Gas Phase Combustion Synthesis of Nanopowders, Modeling and Processing Duplex Microstructures

非技术描述：金属氧化物纳米粉末在包括记录介质、催化剂、塑料填料或形成陶瓷假体（髋关节置换术）在内的应用中发挥着重要作用。大多数商用纳米粉末是通过火焰处理挥发性、有毒和污染的金属氯化物制成的。密歇根大学（UM）的研究人员已经开发出一种工艺，可以避免金属氯化物提供相同的产品，同时大大增加了可获得的氧化物的数量和类型。这种方法产生了金属氧化物纳米粉末，提供了新的激光行为；作为汽车和柴油废气清理的新催化剂，以及为具有特殊控制最终性能的假体陶瓷提供便捷的途径。UM工艺使用湍流火焰燃烧溶解在醇中的金属有机络合物（不是氯化物）。尽管制造了独特的材料，但燃烧产生金属离子并凝结成核的确切过程尚不清楚，这些金属离子凝聚成主要的动力学产物颗粒。考虑到这一过程在创造新型纳米材料方面的巨大潜力，UM的研究人员正在进行包括计算机建模在内的基础研究，以描绘颗粒形成的步骤，以确定纳米粉末形成的科学原理。然后，这些原理将用于设计合成新的纳米粉末，用于催化剂、具有可控/新颖性能的陶瓷材料（例如透明陶瓷或锂电池电解质）。技术细节：UM开发的液体进料火焰喷雾热解（LF-FSP）提供了多种单一和混合金属氧化物纳米粉末，这些纳米粉末通常是动力学相，而不是在大多数其他纳米颗粒合成中观察到的热力学相。它们表现出独特的催化、光子、电子和离子导电特性。LF-FSP使用湍流火焰而不是层流火焰。层流火焰很容易建模，而湍流火焰就不那么容易了。因此，大多数UM的发现都来自经验性的努力。UM的研究人员认为，建立对LF-FSP工艺的科学基础的详细了解，将为其在提供具有新特性的新型纳米粉末方面的应用提供基础，特别是在催化剂、光子材料和致密陶瓷材料的低温加工方面。Laine和Violi团队合作开发了一个预测模型，该模型可以确定特定的加工参数（例如温度）如何影响纳米粉末的尺寸和化学成分。模型的开发是由实验技术指导和验证的。特别是，他们将探索在热力学相场之外的成分中尖晶石相材料MOAl2O3 （M = Mg, Co， Ni等）的形成。控制这些纳米粉末形成的工艺变量正在被深入评估，以建立在建模研究中使用的工艺-性能关系。预期的结果需要对多种实际应用的新型纳米粉末的控制方法。这两个小组所做的研究正被用于培养研究生和本科生在纳米粉末的设计、合成、表征和加工（和处理）方面的能力。在本科阶段，来自本科研究机会计划（UROP）的学生正在与研究生一起学习如何使用多种光谱工具表征纳米粉末，绘制属性并使用表征数据开发形成过程的理论模型和控制材料/纳米粉末形成的方法。

NON-TECHNICAL DESCRIPTION: Metal oxide nanopowders play major roles in applications including recording media, catalysts, as fillers for plastics, or for forming ceramic prosthetics (hip replacements). Most commercial nanopowders are made by flame processing volatile, toxic and polluting metal chlorides. Researchers at the University of Michigan (UM) have developed a process that escapes metal chlorides furnishing the same products while greatly expanding the number and types of oxides accessible. This approach has generated metal oxide nanopowders that offer novel lasing behavior; act as new catalysts for auto and diesel exhaust cleanup as well as providing facile routes to prosthetic ceramics with exceptional control of final properties. The UM process uses turbulent flames to combust metal-organic complexes (not chlorides) dissolved in alcohols. Despite the unique materials made, the exact process(es) whereby combustion generates metal ions that condense to form nuclei, which coalesce to form particles primarily of kinetic products are unknown. Given the considerable potential of this process for creating novel nanomaterials, researchers at UM are conducting basic studies including computer modeling to delineate the steps involved in particle formation to identify the scientific principles whereby nanopowders form. These principles will then be used to design the synthesis of new nanopowders for applications including catalysts, ceramic materials with controlled/novel properties including for example transparent ceramics or lithium battery electrolytes.TECHNICAL DETAILS: Liquid feed flame spray pyrolysis (LF-FSP), as developed at UM, provides a wide variety of single and mixed-metal oxide nanopowders that are often kinetic rather than the thermodynamic phases observed in most other nanoparticle syntheses. They have been shown to exhibit unique catalytic, photonic, electronic and ion conducting properties. LF-FSP uses a turbulent rather than a laminar flow flame. While laminar flow flames are easily modeled, turbulent flames are much less so. Consequently, most of the UM discoveries arise from empirical efforts. Researchers at UM believe that establishing a detailed understanding of the scientific underpinnings to LF-FSP processing will provide the basis for greatly expanding its utility in providing new nanopowders with novel properties especially for catalysts, photonic materials and in low temperature processing of dense, ceramic materials. The Laine and Violi groups have teamed together to develop a predictive model that identifies how specific processing parameters (e.g., temperature) contribute to the size and chemical composition of nanopowders. The model development is being guided and validated by the experimental techniques. In particular, they will explore the formation of spinel phase materials MOAl2O3 (M = Mg, Co, Ni, etc.) at compositions outside thermodynamic phase fields. The process variables that control the formation of these nanopowders are being assessed incisively to establish processing-property relationships of use in the modeling studies. The expected outcome entails controlled approaches to novel nanopowders for multiple practical applications. Research done in both groups is being used to train graduate and undergraduate students in the design, synthesis, characterization and processing (and handling) of nanopowders. At the undergraduate level, students from the undergraduate research opportunity program (UROP) are working with graduate students to learn how to characterize nanopowders using multiple spectroscopic tools, to map properties and to use the characterization data to develop theoretical models of the formation processes and methods of controlling what materials/nanopowders form.