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Abstract Summary
 
 
 
Conference:   105th Annual Meeting & Exposition  
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Symposium:   20. Ceramic Matrix Composites
Session:   Geopolymer Composites - 1:00:00 PM - 5:00:00 PM 4/28/2003
Abs. Title:   Fiber Reinforced Geopolymers with Alkali- Activated Alumino-Silicate Matrix  
Abstract #:   7406  
 
 
 
 
Type:   Invited
Submitted:   11/27/2002 12:30:23 PM
Status:   Accepted
Scheduled?   Yes
Abstract:   Chemically bonded ceramics with and without fibres were developed and characterized. The matrix used was a commercially available alkali-activated aluminosilicate binder with the synonym Geopolymite*. Bonding of this ceramic occurs through chemical reactions between a solid and a liquid sol phase at temperatures below 300°C. Geopolymite* is a rapidly hardening inorganic binder based on a potassium-silicate-sol, metakaolinite, fly ash, and Na2SiF6. Rapid hardening occurs between 50 and 90°C by an exothermal polycondensation of hydrolysed mononuclear and polynuclear SiO44*-species accompanied by the formation of crystalline alkalifluorides. Shrinkage is below 0.1% during curing at 80°C . The matrix has a fine grained, heterogeneous and highly porous (30 vol%) microstructure. The main part of the structural backbone is formed by an X-ray-amorphous K2O*SiO2- low temperature amorphous phase that incorporates residues of metakaolinite and fly ash. The crystalline phases of NaF, K2SiF6 and K2NaAlF6 are located in the pores and on the pore surfaces. The chemically bonded ceramic behaves brittle and shows low to moderate strength. The mechanical properties can drastically be improved by the incorporation of weaves and unidirectional long-fibers. Samples were made by a combined hand-lay-up-impregnation and pressure molding process. With 70 vol% of unidirectional long-fibers a 3-point bending strength of 425 MPa and a fracture toughness of 17.55 MPa*m0.5 and a work of fracture of 19.88 kJ/m2 were obtained. Composites including particle-, platelet- and short-fiber-reinforcements yielded moderate strength and toughness, but complex shapes could be molded by casting. In contact with water the crystalline phases of the matrix completely dissolve. The amorphous K2O*SiO2-phase alters by an ion-exchange process. Therefore, mechanical and dielectric properties are negatively affected by leaching in water. The hygroscopic behaviour of the matrix affects the dielectric properties . Under dry conditions low permittivities of 2.56 as well as a low loss tangent of 2.64*10-3 were achieved. Main loss mechanisms are induced by ion-jump-processes and interfacial- as well as dipole-polarization-processes. The composites show good potential for structural applications at slightly elevated temperatures. Castable composites show promising results for applications such as packaging materials for integrated circuits and for humidity sensors.
 
 Abstract Author(s)
 
 
 1   Primary   Ludwig Gauckler - 1011271
Organization   Swiss Federal Institute of Technology
Phone #  
Fax #  
Professional Title  
Street Address   Sonneggstr. 5

City   Zurich
State  
Country   Switzerland
Postal Code   CH-8092
 
 
 2   Presenting   David Sager - 1010561
Organization   Swiss Federal Institute of Technology
Phone #   0041 1 632 71 84
Fax #   0041 1 632 11 32
Professional Title  
Street Address   Sonneggstr. 5
ETHZ
NO H30
City   Zurich
State  
Province  
Country   Switzerland
Postal Code   CH-8092
 
 
 3   Co-Author   Stefan Förster - 1011707
Organization   ETH-Zurich
Phone #  
Fax #  
Professional Title  
Street Address  

City  
State  
Country   United States
Postal Code  
 
 
   

 
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