나노크기 실리카 입자의 합성을 위한

최적조건에 관한 연구

박성규, 김기도, 김희택

한양대학교 화학공학과

A study on the optimal conditions for the synthesis

of nano-sized silica particles

Sung-Kyoo Park, Ki-Do Kim, Hee-Taik Kim

Department of Chemical Engineering, Hanyang University

INTRODUCTION

The importance and advantages of monodispersed nanometer-sized particles were not only in the scientific field, but also in various industrial applications, e.q. catalyst, pigments, pharmacy, etc. Of those particles, SiO2 nanoparticles are used to make electronic substrates, thin film substrates, electrical insulators, thermal insulators, humidity sensors, etc. The silica particles play a different role in each of these products. The quality of some of these products is highly dependent on the size and size distribution of the silica particles. Commercial silica have a broad size distribution and varying levels of metal contaminants. It is imperative to have silica particles of narrow distribution and high purity to conduct model studies. Thus, we prepared SiO2 nanoparticles by sol-gel method using a semi-batch process that is easier than batch process for controlling the size and size distribution.

Bogush and Zukoski prepared monodispersed silica particles having sizes ranging from 40nm to several micrometers by controlled hydrolysis of TEOS in ethanol, followed by condensation of the dispersed phase material. The reactions are written in abbreviated form as

[eqn: rmSi(OR)_4 + 4H_2 O~ -> ~Si(OH)_4 + 4ROH]

[eqn: n rmSi(OH)_4 ~ -> ~itn rmSiO_2 + 2it n rmH_ 2 O]

They found that five primary factors affecting the size and size distribution of silica particles. They were : (1) concentration of TEOS; (2) concentration of ammonia; (3) concentration of water; (4) alcohol used as the solvent; (5) reaction temperature.

In this work, we examine the effects of R=[H2O]/[TEOS], ammonia(NH3), feed rate of reactant, and reaction temperature on the formation of SiO2 nanoparticles. In addition, we used a statistical experimental method to establish the optimal conditions and to find the main parameters affecting the properties of SiO2 nanoparticles.

EXPERIMENTAL

Materials

The starting solutions were TEOS(99.9%, supplied by Aldrich Chemical Co.), ethanol(99.9%, supplied by Sigma Chemical Co.) solution, and water-ethanol solution with ammonium hydroxide (28% in NH3, Yukuri Pure Chemicals Co. LTD.). Ammonia was used as a catalyst. The reactants were used as prepared without any purification.

Synthesis of Silica Nanoparticles

Monodispersed spherical silica nanoparticles were prepared by the hydrolysis of alkoxide in a semi-batch reactor. The apparatus consists of a reservoir of starting solutions, a micro feed pump with a constant flow rate feeding the starting solution A(TEOS and ethanol) into the reactor with another solution B(water, ethanol and ammonia) and the experiment was conducted with dry nitrogen.

Design of Statistical Experimental Method

We used a statistical experimental method to find the optimal conditions for satisfying the two properties at the same. We carried out twelve experiments and took three levels for each factor (4 factors, 3 levels, and L12(34)).

Measurement

Particle size, particle size distribution, and shape of the powders were determined by a Field Emission Scanning Electron Microscope (FE-SEM, JEOL, JSM-6330F, Japan), Transmission Electron Microscope (TEM, JEOL, JEM-2010, Japan), and a Laser Particle Size Analyzer (Otsuka Electronics, LPA-3000, 3100, Japan).

RESULTS AND DISCUSSION

Figure 1 shows the relation of particle size and four parameters. Figure 1a illustrates that the particle size decreases while increasing the feed rate of reactant and reaction temperature. But we find that the increase in the R=[H2O]/[TEOS] and ammonia increase the particle size(see Figure 1b).

Figure 2 shows the relation of particle size distribution and four parameters. Figure 2a shows that prompt adjustment of the R=[H2O]/[TEOS] and ammonia concentration can decrease particle size distribution. A decrease in the standard deviation of particle size with the decreasing of the feed rate of reactant with the increasing of the reaction temperature, was observed(see Figure 2b).

Figure 3 is SEM images of SiO2 particles obtained by a design of the statistical experimental.

CONCLUSION

SiO2 nanoparticles were formed from the hydrolysis and concentration of TEOS by using a semi-batch process. The properties of SiO2 nanoparticles were controlled by varying the molar ration R, concentration of ammonia, feed rate of reactant solution (TEOS/Et(OH)) and reaction temperature. Statistical design of experiments was used to select the major factors that significantly influenced the synthesis of monodispersed SiO2 nanoparticles.

As a result of this work, the main factors effecting the preparation of nanoparticles were decreased in the order of reaction temperature> concentration of ammonia> R(=[H2O]/[TEOS])> feed rate of reactant. And also, we prepared monodispersed silica particles having ranging from 10nm to 300nm by our experiment.

REFERENCES

1.	A. Van Blaaderen, J. Van Geest and A. Vrij; "Monodisperse Colloidal Silica	Spheres from tetraalkoxysilanes: Particle formation and growth	mechanism", J. Colloid Interface Sci., 154, 2, 481-501 (1992)

2.	G. H. Bogush and C. F. Zukoski IV; "Studies of the kinetics of the	precipitation of Uniform silica particles through the hydrolysis and	condensation of silicon alkoxides", J. Colloid Interface Sci., 142, 1, 1-18	(1991)

3.	T. Matsoukas and Erdogan Gulari; "Dynamics of Growth of silica particles	from Ammonia-Catalyzed Hydrolysis of Tetra-ethyl-orthosilicate", J.	Colloid Interface Sci., 124, 1, 252-261 (1988)

4.	V. K. Lamer, R. H. Dineger; "Theory, Production and Mechanism of	Formation of Monodispersed Hydrosols", J. Che. Soc., 72 , 17, 4847 (1950)

5.	S. Roy, S. Bandyopadhyay and D. Chakravorty; "Sol-gel synthesis of	colloidal silica using cyclohexane", J. Mater. Sci. Letters, 15, 1872-1874	(1996)

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Figure

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1. Effect of factors on particle size

Figure 2. Effect of factors on standard deviation of particle size

Figure 3. SEM images of SiO2 particles obtained by the statistical exprimental