Isolating Field Effects in Sintering via Ultrahigh Temperature In Situ Nanomechanics

非技术描述：大多数陶瓷产品和设备起源于在高温下凝固的结晶粉末；这一过程称为烧结。传统的烧结通常需要大量的能源投入、巨大的设备成本和相对较长的制造时间。在烧结过程中施加电场可以大大减少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)烧结的几何复杂性，以及(2)对烧结过程中粉末结合的晶体表面上的原子运动和成键的了解很少。缺乏科学的理解削弱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，有效地将材料的物理属性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成键和原子运动的前所未有的信息。这些信息可以定义在电场辅助烧结过程中哪些参数是最重要的，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。该项目支持培养一名材料科学和工程专业的研究生。然后，毕业生通常在大型制造公司的工业研究实验室工作。该项目还为任职人数不足的高中生和职前教师提供研究机会，并针对K-12学生开展外联活动。这些活动旨在吸引学生从事科学和工程职业。技术细节：电场可以极大地加速烧结动力学，这在放电等离子烧结或闪速烧结中经常观察到。然而，这些过程背后的机制仍然存在很大争议，而且人们对此知之甚少。基础知识的缺乏源于烧结过程的复杂性，以及电场与所有相关的扩散系数和热力学系数的耦合。这些实验通过(1)在外加电场下利用纳米尺度的零蠕变实验测量氧化锆中晶界和表面的电毛细管系数，(2)分别通过纳米尺度的单晶界Coble蠕变和表面平滑实验来量化晶界和表面扩散系数，以及(3)通过使用具有代表性的低能和高能双晶几何来控制各向异性，从而隔离了这些影响。这项工作源于基于超高温原位电子显微镜的纳米机械测试方法的发展。对该学科的变革影响是对电场对烧结影响的新的机械理解，对氧化物中依赖于场的界面热力学的新见解，以及有助于解决陶瓷科学中的许多问题的新的实验方法的发展。该奖项反映了NSF的法定使命，并通过使用基金会的智力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.