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Thermal Conductivity of 2/1-Mullite Single Crystals

Hildmann, Bernd and Schneider, Hartmut (2005) Thermal Conductivity of 2/1-Mullite Single Crystals. Journal of the American Ceramic Society, 88 (10), pp. 2879-2882. doi: 10.1111/j.1551-2916.2005.00530.x. ISSN 0002-7820.

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The thermal diffusivities Dth of mullite single crystals with about 2/1-composition parallel to the crystallographic a, b, and c axes (i.e., parallel to [100], [010], and [001]) and of monophase, dense mullite ceramics were measured between room temperature and 1200°C using the laser flash method. The semi-transparent mullite disks were covered by thin layers of argon-sputtered platinum and sprayed colloidal graphite in order to minimize heat radiation transfer effects. The phonon-produced thermal conductivity of mullite was calculated according to K=DthCp? using experimentally measured values for thermal diffusivity, Dth(T), and specific heat, Cp(T), and thermal expansion coefficients, ?i, for the determination of temperature-dependent density ?(T) and sample thickness d(T). The anisotropy of thermal diffusivity and conductivity is evident with highest values parallel to the crystallographic c axis (i.e., [001]; e.g., at T=100°C K[001]=6.862 W/mK), corresponding to the direction of strongest bonds and highest elastic stiffness in the mullite crystal structure. Perpendicular to the c axis, thermal diffusivities and conductivities are smaller, with the values parallel to the a axis (i.e., [100]) being slightly higher than parallel to b (i.e., [010]; e.g., at T=100°C K[100]=4.563 W/mK and K[010]=4.400 W/mK), indicating lower bond strength and elastic stiffness in these crystallographic directions. Conductivity anisotropy factors are around 1.33 for K[001]/Kaverage, 0.90 for K[100]/Kaverage, and 0.85 for K[010]/Kaverage with little variation between room temperature and 1200°C. The thermal diffusivity and conductivity of dense, monophase mullite ceramics display similar values as the averaged single crystal data, thus providing a master curve for the temperature-dependent thermal conductivity.

Item URL in elib:https://elib.dlr.de/49955/
Document Type:Article
Title:Thermal Conductivity of 2/1-Mullite Single Crystals
AuthorsInstitution or Email of AuthorsAuthor's ORCID iDORCID Put Code
Journal or Publication Title:Journal of the American Ceramic Society
Refereed publication:Yes
Open Access:No
Gold Open Access:No
In ISI Web of Science:Yes
Page Range:pp. 2879-2882
Keywords:thermal diffusivity, mullite, single crystal
HGF - Research field:Aeronautics, Space and Transport (old)
HGF - Program:Aeronautics
HGF - Program Themes:Propulsion Systems (old)
DLR - Research area:Aeronautics
DLR - Program:L ER - Engine Research
DLR - Research theme (Project):L - Combustion Chamber Technologies (old)
Location: Köln-Porz
Institutes and Institutions:Institute of Materials Research > Structural and Functional Ceramics
Deposited By: Mechnich, Dr.rer.nat. Peter
Deposited On:18 Jul 2007
Last Modified:27 Apr 2009 14:05

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