I have a TGA analysis from a soil sample from room temp. to 600ºC.
I've noticed four different stages (slopes) in the mass loss curve. Those stages are expressed in the differential curve as well.
- Room temp. - 110ºC - Water (2% mass loss) - The soil have been previously dehydrated.
- from 170ºC to 300ºC - ? (0.83% mass loss)
- from 300ºC to 460ºC - ? (2.267% mass loss)
- form 460ºC to 560ºC - ? (2.18% mass loss)
I've read many articles but I am having some trouble adapting the case studies to my sample.
My sample is from an agricultural soil. I know that have an important clay proportion and some organic matter.
What does mean every slope (and mass loss associated) that I have in my sample?
Many thanks in advance for any kind of help!
Dear David Ferreira
I agree with listed by Mina-Karimi-Avargani , the slopes are related to loss of volatile of some soil constituents at each temperature range.
To accurately interpret the thermal analysis, you have to know the origin of your soil. For instance, if you have kaolinite at higher temperatures, it is expectable to see halloysite as dehydration product and so other physico-chemical transformations that are possible to happen.
I guess the first task is to get a good XRD from your soil; if you have a petrographic analysis, it will significantly help you with the full identification and interpretation of the thermal phenomena already observed in your sample.
Also, repeat the XRD after the thermal experiment, many precise identifications need a comparison before and after the thermal effects.
The information on human interference in the soil would help you significantly if some pesticide or soil correction with chemicals was performed.
It will help you precisely identify the real thermal phenomenon that is directly related to natural soil constituents of agricultural additions, as expected in soil corrections.
Best regards,
WNM
The 170oC- 300oC range will be due to water of Hydration form soil minerals such and gypsum as well as some loss of volatile organic compounds if present. the 300oC-460oC will be due to mostly loss of Organic matter. This is the range (370oC) that is used for soil organic matter measurement by loss-on-ignition (LOI). Also may have some loss of water trapped in some soil minerals. The 460oC-560oC range will result in further loss of organic matter compounds plus possibly interlattice layer water or even rearrangement of some crystal lattices (sometimes used for clay mineralogy determination by XRD). This higher range is sometimes used to approximate soil organic C by high temperature combustion (but at best is only an approximation).
Without removal of organic matter before TGA it is difficult to study the clay properties because of the oxidation of the organic matter which can mask any other properties you might be looking at. High organic matter soils (>3-5 %) will make your work more difficult as will large amounts of gypsum, carbonates or salta.
- Badges
- Science topic