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What are DSC and DTA ?

Differential Scanning Calorimetry (DSC) and Differential Thermal Analysis (DTA) are both thermal analysis techniques that involve comparing heat flow between a sample and a reference material. While they share many similarities, such as providing insights into glass transitions, melting points, sample purity, and crystallization, there are key distinctions between them.

Let’s explore the differences in testing methods, instruments, and measurements, and understand when to choose one technique over the other.

Features of DSC : Differential Scanning Calorimetry 

1. As the furnace temperature increases, both the sample and the reference material are heated at a slightly slower rate than the furnace itself.

2. When the sample begins to melt, its temperature ceases to increase (since energy is being used for the melting process), while the reference material’s temperature continues to rise.

3. Once the melting is complete, the sample’s temperature begins to increase again, following the temperature of the furnace.

4. The difference between the sample temperature and the reference material temperature generates the DSC signals.

Features of DTA : Differential Thermal Analysis

1. Differential Thermal Analysis (DTA) is an analytical chemistry method used to identify and quantitatively analyze the chemical composition of materials by examining how a sample responds to heat.
2. The principle behind DTA is that substances undergo reactions and phase transitions when heated, which result in the absorption or release of heat.
3. In DTA, the temperature of the sample is measured in comparison to that of an adjacent inert material. A thermocouple is placed in both the sample and the inert material, and any temperature differences generated during heating are recorded as a series of peaks on a moving chart.
4. The heat involved and the temperatures at which these changes occur are unique to specific elements or compounds. Therefore, the identification of a substance is made by comparing its DTA curve with those of known substances.
5. Furthermore, the quantity of a substance in a mixed sample is related to the area under the peaks, and this can be determined by comparing the area of a specific peak with those from standard samples analyzed under the same conditions. DTA is commonly employed in the identification of minerals and mineral mixtures.

Two types DSC instruments

Heat Flux DSC

In Heat Flux DSC, both the sample and reference material are placed on a single holder with built-in temperature sensors. Both are heated together in the same oven. As the sample undergoes phase changes, a temperature difference arises between it and the reference material. This difference is measured to calculate heat flow, allowing for quantitative analysis of the phase change. Heat Flux DSC ensures the sample and reference are exposed to identical conditions, improving measurement accuracy if calculations are done correctly.

Power-Compensated DSC

In Power-Compensated DSC, two separate thermally-insulated furnaces are used to heat the sample and reference material independently. A Platinum Resistance Thermometer detects the thermal event that causes phase changes in the sample. Both materials are heated at the same rate, and when a phase change occurs, the furnaces adjust the power to maintain temperature balance. The energy needed to keep the furnaces at equilibrium reflects the energy changes in the sample. While this method provides faster results than Heat Flux DSC, the accuracy may not be as high because no post-test calculations are required

Both techniques assess the thermal characteristics of a sample and a reference material. DSC measures the heat flow, while DTA examines how the applied temperature influences the material's temperature.