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Investigation of Thermal Decomposition Investigation of Thermal Decomposition Process of Hydroxyapatite Crystals by Process of Hydroxyapatite Crystals by In In-

• Situ Scanning Electron Microscopy and

Situ Scanning Electron Microscopy and Cathodoluminescence Microscopy Cathodoluminescence Microscopy

Toshiyuki ISSHIKI, Mitsuhiro NAKAMURA, Toshiyuki ISSHIKI, Mitsuhiro NAKAMURA, Masato TAMAI and Koji NISHIO Masato TAMAI and Koji NISHIO Kyoto Institute of Technology 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)

Contents Contents

• Equipment for High Temperature

Equipment for High Temperature In In-

• Situ

Situ SEM SEM Observation Observation

– – Heating stage using direct heating method. Heating stage using direct heating method. – – Problems and their solutions for the Problems and their solutions for the in in-

• situ

situ SEM SEM

• bservation.
• bservation.
• Thermal Decomposition Process of Hydroxyapatite

Thermal Decomposition Process of Hydroxyapatite

– – Direct observation of morphology change in thermal Direct observation of morphology change in thermal treatment. treatment. – – Nano precipitates created in electron beam irradiation. Nano precipitates created in electron beam irradiation.

Heating Stage for In Heating Stage for In-

• situ Observation of

situ Observation of High Temperature Reactions High Temperature Reactions

• Direct heating method for TEM

Direct heating method for TEM (developed by Kamino and Saka).

(developed by Kamino and Saka).

– – Specimen is mounted on a narrow tungsten filament ( Specimen is mounted on a narrow tungsten filament (∼ ∼20 20µ µm mφ φ) ) and heated directly by current through th and heated directly by current through the filament. e filament. Simple and Small heating unit Simple and Small heating unit → → Small thermal capacity Small thermal capacity

◎ ◎ Reachable temperature is over 1500

Reachable temperature is over 1500o

• C with small current.

C with small current.

◎ ◎ Temperature and specimen drift are settled in a short time

Temperature and specimen drift are settled in a short time. .

△ △ Difficult to measure precise temperature.

Difficult to measure precise temperature. (× thermocouple)

• ◎

◎ Non Non-

• contact method with

contact method with radiation thermometer. .

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

Incident light to photon multiplier tube (PMT)

to photon multiplier tube (PMT)

Thermal electron emitted from the filament

emitted from the filament Influence of the incident light Influence of the incident light

– – Secondary electrons are converted with scintillator to blue ligh

Secondary electrons are converted with scintillator to blue light, and then t, and then detected with PMT. ( detected with PMT. (ET ET-

• detector

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.

Influence of Thermal Electrons Influence of Thermal Electrons

• Around 1,000

Around 1,000o

• C,

C, thermal electrons emitted from a filament increase emitted from a filament increase about about tenfold as temperature rises as temperature rises at each 100oC. .

• The thermal electrons

The thermal electrons saturate an SE-detector and contrast of SEM and contrast of SEM images decrease. images decrease.

• Energy of thermal electrons

Energy of thermal electrons

→ → less than 1 eV

less than 1 eV

• Energy of secondary electrons

Energy of secondary electrons

→ → around a few tens eV

around a few tens eV Electrostatic filter is effective to Electrostatic filter is effective to separate these electrons. separate these electrons.

Emission density of thermal electrons from tungsten filament. Energy distribution of thermal electrons.

Design of In Design of In-

• situ Heating System for SEM

situ Heating System for SEM

• Key points of the system

Key points of the system

• Dichroic filter

Dichroic filter

Cutting off the

Cutting off the light from filament

• Thermal electron filter

Thermal electron filter

Suppression of the

Suppression of the thermal electrons

• Radiation thermometer

Radiation thermometer

Precise

Precise measurement of temperature

Schematic illustration of heating system for in-situ SEM observation.

Overview of the Heating Unit Overview of the Heating Unit

Thermal electron filter

20 20µ µm mφ φ tungsten wire tungsten wire wounded wounded

• n the frame with 70mm(W) x
• n the frame with 70mm(W) x

10mm(H) at 4turns/mm. 10mm(H) at 4turns/mm. Placed between the filament Placed between the filament and the detector and the detector

Disposable heating stage

Light bulb Light bulb removed grass cover removed grass cover

• Specimens are mounted on and

Specimens are mounted on and between tungsten filament between tungsten filament

I Industrial mass product

ndustrial mass product

• Easy to get

Easy to get, , g good uniformity

• od uniformity

and low price and low price

Micrographs of heating stage (Light bulb removed grass cover). Overview of heating stage equipped with thermal electron filter.

