1. Thermal Analysis

2. Thermal Analysis: A group of methods by which the physical & chemical properties of a substance, are determined as a function of temperature and/or time, while sample is subjected to a controlled temperature program
Thermal Gravimetric Analysis (TGA)
Measure change in weight during heating or cooling
Differential Scanning Calorimetry (DSC)
Measure heat absorbed or liberated during heating or cooling
Thermomechanical Analysis (TMA)
Measure change in dimensions during heating or cooling
Differential Thermal Analysis (DTA)
They are use for thermal investigation where thermal change can be observed and characterised

3. Thermal Gravimetric Analysis (TGA)
Concept: Sample is loaded onto an accurate balance and it is heated at a controlled rate, while its mass is monitored and recorded. The results show the temperatures at which the mass of the sample changes.
Selected applications:
determining the presence and quantity of hydrated water
determining oxygen content
studying decomposition

4. TG Instrumentation Components: Sensitive analytical balance Furnace
Purge gas system
Computer

5. Applications of TGA Decomposition of calcium oxalate Composition
H20
Ca(C00)2 CO
CaC03
CO2
Ca0
Sample Temperature (°C)
Sample Weight
Decomposition of calcium oxalate
Composition
Moisture Content
Solvent Content
Additives
Polymer Content
Filler Content
Dehydration
Decarboxylation
Oxidation
Decomposition

6. Typical TGA of a Pharmaceutical
Green line shows mass changes
Blue line shows derivative

7. Differential Thermal Analysis (DTA)
Concept: sample and a reference material are heated at a constant rate while their temperatures are carefully monitored. Whenever the sample undergoes a phase transition (including decomposition) the temperature of the sample and reference material will differ.
At a phase transition, a material absorbs heat without its temperature changing
Useful for determining the presence and temperatures at which phase transitions occur, and whether or not a phase transition is exothermic or endothermic.

8. DTA Instrumentation

9. General Principles of DTA
H (+) endothermic reaction - temp of sample lags behind temp of reference
H (-) exothermic reaction - temp of sample exceeds that of reference

10. General Principles of DTA
T = Ts - Tr
Glass transitions
Crystallization
Melting
Oxidation
Decomposition
Endothermic Rxns:
fusion, vaporization, sublimation, ab/desorption
dehydration, reduction, decomposition
Exothermic Rxns:
Adsorption, Crystallization
oxidation, polymerization and catalytic reactions

11. Applications of DTA simple inorganic species Phase transitions
determine melting, boiling, decomposition
polymorphism
Jacobson (1969) - studied effects of stearic acid and sodium oxacillin monohydrate

12. Differential Scanning Calorimetry (DSC)
Analogous to DTA, but the heat input to sample and reference is varied in order to maintain both at a constant temperature.
Key distinction:
In DSC, differences in energy are measured
In DTA, differences in temperature are measured
DSC is far easier to use routinely on a quantitative basis, and has become the most widely used method for thermal analysis

13. DSC Instrumentation There are two common DSC methods
Power compensated DSC: temperature of sample and reference are kept equal while both temperatures are increased linearly
Heat flux DSC: the difference in heat flow into the sample/reference is measured while the sample temperature is changed at a constant rate

14. Heat Flow in DSC

15. DSC Step by Step Recrystallization Glass transition Melting

16. Applications of DSC
DSC is usually carried out in linear increasing-temperature scan mode (but can do isothermal experiments)
In linear scan mode, DSC provides melting point data for crystalline organic compounds and Tg for polymers
DSC trace of polyethyleneterphthalate (PET)
Easily used for detection of bound crystalline water molecules or solvents, and measures the enthalpy of phase changes and decomposition

17. Applications of DSC
DSC is useful in studies o polymorphism in organic molecular crystalline compounds (e.g. pharmaceuticals, explosives, food products)
Example data from two “enantiotropic” polymorphs

