High-Resolution Transmission Electron Microscopy Observation of - PowerPoint PPT Presentation

High-Resolution Transmission Electron Microscopy Observation of Thermal Decomposition Process of Ca-Deficient Hydroxyapatite Koji NISHIO, Masato TAMAI, Mitsuhiro NAKAMURA and Toshiyuki ISSHIKI Nano-Structural Science Laboratory, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan

Hydroxyapatite a Hydroxyapatite ( Ca 10 ( PO 4 ) 6 ( OH ) 2 : HAp) • Crystal structure: Similar to a bone Hexagonal ( a = 0 . 943 nm , c = 0 . 688 nm ) ⇓ b widely noticed and expected [00¯ 1] • As an alternative material for bone c • Application to a biosensor making good use of biocompatibility b [100]

Synthesis of Hydroxyapatite Dry process ⇒ Stoichiometric HAp (s-HAp) 6CaHPO 4 + 4CaCO 3 → s - HAp + 2H 2 O + 4CO 2 Wet process ⇒ Non-stoichiometric HAp • Sol-gel method • Hydrolysis method A. Nakahira et al. , J. Am. Ceram. Soc. 82 (1999) 2029-2032

Hydrolysis Method α -tricalcium phosphate ( α - Ca 3 ( PO 4 ) 2 : α -TCP) α -TCP α -TCP α -TCP α -TCP α -TCP ⇓ Hydrolysis in a mixture of water and alcohol 500 nm 500 nm 0 h 0 h 500 nm 0 h 500 nm 500 nm 0 h 0 h ⇓ ⇓ ⇓ ⇓ ⇓ α -TCP α -TCP α -TCP Calcium-deficient HAp α -TCP α -TCP ( Ca 10 − Z ( HPO 4 ) Z ( PO 4 ) 6 − Z ( OH ) 2 − Z ⋅ n H 2 O ( Z = 0 - 1 ) : 1 h 1 h 1 h 1 h 1 h Ca-def HAp) ⇓ ⇓ ⇓ ⇓ ⇓ Ca-def HAp Ca-def HAp Ca-def HAp Ca-def HAp Ca-def HAp Advantage of this method: • Easy to systhesis within several hours 2 h 2 h 2 h 2 h 2 h ⇓ ⇓ ⇓ ⇓ ⇓ under mild conditions • Easy to control of crystal morphology plate-, blade-, whisker-like shape, etc. 3 h 3 h 3 h 3 h 3 h

Ca-Deficient Hydroxyapatite 770 ° C 770 ° C 770 ° C 770 ° C 770 ° C Ca-def HAp → s-HAp + β -TCP Important reaction to develop 900 ° C 900 ° C 900 ° C 900 ° C 900 ° C new biomaterials Whisker-like shape is favorable 980 ° C 980 ° C 980 ° C 980 ° C 980 ° C as a source to produce porous biomaterials 1040 ° C 1040 ° C 1040 ° C 1040 ° C 1040 ° C TEM observation of the whisker-like shape, Ca- 1 µ m 1 µ m 1 µ m 1 µ m 1 µ m def HAp crystals

Experimental Procedure Specimen Source: Whisker-like shape, Ca-def HAp synthesized by hydrolysis method (Ca/P molar ratio = 1.58) Annealed at 200-1100 ° C in air Heat (heating rate: 5 ° C/min, keep time: 2-6 hours) treatment: Equipment TEM JEOL, JEM-2010/SP (EDS) Noran, Vantage XRD Rigaku, RINT 2000 FT-IR JEOL, IR-WINSPEC100

TEM images of samples before & after annealing annealed at 600 ° C annealed at 600 ° C annealed at 600 ° C annealed at 600 ° C annealed at 600 ° C before annealing before annealing before annealing before annealing before annealing Ca-def HAp whiskers 2 ∼ 5 µ m Length ( c axis): ∼ 0.1 µ m Width: Ca/P molar ratio: 1.58 5 ° C/min Heating rate: Keep time: 2 hours 700 ° C 700 ° C 800 ° C 800 ° C 900 ° C 900 ° C 700 ° C 800 ° C 900 ° C 700 ° C 700 ° C 800 ° C 800 ° C 900 ° C 900 ° C 500 nm 500 nm 500 nm 500 nm 500 nm

Analysis of XRD patterns 900 ° C 900 ° C 900 ° C 900 ° C 900 ° C 1100 ° C 800 ° C 800 ° C 800 ° C 800 ° C 800 ° C 1000 ° C 900 ° C ✟ ✯ ✟✟ Intensity [a.u.] β -TCP 800 ° C HAp ✲ 600 ° C 600 ° C 600 ° C 600 ° C 600 ° C 600 ° C ✲ 400 ° C before annealing before annealing before annealing before annealing before annealing 200 ° C before annealing ✲ 20 30 40 50 60 500 nm 500 nm 500 nm Diffraction angle 2 θ [degree] 500 nm 500 nm

