SETLINE® DSC and DSC · • The ordinate of the DSC curve corresponding to the difference in heat flow is expressed as d(∆ Q)/dt rather than dH/dt, as Q is a heat quantity while

SETLINE® DSC and DSC DSC Basics and Practical Experiments

+

CONTENTS

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

2. DEFINITIONS AND VOCABULARY ......................................................................... 3 2.1. Differential scanning calorimetry (dsc) ......................................................................... 4 2.2. Vocabulary ............................................................................................................................................ 4

3. PRACTICAL EXPERIMENTS AND DATA PROCESSING .......................................... 4 3.1. Polyethyleneterephtalate (pet) analysis ....................................................................... 5

3.1.1. Presentation .............................................................................................................. 5 3.1.2. Testing ......................................................................................................................... 5 3.1.3. DSC data treatment ................................................................................................ 6 3.1.4. Determining the crystallinity ratio ................................................................... 10

3.2. Gypsum content in cement ............................................................................................ 11 3.2.1. Presentation ............................................................................................................ 11 3.2.2. Testing ....................................................................................................................... 12 3.2.3. DSC data treatment .............................................................................................. 13

3.3. Calcium oxide content in a (cao + caco3) mixture ................................................ 17 3.3.1. Presentation ............................................................................................................ 17 3.3.2. Testing ....................................................................................................................... 18 3.3.3. DSC data treatment .............................................................................................. 19

3.4. Chocolate melting and determination of the solid fat index (sfi) ....................... 20 3.4.1. Presentation ............................................................................................................ 20 3.4.2. Testing ....................................................................................................................... 21 3.4.3. DSC data treatment ......................................................................................................... 22

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1. INTRODUCTION

This Practical Experiments booklet relates to operations with the SETLINE® DSC or DSC+. It is designed for people discovering DSC 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.

This chapter only relates to applications of the instrument’s temperature scanning mode.

For more-into-depth information about DSC 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

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. 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).

2.2. VOCABULARY

• The symbol T is used for the expression in Celcius degrees (°C) or Kelvin (K). • The symbol t is used for the expression in seconds (s), minutes (min) or hours

(h). • The heating (or cooling) scanning rates are expressed by the derivative

dT/dt. In practice, as this involves an average value during heating, it is represented by β and is expressed in °C. mn-1 or K. mn-1.

• The ordinate of the DSC curve corresponding to the difference in heat flow is expressed as d(∆Q)/dt rather than dH/dt, as Q is a heat quantity while H is a heat content. The difference in heat flow is expressed in milliwatts (mW).

3. PRACTICAL EXPERIMENTS AND DATA PROCESSING

Various practical experiments are given as a way of getting to know the DSC method, using the various applications and working with the main items of data processing such as determining temperatures for melting, crystallisation, glass transition, etc.

Each practical application is distinguished by:

• How the application is represented • How the test is carried out • How use is made of the DSC signal • How data are processed

It is considered that temperature correction and enthalpy calibration of SETLINE® DSC or DSC+ 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.

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3.1. POLYETHYLENETEREPHTALATE (PET) ANALYSIS

3.1.1. Presentation

The goal of the presented work is to highlight the glass transition as well as the recrystallisation and fusion of a semi-crystalline polymer. The DSC data will be used for calculating the polymer’s degree of crystallinity.

Polyethyleneterephtalate (PET) is part of the family of saturated polyesters which have led to the development of products known under the brands of MYLAR® (films) or DACRON®and TERGAL® (textiles), as well as the production of hollow bodies (bottles).

PET is produced by the condensation reaction of ethylene glycol and terephtalic acid giving the formula:

Polymerisation is carried out to 280°C. Depending on additional heat treatment the resin can be made in its amorphous state or more or less crystallised.

Reaching the amorphous state is done by heating the polymer above its melting temperature (around 255°C) followed by fast cooling.

This state is maintained from ambient temperature up to about 100°C, the transition temperature, above which crystallisation starts.

Analyzing a PET pellet with the SETLINE® DSC or DSC+ enables the transitions between these various states to be detected.

3.1.2. Testing

Weigh a PET sample (about 20 mg) in a 30 µl aluminium crucible (S08/HBB37408, Diam 6.7 mm, Height 3 mm).

Close the crucible with the adapted cover (S08/HBB37409) and introduce it on the SETLINE® DSC or DSC+ sensor. An empty and closed aluminium crucible of same dimensions will be used as a reference.

Close the SETLINE® DSC or DSC+ furnace with its cover and the device with its cap.

