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Science of Colloidal Processing
Published in M. N. Rahaman, Ceramic Processing and Sintering, 2017
In the processing of ceramics, colloidal suspensions (also referred to as sols), consisting of a dispersion of solid particles in a liquid, are of particular interest. They are being used increasingly in the consolidation of ceramic powders to produce the green body. Compared to powder consolidation in the dry or semidry state (e.g., pressing in a die), colloidal methods can lead to better packing uniformity in the green body which, in turn, leads to a better microstructural control during firing. Colloidal solutions consist of polymer molecules dissolved in a liquid. The size of the polymer molecules in solution falls in the colloidal size range so that these systems are considered part of colloid science. Polymer solutions are relevant to the fabrication of ceramics by the solution sol–gel route, which we shall consider in the next chapter. For the present chapter, we concentrate on colloidal suspensions.
Sintering and Microstructure Development
Published in Mohamed N. Rahaman, Ceramic Processing, 2017
Although the sintering behavior of real powders is considerably more complex than that assumed in the models, the sintering theories clearly indicate the key parameters that must be controlled to optimize sintering. The particle size and particle packing of the green body are key factors, but characteristics such as size distribution, shape, and structure of the particles, can also exert a significant influence.
The effective elastic properties and thermal conductivity of porous fired clay bricks
Published in European Journal of Environmental and Civil Engineering, 2022
Zeye Tian, Ariane Abou-Chakra, Sandrine Geoffroy, Djimédo Kondo
Before firing, clay minerals, agricultural or mineral additives, plasticiser and sands constitute the main composition of green body. During firing, these mixtures could occur complex reactions and be formed into new compounds that form the solid backbone of fired bricks, which hosts micropores at sub-millimeter scale, involving calcium silicates, residual crystal phases quartz and K-feldspar, amorphous phase and so on (Dondi, Guarini, & Raimondo, 1999; Krakowiak et al., 2011). The amounts of these crystalline and amorphous phases largely depend on the CaO content and firing temperature. The effects of the two factors on the mass fraction of various phases have been analysed in the literature (Dondi et al., 1999). Figure B1 exhibits the XRD spectra of fired bricks with additives fired at 1000 °C and 1100 °C. From the results, the brick fired at 1100° shows higher crystallinity than the one fired at 1000° because of the formation of anorthite phase at higher firing temperature (Sutcu, 2010).
Application of silica opals to ceramic pottery
Published in Journal of Asian Ceramic Societies, 2020
Pottery is one of the oldest human inventions. It is made by forming a ceramic green body into an object of the desired shape and subsequently sintering it at high temperature. The green body is usually sintered at above 600°C to enhance such properties as strength and toughness by densification of the ceramic particles and to achieve the performance characteristics required in use [24]. Pigments are used for painting. It is often applied to the pottery after it has been sintered once and may then be overlaid with glazes afterward. The materials used for pottery must have thermal stability in addition to high mechanical properties, and organic materials are therefore inappropriate. It is noted, however, that the majority of studies on artificial opals have focused on the use of polymer colloids. In the previous paper (Fukazawa and Jin [22]), which is the only paper demonstrating the application of artificial opal to pottery as far as we know, an organic polymer was used as the artificial opal. One of the reasons for this may be the ease of controlling the diameters of the polymer colloids in sizes in the submicron range compared with silica [25]. Of course, there is no doubt that silica has attracted a great deal of interest for a long time, as it is one of the most abundant families of materials obtainable with highly inert chemical behavior. Based on this background, we found it an attractive challenge to construct silica opals producing structural colors on pottery.