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Thermal Analysis
Associate Professor Dr. Yupaporn Ruksakulpiwat
Thermal Analysis
ความหมาย หลกการ และ วธการ
กระบวนการวเคราะหทางความรอนโดย
Differential Thermal Analysis, DTA
กระบวนการวเคราะหทางความรอนโดย Thermogravimetry, TGA
Thermal Analysis
physical and/or chemical properties
are measured as functions of temperature and time
Specimens are subject to a defined temperature
program in special ovens at a defined gas
atmosphere (e.g., air, inert gases) whereby
corresponding heating or cooling curves are recorded.
Thermal analysis Structural changes (glass transition,
melting/crystallization, crosslinking,volatilization,
phase transitions in the solid and liquid state),
Mechanical properties (elastic behavior,
damping),
Thermal properties (expansion/shrinkage, specific
heat capacity, melting/crystallization temperature,
coefficient of expansion
Chemical reactions (decomposition and thermal
stability in different gaseous environments,
chemical reactions in solutions or liquid phase, reactions with the purge gas, dehydration).
Thermal Analysis Techniques
Differential Thermal Analysis (DTA)
การวดการเปลยนแปลงอณหภมของสารตวอยางเทยบกบสารอางองDifferential Scanning Calorimetry (DSC)
การวดการเปลยนแปลงความจความรอนของสารตวอยางเทยบกบสารอางองThermogravimetric Analysis (TGA)
การวดการเปลยนแปลงมวลเมออณหภมหรอเวลาเปลยนไปThermomechanical Analysis (TMA)
การวดการเปลยนแปลงขนาด เชน ความยาว หรอ สมบตหยนหนด(viscoelastic change)
Thermal Analysis Techniques
Dynamic Mechanical Analysis (DMA)
การวดการเปลยนแปลงความเคน ความเครยด รแลกเซชน (relaxation spectra)
DSC – Differential Scanning Calorimetry
DSC – Differential Scanning Calorimetry
for obtaining characteristic temperatures, such as melting temperature Tm and glass transition temperature Tg
caloric quantities,
such as specific heat capacity cp
morphology quantities, such as crystallinity
Proof of annealing and curing.
Heat flow dQ/dt to a specimen compared to a reference is measured.
Blend compatibility
Thermogravimetric Analysis (TGA)
Dynamic Mechanical Analysis (DMA)
Thermomechanical Analysis (TMA)
Applications Thermogravimetric Analysis (TGA)
- Degradation or thermal stability
- Plasticizer or solvent loss
Thermomechanical Analysis (TMA)
- dimensional changes, glass transition temperature
Tg and linear coefficient of thermal expansion
Dynamic Mechanical Analysis (DMA)
- a form of dynamic-mechanical analysis for
determining dynamic moduli and loss factor tanδ as
functions of test temperature and for establishing
transition temperatures
TOA – Thermooptical Analysis
for determining changes in crystalline
supermolecular structure
mostly using a hot-stage and a microscope.
Differential Thermal Analysis ( DTA)
andDifferential Scanning Calorimetry (DSC)
DSC devices
DSC devices are designed according to two basic
measuring principles:
- heat-flux calorimetry
- power compensation calorimetry.
Heat-flux calorimetry
sample and reference lie in a cylindrical oven.
Given thermal symmetry of the arrangement,
no temperature difference occurs between
pans when the oven is heated.
However, if the specific heat capacity of the
sample changes with elevated temperature,
a temperature difference arises, which
theoretically is proportional to the specific heat capacity.
Principle of Differential Thermal Analysis ( DTA)
power compensation calorimetry
Sample and reference are completely separated.
Sample and reference trays have their own heaters
and temperature sensors.
Sample and references are heated up at the same
rate with the aid of a control unit in such a way that
no temperature difference arises between them.
When the specific heat capacity of the sample
changes, more (in endothermic processes) or less (in
exothermic processes) heating power is transferred to the sample to avoid a temperature difference.
Differential Scanning Calorimetry (DSC)
S R
TS
TR
DTA = TS –TR
SDTA: TR is not measured but
calculated from the furnace
temperature
Sample run: TS
Blank run: no sample, TR
TF
If you run a sample and a blank:
DTA and DSC
Change in enthalpy and specific heat capacity
DSC Applications
DSC CURVE OF HDPE
DSC CURVE OF LLDPE
DSC CURVE OF PP
DSC CURVE OF PET
• Sampling
• Choosing a crucible
• The main goals of sample preparation
• Tips on DSC sample preparation
• Requirements for the crucibles
• Summary
How to run DSC experiments
• Is the sample representative for the material which has to
be analyzed (i.e. an average or typical sample)?
