NSF-Europe: Nanoparticle Sintering Under the Influence of External Electrical Fields

该项目是与德国Fraunhofer Institute Silicatforschung(ISC)关于在外部电场影响下烧结纳米颗粒的联合研究。最终目标是了解基本原理，并利用现场辅助烧结的好处，使块体纳米材料的加工和制造成为可能。场辅助处理已经成为当前感兴趣的主题，这是由于在场暴露时出现的新现象，例如微放电，以及由此产生的表面效应和电扩散。在技术上，电场应用有明显的好处：提高烧结率，控制和生产新的微结构，以及灵活的制造能力(近净形状，调制结构)。加州大学戴维斯分校的实验室实验已经成功地利用场辅助烧结技术(FAST)处理了难以烧结的材料，该技术同样适用于陶瓷和金属、复合材料和纳米粉末。ISC开发了一种能够控制微波能量和热流的微波处理(MWP)设施。该系统还可以应用极高的加热速度，这是众所周知的，在粉末烧结过程中抑制颗粒生长。ISC的高灵敏度热光测量(TOM)技术能够监测颈部的形成、接触点化学成分的变化和粉末的致密化。这项研究的目的是研究纳米粉末烧结早期阶段的操作机制，并量化它们与外部电场的相互作用。与德国建立伙伴关系将通过提高纳米粉末加工的知识和预测能力为科学界带来好处。由于这种伙伴关系而可能产生的场效应的量化对于场激活处理的发展至关重要，对研究和教学都有价值。这一合作工作打开的新视角将使研究生更好地为在日益相互依存的世界经济中工作做好准备，并激励本科生攻读博士学位。该NSF项目由设计、制造和工业创新司和国际办公室(西欧)共同资助，作为NSF和欧洲之间在材料研究方面的合作活动(NSF 02-135)。该项目是与德国维尔茨堡的弗劳恩霍夫研究所合作进行的。

This project is a joint study with Fraunhofer Institute Silicatforschung (ISC) in Germany on sintering nanoparticles under the influence of an external electrical field. The final goal is to understand the fundamentals and exploit the benefits of field-assisted sintering to enable the processing and manufacture of bulk nanomaterials. Field-assisted processing has emerged as a topic of current interest due to new phenomena, which occur upon field exposure such as microdischarges, with resultant surface effects and electrodiffusion. Technologically, electrical field application has distinct benefits: enhanced sintering rates, control and production of novel microstructures, and flexible manufacturing capabilities (near net shape, modulated structures). Laboratory experiments at UC Davis have succeeded in processing difficult-to-sinter materials by a field assisted sintering technique (FAST) equally applicable to ceramics and metals, to composites and nanometer size powders. ISC has developed a microwave processing (MWP) facility capable to control the MW energy and heat flow. The system also enables the application of extremely high heating rates, which are known to suppress grain growth during powder sintering. A high sensitivity thermo-optical measuring (TOM) technique at ISC is capable of monitoring neck formation, changes of the chemistry of contact points, and densification of powders. The objective of this proposed research is to study the operative mechanisms in the early stages of sintering of nanopowders and to quantify their interaction with the externally applied fields. Building the partnership with Germany will bring benefits to the scientific community by advancing the knowledge and predictive capability for processing of nanopowders. The quantification of field effects possible due to this partnership is critical to the advancement of field-activated processing and is valuable for both research and teaching. The new perspectives opened by this collaborative work will better prepare graduate students to work in an increasingly interdependent world economy and motivate undergraduate students to pursue doctoral studies. This NSF project is co-funded by the Division of Design, Manufacture, and Industrial Innovation and the International Office (Western Europe) as a Cooperative Activity in Materials Research between the NSF and Europe (NSF 02-135). This project is being carried out in collaboration with the Fraunhofer Institute Silicatforschung (ISC), Wuertzburg, Germany.