Strength of Gel-Derived SiO 2 Fibers
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STRENGTH OF GEL-DERIVED SiO2 FIBERS WILLIAM C. LaCOURSE Inst. of Glass Science and Engineering N.Y.S. College of Ceramics, Alfred University Alfred, N.Y. ]4802 ABSTRACT Strengths of as drawn gel-derived SiO fibers are found to depend on H 0 and alcogol content of the sol, as well as drawing viscosity. Additional factors, including fiber diameter and drying and consolidation schedules are found to dramatically influence strengths of the consolidated glass fibers. INTRODUCTION Sakka and Kamiya [1-3] have provided considerable information regarding production of fibers from tetraethoxysilane Acid catalysed TEOS with HB0/TEOS ratios of less (TEOS) sols. than 2 yields sols with viscosities whicA rise slowly through the fiberizing range (5-500N-s/m 2 ) and structures which permit Fibers can be consolidated continuous filaments to be drawn. at temperatures near 800 oC to produce 20 1Am diameter glass fibers with strengths near 600 MN/m 2 . Strengths decrease rapidly with increasing diameter, and with increasing consolidation temperature above 800 oC. [3] A number of factors, including diameter and consolidation temperature are expected to influence the strength of gelThese include derived SiO2 fibers. A.
SOL 1. 2. 3. 4. 5.
STRUCTURE H2 0/TEOS ratio Humidity-Temperature Solvent (alcohol) content pH and acid type Sol viscosity
B.
DRYING AND CONSOLIDATION 1. Sol structure 2. Ageing prior to consolidation 3. Atmosphere 4. Heating rate 5. Maximum temperature 6. Fiber diameter
In the present paper several of these factors are investigated to determine effects on the strength of "as drawn" (unconsolidated) and consolidated Si0 2 fibers. PROCEDURES Sols were prepared using the procedure of Dahar [4,5]. TEOS and anhydrous ethyl alcohol were premixed at room temperAn aqueous solution of 0.1N HC1 was then ature for ½ hour. added to provide the desired water content. The sol was allowed to react further while covered, for an additional 2 Mat.
Res.
Soc.
Symp.
Proc. Vol.
32 (1984)
Published by Elsevier Science Publishing Co.,
Inc.
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hours. It was then uncovered and placed in an oven at 50 OC and 20% relative humidity until the viscosity reached desired levels. This required 1.5 to 5 days depending on the alcohol and water contents. Sols having H2 0/TEOS molar ratios of 1.4, 1.5, 1.6, 1.7 and 2.4 were prepared with a volume ratio of alcohol to TEOS of 0.5. The ROH/TEOS ratio was varied from 0.25 to 0.75 at a The acid content, humidity and temperH2 0/TEOS ratio of 1.6. ature were held constant. Fibers could be drawn when the viscosity reached 5-500 N-s/m 2 . Drawn fibers were aged at room temperature in air for various times and then fired in air using heating rates of either 2.0 or 4.0 °C/min. Strengths were determined at various stages in processing using a tensile test at a strain rate Fibers were of 10 mm/min, and a guage length of 75-150 mm. first fixed between two pieces of paper, using either tape or glue, and the paper was then placed in the tensile apparatus for testing. RESULTS AND DISCUSSION 1.
As Drawn Fibers
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