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Title: First stage of reaction of molten Al with MgO substrate

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 bymore » 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.« less
Authors:
 [1] ;  [2] ;  [3] ;  [1] ;  [2]
  1. Institute of Metallurgy and Materials Science, Polish Academy of Sciences, 25 Reymonta St., 30-059 Kraków (Poland)
  2. Foundry Research Institute, 73 Zakopiańska St., 30-418 Kraków (Poland)
  3. (Poland)
Publication Date:
OSTI Identifier:
22476091
Resource Type:
Journal Article
Resource Relation:
Journal Name: Materials Characterization; Journal Volume: 103; Other Information: Copyright (c) 2015 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
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