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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

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SLIDE 1

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

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SLIDE 2

Hydroxyapatite

Hydroxyapatite (Ca10(PO4)6(OH)2: HAp)

  • Crystal structure: Similar to a bone

Hexagonal (a = 0.943 nm, c = 0.688 nm) ⇓ widely noticed and expected

  • As an alternative material for bone
  • Application to a biosensor making

good use of biocompatibility

[00¯ 1] a b [100] b c

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SLIDE 3

Synthesis of Hydroxyapatite

Dry process

⇒ Stoichiometric HAp (s-HAp) 6CaHPO4 + 4CaCO3 → s-HAp + 2H2O + 4CO2

Wet process

⇒ Non-stoichiometric HAp

  • Sol-gel method
  • Hydrolysis method
  • A. Nakahira et al., J. Am. Ceram. Soc. 82 (1999) 2029-2032
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SLIDE 4

Hydrolysis Method

α-tricalcium phosphate (α-Ca3(PO4)2: α-TCP) ⇓ Hydrolysis in a mixture of water and alcohol Calcium-deficient HAp

(Ca10−Z(HPO4)Z(PO4)6−Z(OH)2−Z ⋅ nH2O (Z = 0-1): Ca-def HAp)

Advantage of this method:

  • Easy to systhesis within several hours

under mild conditions

  • Easy to control of crystal morphology

plate-, blade-, whisker-like shape, etc. ⇓ ⇓ ⇓ ⇓ ⇓ ⇓ ⇓ ⇓ ⇓ ⇓ ⇓ ⇓ ⇓ ⇓ ⇓

0 h 0 h 0 h 0 h 0 h 1 h 1 h 1 h 1 h 1 h 2 h 2 h 2 h 2 h 2 h 3 h 3 h 3 h 3 h 3 h α-TCP α-TCP α-TCP α-TCP α-TCP α-TCP α-TCP α-TCP α-TCP α-TCP Ca-def HAp Ca-def HAp Ca-def HAp Ca-def HAp Ca-def HAp

500 nm 500 nm 500 nm 500 nm 500 nm

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SLIDE 5

Ca-Deficient Hydroxyapatite

Ca-def HAp → s-HAp + β-TCP Important reaction to develop new biomaterials Whisker-like shape is favorable as a source to produce porous biomaterials TEM observation of the whisker-like shape, Ca- def HAp crystals

770 °C 770 °C 770 °C 770 °C 770 °C 900 °C 900 °C 900 °C 900 °C 900 °C 980 °C 980 °C 980 °C 980 °C 980 °C 1040 °C 1040 °C 1040 °C 1040 °C 1040 °C 1 µm 1 µm 1 µm 1 µm 1 µm

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SLIDE 6

Experimental Procedure

Specimen

Source: Whisker-like shape, Ca-def HAp synthesized by hydrolysis method (Ca/P molar ratio = 1.58) Heat Annealed at 200-1100 °C in air treatment: (heating rate: 5 °C/min, keep time: 2-6 hours)

Equipment

TEM JEOL, JEM-2010/SP (EDS) Noran, Vantage XRD Rigaku, RINT 2000 FT-IR JEOL, IR-WINSPEC100

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SLIDE 7

TEM images of samples before & after annealing

before annealing before annealing before annealing before annealing before annealing annealed at 600 °C annealed at 600 °C annealed at 600 °C annealed at 600 °C annealed at 600 °C 700 °C 700 °C 700 °C 700 °C 700 °C 800 °C 800 °C 800 °C 800 °C 800 °C 900 °C 900 °C 900 °C 900 °C 900 °C 500 nm 500 nm 500 nm 500 nm 500 nm Ca-def HAp whiskers

Length (c axis): 2 ∼ 5 µm Width: ∼ 0.1 µm Ca/P molar ratio: 1.58 Heating rate: 5 °C/min Keep time: 2 hours

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SLIDE 8

Analysis of XRD patterns

20 30 40 50 60 Intensity [a.u.] Diffraction angle 2θ [degree]

900 °C 900 °C 900 °C 900 °C 900 °C 800 °C 800 °C 800 °C 800 °C 800 °C 600 °C 600 °C 600 °C 600 °C 600 °C before annealing before annealing before annealing before annealing before annealing

