1. Investigation of Thermal Decomposition Process of Hydroxyapatite Crystals by In-Situ Scanning Electron Microscopy and Cathodoluminescence Microscopy Toshiyuki ISSHIKI, Mitsuhiro NAKAMURA, Masato TAMAI and Koji NISHIO Kyoto Institute of Technology Seminar on Nanotechnology for Fabrication of Hybrid Materials, 6-8, Nov., 2002, Toyama, Japan (4th Japanese-Polish Joint Seminar on Materials Analysis)

2. Contents Equipment for High Temperature In-Situ SEM Observation Equipment for High Temperature In-Situ SEM Observation –Heating stage using direct heating method. –Problems and their solutions for the in-situ SEM observation. Thermal Decomposition Process of Hydroxyapatite –Direct observation of morphology change in thermal treatment. –Nano precipitates created in electron beam irradiation.

3. Heating Stage for In-situ Observation of High Temperature Reactions Direct heating method for TEM (developed by Kamino and Saka). Direct heating method for TEM (developed by Kamino and Saka). –Specimen is mounted on a narrow tungsten filament (  20  m  ) and heated directly by current through the filament. and heated directly by current through the filament. Simple and Small heating unit → Small thermal capacity Simple and Small heating unit → Small thermal capacity ◎ Reachable temperature is over 1500 o C with small current. ◎ Temperature and specimen drift are settled in a short time. △ Difficult to measure precise temperature. △ Difficult to measure precise temperature. (× thermocouple)  ◎ Non-contact method with.  ◎ Non-contact method with radiation thermometer.

4. Problem of High Temperature In-Situ SEM Disturbance of image detection Disturbance of image detection Saturation of secondary electron detector caused by Saturation of secondary electron detector caused by  to photon multiplier tube (PMT)  Incident light to photon multiplier tube (PMT)  emitted from the filament  Thermal electron emitted from the filament Influence of the incident light Influence of the incident light – Secondary electrons are converted with scintillator to blue light, and then detected with PMT. (ET-detector)  Strong light from thermal filament saturates the PMT. Arrange the filament not to face the detector. Arrange the filament not to face the detector. Cut off the light emitted from the filament with optical filter. Cut off the light emitted from the filament with optical filter.

5. Influence of Thermal Electrons Around 1,000 o C, emitted from a filament increase about as temperature rises. Around 1,000 o C, thermal electrons emitted from a filament increase about tenfold as temperature rises at each 100 o C. The thermal electrons and contrast of SEM images decrease. The thermal electrons saturate an SE-detector and contrast of SEM images decrease. Energy of thermal electrons → less than 1 eV Energy of secondary electrons → around a few tens eV Electrostatic filter is effective to separate these electrons. Emission density of thermal electrons from tungsten filament. Energy distribution of thermal electrons.

6. Design of In-situ Heating System for SEM Key points of the system Key points of the system Dichroic filter  Cutting off the Dichroic filter  Cutting off the light from filament Thermal electron filter  Suppression of the Thermal electron filter  Suppression of the thermal electrons Radiation thermometer  Precise Radiation thermometer  Precise measurement of temperature Schematic illustration of heating system for in-situ SEM observation.

7. Overview of the Heating Unit Thermal electron filter 20  m  tungsten wire wounded on the frame with 70mm(W) x 10mm(H) at 4turns/mm. 20  m  tungsten wire wounded on the frame with 70mm(W) x 10mm(H) at 4turns/mm. Placed between the filament and the detector Placed between the filament and the detector Disposable heating stage Light bulb removed grass cover  Specimens are mounted on and between tungsten filament I ndustrial mass product  Easy to get, good uniformity and low price Micrographs of heating stage (Light bulb removed grass cover). Overview of heating stage equipped with thermal electron filter.

8. Effect of Thermal Electron Filter by using thermal electron filter, while it becomes difficult to observe images without the filter above 1300 o C. Good contrast images can be obtained over 1400 o C by using thermal electron filter, while it becomes difficult to observe images without the filter above 1300 o C. There is as temperature changes. This make possible to record images with short intervals. There is no need to re-adjust brightness and contrast of images as temperature changes. This make possible to record images with short intervals. thermal electron filter loaded  20V with thermal electron filter loaded  20V Specimen: SiC particles thermal electron filter without thermal electron filter Accel. voltage: 15 kV Probe current: 1 nA Magnification: x10,000

9. Thermal reaction of Ca-deficient hydroxyapatite Calcium deficient hydroxyapatite Calcium deficient hydroxyapatite (Ca 10-Z (HPO 4 ) Z (PO 4 ) 6-Z (OH) 2-Z ·nH 2 O, (Z=0~1): Ca-def HAp) (Ca 10-Z (HPO 4 ) Z (PO 4 ) 6-Z (OH) 2-Z ·nH 2 O, (Z=0~1): Ca-def HAp) above 800 o C above 800 o C Stoichiometric HAp ((Z=0): s-HAp) ＋ Stoichiometric HAp ((Z=0): s-HAp) ＋  -tricalcium phosphate (  -Ca 3 (PO 4 ) 2 :  -TCP)  -tricalcium phosphate (  -Ca 3 (PO 4 ) 2 :  -TCP) The nano-composites composed of s-HAp and  -TCP, especially having porous morphology, show high bioactivities. They are taken a great interest as important bio-ceramics. They are taken a great interest as important bio-ceramics.

