Photoacoustic determination of the speed of sound in single crystal cyclotrimethylene trinitramine at acoustic frequencies from 0.5 to 15 GHz

Abstract

We report photoacoustic measurements of the quasi-longitudinal speed of sound along different crystallographic directions in the energetic molecular crystal cyclotrimethylene trinitramine (RDX). Measurements in (100)-oriented RDX were made using two complimentary techniques to probe acoustic frequencies from 0.5 to 15 GHz to resolve large discrepancies in reported sound speed values measured using different techniques and frequency ranges. In impulsive stimulated light scattering (ISS), two laser beams were crossed at various angles in a sample to generate coherent acoustic waves with well-defined wavevectors. Picosecond acoustic interferometry (PAI) measurements were conducted in which a laser pulse heated a thin metal transducer layer coated on the sample surface to generate a broadband acoustic wave-packet that propagated into the sample. Time-dependent coherent Brillouin scattering of probe light from the acoustic waves revealed frequencies in the 0.5–3.5 GHz range in ISS measurements and at ∼15 GHz in the PAI measurements, yielding the speed of sound in each case. Our ISS results are in agreement with previous ultrasonic and ISS measurements at kilo- and megahertz frequencies. Our PAI results yielded a 15 GHz sound speed essentially equal to those at megahertz frequencies in contrast to an earlier report based on Brillouin light scattering measurements. The lack of acoustic dispersion over six orders of magnitude in frequency indicates that there is no relaxation process that significantly couples to acoustic waves in RDX at acoustic frequencies up to 15 GHz.

Interlayer thermal conductivity of rubrene measured by ac-calorimetry

“…2) and that the acoustic phonon specific heat is close to its Dulong-Petit value, as discussed above, then this would give an interlayer acoustic phonon velocity v c  3 c /(c acoustic )  3 x 10 5 cm/s, (6) which is actually a value fairly typical for organic molecular crystals. 30,31 Since v c is probably somewhat smaller than this, reflecting the weak interlayer coupling, the mean-free-path must instead be at least a few layers.…”

“…30,31 Since v c is probably somewhat smaller than this, reflecting the weak interlayer coupling, the mean-free-path must instead be at least a few layers.…”

Global Analysis of the Mechanical Properties of Organic Crystals

“…[34] Being crystalline and light, organic crystals are expected to deliver high power-to-weight ratios in energy-transducing and acoustic devices.T he longitudinal wave speeds (v)i n organic crystals,given by afamily of contours at v = (E/1) 1/2 in Figure 1b,a re 0.13-5.5 10 3 ms À1 ,w ith an average of 2.24 10 3 ms À1 .T hese values are in line with speeds obtained by ultrasonic pulse-echo,r esonant ultrasonic spectroscopy,i mpulsive stimulated thermal scattering, and Brillouin light scattering. [35,36] Organic crystals (see Figures 1a and 2a,a sw ell as Table S9) typically have Youngsm oduli (E)i nt he range 1-25 GPa, with approximately 8% having E < 1GPa and approximately 8% with E > 25 GPa (E ¯= 12.05 GPa, E ˜= 10.35 GPa, s = 8.35 GPa). Theh ardness (H)o fo rganic crystals is between 0.04 and 1.67 GPa (H ¯= 0.50 GPa, H ˜= 0.40 GPa, s = 0.35 GPa).…”

Application of the Peng–Robinson Equation of State to Energetic Materials RDX and TNT: Pure Components, Liquid Mixtures, and Solid Mixtures

“…Haycraft et al compare results for K T from a number of experimental and computational studies. Although there is a sizable disagreement among a few studies over the value of a particular elastic constant (about a 40% deviation − ), the reported results for K T all lie within the range 11.2–12.3 GPa, if one takes the true value of K T to be the average of that produced by the Voigt and Ruess schemes. Sewell and Bennett present Young’s modulus E and Poisson ratio ν predictions for RDX at 304 and 333 K. These quantities are obtained from Monte Carlo simulations of the elastic constants.…”