Most of ultrafine particles of metallic copper reported so far were of polycrystalline structures. Here, some ultrafine particles of metallic copper of single-crystalline structure were synthesized in gas phase. Some mixtures of a raw copper powder (about 79 mu m) and sodium chloride powder were used as the precursor materials. The materials were chlorinated by dry chlorine at 400 degrees C. Some anhydrous eutectics composed of copper chlorides and sodium chloride were thus obtained. The eutectics were first heated in situ up to 900 degrees C and then carried to a gas space by evaporation using a flowing Argon, where they met H-2 and were reduced to metallic copper particles. It was found that all these copper particles prepared were of single-crystalline structure irrespective of the molar ratio of raw copper and sodium chloride. When the molar ratio of NaCl to Cu in the precursor materials was 1 to 3, some dispersed octahedral particles of single-crystalline copper with an average size of 776 nm were prepared. However, when the ratio was increased to 4 to 1, some dispersed spherical particles of single-crystalline copper with a size of 92 nm were obtained. No impurities from the two shapes of copper particles were detected. The mechanisms involved in controlling the shape and size of copper particles were proposed. (C) 2016 Elsevier B.V. All rights reserved.