Preparation of diopside with apatite-forming ability by sol–gel process using metal alkoxide and metal salts

doi:10.1016/j.colsurfb.2003.07.004

Colloids and Surfaces B: Biointerfaces

Volume 33, Issue 1, 1 January 2004, Pages 1-6

https://doi.org/10.1016/j.colsurfb.2003.07.004 Get rights and content

Abstract

The thermal and biological properties of diopside, CaMgSi₂O₆ prepared by a sol–gel process using a metal alkoxide and metal salts were investigated for its applicability as a biomaterial. Precursor wet gel was synthesized by hydrolyzing a homogeneous solution consisting of Ca(NO₃)₂·4H₂O, MgCl₂·6H₂O and Si(OC₂H₅)₄ dissolved in ethanol. The effect of thermal treatment on crystallization of the hydrolyzed product was examined by DTA, XRD and TG–MS measurements. The dried gel powder was X-ray amorphous and crystallized into diopside single phase at 751.4 °C. This crystallization temperature was lower than that for the dried gel powder prepared by a sol–gel process using metal alkoxides reported by Nonami et al., which suggests that acidic compounds such as HNO₃ and HCl generated in the powder during the heating process promotes the crystallization. Moreover, when the sintered body of diopside was immersed in simulated body fluid, an apatite layer was formed on the surface. Thus, the diopside prepared by the sol–gel process using the metal alkoxide and the metal salts without acidic catalysts addition was found to have an apatite-forming ability.

Introduction

Diopside (CaMgSi₂O₆), one of the pyroxene minerals, is known as an excellent bioactive material and has been the subject of many studies [1], [2], [3], [4], [5], [6], [7], [8]. According to these studies, when diopside is immersed in simulated body fluid (SBF) apatite-like calcium phosphates are formed on its surface, giving a good bioactivity [9], [10]. In addition, the sintered body of diopside seems to bond to living bone tissues more rapidly than apatite [11], [12]. Moreover, diopside has a fairly high mechanical strength and superb biological affinity [13], [14], [15]. Diopside is therefore considered to have a potential as a biomaterial for artificial bone and tooth.

There have been several reports on ceramic powder preparation from solution [16], [17], [18]. These reports describe that sol–gel process is effective in obtaining fine particles with a high sinterability. The process is also possible to achieve multi-component products with various shapes and forms such as dense or porous bulk-solids, fibers and films [19], [20], [21], [22], [23]. In addition, sol–gel process allows us to prepare highly homogeneous complex amorphous and crystalline products at comparatively low temperatures.

In sol–gel process, metal alkoxides (M(OR)_n, where M and R represent metal and alkyl groups, respectively) are usually employed as the raw materials. Since the rate of hydrolysis of metal alkoxides considerably differs from one species to another, it is often difficult to establish synthetic processes for reproducibly preparing expected products [24]. In addition, almost all metal alkoxides are quite unstable in the air and cannot be handled easily in the preparing process.

We expect that the synthesis of diopside by sol–gel process using not only metal alkoxides but also metal salts as the starting materials is useful to solve the problems mentioned above. In the present study, we prepared diopside by a sol–gel process using a metal alkoxide and metal salts without acidic catalysts addition and examined the effect of thermal treatment on crystallization of the dried gel powder. Furthermore, the bioactivity of the sintered body of diopside was also evaluated by means of the immersion of the diopside in SBF.

Section snippets

Diopside preparation

At first, 0.125 mol of Ca(NO₃)₂·4H₂O and 0.125 mol of MgCl₂·6H₂O were dissolved in 150 ml of ethanol as a solvent. The starting solution was vigorously stirred with a hot-stirrer at 80 °C for 30 min. After that, 0.250 mol of Si(OC₂H₅)₄ was added to the solution. The homogeneous solution was slowly stirred for a few hours to yield a precursor wet gel. The wet gel was dried in an oven at 100 °C for 24 h. The dried gel powder ground with an agate mortar and pestle was calcined at 700 °C for 2 h in

Thermal properties of dried gel powder

In order to design ceramic materials with desired properties, a through understanding of the thermal behavior of raw powder during heating process is essential. Fig. 1 shows the TG–DTA curves of a gel powder dried at 100 °C for 24 h. The exothermic peak observed at 751.4 °C is presumed to be caused by crystallization of the dried gel powder into diopside. Nonami et al. synthesized diopside by a sol–gel process using metal alkoxides, i.e., Ca(OC₂H₅)₂, Mg(OC₂H₄OC₂H₅)₂ and Si(OC₂H₅)₄ (TEOS), which

Conclusions

Diopside was prepared by a sol–gel process using a metal alkoxide and metal salts as the starting materials, and the effect of thermal treatment on crystallization of the dried gel powder and the bioactivity of the sintered body of diopside were examined by means of the immersion of the diopside in simulated body fluid (SBF). Referring to DTA and XRD measurements, the dried gel powder prepared by this method was suggested to crystallize into diopside single phase at 751.4 °C. The resultant

Acknowledgements

This work was partly supported by a High-Tech Research Center Project Grant from the Ministry of Education, Culture, Sports, Science and Technology of Japan. The authors are grateful to T. Takahashi, Thermal Analysis Division, Rigaku Corporation, for the TG–MS measurement, and to Y. Abe and T. Nakamura, Analytical Sciences Laboratory, Mitsubishi Chemical Corporation, for the SEM-EPMA work. Special thanks are also due to Dr. Y. Hirano, Toin University of Yokohama, for his fruitful guidance and

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Preparation of diopside with apatite-forming ability by sol–gel process using metal alkoxide and metal salts

Abstract

Introduction

Section snippets

Diopside preparation

Thermal properties of dried gel powder

Conclusions

Acknowledgements

Biomaterials

J. Non-Cryst. Solids

J. Non-Cryst. Solids

J. Jpn. Dent. Mater.

J. Jpn. Dent. Mater.

J. Dent. Res.

J. Jpn. Soc. Biomater.

J. Ceram. Soc. Jpn.

J. Ceram. Soc. Jpn.

J. Ceram. Soc. Jpn.

J. Jpn. Dent. Mater.

Shikwa Gakuho

Mater. Res. Soc. Symp. Proc.

Shikwa Gakuho

Mater. Res. Soc. Symp. Proc.

J. Ceram. Soc. Jpn.

J. Ceram. Soc. Jpn.

J. Jpn. Soc. Biomater.