太阳能吸热器用β-Sialon/Si3N4复相陶瓷材料的研究

Study on β-Sialon/Si2N4Composite Ceramics for Solar Heat Absorber

作者: 专业:材料学 导师:吴建锋 年度:2014 学位:硕士  院校: 武汉理工大学

关键词
β-Sialon β-Sialon/Si3N4复相陶瓷 太阳能热发电 吸热体材料

Keywords
β-Sialon, β-Sialon/Si3N4composite ceramics, Solar thermal generation, Heat absorber material, Foam ceramic, Thermal shock resistance, Oxidationresistance, Microstructure and properties
        太阳能储量大、分布广泛,是开发和应用潜力最大的清洁能源,近年来成为国内外研究的热点。太阳能热发电是太阳能利用的重要方式,是最具发展空间和应用前景的太阳能利用技术。本课题以国家"973计划”为依托,针对目前塔式太阳能热发电系统中吸热体材料的需求,展开了高性能吸热体材料的研究。本文以α-Si3N4、AIN和各种含铝矿物为主要原料,采用无压、埋粉烧结法,设计并制备了用于塔式太阳能热发电吸热体材料的β-Sialon以及β-Sialon/Si3N4复相陶瓷。探讨了不同金属氧化物和稀土氧化物作为烧结助剂对样品结构和性能的影响。测试了烧成样品的吸水率、气孔率、体积密度、烧成收缩、抗折强度、抗热震性、抗氧化性以及相组成和微观结构测试。探讨了样品组成、制备工艺、微观结构和性能之间的关系。重点研究了影响样品抗热震性能和抗氧化性能的因素,探讨了样品抗热震和抗氧化机理。主要研究成果如下:(1)以α-Si3N4、煅烧铝矾土和AlN为主要原料,添加MgO和Y2O3为烧结助剂,设计了C系列配方。实验发现,MgO和Y2O3的助烧作用显著,C1-C4样品均按预期合成了Z值从1到4的β-Sialon。经1560℃烧成C2样品(62.17wt%Si3N4、28.71wt%煅烧铝矾土、9.12wt%AlN、外加5wt%MgO和3wt%Y2O3)的性能最优。样品吸水率为7.38%,气孔率为19.22%,体积密度为2.61g·cm-3,抗折强度为88.43MPa,热膨胀系数为6.64×10-6℃-1(室温~900℃),室温导热系数为5.56W/m·K。样品的相组成为镁铝尖晶石(MgAl2O4)、β-Sialon、 α-Si3N4和β-Si3N4。研究表明,随着Z值增大,β-Sialon晶体尺寸增大,结构疏松。当Z=2时,β-Sialon具有较高的强度和良好的高温稳定性,含量越高,样品的强度和抗热震性能越好。(2)为进一步提高样品的强和度致密度,在C2基础上,采用Y2O3、La2O3和硼砂为烧结助剂设计了D系列配方。研究表明,经1580℃烧成D2样品(62.17wt%Si3N4、28.71wt%煅烧铝矾土、9.12wt%AIN、外加3wt%Y2O3和3wt%La2O3)性能最佳,吸水率为3.33%,气孔率为9.45%,体积密度为2.84g·cm"3,抗折强度为160.73MPa,热膨胀系数(室温~900℃)为6.06×10-6℃-1,室温导热系数为7.8W/m·K。经1300℃氧化100h后样品的增重率为25.56mg·cm-2。样品强度和高温性能较C2有了很大提高。D2样品的相组成为β-Sialon、β-Si3N4和刚玉。微观结构致密,气孔少且分布均匀,样品综合性能优于C2。(3)抗热震机理研究表明,样品中生成大量β-Sialon,与Si3N4紧密结合,赋予样品高的致密度、强度和导热性能,保证样品在热震过程中不会产生过大的表面张应力而发生破坏。样品抗热震性能优异,经30次热震循环实验后(室温~1100℃)C2和D2样品完好,抗折强度比热震前有不同程度的提高。抗氧化机理研究表明,β-Sialon/Si3N4复相陶瓷具有良好的抗氧化性能,氧化过程属于“钝化氧化”。样品的致密度高,氧气扩散进入其内部的速率较小。β-Sialon和Si3N4氧化后在样品表面形成致密的石英和莫来石层,随着时间的延长,氧化物层增厚,氧化速率减慢,符合抛物线增长规律。(4)以D2为粉料配方,加入各种添加剂配制陶瓷料浆,采用前驱体浸渍法制备了β-Sialon/Si3N4复相泡沫陶瓷。经154℃C烧成E2样品的气孔率为82.55%、抗压强度为0.89MPa。经30次热震后(室温~1100℃)样品外观完好,满足国标GB/T25139-2010对泡沫陶瓷的要求。XRD分析表明E2具有与D2相同的相组成。SEM分析表明,样品筋骨粗壮,气孔发育完好,以连通气孔为主,保证空气在其中的顺畅流通,三维连通的结构赋予样品高的换热效率。适合用作塔式太阳能热发电系统的吸热体材料。
    Since solar energy is huge reserves, broad distribution, it is generally considered as one of the clean and renewable energy. In recent years, it has been researched by many scholars at home and abroad. Solar thermal power generation is an important way for utilization of solar energy. It has been known as the most potential method for the development and application of solar energy. This topic is based on the national "973Program", according to the present needs of heat-absorber materials in the solar thermal power generation system, researching the heat-absorber materials with high performance.In this paper,β-Sialon and β-Sialon/Si3N4composite ceramics used for solar thermal power generation were designed and prepared with the method of pressureless sintering and the main raw materials of α-Si.3N4, AN and different aluminum-containing compounds. The effects of different metal oxides and rare earth oxides as sintering aids on the sintering process and integrated performance were discussed. The water absorption, porosity, bulk density, firing shrinkage, flexural strength, thermal shock resistance and oxidation resistance were tested. Phase composition and microscopic morphology were tested and analysised with modern techniques such as XRD and SEM. Relationships between sample formula composition, processing technology, microstructure and properties were discussed. The mechanism of thermal shock resistance and oxidation resistance properties of samples were studied. The