Setline STA Practical Work Experiments · 2020. 9. 14. · 1. INTRODUCTION This Practical Experiments booklet relates to operations with the SETLINE® STA or STA+. It is designed

CONTENTS

1. INTRODUCTION ............................................................................................. 3

2. DEFINITIONS AND VOCABULARY ............................................................... 32.1. THERMOGRAVIMETRIC ANALYSIS (TGA) ............................................... 42.2. DIFFERENTIAL SCANNING CALORIMETRY (DSC) ............................... 42.3. VOCABULARY ................................................................................................. 4

3. PRACTICAL EXPERIMENTS AND DATA PROCESSING ............................. 43.1. Thermal decomposition of calcium carbonate (CaCO3) ............................ 5

3.1.1. Presentation .......................................................................................... 53.1.2. Testing ................................................................................................... 53.1.3. TG data treatment ................................................................................ 6

3.2. Thermal decomposition of CaC2O4, H2O ..................................................... 83.2.1. Presentation .......................................................................................... 83.2.2. Testing ................................................................................................... 83.2.3. TG and DSC data treatment ............................................................. 10

3.3. Thermal decomposition of CaC2O4, H2O under air .................................. 113.3.2. TG and DSC data treatment ............................................................. 12

4. QUIZ ANSWERS ............................................................................................... 15

1. INTRODUCTION This Practical Experiments booklet relates to operations with the SETLINE® STA or STA+. It is designed for people discovering Simultaneous Thermal Analysis as well as for students wanting to become familiar with this technique.

Note that some reference will be made to the user’s instrument manual, especially to the paragraphs dealing with temperature correction and enthalpy calibration of the sensor.

For more in-depth information about STA applications, the user may also refer to the following books:

§ Thermal Analysis, Bernhard WUNDERLICH , Academic Press (New York ), 1990

§ Thermal Analysis : Techniques and Applications, E.L. CHARSLEY et S.B. WARRINGTON , Royal Society of Chemistry ( UK ), 1991

§ Handbook of Thermal Analysis and Calorimetry - Principles and Practice - Vol1, Michael E. BROWN, Elsevier ( Pays Bas ), 1998

§ Calorimetry and thermal methods in Catalysis, Aline AUROUX, Springer, 2013

§ Thermal Characterization of Polymeric Materials, Edith TURI, 2nd edition, Academic Press (USA), 1997

§ Thermal Analysis of Pharmaceuticals, Duncan Craig, CRC Press 2007

§ Calorimetry in Food processing, Gönul KALETUNC, Wiley-Blackwell, 2009

§ Biocalorimetry, J. E. LADBURY et B. Z. CHOWDHRY, Wiley, 1998

2. DEFINITIONS AND VOCABULARY Simultaneous Thermal Analysis, or STA, is a combination of Thermogravimetric Analysis (TGA) and of Differential Thermal Analysis (DTA) or Differential Scanning Calorimetry (DSC). SETLINE STA being a combined TG-DSC, the present document will focus on this technique.

The definitions and vocabulary used in this chapter have been published by the International Confederation for Thermal Analysis (ICTA) in a compilation entitled For Better Thermal Analysis and Calorimetry (John O. Hill, Editor).

The definitions concur with the ISO standards published by the International Standardization Organization.

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2.1. THERMOGRAVIMETRIC ANALYSIS (TGA)

Thermogravimetric analysis is a technique in which the mass of a sample is measured as a function of time or temperature when the temperature of this sample is scanned in a controlled atmosphere.

2.2. DIFFERENTIAL SCANNING CALORIMETRY (DSC)

Differential Scanning Calorimetry is a technique in which the heat flow (thermal power) of the sample is measured as a function of time or temperature when the temperature of this sample is scanned, in a controlled atmosphere.

In practice what is measured is the difference in heat flow between a crucible containing the sample and a reference crucible (the latter is generally empty, but may also contain a material which is thermally inert in the temperature range being studied).

2.3. VOCABULARY

• The symbol T is used for the expression in Celcius degrees (°C) orKelvin (K).

• The symbol t is used for the expression in seconds (s), minutes (min) orhours (h).

• The symbols m for mass and W for weight are recommended.• The heating (or cooling) rates are expressed by the derivative dT/dt. In

practice, as this involves an average value during heating, it isrepresented by β and is expressed in °C. min-1 or K. min-1.

• The ordinate of the DSC curve corresponding to the difference in heatflow is expressed as d(ΔQ)/dt rather than dH/dt, as Q is a heat quantitywhile H is a heat content. The difference in heat flow is expressed inmilliwatts (mW).

