Thermal analysis, C alorimetry and ThermoMechanical Analysis

1. Thermal analysis, Calorimetryand ThermoMechanicalAnalysis

2. Thermal analysis

3. Basic Principle • Substance subjected to thermal treatment may undergo physical or chemical changes • Changes can occur: • in dimension • magnetic properties • weight • crystalline transition • mechanical properties • …

4. Thermal analysis → Differential thermal analysis (DTA): in this technique the heat flow to the sample and reference is the same. As the sample and the reference are heated identically, phase changes and other thermal processes occurring in the sample will cause a difference in temperature between the sample and reference. DTA measures this temperature difference. → Differential scanning calorimetry (DSC): in this technique the difference in the amount of heat required to increase the temperature of a sample and thereference is measured as a function of temperature. Sample and reference are maintained at the same temperatures throughout the experiment. → Thermogravimetric analysis (TGA) is a technique to determine changes in sample weight in relation to changes in sample temperature.

5. Basic Principle • Sample’s Property Measured • Weight TGA (also called TG) • Heat Flow DSC • Temperature DTA In concrete science TG and DTA are the most commonly used techniques

6. Different Techniques • Thermometric Titration (TT) • Heat of mixing • Thermal Mechanical Analysis (TMA) • Thermal Expansion Coefficient • Dynamic Mechanical Analysis (DMA) • Viscoelastic Properties • Differential Scanning Calorimetric (DSC) • Heat flow during Transitions • Thermal Gravimetric Analysis (TGA) • Weight Loss due to decomposition • Derivative Thermogravimetric Analysis (DTG) • Differential Thermal Analysis (DTA) • Heat of Transitions • Temperature Programmed Desorption (TPD) • Temperature at which gas is desorbed from (catalyst) surface • Emission gas Thermoanalysis (EGT) Just for knowingthattherearemoretechniquesthan the oneswediscuss!

7. TGA – thermal gravimetry

8. TGA - principle • Tests performed on samples to determine changes in weight in relation to change in temperature. • A sample is suspended on a highly sensitive balance over a precisely controlled furnace • Different components decompose by different characteristic temperatures  • Possible to identify component knowing the decomposition graphs (weight change vs time)

9. TGA - measurements • Constant Heating Rate • Initial Temp • Final Temp • Heating Rate (°C/min) • Data • Weight vs Time • Weight vs Temp. • Obtained data are shown as differentiated values (DTG)

10. TGA – application • TG as used in concrete science: • Usually combined with other techniques (most commonly with DTA) • Gives quantitative test results • Used to study e.g. • Cement hydration • Deterioration processes

11. TGA - examples

12. TGA - examples

13. TGA - examples

14. DTA – differential thermal analysis

15. DTA involves heating or cooling a test sample and an inert reference under identical conditions, while recording any temperature difference between the sample and reference. • Changes in the sample which lead to the absorption or evolution of heat can be detected relative to the inert reference. • DTA curve can be used as a fingerprint for identification purposes.

16. DTA-principle • Difference in Temp ∆T between sample and reference material is recorded • The heating regime is the same in both cases • As example: In an endothermic process or reaction (in which the system absorbs energy from the surroundings in the form of heat) such as the decomposition of calcite or melting of a material, the temperature of the sample, Ts, will lag behind the temperature of the reference, Tr. • The output, ΔT = Ts -Tr is recorded as a function of Tr. • Thermal effects are reported in terms of the characteristic temperature, peak temperature, temperature range of the peak, peak width, peak amplitude or height, and peak area. • Results can be utilized for quantitative and qualitative analysis

17. DTA-examples DTA + DTG

18. DTA-examples DTA of tricalcium aluminate hydrated at 7 days (168 h) in the presence or absence phosphogypsum.

19. DTA-examples Hydration of calcium silicates • A knowledge of the hydration of individual cement compounds and their mixtures forms a basis of interpreting the complex reactions that occur when portland cement is hydrated under various conditions • Tricalcium silicate and dicalcium silicate together make up 75–80% of portland cement • In the presence of water the reaction products are calcium silicate hydrate (endothermal effects below 200°C) and calcium hydroxide, with an endothermal effect in the range 450–550°C. • Some calcium carbonate may also be detected in the range 750–900°C by an endotherm • The calcium silicate hydrate is poorly crystallized and gives only weak diffusion lines in XRD.

20. DTA-examples Hydration of calcium aluminates • The aluminate phases, although present in small amounts, exert a significant effect on the setting and early strength development in cement pastes. • In the hydration of tricalcium aluminate, the initial formation of hexagonal phases is identifiable by the endothermal effects at 150–200°C and 200–280°C. • These are converted to a cubic phase of formula C3AH6. • The cubic phase shows characteristic endothermal effects at 300–350°C and 450–500°C.

21. DTA-examples

22. DTA-examples Hydrogarnet

23. DSC – differential scanning calorimetry

24. DSC

25. DSC • Constant Heating Rate • Initial Temp • Final Temp • Heating Rate (°C/min) • Data • Heat flow to sample minus Heat flow to reference vs Time (Temp.) • Measures heat of crystallization

26. DSC-examples

27. DSC-examples • DSC of the C,A-H20 system shows endothermal effects even at 5 min, signifying the presence of hydration products (Fig. 6a). • Peaks at about 145-150 ˚C and 265-280 ˚C represent the presence of metastable hexagonal phases (C2AH,-C,AH,). • The endothermal effect at about 150 ˚C increases up to 4 h and that at 265-300°C continues to increase up to 2 days. • The large peak at about 300˚C (4 h to 2 days) is mainly due to the presence of cubic phase (C3AH,).

28. Calorimetry

29. science of measuring the heat of chemical reactions or physical changes Calorimetry Adiabatic Isothermal Semiadiabatic measuring the heat produced by chemical reactions or physical changes as function of time measuring the temperature rise/drop by chemical reactions or physical changes under insulated or semi-insulated conditions as function of time measuring the temperature rise/drop by chemical reactions or physical changes under semi-insulated conditions as function of time

30. Conduction Calorimetry

31. Cement hydration is a very exothermic process => produces heat: C3S + 3.43 H e C-S-H + 1.33 CH ΔH = -121.1 KJ/mol C2S + 2.43 H e C-S-H + 0.33 CH ΔH = -45.1 KJ/mol C3A + 6 H e C4AH6 ΔH= -263.0 KJ/mol The heat of hydration (ΔH) can be measured by calorimetry Calorimeter: Device to measure the heat (Q) exchanged or stored by the calorimetric vessel (and its contents) in which the transformation studied takes place.

33. Adiabatic calorimetry An adiabatic calorimeter is a calorimeter where the heat flow between the calorimetric vessel and the surrounding shield is minimized. Its basic equation may be written as: C dT(t)/dt = P (t) where P(t) is the thermal power within the sample cell and where C is the heat capacity of the calorimetric vessel and its contents (i.e. the sample). C of the vessel is known A calorimeter is considered to be adiabatic if the temperature loss of the sample is not greater than 0.02 K/h

36. Isothermal calorimetry A. Syringe B. Insulation jacket C. syringe holder D. U-shaped holder E. Glass ampoule F. Aluminum cup G. Reference cup/sample H. Heat sink I. Thermocouple plate (TCP) Wadsö et al

50. Conduction calorimetry of C3S and cement shows five steps during the hydration process