High-Temperature Testing Accelerates Refractory Development

The Challenge

Refractory castable development faces a fundamental dilemma: calcium aluminate cement (CAC) bonding causes problems at high temperature due to CaO content and requires careful drying. Colloidal silica (CS) alternatives avoid these issues but create structural instabilities at elevated temperatures where viscous phases form. Alternative sols like spinel and mullite offer better high-temperature performance but suffer from extended setting times and low green strength because their initial solid content (5-10 wt%) is much lower than commercial CS (30 wt%).

The Solution

This research developed spinel suspensions with 30-50 wt% solid content to overcome the green strength limitations while maintaining high-temperature advantages. The team analyzed how solid content affects setting behavior, green mechanical properties, and thermomechanical performance including elastic modulus and hot modulus of rupture (HMOR).

The GrindoSonic MK7 coupled with a high-temperature furnace enabled in-situ measurement of elastic modulus during thermal cycling up to 1500°C. This provided direct feedback on how formulation changes affected property evolution through the entire temperature range, accelerating development cycles that would otherwise require extensive destructive testing.

Key takeaway: In-situ elastic modulus measurement during thermal cycling up to 1500°C replaced extensive destructive testing, enabling rapid iteration of spinel suspension formulations with 30-50 wt% solid content.

Results

Higher solid content enhanced green mechanical properties of spinel-bonded castables, though with longer demoulding times than CS-bonded versions. Critically, thermomechanical properties improved significantly during initial heating, surpassing CS-bonded castables especially above 1000°C where colloidal silica systems begin forming problematic viscous phases. The research demonstrates a practical pathway to castables with both good handleability and superior hot performance.