BaO-B2O3-SiO2系中温SOFC密封玻璃的设计与表征
文献类型：学位论文
| 作者 | 彭练 |
| 学位类别 | 博士 |
| 答辩日期 | 2008-06-02 |
| 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 密封玻璃定量设计 密封玻璃 密封玻璃热循环寿命 热循环性能衰减机理 |
| 其他题名 | Sealing Glass Design and Characterization in the BaO-B2O3-SiO2 System for Intermediate-Temperature Planar SOFC Applications |
| 学位专业 | 化学工程 |
| 中文摘要 | 固体氧化物燃料电池（SOFC）是高效、清洁的发电装置，高温“密封”是平板式SOFC（pSOFC）尚未解决的最主要技术难题。玻璃是pSOFC最常用的密封材料，当前的主要问题是基于经验设计的密封玻璃难以同时满足热膨胀系数、粘度、热稳定性和化学相容性等诸多要求，因此发展密封玻璃定量设计方法是pSOFC玻璃类密封材料研发的关键。 本论文针对BaO-B2O3-SiO2玻璃体系，构建了密封玻璃定量设计框架。针对传统的转变温度模型和热膨胀系数模型因没有考虑硼配位数变化而导致预测精度差、无法用于密封玻璃定量设计的问题，本论文提出了通过化学平衡定量计算三种硼结构单元浓度的思路，并据此建立了新的转变温度模型和热膨胀系数模型。研究结果表明，新模型的预测精度远远好于传统模型。通过对玻璃结构进行分析并结合硼三及硼四配位浓度的定量计算，实现了BaO-B2O3-SiO2玻璃体系热稳定区域的理论预测，并且玻璃热稳定性实验结果与理论预测相吻合。在此基础上实现了BaO-B2O3-SiO2玻璃体系热膨胀系数、转变温度及热稳定性的定量设计，得到了优化的密封玻璃。 对优化设计的密封玻璃的封接性能、热膨胀系数、热稳定性和化学相容性等进行了详细表征。结果表明，该玻璃的转变温度为631 oC，封接温度为810 oC，适合在750 oC以下的pSOFC使用。该玻璃的热膨胀系数为9.8 × 10-6 oC-1（室温～Tg），与电解质8YSZ的热膨胀系数匹配良好。化学相容性研究表明，该玻璃在700 oC下与8YSZ接触5000 h后界面没有发现新物相生成，显示了与8YSZ非常好的化学相容性。热稳定性研究表明，该玻璃在700 oC下热处理5000 h后热膨胀系数几乎没有发生任何变化，显示了优异的高温热稳定性。上述综合性能指标，尤其是热稳定性能远优于目前文献公开报道的玻璃类密封材料（如玻璃类密封材料热稳定性最长不过2000 h）。 对新开发的密封玻璃封接pSOFC常用连接体材料－SS410进行了热循环寿命研究。发现随着热循环次数的增加，封接的泄漏速率逐渐增加，至42次热循环时泄漏速率已超过SECA规定的泄漏上限。系统地研究了封接性能衰减机理，发现高温下在密封玻璃/SS410/空气三相界面处因反应而形成了具有高热膨胀系数的BaCrO4相，其在热循环降温过程中因热应力而在封接界面产生的裂纹是封接性能衰减的主要原因，并据此提出且验证了热循环性能衰减机理：三相界面处BaCrO4形成→剥离发生→O2进入→更多BaCrO4形成→剥离延伸→O2进入。据此机理找到了提高密封玻璃热循环寿命的方法－在SS410表面制备涂层阻止界面BaCrO4的形成。研究结果表明在SS410表面制备8YSZ涂层可大幅提高密封热循环寿命。 |
| 英文摘要 | Solid oxide fuel cell (SOFC) is an effective and clean energy conversion device. High temperature sealing is becoming a major obstacle which has not yet been resolved for planar SOFC (pSOFC). Glass materials are the most commonly used sealants for pSOFC. Sealing glasses based “trial and error” method are difficult to meet all the requirements, such as coefficient of thermal expansion (CTE), viscosity, thermal stability and chemical compatibility etc. It is therefore crucial to establish a quantitative design method for the glass development. In the present thesis, a scheme was formulated for quantitative design of sealing glass in the BaO-B2O3-SiO2 system. To realize the design scheme, new Tg and CTE models were first developed through accounting the different contributions of three kinds of B-O structures to the Tg and the CTE of glasses, where the concentrations of the B-O structures was proposed to be quantified through chemical equilibrium calculation. The new models have been validated by experiments better than those of the traditional Tg and CTE models, which have not distinguished the contributions of the different B-O structures. Furthermore, thermal stability of sealing glasses was designed based on the newly developed thermal stable diagram of the BaO-B2O3-SiO2 system, which was established through the analysis of glass structure and the quantification of B(3) and B(4) contents. Validation experiments revealed that the predicated thermal stability results were in accord with the experimental results. Consequently, a sealing glass