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

InIn--Situ Scanning Electron Microscopy and 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)

ContentsContentsEquipment for High Temperature Equipment for High Temperature InIn--SituSitu SEM SEM Observation Observation

–– Heating stage using direct heating method. Heating stage using direct heating method. –– Problems and their solutions for theProblems and their solutions for the inin--situsitu SEM SEM

observation. observation.

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 InHeating Stage for In--situ Observation of situ Observation of High Temperature ReactionsHigh 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 (∼∼2020µµmmφφ) ) and heated directly by current through thand heated directly by current through the filament.e 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)

◎◎ NonNon--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 bySaturation of secondary electron detector caused by

Incident light to photon multiplier tube (PMT) to photon multiplier tube (PMT) Thermal electron emitted from the filamentemitted from the filament

Influence of the incident light Influence of the incident light –– Secondary electrons are converted with scintillator to blue lighSecondary electrons are converted with scintillator to blue light, and then t, and then

detected with PMT. (detected with PMT. (ETET--detectordetector))

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 ElectronsAround 1,000Around 1,000ooC, C, thermal electronsemitted 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 InDesign of In--situ Heating System for SEMsitu Heating System for SEM

Key points of the systemKey points of the systemDichroic filter Dichroic filter Cutting off the Cutting off the light from filamentThermal electron filter Thermal electron filter Suppression of the Suppression of the thermal electronsRadiation 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 UnitThermal electron filter2020µµmmφφ tungsten wiretungsten 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 Placed between the filament and the detectorand the detector

Disposable heating stageLight bulbLight bulb removed grass coverremoved grass cover

Specimens are mounted on and Specimens are mounted on and between tungsten filamentbetween tungsten filament

IIndustrial mass productndustrial mass productEasy to getEasy to get,, ggood uniformity ood uniformity

and low priceand low priceMicrographs 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 thefilter, while it becomes difficult to observe images without the filter above 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 　　　　　　　　　　　　CaCa--deficient hydroxyapatitedeficient hydroxyapatite

Calcium deficient hydroxyapatiteCalcium deficient hydroxyapatite　　 (Ca(Ca1010--ZZ(HPO(HPO44))ZZ(PO(PO44))66--ZZ(OH)(OH)22--ZZ··nnHH22O, (O, (ZZ=0~1): =0~1): CaCa--def HApdef HAp))

above 800above 800ooC C

Stoichiometric HAp ((Stoichiometric HAp ((ZZ=0): =0): ss--HApHAp) ) ＋＋

ββ--tricalcium phosphate (tricalcium phosphate (ββ--CaCa33(PO(PO44))22: : ββ--TCPTCP))

The nanoThe nano--composites composed of scomposites composed of s--HAp and HAp and ββ--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 biobio--ceramicsceramics..

ExperimentalExperimental

Synthesis of CaSynthesis of Ca--def HAp whiskerdef HAp whisker–– Prepared by hydrolysis of Prepared by hydrolysis of αα--

tricalcium phosphate (tricalcium phosphate (αα--CaCa33(PO(PO44))22) ) in octanol/water binary emulsion. in octanol/water binary emulsion.

InIn--situ SEM observationsitu SEM observation–– JEOL JSMJEOL JSM--845 equipped with the 845 equipped with the

heating stage for heating stage for inin--situ situ observation.observation.

–– 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 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 otherabove 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.

InIn--situsitu observation of sintering process of Caobservation of sintering process of Ca--def HAp whiskers.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 nanoporous nano--composite composite composed of scomposed of s--HAp and HAp and ββ--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 highC is preferred to obtain high--porosity composite.porosity composite.

IInn--situ SEM observation of sintering process from aggregates of whisitu SEM observation of sintering process from aggregates of whiskersker--shaped Cashaped Ca--def HAp into porous body.def HAp into porous body.

Nano Particles Precipitated on CaNano Particles Precipitated on Ca--def HApdef 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 900oCand the particles grew over a hundred nm in size with temperaturand 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 ββ--TCP particlesTCP particles. The particles were considered to be . The particles were considered to be ββ--TCP.TCP.

β-TCP

HAp

Decomposition process of CaDecomposition process of Ca--def HAp whiskers under dense electron beam irradiation.def HAp whiskers under dense electron beam irradiation.RoundRound--shaped particles are shaped particles are ββ--TCP to check difference of reaction between HAp and TCP to check difference of reaction between HAp and ββ--TCPTCP. .

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 sthough 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 vacancieselectron beam irradiation makes Ca vacancies inside inside the sthe s--HAp crystals and they decompose as well as CaHAp crystals and they decompose as well as Ca--def HAp crystals.def HAp crystals.

Decomposition process of sDecomposition process of s--HAp under dense electron beam irradiation.HAp under dense electron beam irradiation.

Cathodoluminescence observation of PrecipitatesCathodoluminescence 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 ββ--TCP powder. TCP powder.

The precipitates were confirmed to beThe precipitates were confirmed to be ββ--TCPTCP

Cathodoluminescence image of the nanoCathodoluminescence image of the nano--precipitates.precipitates.NanoNano--particles precipitated fromparticles precipitated from ss--HApHAp..

SummarySummaryThermal decomposition process of HAp was investigated by Thermal decomposition process of HAp was investigated by inin--situ scanning electron microscopy with the aid of cathodositu scanning electron microscopy with the aid of cathodo--luminescence microscopy.luminescence microscopy.–– Direct heating method was applied to heating stage for inDirect heating method was applied to heating stage for in--situ SEM.situ SEM.

It was revealed that the formation process of porous nanoIt was revealed that the formation process of porous nano--composites of scomposites of s--HAp and HAp and ββ--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.

NanoNano--size size ββ--TCP particles precipitate above 850TCP particles precipitate above 850ooC not only C not only on Caon Ca--def HAp whiskers but also on sdef 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 inducesirradiation 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 ββ--TCP. TCP.