Developments in Ceramic Materials Research

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214 R. Ramesh, H. Kara, Ron Stevens and C. R. Bowen production. The polymeric sponge technique is being used successfully to commercially produce high temperature ceramic filters [31].. The processing technique involves impregnation of polyethylene foams with a ceramic slip and controlled sintering with an intermediate temperature hold for removal of the foam. The BURPS technique produces a porous structure by mixing ceramic powders with polymer spheres followed by compaction and controlled sintering. A 3-3 BURPS piezocomposite showed that the hydrostatic figure of merit increases with increasing polymer fraction [28]. However, the polymer fraction is only varied between 30 and 70% volume, since it is not feasible to produce a higher pore content ceramics using the BURPS technique. Creedon et al. [30] produced PZT/polymer composites having 85-90 vol. % porosity by a polymeric sponge technique and they also found an increase in hydrostatic sensitivity with increasing polymer fraction. 3-3 piezocomposites are usually produced by manufacturing a porous ceramic structure and subsequently impregnating the porosity with a polymer. The porosity can also be left as air. This section describes the production of a range of porous ceramics of PZT-5H ranging from 9 to 92 vol. % porosity using both the BURPS and polymeric sponge techniques, characterisation in terms of d33, d31, ε, dH, gH and Figure-of-Merit before and after polymer impregnation and the effect of ceramic/ polymer volume fraction on the properties. 2.1. Material Synthesis Porous piezoceramics are synthesised using two techniques, namely, BURPS and foamreticulation techniques. Commercially available PZT-5H spray dried powder (Morgan Electroceramics, Vauxhall Industrial Estate, Wrexham, UK) is compacted and sintered at 1200°C for 2 hours to form monolithic PZT ceramics of 4 mm thickness and 40 mm diameter. For the BURPS technique, the PZT powder is mixed with acrylic thermoplastic resin (ATR) and polyethylene oxide (PEO) at various weight ratios to produce a range of pore volume fractions. The mixed powder is then uniaxially compacted at 50 MPa. The compacts are then subjected to a burnout cycle, heating with a ramp rate of 1°C/min (to 600°C for an hour) to remove the organic phase, before final sintering at 1200°C for 2 hours. For the polymer sponge technique, a ceramic slip of 80 wt. % PZT, 3 wt. % PVA, 0.75 wt. % dispersing agent and distilled water is prepared by ball milling for at least 6 hours. A number of polyethylene sponges of different cell sizes are cut and impregnated with the PZT slip. The excess ceramic slip is removed by compressed air. The green ceramic foams are then introduced to the same burnout cycle as above, before final sintering at 1200°C for 2 hours. Self-adhesive aluminium electrodes (150μm) are used for the porous samples (PZT-air composites) while dense PZT and PZT-polymer composites are electroded with a silver paste. All the samples are individually poled at 110°C and 12.5 kV for 10 minutes using corona poling. The corona tip height is set to 30 mm. Some of the poled samples are filled with suitable low viscosity polymer under vacuum in order to obtain PZT-Polymer composites.
2.2. Characterisation Progress in Porous Piezoceramics 215 The porous piezoceramics are characterized first, using Scanning Electron Microscopy (SEM) studies to verify the structural connectivity and then, by measuring different material coefficients. Piezoelectric charge coefficients (d33 and d31) and permittivity are measured using Berlincourt d33 Piezo Meter (Take Control, University of Birmingham Research Park, Vincent Drive, Birmingham, UK) and LCR meter (HP 4263B, Hewlett Packard Japan Ltd., Hyogo, Japan) respectively. These values are used to derive the hydrostatic charge (dH) and voltage (gH) coefficients and hydrostatic figure of merit (FoM). 2.3. Microstructures The microstructure of the various PZT-air/ polymer composites synthesised are characterised to verify the connectivity pattern of the composite structure. Microstructures of the various PZT-Air and PZT-Polymer composites are shown in Figures 1 and 2, respectively. Depending on the PZT ceramic volume fraction, there are two distinct connectivity patterns observable in the composites. The composites with high PZT volume content (>60%) shows 3-0 connectivity (i.e. discrete polymer or pore phases within PZT matrix), while composites with low PZT volume content (
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DEVELOPMENTS IN CERAMIC MATERIALS R
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Copyright © 2007 by Nova Science P
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PREFACE Ceramics are refractory, in
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Preface ix crystals is discussed. A
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Preface xi spectra and the directio
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2 Leslie G. Cecil comprehensive dat
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4 Leslie G. Cecil Ringle et al. (19
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6 Leslie G. Cecil The main architec
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8 Leslie G. Cecil can study “the
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10 Leslie G. Cecil Middleton et al.
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12 Leslie G. Cecil The laser ablate
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14 Leslie G. Cecil There are two ge
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16 Leslie G. Cecil distinct recipes
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18 Leslie G. Cecil second group (Fi
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20 Leslie G. Cecil The Vitzil-Orang
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22 Leslie G. Cecil Table 3. Mahalan
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24 Leslie G. Cecil Ixlú and Ch’i
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26 Leslie G. Cecil structures (D. R
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28 Leslie G. Cecil paste and Macanc
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30 Leslie G. Cecil Bieber, A. M. Jr
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32 Leslie G. Cecil Kepecs, S. M., a
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34 Leslie G. Cecil Schele, L., Grub
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36 Z. C. Li, Z. J. Pei and C. Tread
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62 I, % 100 80 60 40 20 0 T. T. Bas
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82 Photon counts 300 250 200 150 10
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88 Fluorescence, a.u. I transfer ,
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In: Developments in Ceramic Materia
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Synthesis, Spectroscopic and Magnet
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a c Synthesis, Spectroscopic and Ma
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Sm (J/Kmol) Sm (J/Kmol) 15 10 5 Syn
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In: Developments in Ceramic Materia
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The Use of Ceramic Pots in Old Wors
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3.2. Wall-in Positions The Use of C
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IACC ( τ ) = t2 ∫ The Use of Cer
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where σ res is the scattering cros
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Page 260 and 261: 246 Li Chen The continuing evolutio
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A absorption spectra, 66, 67, 77, 7
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correlation function, 156 corrosion
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group membership, 13, 20, 21, 22, 2
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microstructure(s), x, xi, 73, 74, 2
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time, vii, ix, 1, 3, 7, 8, 11, 26,
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