differential scanning calorimetry (DSC)
As one of the most important methods for thermal analysis, using differential scanning calorimetry (DSC) it is possible to characterise not only the thermal characteristics of a sample, the temperature at which certain phase transitions of a substance occur can also be determined.
Table of contents
What is differential scanning calorimetry (DSC)?
Differential scanning calorimetry – (DSC) is a thermal measurement method. It provides information about the amount of heat absorbed or emitted by a sample in isothermic conditions during heating or cooling. Consequently it measures, along with the endothermic and exothermic transitions, also the transformation temperatures and enthalpy of a sample in varying thermal conditions.
Differential scanning calorimetry (DSC) at Quality Analysis
Polymers and other plastics must withstand varying conditions so they can be used safely. Whether they meet the requirements is determined during a test on the plastic; this test is undertaken by a qualified test laboratory such as Quality Analysis. Our experts from chemical analytics determine parameters that characterise the thermal properties of your material, e.g. glass transition temperature and melting point, enthalpies, degree of crystallinity, as well as the specific heat capacity, using differential scanning calorimetry. The characteristics of the material are measured while strictly complying with all applicable standards.
The state-of-the-art analyser Netzsch DSC 204 F1 Phoenix our experts utilise for the thermal analysis provides informative results and covers a temperature range from -180 °C to 700 °C. The device also has highly sensitive thermal sensors made of nickel-chromium constantan. As a result the sensors have a particularly high calorimetric sensitivity and can deliver very accurate results.
What are the measuring principles of differential scanning calorimetry?
During differential scanning calorimetry, a crucible (container) with the sample and an empty crucible as a reference are subjected to the same temperature program. The DSC measurement is undertaken using a device that can heat or cool the samples to the required temperature and that monitors any temperature changes with very high precision. Due to the heat capacity of the sample, endothermic or exothermic processes or material state changes occur, that is phase transitions such as melting or sublimation. The heat flux characteristics of the sample can thus be measured as a function of the temperature.
Because thermal energy flows into or out of the related processes, there are temperature differences between the sample and the reference. This temperature difference is used as a measurement signal for the older differential thermal analysis (DTA). With the newer analytical method DSC, the heat flux derived from the temperature difference is used as the measurand.
There are two methods for determining the heat flux during DSC, heat flux differential scanning calorimetry and power compensating differential scanning calorimetry.
Heat flux differential scanning calorimetry
During heat flux DSC, the enthalpy changes (heat flux) in a sample are calculated by integrating the ΔT-TRef curve. For this purpose sample and reference must be in an oven on a disc-type measuring system with good thermal conductivity. Under the disc there are sensors that measure the heat that flows through the sample and reference. If the sample and reference emit the same heat to the disc, heat fluxes of the same magnitude are flowing through them. In this situation the heat flux differential is zero. However, if the sample changes, e.g. due to sublimation or melting, during the execution of the temperature program, the heat emitted also changes and there is a difference in the heat flux. The heat flux differential is always proportional to the temperature difference (ΦFP-ΦFR ~ ΔT, where ΦFP is the heat flux in the sample and ΦFR the heat flux in the reference and ΔT the difference in the temperature).
Power compensating differential scanning calorimetry
With this method the sample and reference are placed in two different, thermally insulated ovens. The ovens are adjusted such that the temperature is the same. It is now measured how much electrical energy is required to maintain the temperature in the ovens; the energy is acquired as a function of the temperature.
Applications
Differential scanning calorimetry (DSC)
The many different applications are a reason for the frequent use of DSC.
As such differential scanning calorimetry is used in the following areas, among others:
- Plastics analytics
- Polymer chemistry
- Cell biology
- Pharmacology
- Nanoscience
- Foodstuff analytics
Which materials can be analysed using DSC?
The possibilities for analysing different materials are as varied as the applications and the information content of DSC:
- Solids (e.g. polymers, metals, base materials)
- Powders
- Fibres
- Viscous samples (e.g. creams)
- Liquid samples
Which information does DSC provide?
DSC determines parameters for the characterisation of the thermal properties of a sample, e.g.
- The characteristic temperatures for the glass transition and melting area
- The crystallisation behaviour
- Enthalpies (heat of fusion, heat of crystallisation, heat of transformation and heat of reaction)
- Specific heat capacity
- Oxidation stability
These characteristics provide meaningful information about the sample, for instance:
- Degree of curing/curing state of adhesives
- Material identity and formulation components
- Modification and additional components
- Material composition
- Purity and contamination
- Thermal history
- Degree of crystallinity
- Phase transitions
