Heterogeneous nucleation and crystal growth of Ba1-xSrxZn2Si2O7 solid solutions with negative thermal expansion studied by X-ray microscopy

X射线显微镜研究负热膨胀Ba1-xSrxZn2Si2O7固溶体的异质成核和晶体生长

• 批准号: 382900969
• 负责人: Dr.-Ing. Christian Thieme
• 金额: --
• 依托单位: Fraunhofer-Institut für Mikrostruktur von Werkstoffen und Systemen (IMWS)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2017
• 资助国家: 德国
• 起止时间: 2016-12-31 至 2020-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/382900969?language=en
• 关键词: Heterogeneous; nucleation; crystal; growth; Ba1

This proposal focuses on recently developed solid solution phases with the composition Ba1-xSrxZn2Si2O7 and their crystallization from glasses. These phases show negative thermal expansion in wide concentration ranges and hence, glass-ceramics containing high concentrations of this phase will be suitable as materials with low or even zero thermal expansion. Such glass ceramics exhibit melting temperatures below 1450 °C, making them a real alternative to conventional zero thermal expansion materials from the lithium-aluminum-silicate system (melting at temperatures above 1600 °C). However, glasses from the system BaO-SrO-ZnO-SiO2 show a high tendency to surface crystallization and micro cracking. The latter is caused by the high anisotropy of the coefficient of thermal expansion of the Ba1-xSrxZn2Si2O7 phase, and thus potentially deteriorates the mechanical properties of respective samples. To overcome these issues, volume crystallization has to be triggered and the size of the crystals has to be kept small enough to prevent micro-cracking. For this purpose, different nucleation agents will be added to the glass in order to promote volume crystallization. Standard techniques of microstructural characterization, such as electron microscopy, X-ray diffraction, and UV-Vis spectroscopy shall be applied to study phase formation and crystal growth. This includes information on the growth mechanisms in general, epitaxial growth on the nuclei, and nucleation rates. In addition, cutting-edge X-ray microscopy shall be applied to fathom the limits of the latter method with respect to the sample system under consideration. Especially the detection of micro cracks inside the sample volume facilitated by the three-dimensional nature of information provided by this technique will be very helpful in finding crack origins and thus understanding the mechanisms of crack formation. Furthermore, X-ray microscopy will be used for the first time to determine nucleation rates in three dimensions at a tens-of-nanoscale level, which will lead to much more precise values, compared to those gained by conventional techniques. These nucleation rates can then be used to control the number and also the size of the crystals inside the sample volume. It is the aim of this project to gain a general understanding of the crystal growth mechanisms in the new glass system BaO-SrO-ZnO-SiO2, and to find a correlation between size and orientation of the crystals and the appearance of micro cracks. Furthermore, the mechanisms of crack formation and growth during crystallization of glasses will be studied using the mentioned new glass system as a model. This will significantly contribute to both, the development of Ba1-xSrxZn2Si2O7 containing glass ceramics with low thermal expansion and the development of other glass ceramics containing phases with a high anisotropy of the coefficients of thermal expansion.

该提案的重点是最近开发的固定溶液阶段，其组成BA1-XSRXZN2SI2O7及其从玻璃杯中结晶。这些阶段在较大浓度范围内显示了负面的热膨胀，因此，含有高浓度的玻璃陶瓷将作为具有低或零热膨胀的材料。这种玻璃陶瓷暴露于1450°C以下的熔融温度，使其成为锂铝硅酸盐 - 硅酸盐系统（在1600°C以上的温度下熔化）的常规零热膨胀材料的真正替代品。然而，系统的玻璃BAO-SRO-ZNO-SIO2显示出表面结晶和微裂纹的高趋势。后者是由BA1-XSRXZN2SI2O7相的核心热膨胀的高各向异性引起的，因此有可能检测到各个样品的机械性能。为了克服这些问题，必须触发体积结晶，并且必须保持足够小的晶体大小以防止微裂纹。为此，将在玻璃中添加不同的成核剂，以促进体积结晶。显微结构表征的标准技术，例如电子显微镜，X射线衍射和UV-VIS光谱法，应应用于研究相的形成和晶体生长。这包括有关总体增长机制，核上外延生长的信息以及核率。此外，应将最先进的X射线显微镜用于fathom，相对于所考虑的样品系统，后一种方法的限制。特别是通过该技术提供的信息的三维性质制备的样品体积内部的微裂纹检测将非常有助于寻找裂纹起源，从而了解裂纹形成的机制。此外，与传统技术相比，X射线显微镜将首次使用纳米级水平的三个维度确定成核速率，这将导致更精确的值。然后，这些成核速率可用于控制样品体积内晶体的数量和大小。该项目的目的是对新玻璃系统BAO-SRO-ZNO-SIO2的晶体生长机理进行一般了解，并找到晶体的大小与方向和微裂纹外观之间的相关性。此外，将使用上述新玻璃系统作为模型来研究玻璃结晶过程中裂纹形成和生长的机制。这将显着有助于两者，这两者都有含有低热膨胀的玻璃陶瓷的BA1-XSRXZN2SI2O7的发展以及其他玻璃陶瓷的发展，这些玻璃陶瓷含有较高的热膨胀核心各向异性。