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

本项目是与德国弗劳恩霍夫硅酸盐研究所（ISC）共同研究在外加电场影响下烧结纳米颗粒。最终目标是了解基本原理，并利用场辅助烧结的好处，使大块纳米材料的加工和制造成为可能。现场辅助加工已经成为当前人们感兴趣的话题，因为在现场暴露时发生的新现象，如微放电，以及由此产生的表面效应和电扩散。从技术上讲，电场的应用有明显的好处：提高烧结速度，控制和生产新的微观结构，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通过场辅助烧结技术（FAST）处理了难以烧结的材料，这种技术同样适用于陶瓷和金属，复合材料和纳米尺寸的粉末。ISC开发了一种能够控制兆瓦能量和热流的微波处理（MWP）设备。该系统还可以应用极高的加热速率，这是已知的抑制粉末烧结过程中的晶粒生长。ISC的高灵敏度热光学测量（TOM）技术能够监测颈部的形成、接触点的化学变化和粉末的致密化。本研究的目的是研究纳米粉体烧结初期的运行机制，并量化其与外界电场的相互作用。与德国建立伙伴关系将通过推进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，可能对场效应进行量化，这对推进场激活处理至关重要，对研究和教学都很有价值。这项合作工作开辟的新视角将更好地为研究生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。本项目是由设计、制造和工业创新处和国际办公室（西欧）作为美国国家科学基金会与欧洲材料研究合作项目（NSF 02-135）共同资助的。该项目是与德国维尔茨堡的弗劳恩霍夫硅酸盐研究所（ISC）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.