High Temperature Reactivity: Methods and Mechanisms

高温反应性：方法和机制

• 批准号: 1005779
• 负责人: Simon Phillpot
• 金额: $ 50万
• 依托单位: University of Florida
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-10-01 至 2013-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1005779&HistoricalAwards=false
• 关键词: Temperature; Reactivity; Methods; Mechanisms

TECHNICAL SUMMARYThe Division of Materials Research and the Office of Cyberinfrastrcture contribute funds to this award. It supports computational research and education to further develop advanced materials simulation methods and to characterize the mechanisms and dynamics of the high-temperature reactive processes associated with the oxidation and hydroxylation in one class of ionic-covalent materials: metallic nitrides. Nitrides are chosen as the focus of this work both as archetypes of high-temperature reactive materials and because of the large amount of available experimental information, largely driven by their wide range of applications.The dynamics of reactive processes at surfaces are often very different at high temperatures than at low temperatures. In some cases, entirely new processes are activated as the thermal energy allows ever higher energy barriers to be overcome. In addition, even well-known low-temperature processes, such as those associated with surface oxidation and hydroxylation, manifest new personas at high temperatures. This is most evident in systems with mixed ionic and covalent bonding, which are largely non-reactive at low temperatures, but become highly reactive at high temperatures.Using a judicious combination of electronic-structure density functional theory calculations, density functional theory-molecular dynamics simulations, and classical, atomistic molecular dynamics and temperature-accelerated dynamics simulations that will be compared to, and validated by, data from experimental collaborators, the PIs will focus on answering three key questions: (1) How does composition and structure control surface reaction mechanisms? (2) How do the surface reactions modify the surface? and (3) How does surface microstructure and stress affect surface reactivity?Atomistic simulations will be facilitated by, and build upon, the PIs previous work by extending the many-body, variable-charge, reactive Charge Optimized Many Body potentials, called COMB potentials, they have previously developed. The PIs will model the chemical processes associated with the reaction of molecular oxygen and water vapor on the nitride surfaces. In particular, the key issues to be examined include adsorption and dissociation of oxygen and/or water molecules on the surfaces, the incorporation of individual oxygen atoms into the surface structure, oxidation of the first atomic layer of the nitride, and diffusion of oxygen through the material. The PIs aim to obtain a systematic atomic-level understanding of the complex processes involved in the development of passivating oxide layers, catastrophic oxidation, and hydroxylation processes. In addition, the research will provide the foundational understanding needed for the development of systematic approaches to the mitigation of these degradation processes, key to the further exploitation of this class of materials at high temperatures. The continued development of the COMB methodology will firmly establish it as a powerful method for the simulation of systems in which metals, ionics, semiconductors and gaseous phases coexist and interact both physically and chemically. This will open up a large number of physio-chemical problems involving the chemical degradation of a wide range of materials to investigation with atomistic methods. Among these problems are: oxidation of nitride nuclear fuels, complex chemistries involving oxygen and nitrogen for fossil fuel application, catalysis, corrosion, and protection against hot corrosion and thermal oxidation of alloys. The PIs will visit colleges and universities in the Southeast, especially Historically Black Colleges and Universities and Hispanic-serving institutions, to discuss the graduate program in Materials Science and Engineering at the University of Florida in general, and their computational program in particular. They will disseminate implementations of the COMB framework in well-known computer codes for lattice statics and molecular dynamics simulations, respectively. The PIs will also bring together the community working on reactive potentials in an MRS Symposium and a symposium at the Fall MS&T meeting. The PIs intend for the MRS activity to be accompanied by a one-day tutorial program aimed primarily at graduate students and postdocs. NONTECHNICAL SUMMARYThe Division of Materials Research and the Office of Cyberinfrastrcture contribute funds to this award. It supports computational research and education to develop advanced computer simulation tools and to apply them to study materials at high temperatures. The computational tools will be able to simulate materials at the atomic level and include not only physical processes but chemical processes as well. This is a challenge in computational materials research. Materials can behave quite differently at temperatures well above room temperature. For example, some materials are strong and seemingly inert in their environment at room temperature, but at the elevated temperatures typical inside, say, aircraft engines they may oxidize and degrade rapidly. The PIs will use their advanced simulation tools to understand reactions that occur on the surfaces of materials and how they affect the surfaces of materials. They will focus on classes of materials that are well studied in the laboratory and have technological applications. These include some metallic nitrides that are used to make hard coatings on cutting tools and machine parts and for hard coatings on prosthetic hips.The PIs will disseminate computational tools developed under NSF support through computer code packages for materials simulation that are popular in the materials research and other scientific communities. The PIs will also disseminate information about their simulation tools by bringing the materials simulation community together through professional society meetings that will include tutorial programs for graduate students and postdocs. The PIs will visit colleges and universities in the Southeast, especially Historically Black Colleges and Universities and Hispanic-serving institutions, to discuss the graduate program in Materials Science and Engineering at the University of Florida in general, and their computational program in particular.

