|Monthly Tech-Tip |
This test measures weight changes in a material as it is heated and provides a convenient method for characterizing the decomposition process in inorganics. The test results are plotted on an x-y graph as temperature vs. weight. For example, calcium oxalate monohydrate, a standard material often used to verify TGA performance, exhibits three weight losses with temperatures in an inert atmosphere that appear to represent the loss of water, carbon monoxide and carbon dioxide via the process:
CaC2O4 . H2O --> CaC2O4 --> CaCO3 --> CaO
Absolute confirmation of conclusions can be done by analyzing the gaseous by-products as there evolve. Also, if a mass spectrometry (MS) curve is overlaid onto a TGA plot a more complete understanding of the decomposition process can be had. In the case of the above material, for example, the MS curve shows that the decomposition process is more complex than shown by the TGA alone. The second weight loss produces both CO and CO2. This can be explained based on further reaction of some of the CO initially formed into CO2 and pure C (this is confirmed by the presence of grey residue in the material after heading).
TGA Analysis graph with overlaid mass spectrometry curve
The result of the variables need to be compiled
Test conducted primarily on materials use to make bodies or glazes.
Organic Matter in Clays: Detailed Overview
A detailed look at what materials contain organics, what its effects are in firing (e.g. black core), what to do to deal with the problem and how to measure the amount of organics in a clay material.