Impact on aggregate/matrix bonding when a refractory contains zinc aluminate instead of spinel and magnesia‐chrome
Somnath Mandal, James G. Hemrick, Manoj K. Mahapatra
Abstract
Abstract The high hot strength of MgO–Cr 2 O 3 refractory is often ascribed to its intimate aggregate/matrix bonding. For a fundamental comparison with it, ∼2 mm aggregates of MgO and Al 2 O 3 were separately embedded in ZnAl 2 O 4 and MgAl 2 O 4 matrices, sintered at 1600°C, and examined. It was found that similarity of thermal expansion coefficient (TEC) between the aggregate and the matrix is critical to achieve good bonding and this is more important than the extent of interdiffusion. The TEC mismatch of ≥5.7 × 10 −6 K −1 caused significant undesirable debonding in MgO aggregate/MgAl 2 O 4 matrix sample and MgO/ZnAl 2 O 4 despite >736 μm Zn 2+ diffusion depth in the latter. Direct bonding, as inferred from a thicker interfacial reaction layer and a greater shift of the aggregate/matrix interface before and after firing, was better in MgAl 2 O 4 /ZnAl 2 O 4 combination, followed by tabular Al 2 O 3 /ZnAl 2 O 4 and Al 2 O 3 /MgAl 2 O 4 . Powder X‐ray diffraction indicated that the volatilization of ZnAl 2 O 4 at 1600°C in air was negligible compared to MgO–Cr 2 O 3 .