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DIVISION S-9—SOIL MINERALOGY

Characterization of Iron, Manganese, and Copper Synthetic Hydroxyapatites by Electron Paramagnetic Resonance Spectroscopy

^a National Research Council, NASA Ames Research Center, Moffett Field, CA 94035
^b Dep. of Physics and Astronomy, Georgia State Univ., Atlanta, GA 30303
^c Dep. of Chemistry, Texas A&M Univ., College Station, TX 77843
^d Dep. of Soil and Crop Sciences, Texas A&M Univ., College Station, TX 77843
^e NASA Johnson Space Center, Houston TX 77058

* Corresponding author (b-sutter{at}mail.arc.nasa.gov)

The incorporation of micronutrients (e.g., Fe, Mn, Cu) into synthetic hydroxyapatite (SHA) is proposed for slow release of these nutrients to crops in NASA's Advanced Life Support (ALS) program for long-duration space missions. Separate Fe³⁺ (Fe-SHA), Mn²⁺ (Mn-SHA), and Cu²⁺ (Cu-SHA) containing SHA materials were synthesized by a precipitation method. Electron paramagnetic resonance (EPR) spectroscopy was used to determine the location of Fe³⁺, Mn²⁺, and Cu²⁺ ions in the SHA structure and to identify other Fe³⁺-, Mn²⁺-, and Cu²⁺-containing phases that formed during precipitation. The EPR parameters for Fe³⁺ (g = 4.20 and 8.93) and for Mn²⁺ (g = 2.01, A = 9.4 mT, D = 39.0 mT and E = 10.5 mT) indicated that Fe³⁺ and Mn²⁺ possessed rhombic ion crystal fields within the SHA structure. The Cu²⁺ EPR parameters (g_z = 2.488, A_z = 5.2 mT) indicated that Cu²⁺ was coordinated to more than six oxygens. The rhombic environments of Fe³⁺ and Mn²⁺ along with the unique Cu²⁺ environment suggested that these metals substituted for the 7 or 9 coordinate Ca²⁺ in SHA. The EPR analyses also detected poorly crystalline metal-oxyhydroxides or metal-phosphates associated with SHA. The Fe-, Mn-, and Cu-SHA materials are potential slow release sources of Fe, Mn, and Cu for ALS and terrestrial cropping systems.

Abbreviations: ALS, Advanced Life Support • EPR, electron paramagnetic resonance • INAA, instrumental neutron activation analysis • NMR, nuclear magnetic resonance • SHA, synthetic hydroxyapatite • XRD, x-ray diffraction • ZFS, zero field splitting

This article has been cited by other articles:

				B. Sutter, L. R. Hossner, and D. W. Ming Dissolution Kinetics of Iron-, Manganese-, and Copper-Containing Synthetic Hydroxyapatites Soil Sci. Soc. Am. J., March 1, 2005; 69(2): 362 - 370. [Abstract] [Full Text] [PDF]

				B. Sutter, D. W. Ming, A. Clearfield, and L. R. Hossner Mineralogical and Chemical Characterization of Iron-, Manganese-, and Copper-Containing Synthetic Hydroxyapatites Soil Sci. Soc. Am. J., November 1, 2003; 67(6): 1935 - 1942. [Abstract] [Full Text] [PDF]