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

In-Situ Scanning Electron Microscopy and In-Situ Scanning Electron Microscopy and Cathodoluminescence MicroscopyCathodoluminescence Microscopy

Toshiyuki ISSHIKI, Mitsuhiro NAKAMURA, Toshiyuki ISSHIKI, Mitsuhiro NAKAMURA, Masato TAMAI and Koji NISHIOMasato TAMAI and Koji NISHIO

Kyoto Institute of TechnologyKyoto 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)

ContentsContents Equipment for High Temperature In-Situ SEM ObsEquipment for High Temperature In-Situ SEM Obs

ervation ervation

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

ion. ion.

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-situ Observation of Heating Stage for In-situ Observation of High Temperature Reactions High Temperature Reactions

Direct heating method for TEMDirect 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 (2020mm) ) and heated directly by current through the filament.and heated directly by current through the filament.

Simple and Small heating unitSimple and Small heating unit → → 　　 Small thermal capacitySmall thermal capacity

◎ Reachable temperature is over 1500Reachable temperature is over 1500ooC with small current.C with small current.◎ Temperature and specimen drift are settled in a short timeTemperature 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..

Problem of High Temperature In-Situ SEM

Disturbance of image detection Disturbance of image detection

Saturation of secondary electron detector caused bySaturation 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 light, and then Secondary electrons are converted with scintillator to blue light, and then

detected with PMT. (detected with PMT. (ET-detectorET-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 ElectronsInfluence of Thermal Electrons Around 1,000Around 1,000ooC, 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 electronsEnergy of thermal electrons → → 　　 less than 1 eVless than 1 eV Energy of secondary electronsEnergy of secondary electrons

　→　　→　 around a few tens eVaround 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-situ Heating System for SEMDesign of In-situ Heating System for SEM

Key points of the systemKey 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 UnitOverview of the Heating Unit Thermal electron filter 2020mm tungsten wire tungsten wire wounded wounded

on the frame with 70mm(W) x on the frame with 70mm(W) x 10mm(H) at 4turns/mm.10mm(H) at 4turns/mm.

Placed between the filament anPlaced between the filament and the detectord the detector

Disposable heating stage

Light bulbLight bulb removed grass cover removed grass cover Specimens are mounted on and Specimens are mounted on and

between tungsten filamentbetween tungsten filament

IIndustrial mass productndustrial mass product

Easy to get,Easy to get, good uniformity good uniformity and low priceand low price Micrographs of heating stage (Light bulb removed grass cover).

Overview of heating stage equipped with thermal electron filter.

Effect of Thermal Electron FilterEffect 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 above filter, while it becomes difficult to observe images without the filter above 13001300ooC. 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 intervalsrecord images with short intervals. .

with thermal electron filter loaded thermal electron filter loaded 20V20V Specimen: SiC particlesSpecimen: SiC particles

without thermal electron filterthermal electron filter

Accel. voltage: 15 kV Accel. voltage: 15 kV Probe current: 1 nAProbe current: 1 nAMagnification: x10,000Magnification: x10,000

Thermal reaction of Thermal reaction of 　　　　　　　　　　　　 Ca-deficient Ca-deficient hydroxyapatitehydroxyapatite

Calcium deficient hydroxyapatiteCalcium deficient hydroxyapatite

　 　 (Ca(Ca10-10-ZZ(HPO(HPO44))ZZ(PO(PO44))6-6-ZZ(OH)(OH)2-2-ZZ··nnHH22O, (O, (ZZ=0~1): =0~1): Ca-def HApCa-def HAp))

above 800above 800ooC C

Stoichiometric HAp ((Stoichiometric HAp ((ZZ=0): =0): s-HAps-HAp) ) ＋＋ -tricalcium phosphate (-tricalcium phosphate (-Ca-Ca33(PO(PO44))22: : -TCP-TCP))

The nano-composites composed of s-HAp and The nano-composites composed of s-HAp and -TCP, especially -TCP, especially having porous morphology, show having porous morphology, show high bioactivitieshigh bioactivities. .