Standards ASTM E 105, E 122, DIN 83 803, company
internal instructions or procedures
• When taking a sample: do not modify the material (e.g.
through mechanical or thermal treatment).
• Is the sample clean?
• Are the tools used to take the sample clean?
• Storage of the sample
Sampling
Why do we need pans and “atmosphere control” ?
• to contain the sample
• to remove the sample
• to prevent contamination
• to control gas exchange, vaporization, reaction
• to define the heat path
• to obtain a desired catalytic effect (e.g. with copper pans and insulation materials)
• to prevent oxidation (inert gas)
• for specific oxidation (OIT)
Selection of pan and atmosphere
How much sample do you need ?
Most important: what do you want to measure ?
• Glass transition: typical mass 10 mg
• Melting/crystallisation: low samples masses are sufficient (1 mg)
• Specific heat: heat flow should be about 4 mW 30 mg
• Comparison good/bad: same sample mass
• Additives: depends on its concentration, usually rather
large sample masses (low contents)
• Decomposition: usually huge effect small sample mass
Examples :
• Normal case:
40 µl aluminum standard pan with pierced lid
• Peak separation:
light 20 µl aluminum crucible with helium as purge gas
• Sample possibly reacts with Al:
medium pressure crucible
high pressure gold-plated crucible (standard for safety investigations)
glass crucible (up to 500 °C, max. 5 MPa; furnace expander)
gold crucible
Choice of crucible
Most important: good heat transfer
How to prepare samples
Good thermal contact between sample and crucible to minimizetemperature gradients within the sample.
• Solid samples: flat, if possible uniform thickness
• Powder: press gently into the crucible with a Teflon rod. Make sure the bottom of the crucible remains flat.
• Hard, coarse samples: grind in a mortar. Be careful with polymorphous samples. Grinding can cause a transition.
• Pastes, waxes: transfer to the crucible using a spatula, and then gently press with a Teflon rod.
• Liquids: use a syringe, spatula or needle (depending on the viscosity); deposit the sample in the middle or on the inside edge of the crucible
• Fibers: if possible cut into small pieces, which fit into the crucible; possibly pack in aluminum foil and press together gently before the sample is put in the crucible; if the fiber cannot be cut, wind it round the end of a pair of tweezers and then pack it into aluminum foil.
How to prepare samples
• With strongly exothermic samples (e.g.
explosives): dilute the sample in an inert
substance (e.g. aluminum oxide).
• With sequential measurements or comparison
measurements: always use the same amount of
sample, the same pretreatment, the same batch
of sample and identical storage conditions.
• With samples that contract or roll up: use a 20 l
crucible, or in the 40 l crucible use the lid of a 20
l aluminum crucible.
How to prepare sample (continued)
Temperature program
General types:
• Dynamic heating/cooling
• Isothermal
Parameters:
• Start- and end-temperature
• Heating rate (dynamic)
• Time (isothermal)
• Period, amplitude
Temperature program (continued)
Heating rate
high heating rate large DSC signal, poor resolution
larger temperature gradients within the sample
low heating rate small DSC signal, good resolution
Start temperature: if possible at least 3 min before the first event
End temperature: if possible at least 3 min after the event
Example: heating rate 10 K/min, first event at 50°
start temperature < 20°C
Amyl alcohol 1=crystallization
2=melting 3=boiling
Amyl alcoholcrystallization
meltingboiling
Tg
Tc
TmTd PET
Iron soild-solid
transition- - -fusio
n
Slow heating=various reorganization process and fusion of
perfect crystal
One type of small metastable crystal
Fast heating=super heating=very broad melting peak
Reference
Polymer Characterization - Laboratory
Techniques and Analysis
By: Cheremisinoff, N.P. © 1996; William
Andrew Publishing/Noyes
Rapra Collection of DSC Thermograms of
Semi-Crystalline Thermoplastic Materials
By: Price, C.D. © 1997; Rapra
ThermogravimetricAnalysis, TGA
