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