Phase diagrams nitrogen

E8.1 From the following data, sketch the phase diagram for nitrogen at low... 

All phase diagrams share the ten common features listed above. However, the detailed appearance of a phase diagram is different for each substance, as determined by the strength of the intermolecular interactions for that substance. Figure 11-40 shows two examples, the phase diagrams for molecular nitrogen and for carbon dioxide. Both these substances are gases under normal conditions. Unlike H2 O, whose triple point lies close to 298 K,... 

N2 and CO2 have triple points that are well below room temperature. Although both are gases at room temperature and pressure, they behave differently when cooled at P = 1 atm. Molecular nitrogen liquefies at 77.4 K and then solidifies at 63.3 K, whereas carbon dioxide condenses directly to the solid phase at 195 K. This difference in behavior arises because the triple point of CO2, unlike the triple points of H2 O and N2, occurs at a pressure greater than one atmosphere. The phase diagram of CO2 shows that at a pressure of one atmosphere, there is no temperature at which the liquid phase is stable. 

Phase diagrams for molecular nitrogen and carbon dioxide, two substances that are gases at room temperature and pressure. 

The phase diagrams in Figures 11-39 and 11-40 do not show critical points, because the critical points of water, carbon dioxide and nitrogen occur at higher pressures than those shown on these diagrams. The critical point of water is P = 218 atm, T = 647 K that of CO2 is P = 72.9, T — 304 K and that of N2 is P = 33.5 atm, P = 126 K. 

Data at two temperatures were obtained from Zeck and Knapp (1986) for the nitrogen-ethane system. The implicit LS estimates of the binary interaction parameters are ka=0, kb=0, kc=0 and kd=0.0460. The standard deviation of kd was found to be equai to 0.0040. The vapor liquid phase equilibrium was computed and the fit was found to be excellent (Englezos et al. 1993). Subsequently, implicit ML calculations were performed and a parameter value of kd=0.0493 with a standard deviation equal to 0.0070 was computed. Figure 14.2 shows the experimental phase diagram as well as the calculated one using the implicit ML parameter estimate. 

Nitrogen Phase Diagrams, Office of Naval Research, Titanium, Washington, 153 (1949)-... 

Carbon Monoxide. There are close similarities between carbon monoxide and nitrogen. The molecules are isoelectronic, and the bond lengths and dissociation energies are quite comparable. The phase diagrams of the two compounds show the same trends in the moderate pressure range with a variety of phase transitions between essentially alike crystal structures [333], when allowance is made for the lack of the inversion center and the presence of a weak electric dipole moment in carbon monoxide. However, the behavior and stability at higher... 

Figure 1.2. Phase diagram of nitrogen. Adapted from Bini et al., 2000 Gregoryanz et al., 2002.

Nikitin, S.A., Tereshina, I.S., Verbetsky, V.N., Salamova, A.A. (2001) Transformations of magnetic phase diagram as a result of insertion of hydrogen and nitrogen atoms in crystalline lattice of RFenTi compounds, J. Alloys Comp. 316 46-50. 

Hagg carbide was the final phase up to 500°C., whereas cementite was formed at 700°C. Hagg carbide appeared when N had been decreased below 0.18, i.e., when about 64% of the nitrogen corresponding to the upper limit of the e-phase (Fe N) had been replaced by carbon. According to Jack s phase diagram (Fig. 2), the upper limit of the ("-carbonitride phase may be as high as C + N = 0.56. 

Nitrogen dissolves in iron to form a solid solution and several nitride phases the phase diagram is complex. Specific nitrides are best obtained via reaction of iron with ammonia. At 400 500 °C, gray orthorhombic Fc2N is obtained, which when heated at abont 500 °C in vacuo, loses nitrogen to give face-centered cubic Fc4N. 

In the vanadium-nitrogen system, the phases /3-V2N and 5-VNi x have cph and fee struetures, respeetively. Carlsson et have reviewed the V-N system and reinvestigated the vanadium-rieh portion. Compiled data and results of a phase diagram study based on diffusion eouples have been used to eonstruet the phase diagram shown in Figure 7. 

Figure 6 Phase diagrams of group 4 transition metal-nitrogen systems, (a) Zr-N. (Ref. 11. Reproduced by permission of Materials Information Society/ASM International), (b) Hf-N. (Reprinted from Ref 28. 1991, with permission from Elsevier)...

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