Sintering and hot corrosion of yttria silicate tablets in molten salts prepared by spark plasma sintering

Purpose: This paper aims to study the microstructural hot corrosion behaviour of the sintered Y₂SiO₅ ceramic silicate under a Na₂SO₄ + V₂O₅ mixture at an engine representative temperature of 1150°C. Y₂SiO₅ is a promising candidate for thermal barrier coatings (TBC) due to its excellent chemical stability at high temperatures. As a continuous source of Y₃+, it is expected that Y₂SiO₅ environmental barrier coating may prolong the lifetime of TBC systems by stopping the degradation caused by the loss of the Y₂O₃ stabilizer. Design/methodology/approach: Two routes were chosen for the yttria silicate powder synthesis by sol-gel from TEOS and APTES precursors as the difference in Si source changed the ratio of Y₂SiO₅/Y₂Si₂O₇ phases. Hot corrosion studies using Na₂SO₄ and V₂O₅ mixtures were conducted on both surfaces of APTES and TEOS tablets at 1150°C for 8 h in atmospheric air. The morphology and microstructure analyses of the silicate samples after hot corrosion tests were carried out using a SEM and X-ray diffraction analyse techniques. Findings: Based on the degradation, the general status of the APTES tablet after hot corrosion presents a better hot corrosion resistance at a temperature of 1150°C than does that of the TEOS tablet. In the TEOS tablet, the crystal morphology of NaY9Si60O26 woodchip shapes with a size of 60 µm is developed on the surface for finally initiating some cracks. In the APTES case, the crystal morphology of rod-like shapes with a size of 100 µm is developed; hence, a dense thick layer predominately postpones the reaction of V₂O₅ and Na₂SO₄ with yttria silicate, and consequently, less damage is observed. Originality/value: Coating yttria silicate preparation is very complicated; the problems of a high synthesis temperature, long production period and low yield still need to be solved. Under these perspectives, ceramics prepared via spark plasma sintering (SPS) can reach theoretical high densities and a fine grain size can be retained after the SPS process; hence, well resistance to the corrosion in molten salts is expected to obtain for the sintered yttria silicate tablets.