Coal fly ash utilization: low temperature sintering of wall tiles

Area of Science:

• Materials Science
• Ceramics Engineering
• Waste Valorization

Background:

• Fly ash utilization in construction materials is crucial for sustainability.
• Traditional sintering activators may have limitations in achieving desired material properties.
• Developing cost-effective and high-performance ceramic tiles from industrial byproducts is an ongoing challenge.

Purpose of the Study:

• To investigate the effect of pyrophyllite addition on the sintering behavior and properties of fly ash-based composites.
• To determine the optimal composition for producing wall tiles meeting Indian Standards.
• To understand the microstructural evolution and phase formation during sintering.

Main Methods:

• Sintering experiments were conducted on fly ash and pyrophyllite mixtures with sodium hexa meta phosphate (SHMP) at temperatures ranging from 925-1050°C.
• Impact strength, apparent density, shrinkage, and water absorption were measured.
• Microstructural analysis using scanning electron microscopy (SEM) was performed.

Main Results:

• Sintering fly ash with SHMP alone resulted in low impact strength.
• Incorporating ≥40% (w/w) pyrophyllite significantly improved impact strength, meeting the Indian Standards Institute limit of 19.6 J/m.
• Increasing pyrophyllite content led to higher apparent density and reduced shrinkage and water absorption.
• Phase analysis revealed silicophosphate formation in fly ash-rich compositions and tridymite-structured T-AlPO(4) in pyrophyllite-rich ones.

Conclusions:

• Low alkali pyrophyllite is an effective additive for enhancing the properties of SHMP-activated fly ash sintered composites.
• Compositions containing ≥40% pyrophyllite are suitable for manufacturing durable wall tiles.
• The formation of T-AlPO(4) crystals contributes to the improved mechanical performance of the sintered tiles.