Advisory Committee Chair
Manoj K Mahapatra
Advisory Committee Members
Shane A Catledge
Robin D Foley
James G Hemrick
Gregory W Kubacki
Haibin Ning
Document Type
Dissertation
Date of Award
2022
Degree Name by School
Doctor of Philosophy (PhD) School of Engineering
Abstract
As used chrome-based refractories may contain toxic Cr6+, the chrome-free phas-es qandilite (Mg2TiO4) and zinc aluminate (ZnAl2O4, gahnite) are being considered which are known to enhance thermomechanical properties and slag corrosion resistance. The pore generation and deleterious expansion during in situ Mg2TiO4 and ZnAl2O4 for-mation can limit their amount in a refractory composition. Hence, preformed, dense ag-gregates are desirable. Dilatometric studies revealed that when dead burned magnesia (DBM) is combined with industrial anatase instead of rutile, it expanded less (1% versus 7.2%) and the reaction occurred earlier (965℃ compared to 1120℃). The anatase-based qandilite aggregate had 0% porosity and a thermal expansion coefficient (TEC, 70-1600℃) of 13.5x10-6 K-1. Preformed ZnAl2O4 aggregates were synthesized from indus-trial ZnO and reactive Al2O3 by two-stage firing at 1050℃ and 1700℃, resulting in 0% open porosity. The ZnAl2O4 powder calcined at 1050℃ is also a good refractory matrix material as it has better sinterability than preformed refractory-grade MgAl2O4 and cal-cined alumina. The TEC of ZnAl2O4 aggregate was found to be 10.7×10-6 K-1, which is similar to tabular Al2O3 (10.3×10-6 K-1) and MgAl2O4 (10.3×10-6 K-1), but lower than DBM (16.4×10-6 K-1), creating the possibility of developing thermal shock resistant re-fractories by utilizing this mismatch. Hot strength of a refractory is directly related to an improved solid solution formation and reaction between aggregates and matrix. Contrary to multi-ingredient refractory samples, binary combinations were used to examine the iv bonding efficacy of zinc aluminate. It was observed that a better direct bonded micro-structure results when a high degree of solid solution is present, as in the sample of MgAl2O4 aggregate embedded in ZnAl2O4. Direct bonding also results when interfacial phase changes occur, for example, the ZnO-rich ZnAl2O4 layer in tabular Al2O3 aggre-gate/ZnAl2O4 matrix sample. However, this was absent and instead an interfacial debond-ing was seen in the DBM aggregate/ZnAl2O4 matrix and DBM aggregate/spinel matrix specimens. The degree of solid solution formation of tabular alumina with MgAl2O4 was found to be higher than that with ZnAl2O4. Finally, qualitative XRD revealed ZnAl2O4 is more sublimation resistant than fused magnesia-chrome aggregates at 1600℃ in air.
Recommended Citation
Mandal, Somnath, "Investigation of Zinc Aluminate as a Refractory Material" (2022). All ETDs from UAB. 473.
https://digitalcommons.library.uab.edu/etd-collection/473