Reactive wetting of mullite Al2[Al2+2x Si2-2x] O10-x single crystals by yttrium-aluminosilicate and borosilicate glasses

• Published in: Journal of materials science Vol. 40; no. 9-10; pp. 2335 - 2340
• Main Authors: BRAUE, W, HILDMANN, B, SCHNEIDER, H, ELDRED, B. T, DARRELL OWNBY, P
• Format: Conference Proceeding Journal Article
• Language: English
• Published: Heidelberg Springer 01.05.2005; Springer Nature B.V
• Subjects: Aluminosilicates; Aluminum silicates; Borosilicate glass; Condensed matter: structure, mechanical and thermal properties; Contact angle; Corundum; Crystal structure; Crystallinity; Crystallography; Devitrification; Diffusion rate; Elastic anisotropy; Elastic properties; Exact sciences and technology; Grain boundaries; Interdiffusion; Materials science; Microcrystals; Mullite; Physics; Polycrystals; Single crystals; Solid-fluid interfaces; Substrates; Surface energy; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Wetting; Yttrium; Liquid solid interface; Wetting; Crystal orientation; Contact angle; Experimental study; Borosilicate glass; Oxide ceramics; Aluminium silicates; Interface properties; Optical microscopy; Monocrystals; Yttrium Aluminosilicates; Mullite; Models; Aluminosilicate glass
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-005-1955-2

Mullite, Al2[Al2+2x Si2-2x]O10-x, is introduced as a suitable reactive wetting model system for oxide ceramic compounds. Apparent contact angles on single crystal mullite substrates have been measured from sessile drop experiments involving (i) a highly reactive yttrium aluminosilicate (YAS) glass and (ii) a less reactive borosilicate (BS) glass. The apparent contact angles decrease with crystallographic orientation in the following order: (010) > (100) > (001) independent of glass composition. The surface energy, gammasv, has been identified as the dominant term controlling reactive wetting with gammasv(010) < gammasv(100) < gammasv(001). This order of surface energy values is rationalized in terms of the high anisotropy of the crystal structure and elastic properties of mullite. The YAS glass reacts stronger with the polycrystalline 3/2 mullite substrate due to the grain boundaries acting as fast diffusion paths. In the YAS/mullite system, analytical electron microscopy shows that for the single crystal 2/1 mullite substrate, a corundum + Y2Si2O7-rich crystalline phase assemblage results upon devitrification while in the case of the polycrystalline 3/2 mullite substrate a 2/1 mullite + Y2Si2O7-rich crystalline assemblage is formed instead. In the less reactive borosilicate system secondary 2/1 mullite microcrystals precipitate at the S/L interface with (i) random orientations established on polycrystalline substrates and (ii) characteristic preferred orientations on the single crystal substrate. A thin Al-rich interdiffusion zone (3 mm) right at the S/L interface is revealed for both glass systems.