Differential Scanning Calorimetry: Principle and Factors Affecting
Introduction
Differential Scanning Calorimetry (DSC) is an analytical technique for measuring the amount of heat transfer that occurs within the materials because of the change in temperature relative to a reference. Endothermic processes, which use heat, exothermic release of heat, and thermal transitions such as melting and freezing, boiling and condensation, as well as sublimation and deposition, are vital for determination.
Principle of DSC
As temperature varies concerning a reference, DSC measures heat flux. It distinguishes between endothermic (heat-requiring) activities like melting, evaporation, and sublimation and exothermic (heat-releasing) processes like freezing and condensation.
The measurement of heat flow concerning a reference as a function of temperature is known as differential scanning calorimetry (DSC).
Thermal Transitions Detected by DSC
In DSC, heat flux is observed when materials undergo phase shifts, such as:
- Sublimation
- Melting and Freezing
- Evaporation and Condensation
These transitions involve endothermic (melting and sublimation) and exothermic (freezing and condensation) transitions, which require heat input and release heat. Such transitions are very useful in gaining insights into the thermodynamic properties of a material.
Factors Influencing DSC
| Factors | Details |
| Instrumental factors | The parameters that characterize the operation setup include the furnace’s heating rate, the atmosphere within the furnace, the recording speed, the geometry of sample holders, the location of sensors, the sensitivity of the recording system, and the material of the sample container. |
| Sample characteristics. | Parameters: type and weight of the sample, size of the particle, solubility of evolved gases in the sample, heat of reaction, and thermal conductivity. |
Effects of Thermal History and Atmosphere on DSC analysis:
The majority of investigations carried out on the DSC instrument involve measuring melting points or glass transition temperatures. Still, due to the technique’s adaptability, they can also include a wide range of other tests.
It’s common practice to heat, extrude, and quickly cool some materials. Even if the material is not entirely equilibrated to a global minimum in energy, quick cooling locks the material’s structure in place. This material may take on a different structure, frequently at a lower energy level, if placed in the DSC device, heated, and then gently cooled. The “thermal history” of the sample is frequently cited as the cause of variations in melting points and glass transition temperatures after the material has been warmed.
The gas composition inside the calorimeter is one of the crucial elements, just like in TGA. The two environments in which analyses are most frequently conducted are inert nitrogen and oxidative air. Some sample types contain different routes or mechanisms that might be present in an oxidative environment but not in an inert environment.
Another common application of DSC is assessing a substance’s specific heat capacity, addressed by ASTM E1269 and ISO 11357-4. The definition states that specific heat capacity is “the amount of heat required to raise the temperature of a given mass of material to a certain amount.”
Sample Size
The sample size varies from 5mg to 20 mg depending on the type of test and requirements.
Result
The test adequately determines the material’s onset temperature, glass transition temperature, peak temperature, melting temperature, and thermal stability.
Conclusion
Differential scanning calorimetry is a technique of quantitative thermal analysis that measures heat flow and various thermodynamic properties such as melting, crystallization, and glass transitions. Information received on material stability, phase changes, or reaction kinetics creates a more detailed overview. DSC is an effective method of material characterization and quality control due to its ability to identify and separate samples by their unique thermal signature. Thus, it has emerged as an essential technology for manufacturers and industries to further their product quality.
FAQs
What is differential scanning calorimetry? DSC is a thermodynamical tool for directly assessing the uptake of heat energy in a sample during a regulated increase or decrease in temperature.
What is the difference between DSC and TGA? TGA measures a sample's weight change within a given temperature range. DSC measures heat flow as a function of temperature for a sample.
What is the basic principle of DSC? A technique involving measuring the difference in thermal energy applied to the sample and the reference material per unit of time as a function of the temperature so that their temperature is equalized; the temperature of the sample unit, formed by the sample and the reference material, is varied in a specified program.
What are the two types of DSC? DSC is classified into two types: heat-flux, power differential, and Multi-cell DSC. The heat flux DSC determines the heat flux difference between the sample and a reference. While, Multi-Cell DSC, and Power differential DSC measures the power supply difference between the sample and a reference.
What is the application of DSC? It has various applications, including determining glass transition temperatures, melting points, crystallization, heat capacities, degree of crystallinity, detection of impurities, and various research studies.
