【作者】 黄春舒；

【导师】 刘家臣；

【作者基本信息】 天津大学 ， 材料学， 2012， 硕士

【摘要】 本文以Al₂O₃-SiO₂体系为粘结剂,空心球作为造孔剂,利用凝胶注模成型方法制备出一种新型的多孔莫来石材料。空心球在烧结过程中可以起到烧结助剂的作用,大大的降低了Al₂O₃-SiO₂体系的烧结温度。实验分别研究添加百分比为25%、50%、75%、100%的空心球进行研究,结果表明空心球含量越多,总气孔率越大;其中烧成温度较低的是75%空心球添加量,其在1200℃能烧成轻质多孔莫来石陶瓷。XRD分析表明温度的增加,莫来石衍射峰增强,Al₂O₃的衍射峰降低,说明温度升高促进了Al₂O₃-SiO₂烧成莫来石相。随着空心球含量减少,Al₂O₃-SiO₂粉末含量相对增加,其烧结温度增加,抗弯强度增大。50%空心球1300℃下制备的多孔陶瓷密度在1.09 g/cm³左右,抗弯强度为15 MPa。25%空心球添加量在1400℃烧结得到的多孔陶瓷强度达到38 MPa,密度1.43 g/cm³,孔径结构多为闭气孔,闭气孔率为35%。在上述基础上,实验选取50%的空心球作第一类造孔剂,另外添加B₂O₃和CaCO3作为第二类造孔剂进行研究。实验表明,当添加B₂O₃含量较少时（2.5%左右）,气孔率降低,B₂O₃能够促进烧结。B₂O₃的含量从2.5%开始增加到10%,陶瓷的收缩率反常的降低,总气孔率越来越大。SEM分析其原因为CaCO3和B₂O₃在有水浆料中反应产生CO₂气泡,从而使坯体产生微孔,另一原因为B₂O₃的加入加速孔壁中氧化物液化,使孔中露出凹凸不平的针状莫来石,从而提高气孔率。B₂O₃的加入促进Al₂O₃-SiO₂在低温下烧成莫来石相,烧结温度降低了100²00℃左右。10% B₂O₃添加量在1200℃烧结后,气孔率增加到81%,密度降低到0.64 g/cm³。从热学上来分析,本实验所制备的多孔莫来石陶瓷具有较低的导热系数(0.09-0.30 W.（m.k）^-1)。而且材料的导热存在一定的弛豫时间,导热系数越小,弛豫时间越长,说明这种多孔材料具有良好的隔热性能。更多还原

【Abstract】 In this paper, a novel porous mullite was fabricated by means of gelcasting method using Al₂O₃-SiO₂ and fly ash cenosphere as basic materials, as well as binder and foaming a gent. The main crystalline phases of fly ash cenosphere are mullite and SiO₂ besides a small amount of amorphous glassy phase. The amorphous glassy phase during sintering can play the role of sintering aids; greatly lower the sintering temperature of Al₂O₃-SiO₂ system. Experiment studied the effect of adding 25%, 50%, 75%, 100% amount of cenospheres. The results showed that the more content of cenospheres, the lower sintering temperature, and the higher the total porosity it was. More than 75% cenospheres adding, light porous mullite ceramics can be sintered at as low as 1200℃. From XRD （X-Ray Diffraction） patterns we knew as the sintering temperature increased, mullite diffraction peaks intensified, and Al₂O₃ diffraction peaks shrinked, indicating that high temperature promotes the growth of mullite crystals. SEM images showed that after 1200℃sintering, the re was glassy phase starting to liquify to accelerate sintering. When the amount of cenospheres decreased, the sintering temperature and flexural strength would obviously increase. And with 50% cenospheres addition, flexural strength and bulk density of porous mullite respectively resulted in 15MPa and 1.09 g/cm³ at 1300℃. The maximum flexural strength reaches 38 MPa with 25% cenospheres in it, which also has a highest closed porosity （35%） and bulk density （1.43 g/cm³）.A small amount of CaCO3 and B₂O₃ are added as sintering aid, as well as second foaming agent, which based on formula of 50% cenospheres. As a result, when adding less than 2.5% amount of B₂O₃, B₂O₃ can promote sintering, but decrease the porosity. The amount of B₂O₃ added from 2.5% to 10%, both of bulk shrinkage and density would decline abnormally because of the second foaming agent. On the other hand, B₂O₃ would eutecticevaporate with other oxides in pore shell, so that needle-like mullite presented in the inner pore. That is why more B₂O₃ resulted in higher porosity. When B₂O₃ added to 10% wt, a higher total porosity rate is up to 81%, and lower density is down to 0.64 g/cm³.The light porous mullite ceramics was prepared in this experiment with low thermal conductivity (0.09⁰.30 W.（m.k）^-1). And thermal conductivity was characterized by a relaxation time. The lower the thermal conductivity, the longer relaxation time it is, indicating that the porous material with good heat insulation properties.更多还原