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Differential Scanning Calorimetry (DSC)
Specifications
Differential Scanning Calorimetry (DSC) is a thermal analysis technique which measures the amount of heat that is necessary to change the temperature of a sample (relative to a reference material). In this technique, the temperature of the sample is increased linearly, and the amount of heat required to maintain this temperature ramp is measured. This can be used to gain significant understanding of the thermal and thermo-dynamic properties of the materials under analysis.
The simplest application of DSC is to measure heat capacity (or specific heat). This is a fundamental thermal property of a material or composite. Using laser flash, we can measure a material's thermal diffusivity. We can convert diffusivity to thermal conductivity using the formula: Thermal conductivity = Cp (heat capacity) * Thermal Diffusivity * Density.
When materials undergo phase transitions, the material may absorb (endothermic transition) or emit heat (exothermic transition). These transitions show up as positive (exothermic) or negative (endothermic) heat flow peaks in a DSC scan. Examples of phase transition probed with DSC includes: melting, freezing, vaporizing, condensing, crystal structure changes, and glass transitions. The DSC peak allows identification of the phase transition type, onset temperature and peak width.
Some specific examples of applications of DSC:
- As discussed below, DSC can be used to measure heat capacity Cp, a critical component in thermal conductivity measurements. This is much more accurate than using the laser flash equipment to estimate Cp.
- The glass transition temperature of a polymer can be measured which is key to understanding mechanical and thermal expansion properties.
- The shape of a melting curve can be measured. This is a critical property of understanding solder behavior. Solder melt and then dissolve adjacent metal forming intermetallic compounds. Both the melting and reaction of the solder with metallization can be analyzed in a DSC as a function of temperature to help design optimum solder re-flow profiles (for a specific metallization).
Temperature & Enviromental Options
Samples can be tested at temperatures from -40°C to 350°C in either an air, nitrogen, or argon enviroment.
Accuracy & Repeatability
- Temperature accuracy +/- 0.1°C
- Temperature precision +/- 0.01°C
- Enthalpy percision +/- 0.1%
Materials Analyzed
- Ceramics (AlN, Alumina, BeO, etc)
- Ceramic composites
- Metals
- Metal matrix composites
- Semiconductors
- Glasses and other dielectrics
- Sapphire and diamond
- Plastics (with and without fillers)
-Polymers (with and without fillers)
Thermal Conductivity & Diffusivity
Measurement Range
CMC's Laser Flash system covers the widest measuring range of all techniques, 0.1 up to 2000W/m*K for Thermal Conductivity and 0.01 up to 1000 mm2/s for Thermal Diffusivity.
(Values may vary for special applications)
Standard Compliance
All DSC runs are calibrated agaisnt the following NIST Standards.
- Temperature Calibration: Indium
- Cp Calibration: Sapphire
(DSC) Specific Heat Capacity Analaysis for Laser Thermal Conductivity
Specific Heat Capacity (Cp) is the amount of heat required to raise the temperature of one gram of a particular material one kelvin of temperature. Specific Heat Capacity is due to the molecular motion in a material (units of J/g K).Heat capacity is the amount of heat required to raise the temperature of a material one kelvin of temperature. This is unnormalized specific heat (units of J/K).Specific heat is the specific heat capacity of an analyte compared to the specific heat capacity of a reference material (dimensionless). Crystalline polymers contain more order and thus fewer degrees of molecular motion. Less molecular motion results in lower specific heat capacity. Changes in heat capacity as revealed from a DSC curve gives information about phase changes.
Thermal Diffusivity = α = 0.1388 L2/ t1/2m2/s
Thermal Conductivity = k = Cp p α
Cp = Heat Capacity p = Density
Other examples of uses of Differential Scanning Calorimetry (DSC):
Glass Transitions: A reversible change of the amorphous region of a polymer from, or to, a viscous or rubbery condition to, or from, a hard and relatively brittle one. The glass transition temperature is a temperature taken to represent the temperature range over which the glass transition takes place. Glass transition temperature is highly relevant for amorphous material as it is a valuable indicator of stability. Thus, DSC can be used in determination of crystallinity of a sample.
Melting and Boiling Points: The endothermic transition upon heating from a crystalline solid to the liquid state. This process is also called fusion. The enthalpy of melting is the heat energy required for melting, i.e. for breaking down the crystalline lattice. This is calculated by integrating the area of the DSC peak on a time basis. A sharp well defined melting peak corresponds to at well defined crystal structure. Changes in melting temperature and energy gives information about, for instance, content of amorphous material. Thus, the melting endotherm can be used for determination of purity of the sample.
Crystallization time and temperature: Melting is a one-step process while crystallization involves nucleation and crystal growth. Nucleation will be dependent on cooling rate, whereas the melting point is unaffected. Cooling at different rates might lead to discovery of new polymorphic forms.
Percent crystallinity/purity: Only crystalline material has a melting endotherm, i.e. a temperature where the lattice breaks down. If a material contains amorphous material – or other impurities, it will lead to a lowering of the melting point + a reduction in the melting enthalpy. Further, content of amophous material will give rise to a glass transition.
Relative stability of different crystalline forms: Endothermic or exothermic transitions between different crystalline forms (polymorphs) of the same material provide information about their relative stability: From the DSC curve it is possible to reveal whether you have monotropy (one stable form at all temperatures) or anisotropy (a change in relative stability at a given temperature below the melting temperature)