Flame-fusion growth

Fig. 1. The Verneuil technique, or flame-fusion growth, as used for synthetic mby and sapphire.

For crystal-growth laboratories commercial flame-fusion growth equipment had been available from Division 500 of Arthur D. Little (ADL, Cambridge Massachusetts), VEECO (Versailles), and Nakazumi Crystal Corporation (Osaka). 

The Verneuil Techni(jue. The VemeuH technique is also known as flame-fusion. A very pure feed powder is first made by chemical decomposition. For the growth of comndum, ammonium alum [7785-25-0] NH Al/(S0 2 12H20, is recrystallized from water containing added... 

Vemeuil (flame fusion) Crystal growth from the melt mby, sapphires, and stars spinel rutile strontium titanate... 

Crystal Growth from Melts and Solutions 17.2.4.1. Growth from Melts 17.2.4.1.5. Flame Fusion Method. 

Figure 1. (a) Schematic diagram of crystal growth by the flame fusion method, (b) Stages of development of undoped AI2O3 and Cr-doped (ruby) crystals, (c) Furnace room used for AI2O3 production by H. Djevahirdjian Company at Monthey, Switzerland. (Courtesy of V. Djevahirdjian.)... 

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]. 

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... 

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. 

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