Growth from the Melt

The tip of the torch is important. One design used for such a torch is shown in 4.2.44, given on the next page. The center tube is used for ojqrgen gas which transports the powder. The burner is designed so that the outer tubes contain only hydrogen gas, with the interstices between 

Measuring particle size and growing single crystals 

As shown in the following diagram, given as 4.2.45 on the next page, the overall Verneuil apparatus consists of a sealed hopper to contain the powder, the TORCH itself, a refractory pedestal to hold the growing crystal, and an after-furnace to anneal the crystal. Thermal stability is important in this method because the high temperatures reached may be sufficient to cause decomposition of the material. 

Generally, the method is restricted to crystals like AI2O3 whose thermal conductivity is high and whose refractive nature makes it possible to obtain a crystal. For the most part, one is restricted to growing simple oxides by this methods. Complex oxides such as Ca2Si04 or CCI2P2O7 

---

Detailed, critical surveys of the variants and complexities of crystal growth from the melt were published for low-melting metals by Goss (1963) and for high-melting metals (which present much greater difficulties) by Schadler (1963). 

When applied to growth from the melt (despite our reservations in Sect. 3.2), P is normally assumed to take the form... 

Robert A. Brown is Warren K. Lewis Professor of Chemical Engineering and Provost at the Massachusetts Institute of Technology. He received his B.S. (1973) and M.S. (1975) from the University of Texas, Austin, and his Ph.D. from the University of Minnesota in 1979. His research area is chemical engineering with specialization in fluid mechanics and transport phenomena, crystal growth from the melt, microdefect formation in semiconductors and viscoelastic fluids, bifurcation theory applied to transitions in flow problems, and finite element methods for nonlinear transport problems. He is a member of the National Academy of Engineering, the National Academy of Sciences, and the American Academy of Arts and Sciences. 

Kirkpatrick R.J. (1975) Crystal growth from the melt a review. Am. Mineral. 60,... 

D.E. Ovsienko, G.AAlflntsev Crytal Growth from the Melt/Experimental Investigation of Kinetics and Morphology AH.Monish Morphology and Physical Properties of Gamma Iron Oxide... 

The most frequently used techniques for the commercial manufacture of synthetic gemstone materials are summarized in Table 4. More details on these can be found in various texts (2,5—7). An overview including the various manufacturers is also available (3). Only rardy used for synthetics are such alternative growth techniques as the Bridgman technique of solidification in a cmcible and the float zone technique, both involving growth from the melt... 

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

The presence of convection also affects crystal growth from the melt. Single crystals of Te-doped InSb were grown from flic melt on Sivlah. The crystals obtained in space were free of striations caused by convection-driven growth rate fluctuations that are normally seen on eanh. future space experiments will examine the grow th of electronic materials such as GaAs from a sululion subjected to an electric current. 

Theory of Transport Processes in Semiconductor Crystal Growth from the Melt... 

Examples of dimensionless groups that specify ratios of transport mechanisms are listed next in Table II and depend on the size and shape of the domain. The Peclet numbers for heat (Pet) and solute (Pes) and momentum (Re) transport are ratios of scales for convective to diffusive transport and depend on the magnitudes of the velocity field and the length scale for the diffusion gradient. Boundary layers form at large Peclet numbers (Pet or Pes) or Reynolds numbers (Re). The fonnation of a boundary layer at a large Re is particularly important in crystal growth from the melt, because the low... 

Multilayer crystals with a central screw dislocation were commonly seen. A micrograph of a beautiful solution-grown multilayer crystal with regularly rotated terraces was presented by Keller [38]. This mechanism to multiply a single crystal layer into many crystal layers is important for the crystal growth from the melt to form spherulites. 

D. F Ovsienko, G.A. Alfintsev Crystal Growth from the Melt/ExperimentalInvestigation of Kineticsand Morphology (76 ref.)... 

Figure 2. Three spatial scales for modeling melt crystal growth, as exemplified by the vertical Bridgman process. From Theory of Transport Processes in Single Crystal Growth from the Melt, by R. A. Brown, AJChE Journal, Vol. 34, No. 6, pp. 881-911, 1988, [29]. Reproduced by permission of the American Institute of Chemical Engineers copyright 1988 AIChE.

Crystal growth from the melt is preferable to the alternatives, provided there are no adverse factors. Melt growth is more rapid (typically, by one to two orders of magnitude). 

Brown, R.A. Theory of transport processes in sin- 53. gle crystal growth from the melt. AIChE J. 1988,... 

---