3. PRACTICAL EXPERIMENTS AND DATA PROCESSINGVarious practical experiments are given as a way of getting to know the STA method, using the various applications and working with the main items of data processing such as determining mass changes, temperatures and heat of the corresponding effects, etc. Moreover, questions are asked to the reader in order to familiarize with the interpretation of the signals, for example to help attributing reactions to mass changes.

Each practical application is distinguished by:

• How the application is represented• How the test is carried out• How use is made of the mass variation and HeatFlow signals

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• How data are processed

Remark 1 : It is considered that temperature correction and enthalpy calibration of SETLINE® STA or STA+ have already been performed according to the recommendations of the user’s manual.

Moreover, it is vital to respect the instructions of the user’s manual, especially as far as the use of crucibles is considered.

3.1. THERMAL DECOMPOSITION OF CALCIUM CARBONATE (CaCO3)

3.1.1. Presentation

Calcium carbonate CaCO3 decomposes in calcium oxide CaO releasing carbon dioxide CO2 and thus leading to mass loss.

CaCO3 (s) ↔ CaO (s) + CO2 (g)

MCaCO3 = 100.09 g.mol-1

MCaO = 56.08 g.mol-1

MCO2 = 44.01 g.mol-1

Quiz 1: Calculate the theoretical mass loss in weight percent due to this decarbonation !

3.1.2. Testing

Take about 30 mg of calcium carbonate and weigh the sample precisely inside a 90 µl alumina crucible (S08/GR.29467, Diam 3.8 mm, Height 7.3 mm). Place the crucible on the measurement side of the sensor with the help of the ergonomic handle of SETLINE STA (right side of the sensor), or using the autosampler of the SETLINE STA+. An empty alumina crucible of same dimensions will be used as a reference.

Close the SETLINE® STA or STA+ furnace using the furnace control buttons.

Start flowing air at a rate of approximately 15 ml per minute.

Using CALISTO acquisition software, enter the sample mass and program the following temperature profile:

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Heating zone 1

• Start temperature : ambient (≈ 20 °C) • End temperature : 1 000 °C • Scanning rate : 10 °C.min-1

Cooling zone 1

• Sequence 1, scanning• Start temperature : 1 000 °C • End temperature : 20 °C • Scanning rate : 30 °C.min-1

• Sequence 2, isothermal• Temperature : 20 °C • Duration : 30 minutes

Heating zone 2

• Same as heating zone 1

Cooling zone 2

• Same as cooling zone 2

Then start the experiment.

Note that the heating/cooling cycle is repeated once to check that the substance has completely reacted. The second heating zone will be used as a baseline or “blank” experiment.

3.1.3. TG data treatment

Open the saved experiment file using CALISTO Processing.

Display the signal acquired during the first heating zone.

If necessary, plot the mass variation (TG) signal as a function of Temperature by right clicking on the X-axis and selecting “Switch to Sample Temperature”.

Plot the mass variation (TG) signal in percent (%) by right clicking on the TG axis, selecting “Units” and “Display from Zero Percent”.

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Then, it is necessary to subtract the blank experiment (heating zone 2) from the displayed TG signal. For that purpose, in the treeview on the left side of the screen, right click on the zone name corresponding to the first heating zone. Select “Blank Experiment Subtraction” and “Browse…”. A new window opens. It lists all the saved experiments with zones having temperature profiles identical to the one of Heating zone 1. Select your Heating Zone 2 in the list and click OK. The newly displayed TG curve is blank subtracted.

Remark 2 : blank subtraction in thermogravimetric analysis is made necessary because of the so-called buoyancy effect. The buoyancy force (FB in Figure 1 below) is physical phenomenon acting on the rod, crucible and sample of an STA instrument, whatever the thermobalance used. The buoyancy force is proportional to the volume occupied by the rod in the furnace, crucible and sample, and it is also proportional to the density of the flowing gas. So when temperature or gas type changes during the experiment, the density changes, the buoyant force changes, affecting the mass variation (TG) signal, with apparent mass changes as seen on the curves showed on Figure 2 below. This effect can be subtracted by a blank experiment or directly compensated in a symmetrical TGA system.

Figure 1 - Representation of the buoyant forces (FB)

Figure 2 - Simulated mass variations dues to the change of buoyant forces for various gases

Under the tested conditions, decarbonation starts at about 600°C and stops at about 850°C. To determine the corresponding mass variation, click on the TG curve. Select the TG tab in the menu and click on the “Mass change” function.

Select the start and end temperatures of the mass variation and display only the mass variation in % and the temperature at the inflexion point Tinf. On figure 3, the obtained values are 43.5% and 833.7°C respectively.

