Sol-Gel Synthesis of Lead Titanate Fibres for Use in the Fabrication of Piezoceramic-Polymer Composites
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SOL-GEL SYNTHESIS OF LEAD TITANATE FIBRES FOR USE IN THE FABRICATION OF PIEZOCERAMIC-POLYMER COMPOSITES H. JANUSSON, C.E. MILLAR and S.J. MILNE Division of Ceramics, School of Materials, The University of Leeds, Leeds LS2 9JT, U.K. ABSTRACT Lead titanate fibres for use in piezoceramic-polymer composites have been prepared by extrusion of polymeric gels. The gels are formed from solutions of lead acetate, titanium isopropoxide and 2-methoxyethanol. The concentration of the solution, and amount of water and acid added, proved to have a strong influence on the suitability of the gel for extrusion purposes. The drying and firing conditions have been altered to obtain dense, fully crystalline PbTiO3 fibres of 100 pm diameter. INTRODUCTION A range of piezoceramic-polymer composites have b en designed for device applications such as sonar and medical diagnostics[1,2]. The polymer phase lowers density and permittivity and increases the elastic compliance of the composite relative to a single phase ceramic. Composite systems based on unmodified PbTiO 3 are of interest because of their applications in hydrophones. The piezoelectric coefficients of unmodified PbTi0 3 lead to high hydrostatic voltage sensitivity, and the hydrostatic response can be further enhanced by fabricating highly anisotropic structures 1,3]. In this context piezoceramic-polymer composites comprising fibres of unmodified PbTiO 3 offer major benefits. By aligning the fibres anisotropic so-called 1-3 composites can be prepared. The numeric notation relates to the spatial arrangement or 'connectivity' of the ceramic and polymer phases[ 2 . This has a strong bearing on piezoelectric and mechanical properties. In the example quoted the fibres extend in 1-dimension and the polymer is continuous in 3-dimensions. Reports in the literature indicate that fibrous unmodified PbTiO3 can be prepared by hydrothermal reaction of appropriate inorganic salts The diameters of the fibres produced are either in the range 1-10 pmt4] or 0.15 0.2 pm[ ] depending on the conditions employed. We have studied metallo-organic sol-gel routes based on lead acetate and titanium tetraisopropoxide to form gels which may be extruded into PbTiO 3 fibres. The conditions employed for gel and fibre production are now reported together with information on microstructures of composites prepared by combining the fibres with an epoxy resin. EXPERIMENTAL Gels were formed by the hydrolysis and condensation of refluxed solutions of PbýOOCCH 3 )2, Ti(OC 3 H7 ) 4 and methoxyethanol solvent, CH3 OCH 2 CH2 OH[6- 1. After refluxing, water and nitric acid were added to produce a 0.5 M solution of Pb/Ti with a water and acid concentration of 0.75 M and 0.002 M respectively. The gels were piston extruded through either -650 pm or - 250 pm diameter orifices. The fibres were then dried and fired to convert to PbTiO 3 . Hot stage microscopy was used to monitor crack formation during thermal conversion to the oxide. The decomposition Mat. Res. Soc. Symp. Proc. Vol. 180. 01990 Materials Research Society
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