DSC METHOD Flashcards
TGA
• Measurement of changes in sample mass with temperature
• temperature is increased at constant rate for known initial weight of sample and change in weight is recorded with time at different interval time
DTA
• Difference in temperature between a substance and a reference material is measured as a function of temperature
• Both sample & reference material heated in controlled condition.
• If any reaction (physical or chemical changes ) takes place, temperature difference (∆T) will occur between sample & reference material.
DSC
Heat flow rate (power) to the sample is monitored against time or temperature, while the temperature of the sample, in a specified atmosphere, is programmed
Principle of DSC
• It is measure heat into or out of sample.
• Differences in heat flow occur with the occurrence of
two major events
1)The heat capacity of the sample which increases with temperature
2) Transitions occur
• During heating, two types of reactions can be take place:
endothermic and exothermic
Mechanism of DSC
• During a thermal event in the sample, the system will
transfer heat to or from the sample pan to maintain the
same temp. in reference and sample pans.
• In endothermic reaction, more energy needed to
maintain zero temp difference between sample &
reference. E.g. Melting, boiling, sublimation, vaporization
• While in exothermic reaction, less energy needed E.g
crystallization, degradation, polymerization
Instrumentation of DSC
1) POWER-COMPENSATION DSC
2) HEAT-FLUX DSC
The comparison of Heat Flux DSC & Power Compensation DSC (HF DSC)
1) Sample holder; Platinum, Aluminum, and Stainless Steel
2) Sensor: Temperature sensor
3) Furnace: One block for both reference & sample cell
The comparison of Heat Flux DSC & Power Compensation DSC (PC DSC)
1) Sample holder: Platinum, Aluminum, and Stainless Steel
pans
2) Sensor: Platinum resistance thermocouple
3) Furnace: Separate block for both reference & sample cell
Heat Flux DSC
1) The sample and the references cells are heated at a constant rate and thermocouples are used to detect the temperature difference between sample side and reference side using single mass furnace
2) The furnace acts as an infinite heat sink to provide/absorb heat from thee sample
3) Nitrogen is the commom gas
4) Alternate: Helium or Argon
Power Compensation DSC
1) It directly measures heat flow between sample side and reference side using 2 separate low mass furnaces
2) This individual furnace use different amount of power to maintain a constant change of temperature between the sample and the reference
3) Advantages: Faster heating & cooling and better resolution
4) Platinum resistance thermomoters track the temperature variations for the sample and reference cells
5) Holes in the compartment lids allows the purge gas to enter and contact the sample and references
Sampling (DSC)
• ACCURATELY-WEIGH SAMPLES (~3-20 MG)
• SMALL SAMPLE PANS (0.1 ML) OF INERT OR TREATED METALS (AL, PT, NI, ETC.)
• SEVERAL PAN CONFIGURATIONS, E.G., OPEN, PINHOLE, OR
HERMETICALLY-SEALED (AIRTIGHT) PANS
• THE SAME MATERIAL AND CONFIGURATION SHOULD BE USED FOR THE SAMPLE AND THE REFERENCE
• MATERIAL SHOULD COMPLETELY COVER THE BOTTOM OF THE PAN TO ENSURE GOOD THERMAL CONTACT
Factors effecting to thermal analysis
Instrumental
• Furnace Heating rate : Increase heating rate, increase decomposition
• Furnace atmosphere: pure inert gas like nitrogen
Sample Characteristics
• Sample size
• Weight of sample
Factors effecting to thermal analysis
Instrumental
• Furnace Heating rate : Increase heating rate, increase decomposition
• Furnace atmosphere: pure inert gas like nitrogen
Sample Characteristics
• Sample size
• Weight of sample
