Thermogravimetric analysis ppt

thermogravimetric analysis ppt

1. THERMOGRAVIMETRIC ANALYSIS (TGA) Yudhishthir singh baghel (Pharmaceutics) [email protected] 1

2. THERMAL ANALYSIS Thermal analysis is a branch of materials science & a group of analysis which study the property of material when the change with temperature . In this technique mass of the substance is measure as the form of temperature while it a subjected to control temperature. Types of thermal analysis Thermogravimetric Analysis (TGA or TG) Differential Scanning Calorimetry (DSC) Derivative Thermogravimetry (DTG) Differential thermal analysis (DTA) 2

3. INTRODUCTION (TGA) Thermogravimetry (TG) is the branch of thermal analysis which examines the mass change of a sample as a function of temperature (in the scanning mode) or as a function of time (in the isothermal mode). Thermogravimetric analysis is a method of thermal analysis in which changes in physical and chemical properties of materials are measured as a function of increasing temperature rate or as a function of time. 3

4. Types of Thermogravimetry There are three types of Thermogravimetry : Isothermal /static Thermogravimetry Quasistatic Thermogravimetry Dynamic Thermogravimetry 1.Isothermal /static Thermogravimetry : in this technique the sample weight is recorded as a function of time at constsnt temperature. 2. Quasistatic Thermogravimetry : in this technique the sample is heated to constant weight at each of the series of increasing temperature. 3. Dynamic Thermogravimetry : in this technique a sample is heated in an environment whose temperature is changing in temperature manner generally at linear rate . 4

5. Thermo gravimetric analysis(TGA) Principle: In Thermogravimetric analysis, mass of the substance is measure as the function of temperature while it is subjected to control temperature program the resulted is TG curve or Thermogravimetric curve time or temperature is plotted on x-axis or mass is plotted on y-axis. Temperature - 0 °c -2000°c Change in mass of our analyte is studied because of different physical or chemical transition. 5

6. Cont … It is used in analysis of volatile products, gaseous products lost during the reaction in Thermoplastics, Thermosets, elastomers, films, fibers , paints etc. 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. 6

7. Types of transition Two types of transition occurs Physical transition chemical transition 1.Physical transition Adsorption Desorption Sublimation Evaporation Vaporization 2.Chemical transitation Oxidation Reduction Chemosorption Loss on drying degradation 7

8. Types of Graph 1.Disorption 2. Adsorption 3. Polymer analyte 4. Loss on drying 5. Oxidation followed by decomposition Instrumentation Components of instrumentation: A. Recording balance B. Sample holder C. Furnace D. Furnace temperature programmer/ controller E. Recorder 8

9. Block diagram of a Thermobalance 9

10. TG curves are recorded using a Thermobalance . It consists of an electronic microbalance, a furnace It consists of- Microbalance Recorder balance Sample holder Furnace Recorder Data recording unit Heating rate Time measurement 10

11. 1.Microbalance It is the most important component of thermobalance . It is used to record a change in mass of sample or substance. An ideal microbalance must possess following features: It should provide electronic signals to record the change in mass It should have the capacity of auto weight It operating should be user friendly Modern microbalances have the ability to be not affected by vibrations 11

12. 2. Recorder balance Types of recorder balance 1. Deflection balances 2. Null point balances 1. Deflection balances: They are of following types: a) Beam Type b) Helical Type c) Cantilevered Beam d) Torsion Wire 12

13. (a) Deflection balances Deflection balances are 4 types :- In these balance,the conversion of deflected beam take place into weight change In these balance, elongation or contraction of spring occurs with change in weight which is recorded by help of transducer. In this the beam is attached to hard torsion wire which act as fulcrum In this balance, one end of beam is fixed and on the other end sample is placed. (b) Null point balances It consist of sensor which detects the deviation from the null point and restores the balance to its null point by means of restoring force. 13

14. 3. Sample holder The sample to be studied is placed in sample holder or crucible. It is attached to the weighing arm of microbalance. There are different types of crucibles used such as Shallow pans Deep crucibles Loosely covered crucibles Retort cups They are made from platinum,aluminium,quartz or alumina and some other materials like graphite, stainless steel, glass etc. 14

15. 4. Furnace The furnace should be designed in such a way that it produce a linear heating range. It should have a hot zone which can hold sample and crucible and its temperature corresponds to the temperature of furnace. The temperature ranges can affect the internal atmosphere of furnace chamber therefore, it is necessary to choose specific type of furnace according to the temperature ranges. Coils used are made of different materials :- a) Nicrome wire or ribbon b) Platinum c) platinum 10% rhodium Alloy The size of furnace is important . 15

16. 5.Recorder The output from the microbalance and furnace are recorded using either chart recorder. The recording systems are mainly of 2 types:- 1. Time- base potentiometric strip chart recorder 2. X-Y recorder in the X-Y recorder, we get curves having plot of weights directly against temperatures. However, the percentage mass change against temperature or time would be more useful. 16

17. 6.Heating rate It is the rate of temperature increases, which is customarily quated in degrees per minute. The heating or cooling rate is used to be constant when the temperature/time curve is linear. 7.Time measurement It is done by thermocouple. Different materials are used for measuring different ranges of temperatures i.e. chromal or alumel thermocouple are used for T=1100 °c 17

18. Factors affecting the TG curve The factors which may affect the TG curves are classified into two main groups- (1) Instrumental factors (a) Furnace heating rate (b) Furnace atmosphere (c) Sample holder (2) S ample characteristics includes (a) Weight of the sample (b) Sample particle size (c) Heat of reaction (d) Compctness of the sample (e)Previous history of the sample 18

19. 1.Instrumental factors Furnace Heating rate: The temperature at which the compound (or sample) decompose depends upon the heating rate is high, the decomposition temperature is also high. A heating rate of 3.5 °c per minute is usually recommended for reliable and reproducible TGA. Furnace atmosphere: The atmosphere inside the furnace surrounding the sample has a profound effect on the decomposition temperature of the sample. A pure nitrogen gas from a cylinder passed through the furnace which provides an inert atmosphere. 19

20. 2.Sample characteristics a)Weight of sample: A small weight of sample is recommended using a small weight eliminates the existence of temperature gradient throughout the sample b)Particle size of sample: The particle size of sample should be small and uniform. The use of large particle may result in apparent very rapid weight loss. 20

21. Applications Physical transition Chemical transition Loss of drying Purity of analyte Stability of analyte Determination of bound and unbound water begins at room temperature due to dry gas flowing over sample TGA, we can determine the purity and thermal stability of both primary and secondary standard. corrosion studies Automatic Thermogravimetric analysis Evaluation of suitable standards 21

22. References:- Skoog , Douglas A, F James Holler and Timothy Nieman , Principles of Instrumental Analysis,5 th edition 2001. Gurdeep R. Chatwal , Sham k. Anand , instrumental Method of chemical analysis,5 th edition, Himalayan publishing house,page no-2.701 H.H.Willard , L.L Merrit Jr.J.A Dean,F.A Settle Jr.instrumental Method of Analysis.Wadsworth Publishing Company,USA 1986 Sharma B.K. Goel publishing House “Instrumental Methods of Analysis” pg.234-237.  22

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