Measurement of Viscosity of Calcium-Magnesium-Aluminosilicate Glass by Rotating Viscometer Method (CAT#: STEM-PPA-0031-YJL)

Introduction

Fuel efficiency of air-breathing turbine engines is closely related to the operating temperature in the hot sections and overall weight of the engine.Air-breathing turbine engines routinely ingest particulates, namely sand, volcanic ash or other siliceous matter. As hot-section temperatures are pushed above 1300 °C, these particulates melt into glassy deposits consisting of calcium-magnesium-aluminosilicate (CMAS) and other minor oxides. Molten CMAS deposits can consequently adhere to the T/EBCs designed to protect CMCs, followed by thermochemical interactions with the protective coatings. Additionally, due to its lowered viscosity at target operating temperatures (N1300 °C) of next-generation aircraft engines, molten CMAS can infiltrate into the pore channels within the porous coatings leading to undesired stress development that can alter the mechanical properties of the infiltrated layer. Depending on the depth of coating infiltration, which varies with the temperature-dependent viscosity of molten CMAS, these induced stresses can cause the coating to prematurely spall and fail over the heating and cooling cycles regularly experienced during engine operation. A knowledge of the CMAS glass viscosity at elevated temperatures is critical for the design of robust T/EBC (thermal and environmental barrier coatings) protective coatings.