【作者】 章为夷；

【导师】 高宏；

【作者基本信息】 大连交通大学 ， 材料加工工程， 2008， 博士

【摘要】 提出了一种制备可加工氟闪石玻璃陶瓷的新工艺-反应析晶法:将合成氟云母晶体粉末直接与普通钠钙玻璃粉末混合,烧结制备成氟闪石玻璃陶瓷。与传统的熔融法和烧结法不同的是,玻璃陶瓷中的氟闪石晶体不是从母相玻璃中析出,而是在烧结过程中通过氟云母和玻璃间的反应析出。新工艺不仅简化了玻璃陶瓷的制备工艺,降低了生产成本,还能对废玻璃回收利用,是一项极有潜力的氟闪石玻璃陶瓷的制备新工艺。采用X射线衍射、扫描电镜和能谱仪等方法对氟闪石反应析晶机理、反应析晶影响因素、氟闪石玻璃陶瓷烧结机理、玻璃陶瓷组织和性能间的关系以及工艺参数对玻璃陶瓷性能的影响进行了系统研究。在烧结过程中,氟闪石晶体的形成由反应析出和长大两步组成。氟云母类型对氟闪石反应析晶有影响,玻璃类型对氟闪石反应析晶影响不大。氟闪石反应析晶量是氟云母加入量的一倍,反应析晶式为: KMg₃AlSi₃O₁₀F₂ + CaO + Na₂O + 5SiO₂→KNa₂CaAlMg₃Si₈O₂₂F₂提出了氟云母向氟闪石转变的晶体学模型。在氟闪石晶体反应析出阶段,玻璃中的NaO、CaO通过扩散进入氟云母晶体,使氟云母晶体中硅氧四面体平面网断裂形成硅氧四面体双链,导致氟云母晶体转变成氟闪石晶核;同时钾、镁、氟等元素从氟云母晶体向其周围玻璃中扩散促使玻璃的无规网络结构断开,导致玻璃中的硅氧四面体以链状形式在氟闪石晶核上析晶。在氟闪石晶体长大阶段,氟闪石晶体反应析出停止,氟闪石晶体含量不变,晶粒数量减少,晶粒平均直径与等温时间立方根成正比。氟闪石晶体通过小晶粒溶解重新在大晶粒上析出的方式长大,长大规律服从Ostwald熟化机制。氟云母加入量对反应析晶有很大影响,加入量小于20wt%,形成透辉石,加入30 wt%～40wt%,形成氟闪石,加入60wt%,氟云母和氟闪石共存,加入80wt%,大量的氟云母保留下来,仅有少量氟闪石形成。反应析晶产物受晶体中Si/O摩尔比控制,氟云母加入量影响了玻璃陶瓷中的玻璃含量,进而改变了进入氟云母晶体中的氧含量,导致晶体中Si/O摩尔比发生变化。氟闪石玻璃陶瓷烧结致密化主要是通过玻璃相的粘性流动来实现,加入氟云母晶体会阻碍玻璃相粘性流动,玻璃陶瓷相对密度随氟云母加入量增多而下降。提高烧结温度有助于改善玻璃陶瓷密度,但不能完全致密化。存在一适宜的烧结温度范围,在此温度范围内烧结可得到较高的密度。不同氟云母加入量的玻璃陶瓷的烧结温度范围不同,随氟云母加入量增加而提高。氟云母加入量小于50wt%,烧结机制为粘性流动烧结,在此范围内,氟云母加入量与玻璃陶瓷相对密度存在定量关系。氟云母加入量对氟闪石玻璃陶瓷的钻孔速率影响很大,其它工艺参数的影响较小,工艺参数对玻璃陶瓷力学性能的影响不同。通过方差分析,确定的氟闪石玻璃陶瓷最佳制备工艺为:30 wt%～35 wt%氟云母,玻璃粉粒度130目～150目,素坯成型压力150 MPa～200MPa,860℃～900℃烧结2h,按此工艺制备的氟闪石玻璃陶瓷具有良好的机械加工性和较高的力学性能,用普通的机械加工设备可以进行车削、钻孔、攻丝和铣削加工,能够车削出壁厚0.8mm的零件和完整的螺纹。更多还原

