title: A new approach to prepare well-dispersed CaF(2) nanoparticles by spray drying technique.
abstract: Previously, nano-sized calcium fluoride (CaF₂) particles were prepared using a spray drying method by simultaneously feeding Ca(OH)₂ and NH₄F solutions to a two-liquid nozzle. The aim of the present study was to prepare better-dispersed nano-CaF₂ particles by co-forming a soluble salt, sodium chloride (NaCl). NaCl of various concentrations were added to the NH(4) F solution, leading to formation of (CaF₂ +NaCl) composites with CaF₂ /NaCl molar ratios of 4/1, 4/4, and 4/16. Pure nano-CaF₂ was also prepared as the control. Powder X-ray diffraction analysis showed that the products contained crystalline CaF₂ and NaCl. Scanning electron microscopy examinations showed that both the CaF₂ /NaCl composite and pure CaF₂ particles were about (50-800) nm in size and consisted of primary CaF₂ particles of < 50 nm in size. BET surface area measurements showed similar primary particle sizes for all samples. Dynamic light scattering measurements showed that the washed (CaF₂+NaCl) particles were much smaller than the pure CaF₂ as the dissolution of NaCl "freed" most of the primary CaF₂ particles, leading to a greater degree of particle dispersion. The well-dispersed nano-CaF₂ may be expected to be a more effective anticaries agent than NaF by providing longer lasting elevations of fluoride concentrations in oral fluids.
authors.affiliation: American Dental Association Foundation, Paffenbarger Research Center, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8546, USA. limin.sun@nist.gov
authors.forename: Limin
authors.initials: L
authors.lastname: Sun
authors.forename: Laurence C
authors.initials: LC
authors.lastname: Chow
authors.forename: John E
authors.initials: JE
authors.lastname: Bonevich
authors.forename: Tongxin
authors.initials: T
authors.lastname: Wang
authors.forename: James W
authors.initials: JW
authors.lastname: Mitchell
mesh_terms: D064751:Ammonium Compounds; D002124:Calcium Fluoride / Q000138:chemical synthesis* / Q000737:chemistry; D002126:Calcium Hydroxide; D003731:Dental Caries / Q000517:prevention & control*; D005459:Fluorides; D006801:Humans; D008722:Methods; D053758:Nanoparticles / Q000737:chemistry*; D010316:Particle Size; D000644:Quaternary Ammonium Compounds
chemical_list: D064751:Ammonium Compounds; D000644:Quaternary Ammonium Compounds; C024822:ammonium fluoride; D002124:Calcium Fluoride; D002126:Calcium Hydroxide; D005459:Fluorides