Quiz 2: If the same experiment was run under a flow of CO2 instead of a flow of air, what would be the impact on the temperature at the inflexion point Tinf ?

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Figure 3: Analysis of a calcium carbonate sample

3.2. Thermal decomposition of CaC2O4, H2O

3.2.1. Presentation

Calcium oxalate CaC2O4 exists in a hydrated form named calcium oxalate monohydrate or CaC2O4, H2O.

When heated, it goes through three reactions leading to the release of one molecule of water, one molecule of carbon dioxide and one molecule of carbon monoxide. The experiment will help at identifying these successive decomposition steps.

3.2.2. Testing

Take about 40 mg of calcium oxalate and weigh the sample precisely inside a 90 µl alumina crucible (S08/GR.29467, Diam 3.8 mm, Height 7.3 mm). Place the crucible on the measurement side of the sensor with the help of the ergonomic handle of SETLINE STA (right side of the sensor), or using the autosampler of the SETLINE STA+. An empty alumina crucible of same dimensions will be used as a reference.

Close the SETLINE® STA / STA+ furnace using the furnace control buttons.

Temperature (°C)10009008007006005004003002001000

Mas

s lo

ss (%

)0

-5

-10

-15

-20

-25

-30

-35

-40

-45

Δm (%) -43.5 Tinf : 833.7 (°C)

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Start flowing nitrogen at a rate of approximately 100 ml per minute for 20 minutes and decrease the flow rate to about 15 ml per minute. It aims at clearing off the oxygen from the SETLINE STA / STA+ furnace.


Heating zone 1

• Start temperature : ambient (≈ 20 °C) • End temperature : 900 °C • Scanning rate : 10 °C.min-1

Cooling zone 1

• Sequence 1, scanning• Start temperature : 900 °C • End temperature : 20 °C • Scanning rate : 30 °C.min-1


Heating zone 2


Cooling zone 2




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3.2.3. TG and DSC data treatment





Then, it is necessary to subtract the blank experiment (heating zone 2) from the displayed TG signal. For that purpose, in the treeview on the left side of the screen, right click on the zone name corresponding to the first heating zone. Select “Blank Experiment Subtraction” and “Browse…”. A new window opens. It lists all the saved experiments with zones having temperature profiles identical to the one of Heating zone 1. Select your Heating Zone 2 in the list and click OK. The newly displayed TG and DSC curves are blank subtracted.

For an explanation about blank subtraction, see Remark 2, page 7.

The Mass variation (TG) and DSC (Heatflow) signals (Figure 4) show three distinct thermal effects, all leading to mass losses and endothermic peaks.

To determine the corresponding mass variations, click on the TG curve. Select the TG tab in the menu and click on the “Mass change” function.

Select the start and end temperatures of the mass variations and display only the mass variation in %. On figure 4 below, the obtained values are 12.1%, 18.3% and 29.8%.

To determine the heats and temperatures of the corresponding endotherms, click on the HeatFlow curve. Select the HeatFlow tab in the menu, and select the “Baseline Construction” function. Choose one integration point before and after each peak, and a linear baseline. Each heat value obtained corresponds to the surface between the peak and the base line plotted.

To display accurate heat and temperature data, SETLINE STA / STA+ needs to be properly calibrated. See remark 1, page 5.

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Figure 4: Analyzing Calcium Oxalate Monohydrate under inert atmosphere

Quiz 3 : Providing that one molecule of Calcium Oxalate Monohydrate decomposes by releasing one molecule of water, one molecule of carbon dioxide and one molecule of carbon monoxide and knowing the molecular weights below, attribute each mass loss to a gas releasing reaction.

MCaC2O4, H2O= 146.11 g.mol-1 ; MCO= 28.01 g.mol-1 ; MCO2= 44.01 g.mol-1; MH2O= 18.02 g.mol-1

3.3. Thermal decomposition of CaC2O4, H2O under air

3.3.1. Testing

Take about 40 mg of calcium oxalate monohydrate and weigh the sample precisely in a 90 µl alumina crucible (S08/GR.29467, Diam 3.8 mm, Height 7.3 mm). Place the crucible on the measurement side of the sensor with the help of the ergonomic handle of SETLINE STA (right side of the sensor), or using the autosampler of the SETLINE STA+. An empty alumina crucible of same dimensions will be used as a reference.

Close the SETLINE® STA or STA+ furnace using the furnace control buttons.

Start flowing air at a rate of approximately 15 ml per minute.


