First stage of reaction of molten Al with MgO substrate

Journal Article · Fri May 15 04:00:00 EDT 2015 · Materials Characterization

DOI:https://doi.org/10.1016/J.MATCHAR.2015.03.028· OSTI ID:22476091

Sobczak, N. ^[1]; Pomorska, M. ^[2]; Nowak, R. ^[1]

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1. Foundry Research Institute, 73 Zakopiańska St., 30-418 Kraków (Poland)
2. Institute of Metallurgy and Materials Science, Polish Academy of Sciences, 25 Reymonta St., 30-059 Kraków (Poland)

The Al/MgO couple was produced in vacuum (~ 5 × 10{sup −} {sup 4} Pa) by contact heating from RT up to 1000 °C and holding at that temperature for 1 h of a small 4 × 4 × 4 mm aluminium (5 N) sample placed on the [100] MgO single crystal substrate. TEM observations backed with electron diffraction analysis indicated that the interaction between liquid aluminium and MgO starts from a redox reaction producing a continuous layer of MgAl{sub 2}O{sub 4} spinel on the substrate surface. Its growth is controlled by solid state out-diffusion of magnesium and oxygen towards the surface being in contact with liquid metal. The thickening of spinel layer is accompanied by its cracking and infiltration with aluminium. The above process enables local dissolution of the MgO substrate and formation in it of a thin region of interpenetrating metallic channels walled with spinel. The removal of dissolved magnesium through open aluminium channels towards the drop and to vacuum locally produces areas of aluminium enriched with dissolved oxygen, which results in the nucleation of α-Al{sub 2}O{sub 3} at spinel clad walls. The growth of α-Al{sub 2}O{sub 3} is controlled only by the dissolution rate of MgO by aluminium, liquid state diffusion of Mg to drop/vacuum and oxygen to the front of the of α-Al{sub 2}O{sub 3} crystallites growing into MgO substrate. - Highlights: • New unique evidence of first stages of interaction of liquid Al with MgO substrates • Interaction of liquid Al with MgO starts with the formation of a layer MgAl{sub 2}O{sub 4}. • Growth of MgAl{sub 2}O{sub 4} is slow as controlled by solid state out-diffusion of Mg and O. • MgAl{sub 2}O{sub 4} serves as a nucleation site for Al{sub 2}O{sub 3} and consumed by it soon after. • Growth of Al{sub 2}O{sub 3} is fast as controlled by diffusion in liquid state.

• OSTI ID: 22476091
• Journal Information: Materials Characterization, Journal Name: Materials Characterization Vol. 103; ISSN 1044-5803; ISSN MACHEX
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM
ALUMINIUM OXIDES
CRACKING
DIFFUSION
DISSOLUTION
ELECTRON DIFFRACTION
HEATING
INTERACTIONS
LAYERS
LIQUID METALS
MAGNESIUM OXIDES
MONOCRYSTALS
NUCLEATION
OXYGEN
REDOX REACTIONS
SOLIDS
SPINELS
SUBSTRATES
SURFACES
TRANSMISSION ELECTRON MICROSCOPY