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

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Heating sequence

• Start temperature : ambient (≈ 20 °C) • End temperature : 300 °C • Scanning rate : 5 °C.min-1

Cooling sequence

• Start temperature : 300 °C • End temperature : 20 °C • Scanning rate : 20 °C.min-1

Then start the experiment.

3.1.3. DSC data treatment

Open the saved experiment file using CALISTO Processing.

Display the signal acquired during the heating sequence.

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

The chart (Figure 1) brings out three separate thermal effects:

heat flow

EXO121,3 °C

26,82 J/g

117,7 °C

247,9 °C

-44,57 J/g

262,6 °Ctemperature °C

50 100 150 200 250 300 350

T1 = 57,2 °CT2 = 68,1 °CT3 = 71,8 °CCp = 0,358 J/g*°C

-35

-30

-25

-20

-15

-10

0

10

15

5

Figure 1: Analysis of a PET pellet

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• Glass transition at around 70°c • Exothermic crystallisation at around 120°C • Endothermic melting from 240°C

Let us process the experimental signal in order to determine characteristic temperatures and enthalpies of these transitions.

3.1.3.1. Glass transition

a. Glass transition temperature

T

T

T

ig

g

eg

Figure 2: Idealized glass transition effect (note: this chart does not exhibit an endothermic effect of relaxation, although it is frequently met with PET samples)

For the PET granulate sample:

• Replot the glass transition area, magnify it using one of the Zoom functions of CALISTO.

• Determine the characteristic temperatures of the glass transition: Tig, Teg and Tg using the glass transition function of CALISTO processing.

b. Heat capacity change Glass transition is accompanied by a sudden change of the sample’s heat capacity, which is only due to the amorphous phase of the semi crystalline polymer. Measuring the height of this change, that is to say the ΔCP, is sometimes used to measure polymers crystallinity by comparison of this value with the ΔCP, amorphous heat capacity of fully amorphous polymer sample.

Determination of ΔCP

Heat capacity is defined by the derivative of enthalpy versus temperature at constant pressure, that is to say by the following relationship:

𝐶𝐶𝑃𝑃 = �𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑�𝑃𝑃

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or with reference to time

𝐶𝐶𝑃𝑃 = �𝑑𝑑𝑑𝑑/𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑/𝑑𝑑𝑑𝑑�𝑃𝑃

The first term (dH/dt) is equal to the DSC (or HeatFlow) signal.

The second term (dT/dt) corresponds to the temperature scanning rate.

The glass transition function of CALISTO processing allows for an automatic calculation of the ΔCP.

• It draws a vertical line at the temperature of glass transition Tg (as seen on Figure 3 below)

L = ∆ Cp

Figure 3: Measuring the variation of heat capacity (note: this chart does not exhibit an endothermic effect of relaxation, although it is frequently met with PET samples)

• It measures the length of the line segment (L) between the two tangents at the initial and end points expressing it in milliwatts, that is to say milliJoules per second.

• It calculates the variation CP of the sample applying by the following formula, derived from :

∆𝐶𝐶𝑃𝑃 = �𝑑𝑑𝑑𝑑/𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑/𝑑𝑑𝑑𝑑

�𝑃𝑃,𝑒𝑒𝑒𝑒𝑑𝑑

− �𝑑𝑑𝑑𝑑/𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑/𝑑𝑑𝑑𝑑

�𝑃𝑃,𝑖𝑖𝑒𝑒𝑖𝑖𝑑𝑑𝑖𝑖𝑖𝑖𝑖𝑖

As the heating rate stays contant during the effect,

(dT/dt)initial = (dT/dt)end = β (in °C.s-1)

Or

∆𝐶𝐶𝑃𝑃 = �𝑑𝑑𝑑𝑑/𝑑𝑑𝑑𝑑 𝑒𝑒𝑒𝑒𝑑𝑑 − 𝑑𝑑𝑑𝑑/𝑑𝑑𝑑𝑑𝑖𝑖𝑒𝑒𝑖𝑖𝑑𝑑𝑖𝑖𝑖𝑖𝑖𝑖

𝛽𝛽�𝑃𝑃

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𝑑𝑑𝑑𝑑/𝑑𝑑𝑑𝑑 𝑒𝑒𝑒𝑒𝑒𝑒 − 𝑑𝑑𝑑𝑑/𝑑𝑑𝑑𝑑𝑖𝑖𝑒𝑒𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖 is actually equal to L, so :

∆𝐶𝐶𝑃𝑃 = �𝐿𝐿𝛽𝛽�𝑃𝑃

in J.°C-1

Or

∆𝐶𝐶𝑃𝑃 = � 𝐿𝐿

𝑚𝑚.𝛽𝛽�𝑃𝑃

in J.g-1.°C-1

where m is the sample mass in g.

