【作者】 罗志伟；

【导师】 卢安贤；

【作者基本信息】 中南大学 ， 材料科学与工程， 2013， 博士

【摘要】 摘要：氧氮玻璃是氧化物玻璃(如硅酸盐玻璃、硼酸盐玻璃和磷酸盐玻璃等)网络中的部分氧原子被氮原子取代后获得的一类高性能玻璃。与普通氧化物玻璃相比,氧氮玻璃的转变温度、显微硬度、抗弯强度、弹性模量、断裂韧性和折射率等都显著提高,而热膨胀系数明显降低。由于氧氮玻璃具有上述优异性能,其在许多领域有着潜在的应用,如：电脑硬盘的高弹性模量玻璃、陶瓷用封接玻璃、金属涂层、长期存储核废料的封装玻璃、高温应用的高电阻率涂层、玻璃纤维、透明装甲用防弹玻璃等。同时,将氧氮玻璃进行热处理可制备出含特定晶相的氧氮微晶玻璃,这是一种非常有前景的氧化物-氮化物复合材料。其中,原位生长β-Si3N4增强微晶玻璃因具有优良的综合高温力学性能(如高温抗弯强度、高温断裂韧性及抗热冲击性等)而成为近年来材料科学与工程领域的研究热点。本论文选取氧氮玻璃、氧氮微晶玻璃及Si3N4基微晶玻璃复合材料为研究对象。利用示差量热扫描分析(DSC)、X射线衍射(XRD)、扫描电镜(SEM)结合能谱分析(EDS)、红外光谱(IR)等手段研究了氧氮玻璃的成形与制备技术,探索了稀土掺杂和氮含量与氧氮玻璃的结构、热学性能和力学性能间的相关性,考察了化学组成和热处理工艺对氧氮微晶玻璃和Si3N4基微晶玻璃复合材料显微结构和力学性能的影响。获得如下主要研究结果：以Y2O3、La2O3、CaCO3、Al2O3、SiO2、AlF3·3H2O和Si3N4等为原料,使用通氮气保护的真空电阻炉,采用熔体冷却法,在相对较低的温度下(1550-1650℃)成功制备了半透明且无缺陷的RE-Ca-Si-Al-O-N (RE=Y, La)体系大块氧氮玻璃,并获得其大致玻璃形成范围。采用XRD分析方法验证了Y-Ca-Si-Al-O-N样品的玻璃非晶态特征,并利用IR光谱分析了玻璃的基本结构单元。研究了N含量和Y含量对氧氮玻璃的密度、玻璃转变温度、热膨胀系数、析晶峰温度、化学稳定性和维氏显微硬度的影响。结果表明,玻璃的上述性能随N含量或Y含量的变化近似于呈现线性变化趋势。研究了La-Ca-Si-Al-O-N体系氧氮玻璃中La/Ca比和N/O比对玻璃密度、热膨胀系数、玻璃转变温度、析晶峰温度、维氏显微硬度、抗弯强度和化学稳定性的影响。发现N和La对玻璃性能的影响是相互独立和叠加的,讨论了与此相应的性能与结构之间的依从关系。对比研究了La和Y对氧氮玻璃的热膨胀系数、玻璃转变温度、析晶温度、维氏显微硬度以及抗弯强度等性能的不同影响。研究表明,玻璃性能与La或Y含量呈现近似的线性关系,但Y对玻璃的结构和性能的影响比La更大；利用阳离子场强(CFS)讨论了引入La或Y对玻璃结构与性能所产生的不同影响。研究了氮含量对Y-Ca-Si-Al-O-N系氧氮玻璃析晶行为的影响。通过测量玻璃样品的DSC曲线确定了合适的微晶化热处理制度与特征温度。结果表明,N的引入提高了基础氧氮玻璃的玻璃转变温度和析晶峰温度。XRD和SEM分析结果表明,N含量对微晶玻璃的析晶产物、显微结构、晶粒尺寸和晶体分布产生了较大的影响,从而导致微晶玻璃的力学性能也有较大的变化。成功制备了Y-Si-Al-O-N-F氧氮微晶玻璃。采用XRD结合能谱分析(EDS)鉴定氧氮微晶玻璃中的晶相成分,利用扫描电镜(SEM)观察微晶玻璃样品的微观形貌。研究结果表明：F的的增加降低了玻璃的玻璃转变温度和析晶峰温度,并影响微晶玻璃的微观结构以及晶体的尺寸和形貌。N含量的增加对微晶玻璃的晶相产物和微观结构产生了较大影响。微晶玻璃的显微硬度和抗弯强度相对各自的基础氧氮玻璃有一定程度的提高。在相对较低的烧结温度下,采用两步法无压烧结方法成功制备了原位生长β-Si3N4晶粒增强的Y203-La2O3-Al2O3-SiO2(YLAS)微晶玻璃复合材料。利用XRD和SEM分析了复合材料中的相组成。结果表明,加入30-50wt%的YLAS玻璃能作为有效的烧结助剂,提高了Si3N4复合材料中α-Si3N4向β-Si3N4相转变的程度。复合材料中析出高熔点的稀土二硅酸盐能提高复合材料的高温力学性能。β-Si3N4晶粒增强YLAS微晶玻璃基复合材料与未增强的微晶玻璃相比,具有较好的力学性能,这主要归因于复合材料中存在高含量的长棒状β-Si3N4晶粒。采用两步无压烧结方法成功制备了原位生长β-Si3N4和α-SiC共同增强的La2O3-CaO-Al2O3-SiO2(LCAS)微晶玻璃基复合材料。结果表明,复合材料中一定量LCAS玻璃能有效地促进α-Si3N4向β-Si3N4的转变以及β-Si3N4晶粒的长大。但SiC的引入在一定程度上阻碍了α-Si3N4向β-Si3N4的转变,并对复合材料的力学性能有不利的影响。同时还发现复合材料的力学性能随烧结温度的升高而增大。更多还原

【Abstract】 Abstract:Oxynitride glasses are a branch of high performance glasses, obtained by incorporating nitrogen atoms into oxide glass networks of e.g. silicates, borates and phosphates. Compared to oxide glasses, oxynitride glasses present higher glass transition temperature, microhardness, bending strength, elastic modulus, fracture toughness, refractive index and lower thermal expansion coefficient. Due to the unique properties, oxynitride glasses have led to some potential areas of application:high elastic modulus glasses for computer hard discs, ceramic seals, coatings on metals, encapsulation of nuclear waste for long term storage, high electrical resistivity coatings for use at high temperatures, glass fibers and bullet-proof glass for transparent armor. Meanwhile, oxynitride glass-ceramics with some selected crystalline phases prepared after appropriate heat treatments will be a kind of