The heat capacity of a material can be determined with high accuracy using temperaturemodulated DSC. Measurements up to 700 °C can be performed by conventional DSC. In this article, we show how good results can also be obtained above 1000 °C using the TGA/DSC 1. To do this, we present ADSC measurements of nickel, sapphire and molybdenum in the temperature range 900 to 1400 °C. The work originated as part of an interlaboratory test organized in 2012/2013 by the Thermophysics Group of the German Society for Thermal Analysis (Gefta).
Introduction
Several different procedures for determining the specific heat capacity by DSC are available, such as for example the sapphire method [1, 2]. The maximum temperature of the DSC is however 700 °C. The article in reference [3] describes how specific heat capacities can be determined using the sapphire method up to a temperature of 1400 °C with an accuracy of about 10%. Application examples are presented in reference [4].
When the TGA/DSC is used to determine specific heat capacity, the heat flow signal measured simultaneously with the TGA signal is evaluated just as in DSC measurements. Other DSC methods that are available include the temperature-modulated techniques IsoStep® [5], SteadyState [3], ADSC [6] and TOPEM® [7, 8]. TOPEM® is currently not implemented for TGA/DSC.
Compared with the sapphire method, temperature-modulated methods have the advantage that they are less affected by drift and can therefore achieve accuracies of up to 2%. Heat capacities can also be determined for isothermal conditions using Steady-State, ADSC and TOPEM®.
In addition, information is obtained about the contributions of sensible and latent heat capacity. However, these methods require considerably longer measurement times compared with the sapphire method. In this article, we present specific heat capacity measurements determined by ADSC in the temperature range 900 to 1400 °C. The measurements were performed using the TGA/DSC 1.
ADSC method
The temperature-time program T(t) of an ADSC measurement is a function consisting of a constant heating rate β0 overlaid with a sinusoidal component: T(t) = β0*t + TA*sin(ωt) with a temperature amplitude TA and a frequency ω = 2π/p (with a period p)...
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Conclusions
Temperature-modulated measurements using the heat flow signal measured simultaneously with the TGA signal by the TGA/DSC 1 can be used to determine heat capacities in the same way as in DSC measurements. This allows you to benefit from the advantages that temperature-modulated procedures offer compared with the sapphire method when using the TGA/DSC. The advantages include the elimination of drift, the separation of sensible and latent heat capacity, and the possibility of determining isothermal heat capacities.
It was shown that the heat capacity can be determined with an accuracy of better than 5% for temperatures above 1000 °C.
Determination of Heat Capacity by Temperaturemodulated DSC at Temperatures above 700 °C | Thermal Analysis Application No. UC395 | Application published in METTLER TOLEDO Thermal Analysis UserCom 39