In situ Determination of Phase Equilibria in the Quaternary Hafnia-Tantala-Titania-Tungstate System

非技术描述：本项目需要一种新的、更有效的方法来阐明和测量氧化物陶瓷中在特定温度和成分条件下存在的相图或不同形式的“相图”。目前的方法是缓慢的，并且基于在高温下加热陶瓷，冷却它们并在室温（RT）下测量它们。然而，我们不知道在RT下观察到的相或形式是否与在HT下存在的相或形式相同。在这个项目中，已经开发出新的实验工具，可以在高达3400摄氏度的温度下进行测量，从而提供正确和准确的基础科学知识。这种陶瓷相图可以在短时间内方便地确定，这是一种转变。同样的技术可以广泛地用于在基础固态物理和化学知识方面取得重大和快速的进展，从而确定下一代复杂的器件材料。在这项研究中受过训练的本科生和研究生都可能随后受雇于飞机设计和制造部门，或作为基础科学研究人员，特别是在高强度同步加速器x射线实验室。还开展了面向高中学生和教师的外展活动。该研究对空间探索和下一代电子器件的陶瓷材料鉴定具有重要意义。技术细节：本研究展示了一种方法，通过该方法可以在高达3400℃的温度下，在空气中或受控气氛中原位测量季元，钽-铪-钛-钨酸盐（Ta2O5 - HfO2 - TiO2 - wo3）相图。这项工作结合了以下实验技术：(1)通过有机立体夹持法合成均质粉末；(2)在空气中温度可达2000℃的四极灯炉；(3)在受控气氛中温度可达3400℃的锥形喷嘴悬浮器。技术(i)和（ii）是在伊利诺伊大学厄巴纳-香槟分校发明的，（iii）是由两家小公司开发和改进的。此外，本研究还产生了理论建模技术，用于探索晶体结构随温度变化（热膨胀、相变、不变反应）以及跨成分范围的取向关系的数学晶格对应关系。这些方法将应用于构成四元体系的四组分相图。随着实验和理论技术的发展，研究生们正在接受全面的培训，即未来的科学家。反过来，这些毕业生将使用这些新技术来增加必要的基础科学知识，以发明新的，极高温陶瓷和复合材料。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL DESCRIPTION: This project addresses the need for a new, more efficient way to elucidate and measure very high temperature (HT) diagrams of phases or different forms existing under specific conditions of temperature and composition called "phase diagrams" in oxide ceramics. Current methods are slow and based on heating ceramics at high temperatures, cooling them and measuring them at room temperature (RT). However, we do not know that the phase or form observed at RT is the same as what existed at HT. Within this project, new experimental tools have been developed enabling measurements to be made at temperatures up to 3400 C, thereby providing correct and accurate basic scientific knowledge. It is transformational to understand that such ceramic phase diagrams could be determined expediently in a short timeframe. The same techniques can be widely used to make significant and rapid advances in the underlying solid state physics and chemistry knowledge, so as to identify the next generation of complex materials for devices. Both undergraduate and graduate students trained in this research may be subsequently employed in the aircraft design and manufacturing sector, or as basic science researchers, particularly at high intensity, synchrotron X-ray laboratories. Outreach to high school students and teachers is also carried out. This research is relevant to identifying ceramic materials for space exploration and next generation electronic devices. TECHNICAL DETAILS: This research demonstrates a method by which the quaternary, tantala-hafnia-titantia-tungstate (Ta2O5 - HfO2 - TiO2 -WO3) phase diagram can be measured in situ, at temperatures up to 3400 C, in air or under controlled atmospheres. This work combines experimental techniques of (i) homogeneous powder synthesis by the organic steric entrapment method (ii) the quadrupole lamp furnace capable of 2000 C in air and (iii) the conical nozzle levitator capable of 3400 C in controlled atmospheres. Techniques (i) and (ii) were invented at the University of Illinois Urbana- Champaign and (iii) was developed and refined by two small companies. In addition, this research has resulted in theoretical modeling techniques to explore mathematical lattice correspondences for orientation relationships between crystal structures as they change with temperature (thermal expansions, phase transformations, invariant reactions) as well as across compositional ranges. These approaches will be applied to the four-component phase diagram constituting the quaternary system. Alongside the development of experimental and theoretical techniques that are being developed, graduate students are being fully trained, i.e. the scientists of the future. In turn, these graduates will use these new techniques to increase the basic science knowledge necessary to invent new, extremely high temperature ceramics and composites.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.