promising oxide-nitride composites materials. Due to exciting comprehensive high-temperature mechanical properties, such as a good combination of greater high-temperature strength and toughness, superior resistant to thermal-shock, in-situ grown β-Si3N4reinforced glass-ceramic composites has been a hot topic in materials research in recent years.Oxynitride glasses, oxynitride glass-ceramics and Si3N4/glass-ceramics composites were chosen as research object in the present thesis. Differential scanning calorimeter (DSC), X-ray diffraction (XRD), Scanning electron microscopy (SEM) combined with energy dispersive X-ray spectroscopy (EDS) and IR absorption spectra were used to investigate the formation of these oxynitride glasses, the influences of rare-earth and nitrogen content on the structures, thermal properties and mechanical properties of the oxynitride glasses, the influences of composition and heat-treatment process on the microstructures and mechanical properties oxynitride glass-ceramics and Si3N4/glass-ceramics composites. The main results are listed as follows:Y2O3, La2O3, CaCO3, A12O3, SiO2, AlF3-3H2O and Si3N4powders were used as raw materials powders to prepare RE-Ca-Si-Al-O-N (RE=Y, La) oxynitride glasses by melting batches under N2atmosphere, in order to explore the glass forming region of these compositions. Fine appearance, homogeneous, translucent and defect-free bulk oxynitride glasses were prepared successfully at a relatively lower temperature (1550-1650℃).The amorphous nature of the Y-Ca-Si-Al-O-N oxynitride glasses was verified by an X-ray diffractometer. Fourier-transform IR spectroscopy was done to find out the basic structural units in these glasses. The influences of nitrogen and yttrium content on the properties such as density, glass transition temperature, thermal expansion coefficients, the crystallization temperature, chemical durability and Vickers hardness were investigated. The physical properties were found to change linearly with the concentration of nitrogen or yttrium content, respectively.For La-Ca-Si-Al-O-N oxynitride glasses, the effects of N/O ratios and La/Ca ratios on the properties such as density, thermal expansion coefficient, glass transition temperature, the crystallization temperature, Vickers hardness, bending strength and leaching rate were investigated. The effects of nitrogen and lanthanum on the properties are independent and additive. At the same time, the relationship between these properties and the structures of the glasses were discussed.The influences of La or Y on the properties such as thermal expansion coefficients, glass transition temperature, the crystallization temperature, Vickers hardness and bending strength were comparatively studied. The physical properties are found to change linearly with the concentration of lanthanum or yttrium content, respectively. In general, the structure and properties of glasses show a larger dependence on the content