Ru2Si3 single crystals have been grown by the zone melting technique with radiation heating. These crystals contain inclusions, about 500 nm in size, which consist of monocrystalline ruthenium disilicide. Endothermic peaks detected at T = 962degreesC in the DTA traces of RuSix are interpreted as decomposition of RuSi2 to Ru2Si3 and Si. This enabled us to update the Si-rich part of the Ru-Si phase diagram. (C) 2002 Published by Elsevier Science B.V.