Iron-nitride-coated　iron　microparticles　were　prepared　by　nitridation　of　the　surface　of　iron　microparticles　with　ammonia　gas　at　a　temperature　of　510　degrees　C.　The　phases,　composition,　morphology,　magnetic　properties,　and　chemical　stability　of　the　particles　were　studied.　The　phases　were　alpha-Fe,　epsilon-Fe3N,　and　gamma-Fe4N.　The　composition　varied　from　the　core　to　the　surface,　with　99.8　wt%　Fe　in　the　core,　and　93.8　wt%　Fe　and　6　wt%　N　in　the　iron-nitride　coating.　The　thickness　of　the　iron-nitride　coating　was　about　0.28　mu　m.　The　chemical　stability　of　the　microparticles　was　greatly　improved,　especially　the　corrosion　resistance　in　corrosive　aqueous　media.　The　saturation　magnetization　and　the　coercive　force　were　17.1　x　10(3)　and　68　kA/m,　respectively.　It　can　be　concluded　that　iron-nitride-coated　iron　microparticles　will　be　very　useful　in　many　fields,　such　as　water-based　magnetorheological　fluids　and　polishing　fluids.　(c)　2006　Elsevier　B.V.　All　rights　reserved.