CAREER: Thermochemistry of Nanoceramics: Understanding and Controlling Phase Transformation and Sintering via Interface Energetics

非技术描述：当陶瓷材料的尺寸接近纳米尺寸时，通常会显示出新的物理和化学特性。这些新特性激发了多个领域的各种新应用，从纳米传感器到燃料电池和锂电池的正极材料。此外，还为开发新材料提供了可能性，以应对美国日益增长的能源需求、对外国石油的依赖和气候变化等当前能源问题。然而，纳米陶瓷加工的优化仍然是一个挑战，理解基本概念需要进一步研究。在这个项目中，卡斯特罗教授专注于纳米陶瓷中存在的更大体积分数的界面，以改善工艺控制。他假设，在热力学的基础上，可以使用对界面组成的操纵来改变加工和产品属性。特别是，卡斯特罗教授致力于改善致密化和相变，这是加工的两个基本部分，通过调整成分来可控地改变界面能量，从而实现更快、更便宜和更可控的加工和产品。这种独特的热力学方法是通过提供具有重要技术意义的材料的界面能量学(在文献中很少找到)的史无前例的数据来实现的，从而使这些重大进展更接近工业制造。该项目也有一个重要的教育组成部分，重点是在初中和高中推广工程学。该项目名为材料与你，包括在学校活动中展示有趣的加工和特性，让学生接触到基本材料的概念。技术细节：该项目使用独特的量热技术来测量纳米陶瓷的界面能，并使用它们通过监测和操纵驱动力来改进对烧结和相变的控制。其目的是量化掺杂对界面能的影响，并将它们与工艺参数和动力学联系起来。通常，人们完全根据动力学来考虑掺杂剂在加工过程中的影响，但随着加州大学戴维斯分校实验室(最近由卡斯特罗教授及其合作者开发)可用高分辨率热量计的出现，卡斯特罗教授的团队能够量化成分变化对体系能量学的影响，为加工控制开辟了一条新的途径。在这个项目中，使用高温液滴溶液量热法测量了三种技术上相关的氧化物：二氧化锡、氧化锌和氧化锆的界面能(表面和晶界)，以及与烧结和多晶型稳定性相关的数据。更好地了解界面能量学和掺杂剂在纳米陶瓷加工中的作用，可以改进工业中的成分设计，实现更节能、更具成本效益的产品，并具有可预测的相/尺寸/密度。从教育的角度来看，参与该项目的学生得到指导，并使用战略性材料和流程，为他们未来作为材料专业人员的职业生涯提供培训。

NON-TECHNICAL DESCRIPTION: Ceramic materials often exhibit novel physical and chemical properties as their sizes approach nanometer dimensions. These new properties have inspired a variety of new applications in several fields, ranging from nanosensors to cathode materials for fuel cells and lithium batteries. As well, the possibility is opened for the development of new materials in response to the current energy problems such as the U.S. increasing demand for energy, dependence on foreign oils, and climate change. However, the optimization of nanoceramic processing is still a challenge, and understanding the fundamental concepts requires further research. Within this project, Prof. Castro focuses on the larger volume fraction of interfaces present in nanoceramics to improve processing control. He hypothesizes that manipulation of the interface composition can be used to change processing and product properties on a thermodynamic basis. In particular, Prof. Castro works on improving densification and phase transformation, two fundamental parts of processing, by controllably changing interface energies by tuning composition, enabling faster, less expensive, and more controlled processing and products. This unique thermodynamic approach is carried out by providing unprecedented data on interface energetics (rarely found in the literature) on technologically important materials, bringing those significant advances closer to industrial manufacturing. The project also has an important educational component that focuses on the promotion of engineering in middle and high-schools. The program, Materials&You, involves demonstrations of interesting processing and properties at school events to expose students to basic materials' concepts. Two high-schools with significant Latin American students and the underlying goal of getting all students to graduate have been selected.TECHNICAL DETAILS: This project uses unique calorimetric techniques to measure interface energies of nanoceramics and use them to improve the control of sintering and phase transformation by monitoring and manipulating driving forces. The aim is to quantify the effects of dopants on the interface energies and correlate them with processing parameters and kinetics. The effect of dopants in processing is typically considered exclusively on a kinetic basis, but with the advent of high-resolution calorimetry available at the University of California at Davis laboratories (recently developed by the Prof. Castro and collaborators), Prof. Castro's group is capable of quantifying the effect of composition change on the energetics of the system, opening a new avenue for processing control. Within this project, high-temperature drop solution calorimetry is used to measure the interface energies (both surface and grain boundary) of three technologically relevant oxides: tin dioxide, zinc oxide, and zirconia, and those data correlated with sintering and polymorphic stability. The better understanding of the role of interface energetics and dopants in nanoceramic processing enables improvement of composition design in industries, enabling more energy and cost efficient products, with predictable phases/sizes/densities. From the educational perspective, students participating in the project are mentored and work with strategic materials and processes, providing training for their future careers as materials' professionals.