Developments in Ceramic Materials Research

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266 S. Ardizzone, C. L. Bianchi, G. Cappelletti et al. is the major component. The phase compositionof Fe-ZrSiO4 (Figure 2d) is intermediate between V- and Pr-doped samples, the presence of zircon being around 5%. In this case the presence of hematite, either present as an incapsulated phase or segregated can be appreciated. Figure 2. Powder X-ray diffraction lines of a) non doped, b) Pr, c) V, and d) Fe doped pigments at the same metal/Zr content (0.02 molar ratio) calcined at 1000°C. T and M: tetragonal polymorph and monoclinic zirconia (ZrO 2), respectively; Z: zircon (ZrSiO 4); H: hematite. Inset: the relative phase enrichment, by Rietveld refinement. The role played by the metal on the promotion of the crystal growth and formation of the zircon lattice is apparent. This effect has been observed previously in the literature in the case of all the present metal dopants. In the literature the final formation of ZrSiO4 is considered to occur first, by crystallization of a phase having the t-ZrO2 structure followed by a phase transformation from t-ZrO2 to m-ZrO2 and, almost simultaneously, by the reaction between m-ZrO2 and an amorphous silica rich phase, leading to zircon [31,32]. The direct cross-comparison between the effects produced by the three metals in samples obtained by the same preparative route is, instead, not commonly reported in the literature. From results in Figure 2, vanadium appears to be the best promoter of the structure and the promoting sequence is: V>Fe>Pr. The same sequence is maintained also at a higher calcination temperature (1200°C). Figure 3 reports the amount of zircon phase in the samples, obtained by quantitative elaboration of X-ray diffraction data, as a function of the metal loading. The comparison between the three series of pigments is striking.
Coloured ZrSiO4 Ceramic Pigments 267 Figure 3. Zircon-phase mass per cent as a function of the metal/Zr content of pigments calcined at 1200°C. Inset: photographs of the pigment colours. In the case of vanadium the amount of zircon phase ranges in any case around 90% and shows very little dependence on the metal loading. Fe-promoted samples show an average amount of zircon around 50% with a small maximum for Fe/Zr around 0.02. Samples promoted by Pr show, instead, a different trend. The amount of zircon in the samples first rises sharply and goes through a maximum (up to about 40%) for Pr/Zr around 0.03 and subsequently it levels off to low values (around 6%). The trend of the Pr- doped samples might suggest that up to Pr/Zr around 0.03, the guest metal might be present in a solid solution within the t-ZrO2 lattice favouring nucleation and growth of the zircon structure. The 0.03 molar ratio might represent a solubility limit for the solid solution; larger Pr quantities might support the formation of different crystalline Pr containing phases (e.g. the phase Pr2Zr2O7 appreciable into the 5, 8, 10% sample diffractograms) thus reducing the nucleating power of the metal. The largely different effects produced by the three metal ions, on the structural features of ZrSiO4, are not easily interpreted since the function of the guest ion is manifold, complex and not fully clarified. However, since, the metal cations are generally assumed to form a solid solution with the zircon lattice occupying either the tetrahedral silicon sites or the dodecahedral Zr positions, or even both, the matching of the sizes, between the guest metal ion and the ions in the lattice, is not a trivial fact. The size of a tetrahedral Si 4+ is reported to be 0.40-0.54 Å, that of Zr 4+ in the dodecahedral site 0.84-0.98 Å. The radius of V with a number of coordination 6 is 0.59 Å. Literature data show that upon doping with V, the unit cell volume of ZrSiO4 expands [24]. This effect is interpreted as the result of substituting a larger ion (V 4+ ) for a smaller one (Si) in the lattice tetrahedral positions. The sizes of Fe and Pr are 0.645 and 1.013 Å respectively. It appears therefore that in the series V-Fe-Pr the size
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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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54 T. T. Basiev, V. A. Demidenko, K
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62 I, % 100 80 60 40 20 0 T. T. Bas
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68 Fluorescence, a.u. 1 T. T. Basie
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70 Fluorescence, a.u. 1 0.1 0.01 0.
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78 k, cm -1 20 18 16 14 12 10 8 6 4
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82 Photon counts 300 250 200 150 10
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84 Fluorescence, a.u. I transfer ,
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86 ln(I transfer (t)) -4.2 -4.4 -4.
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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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Transmission Transmission Transmiss
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Sm (J/Kmol) Sm (J/Kmol) 15 10 5 Syn
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Intensity (a.u.) Intensity (a.u.) 8
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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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D50 0.8 0.7 0.6 0.5 0.4 0.3 The Use
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Definition (D50) 1 0.95 0.9 0.85 0.
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Modeling of Thermal Transport in Ce
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q x = Modeling of Thermal Transport
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212 R. Ramesh, H. Kara, Ron Stevens
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214 R. Ramesh, H. Kara, Ron Stevens
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Page 260 and 261: 246 Li Chen The continuing evolutio
Page 262 and 263: 248 Li Chen the back contact cathod
Page 264 and 265: 250 Li Chen Figure 3. Vertical side
Page 266 and 267: 252 Li Chen Figure 6. Molybdenum mi
Page 268 and 269: 254 Li Chen Figure 8(a). I-V curve
Page 270 and 271: 256 Li Chen Figure 9. Life time tes
Page 272 and 273: 258 Figure 11(a). Plasma generated
Page 274 and 275: 260 Li Chen [13] C.A. Spindt, K.R.
Page 276 and 277: 262 S. Ardizzone, C. L. Bianchi, G.
Page 295 and 296: A absorption spectra, 66, 67, 77, 7
Page 297 and 298: correlation function, 156 corrosion
Page 299 and 300: group membership, 13, 20, 21, 22, 2
Page 301 and 302: microstructure(s), x, xi, 73, 74, 2
Page 303 and 304: efraction index, 61 refractive inde
Page 305 and 306: time, vii, ix, 1, 3, 7, 8, 11, 26,
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Developments in Ceramic Materials Research

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