Thermogravimetric analysis.pptx

In thermogravimetric analysis, the change in weight in
relation to a change in temperature in a controlled environment is measured. Heat is used in TGA to force
reactions and physical changes in materials. Thermogravimetric analysis (TGA) is a reliable method to determine
endotherms, exotherms, measure oxidation processes, thermal stability, decomposition points of explosives,
characteristics of polymers, solvent residues, the level of organic and inorganic components of a mixture,
degradation temperatures of a material, and the absorbed moisture content of materials. Materials analyzed by
thermogravimetric analysis include explosives, petroleum, chemicals, biological samples, polymers, composites,
plastics, adhesives, coatings, organic materials, and pharmaceuticals.The thermogravimetric analysis instrument usually consists of a high-precision balance and sample pan.
The pan holds the sample
material and is located in a
furnace or oven that is
heated or cooled during the
experiment. A thermocouple
is used to accurately control
and measure the
temperature within the oven.
The mass of the sample is
constantly monitored during
the analysis. An inert or
reactive gas may be used to
purge and control the
environment. The analysis is
performed by gradually
raising the temperature and plotting the
substances weight against temperature. A
computer is utilized to control the
instrument and to process the output
curves.

1. Thermogravimetric analysis Karolinekersin E 4/2/2022 1

2. Contents Introduction Principle Instrumentation Classification of TGA Thermogravimetric curve Interpretation of thermogram Advantages Disadvantages Conclusion 4/2/2022 2

3. Introduction Thermogravimetric Analysis is a technique in which the mass of a substance is monitored as a function of temperature time as the sample specimen is subjected to a controlled temperature program in a controlled atmosphere. The Thermogravimetric Analyzer (TGA) measures the change in weight of a sample as tested through a temperature profile The TGA can provide information about chemical phenomena including chemisorption, desolvation and dehydration, decomposition, and solid-gas reactions such as oxidation or reduction. 4/2/2022 3

4. Thermogravimetric Thermal Analysis (TGA) can be used for materials characterization through analysis of characteristic decomposition patterns. It is an especially useful technique for the study of thermoplastics, thermosets, elastomers, composites, plastic films, fibers, adhesives, coatings, paints, and fuels. TGA is useful for the study of polymeric materials, including thermoplastics, thermosets, elastomers, composites, plastic films, fibers, coatings, paints, and fuels. 4/2/2022 4

5. Principle –Working The main principle of thermogravimetric analysis (TGA) is that mass change of a sample can be studied under programmed conditions. A Thermogravimetric Thermal Analysis (TGA) is performed by gradually raising the temperature of a sample in a furnace as its weight is measured on an analytical balance that remains outside of the furnace. In TGA, mass loss is observed if a thermal event involves loss of a volatile component. 4/2/2022 5

6. Instrumentation 4/2/2022 6

7. Thermobalance 4/2/2022 7

8. Electronic Microbalance The microbalance serves as the most significant component of a thermobalance. The main purpose of a microbalance is to record the changes associated with sample mass. Important characteristics Mass change of a sample should be recorded accurately and in a reproducible manner under various atmospheric conditions as well as temperatures. Electronic signals should be appropriately provided by the microbalance to precisely record the mass change. An immediate and ultimately fast response to mass change must be provided by electronic signals 4/2/2022 8

9. Contd.. An arrangement for automatic mass regulation should be enabled by the microbalance. A high range of mechanical as well as electrical stability must be ensured by the microbalance. The microbalance should not be affected by vibrations . The operation of the microbalance should be user friendly. 4/2/2022 9

10. Sample Holder The sample holder is also called a crucible. The sample to be subjected to investigation or characterization is placed in the crucible, which is attached to the weighing arm of the microbalance. In general, the crucibles used for TGA vary in shape, size, and material. The main materials employed for making crucibles include aluminum, platinum, and quartz. 4/2/2022 10

11. Contd.. In addition to this, a few other materials are utilized occasionally, such as stainless steel, glass, and graphite. The utilization of crucibles made of different materials in TGA depends on the temperature range required for performing experiments. It is necessary that the crucible should possess at least 100 ◦ C higher thermal stability compared to experimental temperature conditions. 4/2/2022 11

12. Contd.. Also, the crucible selected for a certain experiment should efficiently and uniformly transfer heat to the sample. Therefore, it becomes appropriate that the thermal conductivity, shape, and thermal mass of the crucible are the significant parameters that should be taken into consideration before the usage of any crucible under predetermined experimental conditions. All the aforementioned parameters are in turn dependent on the nature and mass of the samples as well as the fixed experimental temperature regime 4/2/2022 12

13. Contd .. In the case of powdered samples, generally flat crucibles are used whereas liquid samples are analyzed using walled crucibles 4/2/2022 13