They are taken a great interest as important They are taken a great interest as important bio-ceramicsbio-ceramics..

ExperimentalExperimental

Synthesis of Ca-def HAp whiskerSynthesis of Ca-def HAp whisker

– Prepared by hydrolysis of Prepared by hydrolysis of -tricalciu-tricalcium phosphate (m phosphate (-Ca-Ca33(PO(PO44))22) in octanol) in octanol/water binary emulsion.  /water binary emulsion.  

In-situ SEM observationIn-situ SEM observation

– JEOL JSM-845 equipped with the heJEOL JSM-845 equipped with the heating stage for in-situ observation.ating stage for in-situ observation.

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

TEM image of Ca-def HAp before thermal treatment.

JEOL JSM-845 scanning electron microscope.

Morphology Change of Morphology Change of HAp WhiskersHAp 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 otherunited 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-situ observation of sintering process of Ca-def HAp whiskers.In-situ observation of sintering process of Ca-def HAp whiskers.

Sintering into Porous Body from HAp WhiskersSintering 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 othercoalesced each other to form to form porous nano-composite porous nano-composite composed of s-HAp and composed of s-HAp and -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 1000Heat treatment below 1000ooC is preferred to obtain high-porosity composite.C is preferred to obtain high-porosity composite.

IIn-situ SEM observation of sintering process from aggregates of whisker-shaped Ca-def HAp into porous body.n-situ SEM observation of sintering process from aggregates of whisker-shaped Ca-def HAp into porous body.

Nano Particles Precipitated on Ca-def HApNano Particles Precipitated on Ca-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 precipitatedfine particles a few tens nm in size precipitated on the whiskers on the whiskers near 900oC and the particles grew over a hundred nm in size with temperature increasing. and the particles grew over a hundred nm in size with temperature increasing.

Above 1100oC, the precipitated particles , the precipitated particles disappeared simultaneously with the disappeared simultaneously with the --TCP particlesTCP particles. The particles were considered to be . The particles were considered to be -TCP.-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 Round-shaped particles are -TCP to check difference of reaction between HAp and -TCP to check difference of reaction between HAp and -TCP. -TCP.

Nano Particles Precipitated on Stoichiometric HApNano 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-HAp particles are though s-HAp particles are usually stable at this temperature range..

It is considered that It is considered that electron beam irradiation makes Ca vacancieselectron beam irradiation makes Ca vacancies inside inside the s-HAp crystals and they decompose as well as Ca-def HAp crystals.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.

Cathodoluminescence observation of PrecipitatesCathodoluminescence observation of Precipitates

The particles showed blue CL emission which color was the saThe particles showed blue CL emission which color was the same as that obtained from pure me as that obtained from pure -TCP powder. -TCP powder.

The precipitates were confirmed to beThe precipitates were confirmed to be -TCP-TCP

Cathodoluminescence image of the nano-precipitates.Cathodoluminescence image of the nano-precipitates.Nano-particles precipitated fromNano-particles precipitated from s-HAp.s-HAp.

SummarySummary Thermal decomposition process of HAp was investigated by Thermal decomposition process of HAp was investigated by

in-situ scanning electron microscopy with the aid of cathodo-in-situ scanning electron microscopy with the aid of cathodo-luminescence microscopy.luminescence microscopy.– Direct heating method was applied to heating stage for in-situ SEM.Direct heating method was applied to heating stage for in-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-HAp and composites of s-HAp and -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-size Nano-size -TCP particles precipitate above 850-TCP particles precipitate above 850ooC not only C not only on Ca-def HAp whiskers but also on s-HAp particles under on Ca-def HAp whiskers but also on s-HAp particles under dense electron beam irradiation. It is considered that the dense electron beam irradiation. It is considered that the irradiation induces Ca vacancies in the HAp crystal and they irradiation induces Ca vacancies in the HAp crystal and they act as nucleation sites of act as nucleation sites of -TCP. -TCP.