Leucite crystals

Figure 6. K2O content on the surface of dental porcelains before and after ion exchange process (value in parenthesis is the volume fraction of leucite crystal). Data from [47]...

Mackert Jr JR, Russell CM. Leucite crystallization during processing of a heat-pressed dental ceramic. International Journal of Prosthodontic 1996 9(3) 261-265. 

Kon M, Kawano F, Asaoka K, Matsumoto N. Effect of leucite crystal on the strength of glassy porcelain. Dental Materials Journal 1994 13(2) 138-147. 

Crystal growth of the main crystal phases begins at the surface and progresses into the volume of the crystal. It is interesting to note that leucite crystals in contrast to cordierite demonstrate preferred growth. The c-axis of the leucite crystal is vertically oriented with respect to the surface of the base glass. 

Figure 1-45 Growth of formed leucite crystals without seed particles with simultaneous precipitation of highiy disordered primary crystals formed by seed particles. SEM.

If the glass is heat treated in monolithic form, isolated leucite crystals grow inward from the surface of the glass specimen as a result of the low nuclei density on the surface. These leucite crystals demonstrate obvious direction of growth (dependent on direction anisotropic growth) in which the apex of the polyhedron is located at the surface of the glass specimen (see Sections 1.4 and 3.2.4). 

Some of the leucite crystals differ considerably in their outer shape from the type of natural leucite crystals. The base glass-ceramic thus produced is distributed by the manufacturer (Ivoclar Vivadent AG) in the form of glass-ceramic ingots in the IPS Empress dental restoration system for further processing in dental laboratories. To complete the formation of the final... 

Figure 2-41 SEM image (etching 10 sec, 3% HF) of the microstructure of apatite-leucite glass-ceramic for dental restorations. Heat treatment of the glass powder at SSO C/I h and 1050°C/1 h. The apatite crystals measure approximately 0.1-0.5 and 1-2 pm in diameter. The leucite crystals measure approx. 2 pm.

Unfortunately, there is no pronounced eutectic in the flint-feldspar system. However, approximately 20% quartz can be added to a pure potash feldspar and 10% to a pure soda spar without materially raising the melting points. Feldspars of different potash-soda ratios are sometimes interchangeably reduced. The development of leucite crystals in melting, which accounts for the high viscosity of molten feldspar, depends upon the amount of potash spar present. Translucency is best with potash spar bodies thermal expansion is highest for bodies with high soda spar content. 

M. Novotna and J. Maixner X-ray powder diffraction study of leucite crystallization. Z. Kristallogr. Suppl., 23, 455-59 (2006). 

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