Influence of the Crucible on TGA Curves
Purpose
To investigate the influence of different crucibles on TGA measurements.
Sample
A technical elastomer made from a blend of NR (approx. 30%), SBR (approx. 45%) and carbon black (approx. 23%).
Conditions
Measuring Cell: Measuring cell: TGA/SDTA851e large furnace
Pan: Different alumina crucibles: 30 µl, 70 µl, 150 µl and 900 µl.
Sample preparation: Elastomer pieces of approx. 5 mg were weighed into different crucibles
TGA measurement: Heating from 50 °C to 600 °C under nitrogen (80 ml/min), then switching to air (80 ml/min) to 900°C. Heating rate: 30 K/min.
Atmosphere: Nitrogen then air, automatically switched
Evaluation
Just as with the investigation of the influence of sample mass, the type of crucible does not seem to significantly influence pyrolysis in the temperature range 350 °C to 500 °C. The combustion of the carbon black after gas switching does, however, depend on the type of crucible used. To illustrate these differences more clearly, the relative change in mass of the samples during combustion is displayed on an expanded scale next to the TGA curve.
The following values were determined for the midpoint of this step for the various types of crucible:
The combustion rate is most rapid with the crucible with the lowest wall height because the gas exchange is then most favorable.
Comments
The slight differences observed in the step heights are due to the relative large degree of inhomogeneity of the samples and not the measurement conditions. It was later discovered that the material contained metal particles due to a faulty production process. This was confirmed by additional measurements.
Conclusions
Crucibles with the lowest wall height are best for performing comparative measurements on the combustion behavior of carbon black in elastomer analysis.
Influence of Crucible on TGA Curves | Thermal Analysis Handbook No.HB414 | Application published in METTLER TOLEDO TA Application Handbook Elastomers, Volume 1