Polymorphism and Melting of Ammonium, Thallous, and Silver Nitrates to 45 kbar

The phase diagrams of NH4NO3 and TlNO3 were determined by means of differential thermal analysis to 40 kbar. The NH4NO3 I/VI, IV/VI, and I/IV transition lines meet at a triple point near 19.5 kbar, 256°C. The TlNO3 I/II transition line can be represented by t(degrees Centigrade) = 144.6+7.91P−0.062P2, and the melting curve of TlNO3 I is given by P (kilobars) = 5.00 [(T/479)3.531−1]. The phase diagram of AgNO3 was determined by means of DTA and volumetric methods to 45 kbar. In addition to the four phases previously known, metastable AgNO3 V can be obtained by suitable manipulation above 21 kbar at temperatures below 50°C. The metastable AgNO3 I/V transition is easily reversible. AgNO3 V reverts to stable AgNO3 II if left under pressure overnight. The melting curve of AgNO3 II is given by P (kilobars) = 9.17[(T/483)4.438−1].