【Abstract】 A novel route-reactive crystallization technology, directly mixing fluormica crystals with soda-lime glass powder and sintering, was proposed to fabricate machinable fluoramphibole glass-ceramics. The new technique is different from the traditional routes: melting and crystallizing and sintering crystallization, fluoramphibole crystals in the glass-ceramics were formed via a reaction between fluormica and glass powder during sintering process instead of a precipitation from parent glass. Therefore, not only the procedure of glass-ceramic preparation was simplified and the production cost was reduced, but also the recycled glass was utilized too, the new technique is a promising and potential route for fabricating fluoramphibole glass-ceramics.The mechanism of reactive crystallizing, the effects on the behaviors of reactive crystallizing, the mechanism of sintering, the correlation between microstructures and properties of glass-ceramics and the effects of processing parameters on the properties of glass-ceramics were systematically investigated by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and energy dispersive X-ray analysis （EDX）.During sintering process, the formation of fluoramphibole crystals consists of two steps: precipitation by the reactive crystallizing and growth. The types of fluormica crystals have a considerable effect on the reactive crystallization of fluoramphibole, and the types of glasses have no effect on it. The content of fluoramphibole crystal by the reactive crystallizing was double one of fluormica addition, the reactive crystallizing formula was as follow: KMg₃AlSi₃O₁₀F₂ + CaO + Na₂O + 5SiO₂→KNa₂CaAlMg₃Si₈O₂₂F₂A crystallography model describing the transformation from fluormica into fluoramphibole was proposed. During the precipitation of fluoramphibole crystals by the reactive crystallizing, the diffusion of Na2O and CaO from glass into fluormica results in the break of [SiO4]4- tetrahedron sheet structure of fluormica crystal, this makes the sheet structure change into a double chain [SiO4]4- tetrahedron structure and fluormica crystal into fluoramphibole crystal. At the same time, the diffusion of K, Mg, F from fluormica crystal to glass also makes the silicate network of the glass be broken, this facilitates [SiO4]4- tetrahedron in glass around fluormica crystal to be precipitated as a chain structure on the nuclei of fluoramphibole. During the growth of fluoramphibole crystal, the precipitation of fluoramphibole crystals stops, the content of fluoramphibole crystal remains unchangeable, the number of grain decreases continuously, and the diameter of grain is directly proportional to the cube root of isothermal time. Fluoramphibole grains grow through the dissolution of smaller grains, and then precipitation on larger grains, the mechanism of grain growth obeys the Ostwald ripening.The fluormica addition had a great effect on the reactive crystallization final phases, while the addition of fluormica was less than 20 wt%, diopside was formed via reactive crystallization; 40 wt% fluormica was added, fluoramphibole was formed; fluormica and fluoramphibole coexisted in compact with 60 wt% fluormica addition; a large amount of fluormica remained unchangeable and only a few of fluoramphibole was formed while 80 wt% fluormica addition. The reactive crystalline final phases are controlled by the O/Si mole ratio in crystals, the fluormica addition has an effect on the glassy phase content in the glass-ceramics, and which affects in turn the oxygen content migrated from glass into fluormica crystal, and finally this results in the change of the O/Si mole ratio in crystals. The densification of fluoramphibole glass-ceramics is mainly achieved by the viscous flow of the glassy phase during the sintering process. The addition of fluormica inhibited the viscous flow of the glassy phase, the relative densities of glass-ceramics decreased with increasing the fluormica content. Raising sintering temperature could improve the densification of glass-ceramics, however, a full densification couldn’t be achieved in the glass-ceramics containing fluormica crystals. A suitable sintering temperature range existed at which the higher densities of glass-ceramics can be obtained. The temperature range for each of the glass-ceramics with different fluormica content was different, and it increased with increasing fluormica content. While the addition of fluormica was less than 50 wt%, the sintering mechanism was a viscous flow one. In this range of fluormica content, there is a quantitative relationship between the fluormica addition and the relative density of glass-ceramic.The fluormica addition had a considerable effect on the drilling speed, and other processing parameters had small effect on it. The processing parameters had different effects on the mechanical properties of fluoramphibole glass-ceramics. The optimal processing parameters for fabricating fluoramphibole glass-ceramics obtained by the analysis of variance are listed below: 30 wt%³5 wt% fluormica additions, the size of 100 mesh¹30 mesh for the glass particles, the forming pressure of 150MPa²00MPa for the green compact, the sintering temperature of 860℃⁹00℃and the firing time of 2 hours. The glass-ceramics fabricated by these optimal processing parameters had good mechanical properties and machinability, they could be turned, drilled, tapped and milled using ordinary metal working tools, and components with a thin wall thickness 0.8 mm and intact screws could be machined .更多还原