Details
| Original language | English |
|---|---|
| Pages (from-to) | 393-400 |
| Number of pages | 8 |
| Journal | Journal of the European Ceramic Society |
| Volume | 28 |
| Issue number | 2 |
| Early online date | 25 Apr 2007 |
| Publication status | Published - 2008 |
Abstract
Traces of OH groups have been identified in the infrared absorption spectra of a nominally anhydrous synthetic mullite single crystal. The OH absorption profiles were resolved with four peaks for polarizations E//a, E//b and E//c, respectively. The integrated absorption intensities correspond to an H2O content of about 10 ppm (wt) using an average extinction coefficient according to the mean wavenumber relation. The length of O1-H⋯O2 bonds (O1-H hydroxyl groups with hydrogen bridging towards a neighboring oxygen, O2) range between 276 and 314 pm following empirical relations for hydrogen bonding in aluminosilicates. According to lattice energy calculations the infrared peak positions can be associated with two different classes of hydrogen positions assuming a substitution Si4+ ⇔ 4H+: one type of H atoms is bound on tetrahedral faces of substituted Si-sites involving intense O1-H⋯O2 hydrogen bridging. A second type of H atoms form more isolated O-H groups directed into the structural channels of mullite running along the crystallographic c axis. These OH dipoles show polarizations perpendicular to the c axis. A third type of OH dipole is oriented parallel to the c axis and could be assigned to appropriate pairs of oxygen in two neighboring unit cells, e.g. Oc1-H⋯Oc2. Heating experiments for 12 h at 1200 °C, 6 h at 1300 °C and 4 h at 1400 °C reveal a significant decrease of OH concentration on ppm level. OH absorption profiles measured on cross-sections by infrared microscope technique yielded for example at 1300 °C diffusion coefficients of Da ≈ Db ≈ 8 × 10-9 (parallel to the a and b axis) and Dc ≈ 1.5 × 10-8 cm2/s (parallel to the c axis). The observation Dc > Da ≈ Db corresponds to a preferred diffusion parallel to the structural channels in c direction. The temperature dependence of the diffusion coefficient Dc of hydrogen outward diffusion is described with an Arrhenius activated behavior (190 kJ/mol). It includes the diffusion coefficient of hydrogen inward diffusion, which was obtained by submitting originally H-free mullite at 1670 °C to a water-rich atmosphere.
Keywords
- Diffusion, Drying, Functional Applications, Impurities, Mullite
ASJC Scopus subject areas
- Materials Science(all)
- Ceramics and Composites
- Materials Science(all)
- Materials Chemistry
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In: Journal of the European Ceramic Society, Vol. 28, No. 2, 2008, p. 393-400.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - Hydrogen bonding and diffusion in mullite
AU - Rüscher, Claus H.
AU - Eils, Nadine
AU - Robben, Lars
AU - Schneider, Hartmut
N1 - Funding Information: We thank the “Deutsche Forschungsgemeinschaft” (DFG, Schn 297/25-1) for financial support, S. Uecker (Institute for Crystal Growth, Berlin-Adlershof, Germany) for the preparation of the mullite single crystals and O. Diedrich (Institute of Mineralogy, Leibniz University of Hannover) for preparing the oriented single crystal cuts.