with desired CTE, Tg and thermal stability was designed and optimized in the BaO-B2O3-SiO2 system. The newly developed sealing glass was subsequently characterized to check its potential to be used as the sealing glass for pSOFC applications. The Tg of the glass was measured to be 631 oC and the glass can keep its shape up to 750 oC, suggesting that the glass is suitable for pSOFC operated below 750 oC. The CTE of the glass was determined to be 9.8 × 10-6 oC-1 (room temperature to Tg), which is very close to that of 8YSZ. Characterization revealed that the sealing glass showed excellent chemical compatibility with 8YSZ, where after being annealed together with 8YSZ at 700 oC for 5000 h, interfacial reaction-induced new phases have not been detected. The glass also exhibited excellent long-term thermal stability, where after being annealed at 700 oC for 5000 h, the CTE change was proved to be marginal. These investigations demonstrated the newly developed sealing glass could meet all the major requirements like Tg, CTE and thermal stability, etc., which is much superior to the current state-of-the-art sealing glasses that normally could only meet one or two requirements. The sealing ability of the glass was tested through measuring the leakage rate of a sealed SS410 chamber. It showed that the initial leakage rate was 4 orders of magnitudes lower than the limit regulated by the SECA program. The lifetime of the seals was further characterized through thermal cyclic tests from 150 oC to 700 oC. It revealed that the leakage rate increased with increasing the number of thermal cycles, where after 42 thermal cycles the leak rate was close to the SECA leakage limit. The degradation mechanism was systematically investigated. It was found that BaCrO4 formed in the three phase boundaries of air/glass/SS410 was responsible for cracking of seal that increases leakage during cooling down from high temperature, owing to the high CTE of BaCrO4. Investigations also revealed that the formation of BaCrO4 was oxygen enhanced, where the formation of BaCrO4 follows the extension of the crack, which causes the penetration of oxygen. Based on these investigations, the degradation mechanism was proposed as: BaCrO4 formation at three phase boundaries → delamination between glass and SS410 → O2 entrance → more BaCrO4 formation → prolongation of delamiantion → O2 entrance. With the understanding of the degradation mechanism, a method was developed to improve the lifetime of the seal under the thermal cyclic conditions, i.e. coating was sprayed on SS410 to prohibit the formation of BaCrO4. The thermal cyclic lifetime has been greatly extended when 8YSZ coating was sprayed on SS410, validating the above-mentioned degradation mechanism. |
| 语种 | 中文 |
| 公开日期 | 2013-09-13 |
| 页码 | 119 |
| 源URL | [http://ir.ipe.ac.cn/handle/122111/1174]  |
| 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 | 彭练. BaO-B2O3-SiO2系中温SOFC密封玻璃的设计与表征[D]. 过程工程研究所. 中国科学院过程工程研究所. 2008. |
入库方式： OAI收割
来源：过程工程研究所
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