3.1.3.2. Crystallisation

Figure 4: Distinguishing temperatures for crystallisation

• Replot the crystallization peak using one of the zoom functions of CALISTO. • Select the baseline integration function of CALISTO • Select one integration point before and after the peak, and a linear baseline • For crystallization temperature

• Display the onset and peak maximum temperatures (the onset temperature corresponds with the intersection of the base line with the tangent at the inflexion point on the peak)

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• For Crystallization heat • Display the heat of crystallization ΔHcryst in J/g • The routine calculation determines the area between the crystallization

peak and the integration baseline in Joules and divides it by the sample mass. It uses the value entered by the user during the experiment set up (converted into grams).

3.1.3.3. Melting

Figure 5: Melting temperatures

Proceed the same way with the melting peak as with the crystallization peak: • Replot the melting peak using one of the zoom functions of CALISTO. • Select the baseline integration function of CALISTO • Select one integration point before and after the peak, and a linear baseline • Display the onset, peak temperatures and heat of melting ΔHmelt in J/g

3.1.4. Determining the crystallinity ratio

The crystallinity ratio K of a semi-crystalline polymer has a strong influence on its mechanical properties. It is thus an important parameter to control.

The DSC signal can be exploited as

• the heat of crystallization is proportional to the amount of amorphous phase in the polymer

• the heat of melting is proportional to the amount of crystalline phase in the polymer at the melting temperature

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So in practice, the crystallinity rate in the PET granulate is proportional to (ΔHmelt - ΔHcryst).

But obtaining the crystallinity rate also requires knowledge of the fusion heat in a sample of 100% crystalline PET sample. This is a purely theoretical value because this type of 100% crystalline polymer cannot be made. So for PET, ΔHmelt, 100% is found in literature to be equal to 145 J.g-1

So, for the example showed on Figure 1:

( )K x%

, ,, %=

−=

44 6 26 8145

100 12 3

Proceed to the same calculation with the ΔHmelt and ΔHcryst data you have determined.

The method can be applied to various types of PET (granulate, fibre, film,...). They will be in an amorphous or semi-crystalline state with differing crystallinity ratios, in principle never above 30%.

For each type of PET, analyze the transformations observed on the curve, measure the distinguishing temperatures and quantities of heat and determine the crystallinity rate.

3.2. GYPSUM CONTENT IN CEMENT

3.2.1. Presentation

Gypsum is used for preparing plaster products. It is also found in small amounts in cements. The residual presence of gypsum causes quicker setting in cement. It is thus important to control the gypsum content in cement powders.

Gypsum content determination by DSC is based on the measurement of its heat of dehydration. Gypsum is a dehydrated calcium sulfate CaSO4, 2H2O. Upon heating, it dehydrates through the following reactions:

(a) CaSO4, 2H2O → CaSO4, 1/2 H2O + 3/2 H2O the formation of plaster (hemihydrate)

Plaster itself dehydrates and leads to the formation of anhydrite:

(b) CaSO4, 12

H2O → CaSO4 + 12

H2O the formation of anhydrite

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The dehydration heat of pure gypsum into hemihydrate needs to be known to measure gypsum content in industrial cement.

3.2.2. Testing

Weigh a gypsum sample (CaSO4, 2 H2O) of about 25 mg in a 120 µl aluminium crucible (S08/12768, Diam 6.7 mm, Height 5.5 mm).

Close the crucible with a semi-tight cover (S08/12726). Note that it is important to use this type of cover as it ensures a good water vapour pressure above gypsum during heating, for a good separation of the two dehydrations.

Introduce the crucible on the SETLINE DSC or DSC+ sensor. An empty and closed aluminium crucible of same dimensions will be used as a reference.

Close the SETLINE DSC or DSC+ furnace with its cover and with its cap.


Heating sequence


Cooling sequence



Repeat the same test with one (or several) sample(s) of cement having a greater mass (about 100 mg).

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Open the saved experiment(s) file(s) using CALISTO Processing.



