ISSN 0862-5468 (Print), ISSN 1804-5847 (online) 

Ceramics-Silikáty 62, (4) 382 - 388 (2018)


HYDROTHERMAL CORROSION RESISTANCE OF SILICON NITRIDE WITH O'-Si Al ON GRAIN BOUNDARY PHASE
 
Vetrecin Michal 1, Lenčéš Zoltán 1, Galusková Dagmar 2, Šajgalík Pavol 1
 
1 Institute of Inorganic Chemistry, Slovak Academy of Sciences, 84536 Bratislava, Slovak Republic
2 Vitrum Laugaricio - Joint Glass Centre of the IIC SAS, TnU AD, FChFT STU and RONA j.s.c., 91150 Trenčín, Slovak Republic

Keywords: Ceramic, Silicon nitride, Sialon, ICP-OES, Corrosion
 

Dense Si₃N₄-based composites with O'-SiAlON bonding phase were prepared by hot pressing of the mixture of Si₃N₄ matrix and polysiloxane (samples SA) and polysilazane (samples SB) based sintering aids. In both samples α-Si₃N₄ and β-Si₃N₄ were identified as major phases and O'-SiAlON with a chemical formula Si1.84Al0.16O1.16N1.84 as a minor phase. The hydrothermal corrosion tests were performed in subcritical conditions at 250 °C for 100 hours. The weight loss was rather low, 0.96 wt.% and 1.32 wt.% for samples SA and SB, respectively. The corrosion rate of samples SA and SB was 206 mg.m-2.h-1 and 233 mg.m-2.h-1. The higher corrosion rate of sample SB prepared with polysilazane-based sintering aid is most probably due to the hydrothermal dissolution of Si₃N₄ grains producing ammonia, as the pH value of eluate of this sample was higher, 8.5 compared to pH = 8.0 determined for sample SA. In sample SA a continuous SiO₂-based passivation layer was formed, while in sample SB the passivation layer was discontinuous and the corrosion medium could easily attack the Si₃N₄ grains. As the corrosion solution was more basic in sample SB, the SiO₂ passivation layer did not form so effectively, or dissolved faster than in sample SA. The higher corrosion resistance of sample SA was partly improved also by using Y₂O₃ sintering additive, which formed a rather stable Y₂SiO₅ phase.


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doi: 10.13168/cs.2018.0034
 
 
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