Green-state ceramics

High-performance ceramics are increasingly used to replace metal products under extreme load. Although their mechanical and chemical properties are superior to metals, 

5 Temperature profiles across axial projections of carbon-black filled rubber cylinders with different contents of carbon-black filler at 10 Hz dynamic shear rate. Adapted fiom [Haul] with permission ftom Wiley-VCH. 

7 H-NMR images of a bisque-fired alumina ceramic impregnated by benzene. The 

L/D ratio is 1.13 and the mean particle size is 0.4 p,m. The three slices correspond to positions at (a) 6.1, (b) 12,4, and (c) 14.8 mm from the reference plane. Various defects with diameters ranging from 0.7 to 4 mm can be detected by decreased signal intensities from lowered porosities. Adapted from [Ack2] with permission by the author. 

The noninvasive nature of NMR spectroscopy combined with the chemical specificity of the NMR method provides direct access to the distribution of various chemical constituents for the histochemistry of plant materials in situ NMR spectroscopy can be used to identify the major constituents, and chemical-.shift imaging can be used to spatially localize them. The latter can be applied to localize aromatics, carbohydrates, as well as water and fat or oil in plant samples. The suitability of many fresh fruits and living plants to be studied by NMR imaging results in a variety of applications in agriculture and food science [Mcc I, Mcc2]. 

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Almost all polymers are exposed to more or less aggressive atmospheres. Quite often degradation is caused by the absorption of liquids or their vapors [125-130]. The amount, spatial distribution and interaction of small molecules with the polymer matrix is an important indicator of polymer aging as demonstrated by an epoxy/water system [131]. Another important application is the spatial distribution of polymer binders such as waxes and oils in green-state ceramics [132, 133], because an inhomogeneous distribution in the prefinished state is likely to cause mechanical failure of the final product. 

W. A. Ellingson, J. L. Ackerman, L. Garrido, J. D. Weyand, R. A. Dimilia 1987, (Characterization of porosity in green-state and partially densified AI2O3 by nuclear magnetic resonance imaging), Ceram. Eng. Sci. Proc. 8, 503—512. 

Successful ceramic/ceramic joints between both similar and dissimilar ceramic materials have been achieved both i) by layering materials in the green state, then firing,and ii) by joining fully dense materials (Fig. 8). In some instances, microwave... 

Briefly explain why it is better to machine in a ceramic component when it is in its green state rather than when it has been fired. 

Machineable Ceramics. All ceramics can be machined in the green state, and in the fired state with diamond tooling. Machineable ceramics are those which can be shaped when fired, to engineering tolerances with ordinary high speed metal cutting tools. See machining, and... 

C. H. Greene State University of New York, Ceramic College) Does not the actual diffusion mechanism involve some cooperative phenomena Before a cation can jump from one normal site to a second normal site the cation occupying this second site must be removed in some way. It is likely that the rate at which cations jump out of such destination sites is increased by the presence of jumping cations at intermediate non-normal tetrahedral or octahedral sites. 

LavaT (synthetic talc) - machinable in green state and then fired to become a hard ceramic (there is approximately 12% shrinkage during firing). 

Tape casting [CHA 94], [MIS 78] produces ceramic sheets of low thickness (25 to 1,000 micrometers) and large surface, whose homogenity, surface quality and mechanical strength in the green state are satisfactory for electrorric applications such as sirbstrates and multilayer capacitors. 

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