Improved apparatus and procedures for isopiestic studies at elevated temperatures

Abstract

A significantly improved apparatus for the isopiestic measurement of thermodynamic activities at elevated temperatures is described. Details of the new design and of an analysis of the propagation of the experimental errors are presented. The apparatus was tested by measurements of calcium chloride against sodium chloride at 353.15 K. Accuracies of better than 0.1% in the osmotic coefficient are routinely achieved. Data are also given for the osmotic coefficient of aqueous sodium hydroxide solutions at 353.15 K as a function of molality ͑up to 13 mol/kg͒, measured with respect to both sodium chloride and calcium chloride solutions as reference electrolytes. © 1997 American Institute of Physics. ͓S0034-6748͑97͒03106-7͔

Vapor pressures and isopiestic molalities of concentrated CaCl2(aq), CaBr2(aq), and NaCl(aq) to T=523 K

“…Grjotheim and co-workers [22][23][24][25][26][27] investigated a series of electrolyte mixtures using an isopiestic device of this type designed for operation at T = 373 K. An updated version, used for measurements at T = 428.15 K, was described by Brendler and Voigt [31]. More recently, Hefter et al [32] described another one, intended for measurements to T = 450 K and tested at T = 353.15 K.…”

Decomposition of Bayer process organics: Low-molecular-weight carboxylates

“…At 180ºC, up to 12 stainless steel reaction vessels each containing 5 mL of solution were placed in a converted isopiestic chamber, partially evacuated, and then heated in a silicone oil bath (Hefter et al, 1997) for up to 12 d. The temperature was controlled to ± 0.5ºC. To minimize the possible effects of oxygen on the present reactions, all solutions were prepared from thoroughly degassed water and care was taken to restrict contact of the solutions with air.…”

The Isopiestic Method: 100 Years Later and Still in Use

“…However, if the temperature of the isopiestic experiment is much lower or much higher than room temperature then condensation of atmospheric moisture or significant evaporation of solvent from the samples could occur when they are removed from the isopiestic apparatus and to prevent this it is essential that the dishes or cups be capped while still inside the apparatus and still at the experimental temperature. See, for example, the studies of Rush and Johnson [7], Humphries et al [27], Grjotheim et al [28] and Hefter et al [29]. Rard and Platford [4] estimated the mass error for samples capped at T = 273.15 K and T = 298.15 K and then weighed at T = 298.15 K as being ~ -1 × 10 −4 g and ~ + 1 × 10 −4 g, respectively, when a w = 0.9 for an isopiestic dish or cup of typical size, which is an essentially negligible contribution to the experimental error.…”