3.2.3.1. Analyzing gypsum

The DSC signal of the gypsum dehydration experiment (Figure 6) shows two distinct endothermic effects corresponding to:

heat flow

0-10-20-30-40-50-60-70-80-90

-100-110

EXO

151,6 °CT2

Td1 T1 Tf1 Td2 T3 T

203,4 °CT4

f 2

∆H 2146,9 J/g

temperature

90 110 130 150 170 190 210 230

∆H 1430,9 J/g

Figure 6: Analyzing pure gypsum

• The dehydration of gypsum into plaster between 120°C and 170°C • The dehydration of the plaster formed into anhydrite between 180°C and

225°C.

3.2.3.1.1. Dehydration gypsum → plaster

• Replot the low temperature dehydration peak using one of the zoom functions of CALISTO

• Select the baseline integration function of CALISTO • Select one integration point before and after the peak, and a linear baseline

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a. Dehydration temperature Use the baseline integration window of CALISTO processing to determine:

• The onset temperature (on Figure 6: T1) corresponding with the intersection of the base line with the tangent at the inflexion point on the dehydration peak.

• The temperature (On Figure 6: T2) on the top of the dehydration peak.

b. Dehydration heat Use the baseline integration window of CALISTO processing to determine the heat of dehydration. It corresponds to the surface between the dehydration peak and the base line plotted.

• Calculate the value of the gypsum dehydration heat in J.g-1, noted on Figure 6 as ∆H1 = 430.9 J.g-1

3.2.3.1.2. Dehydration plaster → anhydrite

• Replot the high temperature dehydration peak using one of the zoom

functions of CALISTO • Select the baseline integration function of CALISTO • Select one integration point before and after the peak, and a linear baseline

a. Dehydration temperature In the same way as for the first dehydration peak, determine:

• The onset temperature (T3 on Figure 6) of the plaster dehydration peak. • The temperature (T4 on Figure 6) on the top of this peak.

In the example: T3 = 193.2°C and T4 = 203.4°C.

b. Dehydration heat • Determine the surface under the peak between temperatures (Td2) and

(Tf2).

• Calculate the value of the plaster dehydration heat in J.g-1, that is ∆H2 (in

the example: 146.9 J.g-1).

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3.2.3.1.3. Analyzing cement Analyzing cement (Figure 7) up to 250°C brings out two distinct endothermic effects corresponding to:

heat flow

-5

-10

-15

150 200 250

temperature °C

EXO150,2 °C

T2

∆H1

16,5 J/g

T142,5 °C

1 T172,4 °C

3

4,6 J/g∆H2185,9 °C

T4

Figure 7: Analyzing a cement containing 5% gypsum

• The dehydration of residual gypsum into plaster between 120°C and 170°C. • The dehydration of the plaster formed into anhydrite, but also possible

dehydration of plaster that was originally present in the sample of cement.

(The example is a clinker containing 5% gypsum).

3.2.3.1.4. Dehydration of gypsum → plaster

• Replot the low temperature dehydration peak using one of the zoom functions of CALISTO

• Select the baseline integration function of CALISTO • Select one integration point before and after the peak, and a linear baseline

Use the baseline integration window of CALISTO to determine:

• T'1 and T'2: the temperatures corresponding to the onset and the top of the peak

• ∆H'1: the heat in J.g-1 corresponding to the dehydration peak. (In the example shown in Figure 7: T'1 = 142.5°C ; T'2 = 150.2°C ; ∆H'1= 16.5 J.g-1)

Note that the temperatures T'1 and T'2 are similar to the temperatures T1 and T2 measured with pure gypsum

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3.2.3.1.5. Dehydration of plaster → anhydrite • Replot the high temperature dehydration peak using one of the zoom

functions of CALISTO • Select the baseline integration function of CALISTO • Select one integration point before and after the peak, and a linear baseline

Use the baseline integration window of CALISTO to determine:

• T'3 and T'4 : the temperatures corresponding to the onset and the top of the peak.

• ∆H'2 : the heat in J.g-1 corresponding to the dehydration peak.

(In the example shown in Figure 7: T'3 = 172.4°C ; T'4 = 185.9°C ; ∆H'2 = 4.6 J.g-1)

Note that plaster dehydrates into anhydrite at a temperature lower than the temperature observed for pure gypsum.

3.2.3.1.6. Determining the gypsum content in cement

Let:

m : be the mass of pure gypsum (1st test)

m’ : be the mass of cement (2nd test)

The content of gypsum G in the sample of cement is:

𝐺𝐺 =𝑚𝑚′.∆𝑑𝑑1′

𝑚𝑚.∆𝑑𝑑1. 100

For the example shown in Figure 7: G = 5.1%

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3.3. CALCIUM OXIDE CONTENT IN A (CAO + CACO3) MIXTURE

3.3.1. Presentation

Calcium oxide CaO is produced by decarbonating CaCO3:

CaCO3 → CaO + CO2

The amount of CaO in a reaction mixture (CaO + CaCO3) can be determined by DSC.