10. Experimental Synthesis of Ca-def HAp whisker Synthesis of Ca-def HAp whisker –Prepared by hydrolysis of  - tricalcium phosphate (  -Ca 3 (PO 4 ) 2 ) in octanol/water binary emulsion. –Prepared by hydrolysis of  - tricalcium phosphate (  -Ca 3 (PO 4 ) 2 ) in octanol/water binary emulsion. In-situ SEM observation In-situ SEM observation –JEOL JSM-845 equipped with the heating stage for in-situ observation. –How to change their morphology in thermal treatment. TEM image of Ca-def HAp before thermal treatment. JEOL JSM-845 scanning electron microscope.

11. Morphology Change of HAp Whiskers There is no morphology change of whiskers below There is no morphology change of whiskers below 800 o C. The morphology of whiskers began to change. Thermal decomposition proceeds in this temperature range. The morphology of whiskers began to change around 850 o C. Thermal decomposition proceeds in this temperature range. The whiskers united each other. The whiskers deformed into gnarled shape. The whiskers united each other above 900 o C. The whiskers deformed into gnarled shape., shape of whisker was lost and gnarled whiskers changed into round shape particles. Above 1000 o C, shape of whisker was lost and gnarled whiskers changed into round shape particles. In-situ observation of sintering process of Ca-def HAp whiskers. In-situ observation of sintering process of Ca-def HAp whiskers.

12. Sintering into Porous Body from HAp Whiskers The morphology of the whisker began to change. The morphology of the whisker began to change around 850 o C. The whiskers coalesced each other to form porous nano-composite The whiskers coalesced each other to form porous nano-composite composed of s-HAp and  -TCP. composed of s-HAp and  -TCP above 900 o C. Each grain of the composite became large. Each grain of the composite became large above 1000 o C. Porosity of the composites decreased rapidly. Porosity of the composites decreased rapidly.  Heat treatment below 1000 o C is preferred to obtain high-porosity composite. I n-situ SEM observation of sintering process from aggregates of whisker-shaped Ca-def HAp into porous body. I n-situ SEM observation of sintering process from aggregates of whisker-shaped Ca-def HAp into porous body.

13. Nano Particles Precipitated on Ca-def HAp Nano Particles Precipitated on Ca-def HAp Deformation of the whiskers also began even under dense electron beam irradiation. Deformation of the whiskers also began around 850 o C even under dense electron beam irradiation. A lot of fine particles a few tens nm in size precipitated on the whiskers and the particles grew over a hundred nm in size with temperature increasing. A lot of fine particles a few tens nm in size precipitated on the whiskers near 900 o C and the particles grew over a hundred nm in size with temperature increasing., the precipitated particles disappeared simultaneously with the  - TCP particles. The particles were considered to be  -TCP. Above 1100 o C, the precipitated particles disappeared simultaneously with the  - TCP particles. The particles were considered to be  -TCP.  - TCP HAp Decomposition process of Ca-def HAp whiskers under dense electron beam irradiation. Decomposition process of Ca-def HAp whiskers under dense electron beam irradiation. Round-shaped particles are  -TCP to check difference of reaction between HAp and  -TCP.

14. Nano Particles Precipitated on Stoichiometric HAp The similar fine precipitates were observed on s-HAp crystals, even though s-HAp particles are usually stable at this temperature range. It is considered that electron beam irradiation makes Ca vacancies inside the s-HAp crystals and they decompose as well as Ca-def HAp crystals. Decomposition process of s-HAp under dense electron beam irradiation. Decomposition process of s-HAp under dense electron beam irradiation.

15. Cathodoluminescence observation of Precipitates Cathodoluminescence observation of Precipitates The particles showed blue CL emission which color was the same as that obtained from pure  -TCP powder.  The precipitates were confirmed to be  -TCP Cathodoluminescence image of the nano-precipitates. Nano-particles precipitated from s-HAp.

16. Summary Thermal decomposition process of HAp was investigated by in-situ scanning electron microscopy with the aid of cathodo- luminescence microscopy. Thermal decomposition process of HAp was investigated by in-situ scanning electron microscopy with the aid of cathodo- luminescence microscopy. –Direct heating method was applied to heating stage for in-situ SEM. It was revealed that the formation process of porous nano- composites of s-HAp and  -TCP and the relationship between the annealing temperature and morphology of the composites. It was revealed that the formation process of porous nano- composites of s-HAp and  -TCP and the relationship between the annealing temperature and morphology of the composites. Nano-size  -TCP particles precipitate above 850 o C not only on Ca-def HAp whiskers but also on s-HAp particles under dense electron beam irradiation. It is considered that the irradiation induces Ca vacancies in the HAp crystal and they act as nucleation sites of  -TCP. Nano-size  -TCP particles precipitate above 850 o C not only on Ca-def HAp whiskers but also on s-HAp particles under dense electron beam irradiation. It is considered that the irradiation induces Ca vacancies in the HAp crystal and they act as nucleation sites of  -TCP.