Two-stage development of aluminosilicate refractories from Ethiopian Kaolin: Taguchi-Grey optimization of chamotte and binder system evaluation

This study presents a data-driven, two-stage framework for valorizing Ethiopian kaolins from the Debre Tabor and Chilga deposits into medium-duty aluminosilicate refractories. In Stage I, a Taguchi L₁₆ orthogonal array coupled with Grey Relational Analysis (GRA) was employed to optimize chamotte production by evaluating four control factors: calcination temperature (1350–1500 °C), holding time (1–6 h), heating rate (2 and 5 °C/min), and kaolin source. The optimal condition—1500 °C, 6 h, and 2 °C/min—yielded a dense, well-consolidated chamotte characterized by interlocking prismatic mullite crystals within a continuous glassy matrix. Analysis of variance identified calcination temperature as the dominant factor, accounting for 73.4% of the total performance variance, while kaolin source contributed a statistically meaningful secondary effect (13.8% and 10.0% amorphous content in Debre Tabor and Chilga kaolins, respectively). In Stage II, refractories fabricated using the optimized chamotte were evaluated with two binder systems: local Debre Tabor kaolin (M1) and commercial high-purity kaolin (M2, Keramix® K-38). The commercial binder formulation exhibited superior performance, achieving a 10.7% reduction in apparent porosity (from 19.6% to 17.5%), a 19.6% increase in cold crushing strength (from 35.7 MPa to 42.7 MPa), and enhanced mullite content from 25.4 wt.% to 27.9 wt.%. Refractoriness-under-load testing confirmed a consistent 15–20 °C improvement in all characteristic deformation temperatures (T₀, T₀.₅, T₁, T₂, T₅) for the commercial-binder formulation, attributed to enhanced mullitization, reduced pore connectivity, and improved intergranular bonding. The results establish clear processing–source–structure–property relationships, demonstrating that both kaolin provenance and binder chemistry are essential design variables. This two-stage strategy provides a scalable, scientifically-grounded pathway for producing competitive medium-duty refractories from indigenous resources, reducing import dependence and contributing to sustainable materials development in emerging economies.