18. DSC of a Pharmaceutical Hydrate
Loss of water
Melt
Decomposition

19. Summary of Pharmaceutically Relevant Information Derived from TGA Analysis
Desolvation – adsorbed and bound solvents, stoichiometry of hydrates and solvates
Decomposition – chemical and thermal stability
Compatibility – interactions between components

20. Analysis of results ~430°C: Ca(OH)2 -> CaO + H2O↑
Software: NETZSCH Proteus® (Marsh procedure) Quantification of portlandite (Ca(OH)2) content in cement
~430°C: Ca(OH)2 -> CaO + H2O↑
So to correct for it, I speacial tool which is available in the software
The data from the flat steps is linearly [linijarli] extrapolated . This method subtracts the mass released from the dehydration of other compounds. It results in a background-corrected weight loss from which the amount of remaining portlandite can be calculated.
Once knowing the mass loss it and stoichiometry of the decomposition reaction, portalndite mass and content can be easily recalculated for the mass of the component.
to quantify amount of portlandite which quantification by QXRD is not straightforward due to sample preparation problems (preferred orientation) which will be explained by Rieko
I use Thermogravimetry to complement XRD results (or vice versa),.
I use the thermal analysis to complement finding from XRD.
“unfortunately the reactions of the individual components often superimpose” peaks from different sample components superimpose
for some phases accurate quantification is possible
Advantages of thermal analysis over XRD
But for the other phases I can only identify them because of overlap of thermal effects.
The TG analyses were used to quantify the amount of portlandite, determined from the weight loss at 430 ◦C by linearly extrapolating the data from 335 ◦C to 370 ◦C and from 490 ◦C to 525 ◦C (Figure 3.4). This method, proposed by Taylor [288] subtracts the amount of water released from the dehydration of other compounds. It results in a background-corrected weight loss from which the amount of remaining portlandite can be calculated.

21. Fig-thermogram of calcium oxalate monohydrate(CaC2O4.H2o)

22. Examples of TGA Curves
TGA curves of crystalline and amorphous substance

23. Lactose monohydrate
DSC and TGA scans of lactose monohydrate

24. Hyphenated Thermal Equipment
Thermal techniques alone are insufficient to prove the existence of polymorphs and solvates
Other complementary techniques are used e.g. microscopy, diffraction and spectroscopy
Simultaneous analysis
Types:
DSC-TGA
DSC-XRD – DSC coupled with X-ray diffraction
TGA-MS – TG system coupled with a mass spectrometer
TGA-FTIR – TG system coupled with a Fourier Transform infrared spectrometer
TGA -MS or -FTIR - evolved gas analysis (EGA)
Other uses of TGA:
Material Thermal Stability.
Moisture and Volatiles Content (TG-IR).
Composition of Multi-Component Systems.
Shelf-Life Studies and Decomposition Kinetics.

