Title : Sintering Behaviour of Cerium-doped Hydroxyapatite Bioceramics

FINAL YEAR PROJECT 2(Semester1, Academic Year 2008/2009)

Prepared by:KELVIN HOH CHEE WAI (ME075719)

Department of Mechanical EngineeringUniversiti Tenaga Nasional (UNITEN)Project Supervisor:

Assoc. Prof. Ir. Dr. Ramesh Singh

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CONTENTS

� Introduction� Objective� Methodology� Experimental techniques� Experimental testing methods� Results & Discussions� Conclusion

INTRODUCTION

� Hydroxyapatite (HA), Ca10(PO4)6(OH)2, exhibits excellent biocompatibility due to its chemistry similarity with the mineral portions of hard tissues.

� However, its mechanical properties limit the usage of HA in clinical application.

� Several approaches have been proposed to improve the mechanical properties of HA, such as:

INTRODUCTION

Control of sintering temperature & atmosphere.

Manipulation of processing parameters.

Addition of sintering additives (i.e. dopants) into the HA powder.

OBJECTIVE

� To investigate the effects of adding small amounts of Cerium Oxide (CeO2) on the sinterability of nanocrystalline HA powder.

METHODOLOGY

Literature Review

Report preparation & presentation

Powder Characterization

Mechanical Testing & Evaluation

Preparation of Cerium-dopedHA powder

Body Preparation

Consolidation Process

FYP 1

FYP 2

Experimental Techniques

� Synthesized HA powder which is produced by wet chemical precipitation method was used and mixed with CeO2 ranging from 0.1 wt% - 1.0 wt% using wet milling method.

� The powder was uniaxially pressed into discs and rectangular bars and subsequently cold isostatically pressed at 200 MPa.

� The compacted samples were sintered at temperature ranging from 1100C to 1300C.

� Sintered samples were polished to 1m finish prior to testing.

Experimental Testing Methods

� Phase analysis X-Ray Diffraction (XRD).

� Bulk density Water Immersion Technique.

� Young�s modulus Sonic Resonance Method.

� Hardness Vicker�s Indentation Method.

� Fracture Toughness Vicker�s Indentation Method.

RESULTS & DISCUSSIONS(XRD Analysis)

� XRD analysis revealed that the doped & undoped HA phase stability were not disrupted regardless of d o p a n t a d d i t i o n s a n d s in te r i ng t empera tu re .

Fig 1: XRD patterns for CeO2-doped HA sintered at 1300 C.(a) undoped HA, (b) 0.1 wt%, (c) 0.5 wt%, (d) 1.0 wt%CeO2, respectively.

Ceria Peaks @ 1 wt%

BULK DENSITY

3.09

3.1

3.11

3.12

3.13

3.14

1100 1200 1300

Sintering Temperature (ºC)

Bu

lk D

ensi

ty (

g/c

m3 )

0wt%0.1wt%0.5wt%1.0wt%

� In general, the bulk density variation of all the composition studied exhibited a similar trend with increasing sintering temperature.

� All the samples attained above 98% of theoretical density when sintered above 1100ºC.

Fig 2: The effects of CeO2 addition on the bulk density ofsynthesized HA.

YOUNG�S MODULUS

117118

119120

121122

123124

125126

1050 1100 1150 1200 1250 1300 1350

Sintering Temperature (°C)

Yo

ung'

s m

odul

us (

GP

a)

undoped0.1 wt%0.5 wt%1.0 wt%

� The relationship between the Young�s modulus of the sintered body, sintering temperature and CeO2additions are shown in Fig 3.

� The inclusion of CeO2 in HA reduces the Young�s modulus.

� However, the Young�s modulus of natural bone is reported to be between 11 GPa to 29 GPa.

Fig 3: The effects of CeO2 addition on the Young�s modulusof synthesized HA.

YOUNG�S MODULUS

Fig 4: Fracture toughness versus Young�s modulus of present biomaterials and human bone.

VICKER�S HARNESS

0

1

2

3

4

5

6

7

1100 1200 1300

Sintering Temperature (°C)

Har

dnes

s (G

pa)

undoped0.1wt%0.5wt%1.0wt%

� A general observation shows measured hardness of all the samples revealed a similar trend.

� The results also revealed that the addition of 1 wt% CeO2was beneficial as samples exhibited higher hardness value in the sintering regime employed as compared to undoped HA.

� The highest hardness value of 6.19 GPa was obtained for HA doped with 1 wt% CeO2 and when sintered at 1200ºC.

Fig 5: The effects of CeO2 addition on the Vicker�s Hardnessof synthesized HA.

FRACTURE TOUGHNESS

00.10.20.30.40.50.60.70.80.9

1100 1200 1300

Sintering Temperature (°C)

Frac

ture

Tou

ghne

ss (M

Pam

1/2 )

Undoped0.1wt%0.5wt%1.0wt%

� The results also show that the addition of CeO2 was effective in enhancing the fracture toughness (KIc) of the synthesized HA, particularly when sintered at 1100ºC.

� The 1 wt% cerium-doped HA samples exhibited the highest fracture toughness of 0.82 MPam1/2 as compared to 0.73 MPam1/2 measured for the undoped HA.

Fig 5: The effects of CeO2 addition on the fracture toughnessof synthesized HA.

CONCLUSIONS

� Incorporation of small amount of cerium oxide can be beneficial in enhancing the mechanical properties without affecting the HA phase stability even when sintered at 1300ºC.

� The addition of 1 wt% CeO2 and when sintered at 1100ºC was found to be most beneficial as the HA samples exhibited the moderate Young�s modulus of 120.53 GPa, enhanced hardness of 6.19 GPa and fracture toughness of 0.82 MPa.m1/2.

FURTHER WORK SUGGESTIONS