Indeed, the DSC method is appropriate for investigating the CaO hydration reaction into calcium hydroxide:

CaO + H2O → Ca (OH)2 + ∆HR

This reaction is accompanied by a release of heat (∆HR). It can be calculated from the enthalpies of formation of each compound.

( ) [ ]∆ ∆ ∆ ∆H H H HR f Ca OH f CaO f H O= − +2 2

From literature, the enthalpies of formation of Ca(OH)2, CaO et H2O are, respectively:

∆Hf Ca(OH)2 = 968.2 kJ.mol-1

∆Hf CaO = 635.1 kJ.mol-1

∆Hf H2O (liq) = 285.9 kJ.mol-1

So ∆HR the enthalpy of the hydration of CaO is equal to

∆HR = 968.2 - [ 635.1 + 285.9 ] = 47.2 kJ.mol-1

The CaO molar mass being equal to 56.08g :

∆HR = 841.7 J.g-1 of CaO

Let’s consider a (CaO + CaCO3) mixture in the presence of an excess of water. Only CaO hydrates with the following pathway:

CaO + CaCO3 + H2O → Ca(OH)2 + CaCO3 + ∆H 'R

The heat of reaction ∆H'R is proportional to the quantity of CaO in the mixture.

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The CaO content in the mixture is thus obtained by the ratio of ∆HR and ∆H’R :

% CaO = ∆∆HH

xR

R

' 100

3.3.2. Testing

1. Weigh about 20 mg of the (CaO + CaCO3) mixture in the Incoloy crucible (S60/58186, Diam 6.8 mm, Height 7 mm) and add 5µl of distilled water.

2. Make sure that there is no trace of water on threading. 3. Close the crucible with its screwed stopper and seal it by using the

appropriate crimping tool. The crucible must be fluid-tight for this test to prevent water from evaporating during heating (with subsequent perturbation of the DSC signal).

4. Introduce the crucible in the SETLINE® DSC or DSC+ (an empty and closed Incoloy crucible is used as reference).

5. Close the SETLINE® DSC or DSC+ furnace with its cover and the device with its cap.


Heating sequence


Cooling sequence



Note that the time interval between the sample preparation and the start of the experiment should be as short as possible so the reaction does not start.

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The hydration reaction of the CaO content of the sample produces an exothermic peak on the HeatFlow signal between 40 °C and 130 °C.

heat flow (mW)

30

20

10

0

EXO

Td T f

temperature °C

20 40 60 80 100 120

Figure 8: Hydrating a CaO + CaCO3 mixture

• Replot the exothermic hydration peak using one of the zoom functions of

CALISTO • Select the baseline integration function of CALISTO • Select one integration point before and after the peak, and a linear baseline

3.3.3.1. Hydration heat

• Display the heat of hydration in J/g • The calculation routine determines the area between the crystallization

peak and the integration baseline in Joules and divides it by the sample mass. It uses the value entered by the user during the experiment set up (converted in grams).

ΔH’R = 722 J.g-1

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Note the value of hydration heat of CaO in J.g-1, that is ΔH’R. In the example shown on Figure 8, ∆H’R = 722 J.g-1.

3.3.3.2. Proportion of CaO in the mixture (CaO + CaCO3) As seen in the paragraph 3.3.1. Presentation, the heat of reaction ∆HR for a pure CaO sample is equal to 47.2 kJ.mol-1. The molecular mass of CaO being 56.08 g, it means that ∆HR = 841.7 J.g-1.

The amount of CaO in the tested mixture can be expressed as:

% CaO = ∆∆HH

xR

R

' 100

Calculate the CaO content of your sample using this equation.

Note that in the example seen on Figure 8, the amount of CaO in the mixture is equal to:

% CaO = 722

8417100

.x that is to say 85.8 %.

3.4. CHOCOLATE MELTING AND DETERMINATION OF THE SOLID FAT INDEX (SFI)

3.4.1. Presentation

Chocolate is made of various fats, and more particularly cocoa butter. Thus chocolate melting does not take place at a specific temperature, as a pure substance would, but over a temperature range which is generally between -30°C and 50°C. Based on the thermal history of chocolate (heating, tempering conditions, etc), modifications appear in the structure of the product and melting may be modified.

