Influence of Niobium Oxide on the Mechanical Properties of HA

Key Engineering Materials Vols. 529-530 (2013) pp 29-33

© (2013) Trans Tech Publications, Switzerland

doi:10.4028/www.scientific.net/KEM.529-530.29

Influence of Niobium Oxide on the Mechanical Properties of

Hydroxyapatite

Nermin Demirkol1,3,a, Faik Nuzhet Oktar2,b and Eyup Sabri Kayali3,c

1Technical Prog. Dept., Vocational School of Degirmendere Ali Ozbay, Kocaeli University, Kocaeli, Turkey

2Medical Imaging Techniques Dept., School of Health Related Professions, Marmara University, Istanbul, Turkey

3Metallurgical&Materials Eng. Dept., Istanbul Technical University, Istanbul, Turkey

anermin.demirkol@kocaeli.edu.tr, bfoktar@marmara.edu.tr, ckayali@itu.edu.tr

Keywords: Sheep hydroxyapatite, synthetic hydroxyapatite, mechanical properties, niobium oxide.

Abstract. The goal of this study is to produce and to investigate the mechanical and microstructural properties of composite materials made of hydroxyapatite, obtained from both natural sheep bone and commercial synthetic hydroxyapatite with niobium oxide addition( 5 and 10 wt%). The samples were subjected to sintering at different temperatures between 1000ºC and 1300ºC. Microstructures and mechanical properties of sheep hydroxyapatite (SHA) and commercial synthetic hydroxyapatite (CSHA)-niobium oxide composites were investigated. The production of hydroxyapatite (HA) from natural sources is preferred due to economical reason. The aim of development of SHA and CSHA based niobium oxide composites is to improve mechanical properties of HA.
The physical and mechanical properties were determined by measuring density, compression strength and Vickers microhardness (HV). Structural characterization was carried out with X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies.

In all composites, density values and mechanical properties increased with increasing sintering temperature. The increase of niobium oxide content in all composites showed better mechanical properties. Both of SHA and CSHA composites with at 1300ºC sintering temperature showed nearly the same compression strength value.

Introduction
Artificial implants of hydroxyapatite (HA), Ca10(PO4)6(OH)2, are very popular for hard tissue (e.g., bone) restorations because they accelerate bone growth around the implant [1]. Nowadays biological apatites (i.e natural apatites) attract special interest since it is believed that the several
substitutions at the Ca2+, PO 3-
and OH-
sites of hydroxyapatite (HA) and the presence of several
trace elements (Na, Mg, K, Cl, F) [2,3] play an important role in the overall physiological functioning [2]. Commercial synthetic hydroxyapatite (CSHA) do not posses this kind of rare minerals. Also CSHA production is costly and time consuming [4]. Natural HA derived from animal bones seems to be an alternative solution for products based on the synthetic HA [5]. Calcination of HA structures from natural bones can be regarded safe and economic [4,6].
Due to the poor mechanical properties of bulk HA ceramics compared with natural bones, they are not suitable for load bearing applications [7]. HA material can be reinforced with a second phase of reinforcement materials (i.e. polymers, metals and ceramics) to make a stronger composite material[8]. From the literature it is known that niobium oxide improves biocompatibility and promote bioactivity of HA [9]. Demirkol et al had conducted sheep hydroxyapatite (SHA)-niobium oxide composites showing its beneficial effect on the properties of HA [6].
The aim of this study is to compare the mechanical properties of SHA, CSHA and the effect of niobium oxide addition to these HAs to determine the effects of the production process and source of HA.

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30 Bioceramics 24


Materials and Methods
In this study, sheep derived hydroxyapatite (SHA) was used as a natural hydroxyapatite. Firstly, fresh cut femurs were deproteinized with NaOH and after reirrigation the samples were subjected to calcination at 750ºC. Then calcinated sheep bones were wet ball milled for 24 h and they were dried in an oven at 105ºC in air for 24 h. The average particle sizes of SHA and CSHA are 10 and 6,5 µm, respectively. The commercial synthetic hydroxyapatite (CSHA) used in this study was received from Across company. The CSHA and SHA powders were seperately mixed with 5 and 10 wt% niobium oxide powder for 4 h. The powder portions were pressed at 350 MPa. Pressed samples were sintered between 1000-1300?C (with the heating rate of +5ºC min-1 ) for 4 h. Density, Vickers microhardness, and compression strength were measured. Microstructural characterization was carried out by optical and scanning electron microscope (SEM) examinations and X-ray diffraction (XRD) analyses. Microhardness values were determined under 200 g. load. The compression tests were done with an universial testing machine (Shimadzu) at the crosshead speed of 3 mm/min. Scanning Electron Microscope (Hitachi TM-1000) was used for microscopic examinations and XRD analyses were conducted on a Brucer D8-Advanced X-ray diffractometer using Cu Kα radiation.
Results and Discussion
Table 1 shows the experimental results of density, compression strength and Vickers microhardness of the SHA and CSHA samples sintered at different temperatures. The density, microhardness and compression strength values of both SHA and CSHA increase with increasing sintering temperature, as seen in Table 1. CSHA showed better properties than SHA between
1000-1200ºC, probably due to the finer particle size of CSHA. However SHA showed higher properties than CSHA at 1300ºC. The maximum values were achieved with SHA at 1300ºC sintering temperature.
Table 1. Density, compression strength and Vickers microhardness values of SHA and CSHA
samples sintered at different temperatures.

