8. Thermal analysis
4 important aspects when choosing crucible:
- provide the best thermal conductivity - fit required temperature range - no interaction with the specimen! - price.
Advantages of Simultaneous Thermal Analysis (STA):
- time effective; - expensive sample material can be saved; - direct comparison of TGA and DSC possible - same measurement conditions on exactly the same sample; - exact determination of enthalpy changes (sample mass continuously monitored - enthalpy recalculated).
Thermogravimetry analysis (TG or TGA)
A technique by which the mass of the sample is monitored as a function of temperature or time, while the sample is subjected to a controlled temperature program in a specified atmosphere
Differential Scanning Calorimetry (DSC)
A technique which measures the energy difference between a substance and a reference material in function of temperature or time when both, sample and reference, follow a controlled temperature program.
Differential Thermal Analysis (DTA)
A technique which measures the temperature difference between a substance and a reference material in function of temperature or time when both, sample and reference, follow a controlled temperature program.
Advantages & disadvantages with TMA:
Advantages: - flexible sample load; - tension mode possible; Disadvantages: Handling more difficult Limited temperature range
Advantages & disadvantages with Dilatometry (DIL):
Advantages: - wide temperature range - easy handling - high accuracy - flexible sample geometry Disadvantages: - limited load range - no tension mode
In the DSC graph, we can we a part of the TS line where it is flat, why is it flat?
Because this is where the sample melts.
Micro-calorimetry (μ-DSC)
Can be used on very small specimen.
Difference between DIL and TMA:
DIL: measures a dimension TMA: measures the deformation
Difference between DSC and DTA?
DSC measures energy difference, while DTA measures temperature difference. Also: - DSC have surface contact between sensor and crucible - DTA have point contact between sensor and crucible
If we want to determine specific heat or determine the tranformation enthalpy, which method is optimal?
DSC, since the crucible is welded to the surface we get better values. Heat conductivity is important in DSC.
What kind of information can we get from the peaks in the DTG curve?
Decomposition temperatures for different elements
If we apply TGA and DSC together, what do we get?
Simultaneous Thermal Analysis (STA)
In a TGA, the TG curve is plotted and its derivative according to time. What does TG and its derivate show?
TG = %mass left, DTG =how fast the mass changes in %min
Difference between peaks when we cool something compared to when we heat them?
The peaks will appear at somewhat lower temperatures when cooling.
In DSC, which three temperatures do we measure?
Tr = Room temperature Ts = Sample temperature Tf = Furnace temperature
Can TG increase?
Yes if oxidation occurs etc.
Dilatometry (DIL):
a technique in which a dimension of a substance under a negligible load is measured as a function of temperature while the substance is subjected to a controlled temperature program.
TMA - Thermomechanical Analysis:
a technique in which the deformation of a substance under a static (non-oscillatory) load is measured as a function of temperature while the substance is subjected to a controlled temperature program.
We can optimize sintering processes with DIL. What is sintering?
the process of compacting and forming a solid mass of material by heat or pressure without melting it to the point of liquefaction.
If we change the heating rate in a TGA, what happens? and how can we use this information
we get a peak shift - allows determination of theactivation energy and so type of the reaction
