Microwave Processing of Sol-Gel Derived Potassium Niobate
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MICROWAVE PROCESSING OF SOL-GEL DERIVED POTASSIUM NIOBATE
Z. Fathi, I. Ahmad and D.E. Clark, University of Florida
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ABSTRACT
Microwave energy has been used in a novel processing method. The relationship between processing, structure and properties of sol-gel-derived potassium niobate sol as well as thin films has been investigated. A comparison has been established between microwave and conventional heating for drying, calcining and crystallizing sol-gel-derived samples. Structural and phase changes were monitored by thermogravimetric analysis (TGA), differential thermal analysis (DTA) and x-ray diffraction (XRD).
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INTRODUCTION
Microwave energy is under evaluation as an alternative means of producing an array of ceramic products. The process consists of a conversion of microwave radiation into heat. The material itself is the source of heat which is generated by the dissipating microwave energy in the body. The origin of heating lies in the ability of the electric field to polarize charges in materials and the inability of these polarizations to follow extremely rapid reversals of the electric field. In addition to these polarization effects, there are direct conduction effects due to redistribution of charged particles under the influence of the externally applied electric field. It has been reported that temperatures and times have been reduced in processing superconducting ceramics [1] using microwave energy. Potassium niobate has a higher electro-optic coefficient than lithium niobate. Therefore, lowering the processing temperatures and heating times of this material would be of extreme interest. The main goal of this study was to investigate the variation of several processing parameters namely times, power levels and temperatures, on sol-gelderived potassium niobate. One sol-gel system (the ethoxides) was selected for preparing the KNbO3 sol and thin film samples. This system is suitable for microwave drying and sintering studies of potassium niobate.
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EXPERIMENTAL APPROACH
(a) MATERIALS The sol-gel-derived samples were prepared by using niobium and potassium ethoxide precursors. Each precursor was diluted with ethanol and mixed to 1:1 molar ratio of potassium and niobium. This mixture was hydrolyzed with water at the ratio of H20/alkoxide - 1.75. Figure 1 is a process flow diagram of the sol-gel process used in this study. The gel samples were obtained by separating the gels from the liquid phase by filtration. The sol-gel-derived thin films were prepared by spin-coating on
Mat. Res. Soc. Symp. Proc. Vol. 180. @1990 Materials Research Society
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SOL GEL + MICROWAVE PROCESSING POTASSIUM ENX1O
SOLVEN1
IOW I
ETNOXDE mix ADD WATIER FiLTRING
Figure 1.
Schematic of the sol gel process.
fused-silica substrates. The substrates were spun at 2500 rpm for 20 sec. (b) MICROWAVE SET UP Drying and calcining were performed in the microwave set up shown in Figure 2. The sample was placed in an insulating material lined with a microwave susceptor. This is referred to as microwave hybrid heating bec
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