Thermo Gravimetric Analysis-1.pptx

Ppt provide information about thermogravimetry ie thermal technique in simple way

1. Thermogravimetric Analysis Presented by - Dhakane Sumeet Sureshrao M. Pharm Pharmaceutics JSPM’s Rajarshi Shahu College Of Pharmacy & Research, Pune 1

2. Content Introduction Types Principle Instrumentation TGA curve Factor affecting TGA curve Application Advantages Disadvantages 2

3. Introduction Thermo - Thermal Gravimetric - Measurement of weight It is thermo - analytical technique that measures weight change of sample at given time and temperature. Definition- TGA is a branch of thermal analysis which examine mass change of a sample as function of temperature or time as sample is subjected to controlled temperature program in controlled atmosphere. 3

4. Types- A) Static TGA- In this type the sample under analysis is maintained at a constant temperature for a period of time during which any changes in weight are observed carefully . B ) Dynamic TGA - In dynamic thermogravimetric analysis a sample is subjected to conditions of predetermined, carefully controlled continuous increase in temperature that is invariably found to be linear with time . C) Quasistatic TGA :- I n this technique sample  is  heated to a constant weight at each of a series of increasing temperature 4

5. Principle:- In thermogravimetric analysis, the sample is heated in a given environment (air, N 2 , Co 2 , He, Ar , etc.) at controlled rate. The change in the weight of the substance is recorded as a function of temperature or time. The temperature is increased at a constant rate for a known initial weight of the substance and the changes in weights are recorded as a function of temperature at different time interval . The plot of weight change against temperature is called thermogravimetric curve or thermogram. T his is the basic principle of TGA. 5

6. Instrumentation:- Essential requirements for an instrument 1) Balance 2) Sample Holder 3) Furnace 4) Temperature Measurement (Thermocouples) 5) Data recorder 6

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8. 1) Balance Null-point Type : This Uses appropriate sensing-element (sensor) which detects any slightest deviation of the balance Null-point mechanism provides a restoring force, directly proportional to the change in weight, so it ensures sample remain in same zone of furnace irrespective of mass change. The weight change signal are differentiated electronically to obtain a Thermogravimetric curve Null detector Restoring Force Weight Change 8

9. B ) Deflection Type : B ased on either a conventional analytical balance It may be helical spring, cantilever, beam and torsion type analytical balance The deviations in weight change are directly recorded as Data for Thermogram Fig – Types of deflection balance 9

10. 2) Sample Holders Made up of Stainless steel, Quartz, Platinum or Alloy May be shallow or Crucible Shaped Selection of holder depend on - nature of sample - weight of sample - Temp range to be used This plays an important role in result of TGA Pan volumes of 20, 50, 100, and 250 μL are common Sample to be studied is places in it and attached to balance 10

11. 3) Furnace Furnace surrounds the sample and sample holder should be capable of producing a wide range of temperature programs accurately Nichrome (1100℃), Platinum, Alloy of platinum and rhodium ( 1500 ℃ ) , Tungsten molybdenum (1750℃), is used as material for furnace. T emperature control of the furnace is achieved via a thermocouple mounted very close to the furnace-winding. High size furnace yield larger hot zone whereas small size may not. Temperature controlling with small size furnace may not possible 11

12. 4) Temperature measurement Thermocouple is a sensor that measure temperature. This thermocouple used in TGA to analyze temperature. Chromel , Tungsten, rhenium thermocouples may used. Position of thermocouple play important role in temperature measurement. Thermocouple in contact with sample or sample holder are preferred. Made as small as possible and placed close to sample, sometimes it placed at bottom of pan 12

13. 5 ) Data Recorder Computer workstation in used to control , collect, and process data for any thermal analysis technique. The data received from the sensors accurately converted and processed to produce the TG curve 13

14. TG Curve Result from above process is recorded as plot of Weight Change VS Temperature or Time This is Referred as TG Curve In Static TGA G raph will be of Weight VS Time In Dynamic TGA Graph will be of Weight VS Temperature 14

15. 15 A A ’ B’ B Horizontal Position indicate that there is no weight change. From this we can know about thermal stability of compound (no change in properties). Curve A to A’ is perfectly horizontal so it will stable up to T i °C. Curved portion (A’ to B’ ) indicate Weight loss T i T f

16. Procedural Decomposition Temperature ( pdt )- It is lowest Temperature at which cumulative mass change reaches a magnitude that thermocouple can detect . Indicated by T i Final Temperature :- Is temperature at which cumulative weight change reaches to maximum value, corresponding to complete reaction Indicated by T f Reaction Interval :- Difference between T f - T i is defined as reaction Interval 16

17. Factor Affecting TG curve Instrumental Factor 1) heating Rate - - If substance heated at faster rate it my decompose . hence appropriate heating rate should used 2) Furnace Atmosphere :– - atmosphere in Furnace Causes irregularities in curve 3) S ample holder :- - Shape and size of Holder affect the heating rate of . . sample so it may affect TG curve 17

18. B) Sample Related Factor 1) Weight - - smaller weight of sample give accurate result while . Large amount causes deviation 2) Particle Size :– - small particle size sample decompose at lower temp. 3) Compactness of sample :- - Compressed sample decompose at higher temperature . . so it may affect nature TG curve 18

19. Application TG curve can used for identification or quality control To study of kinetics of reaction rate. To study thermal stability. To study sublimation behavior of various substance. To study catalyst - change in chemical state of catalyst is determined Used for purity determination of primary and secondary standard 19

20. Advantages Accurate method Easy to use Minimal sample preparation Convenient and time saving technique Instrument can be used at very higher temperature 20

21. Disadvantages Only Solid sample can be analyzed It is destructive Technique. Limited sample quantity Melting or Crystal change can not be analyzed in TGA 21

22. 22 References – Gurudeep R. Chatwal, Sham K. Anand , Himalaya publishing house, 2002, Instrumental Method Of Chemical Analysis, 5 th Ed. Page No 2.701. D.A. Skoog Et al., Principal of Instrumental Analysis, 6 th Ed, H arcourt Publishers, 2001. Page No 892 Alexander , Kenneth, Riga , Alan, Haines , Peter, 2005/01/01, Thermoanalytical Instrumentation and Applications, Ewing's Analytical Instrumentation Handbook

23. Thank You 23