燥玻璃粉末沉积的微结构将相对于亚微米颗粒分数、粒度分布的宽度和玻璃颗粒的热历史（高与低假想温度）而系统地变化。烧结玻璃微珠将作为参考，在这个项目方面的颗粒形状的影响，包装和重排。

Spraying, brushing and dipping of glass powder slurries on/of metal and ceramic substrates are state-of-the-art coating technologies in the enamel and dental-ceramic industries. Process parameters influencing the structure of the green body and the fired glassy coat are mostly empirically developed. A knowledge-driven understanding of the underlying mechanisms that control viscous sintering is up to now still missing. In particular the effect of non-regular and inhomogeneous packing may largely control sintering due to the relative low process temperatures, adhesion of submicron-particle fractions and jagged particles of non-spherical shape. The project aims therefore to gain a deeper understanding of the parameters that control the sinter kinetics. On one hand, this is tackled by exploring the 3D microstructure of the green body and the changes after short periods of firing using X-ray tomography (XCT), X-ray microscopy (XRM) and TEM tomography to visualize local particle contacts in the micron and sub-micron range, respectively (flanked by Hg-porosimetry and BET analysis to cover the development of the overall open porosity). For visualizing the packing structure of the glass powder systems, XCT and XRM seems the method of choice, as these non-destructive techniques give both local and global information on the desired length scales. On the other hand, the densification during sintering of the glass particles is modelled numerically using discrete descriptions of the shrinkage, to account for the local densifying structures of the particulate. A three term model (for particle rearrangement, neck formation and pore spheroidization) will be used with the benefit of direct experimental validation by utilizing geometric parameters of the 3D data. The microstructure of dried glass powder deposition will be varied systematically with respect to the submicron-particle fraction, broadness of the particle size distribution, and thermal history of the glass particles (high vs. low fictive temperature). Sintered glass beads will work as reference in this project with respect to the effect of particle shape on packing and rearrangement.