Definition
Differential scanning calorimetry is a thermal analysis instrument used to measure the change of heat flow difference between a sample and a reference object with temperature or time during the temperature control process. This technology can quantify the thermal effects that occur during the heating or cooling process of substances, such as phase transitions, melting, crystallization, and chemical reactions, providing key data for the study of thermal properties of materials.
Principle
The differential scanning calorimeter works on the principle of thermal equilibrium. The instrument contains a sample crucible and a reference crucible, both placed in the same temperature environment. In the process of program temperature control, when the thermal effect of the sample occurs, the system adjusts the heating power to keep the sample consistent with the temperature of the reference, and the compensated power difference corresponds to the change of heat flow of the sample. The heat flow difference is directly related to the change of heat capacity or the enthalpy of the change of the sample, and its basic relationship can be expressed as:
ΔQ = dH/dt
ΔQ is the heat flow difference, and dH/dt is the change of enthalpy per unit time. By recording the functional relationship between heat flow difference and temperature or time, the differential scanning calorimetry curve can be obtained.
Measurement method
Differential scanning calorimetry usually includes the following steps: first, place the appropriate amount of sample and reference material in the corresponding crucible of the instrument; secondly, set the temperature range, heating rate and atmosphere conditions; Then start the program, and the instrument synchronously records the heat flow difference between the sample and the reference. Finally, the obtained curves are analyzed, and the thermodynamic data are calculated through characteristic parameters such as peak area, peak temperature and baseline change. Measurements should be carried out in accordance with relevant standards, such as ASTM E967, to ensure the comparability and accuracy of the results.
Influencing factors
The results of differential scanning calorimetry are affected by a variety of factors. Sample characteristics, including sample quality, particle size, and uniformity, can affect heat conduction and thermal response. In the instrument parameters, the selection of heating rate is particularly critical, and higher rates may lead to thermal hysteresis, which shifts the transition temperature to high temperature. Lower rates can improve resolution but may reduce detection sensitivity. Atmospheric conditions such as gas type and flow rate can also affect certain reaction processes. In addition, crucible material and tightness, baseline stability, and instrument calibration status are all factors to control.
Application:
Differential scanning calorimeters are widely used in many industrial and scientific research fields. In the field of polymer materials, it is used to determine the glass transition temperature, melting temperature, crystallinity and curing behavior. In the research of energy materials, the heat storage characteristics of phase change materials and the thermal stability of battery materials can be analyzed. In food science, it is useful for studying processes such as oil crystallization and protein denaturation. In addition, in the chemicals and coatings industry, the technology can be used to evaluate purity, compatibility, and reaction kinetics. These applications rely on accurate characterization of the thermal properties of materials.
Selection
When choosing a differential scanning calorimeter, a number of technical indicators should be comprehensively considered. The temperature range should cover the expected transition range of the material to be tested. Sensitivity and resolution directly affect the ability to detect weak thermal effects. The heating rate range and control accuracy are important for dynamic research. The instrument should have good baseline stability and repeatability. The atmosphere control system needs to meet the requirements of the experimental environment. In addition, software functions should support data collection, analysis, and report generation, and meet relevant standards. Users should evaluate the performance and reliability of the instrument based on specific application needs.