It is necessary to know the percentage of crystallised chocolate in relation to melted chocolate at a set temperature during the production phase. This amount is called the Solid Fat Index (or SFI), and specifies the fraction of unmelted product.

The DSC technique offers a fast method for SFI determination based on the treatment of the peak on the DSC signal corresponding to chocolate melting.

The melted fraction can be easily calculated from a chocolate melting peak as seen in Figure 9. At temperature Ti, the partial surface ∆Hi of the melting peak corresponds to the fraction of chocolate that has already melted.

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signal

∆Η

températureTi

i

∆Η

Figure 9: Determining the melted fraction

The difference between the total heat of melting and ∆Hi thus corresponds to the fraction of chocolate that is still solid.

So, the ratio H

HH i

∆∆−∆ provides the non-melted fraction, that is to say the SFI at Ti.

Finally, the variation of the Solid Fat Index with temperature is given by calculating the unmelted fraction at various temperatures Ti.

3.4.2. Testing

Weigh a chocolate sample of about 100 mg in a 120 µl aluminium crucible (S08/12768, Diam 6.7 mm, Height 5.5 mm).

Close the crucible with the adapted cover (S08/HBB37409) and introduce it on the SETLINE® DSC or DSC+ sensor. An empty and closed aluminium crucible of the same dimensions will be used as a reference.

Close the SETLINE® DSC or DSC+ furnace with its cover.

Connect the sub-ambient cooling device you have acquired with your SETLINE® DSC or DSC+. If necessary, refer to the appropriate chapter of the user’s manual for instructions.

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Heating sequence #1


Isothermal sequence #1

• Temperature : 40 °C • Time : 5 min

Cooling sequence

• Start temperature : 40 °C • End temperature : -40 °C • Scanning rate : 5 °C.min-1

Isothermal sequence #2

• Temperature : -40 °C • Time : 5 min

Heating sequence #2

• Start temperature : -40 °C • End temperature : 50 °C • Scanning rate : 5 °C.min-1


Note that a first heating of the chocolate sample is necessary before the real measurement. Only heating sequence #2 will be exploited for the SFI determination.




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The melting of chocolate produces between -40°C and 50°C a complex endothermic peak with contribution of the different fats contained in the tested sample.

In the example shown in Figure 10, the melting range is from -20°C to 40°C.

heat flow (mW)

-5

-10

-15

-20

-25

-30

EXO

Q = - 26,6 J/g

temperature (°C)

-40 -30 -20 -10 0 10 20 30 40

Figure 10: Chocolate fusion

• Replot the melting peak using one of the zoom functions of CALISTO • Select the baseline integration function of CALISTO • Select one integration point before and after the peak, and a linear baseline

3.4.3.1. Heat of melting

• Display the heat of melting in J/g • The calculation routine determines the area between the crystallization

peak and the integration baseline in Joules and divides it by the sample mass. It uses the value entered by the user during the experiment set up (converted in grams).

Note the value of the heat of melting in J.g-1, that is ΔH. In the example shown on Figure 10, ∆H = 26.6 J.g-1.

24

3.4.3.2. Determining the Solid Fat Index

Right-click on the baseline in the CALISTO graph or on the treeview. Select the SFI function. A new curve appears, varying between 100% and 0%, that is to say between a fully solid state and a fully liquid state respectively.

Use the Cursor function on the SFI curve to display the SFI value at selected temperatures (ex: 0, 10 , 20, 30 °C) or to display temperatures corresponding to selected SFI values (ex: 80, 50, 10 %).

The algorithm of CALISTO processing operates the following way :

a) It selects a first temperature point Ti and cuts the melting peak in two sections as shown in Figure 9 above.

b) It determines the surface of the section between the first integration point and Ti and the corresponding amounts of heat ∆Hi.

c) It calculates the value of SFI at Ti : SFI(Ti) = H

HH i

∆∆−∆

d) It starts the same operation again from (a) for the next temperature point Ti+1

Finally CALISTO plots the SFI values as a function of temperature like in Figure 11 below, obtained from the data in Figure 10

S F I (%)

100

75

50

25

0

-40 -30 -20 -10 0 10 20 30 40 50

Temperature

Figure 11: Determining the Solid Fat Index

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SETLINE® DSC and DSC · • The ordinate of the DSC curve corresponding to the difference in heat flow is expressed as d(∆ Q)/dt rather than dH/dt, as Q is a heat quantity while