Ca-def HAp whisker annealed at 800 ° C 50 nm 50 nm 50 nm 50 nm 50 nm HAp HAp HAp HAp HAp 100 100 → → ← ← 100 → ← 100 100 → → ← ← 002 002 002 002 002 HAp HAp HAp HAp HAp → → → → → HAp HAp [010] [010] [010] HAp [010] [010] HAp HAp Planar defect / Layered precipitate • traversing in the whisker • parallel to (100) plane (100) (100) (100) (100) (100) 3 nm 3 nm 3 nm 3 nm 3 nm

Planar defect and layered phase 600 ° C 600 ° C 600 ° C 700 ° C 700 ° C 700 ° C 800 ° C 800 ° C 800 ° C 600 ° C 600 ° C 700 ° C 700 ° C 800 ° C 800 ° C 20 nm 20 nm 20 nm 20 nm 20 nm ↑ ↑ ↑ ↑ ↑ 1.43 nm 1.43 nm 1.43 nm 1.43 nm 1.43 nm ↓ ↓ ↓ ↓ ↓ planar defect planar defect planar defect planar defect planar defect ↑ ↑ ↑ ↑ ↑ (100) (100) (100) (100) (100) (100) (100) (100) (100) (100) 5 nm 5 nm (001) (001) 5 nm (001) 5 nm 5 nm [021] [021] [010] [010] (001) (001) [010] [010] [021] [010] [010] [021] [021] [010] [010] [010] [010]

TEM-EDS microanalysis A (layered phase) Ca Ca B (Ca-def HAp) P Counts [a.u.] A A A A A ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ Counts [a.u.] ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ O ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✾ ✘ ✾ ✘ ✾ ✘ ✘ ✘ ✾ ✘ ✾ ✘ P Ca O Energy [keV] ✏ ✶ ✏ ✶ ✏✏✏✏✏✏✏✏✏✏✏ ✏✏✏✏✏✏✏✏✏✏✏ ✶ ✏ ✶ ✏ ✶ ✏ ✏✏✏✏✏✏✏✏✏✏✏ ✏✏✏✏✏✏✏✏✏✏✏ ✏✏✏✏✏✏✏✏✏✏✏ atomic molar ratio Ca area Ca/P Ca P B B B B B [atom. %] A 1.86 65 35 B 1.27 56 44 Energy [keV] s-HAp 1.67 62.5 37.5 ⇒ Ca-rich 2 nm 2 nm 2 nm 2 nm 2 nm [021]

Analysis of IR absorption spectra IR absorption spectrum of the sample annealed at 800 ° C 900 ° C ⇓ 900 ° C • IR absorption peak at ✻ 800 ° C Transmittance [a.u.] 800 ° C 3570 cm − 1 shifted to 744 cm − 1 Transmittance [a.u.] 3538 cm − 1 ❨ 3538 cm − 1 ❍ ❍ • IR absorption peak ap- 600 ° C 3570 cm − 1 peared at 744 cm − 1 600 ° C 400 ° C ⇓ Ca-rich HAp 400 ° C G. Bonel et al. , Ann. NY Acad. Sci. 523 (1988) 115 3800 3300 2800 1400 900 400 Wave number [cm − 1 ] Wave number [cm − 1 ]

Ca-rich metastable phase The unidentified phase appeared in the annealed Ca-def HAp ⇓ ⇓ TEM-EDS, IR TEM EDS: higher Ca/P molar 600 ° C: planar defect ratio than of s-HAp 700-800 ° C: layered phase IR: shift & appearance 900 ° C: not observed of absorption peaks ⇓ ⇓ Metastable phase Ca-rich phase ⇓ ⇓ Ca-rich metastable phase

Relation between the Ca-def HAp and the phase (100) (100) (100) 1.43 nm 1.43 nm (100) (100) 1.43 nm 1.43 nm 1.43 nm → → ← ← → ← → → ← ← Ca-def HAp 002 002 002 002 002 0.943 nm metastable 100 100 100 100 100 0.688 nm phase [010] HAp [010] HAp [010] HAp [010] HAp [010] HAp [010] 2.86 nm 100 100 100 [011] 100 100 [001] 01¯ 01¯ 01¯ 01¯ 01¯ 1 1 1 1 1 [011] HAp [011] HAp [011] HAp [011] HAp [011] HAp Metastable phase a = 2 . 86 , b = 0 . 943 , c = 0 . 688 [nm] (Orthorhombic) 100 100 (100) HAp || (100) MSP 100 100 100 010 010 010 010 010 [010] HAp || [010] MSP 2 nm 2 nm 2 nm [001] HAp [001] HAp 2 nm 2 nm [001] HAp [001] HAp [001] HAp

Summary • Thermal decomposition of the Ca-def HAp whiskers pre- pared by the hydrolysis method begins at about 800 ° C and finishes at about 900 ° C. • Planar defects, often observed in the specimen annealed at 600-800 ° C, are considered as a metastable phase. • The results of EDS microanalysis and IR analysis suggest the metastable phase is a Ca-rich phase. • Lattice constants of the phase are analyzed into a = 2.86, b = 0.943, c = 0.688 nm with orthorhombic crystal system.