Primary crystallization field

A sample in the primary crystallization field of phase C will behave differently during crystallization. Here phase C precipitates with composition identical to C (no solid solubility) during cooling keeping the A B ratio in the melt constant until the melt hits the intersection of the two primary crystallization fields. At this temperature a will start to precipitate together with further C and from this point on the cooling process corresponds to that observed for the sample with overall composition P after this sample reaches the same stage of the crystallization path. 

The primary crystallization fields of (Cu) and (yFe) in the Cu rich comer are practically merged with the Cu-Fe edge and were not investigated. A sehematie sketeh of the hquidus surface for the whole system is shown in Fig. 4 with exaggerated solubility. 

Kes] redetermined the liquidus surfaee near the Fe comer. Their results eonfirm the presence of the transition reaction Ui and the ternary reaction E2 near the Fe comer. For compositions lying in the primary crystallization field of austenite, the liquidus temperature was given by the following equation T(°C) = 1523 - 49.8X-6.1Y+ 3.3XY- 0.27, where Aand Fare the contents of C and V inmass%. The temperatures of the Ui and E2 reactions were determined to be 1370 and 1120°C, as against -1330 and 1122°C in [1987Rag]. 

Primary crystallization field substrate materials. R123 single ... 

Fig. 14. Expanding ofthe Y123 primary crystallization field and decreasing the lowest temperature of the Y123 primary crystallization by additives (BaFj and Ag) (Yamada et al. 1997b).

While our primary focus has been on stable closed-shell (or low-spin) coordination species in which covalency effects are pronounced, it is also useful to examine the opposite extreme of weak coordinate bonding and free-atom -like spin multiplicities, corresponding to the original assumptions of crystal-field theory. 

Let us now consider the crystallization process operating on a composition C2, initially poorer in component 1 this composition falls into the compositional triangle C -2-3. Crystallization begins in primary phase field y" (T = 1225 °C). Precipitation of y" crystals drives the residual liquid radially away from C2 along direction 2-C2. At T = 1100 °C, the composition of the liquid reaches cotectic line Ejii-P, where crystals y " begin to form together with y". At peritectic point P, crystals y" are partially resorbed by reaction with the liquid to form intermediate compound C . However, the peritectic reaction is not completed, because of ex-... 

Crystal field theory was introduced in the late 1920s by Bethe and Van Vleck and, although initially formulated and applied by physicists, incorporates the inorganic paradigm of primary concern with the consequences at the metal. The crystal field theory... 

Since mullite melts incongruently at 1810 10°C, its composition lies outside its primary phase field. For compositions in the field of mullite with a liquidus temperature below about 1400°C, Schairer and Bowen [4] encountered considerable difficulty in crystallizing this compound. For compositions with liquidus temperatures below around 1200°C, many months were required to form small mullite needles. 

---