Applied Surface Science 357 (2015) 1104–1113 Contents lists available at ScienceDirect Applied Surface Science journal h om epa ge: www.elsevier.com/locate/apsusc Wetting and reaction characteristics of crystalline and amorphous SiO 2 derived rice-husk ash and SiO 2 /SiC substrates with Al–Si–Mg alloys A. Bahrami, M.I. Pech-Canul ∗ , C.A. Gutiérrez, N. Soltani Centro de Investigación y de Estudios Avanzados del IPN Unidad Saltillo, Av. Industria Metalúrgica No. 1062, Parque Industrial Saltillo-Ramos Arizpe, Ramos Arizpe, Coahuila, 25900, Mexico a r t i c l e i n f o Article history: Received 15 June 2015 Received in revised form 17 August 2015 Accepted 15 September 2015 Keywords: Rice husk ash Sessile drop test Wettability Silicon carbide Aluminum alloys a b s t r a c t A study of the wetting behavior of three substrate types (SiC, SiO 2 -derived RHA and SiC/SiO 2 -derived RHA) by two Al–Si–Mg alloys using the sessile drop method has been conducted, using amorphous and crystalline SiO 2 in the experiment. Mostly, there is a transition from non-wetting to wetting contact angles, being the lowest  values achieved with the alloy of high Mg content in contact with amorphous SiO 2 . The observed wetting behavior is attributed to the deposited Mg on the substrates. A strong diffusion of Si from the SiC/Amorphous RHA substrate into the metal drop explains the free Si segregated at the drop/substrate interface and drop surface. Although incorporation of both SiO 2 -derived RHA structures into the SiC powder compact substrates increases the contact angles in comparison with the SiC substrate alone, the still observed acute contact angles in RHA/SiC substrates make them promising for fabrication of composites with high volume fraction of reinforcement by the pressureless infiltration technique. The observed wetting characteristics, with decrease in surface tension and contact angles is explained by surface related phenomena. Based on contact angle changes, drop dimensions and surface tension values, as well as on the interfacial elemental mapping, and XRD analysis of substrates, some wetting and reaction pathways are proposed and discussed. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Reactive metal penetration, in which a molten metal wets, penetrates, and reacts with either a dense or a porous ceramic preform, converting it into a ceramic–metal composite, has been subject of experimental and theoretical investigations [1,2]. Under- standing the reactive wetting behavior of molten alloys in contact with ceramic substrates at high temperatures is of great impor- tance for improving industrial liquid phase-assisted processes and the quality of the final product. The study of the wetting behav- ior at elevated temperatures, therefore, constitutes one of the most important scientific aspects of high-temperature liquid phase materials processing stimulated by the needs of modern metallurgy and foundry industry. Most pure metals exhibit obtuse contact angles on high melt- ing point ceramics (such as SiC, SiO 2 , Si 3 N 4 or Al 2 O 3 ) or graphite, ∗ Corresponding author. Tel.: +52 844 438 9600x8678. E-mail addresses: martin.pech@cinvestav.edu.mx, martpech@gmail.com, martpech@hotmail.com (M.I. Pech-Canul). causing limitation on their application in brazing, bonding, liquid- phase sintering, or infiltration [3]. This problem can be alleviated by alloying with reactive metals such as (Ti, V, Cr, Zr, Nb, Hf, Mg and etc.) into the liquid or controlling the atmosphere of experiment by reactive or inert gases (e.g. argon and nitrogen). These additions can reduce wetting angles to acute, often strongly. Much work has been done on the wetting behavior of SiC, SiO 2 and silica rich ashes (like fly ash) substrates [4–6]. Reactive wetting behavior of SiO 2 substrate by molten pure Al was studied by Shen et al. [7]. They reported that although Al-SiO 2 system is a non-wetting system in nature, the subsequent remarkable decrease in the contact angle during the isothermal dwells mainly results from the decrease in the droplet volume rather than the advance of the solid–liquid interfacial front. In contrast, Laurent et al. [8] believed that the study of wetting behavior of Al-SiO 2 cannot be treated as an investigation of reactive wetting because the SiO 2 reduction reaction by aluminum does not take place during the spreading of aluminum on SiO 2 . Also, they believed that the observed uncertainty regarding to low temperature wetting in Al/SiO 2 is related to the presence of an oxide film on Al, which hinders spreading, while Zhou and De Hosson [9] propose that http://dx.doi.org/10.1016/j.apsusc.2015.09.137 0169-4332/© 2015 Elsevier B.V. All rights reserved.