14. Furnace The furnace should be designed so that a linear heating rate can be achieved. The furnace consists of a hot zone in which both crucible and sample are placed. It should be considered here that the temperature of crucible as well as the sample corresponds to the furnace temperature. It is known that the internal atmosphere of a furnace can be affected by the temperature regime maintained in the furnace. 4/2/2022 14

15. Contd. Hence, it becomes adequate to select a furnace specifically suitable for the temperature regime to be used. It should be ensured that there exists no magnetic interaction among the sample and the heating coil present in the furnace. This is because the presence of magnetic interactions can lead to changes in the weight of the sample. 4/2/2022 15

16. Contd. In addition, the size of the furnace also plays an important role in accurate measurement. A furnace with high mass may withstand an enhanced temperature regime and ensure a uniform hot zone. However, an increased timescale is required for achieving the targeted temperature. On the other hand, low-weight furnaces can be able to provide quick heating with great difficulty in controlling the rate of increase in temperature. Therefore, lightweight furnaces do not allow for proper maintenance of the hot zone. Another significant parameter that affects the quality of analysis is the position of the furnace with respect to balance 4/2/2022 16

17. Thermocouple A thermocouple is used for measuring temperature. Similar to heating coils, various types of material are used for the fabrication of thermocouples, which include tungsten or platinum alloys. Aluminum alloys, namely chromal and alumel , are used as thermocouples for measuring temperature conditions below 1100C. For temperature conditions above 1100C, tungsten materials are used for making thermocouples. The position at which the thermocouple is placed plays a governing role in precise measurement during analysis. 4/2/2022 17

18. Temperature Programmer The temperature programmer is basically used to control the heating rate when the temperature tends to increase during the analysis. The heating rate is customized to be recorded in degrees per minute in terms of the Kelvin or Celsius scale. The rate of heating or cooling can be considered constant when the temperature versus time curve appears to be linear. 4/2/2022 18

19. Data Recording Unit The data recording unit is basically a chart recorder or microcomputer that is used for recording the output provided by balance and furnace. A microcomputer enables one to both save and plot the temperature versus weight loss curve using preinstalled software while performing mathematical problems, whereas this feature is not present in a chart recorder. Also, a microcomputer helps in plotting the multiple weight loss curves in a simultaneous manner as a function of temperature or time. In addition to chart recorder and microcomputer, some other types of data recorder unit include X-ray recorder and time-base potentiometric strip chart recorder. 4/2/2022 19

20. Classification of Thermogravimetric Analysis 4/2/2022 20

21. Dynamic Thermogravimetric Analysis 4/2/2022 21

22. Static or Isothermal Thermogravimetric Analysis 4/2/2022 22

23. Quasistatic Thermogravimetric Analysis In this method, the sample is heated to a constant weight at each in a series of increasing temperatures 4/2/2022 23

24. THERMOGRAVIMETRY CURVE The TG curve usually represents a plot of weight change as a function of temperature or time. “ T i ” -the temperature at which the onset of decomposition is initiated, “ T f ”- the temperature at which the decomposition reaction is terminated or completed. It should be understood that the values of T i and T f depend on the thermal stability of the sample being analyzed 4/2/2022 24

25. Types of Thermogravimetry Curve Type 1: This type of curve exhibits no weight change throughout the entire temperature range used for analysis. The possible reason for this phenomenon may be the fact that the thermal stability of the sample is higher than the temperature range. Type 2: This type of curve exhibits a mass loss region , which is then followed by a constant line. TG curves of type 2 result from certain processes such as drying in which volatile compounds are evaporated and desorption occurs. 4/2/2022 25

26. Contd.. Type 3: TG curves that demonstrate a single stage of weight loss or decomposition correspond to type 3 Type 4: This type of curve can be exhibited by samples that undergo a multistage decomposition process . Type 5: This type of curve can result when there is an increment in sample weight due to surface oxidation reactions that take place in a reacting atmosphere . Type 6: This type of curve can be possible if there are multiple reactions with respect to a rise in temperature . The increase in weight is due to the surface oxidation reaction, whereas the decrement in weight with further rise in temperature corresponds to the decomposition process of the reaction products 4/2/2022 26

27. Types of curves 4/2/2022 27

28. Region of TG curve Plateau Initial decomposition temperature Final decomposition temperature Reaction interval Determination of Isobaric change Evolved gas analysis 4/2/2022 28

29. Plateau The plateau is the region present in the TG curve that corresponds to a constant line that follows after the weight loss portion. In this region, the mass of the sample is constant or else no weight change can be found. 4/2/2022 29

30. Initial Decomposition Temperature The initial decomposition temperature ( T initial ) corresponds to the temperature point at which the cumulative weight change attains a magnitude that can be detectable by a thermobalance. 4/2/2022 30

