The　preparation　of　cobalt　blue　pigment　(CoAl2O4)　using　freeze-drying　technology　was　investigated.　Cobalt　blue　nanopowder　was　prepared　using　cobalt　acetate　[Co(CH3COO)(2)center　dot　4H(2)O]　and　aluminum　sulfate　[Al-2(SO4)(3)center　dot　18H(2)O],　with　liquid　nitrogen　as　the　cryogenic　medium.　Cobalt　blue　nanopowder　samples　with　Co/Al　=　1:2　and　1:2.4　were　obtained　by　using　processes　including　pre-freezing　spraying,　vacuum　drying,　and　calcination.　X-ray　diffraction,　transmission　electron　microscopy　and　ultraviolet　spectroscopy　were　used　to　analyze　the　freeze-dried　precursors　and　calcined　products.　The　freeze-dried　precursor　was　amorphous.　Co2AlO4　appeared　at　the　calcination　temperature　of　750　degrees　C,　while　CoAl2O4　was　converted　from　CO2AlO4　at　900　degrees　C,　and　the　particle　size　was　about　25　nm.　The　higher　the　calcination　temperature,　the　greater　the　degree　of　crystallization.　The　cobalt　blue　pigment　with　Co/Al　=　1:2　was　a　lighter　but　more　saturated　color　than　the　1:2.4　sample.　Increasing　the　calcination　temperature　and　lengthening　the　time　could　optimize　the　optical　performance　of　the　pigment.　(C)　2012　Elsevier　B.V.　All　rights　reserved.