25. Thermal analysis (TGA/DSC) in a nutshell
TG analysis – mass (T)
DSC analysis – heat flow (T)
Examples of thermal reactions resulting in mass change, measured by TG analysis:
loss of free water
loss of bound water
decomposition
TG applications:
identification and quantification of sample components
thermal stability studies
Examples of thermal reactions resulting in heat flow, measured by DSC analysis:
crystallization
melting
glass transitions
DSC applications:
thermodynamic characterization of pure substances
quality control: sample purity
thermal stability studies
1 On the left you can see an example of TG result, which shows sample mass in function of temperature – which is the solid green line,
Often first derivative [deriwatiw] of the TG curve is calculated, which is also shown here as the dotted line (solid curve), it is called DTG curve. Differentiation of the TG -> DTG allows a better resolution of consecutive [konsekjutiw] weight changes. (DTG until 150 reveals that there are 2 mass loss steps in this temperature range)
You can see from the TG result, that with raising temperature sample looses mass, what is caused by thermal reactions taking place, such as:
These thermal reactions are temperature specific (occur at a characteristic temperature), for example in this example above of cement samples, the rapid mass loss which takes place at about 430 C, is due to portlandite decomposition, (one of the components of hydrated cement). Therefore TG allows to identify sample components, and measuring the weight loss associated with the thermal process allows to quantify the content of this component, what will be shown later. TG is also used for thermal stability studies.
On the right you can see an example of DSC curve, which shows heat flow [mW] in function of temperature for some polymer sample. DSC analysis allows to identify and characterize phase changes and glass transitions, in this graph we can see a negative [negatiyw] peak, which is associated with sample giving up heat due to crystallisation and the other positive peak which is associated with heat absorption during thermal melt of the polymer. The small bump before crystallisation was identified as glass transition (heat capacity change).
Some of the application of DSC are:
DSC [mW] – colours, heat transfer (Watt – power / time [J/s = Nm/s], heat – J)
Wiki:
glass transition is not a formal phase change – but it can be detected because heat capacity of a sample changes,
determine transition temperatures and enthalpies – producing phase diagrams
This curve can be used to calculate enthalpies of transitions. This is done by integrating the peak corresponding to a given transition
“less pure compounds will exhibit a broadened melting peak that begins at lower temperature than a pure compound”
Measuring effects of these reactions (recording mass loss due to dehydration, heat transfer of a phase change) may be helpful in identifying sample composition (start of a reaction), quantifying amount of certain components (some components decompose only at a certain temperature) and thus and determining the properties of a sample.
DSC graph:
Notes:
DSC: measures heat flows and temperatures associated with exothermic and endothermic transitions
DTG: thermal reactions associated with mass change reactions
Thermodynamic data for pure substances include melting and boiling points, heat capacity, heat of fusion, heat of solution, and heat of vaporization
Differentiation of the TG curve (Derivative Thermogravimetry or Differential Thermogravimetry 121 – DTG) allows a better resolution of consecutive weight changes (Emmerich 2011).

26. Differential Scanning Calorimetry (DSC)
A thermal analysis technique in which the amount of energy absorbed (endothermic) or released (exothermic) by a material is measured.
Both events are the result of physical and/or chemical changes in a material.
Normally the weight of sample is 5 – 10 mg,
Sample can be in solid or liquid form.
Many of the physical (e.g evaporation) or chemical (e.g decomposition) transformation are associated with heat absorption (endothermic) or heat liberation (exothermic).

27. DSC provides a direct calorimetric measurement of the transition energy at T of transition. Often used to characterize thermal transition in polymers – glass transition T (Tg) and melting point (Tm). Organic liquids or solids, and inorganic can be analysed.

28. Features of DSC curves

29. DSC – Applications :
Identify melting point, glass transition, Curie temperature, energy required to melt material. Evaluation of phase transformation.
Decomposition, polymerization, gelation, curing.
Evaluation of processing, thermal & mechanical histories.
Process modeling, material’s min process temperature (processing condition).
Determine crystallization temperature upon cooling.
Perform oxidative stability testing (OIT).
Compare additive effects on material.

30. Computer makes sure that the 2 separate pans heat at the same rate (usually 10°C/min or lower) as each other. So if endothermic or exothermic events, results in more or less energy has to be supplied to the sample.

31. Differential Scanning Calorimeter

32. 2 modes – depending on method of measurement used.

33. Heat absorbed by polymer, heat flow given by q/t, q heat supplied per unit time. Heat capacity, Cp amount of heat it takes to increase T. displacement, h = BØCp. Ø is heating rate & B calibration factor.
Heat is being absorbed by sample (increase in its heat capacity). Polymers gone thru Tg, but transition occur over a temperature range. So Tg is taken as middle of the incline.

34. Crystallization point – Tc where at this temperature polymer have enough energy to arrange into ordered arrangements, crystal. Polymers give off heat at this point. Area of peak = latent energy of crystallization.
Heat absorbed in order to melt – additional heat to increase temperature. Area of dip = heat of melting.

35. Typical DSC curve for polymer (especially thermoplastic), for polymers that don’t crystallize (amorphous), Tc & Tm will not present.
Comparing Tg with Tc & Tm, Tg only involve changes in heat capacity.

