Thermal Stability and Decomposition Behaviour of Bentonite Clay-Zirconium Silicate-Cow Dung Composites: A TGA/DTA Study

Abstract

The development of thermally stable and application specific composites from local raw materials is important for refractory, insulating, filtration, and structural ceramic industries. This study investigates the thermal stability and decomposition behavior of bentonite clay (C), zirconium silicate (Z), and cow dung (CD) composites using thermogravimetric and differential thermal analysis (TGA/DTA). Bentonite clay served as the aluminosilicate matrix, zirconium silicate as the refractory inorganic additive, and cow dung as a biomass-derived pore-forming agent. Pure samples (C100, Z100, CD100), binary, and ternary formulations were evaluated using a Thermal Stability Index (TSI) derived from phase transition temperatures, derivative weight loss, and residual weights. TSI performance was categorized into three regimes: high (TSI ≥ 220), moderate (175 ≤ TSI < 220), and low (TSI < 175). The composites underwent characteristic thermal events including moisture removal, organic burnout, dehydroxylation, and structural transformation. Pure Z100 exhibited the highest individual stability TSI of 255, as zirconium bearing phases effectively resisted degradation and stabilized the ceramic matrix. Conversely, cow dung rich compositions showed heightened decomposition due to organic burnout, promoting pore formation while reducing overall stability. Pure C100 and CD100 yielded TSI values of approximately 233 and 196, respectively. Crucially, specific ternary blending demonstrated strong synergistic behavior; the C40Z40CD20 formulation achieved a TSI of approximately 250, matching pure Z100 while incorporating functional porosity. Conversely, equal ratio binary (C50Z50) and high dung ternary (C20Z30CD50) blends showed low stability (TSI < 175). These findings demonstrate that targeted ternary formulation enables cost effective material design without sacrificing thermal endurance, providing composition selection pathways for refractory and porous ceramic manufacturing.