| 초록 |
The low thermal expansion ceramics, such as cordierite (2MgO · 2Al2O3 · 5SiO2) and petalite (Li2O · Al2O3 · 8SiO2) were synthesized by using pyrophyllite, and their characteristics were examined. Pyrophyllite is consisted of SiO2 and Al2O3, which are the main component of cordierite and petalite. For the synthesis of the low thermal expansion ceramics, MgCO3, Li2CO3 and LiOH·H2O were added to the pyrophyllite as the sources of MgO, Li2O. For the synthesis of cordierite, MgCO3 and Al(OH)3 were added to pyrophyllite in the mixing ratio of 20 wt% and 1.7 wt%, respectively. The mixing of Al(OH)3 resulted in the reduction of un-reacted SiO2 increasing a yield of cordierite. The powder compacts of synthesized cordierite were densified betwwn 1300°C - 1400°C and the sample showed a low thermal expansion coefficient of 2.80 X 10-6/°C. For the synthesis of Petalite, Li2CO3 or LiOH·H2O were used as a source of Li2O. In the mixing ratio of 6.7 : 1 wt% (pyrophyllite : Li2CO3), fully crystallized petalite was observed, and the powder compacts were densified at 1050°C - 1100°C. The petalite phase was transformed to β-spodumene during heating process, and the sintered β-spodumene showed a negative thermal expansion coefficient of -0.43 X 10-6/°C. |