36. DSC Responses Physical changes : Chemical changes :
Exothermic – adsorption, crystallization.
Endothermic – desorption, melting, vaporization.
Chemical changes :
Exothermic – oxidation, decomposition, curing.
Endothermic – reduction, decomposition, dehydration.

37. DSC curve for typical organic polymer.
Tg – change in heat capacity but no change in enthalpy, ∆H = 0.
DSC directly measures ∆H of transitions. Also degree of crystallinity, degree of curing.

38. During curing, polymer chains cross-link, this process release heat, which is reflected DSC curve;
When polymer going through curing process, its DSC curve will show a broad peak at the curing temperature at first scan;
When cross-linking is complete, the curing peak disappear and its replaced by a feature of glass transition as shown in the curve of the second scan

39. Differential Scanning Calorimetry (DSC)
DSC have many applications in field of polymer science & engineering.
Tg, Tc & Tm transitions are characteristic of each polymer  identification.
Curing conditions (Curing of concrete is defined as providing adequate moisture, temperature, and time to allow the concrete to achieve the desired properties for its intended use) for thermoset – heat for curing which allows calculation of degree of curing.

40. Summary of Pharmaceutically Relevant Information Derived from DSC Analysis
Melting points – crystalline materials
Desolvation – adsorbed and bound solvents
Glass transitions – amorphous materials
Heats of transitions – melting, crystallisation
Purity determination – contamination, crystalline/amorphous phase quantification
Polymorphic transitions – polymorphs and pseudopolymorphs
Processing conditions – environmental factors
Compatibility – interactions between components
Decomposition kinetics – chemical and thermal stability

41. Typical Features of a DSC Trace
Exothermic upwards
Endothermic downwards
CRYSTALLISATION
DESOLVATION
GLASS TRANSITION
MELTING
DECOMPOSITION
H2O
Y-axis – heat flow
X-axis – temperature (and time)

42. Melting Point
Onset = melting point (mp)
MELTING
Heat of fusion (melting) = integration of peak
DSC scan of a crystalline material – one polymorphic form

43. Polymorphic Forms
TRANSITION
STABLE
FORM
METASTABLE
FORM
DSC scan of a crystalline material – polymorphic transition

44. Pseudopolymorphism
MELTING
DEHYDRATION
DSC scan of a hydrate

45. Amorphous Material
DEHYDRATION
Midpoint = glass transition (Tg)
GLASS TRANSITION
Polyvinylpyrrolidone (PVP) co-processed with hydroflumethiazide

46. Purity Determination Purity of phenacetin
Source: TA Instruments, Cassel RB,
Purity Determination and DSC Tzero™ Technology

47. Compatibility Studies
Source: Schmitt E et al. Thermochim Acta 2001, 380 , 175 – 183

48. Variants of DSC
Conventional – linear temperature (cooling, heating) programme
Fast scan DSC – very fast scan rates (also linear)
MTDSC (modulated temperature DSC) – more complex temperature programmes, particularly useful in the investigation of glass transitions (amorphous materials)
HPDSC (high pressure DSC) – stability of materials, oxidation processes

49. Measurement conditions
furnace
Netzsch STA 409 PC Luxx®:
T [25 – 1000 °C]
heating rate 10 °C/min
N2 atmosphere (60 ml/min)
alumina crucibles
simultaneous measurement of mass change (TG) and heat flow (DSC)
1 analysis (25100025 °C) = 3 hrs
microbalance
Here on the right you can see a picture of the instrument, the upper tube is a furnace and the middle unit is the microbalance system. During a measurement sample is heated in this furnace according to a controlled temperature program.
The instrument operates over the range of temperatures from 25 to 1000C at the heating rate of 10C/min. (standards, baseline correction), the measurement is carried out under inert atmosphere of nitrogen [najtrodzen] at a constant flow of 60 ml/min. The crucibles which are used are made of alumina.
(The instrument is calibrated for a following set of measurement conditions: it)

