TGA.pptx principle, instrumentation, theory

TGA.pptx principle, instrumentation, theory

1. Thermogravimetric Analysis Presente d by : Dr. Vijaya U. Barge (Vice Principal & Professor) Pune District Education Association’s Shankarrao Ursal College of Pharmaceutical Sciences & Research Centre.

2. Contents : Introduction Types Principal TGA Curve Instrumentation F a ct o rs a f f e cti ng r e su l ts Advantages Limitations P h a rmaceu t i c a l a p p l i c a t i ons

3. Thermogravimetric analysis(TGA) Thermogravimetric analysis or thermal gravimetric analysis (TGA) is a met h o d o f th e rm a l a nal y s i s i n w h i c h t h e ma s s of a s a mp l e i s m e as u r e d o v e r t i me a s th e t e m p e r a ture ch a nge s . This information meas u r e me n t about prov i d es phy s i c a l phenomena, such as phase transitions, absorption and desorption as well as chemical phenomena including c h e mi s o rpti o n s , th e rm a l decomposition, and solid-gas reactions ( e . g ., o x i dation or r e d u c tion)

4. Three t y pes o f the r mog r a v imet r y : I s o t h er m al o r sta t i c thermogravimetry: In this technique the sample weight is recorded as function of time at c o n s t a nt t emp e r a ture . Quasistatic thermogravimetry: In this techn i que th e s a mp l e i s h e a ted to c o n s t a nt weight at each of series of increasing temperatures. Dynamic thermogravimetry : In this technique the sample is heated in an environment whose temperature is changing in a predetermined manner generally at linear rate. This type is g e n e r a ll y u s e d.

5. P r inci p le of T G A: In thermo-gravimetric analysis, the sample is heated in a given environment (air, N2, CO2, He, Ar, etc.) at controlled rate. T h e c h a nge i n t h e w e i g h t o f the s u b s t a n c e 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 a t d i ff e r e nt t i me i nte r v a l . This plot of weight change against temperature is called thermo-gravimetric curve or thermo-gram, this is the basic pr i n c i ple o f T GA.

6. T G A cu r v e : The instrument used for themo- gravimetry is a programmed precision balance for rise in temperature known a s T h e rmo - b a l a n c e . Re s u l t s a re dis p l a y e d b y a p l o t o f ma s s c h a nge v e r s u s tem p e r a ture o r ti m e a nd a re k nown a s T h e rm o g r a v i metr i c c u r v e s o r T G c u r v e s .

7. T G A cu r v e: TG curves are normally plotted with the ma s s c h a nge ( Dm) i n p e r c e nt a g e on the y - a x i s a nd t e mp e r a ture ( T) o r ti m e ( t ) o n the x - a x i s . There are two temperatures in the reaction, Ti(procedural decomposition temp.) and Tf(final temp.) representing the lowest temperature at which the onset of a mass change is seen and the lowest temperature at which the process has been completed respectively. T h e r e a c tion tem p e r a ture a nd i nte r v a l (Tf-Ti) depend on the experimental condition; therefore, they do not have a ny fixed v a l u e .

8. In s t r u mentation of T G A:

9. In s t r u mentation of T G A: R e c o rd i ng b a l a n c e S a mp l e h o l d e r Furnace Temperature programmer /controller (thermocouple) Recorder

10. Recording balance : A microbalance is u s e d to r e c o rd a chan g e i n ma s s of s a mp l e/ substance. A n i d e a l m i c r o b a l a n c e mu s t po s s e s s f o ll o w i ng f e a ture s : It should accurately and reproducibly record the change in mass of sample in ideal ranges of atmospheric conditions and temperatures. It should provide electronic signals to record the change in mass using a recorder. The electronic signals should provide r a p i d r e s pon s e to cha n g e i n ma ss .

11. R ec o r ding balan c e : It should be stable at high ranges, mechan i c a ll y and e l e c tric a ll y . Its operation should be user friendly. After the sample has been placed on microbalance, it is left for 10-15min to stabilize. Recorder balances are of to types: D e f l e c tio n - typ e i n s t r u me nts a nd Nu l l - t y pe i n strum e nt

12. R ec o r ding balan c e : I . De f l ec t i on b a l a n c es : T h e y a re f o ll o w i ng ty p e s - Beam t y pe H e li c a l t y pe iii. C a nti l e v e r e d b e a m i v . Tors i o n w i re

13. I I . Null p o i n t b a l a n c e s : It consist of a sensor which detects the deviation from the null point and restores the balance to its null points by means of r e s t o ri ng f o r c e .

