Interactions between bismuth oxide and ceramic substrates for thick film technology
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Interactions between bismuth oxide and ceramic substrates for thick film technology Simona Immovilli, Bruno Morten, and Maria Prudenziati Istituto Nazionale per la Fisica della Materia (INFM) and Department of Physics, University of Modena, 41100 Modena, Italy
Alessandro Gualtieri Department of Earth Sciences, University of Modena, 4100 Modena, Italy
Massimo Bersani CMBM (Centre of Medical Biophysics and Materials), Povo, Trento, Italy (Received 10 July 1997; accepted 15 October 1997)
We investigated the interactions between screen printed and fired layers of Bi2 O3 and ceramic substrates of alumina and beryllia. It was found that the reaction products are invariably crystalline in nature. Several transitions of Bi2 O3 in its polymorphic phases were found to occur on BeO substrates, while newly formed compounds have been observed to grow on alumina substrates, i.e., Al4 Bi2 O9 on 99.9% Al2 O3 and Bi12 SiO20 on 96% Al2 O3 . Bismuth deeply penetrates in the ceramic interstices in all the cases. Until Bi2 O3 is not completely reacted, this penetration is diffusion limited (penetration depth 1/2 w ΓΈ td , where td is the reaction time) with values of the activation energy ranging from 3.7 6 0.6 eV (BeO substrate) to 1.4 6 0.06 eV (96% Al2 O3 substrate). It is shown that these processes are notably different to those occurring in PbO/ceramic systems; moreover, they imply different adhesion phenomena of thick films on different substrates.
I. INTRODUCTION
Surprisingly, limited knowledge is presently available on interaction mechanisms between metal oxides and ceramic substrates for screen printing technology, with a consequent diffused empiricism in the choice of the binding agent, its concentration, and process conditions. In this context, a systematic investigation has been recently undertaken to clarify the interaction kinetics between PbO and ceramic substrates consisting of alumina and beryllia.1 In both cases, the controlling interaction does not involve the primary phase (Al2 O3 and BeO, respectively) of the substrate but rather its intergranular glassy phase. In the present work, we discuss the results of a study dealing with mechanism and kinetics of interactions between Bi2 O3 and aluminas (99.9% Al2 O3 and 96% Al2 O3 ), and beryllia (99.5%). Interest in these systems stems from the wide field of applications of Bi2 O3 in thick film technology; they include the use of Bi2 O3 as adhesion promoter in hybrid microelectronics components and thick film sensors, e.g., spineltype based films for humidity sensors2 as well as ion conductors for electrochemical devices.3 The results of our investigations allowed us to identify different phase transitions of Bi2 O3 in its various polymorphic forms during the thermal process, and to observe the appearance of newly formed phases whose composition and kinetics are strongly affected not only by the substrate major phase (BeO and Al2 O3 ), but also by J. Mater. Res., Vol. 13, No. 7, Jul 1998
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