Direct measurement of the liquid 4:1 methanol–ethanol equation of state up to 5 GPa

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Abstract
Despite the widespread use of the 4:1 methanol–ethanol mixture as a hydrostatic medium by the high-pressure community, its equation of state (EOS) is usually substituted by that of pure methanol. Here we report accurate direct volumetric measurements of the room temperature EOS for this mixture up to 5 GPa. A brief description of the optical technique (imaging+interferometric) specifically developed for this purpose is given, as well as the general characteristics of the required miniature diamond anvil cell. Our results are compared with the available data of similar pure fluids’ EOS in the same pressure range. We find that there exist noticeable differences between the EOS of the mixture and that of pure methanol in terms of molar quantities.