Isolating Field Effects in Sintering via Ultrahigh Temperature In Situ Nanomechanics

非技术描述：大多数陶瓷产品和器件来源于高温固化的结晶粉末；这个过程叫做烧结。传统的烧结通常需要大量的能源投入，显著的设备成本和相对较长的制造时间。在烧结过程中应用电场可以大大降低这些成本和加工时间。不幸的是，电场效应仍然知之甚少，这在很大程度上是由于(1)烧结的巨大几何复杂性和(2)对烧结过程中粉末结合的晶体表面的原子运动和键合的理解不足。缺乏科学的理解损害了工程师设计最佳制造条件和生产新材料的能力。该项目开发了一种新的方法，可以有效地将材料的物理性质与粒子几何效应隔离开来。因此，可以获得有关电场如何影响表面上的键和原子运动的前所未有的信息。这些信息可以确定电场辅助烧结过程中最重要的参数，从而确定优化制造条件的策略。这项工作在技术上与新型超高温航空航天材料、先进光学陶瓷和微电子陶瓷的开发有关。该项目支持材料科学与工程研究生的培训。毕业生通常在大型制造企业的工业研究实验室工作。该项目还为代表性不足的高中生和职前教师提供研究机会，并针对K-12学生开展外展活动。这些活动旨在吸引学生从事科学和工程事业。技术细节：电场可以显著加速烧结动力学，在火花等离子烧结或闪光烧结中经常观察到。然而，这些过程背后的机制仍然存在很大的争议，人们对其知之甚少。缺乏基本知识源于烧结过程的复杂性以及电场与所有相关扩散和热力学系数的耦合。实验通过(1)在应用电场中使用纳米级零蠕变实验测量氧化锆晶界和表面的电毛细系数，(2)分别通过纳米级单晶界Coble蠕变和表面平滑实验量化电场依赖的晶界和表面扩散系数，以及(3)通过具有代表性的低能和高能双晶几何形状控制各向异性来隔离这些影响。这项工作源于基于超高温原位透射电子显微镜的新型纳米力学测试方法的发展。对该学科的变革影响是对电场对烧结的影响的新的机制理解，对氧化物中依赖场的界面热力学的新见解，以及对解决陶瓷科学中许多问题有用的新实验方法的发展。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: Most ceramic products and devices originate from crystalline powders consolidated at high temperatures; a process called sintering. Traditional sintering typically requires a large input of energy, significant equipment costs, and relatively long manufacturing times. Application of electric fields during sintering can greatly reduce these costs and processing times. Unfortunately, electric field effects remain poorly understood owing in large part to (1) the great geometrical complexity of sintering and (2) a poor understanding of atomic motion and bonding at crystal surfaces where powder bonds during sintering. The lack of scientific understanding impairs engineers' ability to design optimal manufacturing conditions and produce new materials. This project develops a new methodology that efficiently isolates the physical properties of the material from particle geometry effects. As a result, unprecedented information about how electric fields affect bonding and atomic motion on surfaces can be obtained. This information can define which parameters are most important during electric field assisted sintering, and as a result, strategies to optimize manufacturing conditions. The work is technologically relevant to development of new ultrahigh temperature aerospace materials, advanced optical ceramics, and ceramics in microelectronics. The project supports the training of a graduate student in materials science and engineering. Graduates then typically work in industrial research laboratories in large manufacturing firms. The project also provides research opportunities for underrepresented high school students and pre-service teachers, and outreach activities targeted towards K-12 students. These activities are intended to attract students to science and engineering careers.TECHNICAL DETAILS: Electric fields can dramatically accelerate sintering kinetics, as is often observed during spark plasma sintering or flash sintering. However, the mechanisms underlying these processes remain highly controversial and poorly understood. The lack of fundamental knowledge derives from the complexity of the sintering process and the coupling of the electric field to all relevant diffusional and thermodynamic coefficients. The experiments isolate these effects by (1) measuring electrocapillarity coefficients of grain boundaries and surfaces in zirconia using a nanoscale zero creep experiment in applied fields, (2) quantifying electric field dependent grain boundary and surface diffusion coefficients via nanoscale single grain boundary Coble creep and surface smoothing experiments, respectively, and (3) controlling for anisotropy by using representative low and high energy bicrystal geometries. The work emerges from the development of novel ultra-high temperature in situ transmission electron microscopy based nanomechanical testing methods. The transformational impacts on the discipline are a new mechanistic understanding of electric field effects on sintering, new insights into field dependent interface thermodynamics in oxides, and the development of novel experimental methodologies useful for addressing many problems in ceramic science.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.