Temperature (ºC)

Density (g/cm3)

Compression Strength

(MPa)

Vickers Microhardness

(HV)

 

SHA

CSHA

SHA

CSHA

SHA

CSHA

1000

2,09

2,20

31

38

49

68

1100

2,16

2,32

38

49

67

85

1200

2,40

2,44

50

60

138

152

1300

2,59

2,53

69

64

189

165

Table 2 and 3 show density, compression strength and Vickers microhardness values of
SHA-Nb2Oand CSHA- Nb2Ocomposites sintered at different temperatures, respectively.
Table 2. Density, compression strength and Vickers microhardness values of SHA- Nb2O5
composites sintered at different temperatures [6].

Temperature (ºC)

Density (g/cm3)

Compression Strength

(MPa)

Vickers Microhardness

(HV)

 

5wt%

10wt%

5wt%

10wt%

5wt%

10wt%

1000

2,13

2,19

31

58

52

89

1100

2,21

2,26

39

62

84

107

1200

2,44

2,55

59

72

163

183

1300

2,64

2,66

80

88

214

298

Key Engineering Materials Vols. 529-530 31


Table 3. Density, compression strength and Vickers microhardness values of CSHA- Nb2O5
composites sintered at different temperatures.

Temperature (ºC)

Density (g/cm3)

Compression Strength

(MPa)

Vickers Microhardness

(HV)

 

5wt%

10wt%

5wt%

10wt%

5wt%

10wt%

1000

2,20

2,33

43

60

99

118

1100

2,45

2,62

67

75

196

222

1200

2,60

2,72

74

80

285

295

1300

2,71

2,95

82

89

322

390

Fig. 1 and 2 show the comparison of Vickers microhardness and compression strength properties of SHA and CSHA composites. At all composites, density, compression strength and Vickers microhardness values increased with increasing sintering temperature. The density and Vickers microhardness of both composites increased with the addition of niobium oxide. Niobium oxide addition also causes increases in compression strengths of both composites, except 5 wt% Nb2Ocontaining SHA sintered at 1000 and 1100 ºC. The compression strengths of SHA and SHA-5 wt% Nb2Oare nearly the same at these temperatures. When we compared the measured properties of SHA and CSHA composites, the density, hardness and compression strength values of CSHA composites were higher than that of SHA composites, except compression strengths of composites at
1300ºC. The Nb2Oaddition to SHA and CSHA improved to strength properties of composites up to
28% and 39%, respectively. SHA and CSHA composites sintered at 1300ºC showed nearly the same

compression strength values.
(a) (b)
Fig.1. Comparison of hardness values of SHA and CSHA composites containing 5wt% Nb2O(a)

and 10wt% Nb2O(b) sintered at different temperatures.
(a) (b)
Fig.2. Comparison of compression strength values of SHA and CSHA composites containing 5wt% Nb2O(a) and 10wt% Nb2O(b) sintered at different temperatures.

32 Bioceramics 24


As an example of XRD studies, XRD patterns of composites containing 10 wt% Nb2Osintered at 1300ºC are given in Fig.3. The present phases in both composites are the same. They are: hydroxyapatite, calcium phosphate, niobium oxide, calcium niobium oxide and whitlockite. It is concluded that the same compression strengths of SHA and CSHA composites sintered at 1300ºC due to presence of the same phases in both composites sintered at 1300ºC.

Fig.3. XRD patterns of composites containing 10 wt% Nb2Osintered at 1300ºC.
Fig.4. shows the microstructures of CSHA and SHA composites with 10 wt% Nb2Osintered at
1300ºC. The similar microstructures and good densification were observed on both composites as
seen in Fig.4. White coloured regions determined as calcium niobium oxide phase obtained from
EDS analyses.

(a) (b)
Fig.4. Microstructures of composites containing 10 wt% Nb2Osintered at 1300ºC (a) CSHA, (b) SHA.
Summary
The aim of this study is to compare the mechanical properties of SHA, CSHA and the effect of niobium oxide addition to these HAs to determine the effects of the production process and source of HA.
The following conclusions were obtained.
1. Density, compression strength and hardness values of SHA, CSHA and all composites increased with increasing sintering temperature.
2. CSHA showed better properties than SHA between 1000-1200ºC. However SHA showed higher properties than CSHA at 1300ºC. The maximum values were achieved with SHA at
1300ºC sintering temperature.
3. Density and hardness values of both composites increased with the addition of niobium oxide.

Key Engineering Materials Vols. 529-530 33


4. Niobium oxide addition causes increases in compression strengths of both composites, except 5 wt% Nb2Ocontaining SHA sintered at 1000 and 1100 ºC.
5. Density, hardness and compression strength values of CSHA composites were generally
higher than that of SHA composites.
6. SHA and CSHA composites sintered at 1300ºC showed nearly the same compression strength values.
7. The present phases in both composites sintered at1300ºC are the same.
8. The similar microstructures and good densification were observed on both composites sintered at1300ºC.
Biocompatibility studies are going on. If the results are positive, Nb2Ocontaining HA composites seems to be very good material for orthopedic applications with better mechanical properties than HA.
References
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DOI:10.1002/jbm.b.30295