| 题名 | 固体氧化物燃料电池密封材料的研究及其断裂分析 |
| 作者 | 张涛 |
| 学位类别 | 博士 |
| 答辩日期 | 2009-05-27 |
| 授予单位 | 中国科学院过程工程研究所 |
| 授予地点 | 过程工程研究所 |
| 导师 | 朱庆山 |
| 关键词 | 固体氧化物燃料电池 玻璃基密封材料 断裂模型 热循环 耐久性 |
| 其他题名 | Development and cracking analysis of the seals for solid oxide fuel cell |
| 学位专业 | 化学工程 |
| 中文摘要 | 固体氧化物燃料电池(SOFC)是一种高效、环境友好的直接将化学能转化成电能的装置，也是绿色能源转化装置的一个重要发展方向。密封材料是平板式SOFC电池堆的关键材料之一，缺乏高性能密封材料是板式SOFC进一步发展面临的最主要瓶颈，密封材料也因此成为国内外SOFC界研发的焦点之一。在各种密封材料中，玻璃是唯一一种具有良好自愈合能力的自适应密封材料，但存在不能同时获得长期热稳定性和CTE匹配性的问题，因此，玻璃以及玻璃基密封材料易于断裂（热应力引起的），不能满足SOFC对密封材料的耐久性和热循环性能的要求。针对上述问题，本文一方面从材料设计的角度对SOFC的密封进行了研究，另一方面，对玻璃基材料的断裂进行分析，以图避免断裂的发生。本文取得了如下的创新性研究结果： （1）针对现有玻璃密封材料难以同时满足SOFC所要求的高热膨胀系数(CTE）和长期热稳定性、化学稳定性、化学相容性等性质的难题，本研究从对BaO-CaO-MgO- B2O3-SiO2系逆性玻璃的微观结构分析入手进行玻璃设计与优化，结果显示影响逆性碱土硼硅酸盐玻璃长期热稳定性的因素主要是[B2O3]/[SiO2]比和碱土金属原子之间的半径比，当[B2O3]/[SiO2]比略小于1，并且原子半径比较大时([rBa/rMg]> [rBa/rCa])，可获得最好的热稳定性。根据建立的设计原则并结合实验研究，开发了G8密封玻璃，G8的转变温度约为582oC, 热膨胀系数为11.4×10-6K-1。经过650oC、5000h热处理之后，G8没有析晶，完全透明，CTE变化小于1.7%，即，它在获得高热膨胀数的同时具有很好的热稳定性。其次，经过湿还原气氛热处理1000h，G8也无明显的失重，体现出良好的化学稳定性。再次，8YSZ-G8封接结构经过650oC、1000h的热处理之后，密封扩散区稳定于1μm的厚度，体现出良好的化学相容性。 （2）G8密封玻璃的循环寿命测试结果显示它在经过8500h、710次热循环的稳定运行之后，仍然保持着完好的状态。G8同时具有长期耐久性及很强的热循环性能，解决了当前玻璃基密封材料不能同时获得长期耐久性和多次热循环的难题。本研究G8密封玻璃在耐久性及热循环性能方面表现优异是因为它具有稳定的微观结构以及合理的密封结构。 （3）针对玻璃复合密封材料的长期CTE稳定性和相间化学相容性问题，我们对相间反应进行了考察。实验结果显示导致CTE变化的相间反应一般由扩散控制，若把扩散驱动力dc/dx降低至很低或等于零，相间反应受到抑制，CTE也就不会发生变化。通过调控玻璃组成降低扩散驱动力，我们得到了具有良好相间相容性、长期CTE稳定性的玻璃复合材料—G9/MgO/3YSZ复合材料。经过800oC空气氛围热处理5000h之后，这种复合材料（同一个样品）的CTE变化率小于3.1%。另外，G9/MgO/3YSZ复合材料的CTE可以根据[MgO]/[3YSZ]摩尔比进行调节使之在11.9~13.0×10-6K-1变动，能实现与被封接材料的完美CTE匹配，解决了目前玻璃基密封材料中存在的CTE匹配性较差的问题。 （4）针对玻璃基密封材料的断裂以及对断裂机理的完整认识的缺失，我们依据经典弯曲梁理论和陶瓷材料的断裂原理分析了玻璃基密封材料的断裂机理，得出了断裂模型(断裂相图)。相图显示断裂不只受到CTE匹配性的影响（传统观点认为，断裂主要由CTE不匹配引起），还与密封层的厚度密切相关。这两种因素共同影响着玻璃基密封材料的断裂行为，为避免断裂，热膨胀系数差异较大时，则需要较小的密封厚度，反之亦然。当热膨胀系数差异、密封层厚度均较小时，密封的可靠性更高。对于一个固定的密封体系来说，存在一个临界厚度，当密封层厚度<临界厚度时，密封材料将不会断裂。断裂模型已被通过实验证实。 （5）根据SOFC玻璃基密封材料的断裂模型和断裂相图，为提高密封的可靠性，我们认为对于密封结构：①金属箔应采用“柔性”结构，它可分为三个区域：密封区1、应变缓冲区和密封区2，应变缓冲区可阻止力的传递，避免密封结构1和2之间的互相影响，能降低密封区的外加应力；②密封材料的CTE应趋近于而略小于最硬层的CTE；③ 应在满足密封过程中形变要求的前提下愈薄愈好，可以低至0.1mm。 |
| 英文摘要 | Solid oxide fuel cell (SOFC) is an energy conversion device, which generates electricity by electrochemically reaction. It has advantages of high energy conversion efficiency, environmentally friendly and so on, and is expected to become a major electric power source in the future. The seal is one of the key materials for planar SOFC stacks. It has become one of the hardest challenges in the development of advance SOFC because of absence of reliable seals. Glass is a unique sealing material because of its self-healing properties. But it is very difficult for designing a sealing glass with both long-term stability and higher CTE. Generally, the sealing glass is prone to crack (due to thermal stresses) during serving and can not meet the requirements of durability and thermal cycle stability. To overcome these problems, firstly, researches on the development of glass-based sealing materials have been carried out, secondly, to avoid cracking, the cracking criterion of the glass-based seal has been analyzed and then a cracking diagram has been established. The main conclusions obtained are listed as follows: (1) It is a challenge for designing a sealing glass with higher coefficient of thermal expansion (CTE), long-term thermal stability, chemical compatibility and chemical stability. To overcome this challenge, the microstructures of invert alkaline earth borosilicate glass have been analyzed, showing that the thermal stability is mainly affected by [B2O3]/[SiO2] ratio and the radius ratio of alkaline earth atoms. The best thermal stability is achieved when the [B2O3]/[SiO2] ratio approaches to but is less than 1 and the radius ratio of alkaline earth atoms is relatively larger. Based on the design principle and experiments, a sealing glass, which is named as G8, has been developed. The transition point, Tg, of G8 is around 582oC, and CTE between room temperature and Tg is about 11.4×10-6K-1. After thermal aging in air at 650 oC for 5000 hours, it does not devitrify, and its CTE varies in the range of 1.7%. It means that the sealing glass G8 has both higher CTE and long-term thermal stability. Furthermore, during thermal aging in H2-H2O(3mol.