Experimental study and thermodynamic modeling of a novel heat-resistant explosive in different mono solvents

In this paper, the solubility of 5,5′-bis(2,4,6-trinitrophenyl)-2,2′-bis(1,3,4-oxadiazole) (TKX-55) was first determined by a dynamic laser monitoring at T = (293.15, 298.15, 303.15, 308.15, 313.15, 318.15, 323.15, 328.15 and 333.15) K in fourteen pure solvents, including nitrobenzene (NB), methylethylketone (MEK), dimethyl carbonate (DMC), N,N-dimethylformamide (DMF), methoxybenzene (MOB), ethenyl acetate (VAC), 1,2-propanediol (PDO), cyclohexanone (CYC), epichlorohydrin (ECH), 1-butanol (NBA), n-butyl acrylate (BA), dimethyl sulfoxide (DMSO), tributyl phosphate (TBP) and 2-butanol (IBA), under atmospheric pressure (P = 0.1 MPa). Besides, supersolubility as well as the metastable zone width of TKX-55 in PDO, BA, DMSO and IBA was determined by the dynamic laser monitoring method. The experimental results showed that the solubility of TKX-55 in fourteen pure solvents increases with increasing temperature and the metastable zone width decreases with increasing temperature. The metastable zone width is approximately 2.49 K–43.26 K. In addition, in order to improve the applicability of the solubility, the modified Apelblat equation, λh equation, the polynomial empirical equation, van't Hoff equation and NRTL equation were used to correlate the solubility data of TKX-55, and the results showed that all models can give a satisfactory correlation. The average root-mean-square deviation (102RMSD) values were 1.71, 8.91, 2.33, 6.12 and 3.30, respectively. Moreover, Hansen solubility parameter was used for explaining the solubility order of TKX-55 in selected solvents, the consequences showed that solubility order of TKX-55 resulted from the comprehensive function of several solubility parameters. The solubility parameter of Δδt between TKX-55 and solvents reached from 1.27 MPa0.5 to 15.28 MPa0.5. Furthermore, three kinds of thermodynamic properties of the mixing enthalpy (ΔmixH), the mixing entropy (ΔmixS) and the mixing Gibbs energy (ΔmixG) of TKX-55 in selected solvents were calculated by NRTL equation and the results turned out that the dissolution process was spontaneous. Besides, thermal properties of TKX-55 were measured by differential scanning calorimetry (DSC). The results showed that the melting temperature and the fusion enthalpy were 640.65 K and 19.60 kJ·mol−1, respectively. Finally, solubility values and thermodynamic relations of TKX-55 in fourteen pure solvents would be invoked as fundamental data and models regarding the purification process. •The