04-12 corundum aggregate fracture modes

[Image above] Researchers in China investigated the effects of different corundum aggregates on the slag resistance of Al2O3-SiC-C bricks. Pictured are the various fracture modes of the samples after different heat treatments. Credit: Gao et al., International Journal of Applied Ceramic Technology

Where there’s a will, there’s a way, and nothing quite demonstrates this statement like our continued insistence on consuming dairy products despite most people being lactose intolerant. But the consequences of this decision can be mitigated by turning milk into cheese, which reduces the lactose content, and this trick has been used since the Neolithic era, as reported on CTT last Friday.

As the above example shows, small differences in otherwise similar materials can result in substantially different outcomes during application. This concept shows up frequently in studies on refractory composition.

Refractory ceramics, like concrete, consist largely of fine and coarse aggregates held together with a binder. But while concrete is quite forgiving in terms of what can be used as an aggregate, refractory performance can be greatly affected by differences in aggregate chemical composition and microstructure.

Consider, for example, the effect of different magnesium sources on the production of magnesium aluminate spinel. A study highlighted on CTT in May 2023 reported noticeable differences in the physical properties of spinel samples created using magnesite, fused magnesia, and light burned magnesia, respectively, despite the similarities between these common magnesium sources.

Similarly, in July 2023, CTT reported on the effects of different carbon sources on magnesia carbon bricks. This study again demonstrated how the slight differences between chemically similar starting materials may markedly alter the results.

Today, we share another study that explores the impact of starting material on refractory properties. In this case, researchers from Wuhan University of Science and Technology in China investigated the effects of different corundum aggregates on Al2O3-SiC-C bricks.

Al2O3-SiC-C bricks are widely used in hot metal pretreatment equipment, such as hot metal ladles and torpedo tanks, because of their excellent resistance to oxidation, slag corrosion, permeability, and thermal shock. But as metallurgical material developments lead to hotter and more corrosive processing environments, as described in the recently published April 2024 Bulletin cover story, the required mechanical properties and slag resistance of refractories are becoming more stringent.

Currently, there are many types of corundum refractory aggregates used to create Al2O3-SiC-C bricks. For this study, the researchers tested the effects of using bauxite, fused brown corundum, tabular corundum, fused white corundum, and microporous corundum.

Their tests revealed two characteristics of the corundum aggregate that most affect the brick’s slag resistance:

  1. Impurity phase content of the aggregate. When the aggregate is in contact with the slag, the impurity phase in the aggregate is more likely to react with the slag and aggravate the corrosion of the slag on the aggregate.
  2. Microstructure of the aggregate. The microcracks in the aggregate, or the through-holes produced by re-sintering, will provide a channel for slag corrosion and aggravate the corrosion of the slag on the aggregate.

Of the five corundum aggregates tested in this study, bricks made with tabular corundum, which had lower porosity and impurity content, exhibited the best slag resistance.

But with this newfound knowledge of the aggregate structure–property relationship, “The scope of the study can be expanded to conduct more comprehensive and systematic research,” the researchers conclude.

The paper, published in International Journal of Applied Ceramic Technology, is “Effect of aggregate type on the mechanical properties and slag resistance of Al2O3-SiC-C hot metal ladle bricks” (DOI: 10.1111/ijac.14589).