Poly crystalline ceramics

As was the case for metals, poly crystalline ceramics show a dependence of mechanical properties on grain size, as given earlier by the Hall-Petch relation in Eq. (5.22), which in this case applies to fracture strength, ay ... 

Use Refractories, especially for steel furnace linings, poly crystalline ceramic for aircraft windshields, electrical insulation, pharmaceuticals and cosmetics, inorganic rubber accelerator, oxychloride and oxysulfate cements, paper manufacture, fertilizers, removal of sulfur dioxide from stack gases, adsorption and catalysis, semiconductors, pharmaceuticals, food and feed additive. 

Salamu G, lonescu A, Brandus CA, Sandu O, Pavel N, Dascalu T (2012) High-peak power, passively Q-switched, composite, all-poly-crystalline ceramics Nd YAG/Cr YAG laser and generation of 532-nm green light Laser Phys 22 68-73... 

Feldmm R, Golan Y, Burshtein Z, Jackel S, Moshe I, Meir A et al (2011) Strengthening of poly-crystalline (ceramic) Nd YAG elements for high-power laser applications. Opt Mater 33 695-701... 

Some ceramics are semiconductors. Most of these are transition metal oxides, such as zinc oxide. Ceramicists are most interested in the electrical properties that show grain boundary effects. Semiconducting ceramics are also employed as gas sensors. When various gases are passed over a poly crystalline ceramic, its electrical resistance changes. With tuning to the possible gas mixtures, very inexpensive devices can be produced. 

On several occasions throughout this book, no distinction was made whether single or poly crystalline ceramics were used to exemplify certain topics. Single and polycrystalline ceramics were interchangeably used to emphasize the subjects under consideration. Now, this section will focus on several cases of deformation in polycrystalline ceramics not yet discussed in depth. First among the topics to be considered below is that of preferred orientation, a well-known aspect influencing not only the physical properties of ceramics, but also their mechanical behavior. 

Now, the focus shifts to TZ-3YP which is an yttria-stabilized tetragonal zirconia poly crystalline ceramic (equivalent to 3Y-TZP) containing three moles of yttria. Its hardness was evaluated by an equation given in Sect. 1.10b, as ... 

In a poly crystalline mixture of solid reactants, we might expect the particle size to be of the order of 10 pm even careful and persistent grinding will only reduce the particle size to around 0.1 pm. Diffusion during a ceramic reaction is therefore taking place across anywhere between 100 and 10,000 unit cells. Various ingenious methods, some physical and some chemical, have been pioneered to bring the components of the reaction either into more intimate contact, or into contact at an atomic level, and so reduce this diffusion path in doing so, the reactions can often take place at lower temperatures. 

There are at this time no IR-fibers which fulfill all of these demands. The mainly used fibers are made of poly-crystalline silver halide (refractive index 2.2 at 10.6 pm) with very good transmission over the whole MIR (2 to 16 pm, see Fig.6.5-5), and good mechanical properties. The disadvantages are that they react with many commonly used metals and that they are sensitive to visible radiation, especially to UV radiation (Ceram optec, 1991). 

Paladino AE, Maguire EA, Rubin LG (1964) Oxygen ion diffusion in single-crystal and poly crystalline yttrium im garnet. J Am Ceram Soc 47 280-282... 

Kijima T and Tsutsumi M (1979) Preparation and thermal properties of dense poly crystalline oxy hydroxy lapatite. J Am Ceram Soc 62 455-460 Kim HM (2001) Bioactive ceramics challenges and perspectives. J Ceram Soc Japan 109 S49-S57 Kim HM, Miyaji F, Kokubo T, Nakamura T (1997) Apatite-forming ability of alkali-treated Ti metal in body enviromnent. J Ceram Soc Japan 105 111-116... 

A similar two-step process, i.e., HP followed by HIP, has been used to prepare optically transparent poly crystalline spinel ceramics [193, 195]. The elfect of HP temperature on optical properties of the final ceramics HIP sintered at 1900 °C for 1 h under a pressure of 189 MPa was studied. Three HP temperatures, 1400, 1450, and 1500 °C in vacuum of 10 Pa for 1 h at 50 MPa, were examined. The sample HP pre-sintered at 1400 °C had the maximum transmittance of over 60 and 70 % in the UV-visible and near-IR wavelength regions, respectively. The light transmittance was well correlated with the microcracked grain boundary surface area per unit volume of the samples. 

Abstract. The crystallographic texture is defined as the relative organization of the grains in an anisotropic solid which infiuences frequently its physics and mechanical properties. This is the case of majority of poly crystalline materials rocks, ceramics, metals, polymers, etc. 

D. J. Pysher and R. E. Tressler, Tensile creep rupture behavior of alumina based poly-crystalline oxide fibers, Ceram. Eng. Sd. Proc., 13 [7-8], 218-226 (1992). 

Pb(ZrxTii x)03 (PZT) ferroelectric thin films are studied for their high dielectric constant and ferroelectric properties (e.g. high remanent polarization). Material is an excellent material in bulk ceramic applications. The dielectric constant lOSSeo at 1 MHz frequency was reported for poly crystalline PZT (x=0.50) thin film, remanent polarizationPr = 21.5 x 10 Ccm and coercive field of 3.9 kVmm ... 

One type of such materials are particulate composites, consisting of a poly-crystalline matrix in which are dispersed micrometre-sized or sometimes nanometre-sized particles of a second solid phase. The processing used to produce the composites is common to most kinds of ceramics, i.e. shaping and sintering of powder mixes ( Fig. 1.7). 

So far our descriptions of crystalline solids have been restricted to discussions based on single crystals. In practice, most materials, although made up of a single chemical phase, are poly crystalline for example, a metal wire or a ceramic component. The individual crystallites or grains are single crystals in there own right and may be randomly oriented with respect... 

Here one must differentiate between glassy and/or poly crystalline fibers, which are applied for the manufacture of insulating refractory products (mats / blankets, modules, vacuum-shaped components, etc.) and such fibers that are made by extrusion of raw materials including clay, mullite-based compositions, or AI2O3 (10). The latter type is subsequently fired ( ceramic studs ). They have... 

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