Synthesis parameters and formulation of metakaolin based geopolymer matrix composites for high‐temperature applications (1150°C)

Abstract Geopolymer matrix composites (GMCs) are actively being developed for high‐temperature applications. In this work, we investigated different composite preparation parameters, such as the elaboration conditions (time, temperature and pressure) and composite dimensions (number of folds and surface area). In addition, we studied the effect of alkali cations (NaK or K), on metakaolin based geopolymer matrix composition, and textile type (N312, N610) of the composites on fiber–matrix interactions in high‐temperature geopolymer composites and their flexural behavior. The process we ultimately selected was as follows: an 8.5‐fold composite of surface area 100 cm2 was pressed for 2 h at 120°C. After thermal treatment at 1150°C, composites containing the N312 textile with B2O3 showed greater heterogeneity, viscous flow and lower flexural strength (7 MPa) due to fiber–matrix interactions. In contrast, above 1150°C, composites with the N610 textile had no fiber–matrix interactions and showed greater flexural strength (51 MPa). The specific flexural strength correlated well with the overmodifying element ratio based on the composite composition. In fact, the presence of viscous flow suggested that boron and some aluminum atoms could act as network modifiers. Thus, the two ratios were nSigeo+nAlgeonMgeo or nSigeo+N312+nAlgeo×0.5+nAlN312nMgeo+nBN312+nAlgeo×0.5 depending on the presence of viscous flow.