Differential Thermal Analysis (DTA)

Introduction:

Differential Thermal Analysis (DTA) is a thermal analytical technique that shares many similarities with Differential Scanning Calorimetry (DSC).

DTA is used to study thermal changes in materials by comparing the temperature of a sample with that of a reference (usually an inert substance). While DSC measures the heat flow required to maintain the same temperature between the sample and reference, DTA records the temperature difference directly.

In DTA, both the sample and the inert reference must undergo the same thermal cycle (i.e., the same heating or cooling program), while any temperature difference between them is recorded. This temperature difference is plotted against time or temperature.

In a DTA curve, any transformation in the sample that leads to heat release or absorption results in a deviation from the reference temperature. This temperature difference, compared to the program’s reference temperatures at which the changes start, provides the analyst with information about the nature of the transition and whether the heat flow is endothermic or exothermic. Determining the thermal content and specific heat capacity of the sample are among the key applications of this technique.

Working Principle:

DTA is an advanced analytical technique used to study thermal changes in materials when subjected to temperature variation. The test involves two identical crucibles: one holds the sample, and the other holds a reference material, which may be an empty crucible in some cases.

A differential thermocouple placed between the crucibles measures the temperature difference between the sample and the reference during heating or cooling. This allows researchers to identify temperatures at which phase transitions (like melting or freezing) or chemical reactions occur.

As both the sample and reference are heated or cooled simultaneously, the temperature difference between them is measured. When a change occurs in the sample (e.g., melting or a chemical reaction), it appears as a peak or dip on the curve, indicating a temperature difference.

Phase transitions or chemical reactions are usually accompanied by the release or absorption of heat. For instance, if the sample melts, the process absorbs heat, causing its temperature to rise relative to the reference. Conversely, in an exothermic reaction (like some decomposition processes), the sample releases heat, making its temperature lower than the reference.

Measurement Benefits:

DTA is widely used in fields such as materials science, chemistry, and chemical engineering, providing valuable insights into the thermal properties of materials, including:

1.      Transition Temperatures: Identifying the points where phase changes occur.

2.      Released or Absorbed Energy: Measuring the amount of heat involved in reactions.

3.      Thermal Stability Properties: Assessing how stable materials are at high or low temperatures.

Result Interpretation:

The horizontal axis represents temperature (°C or K).

The vertical axis represents the temperature difference between the sample and the reference (usually in °C).

Interpreting Peaks:

A peak or dip on the curve indicates a change in the sample’s state (e.g., melting, freezing, or a chemical reaction).

• Upward peak: Indicates the sample requires additional heat to surpass a transition point (e.g., melting).

• Downward dip: Indicates the sample releases heat during the transformation (e.g., solidification).

Determining Thermal Points:

Phase transition temperatures (like melting or freezing points) can be determined from the location of peaks and dips on the curve.

• Thermal peaks signify changes in physical states (e.g., melting or evaporation).

• Minor changes may reflect chemical reactions or phase transitions.

• Released energy is represented by the area under the thermal peak, helping estimate reaction enthalpy.

It is essential for the analyst to understand how to interpret the results and handle any discrepancies or anomalies. Additional valuable insights that contribute to research and development can be gained through collaboration with experts at the Photon Center.