Development of Composite Aluminosilicate Materials Based on Iron-Carbon Fly Ash from CHPP-2: A Comparative Analysis of the Effect of Saryozek and Alekseevskaya Clay Structural Types on Phase Formation During Semi-Dry Pressing.

This study presents a comparative analysis of the effect of the structural-mineralogical type of clay matrices on the phase and structure formation in composite aluminosilicate materials within the multi-component Fe-Al-C-Si system. Highly plastic Saryozek montmorillonite clay and moderately plastic Alekseevskaya kaolinite-illite clay were investigated as binding matrices to consolidate iron-aluminosilicate fly ash from the Almaty CHPP-2. The raw materials and binary batches containing 10 to 50 wt.% fly ash were evaluated using XRD, XRF, TG/DTA, and SEM techniques. The results demonstrate that the superior plastic and binding properties of the Saryozek clay ensure enhanced consolidation of the non-plastic, fragmented ash particles. Simultaneous thermal analysis reveals that increasing the compaction pressure from 20 to 30 MPa induces a kinetic shift in the montmorillonite dehydroxylation interval toward higher temperatures (580-720 °C) due to increased partial water vapor pressure within the dense green body. This thermal shift scientifically necessitates introducing an isothermal dwell at 600 °C to mitigate firing defects. The optimal composite properties are achieved at a molding pressure of 30 MPa, a firing temperature of 1050 °C, and a fly ash concentration of 10-20 wt.%, yielding a peak compressive strength of 38.4 MPa. SEM confirmed that under these conditions, the locally formed silicate melt uniformly encapsulates the crystalline mullite and quartz microparticles, whereas increasing the ash content to 50 wt.% results in a loose, highly porous structure that degrades strength down to 17.9 MPa. These findings lay a scientifically substantiated foundation for optimizing composite ceramic synthesis and reducing structural defects.