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Molecular Inclusion of Small Aging Products into the Hexanitrohexaazaisowurtzitane (CL-20) Lattice: Part I, Infrared Spectra

Propellants, Explosives, Pyrotechnics

Beste, Ariana; Alam, Mary K.

Accelerated aging studies of β CL-20 thin films deposited on glass surfaces in different environments (N2, air, air/water) were conducted. Samples were analyzed with attenuated total reflectance infrared (ATR-IR) spectroscopy. Spectral features of molecular lattice inclusions in CL-20 films aged in an air/water environment were observed. The features occurred after β CL-20 polymorph transformation to α CL-20 and were accompanied by the appearance of lattice water peaks. To assist ATR-IR peak assignment, density functional theory studies were performed, and IR spectra of α CL-20 lattice inclusions of small molecules that were identified as degradation products of CL-20 were computed. Simulated spectra of NO2, HNCO, N2O, and CO2 incorporated into partially hydrated α CL-20 matched the experimental spectrum of β CL-20 thin films aged in air/water.

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TYPE Journal Article YEAR 2022
DOIOSTIScopus

Phase transitions in high-purity zirconium under dynamic compression

Physical Review B

Greeff, C.W.; Brown, Justin L.; Velisavljevic, N.; Rigg, P.A.

We present results from ramp compression experiments on high-purity Zr that show the α→ω, ω→β, as well as reverse β→ω phase transitions. Simulations with a multiphase equation of state and phenomenological kinetic model match the experimental wave profiles well. While the dynamic α→ω transition occurs ∼9GPa above the equilibrium phase boundary, the ω→β transition occurs within 0.9 GPa of equilibrium. We estimate that the dynamic compression path intersects the equilibrium ω-β line at P=29.2GPa, and T=490K. The thermodynamic path in the interior of the sample lies ∼100K above the isentrope at the point of the ω→β transition. Approximately half of this dissipative temperature rise is due to plastic work, and half is due to the nonequilibrium α→ω transition. The inferred rate of the α→ω transition is several orders of magnitude higher than that measured in dynamic diamond anvil cell (DDAC) experiments in an overlapping pressure range. We discuss a model for the influence of shear stress on the nucleation rate. We find that the shear stress sji has the same effect on the nucleation rate as a pressure increase δP=cϵijsji/(ΔV/V), where c is a geometric constant ∼1 and ϵij are the transformation shear strains. The small fractional volume change ΔV/V≈0.1 at the α→ω transition amplifies the effect of shear stress, and we estimate that for this case δP is in the range of several GPa. Correcting our transition rate to a hydrostatic rate brings it approximately into line with the DDAC results, suggesting that shear stress plays a significant role in the transformation rate.

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TYPE Journal Article YEAR 2022
DOIOSTIScopus
Results 7051–7075 of 99,299
Results 7051–7075 of 99,299