of yttrium than on the content of lanthanum. At the same time, the relationship between these properties and the structures of the glasses were discussed by using cationic field strength (CFS).The effect of nitrogen substitution on the crystallisation of oxynitride glass in the Y-Ca-Si-Al-O-N system has been studied. The appropriate heat treatment temperatures were selected according to the information provided by the differential scanning calorimeter (DSC) measurement. There is a significant increase in Tg and Tc with increasing nitrogen content. XRD and SEM analysis demonstrated that, N content has significant effect on crystallized products, microstructure, crystalline size and crystalline contribution of the oxynitride glass-ceramics, resulting different mechanical properties.Y-Al-Si-O-N-F oxyfluoronitride glass-ceramics were prepared successfully. Crystalline phases in the oxyfluoronitride glass-ceramics were identified by X-ray diffraction and energy dispersion spectrometer (EDS). Microstructures of the glass-ceramics were observed by scanning electron microscopy (SEM). The results show that, addition of fluorine lowers the Tg and Tc of oxyfluoronitride glasses and influences the microstructures, including crystal size and morphology. Nitrogen influences the crystallization products and microstructures. The glass-ceramics all exhibit higher micro-hardness and bending strength compared with their corresponding glasses at different fluorine or nitrogen contents.In-situ grown β-Si3N4reinforced Y2O3-La2O3-Al2O3-SiO2(YLAS) glass-ceramic matrix composites were obtained by a two-step sintering process at a relatively lower temperature. Analyses of resultant products were carried out using X-ray diffraction and scanning electron microscope. The results showed that adding30-50wt%YLAS glass could promote effectively densification of Si3N4composites and a-Si3N4to (3-Si3N4phase transformation. The crystallized rare-earth disilicate phases with a high melting point significantly benefited the high-temperature mechanical properties of the composites. The YLAS glass-ceramic matrix Si3N4composites exhibit excellent mechanical properties compared to unreinforced glass-ceramic matrix, which is undoubtedly attributed to the high concentration of rod-like β-Si3N4grains.In-situ grown (3-Si3N4and a-SiC co-reinforced La2O3-CaO-Al2O3-SiO2(LCAS) glass-ceramic matrix composites were obtained by a two-step sintering process. Densities of samples were measured and analyses of result products were carried out using X-ray diffraction and scanning electron microscope. The results show that LCAS glass-ceramic could effectively promote a-Si3N4to β-Si3N4phase transformation. However, β-Si3N4grain growth was hindered by the existent a-SiC to a certain extent, resulting an adverse effect on mechanical properties of the composites. The mechanical properties of the composites were found to enhance with increasing sintering temperature.更多还原