Deviation from classical laws in shock-driven gas mixtures at moderate Mach numbers.*

We conducted a series of experiments where planar shocks propagated through mixtures of helium and sulfur hexafluoride. Even at modest Mach numbers, the bulk temperatures and pressures measured in the shocked mixture deviated significantly from the predictions of both Dalton's and Amagat's laws. As early as in the 1960s, it was already known that the behavior of gas mixtures in the immediate vicinity of a shock front was highly non-classical, however, our measurements show that the observed non-classical behaviors may persist far beyond the temporal and spatial scales associated with the shock passage. Simple molecular physics considerations can help explain some of the observed discrepancy. Numerical simulation of the experiments helps elucidate the observed disagreement between observations and models.