Study of relationship between Sr2SiO4 polymorphic and grain size and their high temperature behaviors

• Main Authors: Han-YangHu, 胡瀚陽
• Other Authors: Jennifer Kung
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/93383774361163994995

碩士 === 國立成功大學 === 地球科學系碩博士班 === 101 === The phase transition between low temperature (LT) and high temperature (HT) phase of Sr2SiO4 is displacive with 1st-order thermodynamic characteristic. However, the HT phase was found to be stable at room temperature in synthesized powder samples with the reasons remain unknown. In this study, by synthesizing powder samples via solid state reaction and sol-gel method with series of sintering condition to observe the relationship between grain size and crystal structure. Also, LT and HT phase samples were examined via in-situ high temperature and thermal treatment experiments to observe the structure change through variation of temperature to study the phase stabilization factors of Sr2SiO4 and its high temperature behavior. The synthesis results from sol-gel method showed the Sr2SiO4 phase cannot be obtained till up to 1400℃ and which were all LT phase dominant. However, Sr2SiO4products can be synthesized as low as 900℃ in solid state reaction and were noticed the amounts of LT phase would increase with increasing synthesis temperature or period of time. The SEM images indicated that the grain size of sol-gel method products is larger than those from solid state reaction. With in-situ high temperature and thermal treatment experiments, the HT phase is tend to appear with smaller grain size and by faster cooling rate. The factors of stabilization of HT phase at room temperature are suggested to affect by thermal hysteresis and grain size effect. The former is its intrinsic property and is affected by the latter at some extent. Those smaller grains have larger curvature which makes it have larger strain in structure. This leads to smaller grains cannot overcome the energy barrier to transform back to its equilibrium positions (LT phase). From SEM images, the critical grain size for stabilizing HT phase is about 0.7~1 μm and propose that this effect doesn’t only occur in nano-scale but also in sub-micron scale. For the first time, we have the thermal expansion data of Sr2SiO4. Though we can’t tell the difference from α'L(modulated structure) and α'H now, we discover the thermal expansion behavior is very different from similar material - Mg2SiO4.