Investigation of Thermal Decomposition Investigation of Thermal - PowerPoint PPT Presentation

Seminar on Nanotechnology for Fabrication of Hybrid Materials, 6-8, Nov., 2002, Toyama, Japan (4th Japanese-Polish Joint Seminar on Materials Analysis) Investigation of Thermal Decomposition Investigation of Thermal Decomposition Process of Hydroxyapatite Crystals by Process of Hydroxyapatite Crystals by In- -Situ Scanning Electron Microscopy and Situ Scanning Electron Microscopy and In 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

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 – 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 In- -situ Observation of situ Observation of Heating Stage for In 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 µ m φ ) – ∼ 20 µ m φ ) and heated directly by current through the filament. and heated directly by current through th e filament. Simple and Small heating unit → Small thermal capacity Simple and Small heating unit → Small thermal capacity ◎ Reachable temperature is over 1500 Reachable temperature is over 1500 o o 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. (ET ET- -detector detector) ) detected with PMT. ( � 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 o o C, C, thermal electrons Around 1,000 � � emitted from a filament increase emitted from a filament increase about tenfold as temperature rises as temperature rises about at each 100 o C. . The thermal electrons saturate an The thermal electrons � � SE-detector and contrast of SEM and contrast of SEM images decrease. images decrease. Emission density of thermal electrons from tungsten filament. � 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. Energy distribution of thermal electrons.

Design of In- -situ Heating System for SEM situ Heating System for SEM Design of In Schematic illustration of heating system for in-situ SEM observation. � 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 �

Overview of the Heating Unit Overview of the Heating Unit � Thermal electron filter 20 µ m φ φ tungsten wire tungsten wire wounded wounded 20 µ m 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 detector and the detector � Disposable heating stage Light bulb removed grass cover removed grass cover Overview of heating stage equipped with thermal electron filter. Light bulb � Specimens are mounted on and Specimens are mounted on and � between tungsten filament between tungsten filament ndustrial mass product I ndustrial mass product I � Easy to get Easy to get, , g good uniformity ood uniformity � and low price and low price Micrographs of heating stage (Light bulb removed grass cover).

Effect of Thermal Electron Filter Effect of Thermal Electron Filter 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 � Good contrast images can be obtained over 1400 o C 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 1300 o o C. C. 1300 There is no need to re-adjust brightness and contrast of images as temperature as temperature There is � � changes. This make possible to record images with short intervals record images with short intervals. . changes. This make possible to

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

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 ( α -Ca Ca 3 (PO 4 ) 2 ) tricalcium phosphate ( α - 3 (PO 4 ) 2 ) in octanol/water binary emulsion. in octanol/water binary emulsion. TEM image of Ca-def HAp before thermal treatment. � In In- -situ SEM observation situ SEM observation � – JEOL JSM JEOL JSM- -845 equipped with the 845 equipped with the – heating stage for in in- -situ situ observation. observation. heating stage for – How to change their morphology in How to change their morphology in – thermal treatment. 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 800 o C. The morphology of whiskers began The morphology of whiskers began � � to change around 850 o C. Thermal . Thermal to change decomposition proceeds in this decomposition proceeds in this temperature range. temperature range. The whiskers united each other united each other The whiskers � � above 900 o C. The whiskers . The whiskers deformed into gnarled shape. deformed into gnarled shape. � Above 1000 o C, 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 situ observation of sintering process of Ca observation of sintering process of Ca- -def HAp whiskers. def HAp whiskers. In