Powder compact glass-ceramics

A. Caprihan, C. F. M. Clewett, D. O. Kuethe, E. Fukushima, S. J. Glass 2001, (Characterization of partially sintered ceramic powder compacts using fluori-nated gas NMR imaging), Magn. Reson. Imag. 19, 311-317. 

Sachs, M., and Tseng, T., Preparation of Si02 glass from model powder compacts II, sintering, J. Am. Ceram. Soc., 67, 532, 1984. 

S. J. Glass and D. J. Green, "Fabrication of Multiphase Particulate Ceramics by Infiltration into Powder Compacts" pp. 784-91 in Ceramic Transactions, Vol. IB, Ceramic Powder Science II. Edited by G. L. Messing, E. R. Fuller, Jr., and H. Hausner, American Ceramic Society, Westerville, OH, 1988. 

Glass SJ, Ewsuk KG (1997) Ceramic powder compaction. MRS Bull 22 24—28... 

Solids can be prepared as single crystals, glasses, thin films, powders, or sintered powder compacts (ceramics). Powders may be noncrystalline or polycrystalline, exhibit-... 

In 1981, Kokubo et al. [13] developed a glass-ceramic containing 38 wt% of crystalline oxyfluoroapatite (Caio(P04)6(0,F2)) and 34wt% of -wollastonite (CaSi03) 50-100 nm in size, in a MgO—CaO—SiOj glassy matrix by the sintering and crystallization of a glass powder compact with composition... 

Although in principle this route can be used for the production of both glasses and polycrystalline ceramics, in practice it is hardly ever used for glasses because of the availability of more economical fabrication methods (e.g., melt casting). It is, however, by far the most widely used method for the production of polycrystalline ceramics. The various processing steps are shown in Fig. 1.15. In its simplest form, this method involves the consolidation of a mass of fine particles (i.e., a powder) to form a porous, shaped powder (referred to as a green body or powder compact), which is then fired (i.e., heated) to produce a dense product. Because of its importance and widespread use, the fabrication of polycrystalline ceramics from powders will form the main focus of this book. In the next section, we provide an overview of the fabrication of polycrystalline ceramics from powders which will form the basis for the more detailed considerations in subsequent chapters. 

The mercury porosimetry results presented in Figure 5.6 illustrate the influence of particle size and size distribution on the size and size distribution of the porosity in green ceramic filled glass (CFG) composites consisting of 65 vol % of 0.4—1.5-)lm median particle size alumina and 35% borosilicate glass. The porosimetry results reveal that a relatively broad size distribution of pores exist within the green powder compacts and that pore size distribution and mean pore radius decreases with the substitution of fine alumina for the coarse in the CFG composites. The mean equivalent cylindrical pore radius, r, and surface-volume mean equivalent spherical particle radius, of a powder compact consisting of >l- J,m particles are proportional to one another and related by the fractional porosity, e, of the powder compact by... 

The preferential crystallization mechanism is that of volume crystallization. However, surface reactions cannot be neglected when considering crystallization and nucleation in powder compacting and subsequent sintering and crystallization. In these processes, water has a special effect on the production of lithium disilicate glass-ceramics, as demonstrated by Helis and Shelby (1983) and Davis (1997). 

Figure 3-25 EGA of a lithium disilicate glass-ceramic powder compact in comparison to DTA.

Fig. H-3 Glass-ceramics from powdered glass, (a) powdered glass compact, (b) densification and incipient crystallization, (c) frit-derived glass-ceramic.

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