main results of the research are as follows:(1) Using a-Si3N4, calcined bauxite, AlN as main raw materials and MgO, Y2O3as sintering aids, C series formula was designed. The experiment results show that the effect of MgO and Y2O3is remarkable. β-Sialon with Z values range from1to4are synthesized as expected in C1~C4samples. C2sample (62.17wt%Si3N4,28.71wt%calcined bauxite,9.12wt%AN, plus5wt%MgO and3wt%Y2O3) has better performance after firing at1560℃. Water absorption is7.38%, porosity19.22%, bulk density2.61g·cm-3, the flexural strength88.43MPa. The thermal expansion coefficient is6.64×10-6℃-1(RT~900℃), thermal conductivity is5.56W/m·K at room temperature. The phase compositions of C2sample are MgAl2O4, β-Sialon, α-Si3N4 and β-Si3N4. Research shows that with the increase of Z value, the size of β-Sialon increase, structure loose. When Z=2, β-Sialon has high strength and good thermal stability, the higher content of β-Sialon is, the better strength and thermal shock resistance of the sample have.(2) In order to achieve higher strength and density, D series was designed on based of C2formula with Y2O3, La2O3and borax as sintering aids. The results show that, D2sample (62.17wt%Si3N4,28.71wt%calcined bauxite,9.12wt%AN, plus3wt%Y2O3and3wt%La2O3) has better performance after firing at1580℃. Water absorption is3.33%, porosity9.45%, bulk density2.84g·cm-3, the160.73MPa. The thermal expansion coefficient (RT~900℃) is6.06×10-6℃-1,thermal conductivity is7.8W/m-K at room temperature. After100h oxidation experiment at1300℃, the weight gain rate of the sample is25.56mg·cm-2. The crystal phases of D2sample are β-Sialon, β-Si3N4and corundum. D2has dense microstructure, less and evenly distributed porosity, so it has more comprehensive performance than C2.(3) Mechanism investigation of thermal shock resistance shows that the sample has high thermal conductivity, density and strength because of the generation of β-Sialon and its connection with Si3N4, decreasing the tensile stress on the surface of the sample during the process of thermal shock cycles, which may damage the sample. The sample has excellent thermal shock resistance, after30times’ thermal shock (RT~1100℃), the bending strength of C2and D2samples increased comparied with the initial samples. Mechanism of oxidation resistance shows that β-Sialon/Si3N4composite ceramic has good oxidation resistance performance. The process of oxidation belongs to the passivation oxidation. The diffusion rate of oxygen into the internal is slower because of its high density. There exists dense surface layer of quartz and mullite because of the oxidation of β-Sialon and Si3N4, and the thicker the surface layer is, the lower oxidation rate the sample has. It is complying with the parabolic law.(4) β-Sialon/Si3N4composite foam ceramic was prepared by precursor impregnation method, using D2as the powder formula, adding adhesive, rheological agent, defoaming agent and so on. After firing at1540℃, the porosity of sample is82.55%, compressive strength0.89MPa. After30times’ thermal shock (RT~1100℃), the appearance of sample is intact, meetting the requirements of the national standard GB/T25139-2010. XRD results show that the phase composition of E2sample is the same as D2. SEM results show that E2sample has connected and thick pores. It guarantees the smooth circulation of air and three-dimensional connecting structure, which ensure the higher efficiency of heat exchange. It is suitable for the absorber material of solar tower thermal power generation system.
        

