University of Oulu

I.J. Induja, M.T. Sebastian, Microwave dielectric properties of mineral sillimanite obtained by conventional and cold sintering process, Journal of the European Ceramic Society, Volume 37, Issue 5, 2017, Pages 2143-2147, ISSN 0955-2219,

Microwave dielectric properties of mineral sillimanite obtained by conventional and cold sintering process

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Author: Induja, I.J.1; Sebastian, M.T.2
Organizations: 1Materials Science & Technology Division, National Institute for Interdisciplinary Science Technology, Thiruvananthapuram, 695019, India
2Microelectronics Research Unit Faculty of Information Technology & Electrical Engineering, University of Oulu, Oulu, P.O. Box 4500, FI90014, Finland
Format: article
Version: accepted version
Access: open
Online Access: PDF Full Text (PDF, 0.8 MB)
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Language: English
Published: Elsevier, 2017
Publish Date: 2019-05-31


The sillimanite (Al₂SiO₅) mineral has been sintered by conventional ceramic route and by cold sintering methods. The mineral has very poor sinterability and transformed to mullite on sintering above 1525 °C. The dielectric properties of sillimanite mineral (Al₂SiO₅) are investigated at radio and microwave frequency ranges. The mineral sintered at 1525 °C has low εᵣ of 4.71 and tanδ of 0.002 at 1 MHz and at microwave frequency εᵣ = 4.43, Qᵤ × f = 41,800 GHz with τf = −17 ppm/°C. The sintering aid used for cold sintering Al₂SiO₅ is sodium chloride (NaCl). The Al₂SiO₅—NaCl composite was cold sintered at 120 °C. XRD analysis of the composite revealed that there is no additional phase apart from Al₂SiO₅ and NaCl. The densification of the Al₂SiO₅—NaCl composite was confirmed by using microstructure analysis. The Al₂SiO₅—NaCl composite has εᵣ of 5.37 and tanδ of 0.005 at 1 MHz whereas at microwave frequency it has εᵣ = 4.52, Qu × f = 22,350 GHz with τf = −24 ppm/°C. The cold sintered NaCl has εᵣ = 5.2, Qu × f = 12,000 GHz with τf = −36 ppm/°C.

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Series: Journal of the European Ceramic Society
ISSN: 0955-2219
ISSN-E: 1873-619X
ISSN-L: 0955-2219
Volume: 37
Issue: 5
Pages: 2143 - 2147
DOI: 10.1016/j.jeurceramsoc.2017.01.007
Type of Publication: A1 Journal article – refereed
Field of Science: 216 Materials engineering
Copyright information: © 2017 Elsevier Ltd. All rights reserved. This manuscript version is made available under the CC-BY-NC-ND 4.0 license