Effect of Thermal Electron Filter Effect of Thermal Electron Filter

Good contrast images can be obtained over 1400oC by using thermal electron

by using thermal electron filter, while it becomes difficult to observe images without the filter, while it becomes difficult to observe images without the filter above filter above 1300 1300o

• C.

C.

• There is

There is no need to re-adjust brightness and contrast of images as temperature as temperature

• changes. This make possible to
• changes. This make possible to record images with short intervals

record images with short intervals. .

with thermal electron filter loaded thermal electron filter loaded − −20V 20V

Specimen: SiC particles Specimen: SiC particles

without thermal electron filter thermal electron filter

• Accel. voltage: 15 kV
• Accel. voltage: 15 kV

Probe current: 1 nA Probe current: 1 nA Magnification: x10,000 Magnification: x10,000

Thermal reaction of Thermal reaction of Ca Ca-

• deficient hydroxyapatite

deficient hydroxyapatite

• Calcium deficient hydroxyapatite

Calcium deficient hydroxyapatite

(Ca

(Ca10

10-

• Z

Z(HPO

(HPO4

4)

)Z

Z(PO

(PO4

4)

)6

6-

• Z

Z(OH)

(OH)2

2-

• Z

Z·

·n nH H2

2O, (

O, (Z Z=0~1): =0~1): Ca Ca-

• def HAp

def HAp) ) above 800 above 800o

• C

C Stoichiometric HAp (( Stoichiometric HAp ((Z Z=0): =0): s s-

• HAp

HAp) ) ＋ ＋ β β-

• tricalcium phosphate (

tricalcium phosphate (β β-

• Ca

Ca3

3(PO

(PO4

4)

)2

2:

: β β-

• TCP

TCP) ) The nano The nano-

• composites composed of s

composites composed of s-

• HAp and

HAp and β β-

• TCP, especially

TCP, especially having porous morphology, show having porous morphology, show high bioactivities high bioactivities. .

They are taken a great interest as important They are taken a great interest as important bio bio-

• ceramics

ceramics. .

Experimental Experimental

• Synthesis of Ca

Synthesis of Ca-

• def HAp whisker

def HAp whisker

– – Prepared by hydrolysis of Prepared by hydrolysis of α α-

• tricalcium phosphate (

tricalcium phosphate (α α-

• Ca

Ca3

3(PO

(PO4

4)

)2

2)

) in octanol/water binary emulsion. in octanol/water binary emulsion.

• In

In-

• situ SEM observation

situ SEM observation

– – JEOL JSM JEOL JSM-

• 845 equipped with the

845 equipped with the heating stage for heating stage for in in-

• situ

situ observation.

• bservation.

– – How to change their morphology in How to change their morphology in thermal treatment. thermal treatment.

TEM image of Ca-def HAp before thermal treatment. JEOL JSM-845 scanning electron microscope.

Morphology Change of Morphology Change of HAp Whiskers HAp Whiskers

• There is no morphology change of

There is no morphology change of whiskers below whiskers below 800oC.

• The morphology of whiskers began

The morphology of whiskers began to change to change around 850oC. Thermal . Thermal decomposition proceeds in this decomposition proceeds in this temperature range. temperature range.

• The whiskers

The whiskers united each other united each other above 900oC. The whiskers . The whiskers deformed into gnarled shape. deformed into gnarled shape.

Above 1000oC, shape of whisker

, shape of whisker was lost and gnarled whiskers was lost and gnarled whiskers changed into round shape particles. changed into round shape particles.

In In-

• situ

situ observation of sintering process of Ca

• bservation of sintering process of Ca-
• def HAp whiskers.

def HAp whiskers.

Sintering into Porous Body from HAp Whiskers Sintering into Porous Body from HAp Whiskers

• The morphology of the whisker began to change

The morphology of the whisker began to change around 850oC. .

• The whiskers

The whiskers coalesced each other coalesced each other to form to form porous nano porous nano-

• composite

composite composed of s composed of s-

• HAp and

HAp and β β-

• TCP

TCP above 900oC. .