PY - 2008
Y1 - 2008
N2 - Traces of OH groups have been identified in the infrared absorption spectra of a nominally anhydrous synthetic mullite single crystal. The OH absorption profiles were resolved with four peaks for polarizations E//a, E//b and E//c, respectively. The integrated absorption intensities correspond to an H2O content of about 10 ppm (wt) using an average extinction coefficient according to the mean wavenumber relation. The length of O1-H⋯O2 bonds (O1-H hydroxyl groups with hydrogen bridging towards a neighboring oxygen, O2) range between 276 and 314 pm following empirical relations for hydrogen bonding in aluminosilicates. According to lattice energy calculations the infrared peak positions can be associated with two different classes of hydrogen positions assuming a substitution Si4+ ⇔ 4H+: one type of H atoms is bound on tetrahedral faces of substituted Si-sites involving intense O1-H⋯O2 hydrogen bridging. A second type of H atoms form more isolated O-H groups directed into the structural channels of mullite running along the crystallographic c axis. These OH dipoles show polarizations perpendicular to the c axis. A third type of OH dipole is oriented parallel to the c axis and could be assigned to appropriate pairs of oxygen in two neighboring unit cells, e.g. Oc1-H⋯Oc2. Heating experiments for 12 h at 1200 °C, 6 h at 1300 °C and 4 h at 1400 °C reveal a significant decrease of OH concentration on ppm level. OH absorption profiles measured on cross-sections by infrared microscope technique yielded for example at 1300 °C diffusion coefficients of Da ≈ Db ≈ 8 × 10-9 (parallel to the a and b axis) and Dc ≈ 1.5 × 10-8 cm2/s (parallel to the c axis). The observation Dc > Da ≈ Db corresponds to a preferred diffusion parallel to the structural channels in c direction. The temperature dependence of the diffusion coefficient Dc of hydrogen outward diffusion is described with an Arrhenius activated behavior (190 kJ/mol). It includes the diffusion coefficient of hydrogen inward diffusion, which was obtained by submitting originally H-free mullite at 1670 °C to a water-rich atmosphere.
AB - Traces of OH groups have been identified in the infrared absorption spectra of a nominally anhydrous synthetic mullite single crystal. The OH absorption profiles were resolved with four peaks for polarizations E//a, E//b and E//c, respectively. The integrated absorption intensities correspond to an H2O content of about 10 ppm (wt) using an average extinction coefficient according to the mean wavenumber relation. The length of O1-H⋯O2 bonds (O1-H hydroxyl groups with hydrogen bridging towards a neighboring oxygen, O2) range between 276 and 314 pm following empirical relations for hydrogen bonding in aluminosilicates. According to lattice energy calculations the infrared peak positions can be associated with two different classes of hydrogen positions assuming a substitution Si4+ ⇔ 4H+: one type of H atoms is bound on tetrahedral faces of substituted Si-sites involving intense O1-H⋯O2 hydrogen bridging. A second type of H atoms form more isolated O-H groups directed into the structural channels of mullite running along the crystallographic c axis. These OH dipoles show polarizations perpendicular to the c axis. A third type of OH dipole is oriented parallel to the c axis and could be assigned to appropriate pairs of oxygen in two neighboring unit cells, e.g. Oc1-H⋯Oc2. Heating experiments for 12 h at 1200 °C, 6 h at 1300 °C and 4 h at 1400 °C reveal a significant decrease of OH concentration on ppm level. OH absorption profiles measured on cross-sections by infrared microscope technique yielded for example at 1300 °C diffusion coefficients of Da ≈ Db ≈ 8 × 10-9 (parallel to the a and b axis) and Dc ≈ 1.5 × 10-8 cm2/s (parallel to the c axis). The observation Dc > Da ≈ Db corresponds to a preferred diffusion parallel to the structural channels in c direction. The temperature dependence of the diffusion coefficient Dc of hydrogen outward diffusion is described with an Arrhenius activated behavior (190 kJ/mol). It includes the diffusion coefficient of hydrogen inward diffusion, which was obtained by submitting originally H-free mullite at 1670 °C to a water-rich atmosphere.
KW - Diffusion
KW - Drying
KW - Functional Applications
KW - Impurities
KW - Mullite
UR - http://www.scopus.com/inward/record.url?scp=35648938272&partnerID=8YFLogxK
U2 - 10.1016/j.jeurceramsoc.2007.03.018
DO - 10.1016/j.jeurceramsoc.2007.03.018
M3 - Article
AN - SCOPUS:35648938272
VL - 28
SP - 393
EP - 400
JO - Journal of the European Ceramic Society
JF - Journal of the European Ceramic Society
SN - 0955-2219
IS - 2
ER -