# Microhardness of Hydroxyapatite Doped ZrO2 using Sol-Gel Method

S Helen, A Ruban Kumar

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S Helen, A Ruban Kumar. Microhardness of Hydroxyapatite Doped ZrO2 using Sol-Gel Method . Mechanics, Materials Science & Engineering MMSE Journal. Open Access, 2017, 9 (1), 10.2412/mmse.48.98.680 . hal-01498160

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Distributed under a Creative Commons Attribution 4.0 International License
# Microhardness of Hydroxyapatite Doped ZrO₂ using Sol-Gel Method

S. Helen¹, A. Ruban Kumar¹, a

1. Centre for Crystal Growth, VIT University, Vellore, India

a. arubankumar@vit.ac.in

<figure><img src="image_2.png" /></figure>

DOI 10.2412/mmse.48.98.680 provided by [Seo4U.link](https://linkages.seo4u.ac.kr/10.2412/mmse.48.98.680)

**Keywords:** hydroxyapatite, zirconium oxide, sol-gel method, micro-hardness.

**ABSTRACT.** Calcium Phosphate based bio-ceramics in the form of hydroxyapatite (HA) with high biocompatibility in hard tissues. In this work HA mixed with ZrO₂ using Sol-gel method. Calcium nitrate with Di-ammonium hydrogen phosphate used for the formation of HA, which exhibited less mechanical property. To overcome these problems ZrO₂ were used to increase its mechanical strength. XRD and FTIR confirmed the phases and functional groups and its hardness was analysed and confirmed it is a soft material used in various medical applications especially in orthopaedics field.

**Introduction.** Hydroxyapatite is an inorganic material with minerals present in bone and teeth which have low mechanical property, which does not support for load bearing applications. To sustain these problems, HA incorporates with different composites to increase mechanical strength in the field of implants. The combination of hydroxyapatite with composites improves hardness and fracture toughness. YSZ/HA used to improve wear resistance, strength of HA using co-precipitate method [1]. For load-bearing applications various metals, as alloys were used but using of metals has some drawbacks such as corrosion, negative tissue reactions, the slack of implants and stress due to high stiffness, which used in various medical applications. To prevent the decomposition of HA doped ZrO₂ must less than 10% unless specific sintering temperature should apply. ZrO₂ has an eminent potential to be used in bone implantations which are tougher than Al₂O₃. And the stable phase of HA produced with some OH⁻ bond. However, while sintering the H₂O vapour and decay at 1300°C, which produces secondary phases. ZrO₂ has tetragonal or cubic structure at room temperature. ZrO₂ has high mechanical strength and low toxicity for living organisms. The HA synthesized using ZrO₂ which can be used in various applications in both dentistries and in orthopedics which has the mechanical strength greater than the cortical bone [2]. Zirconium oxide is known as ceramic which has a high thermal expansion with high resistance to crack propagation. HA improves bending strength and coatings for medical applications by adding the small amount of ZrO₂. The hardness and flexural strength for HA were 5.4GPa and 94MPa; ZrO₂ has 14.2GPa and 929MPa [3]. As catalytic ZrO₂ has the potential application due to less toxicity, less volatile and more stable at high temperature and eco-friendly with environmental. ZrO₂ and Al₂O₃ are bioinert materials with high fracture strength and high toughness. Ceramics such as ZrOCl₂ and AlCl₃ using a precipitate method using calcium nitrate with di-ammonium hydrogen phosphate to improve both bending strength and disintegration toughness [4]. Composites synthesized using sol-gel with polymers to ceramics in that ZrO₂ with PEG used as a plasticizer for medical applications. The polyethylene glycol (PEG) added with Zirconium oxide (ZrO₂) which increase the coating ability and films were more homogeneous [5]. HA added with PEG/ZrO₂ as the bioactive material used widely in wear resistance in joint applications using the sol-gel method. The aim of this paper is about the micro hardness of HA with inorganic (PEG) and ceramic (ZrO₂) combinations using sol-gel method which does not report yet.

<footnote n="22">²² © 2017 The Authors. Published by Magnolithe GmbH. This is an open access article under the CC BY-NC-ND license
http://creativecommons.org/licenses/by-nc-nd/4.0/</footnote>
**Synthesis Method.** The precursor's calcium nitrate tetra hydrate with Diammonium hydrogen phosphate for synthesized HA and Ammonium hydroxide for maintaining the pH. The HA will form stable at high pH give chemical stability and biological activity. Adding Diammonium hydrogen phosphate into Calcium nitrate maintaining pH form 9-11 using NH4OH. And adding of HA with PEG which increases the ability of HA to sustain in coatings and ZrO2 which is an oxide in form for increase hardness of HA. The pure hydroxyapatite (HA) and doped zirconium oxide with both HA and polyethylene glycol (HPZ). The flow chart for synthesizing HA with PEG and ZrO2 given below.

