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A drawing of  Randy Chitto’ s Chemist Koshare (R. Boyett).

A drawing of Randy Chitto’s Chemist Koshare (R. Boyett).

High Pressure DSC - you need a good calibrated gauge

HPDSC (High-Pressure Differential Scanning Calorimetry) is often used to speed up OIT tests, but it can also be used for other tests. One example is to determine vapor pressure by the Clausius-Clapeyron Equation. By measuring boiling points under different pressure, we can use this equation to calculate vapor pressure. One can also measure heat capacity at various pressures.

In all HPDSC studies, accuracy suffers due to solvent vaporization, gauge inaccuracy, and dynamic gas flow all introduce inconsistencies. Gauge inaccuracy is a large enough problem that ASTM methods suggest corrections based on a standard like water. This is because most HPDSCs use a simple analog gauge about 2” in diameter. Often these gauges have percent errors, so a 5% error means being 5 psi off at 100 psi and 50 psi off at 1000 psi. Replacing or supplementing that gauge with a traceable calibrated gauge of sufficient accuracy can eliminate this need. For example, in measuring the boiling point of water at 1000 psi, we found the manufactor’s gauge required a 5% correction while the NIST traceable gauge attached to the exit line was dead on.

Kevin Menard