%) atmosphere, the weight of G8 does not vary with time, showing good chemical stability; after thermal aging in air for 1000 hours, the interface between G8 and 8YSZ is still intact, showing good chemical compatibility. (2) The sealing glass G8 has served at 650 oC for 8500 hours and 710 thermal cycles. After serving, it is still gastight and maintains good self-healing properties. It means that G8 shows both good durability and excellent thermal cycle stability (there is not any sealing material with both good durability and thermal cycle stability reported before). It is because the reasonable design of the microstructures of G8 and the sealing structure. (3) To overcome the problem in long-term CTE stability and chemical compatibility of glass composite seals, the reactions between phases have been studied. The experimental results show that the reactions of the filler phase and the glass phase are mostly controlled by the diffusion. So, the long-term CTE stability and chemical compatibility can be achieved if the diffusion is prevented. A glass, G9, has been designed to prevent the diffusion, and then the glass composite seals of G9/MgO/3YSZ with both long-term CTE stability and good chemical compatibility have been developed. During thermal aging at 800 oC in air for 5000 hours, the CTE of any glass composite seal with fixed compositions varies in the range of 3.1%. Another advantage of the glass composite seals is that the CTE could vary in the range of 11.9~13.0×10-6K-1 throughadjusting [MgO]/[3YSZ] ratio, to match the joined materials. (4) The failure of the glass-based seal is mainly caused by cracking, but the failure mechanism of the seal has not yet been well clarified. A model based on the classical beam bending theory and the fracture theory of ceramic materials has been developed for predicting cracking of the SOFC seals, and then a cracking diagram has been established. The cracking diagram shows that besides the effect of CTE mismatch, cracking of the seal is also significantly influenced by its thickness. To avoid cracking, the thinner seal layer will be needed when is relative larger, and vice versa. For a given sealing system, there exists a critical thickness, below which cracking of the seal will not occur. A seal with less thickness and CTE mismatch between itself and the adjacent layers is more reliable. The model has been validated using experimental data obtained on a sandwich sealing structure consisting of interconnect-seal-interconnect multiple layers. (5) The following principles are proposed for sealing design of SOFC according to the model: a. the metal foil with ‘flexible’ structure, which includes three parts: the part for seal 1, the part for relaxing the strain and the part for seal 2; b. the seal CTE should approach to but be less than that of the stiffest component; c. the seal thickness should be as thin as possible on the premise that the gastight is insured, and the thickness can be as thin as 0.1 mm. |
| 语种 | 中文 |
| 公开日期 | 2013-09-16 |
| 页码 | 144 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.ipe.ac.cn/handle/122111/1308]  |
| 专题 | 过程工程研究所_研究所（批量导入） |
| 推荐引用方式 GB/T 7714 | 张涛. 固体氧化物燃料电池密封材料的研究及其断裂分析[D]. 过程工程研究所. 中国科学院过程工程研究所. 2009. |
| 个性服务 |
| 查看访问统计 |
| 相关权益政策 |
| 暂无数据 |
| 收藏/分享 |
除非特别说明，本系统中所有内容都受版权保护，并保留所有权利。
修改评论