Structural origin of negative thermal expansion of cordierite honeycomb ceramics and crystal phase evolution with sintering temperature

• Published in: Journal of the European Ceramic Society Vol. 39; no. 7; pp. 2484 - 2492
• Main Authors: Son, Min-A, Chae, Ki-Woong, Kim, Jeong Seog, Kim, Shin-Han
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.07.2019
• Subjects: Bond length; Covalent character; Electron density distribution; Extruded cordierite; Negative thermal expansion; Covalent character; Bond length; Negative thermal expansion; Extruded cordierite; Electron density distribution
• ISSN: 0955-2219; 1873-619X
• DOI: 10.1016/j.jeurceramsoc.2019.02.017

The structural origin of the negative coefficient of thermal expansion (CTE) along the c-axis in cordierite is investigated using high temperature X-ray diffraction. The evolution of the lattice parameters, bond length, covalent character, and electron density distributions are analyzed with increasing temperature. The increase of covalent character of the tetrahedral bonds in the six-membered hexagonal ring is considered as the possible origin for the negative expansion. In addition, the bridging oxygen can act as a buffer absorbing thermal energy and prevents the increase in M1-O-M2 bond. The electron density distribution indicates that the linking oxygen strongly vibrates transversely across two coordinate M1-O-M2 linkages. The CTE and pore size and distribution change drastically at near 1300 °C due to the substantial increase in cordierite phase proportion and the formation of a liquid phase. Raw materials are consumed completely at 1450 °C and the CTE decreases to 1.3 ppm K−1.