• Each grain of the composite became large

Each grain of the composite became large above 1000oC. . Porosity of the composites decreased rapidly. Porosity of the composites decreased rapidly.

• Heat treatment below 1000

Heat treatment below 1000o

• C is preferred to obtain high

C is preferred to obtain high-

• porosity composite.

porosity composite.

I In n-

• situ SEM observation of sintering process from aggregates of whi

situ SEM observation of sintering process from aggregates of whisker sker-

• shaped Ca

shaped Ca-

• def HAp into porous body.

def HAp into porous body.

Nano Particles Precipitated on Ca Nano Particles Precipitated on Ca-

• def HAp

def HAp

• Deformation of the whiskers also began

Deformation of the whiskers also began around 850oC even under dense electron even under dense electron beam irradiation. beam irradiation.

• A lot of

A lot of fine particles a few tens nm in size precipitated fine particles a few tens nm in size precipitated on the whiskers

• n the whiskers near 900oC

and the particles grew over a hundred nm in size with temperatur and the particles grew over a hundred nm in size with temperature increasing. e increasing.

Above 1100oC, the precipitated particles

, the precipitated particles disappeared simultaneously with the disappeared simultaneously with the β β-

• TCP particles

TCP particles. The particles were considered to be . The particles were considered to be β β-

• TCP.

TCP.

β-TCP HAp

Decomposition process of Ca Decomposition process of Ca-

• def HAp whiskers under dense electron beam irradiation.

def HAp whiskers under dense electron beam irradiation. Round Round-

• shaped particles are

shaped particles are β β-

• TCP to check difference of reaction between HAp and

TCP to check difference of reaction between HAp and β β-

• TCP

TCP. .

Nano Particles Precipitated on Stoichiometric HAp Nano Particles Precipitated on Stoichiometric HAp

• The similar fine precipitates were observed on

The similar fine precipitates were observed on s-HAp crystals, even crystals, even though s though s-

• HAp particles are

HAp particles are usually stable at this temperature range. .

• It is considered that

It is considered that electron beam irradiation makes Ca vacancies electron beam irradiation makes Ca vacancies inside inside the s the s-

• HAp crystals and they decompose as well as Ca

HAp crystals and they decompose as well as Ca-

• def HAp crystals.

def HAp crystals.

Decomposition process of s Decomposition process of s-

• HAp under dense electron beam irradiation.

HAp under dense electron beam irradiation.

Cathodoluminescence observation of Precipitates Cathodoluminescence observation of Precipitates

• The particles showed blue CL emission which color was the

The particles showed blue CL emission which color was the same as that obtained from pure same as that obtained from pure β β-

• TCP powder.

TCP powder.

• The precipitates were confirmed to be

The precipitates were confirmed to be β β-

• TCP

TCP

Cathodoluminescence image of the nano Cathodoluminescence image of the nano-

• precipitates.

precipitates. Nano Nano-

• particles precipitated from

particles precipitated from s s-

• HAp

HAp. .

Summary Summary

• Thermal decomposition process of HAp was investigated by

Thermal decomposition process of HAp was investigated by in in-

• situ scanning electron microscopy with the aid of cathodo

situ scanning electron microscopy with the aid of cathodo-

• luminescence microscopy.

luminescence microscopy.

– – Direct heating method was applied to heating stage for in Direct heating method was applied to heating stage for in-

• situ SEM.

situ SEM.

• It was revealed that the formation process of porous nano

It was revealed that the formation process of porous nano-

• composites of s

composites of s-

• HAp and

HAp and β β-

• TCP and the relationship between

TCP and the relationship between the annealing temperature and morphology of the composites. the annealing temperature and morphology of the composites.

• Nano

Nano-

• size

size β β-

• TCP particles precipitate above 850

TCP particles precipitate above 850o

• C not only

C not only

• n Ca
• n Ca-
• def HAp whiskers but also on s

def HAp whiskers but also on s-

• HAp particles under

HAp particles under dense electron beam irradiation. It is considered that the dense electron beam irradiation. It is considered that the irradiation induces irradiation induces Ca vacancies in the HAp crystal and they Ca vacancies in the HAp crystal and they act as nucleation sites of act as nucleation sites of β β-

• TCP.

TCP.