Organic Catalysts in the Silica Sol-Gel System
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ORGANIC CATALYSTS IN THE SILICA SOL-GEL SYSTEM T.A. Gallo, B.L. Simms%,. V.T. Brice Akzo Chemicals Inc., ARLDF, Livingstone Avenue, 10522.
Dobbs Ferry,
NY
ABSTRACT
gels were synthesized with Ethyl silicate-derived silica organic acid and base hydrolysis catalysts. The nature of the organic catalyst was found to strongly affect dry gel structure No consistent relationship between dry gel and carbon content. structure and water content of the calcined gels was identified.
INTRODUCTION Catalysts can strongly influence structure development in silica gels derived from metal alkoxides. Catalyst influence on gel structure has been demonstrated by Nogami and Moriya(l) and Researchers have also studied the relationship many others(2) . Few between dry gel structure and calcination behavior(3) . authors have characterized both dry gel structure and calcined gel properties from the perspective of catalyst effects. Organic catalysts are attractive for high purity applications because catalyst removal is complete at low temperatures(4).
EXPERIMENTAL PROCEDURE TEOS, Si(OCH2CH3)4 (Silbond Pure®, Akzo Chemicals Inc.), anhydrous ethanol, 18 megaohm water, and reagent grade catalysts at 35*C Reagents were mixed were used as starting materials. with the use of a shaker bath set at maximum speed. Acid while a catalysts were used for the Series I hydrolyses, combination of acid and base catalysts were used for the Series II and Series III hydrolyses. The mol ratio of TEOS: acid: water The mol ratio of for the Series I and III gels was 1:0.5:6.25. TEOS : acid : water for Series II gels was 1: 0.00045: 6.25. After lhr. of reaction time with the acid catalyst, aqueous base was added to Series II and III hydrolyses bringing the final Series I-III samples are to 1: 8.71. TEOS: water ratio identified in Table 1. 0 dried at 110 C, ground to -300/+106g Gel samples were air 0 C. Surface characteristics were under vacuum at 180 and dried examined with a Micromeritics Digisorb 2600 using N2 on samples 0 outgased at 200 C. TGA and DSC experiments were performed in Samples were then calcined in a tube oxygen at 20°C per minute. furnace under dry oxygen (2.6 ppm water). Samples were fired rapidly to 1125 0 C, held for one hour and then heated over one
Mat. Res. Soc. Symp. Proc. Vol. 180. §1990 Materials Research Society
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hour to 1275 0 C and held for 2 hours. Water content of calcined samples was determined by IR spectroscopy on samples charged to a 3mm KBr cell. Reported water values were calculated assuming a molar absorptivity of 142(5) and are precise to ±5%. TABLE 1. SAMPLE # I-A I-B I-C I-D II-A II-B II-C II-D II-E II-F III-A III-B Iii-C III-D
SAMPLE IDENTITY FOR SERIES I-III ACID formic oxalic acetic nitric nitric nitric nitric nitric nitric nitric formic formic formic formic
BASE NH4 OH (NH4)2CO3 N(CH2CH3)3 N(CH2CH3)40H (NH2)2CO -
N(CH2 CH3 ) 40H N(CH2CH 3 ) 4 0H N(CH2CH3) 4 0H N(CH2CH 3 ) 4 0H
GELS TEOS:ACID:BASE 1:0.5:0 1:0.5:0 1:0.5:0 1:0.5:0 1:0.00045:0.00135 1:0.00045:0.00135 1:0.00045:0.00135 1:0.00045:0.00135 1:0.000
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