太阳能吸热器用β-Sialon/Si_3N_4复相陶瓷材料的研究

摘要4-6
Abstract6-8
第1章 绪论11-26
    1.1 本课题研究的目的和意义11-14
    1.2 国内外相关研究进展及发展趋势14-24
        1.2.1 太阳能吸热体材料的研究进展和发展趋势14-16
        1.2.2 Sialon陶瓷的研究进展和发展趋势16-19
        1.2.3 Si_3N_4陶瓷的研究进展和发展趋势19-22
        1.2.4 Sialon基复相陶瓷材料的研究进展和发展趋势22-23
        1.2.5 泡沫陶瓷的研究进展和发展趋势23-24
    1.3 本课题研究的主要内容24-26
第2章 β-Sialon陶瓷的制备、结构与性能研究26-57
    2.1 实验26-34
        2.1.1 样品的制备26-29
        2.1.2 样品的结构与性能表征29-34
    2.2 结果分析与讨论34-55
        2.2.1 影响样品烧成收缩率的因素34-36
        2.2.2 影响样品吸水率、气孔率和体积密度的因素36-38
        2.2.3 影响样品抗折强度的因素38-39
        2.2.4 影响样品重烧收缩的因素39-40
        2.2.5 样品相组成分析40-42
        2.2.6 样品微观结构研究42-47
        2.2.7 影响样品热膨胀系数的因素47
        2.2.8 样品热导率、比热容和导温系数分析47-48
        2.2.9 样品抗热震机理探讨48-55
    2.3 本章小结55-57
第3章 β-Sialon/Si_3N_4复相吸热陶瓷的致密化途径及抗热震和抗氧化机理57-91
    3.1 实验57-62
        3.1.1 样品的制备57-60
        3.1.2 样品的结构与性能表征60-62
    3.2 结果分析与讨论62-89
        3.2.1 影响样品烧成收缩率的因素62-64
        3.2.2 影响样品吸水率、气孔率和体积密度的因素64-67
        3.2.3 影响样品抗折强度的因素67-69
        3.2.4 样品致密化机理探讨69-70
        3.2.5 影响样品重烧收缩的因素70-71
        3.2.6 样品抗热震机理探讨71-78
        3.2.7 影响样品热膨胀系数的因素78-79
        3.2.8 样品热导率、比热容和导温系数分析79-80
        3.2.9 样品抗氧化机理探讨80-82
        3.2.10 样品相组成分析82-84
        3.2.11 样品微观结构研究84-89
    3.3 本章小结89-91
第4章 塔式太阳能吸热器用β-Sialon/Si_3N_4复相泡沫陶瓷的制备与研究91-102
    4.1 实验91-94
        4.1.1 前驱体及添加剂的选择91-92
        4.1.2 样品的制备92-94
    4.2 样品的结构与性能分析94-100
        4.2.1 泡沫陶瓷气孔测定与分析94-95
        4.2.2 泡沫陶瓷抗压强度测定与分析95-97
        4.2.3 泡沫陶瓷相组成分析97-98
        4.2.4 泡沫陶瓷宏观和微观结构分析98-99
        4.2.5 泡沫陶瓷抗热震性能分析99-100
    4.3 本章小结100-102
第5章 全文结论及展望102-104
    5.1 全文结论102-103
    5.2 本研究的创新点103
    5.3 下一步工作建议103-104
参考文献104-109
致谢109-110
攻读硕士学位期间发表的论文及参与的科研项目110


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