A METHOD FOR DECREASING BASE-LINE NOISE IN THERMOGRAVIMETRIC MEASUREMENTS

A simple modification to the flow system of a Cahn Model 113 thermogravimetric analyzer (TGA) resulted in an order of magnitude improvement in the baseline noise of the instrument for a broad range of operating conditions. At typical operating conditions of 900 K and gas flow rate of 180 cm3(STP)/min, baseline noise levels were approximately 0.5-mu-g. This low noise level was obtained by placing a critical (choked) flow orifice at the gas outlet, which isolated the gas in the TGA from ambient aerodynamic disturbances and provided a stable flowing gas environment. Apparently, local atmospheric pressure fluctuations caused by aerodynamic disturbances are largely responsible for most of the baseline noise in a flowing gas TGA.