50. Measurement conditions
furnace
Netzsch STA 409 PC Luxx®:
T [25 – 1000 °C]
heating rate 10 °C/min
N2 atmosphere (60 ml/min)
alumina crucibles
simultaneous measurement of mass change (TG) and heat flow (DSC)
1 analysis (25100025 °C) = 3 hrs
sample + reference
Now you can see the picture of the interior of the furnace, because the furnace cover is lifted up.
Inside the furnace there is a sample holder which is connected to a microbalance, and on top of this sample holder a sample and a reference [refrens] are placed.
During a measurement, the microbalance [majkrobalans] records mass of the sample in function of temperature, what is referred [riferd] to thermogravimetric analysis - TG.
The sample holder measures also the difference of temperature between sample and reference, what after calibration allows to determine [ditermin] heat flow (associated with exo and endothermic transitions), and such measurement is referred to a differential scanning calorimetry.
“both signals – mass (change) and heat flow - from the same sample are measured under exactly the same conditions at the same time.“ Proteus help
A single analysis in the range of temperatures from room temperature to 1000C takes about 3hrs
More detailed instrument parameters:
Max temperature: 1550, heating rate (Heating rate: max 50K/min, K/min recommended))
balance measurement range: 18g, resolution: 2ug,
From Proteus help:
"A group of techniques in which a physical property of a substance is measured as a function of temperature while the substance is subjected to a controlled temperature program." (ICTA, ASTM )
microbalance

51. Sample compatibility Requirements: no reaction with alumina crucible
no expansion or creep during thermal decomposition
Compatible materials (KUL expertise):
clays and other geological materials
cements
slags
Limitations:
polymers can be hazardous, as they can foam at high temperatures,
compatibility assessment is necessary for new materials
Before running a measurement we need to make sure, that the material doesn’t show hazardous [hazardus] behaviour during measurement, that no reaction takes place between crucible and the sample or that the sample doesn’t expand or creep.
Based on our experience, we know that materials like …. Are compatible [kompatybyl]
However measurements of polymers can be hazardous, some polymers may decompose in a not controlled way, by foaming during decomposition what is hazardous [hazardus] for the fragile sample holder
Therefore any new material should be evaluated for its compatibility with our setup:

52. Evaluation of new materials
Compatibility assessment:
by providing a reference to a thermal analysis or
by burning the sample in a furnace
at the conditions foreseen for the measurement:
sample composition
temperature range (max °C)
inert atmosphere
alumina crucible
We propose two ways for assessing the compatibility:
By providing a reference to a thermal analysis, or by burning the sample in a furnace,
But both the reference or the burning must be at the conditions foreseen for the measurement:
So the sample composition and the measurement conditions are limited to

53. Sample preparation Sample form:
fine powders
compact solids
films, fibers
Ensure good thermal contact between sample and heat flux-sensor:
powders: evenly distributed at the bottom of the sample crucible, gently tamped
Always use the same sample mass (~ mg)
Sample in different forms may be tested, we use usually fine powders, but also compact solids, films and fibers [fajbers] may be measured
For the optimal quality of result you should ensure good thermal contact between sample and heat flux-sensor, which is just below the bottom of the crucible, in case of powders it is done by simply evenly distributing the powder over the bottom surface of a crucible and tamping it gently
Films – place the film piece flat at the bottom one on another, a small stack
3. You can see on the bottom pictures, that sample is placed into a very small alumina crucible. Usually sample mass between mg are used so even only 10 mg of sample is enough. But what is important, always use the same mass of the sample.
(On the side picture you can see the interior of the furnace with a sample holder, and a sample being placed onto it with tweezers)

54. Thermogravimetric Analysis
Factors affecting TG curve
heating rate
sample size
particle size of sample
the way it is packed
crucible shape
gas flow rate
DTG – derivative of TG curve, often useful in revealing extra detail.
TG also often used with DTA (differential thermal analysis).
DTA – record difference in T (∆T) between sample and reference material. Each DTA curve should be marked with either endothermic or exothermic direction.
Curve – peak represent exothermic or endothermic reaction.

