Dissemination of IT for the Promotion of Materials Science (DoITPoMS)

DoITPoMS Micrograph Library Full Record for Micrograph 148

Full Record for Micrograph 148

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Micrograph no
148
Brief description
Magnesia-chrome refractory brick
Keywords
aluminium Link to MATTER Glossary entry for aluminium, bond Link to MATTER Glossary entry for bond, brick Link to MATTER Glossary entry for brick, calcium Link to MATTER Glossary entry for calcium, ceramic Link to MATTER Glossary entry for ceramic, chromia, chromite, chromium, grain Link to MATTER Glossary entry for grain, iron, magnesia, magnesium, silicon Link to MATTER Glossary entry for silicon
Categories
Ceramic
System
MgO-Cr2O3
Composition
MgO 70, Cr2O3 19, Al2O3 4, Fe2O3 4, CaO 1, SiO2 1 (wt%)
Standard codes
Reaction
Direct bonded brick i.e. fine MgO and Cr<sub>2</sub>O<sub>3</sub> react to form MgCr<sub>2</sub>O<sub>4</sub> spinel bonds
Processing
MgO and Cr2O3 grain and finer bond powders pressed with organic binder and fired to 1850 °C in neutral atmosphere.
Applications
Secondary steel making e.g. high wear areas of vacuum degassers. Were used extensively in cement kiln linings but formation of carcinogenic Cr<sup>6+</sup> in use means they are no longer used.
Sample preparation
Polished but unetched.
Technique
Reflected light microscopy
Length bar
1 mm
Further information
The micrograph shows the large sintered MgO aggregate (grey) with white chromite and dark pores. In particular, small (5mm) Cr2O3 precipitates are seen in the MgO. Fine particles react to form spinel which directly bond the aggregates conferring high temperature strength.
Contributor
Prof W E Lee
Organisation
Department of Engineering Materials, University of Sheffield
Date
10/05/02
Licence for re-use
Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales
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