Wetting of (0 0 0 1) alpha-Al2O3 single crystal by molten Mg was studied by an improved sessile drop method in a purified flowing Ar atmosphere. A distinct pinning-depinning behavior was observed during the evaporation-coupled wetting process. The underlying mechanism for this behavior was expatiated from the viewpoints of energetics and geometries at the triple junction. (C) 2011 Elsevier B. V. All rights reserved.