Verneuil crystal growth

Figure 36 Schematic of the Bridgeman crystal growth method (a). Verneuil crystal growth method (b)...

The main part of a conventional Verneuil apparatus is a vertical inverted oxyhydrogen burner. The burner consists of several concentric tubes [1, 2]. The inner tube supplies oxygen and crystal powder to the flame, which burns into a ceramic muffle. A seed crystal is positioned in such a manner that only a thin film of liquid phase is on the top surface of the crystal. If the powder supply, i.e. the feeding of molten droplets into the molten layer, and the crystal growth rate are weU balanced, the crystal will grow under constant conditions. The principal design and operation of a Verneuil flame fusion apparatus was described earlier [3]. 

Thus, the flame-fusion process is a crucible-free crystal growth process for high-melting compounds, an economic process that allows control of nucleation and crystal diameter within a relatively simple apparatus, and was a signiflcant breakthrough achieved by Auguste Verneuil around 1900. 

The Growth of Functionally Graded Crystals by Verneuil s Technique... 

Because of the small volume of liquid phase, the Verneuil process is predestined to the growth of graded materials. The development of the flux-Verneuil technique [4] enables the variation of the material support to the growing crystal. In this way, a specific influence on the stoichiometry of the liquid phase is possible. 

The Verneuil, or flame-fusion, method is illustrated in Figure 29.1. It is a well-established technique for growing single crystals of oxides that have high melting temperatures. The largest application of the Verneuil method is for the growth of sapphire and ruby. 

Single crystals of pure and doped alumina can be grown using well-established techniques such as flame fusion (Verneuil process), Czochralski crystal puUing, and top-seeded solution growth (TSSG), as well as under hydrothermal conditions and from the vapor phase (Franke et al., 1968). Some of these applications will be... 

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