55. TG/DTA scan of montmorillonite clay.
Large endotherm at 114°C is assigned to loss of interlayer absorbed water.
2nd endotherm at 704°C is dehydroxylation reaction of the mineral.
Last 2 peaks are attributed to structural changes, since no weight loss are evident in TG.

56. THERMO-MECHANICAL ANALYSIS (TMA)
Dimensional properties of a sample are measured as sample is heated, cooled or held under isothermal conditions. Loading or force applied can be varied.
Change of dimensions as a function of temperature is recorded.
TMA measurements record changes caused by changes in free volume of polymer.
Changes in free volume – by absorption or release of heat associated with that change, loss of stiffness, increase flow, change in relaxation time.
Free volume related to viscoelasticity, aging, penetration by solvents, & impact properties.

57. As the space between the chains increases, the chain can move.
Physical aging Tg
Increase in free volume caused by increased energy absorbed in chains and this increased free volume permits various types of chain movement to occur. Below Tg various paths with different free volume exist depending on heat history & processing of polymer, where the path with the least free volume is most relaxed.

58. Tg in polymer corresponds to the expansion of free volume allowing greater chain mobility above this transition.

59. Thermo-Mechanical Analysis (TMA)
Application :
Determine coefficient of thermal expansion (CTE ) of material.
Identify Tg & Tm of material.
Measure material’s heat deflection temperature (HDT).
Composite delamination temperature.
All types of solid – powders, films, fibers, molded pieces, etc.
Use of probe resting on sample under a positive load. As sample is heated, cooled or held isothermally, dimensional changes in sample is translated into linear displacement of probe.

60. Thermo-Mechanical Analysis (TMA)
Probe configuration – expansion, penetration, compression, flexure, extension & dilatometry.

61. TMA : (a) penetration & (b) extension.
LVDT – linear variable differential transformer. Also use other types of transducer – laser, optoelectronic.

62. TMA : (c) flexure & (d) torsional measurement.
Dimensional changes are monitored and transducer transform responses into electrical signal (output).

63. Measurement of Tg of epoxy PCB – probe rest on surface under low load
Measurement of Tg of epoxy PCB – probe rest on surface under low load. As sample expands during heating, probe is pushed up & resulting expansion of sample is measured. At Tg, epoxy matrix exhibits significant change in slope due to an increase in its rate of expansion. Onset T of this expansion = Tg.

64. CTE measurement – quantitative assessment of expansion over a T interval. CTE before Tg = 50.5 µm/m°C, while above Tg, CTE increases to µm/m°C. Also shows residual thermal stress – 1st heat result show undulation in region near Tg  reflects release of stresses.

65. TMA penetration probe – during measurement, loading is added so probe moves down thru sample as it softens. Useful for measuring Tg of coatings on substrate. TMA of wire sample with 2 coatings – inner coating prevents electrical contact between adjacent wires and outer coating used to bond the coil.

66. TMA penetration results on crosslinked and non-crosslinked polyethylenes. Crosslinked sample exhibits smaller degree of penetration due to higher viscosity in liquid region above Tm.
High sensitivity of TMA tech allows it to detect weak transitions otherwise may not be observed by DSC.

67. Extensive crystalline transition, & softening point, Tg.

68. Another sample shows significantly smaller crystalline to amorphous transition dimension increase compared to 1st sample.

69. Thermo-Mechanical Analysis (TMA)
Since many materials are used in contact with dissimilar material, rate & amount of expansion needs to be known to help design around mismatches that can cause failure of final product.
Limitation – only for solid samples. Also material creep occurring concurrently with normal dimensional changes.
Thermodilatometry – dimensional changes over wider T range, up to 2000°C in variety of atm (inert, vacuum, air, etc)
TD – sintering behavior of ceramic, clays.

70. Sintering behavior of kaolin & kaolinitic clays – on heating loses water & form metakaolin structure. Then converts to spinel structure (above 960°C) & then above 1100°C to mullite.

71. DSC scan of amorphous metal alloy.

72. TMA of LDPE sample – compression mode

73. TMA of polyester partially oriented fibers – extension mode