Interfacial reactions between a lead borosilicate glass containing CuO and an Al/Si alloy - evidence for galvanic cells
UNSPECIFIED. (2001) Interfacial reactions between a lead borosilicate glass containing CuO and an Al/Si alloy - evidence for galvanic cells. JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 21 (3). pp. 427-436. ISSN 0955-2219Full text not available from this repository.
A PbO-rich borosilicate glass with the additions of CuO and Al2O3 has been developed as a thick-film, dielectric coating for a high Si content Al/Si alloy produced by the Osprey process (Al-70Si wt.%). Wetting behaviour and interfacial reactions were investigated using sessile drop experiments at temperatures between 520 and 583 degreesC under air and argon atmosphere. The wetting behaviour of the glass was found to be a function of atmosphere and wetting angle decreased with increasing temperature and time. Coatings applied in air in the range 520-565 degreesC showed < 1% porosity, whereas those applied at 583<degrees>C in argon exhibited relatively high porosity (similar to8%) and both coating and un-wetted substrate surface supported large Al-Si spheres containing similar to 21 wt.% Si. Coatings heated in air at 520 and 540 degreesC show good bonding with no interfacial reaction products. However, those samples heated in air at 565 degreesC consistently show evidence of excessive interfacial reactions which are the components of a galvanic process, leading to the oxidation and dissolution of the Al regions (anodic) and the deposition of copper ar the glass/Si interface (cathodic). From observations of the rate of copper deposition, the current density arising from the electron flow through the alloy has been calculated to be similar to0.91 A m(-2). The galvanic process is suppressed at the periphery of the coating where oxygen diffused from the atmosphere enables interface oxidation. The onset of the galvanic process between 540 and 565 degreesC occurs when dissolution rate exceeds oxidation rate, exposing the fresh Al anode to the glass melt. Under inert atmosphere (at 583 degreesC). air oxidation is not possible and galvanic cell redox reactions generate an excessive copper interlayer as the system attempts to sustain the oxide layer at the Al anode. Crown Copyright (C) 2001 Published by Elsevier Science Ltd. All rights reserved.
|Item Type:||Journal Article|
|Subjects:||T Technology > TP Chemical technology|
|Journal or Publication Title:||JOURNAL OF THE EUROPEAN CERAMIC SOCIETY|
|Publisher:||ELSEVIER SCI LTD|
|Number of Pages:||10|
|Page Range:||pp. 427-436|
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