The Th-W-N System

The phase relations in this system are important for use of W as a crucible material for the nitrides at elevated temperatures. There is practically no mutual solubility between W and ThN and, a fortiori, Th3N4, as long as the Ng pressure exceeds the decomposition pressure of ThN (cf. p. 20), by a factor of about 100. At lower pressures, ThN dissociates more or less rapidly and the product Th metal reacts rapidly with W above 1700°C to form a metal-rich liquid with a composition very near the eutectic given by Ackermann and Rauh as 1695 C with the atom fraction Xw = 0.012 [9]. The previously reported liquid formation at lower temperatures is discounted [10]. The solubility of W in liquid Th has been reported as given by the equations  

No binary W-Th [9] or ternary Th-W-N compound exist. A suggested 2273-K isotherm is illustrated in Fig. 12. 

Isothermal section in the Th-W-N system at 2273 K, suggested on the basis of the discussions in the text. 

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