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Heating zone 1

• Start temperature : ambient (≈ 20 °C) • End temperature : 900 °C • Scanning rate : 10 °C.min-1

Cooling zone 1

• Sequence 1, scanning• Start temperature : 900 °C • End temperature : 20 °C • Scanning rate : 30 °C.min-1


Heating zone 2


Cooling zone 2




3.3.2. TG and DSC data treatment





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Then, it is necessary to subtract the blank experiment (heating zone 2) from the displayed TG signal. For that purpose, in the treeview on the left side of the screen, right click on the zone name corresponding to the first heating zone. Select “Blank Experiment Subtraction” and “Browse…”. A new window opens. It lists all the saved experiments with zones having temperature profiles identical to the one of Heating zone 1. Select your Heating Zone 2 in the list and click OK. The newly displayed TG and DSC curves are blank subtracted.

For an explanation about blank subtraction, see Remark 2, page 7.

The Mass variation (TG) and DSC (Heatflow) signals (Figure 5) still show three distinct thermal effects, all leading to mass losses. However, unlike under inert atmosphere, the DSC signal shows two endothermic peaks and one exothermic peak corresponding to the intermediate temperature mass loss.

To determine the corresponding mass variation, click on the TG curve. Select the TG tab in the menu and click on the “Mass change” function.

Select the start and end temperatures of the mass variations and display only the mass variation in %. On the figure 5 below, the obtained values are 11.4%, 18.2% and 29.9%. They are very similar to the ones obtained under inert atmosphere, which means that the decomposition pathway is the same.

To determine the heats and temperatures of the corresponding endotherms and exotherm, click on the HeatFlow curve. Select the HeatFlow tab in the menu, and select the “Baseline Construction” function. Choose one integration point before and after each peak, and a linear baseline. Each heat value obtained corresponds to the surface between the peak and the base line plotted.

To display accurate Heat and temperature data, SETLINE STA / STA+ needs to be properly calibrated. See remark 1, page 5.

Quiz 4 : How would you interpret the presence of this exothermic peak ?

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Figure 5: Analyzing Calcium Oxalate Monohydrate under air

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4. Quiz answers

Quiz 1: 1 mole of calcium carbonate CaCO3 leads to the evolution of 1 mole of carbon dioxide CO2, so the theoretical mass loss can be calculated by the ratio between the molecular weight of carbon dioxide and of calcium carbonate:

% 𝑚𝑎𝑠𝑠 𝑙𝑜𝑠𝑠 = M!"#M!"!#$

=44.01 100.09

= 43.97 %

Compare this theoretical value with your experimentally determined mass loss.

Quiz 2: The decarbonation of calcium carbonate is a reversible reaction.

CaCO3 (s) ↔ CaO (s) + CO2 (g)

The presence of carbon dioxide in the atmosphere of the STA would inhibit the reaction and thus delay the formation of CaO. It means that under constant heating conditions, the mass loss due to the release of CO2 by calcium carbonate would be shifted to higher temperatures, leading to a higher value of Tinf. Quiz 3: The same methodology as in Quiz 1 can be applied. The theoretical mass losses corresponding to the release of one molecule of water, of carbon dioxide and of carbon moxide can be determined by the following calculations:

% 𝑚𝑎𝑠𝑠 𝑙𝑜𝑠𝑠,𝐻!0 = M!"#

M!"!#$%,!"# =18.02 146.11

= 12.3 %

% 𝑚𝑎𝑠𝑠 𝑙𝑜𝑠𝑠,𝐶𝑂! = M!"#

M!"!#$%,!"# =44.01 146.11

= 30.1 %

% 𝑚𝑎𝑠𝑠 𝑙𝑜𝑠𝑠,𝐶𝑂 = M!"

M!"!#$%,!"# =28.01 146.11

= 19.2 %

When comparing these results to the experimental data observed on Figure 4, we can attribute the low temperature mass loss (experimentally 12.1%) to water release. The intermediate temperature mass loss (experimentally 18.3%) can be attributed to carbon monoxide release and the high temperature mass loss (experimentally 29.8%) can be attributed to carbon dioxide release. Quiz 4: The oxygen content of air leads to a secondary reaction on the temperature range of the intermediate temperature mass loss. Indeed, we have attributed this mass loss to the release of carbon monoxide. At high temperature, in presence of air it oxidizes to form CO2. This reaction, also known as the Boudouard reaction, is very energetic. It is so fast and exothermic that it completely hides the endothermic effect of CO release from the calcium oxalate sample, which was observed under inert conditions.

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Setline STA Practical Work Experiments · 2020. 9. 14. · 1. INTRODUCTION This Practical Experiments booklet relates to operations with the SETLINE® STA or STA+. It is designed