31. Final Decomposition Temperature The final decomposition temperature ( T final ) corresponds to the temperature point at which the cumulative weight change attains a maximum and cannot change further. 4/2/2022 31

32. Reaction Interval The temperature difference that occurs among the initial and final decomposition temperatures corresponds to the reaction interval. In the case of a single stage of decomposition, there exists only a single reaction interval. For a multistage decomposition profile, several reaction intervals may be present, according to the decomposition stages revealed by the sample with respect to heating. 4/2/2022 32

33. Determination of Isobaric Mass Change The isobaric mass change curve can be recorded at constant partial pressure of the volatile products released during decomposition. The isobaric mass change curve refers to the equilibrium mass measured as a function of temperature when the sample undergoes heating in a controlled temperature program 4/2/2022 33

34. Evolved Gas Analysis It is well known that the evolution of gaseous compounds takes place when the sample undergoes decomposition under a controlled temperature program. When TGA is coupled to Fourier transform infrared (FTIR) spectroscopy or gas chromatography mass spectrometry instruments, it is possible to analyze the functional composition of gaseous compounds released from a sample subjected to a controlled temperature program. 4/2/2022 34

35. Information From Thermograms 4/2/2022 35 The term “thermogram” refers to a plot obtained by TGA that comprises weight loss versus temperature data.

36. Thermal stability : Thermal stability is determined for a substance using TGA based on its ability to maintain its characteristics as almost unaffected upon exposure to heat. The knowledge of thermal stability is very important for engineers so that it is possible to predict the temperature regime of alloys, polymers, and nanomaterials. 4/2/2022 36

37. Composition of sample Upon increasing the temperature of a sample, it is certain that the sample undergoes weight loss. The information about weight loss remains significant for chemists to determine the composition of a sample so that it is possible to understand the reaction steps involved in the decomposition process. Through the weight loss profile, it is also possible to identify an unknown compound present in the sample or evaluate the amount or percentage of a specific compound present among a mixture of different compounds in the sample. 4/2/2022 37

38. Procedural decomposition temperature With the help of a thermogram, the procedural decomposition temperature, which indicates evaporation or decomposition processes of a substance, can be evaluated. 4/2/2022 38

39. Factors affecting the thermogram Instrumental factors Effect of heating rate Effect of furnace atmosphere Geometry of sample holder Sample characteristics Amount or weight of a sample Sample packing size Particle size Method of preparation 4/2/2022 39

40. Different TGA techniques 4/2/2022 40

41. TGA-FTIR The most general system used for EGA involves the utilization of TGA coupled with an FTIR spectrometer (TGA-FTIR). When a sample is subjected to heating in TGA, volatile or combustion components are generated by burning. Such volatile or combustion components released will then be transferred to an infrared (IR) cell through which identification of released components is done. This instrumental method of analysis is more useful if the gases released correspond to simple components such as carbon dioxide or general solvents that present featured IR spectra 4/2/2022 41

42. TGA –MS TGA-MS serves as a powerful tool for EGA because of its ability to identify even minute levels of components present in the evolved gas. Hence, this technique finds great potential for identification of components in quality control, safety, as well as product development departments. 4/2/2022 42

43. TGA –GCMS Similar to TGA-MS, the gas evolved during the heating of a sample is transferred to a gas chromatograph where the components are collected. ]Thereafter, the collected gas sample is run using GC to separate the different components and the peaks are identified by MS. This technique gained popularity because of its ability to detect even very minute levels of components present in complex mixtures. 4/2/2022 43

44. Advantages of TGA Any type of solids can be analysed. TGA has high accuracy balance. TGA may be convenient and time saving. Easy sample changing and easy change of sample holder. Fast heating rate with good resolution can be maintained. In TGA one can hold the furnace at 1000 ◦ C. TGA is a rapid process. 4/2/2022 44

45. Disadvantages of TGA The primary limitation of TGA methods, namely that mass loss of volatiles is not equivalent to formation of degradants, significantly impedes its ability to provide consistent universal indicators of actual extent of degradation. It cannot study process like melting, transitions from one crystalline form to another, glass transition temperature etc. 4/2/2022 45

46. Applications of TGA A TGA can be used for materials characterization through analysis of characteristic decomposition patterns. It is an especially useful technique for the study of polymeric materials, including thermoplastics, thermosets, elastomers, composites, plastic films, fibers, coatings, paints, and fuels 4/2/2022 46

47. Conclusion Thermo gravimetric analysis (TGA) technique, sample is heated at a given temperature with controlled heating rate to measure the change in the weight of a sample substance as a function of temperature. The results can be interpreted from TGA curve. Thermogram is plotted between the change in mass and temperature. TGA is useful for the study of polymeric materials, including thermoplastics, thermosets, elastomers, composites, plastic films, fibers, coatings, paints, and fuels. 4/2/2022 47

48. THANK YOU 4/2/2022 48