Inductive high-frequency melting technique

FIGURE 4.6 S ample of a zirconia single crystal made by an inductive high-frequency melting technique. (From Zhuiykov, S., Zirconia single crystal analyser for low-temperature measurements, Prvc. Control and Quality 11 (1998) 23-37. With permission.)... 

In several cases authors have reported growing crystals by the recrystallization technique, but did not state a size for the crystals grown. Whittaker (1%8) prepared rods by a cold-crucible technique in which the samples were levitated and melted by high frequency induction. The rods were then heated by induction to 100°C below their melting point for 8 hours. Grains up to 20 mm in length and 7 mm diameter were prepared. In his studies Whittaker (1%8) noted an inverse relationship between the size of crystals grown by this technique and... 

Figure 6.3. Levitation of a molten metal in a radio-frequency field. The coil consists of water-cooled copper tubes. The counter winding above the sample stabilizes levitation. The same coils (and possibly additional ones) act as the induction heater. This technique has been applied to container-less melting and zone refining of metals and for drop calorimetry of liquid metals. It can be also used to decarburize and degas in ultrahigh vacuum mono-crystalline spheres of highly refractory metals (adapted from Brandt (1989)). The arrows indicate the instantaneous current flow directions in the inductors.

One technique that addresses both container reaction and impurity inclusions is a high pressure, RF, melt growth process. With this process, the material is inductively heated by RF energy, oscillating at frequencies between 450 kHz and 4 MHz. Power levels up to 100 kW are available to produce melt temperatures of the order of 2600°C. To prevent decomposition, the chaige is contained in a nitrogen over-pressure of 10 to 100 atm. The liquid aluminium nitride is self-contained in a water-cooled skin, which prevents both container reaction and deleterious inclusions. 

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