Developments in Ceramic Materials Research

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64 T. T. Basiev, V. A. Demidenko, K. V. Dykel’skii et al. It is estimated based on the approved formula taking into account the elastic and hardness characteristics of the material under study [32]. For the Vickers indenter, we have K1C = 0.016(E/H) 1/2 P/C 3/2 , where E is Young's modulus. For fluorite, E = 8.73 10 11 dyne/cm 2 [32]. The experiments demonstrate that the microhardness of ceramic samples is only slightly higher (by 10 - 12%) than that of CaF2 single crystals, but their crack resistance increases significantly: the fracture toughness K1C is higher by a factor of approximately 3 - 6 (see Table 1). Table 1. The values of microhardness H and fracture toughness K1C Samples microhardness H, GPa fracture toughness K1C, MPa⋅m -0,5 Composition Designation at Р=0,5 Н at Р =1 Н at Р = 0,5 Н at Р = 1 Н CaF2 Single crystal - 200± 7 - 1,5 ± 0.15 CaF2 Natural ceramics - 225 ± 5 - 6,3 ± 0.6 CaF2 Artificial ceramics - 260±10 - 4,7±0.3 Ca0.98Er0.02F2.02 Artificial ceramics sample B(2)4-06 305 250 9,9 9,4 The scratch-hardness tests of the ceramic samples (scratches are made from the centre of a circle along the radius with a step of 15 [degree]) does not reveal any hardness anisotropy, whereas for CaF2 single crystals the directions are characterized by the highest hardness. The thermal conductivity k is an important technological parameter. It is due to the high thermal conductivity of calcium fluoride single crystals this material is attractive for the development of powerful laser systems. One of the purposes of this work is to compare the thermal conductivity of a fluorite single crystal and samples of natural and artificial optically transparent CaF2 ceramic. The thermal conductivity is determined experimentally by the absolute stationary method of longitudinal thermal flux [28]. The objects of research are three samples of CaF2 with almost the same geometry dimensions 5 x 5 x 40 mm 3 . One of the samples is cut from a single-crystal boule grown by the method of vertical directed crystallization. Another sample is cut from a piece of natural optical ceramic from the Suran deposit. The third sample is cut from ceramic prepared by the hot pressing method. The distance between the temperature sensors is 20 mm. The temperature range of 50 - 300 K is provided by evacuation of nitrogen vapor from the chamber. The results of measurements are presented in Figure 10. The values of thermal conductivity for all samples coincide within experimental error of 5%. At T = 300 K the thermal conductivity is k = 10.3 ± 0.1 W/m K; and it strongly increases with decreasing temperature to k = 245 ± 7 W/m K at T = 50 K. Analysis of transmission spectra of CaF2 single crystals and ceramic samples in wide spectral range is provided (Figure 11). In the IR spectral range the transmission of the single crystal and ceramics is identical (Figure 11a), but in UV the difference is significant (Figure 11b). The optical losses in the ceramics are determined quantitatively by calorimetric method of absorption coefficients measurement in highly transparent solids described elsewhere [33]. In doing so rectangular parallelepiped samples 8.8 x 14 x 45 mm 3 are cut and polished. The loss factors are found to be 2.05 10 -2 cm -1 and 6.3 10 -3 cm -1 for the ceramics and the CaF2 single crystal, respectively.
Optical Fluoride and Oxysulfide Ceramics: Preparation and Characterization 65 Figure 10. Temperature dependence of the thermal conductivity of the CaF 2 single crystal and optical ceramics. Figure 11. (Continued)
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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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Page 32 and 33: 18 Leslie G. Cecil second group (Fi
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Page 68 and 69: 54 T. T. Basiev, V. A. Demidenko, K
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Sm (J/Kmol) Sm (J/Kmol) 15 10 5 Syn
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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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q x = Modeling of Thermal Transport
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212 R. Ramesh, H. Kara, Ron Stevens
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220 ε S 33 R. Ramesh, H. Kara, Ron
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242 Development of Display Technolo
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244 Li Chen technology moved to the
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246 Li Chen The continuing evolutio
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248 Li Chen the back contact cathod
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250 Li Chen Figure 3. Vertical side
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252 Li Chen Figure 6. Molybdenum mi
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254 Li Chen Figure 8(a). I-V curve
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256 Li Chen Figure 9. Life time tes
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258 Figure 11(a). Plasma generated
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260 Li Chen [13] C.A. Spindt, K.R.
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262 S. Ardizzone, C. L. Bianchi, G.
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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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efraction index, 61 refractive inde
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time, vii, ix, 1, 3, 7, 8, 11, 26,
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Developments in Ceramic Materials Research

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