How to interpret a TGA-DTA curve [Thermogravimetric analysis - Diffrential thermal analysis]

Summary

The video explains how to interpret thermogravimetric analysis (TGA) and differential thermal analysis (DTA) graphs using two sample materials. It breaks down the stages of weight loss during heating, including the drying, pyrolysis, and carbonization stages, and compares the thermal stability of two samples. Key points include the temperature ranges where decomposition occurs, percentage weight loss, and differences in stability between the samples. The video also highlights how the DTA complements the TGA, showing additional thermal events like moisture loss and weight change patterns.

Takeaways

• 😀 The script explains how to interpret a graph produced by Thermogravimetric Analysis (TGA) and Differential Thermal Analysis (DTA).
• 🔍 The TGA graph typically consists of three stages: the drying stage, the pyrolysis stage, and the carbonization stage.
• 💧 The drying stage is associated with the removal of moisture and possibly volatile organic compounds, causing a slight drop in the sample's weight, which is typically less than 10%.
• 🔥 The pyrolysis stage represents the decomposition or degradation of the sample, where the sample undergoes significant weight loss due to thermal breakdown.
• 📉 The pyrolysis stage begins at a certain temperature (around 319°C for one sample) and ends at a higher temperature (around 450°C). Different samples have varying degradation temperatures.
• 🌟 The final stage, carbonization, involves the decomposition of the sample into char, leaving behind residual weight (about 20% for the first sample, and less than 10% for the second sample).
• 📏 The second sample has multi-step degradation, which indicates instability compared to the first sample, which degrades in a more defined manner.
• 🌡️ The DTA graph complements the TGA by showing thermal peaks that correspond to weight loss and moisture removal, helping confirm the TGA findings.
• 📈 The DTA also shows specific temperature points where significant weight loss occurs, confirming the thermal stability of the sample.
• 🔧 The interpretation of both TGA and DTA graphs provides insights into the thermal stability, degradation stages, and residue left by different samples.

Q & A

What is TGA (Thermogravimetric Analysis)?

TGA is a technique used to measure the weight change of a material as a function of temperature. It helps in analyzing thermal stability and composition changes, such as drying and pyrolysis stages.

What are the three main stages identified in a TGA thermogram?

The three stages are: 1) Drying stage, where moisture is removed from the sample; 2) Pyrolysis stage, where the material decomposes; 3) Carbonization stage, where the sample degrades into char or residue.

How is the drying stage identified on a TGA graph?

The drying stage is represented by the initial portion of the graph where there is a slight weight loss. In the example, this weight loss was less than 10%, attributed to moisture removal or volatile organic compounds.

What is pyrolysis, and how is it represented in the TGA graph?

Pyrolysis refers to the decomposition of material due to high temperatures. In the TGA graph, this stage is represented by a slope, indicating significant weight loss as the sample decomposes. For the green line, pyrolysis occurred between 319°C and 450°C.

How does the second sample differ from the first sample in the pyrolysis stage?

The second sample, represented by the pink line, started pyrolysis at a lower temperature (around 248°C), indicating it is less thermally stable than the first sample, which began pyrolysis at 319°C.

What is carbonization, and when does it occur in the TGA graph?

Carbonization is the final stage in TGA, where the sample fully degrades into char or ash. This occurs after pyrolysis when the graph becomes a nearly flat line. For the green sample, carbonization began above 450°C.

How does the residue left after carbonization indicate the stability of the samples?

The amount of residue left after carbonization reflects stability. The first sample had about 20% residue, showing higher stability, while the second sample had less than 10%, indicating it was less stable.

What is DTA (Differential Thermal Analysis), and how does it complement TGA?

DTA measures temperature differences between a sample and a reference during heating. It complements TGA by identifying endothermic and exothermic reactions, helping to confirm phases like moisture loss and degradation observed in the TGA.

What does the endothermic peak at 100°C in the DTA curve indicate?

The endothermic peak at 100°C indicates moisture loss, confirming the drying stage seen in the TGA thermogram.

How do multi-step degradations in the pink sample affect its thermal stability?

The multi-step degradations in the pink sample indicate instability, as it degrades in stages rather than a smooth, continuous process. This is seen as unclear degradatory steps in the TGA and suggests the sample is less stable.