Characterization of Iron, Manganese, and Copper Synthetic Hydroxyapatites by Electron Paramagnetic Resonance Spectroscopy
- B. Sutter *a,
- T. Wasowiczb,
- T. Howardc,
- L. R. Hossnerd and
- D. W. Minge
- 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
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 (gz = 2.488, Az = 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.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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