Article

High pressure-high temperature phase diagram of ammonia.

Institut de Minéralogie et de Physique des Milieux Condensés, Département Physique des Milieux Denses, CNRS UMR 7590, Université Pierre et Marie Curie-Paris VI, Paris Cedex 05, France.
The Journal of Chemical Physics (Impact Factor: 3.12). 05/2008; 128(15):154508. DOI: 10.1063/1.2903491
Source: PubMed

ABSTRACT The high pressure (P)-high temperature (T) phase diagram of solid ammonia has been investigated using diamond anvil cell and resistive heating techniques. The III-IV transition line has been determined up to 20 GPa and 500 K both on compression and decompression paths. No discontinuity is observed at the expected location for the III-IV-V triple point. The melting line has been determined by visual observations of the fluid-solid equilibrium up to 9 GPa and 900 K. The experimental data are well fitted by a Simon-Glatzel equation in the covered P-T range. These transition lines and their extrapolations are compared to the reported ab initio calculations.

5 Bookmarks
 · 
691 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigate via quantum molecular-dynamics simulations the thermophysical properties of shocked liquid ammonia up to the pressure 1.3 TPa and temperature 120 000 K. The principal Hugoniot is predicted from the wide-range equation of state, which agrees well with the available experimental measurements up to 64 GPa. Our systematic study of the structural properties demonstrates that the liquid ammonia undergoes a gradual phase transition along the Hugoniot. At about 4800 K, the system transforms into a metallic, complex mixture state consisting of NH3, N2, H2, N, and H. Furthermore, we discuss the implications for the interiors of Uranus and Neptune.
    The Journal of Chemical Physics 10/2013; 139(13):134505. · 3.12 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We present an equation of state as well as a phase diagram of ammonia at high pressures and high temperatures derived from ab initio molecular dynamics simulations. The predicted phases of ammonia are characterized by analyzing diffusion coefficients and structural properties. Both the phase diagram and the subsequently computed Hugoniot curves are compared to experimental results. Furthermore, we discuss two methods that allow us to take into account nuclear quantum effects, which are of considerable importance in molecular fluids. Our data cover pressures up to 330 GPa and a temperature range from 500 K to 10 000 K. This regime is of great interest for interior models of the giant planets Uranus and Neptune, which contain, besides water and methane, significant amounts of ammonia.
    The Journal of Chemical Physics 06/2013; 138(23):234504. · 3.12 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: High pressure pyrolysis of melamine has been attracting great interest recently, due to it being considered as a suitable precursor to realize the g-C3N4 and even superhard C3N4. In this work, we studied the detailed pyrolysis behavior of melamine at 22 GPa. Melamine was stable at 800 °C, and decomposed to diamond in the form of powder at 1500–2000 °C under this pressure condition. At 2000 °C, the pure cubic diamond powders with 0.1–0.5 μm grain size were obtained. The diamond particles exhibited euhedral forms and dispersed to each other, we proposed that these novel features were caused by the presence of liquid N2 and NH3 during diamond formation. The high pressure pyrolysis of melamine may provide a new means of producing micrometer-sized diamond powders.
    Chinese Physics C 08/2013; 37(8):088002. · 0.34 Impact Factor

Full-text (2 Sources)

View
77 Downloads
Available from
May 28, 2014