技术摘要材料研究部和网络基础设施办公室为该奖项提供资金。它支持计算研究和教育，以进一步开发先进的材料模拟方法，并表征与一类离子共价材料（金属氮化物）氧化和羟基化相关的高温反应过程的机制和动力学。选择氮化物作为本工作的重点，既是高温反应材料的原型，也是因为大量可用的实验信息，主要是由于它们的广泛应用。表面反应过程的动力学在高温下往往与低温下大不相同。在某些情况下，由于热能允许克服更高的能量障碍，全新的过程被激活。此外，即使是众所周知的低温过程，如与表面氧化和羟基化有关的过程，在高温下也会表现出新的特征。这在离子和共价键混合的体系中最为明显，这些体系在低温下基本上不反应，但在高温下变得高度反应。利用电子结构密度泛函理论计算、密度泛函理论-分子动力学模拟、经典原子分子动力学和温度加速动力学模拟（将与实验合作者的数据进行比较和验证）的明智组合，pi将重点回答三个关键问题：(1)组成和结构如何控制表面反应机制？(2)表面反应是如何修饰表面的？(3)表面微观结构和应力如何影响表面反应性？通过扩展他们之前开发的多体、可变电荷、反应电荷优化多体电位（称为COMB电位），原子模拟将得到促进，并建立在PIs先前工作的基础上。pi将模拟与氮化物表面分子氧和水蒸气反应有关的化学过程。特别是，要检查的关键问题包括表面上氧和/或水分子的吸附和解离，单个氧原子与表面结构的结合，氮化物第一原子层的氧化，以及氧气在材料中的扩散。PIs的目标是获得系统的原子水平的复杂过程的理解，涉及到钝化氧化层，灾难性氧化和羟基化过程的发展。此外，该研究将为开发系统方法以减轻这些降解过程提供必要的基础理解，这是在高温下进一步开发这类材料的关键。COMB方法的持续发展将使其成为模拟金属、离子、半导体和气相共存并在物理和化学上相互作用的系统的有力方法。这将开辟大量的物理化学问题，涉及到广泛的材料的化学降解，以原子方法进行研究。这些问题包括：氮化核燃料的氧化、化石燃料应用中涉及氧和氮的复杂化学、催化、腐蚀以及防止合金的热腐蚀和热氧化。pi将访问东南部的学院和大学，特别是历史上的黑人学院和大学以及西班牙裔服务机构，讨论佛罗里达大学材料科学与工程的研究生课程，特别是他们的计算课程。他们将分别在晶格静力学和分子动力学模拟的知名计算机代码中传播COMB框架的实现。pi还将在MRS研讨会和秋季MS&amp；T会议上召集从事反应电位研究的社区。pi计划MRS活动伴随着一天的指导计划，主要针对研究生和博士后。材料研究部和网络基础设施办公室为该奖项提供资金。它支持计算研究和教育，以开发先进的计算机模拟工具，并将其应用于高温下的材料研究。计算工具将能够在原子水平上模拟材料，不仅包括物理过程，也包括化学过程。这是计算材料研究中的一个挑战。在远高于室温的温度下，材料的行为会大不相同。例如，一些材料在室温下很坚固，看起来是惰性的，但在飞机发动机内部的高温下，它们可能会迅速氧化和降解。pi将使用他们先进的模拟工具来了解发生在材料表面的反应以及它们如何影响材料表面。他们将专注于在实验室中得到充分研究并具有技术应用的材料类别。其中包括一些金属氮化物，用于在切削工具和机器部件上制造硬涂层，以及用于假体髋关节的硬涂层。pi将通过在材料研究和其他科学界流行的材料模拟计算机代码包，传播在NSF支持下开发的计算工具。pi还将通过专业协会会议（包括研究生和博士后的指导计划）将材料模拟社区聚集在一起，传播有关其模拟工具的信息。pi将访问东南部的学院和大学，特别是历史上的黑人学院和大学以及西班牙裔服务机构，讨论佛罗里达大学材料科学与工程的研究生课程，特别是他们的计算课程。