Mixed Alkali Effect for Mitigation of Sodium-Accelerated Corrosion of Silicon Nitride Ceramics

混合碱效应减缓氮化硅陶瓷钠加速腐蚀

• 批准号: 0102340
• 负责人: Henry Du
• 金额: $ 24万
• 依托单位: Stevens Institute of Technology
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-06-01 至 2004-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0102340&HistoricalAwards=false
• 关键词: Mixed; Alkali; Effect; Mitigation; Sodium

0102340DuThis project is proposed to study the mixed alkali effect (MAE) in the corrosion behavior of Kyocera's SN282, a turbine-grade Si3N4 ceramic, and chemically vapor deposited Si3N4 in oxygen environments containing single alkali (sodium, cesium) and mixed alkali (sodium and cesium) elements. It aims to reveal the potential and establish the understanding of MAE in high-temperature corrosion retardation of Si3N4 ceramics. Questions that will be answered include: (1) Will the incorporation of Na and Cs in the oxide layer on Si3N4 be mutually retarded compared to a single alkali (Na or Cs) situation, and if so, what is the quantitative correlation? (2) How will the corrosion kinetics (rate and activation energy) and oxide characteristics (composition, phase, morphology, and structure) compare under mixed alkali and single alkali conditions? (3) Is MAE in corrosion a function of alkali ratio (e.g., [Na]/[Cs]) in the oxide and in the environment? (4) Do corrosion minima exist at some alkali composition(s)? (5) How will MAE affect the corrosion mechanism? And (6) What are the effects, if any, of the additive and impurity cations in SN282 on (1)-(5)? The objectives of the project will be achieved by evaluating the corrosion kinetics of Si3N4 in O2-NaNO3, O2-CsNO3, and O2-NaNO3-CsNO3 gas mixtures of selected compositions over a broad temperature range and by characterizing the oxide layers using various analytical tools. %%%The susceptibility of silica-forming ceramics to hot corrosion by sodium salts remains a severe roadblock to the exploitation of ceramic benefits in advanced gas turbine engines and other structural applications. A critical need exists to search for means to mitigate the corrosion problem in order for the realization of their projected applications. This project aims to explore the mixed alkali effect (MAE) in silicate glasses for corrosion retardation of silicon nitride ceramics in sodium-containing environments. MAE refers to the pronounced, non-linear changes in many properties of a glass when a dissimilar alkali oxide is added. The premise of the proposal rests on two known facts. First, sodium-accelerated corrosion of silicon nitride results from the dissolution of the oxidation layer through sodium incorporation. Second, MAE lowers the alkali activity and reduces alkali diffusivity in silicates by 2 to 6 orders of magnitude. This project represents the first known attempt to use the MAE concept to address sodium-accelerated corrosion of silica-forming ceramics. It will yield rich kinetic and analytical information on and insights into MAE in high-temperature corrosion of Si3N4. The knowledge generated will provide the design and user communities with the scientific basis for practical exploitation of MAE for corrosion retardation and durability improvement of silica-forming ceramics for advanced turbine engines and other demanding applications where they would otherwise be unsuitable.

本项目旨在研究京瓷SN282(涡轮级氮化硅陶瓷)和化学气相沉积氮化硅陶瓷在含单一碱(钠、铯)和混合碱(钠和铯)元素的氧气环境中的腐蚀行为中的混合碱效应(MAE)。旨在揭示MAE在Si3N4陶瓷高温缓蚀中的潜力，并建立对MAE的认识。要回答的问题包括：(1)与单一碱(Na或Cs)情况相比，Na和Cs在Si3N4上的氧化层中的结合是否相互抑制，如果是，定量相关性是什么？(2)在混合碱和单一碱条件下，腐蚀动力学(速率和活化能)和氧化物特性(成分、物相、形态和结构)将如何比较？(3)在腐蚀中MAE是碱比例的函数(例如，[Na]/[Cs])在氧化物和环境中？(4)某些碱成分是否存在腐蚀极小值(S)？(5)MAE会如何影响腐蚀机理？以及(6)如果有的话，SN282中的添加剂阳离子和杂质阳离子对(1)-(5)有什么影响？该项目的目标将通过评估Si3N4在选定组成的O2-NaNO3、O2-CsNO3和O2-NaNO3-CsNO3混合气体中的宽温度范围内的腐蚀动力学，并通过使用各种分析工具表征氧化层来实现。%二氧化硅形成的陶瓷对钠盐热腐蚀的敏感性仍然是在先进的燃气轮机发动机和其他结构应用中开发陶瓷优势的严重障碍。迫切需要寻找缓解腐蚀问题的方法，以便实现其预期的应用。本项目旨在探索硅酸盐玻璃中的混合碱效应(MAE)在含钠环境中对氮化硅陶瓷的缓蚀作用。MAE是指当加入不同的碱氧化物时，玻璃的许多性质发生显著的、非线性的变化。这项提议的前提是两个已知的事实。首先，钠加速氮化硅的腐蚀是由于钠的掺入使氧化层溶解所致。其次，MAE降低了硅酸盐中的碱活度，使碱扩散系数降低了2~6个数量级。该项目是已知的第一次尝试使用MAE概念来解决二氧化硅形成陶瓷的钠加速腐蚀问题。这将提供关于Si3N4高温腐蚀过程中MAE的丰富的动力学和分析信息和见解。所产生的知识将为设计和用户群体提供实际开发MAE的科学基础，用于先进涡轮发动机的二氧化硅形成陶瓷的防腐和耐久性改进，以及其他要求苛刻的应用，否则它们将不适用。