Sensitive power compensated scanning calorimeter for analysis of phase transformations in small samples

Abstract

We have designed and developed a sensitive scanning calorimeter for use with microgram or submicrogram, thin film, or powder samples. Semiconductor processing techniques are used to fabricate membrane based microreactors with a small heat capacity of the addenda, 120nJ∕K at room temperature. At heating rates below 10K∕s the heat released or absorbed by the sample during a given transformation is compensated through a resistive Pt heater by a digital controller so that the calorimeter works as a power compensated device. Its use and dynamic sensitivity is demonstrated by analyzing the melting behavior of thin films of indium and high density polyethylene. Melting enthalpies in the range of 40–250μJ for sample masses on the order of 1.5μg have been measured with accuracy better than 5% at heating rates ∼0.2K∕s. The signal-to-noise ratio, limited by the electronic setup, is 200nW.