1100 °C 1000 °C 900 °C 800 °C 600 °C 400 °C 200 °C before annealing

β-TCP HAp 500 nm 500 nm 500 nm 500 nm 500 nm

✟✟ ✟ ✯ ✲ ✲ ✲

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SLIDE 9

Ca-def HAp whisker annealed at 800 °C

50 nm 50 nm 50 nm 50 nm 50 nm

HAp HAp HAp HAp HAp HAp HAp HAp HAp HAp HAp HAp HAp HAp HAp

← ← ← ← ← → → → → → → → → → →

[010] [010] [010] [010] [010] 100 100 100 100 100 002 002 002 002 002

3 nm 3 nm 3 nm 3 nm 3 nm

(100) (100) (100) (100) (100)

Planar defect / Layered precipitate

  • traversing in the whisker
  • parallel to (100) plane
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SLIDE 10

Planar defect and layered phase

600 °C 600 °C 600 °C 600 °C 600 °C 700 °C 700 °C 700 °C 700 °C 700 °C 800 °C 800 °C 800 °C 800 °C 800 °C [021] [021] [021] [021] [021] [010] [010] [010] [010] [010] [010] [010] [010] [010] [010]

20 nm 20 nm 20 nm 20 nm 20 nm

5 nm 5 nm 5 nm 5 nm 5 nm ↑ ↑ ↑ ↑ ↑

planar defect planar defect planar defect planar defect planar defect (100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (001) (001) (001) (001) (001) 1.43 nm 1.43 nm 1.43 nm 1.43 nm 1.43 nm

↓ ↓ ↓ ↓ ↓ ↑ ↑ ↑ ↑ ↑

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SLIDE 11

TEM-EDS microanalysis

Counts [a.u.] Energy [keV] O P Ca Ca

A (layered phase)

[021] 2 nm 2 nm 2 nm 2 nm 2 nm

✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✾ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✾ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✾ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✾ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✘ ✾ ✏✏✏✏✏✏✏✏✏✏✏ ✏ ✶ ✏✏✏✏✏✏✏✏✏✏✏ ✏ ✶ ✏✏✏✏✏✏✏✏✏✏✏ ✏ ✶ ✏✏✏✏✏✏✏✏✏✏✏ ✏ ✶ ✏✏✏✏✏✏✏✏✏✏✏ ✏ ✶

A A A A A B B B B B Counts [a.u.] Energy [keV] O P Ca Ca

B (Ca-def HAp)

atomic molar ratio

area Ca/P

Ca P [atom. %]

A 1.86

65 35

B 1.27

56 44

s-HAp 1.67

62.5 37.5

⇒ Ca-rich

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SLIDE 12

Analysis of IR absorption spectra

Wave number [cm−1] Transmittance [a.u.] 3800 3300 2800 900 °C 800 °C 600 °C 400 °C 3570 cm−1

❍ ❍ ❨ 3538 cm−1

Wave number [cm−1] Transmittance [a.u.] 1400 900 400 900 °C 800 °C 600 °C 400 °C

✻

744 cm−1

IR absorption spectrum of the sample annealed at 800 °C ⇓

  • IR absorption peak at

3570 cm−1 shifted to 3538 cm−1

  • IR absorption peak ap-

peared at 744 cm−1 ⇓

Ca-rich HAp

  • G. Bonel et al., Ann. NY
  • Acad. Sci. 523 (1988) 115
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SLIDE 13

Ca-rich metastable phase

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

  • f absorption peaks

⇓ Ca-rich phase ⇓ Ca-rich metastable phase

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SLIDE 14

Relation between the Ca-def HAp and the phase

[010]HAp [010]HAp [010]HAp [010]HAp [010]HAp [011]HAp [011]HAp [011]HAp [011]HAp [011]HAp [001]HAp [001]HAp [001]HAp [001]HAp [001]HAp

(100) (100) (100) (100) (100) → → → → → ← ← ← ← ← 1.43 nm 1.43 nm 1.43 nm 1.43 nm 1.43 nm

2 nm 2 nm 2 nm 2 nm 2 nm

100 100 100 100 100 002 002 002 002 002 100 100 100 100 100 01¯ 1 01¯ 1 01¯ 1 01¯ 1 01¯ 1 100 100 100 100 100 010 010 010 010 010

Ca-def HAp metastable phase [010] [011] [001]

0.943 nm 0.688 nm 2.86 nm

Metastable phase a = 2.86, b = 0.943, c = 0.688 [nm] (Orthorhombic) (100)HAp || (100)MSP [010]HAp || [010]MSP

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SLIDE 15

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.