TGA application
ตวอยางการใชกาซไนโตรเจนและกาซออกซเจน
ตวอยางการใชกาซไนโตรเจนและกาซออกซเจน
ตวอยางการใชกาซไนโตรเจนและกาซออกซเจน
ถวยใสสารทดสอบ ( Crucible)
มรปราง ขนาดตางๆกน
ตองไมท าปฏกรยากบสารทดสอบ
ท าจากวสดไดหลายชนด
ชนดของถวยใสสารทดสอบAlumina - 70 l, 150 l, 900 l, reusable
- inert against most samples - melting point >1700 °C
Platinum - 30 l, 70 l, 150 l, reusable - use a sapphire disk between crucible and
sample if you go above 1000 °C (otherwise crucible and sample holder glue together)
- good SDTA-signals (heat transfer) - may act as a catalyst - melting point 1770 °C
Aluminum - 40 l, 100 l - melting point 660 °C - good SDTA-signals
Sapphire - 70 l, reusable - inert against most samples - melting point >1700 °C
Critical points: - reaction with the sample
- melting point
การวางภาชนะส าหรบใสสารทดสอบ
ตวอยางเครอง TGA
ตวอยางเครอง TGA
Water cooling
Gas
outlet
Gases
Reactive
Protective
Purgee
The TGA/SDTA851e
ปจจยทอาจมผลตอผลการทดสอบ
อตราการใหความรอน
สารทดสอบ (มวล รปราง และ การเตรยม)
ถวยใสสารทดสอบ ( วสด มวล ลกษณะรปราง)
อากาศในเตาเผาและอตราการไหลเวยนของกาซ
The higher the heating rate the lower thetemperature resolution, i.e. the separationof overlapping effects becomes worse.
The lower the heating rate the longer themeasuring time and the lower the weightloss per unit time.
Typical heating rate: 10 K/min to 30 K/min
อทธพลของอตราการใหความรอน
อทธพลของอตราการใหความรอน
อทธพลของมวลสารทดสอบ
อทธพลของภาชนะใสสาร (Pan)
การชงน าหนกสาร (Weighing in samples)
Weighing in on an external balance
Weighing in on the TGA-balance
Automatic weighing in (pan and sample)
Note: if the mass of the pan and an initial sample mass are indicated, the TGA curve starts at the total current mass (pan+sample) minus the mass of the pan. In this case, the TGA-curve does not necessarily begin at 100 %.
To prevent e.g. loss (or uptake) of moisture during the time before the experiment is started you should seal your pan (only for aluminum pans) and let the sample robot pierce the lid before the experiment begins.
What is essential
• a well thermostatted instrument (otherwise you will observe drifts !)
• good contact of the sample to the pan (SDTA)
• blank curve
• constant protective gas flow through the instrument
Tips and tricks
• use a pierced lid to shift e.g. evaporation reactions
• use an inerst sample as reference for the blank
• use whenever possible aluminum pans (SDTA)
• use not more sample than necessary; heat clean from time to time
the furnace (thermocouples).
How to proceed• Warm-up“ of the instrument
• Calibration check (weekly or if any changes at the instrument have
been
made)
• Check delivers a negative result: check the check
• Instrument needs to be adjusted
- Manual adjustment (use the results of the calibration)
- predefined adjustment procedures:
Single temperature
Single Sample holder ‚calibration‘
Total ‚calibration‘
• Check the new calibration
• The thermocouples may be poisoned by e.g. carbon heat cleaning
• Blank curves to judge the performance of the balance (noise)
What are the smallest weight losses that
can be measured with the
thermobalance?
• Noise: typically about 0.5 – 1 g (RMS)
• Blank: reproducibility 5 g @ 500 °C and 10 K/min
• Drift: typically 5 g/h
To identify a weight step, the weight change should be at least twice as large as
the peak-to-peak noise. The peak-to-peak noise is about 2 g. For unambiguous
identification, the weight change should therefore be at least
4 g.
Determination of residues (ash)
In this case, the reproducibility of the blank curve and the amount
of sample are critical.
Task
An ash content of approx. 1% should be determined with a
relative accuracy of 1%, i.e. 0.01% ?
What sample weight is needed?
Answer
• Assumption: reproducibility of the blank curve 10 g
• 1% accuracy residue must be 1 mg
• the sample must therefore weigh 100 mg.
Applications of TGA
Moisture content
ตวอยาง TGA curve ของ พอลเมอรชนดตางๆ
ตวอยาง TGA curve ของ พอลเมอรชนดตางๆ
ตวอยางการใช TGA ในการหาสภาวะทางความรอนทเหมาะสมในการสงเคราะหสารบรสทธ
ชวงทน าหนกคงท คอ ชวงทสารประกอบแคลเซยมจะเสถยร
ตวอยาง TGA curve