<figure><img src="image_3.png" /><figcaption>Fig. 1. Sol-gel method for synthesis of pure HA and adding of ZrO2 +PEG to HA (HPZ).</figcaption></figure>

**Results & Discussions:**

X-ray Diffraction shows the peaks with good crystallinity with sharp peaks for pure hydroxyapatite and doped zirconium oxide with HA shows the broad peak with 2theta values 31.7 for pure and 31.93 for HPZ with hkl value 211, 300, 112 but in HPZ there was a disappearance of peaks shows decomposition of hydroxyapatite Fig. 2.

<table><caption>Table 1. Lattice parameters and Volume for Pure HA and HPZ</caption><thead><tr><td>Sample</td><td>a Å</td><td>c Å</td><td>Volume (V) Cm³</td></tr></thead><tbody><tr><td>Hydroxyapatite (09-0432)</td><td>9.418</td><td>6.884</td><td>528.80</td></tr><tr><td>HA</td><td>9.418</td><td>6.884</td><td>528.8</td></tr><tr><td>HPZ</td><td>9.418</td><td>6.882</td><td>528.77</td></tr></tbody></table>

The above table gives the lattice parameters and volume of synthesized materials with the JCPDS of hydroxyapatite (09-0432). The obtained HA with JCPDS are same but adding zirconium to HA gives a value same with decrease in c parameter which shows decomposition of HA.
<figure><img src="image_4.png" /><figcaption>Fig. 2. XRD graph of pure HA and HPZ.</figcaption></figure>

The analysis of functional groups for doped Inorganic with ceramics was shown in Fig. 3. The peaks from 500-1442 indicate the presence of PO₄³⁻ groups in stretching mode and OH⁻ in the range 3000-3500 and extra peak at 1300 may be due to zirconium oxide compared with HA doped PEG. The peaks range from 1000-1500cm⁻¹ shows PO stretching mode which confirms the presence of HA.

<figure><img src="image_5.png" /><figcaption>Fig. 3. FTIR analysis for HA +PEG and HA+PEG+ZrO₂.</figcaption></figure>

**Hardness.** Hardness is the ability to determine the surface of the material withstands forces. Vickers's hardness is the capacity to resist plastic deformation. The hardness increase with the load, if n is greater than two if n less than two it will decrease the hardness. The value with the range 1-1.6 is considered as hard materials and greater than 1.6 are called soft materials. The average hardness of HA 6.77GPa. Using Meyer's index hardness value for HPZ is 2.66 shows it is soft material due to RISE. Mechanical stability essential for making devices which can be used in implantations.
<figure><img src="image_6.png" /><figcaption>Fig. 4. Microhardness for HPZ.</figcaption></figure>

**Summary.** Hydroxyapatite doped with zirconium oxide by adding polyethylene glycol which increases the strength of HA which is a less mechanical strength; XRD shows the decomposition of HA and functional group were confirmed by FTIR. The materials were revealed as a soft material, which can use to increase the ability of coatings and implantations.

**Acknowledgement.** The authors thank the management of VIT University Vellore for providing the
excellent research facilities.

**References**

[1] Sung, Y. M., Shin, Y. K., & Ryu, J. J. (2007). Preparation of hydroxyapatite/ zirconia bio ceramic nano composites for orthopaedic and dental prosthesis applications. Nanotechnology, 18 (6), 065602, DOI 10.1088/0957-4484/18/6/065602.

[2] Matsumoto, T. J., An, S. H., Ishimoto, T., Nakano, T., Matsumoto, T., & Imazato, S. (2011). Zirconia-hydroxyapatite composite material with micro porous structure. Dental materials, 27 (11), e205-e212, DOI 10.1016/j.dental.2011.07.009.

[3] Chaudhry, A. A., Yan, H., Viola, G., Reece, M. J., Knowles, J. C., Gong, K., Darr, J. A. (2012). Phase stability and rapid consolidation of hydroxyapatite-zirconia nano-coprecipitates made using continuous hydrothermal flow synthesis. Journal of biomaterials applications, 27 (1), 79-90, DOI 10.1177/0885328212444483.

[4] Mobasherpour I., Hashjin, M. S., Toosi, S. R., & Kamachali, R. D. (2009). Effect of the addition ZrO₂-Al₂O₃ on nanocrystalline hydroxyapatite bending strength and fracture toughness. Ceramics International, 35 (4), 1569-1574, DOI 10.1016/j.ceramint.2008.08.017.

[5] Catauro, M., Bollino, F., & Papale, F. (2014). Biocompatibility improvement of titanium implants by coating with hybrid materials synthesized by sol-gel technique. Journal of Biomedical Materials Research Part A, 102 (12), 4473-4479, DOI: 10.1002/jbm.a.35116.

Cite the paper

S. Helen, A. Ruban Kumar (2017). *Microhardness of Hydroxyapatite Doped ZrO₂ using Sol-Gel Method*. *Mechanics, Materials Science & Engineering*, Vol 9. doi:10.2412/mmse.48.98.680