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알칼리 조건하에서 졸-겔 법에 의한 TEOS의 가수 분해와 축합중합 반응에 대한 속도론적 연구

A Kinetic Study on the Hydrolysis and Condensation of TEOS in Basic Condition by Sol-Gel Method

윤호성 박형상 김상환

Yoon HS Park HS Kim SH

HWAHAK KONGHAK, August 1994, 32(4), 557-565(9), NONE

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Abstract

졸-겔 법에 의한 알칼리 조건하의 실리카 입자 형성 과정에서 TEOS(tetraethyl-orthosilicate)의 가수분해와 축합중합 반응의 속도론적 연구를 수행하였다. 본연구에서는 공정에 관련된 여러 매개 변수들인 NH₃(catalyst) 농도, r(H₂O/Si molar ratio), 온도 그리고 용매의 종류 등을 선정하여, 이들이 반응에 미치는 영향을 알아보고 아울러 이들 결과에 따른 졸-겔 공정의 이해에 관한 기초 연구를 수행하였다. 본 연구 조건에서, 가수분해 반응은 율속 단계이며, 알코올을 형성하는 축합중합보다는 물을 형성하는 축합중합 반응이 지배적이다. 가수분해와 축합중합 반응 속도 상수는 [NH₃] 농도에 비례하며, r의 증가는 가수분해 반응을 빠르게 한다. 온도 증가에 따른 가수분해 반응의 활성화 에너지는 5.99kcal/mole이었다. 용매의 변화는 에스테르 교환반응(transesterification )을 일으키며, 이에 따른 입체 효과(steric effect)와 용매로 사용된 알코올의 분자량은 각 반응 속도에 영향을 미친다.

For a formation reaction of silica particles through hydrolysis and condensation of TEOS by sol-gel method, the effects of [NH₃] concentration, r(H₂O/Si molar ratio), temperature and kinds of solvents are investigated. When hydrolysis and condensation reaction in the sol-gel process take place under the basic conditions of solution, hydrolysis is proved to be the rate-limiting step, and water-forming condensation is dominant over alcohol-forming condensation. The rate constants of hydrolysis and water-forming condensation are proportional to the concentration of NH₃, while the increase of r accelerates the hydrolysis. The activation energies of hydrolysis, alcohol-forming, and water-forming condensation are 5.99, 15.4, and 3.69 kcal/mole, respectively. The transesterification of alkoxide occurs through the change of solvents and the steric effect exists due to the exchange of alkoxy group in the reaction. Steric effect and the molecular weight of alcoholic solvent, it is observed, have a great influence on each reaction rate.

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