Calibration of a fixed-cell temperature-scanning calorimeter to measure precise solution heat capacities from 275 to 398 K at 0.35 MPa

A procedure was developed to calibrate the Calorimetry Sciences Corporation Models 5100 and 6100 Nano-DSCs to measure more precisely volumetric heat capacities of liquids and solutions. These calorimeters are small-volume, twin fixed-cell, power-compensation, differential-output instruments that can scan temperature upward or downward between 263 and 398 K at pressures up to 0.4 MPa. The calibration procedure leads to volumetric heat capacities that have a relative precision and accuracy of 3 x 10(-6) to 5 x 10(-5) for aqueous solutions at concentrations between ca. 0.001 and 1 mol kg(-1). The Nano-DSCs operate on the principle that the volumetric heat capacity of a solution or liquid is proportional to the difference between the calorimetric outputs for two separate experiments: one when both the cells contain a reference liquid (usually water), and one when the reference cell contains the reference liquid and the sample cell contains the solution or some other liquid of interest. The volumetric heat capacity of the reference liquid must be known precisely and accurately at the temperatures and pressures of the experiment. The calibration constant is determined from measurements on a second reference liquid whose volumetric heat capacity is also known precisely and accurately: 1-mol kg(-1) NaCl(aq). Results of calibration and other experiments are used as examples to illustrate the advantages of the calibration procedure described in this paper. (C) 2000 Elsevier Science B.V. All rights reserved.