Thermophysical and Thermodynamic Properties of 1-Butyl-3-methylimidazolium Tetrafluoroborate and 1-Butyl-3-methylimidazolium Hexafluorophosphate over an Extended Pressure Range Gomes de Azevedo, R.; Esperança, J.M.S.S.; Najdanovic-Visak, V.; Visak, Z.P.; Guedes, H.J.R.; Nunes da Ponte, M.; Rebelo, L.P.N.; Journal of Chemical & Engineering Data 2005, 50, 997-1008