In this article, the results of corrosion investigations performed on thermally sprayed ceramic coatings with different compositions in the Al 2 O 3 -TiO 2 system (Al 2 O 3 , Al 2 O 3 -3%TiO 2 , Al 2 O 3 -40%TiO 2 , and TiO x ) are presented. The coatings were deposited on corrosion-resistant steel substrates using atmospheric plasma spraying (APS) and high-velocity oxy-fuel (HVOF) spraying processes and characterized by means of optical microscopy, scanning electron microscopy (SEM), and x-ray diffraction (XRD). The corrosion properties were investigated in 1 N solutions of NaOH and H 2 SO 4 , at room temperature, 60°C, and 85°C, as well as in hydrothermal conditions with deionized water at 100°C and 200°C. The corrosion stability of the coatings depended on coating characteristics (spraying method, microstructure, and crystalline phase composition) and the corrosive environment (media, test temperature, and duration). In contrast to expectations, APS-sprayed coatings were found to be more corrosionresistant than the HVOF-sprayed coatings. Addition of TiO 2 to Al 2 O 3 increased the corrosion stability, especially for the HVOF-sprayed coatings. In this work, TiO x coatings were found to be more corrosionresistant than the Al 2 O 3 -based coatings.
The corrosion behaviour of different technical ceramics (SSiC ,LPS SiC, GPSN, PSZ, TZP, ZTA and alumina) was investigated in acids, bases and under hydrothermal conditions. Besides the mass loss data, the residual strength and the thickness of the corroded layers were used for the characterisation of the corrosion intensity. Investigations in acids, bases and under hydrothermal conditions show that the stability of the materials strongly depends on the composition and the corrosive medium.
The corrosion behavior of silicon nitride materials in aqueous media strongly depends on
the composition and amount of the grain boundary. But there exist no systematic investigations of
the relation between the corrosion behavior and the composition and amount of the grain-boundary
phase. The subject of this study is based on the evaluation of the corrosion mechanisms of Si3N4
ceramics and YSiAlON glasses, both with defined and characterized compositions, in acidic and
basic environments with different concentrations. Special effort has been made in describing the
compositions of grain boundary phases in the sintered Si3N4 ceramics. A model to describe
structural features of YSiAlON-glasses was developed which allows the correlation of the corrosion
behavior of the ceramics and the glasses with their compositions. In combination with SEM and
TEM investigations it became possible to give structural reasons for the different observed
corrosion mechanisms.
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