Heat and Mass Thermogravimetric Analysis Curves Quiz

TGA specifically measures the change in mass of a sample as it is heated cooled or held at a constant temperature. This allows researchers to quantify processes like dehydration decomposition and oxidation.

The Y axis displays the remaining mass of the sample often expressed as a percentage of the initial mass. The X axis usually represents the increasing temperature. The resulting curve shows distinct steps where mass loss occurs.

The Derivative Thermogravimetry DTG curve is the first derivative of the mass change with respect to temperature. It shows peaks that correspond to the steepest slopes on the TGA curve making it easier to distinguish between overlapping decomposition steps.

While most TGA processes involve mass loss like evaporation or decomposition a mass increase occurs if the sample reacts with a gas in the atmosphere. For example a metal heating in an oxygen environment will gain mass as it forms a metal oxide.

TGA detects processes that involve a change in mass. Dehydration sublimation and decomposition all involve the loss of atoms or molecules. Melting is a phase change that does not change the mass so it cannot be detected by TGA alone.

A horizontal line indicates that the sample is thermally stable within that specific temperature range. No mass is being gained or lost meaning any previous reaction has finished and the next decomposition step has not yet begun.

The onset temperature is the point where the curve starts to deviate from the initial baseline. It is a critical parameter for determining the thermal stability of polymers and pharmaceutical compounds.

TGA can be performed in various atmospheres depending on the goal. Inert gases are used to study thermal decomposition without interference whereas reactive gases like Oxygen or Air are used to study oxidation or combustion.

Large samples can develop temperature gradients where the outside is hotter than the inside. Small samples ensure that the entire mass reacts simultaneously providing sharper steps and more accurate temperature data on the TGA curve.

Faster heating rates often shift decomposition steps to higher temperatures. Particle size affects how quickly gases can escape the sample and flow rate ensures that volatile products are removed quickly to prevent secondary reactions.

Calcium Oxalate Monohydrate is often used as a standard to calibrate TGA instruments. It loses water first around 100 to 150 degrees Celsius followed by carbon monoxide and finally carbon dioxide at much higher temperatures.

Because TGA involves heating the sample to the point of chemical decomposition or evaporation the original substance is physically and chemically transformed. The residue remaining in the crucible is usually an ash or oxide.

A TGA requires a microbalance that can detect mass changes as small as one microgram while the sample is inside a high temperature furnace. This precision is necessary to accurately calculate the percentage of components in a material.

TGA is widely used for quality control to verify the amount of fillers in polymers the purity of minerals and the moisture content in various commercial products. Refractive index is an optical property and is not measured by TGA.

This range indicates the temperatures over which the polymer backbone is breaking down into volatile fragments. The stability of the polymer is generally considered to be below the onset temperature of 250 degrees Celsius.