14. Sam p le holder : The sample to be studied is placed in sample holder or crucible. It is attached to the w e i g h i ng a rm o f m i c r o b a l a n c e . There are different varieties of crucibles used. Some differ in shape and size while s o me d i ff e r i n m a ter i a l s u s e d. They are made up from platinum, aluminum, quartz or alumina and some other materials like graphite, stainless s te e l , g l as s , e tc

15. Sam p le holder: Crucibles : C r u c i b l e s s h o u l d h a ve tem p e r a tu r e at least 100K greater than temperature range of experiment and must transfer h e a t u n i f ormly to s a m p l e . T h e r e f o re th e shape, thermal conductivity and th e rm a l ma s s o f cr u c i b l es a re i mpo r t a nt which depends on the weight and nature of sample and temperature range. There are different types of crucibles. Shallow pans(used for volatile substances) Deep crucibles (Industrial scale calcination) 3. Loosely covered g e n e r a ted a t m. S tu d i e s ) crucibles (self 4. Retort cups (Boiling point studies)

16. Ty p es o f c r u c i b l e s:

17. Furnace : T h e f u rn a c e s h o u l d b e d e s i g n e d i n s u c h way that it produces a linear heating range. It should have a hot zone which can hold sample and crucible and its temperature corresponds to the tem p e r a ture of furna c e . There are different combinations of microbalance and furnace available. The furnace heating coil should be wound in such a way that there is no magnetic interaction between coil and sample or there can cause apparent ma s s chan g e .

18. Temperature programmer/controller: Temperature measurement is done in no. of ways thermocouple is the most c o m mo n techn i que. The position of the temperature meas u ri ng d e v i c e r e l a t i ve to th e s a mp l e i s v e ry i mpo r t a nt. T h e m a j o r t y pes a r e : a . The thermocouple is placed near the sample container and it has no c o nt a c t w i th t h e sa m p l e c o nt a i n e r. T h i s isn’t a good arrangement where low- pr e s s u re are e mp l o y e d.

19. Temperature programmer/controller: b . T h e sa mp l e i s k e pt i n s i de t h e sa mp l e holder but not in contact with it. This arrangement is better than that of (a) because it responds to small temperature changes. c . T h e t h e rm o c o u p l e i s p l a c e d e i t h e r i n contact with sample or with the sample container. This is the best arrangement of sa mp l e t e m p e r a ture d e tec t i o n.

20. Temperature programmer/controller: T h e rm o c o u p l e i n a t h e r m o - b a l a n c e :

21. Recorder: T h e r e c o rd i ng s y s te ms a re ma i n l y o f 2types Time-base potentiometric strip chart recorder. X - Y r e c o rd e r.  In some instruments, light beam galvanometer, photographic detail recorders or one recorder with two or m o re p e ns are a l s o u s e d.  In the X-Y recorder, we get curves having plot of weights directly against tem p e r a ture s . How e v e r, percentage mass change t h e a g a i n s t tem p e r a ture o r time w o u l d b e m o re useful.

22. Facto r s aff ecting TGA: The factors which may affect the TGA curves are classified into two main groups.: I n str u me n t a l f a c t o r s: Furna c e h e a ti n g ra t e Furna c e a t m o s p h e re S a m p le c h ara c ter i st i c s i n c l u d es : W e i g h t o f th e sa mp l e S a mp l e p a rtic l e s i ze

23. Facto r s af f ecting TGA: 1. I n str u m e n t a l f a c t o r s : Furnace Heating rate: The temperature at which the compound (or sample) decompose depends upon the heating rate. When the heating rate is high, the decomposition temperature is also high. A h e a ti n g r a te o f 3 . 5 ° C p e r mi n ute i s u s u a l l y recommended for reliable and r e prod u c i b l e T GA. Furnace atmosphere: The atmosphere inside the furnace surrounding the sample h a s a pro f o u nd e ff e c t o n the d e c o mpos ition temperature of the sample. A pure N2 gas f r o m a c y l i n d e r passed th r o u g h the f u rn a c e w h i c h prov i d es an i n e rt a t m o s p h e r e .

24. Facto r s af f ecting TGA: 2. Sam p le c h ara c teris t i c s: W e i g h t o f t h e sa mp l e : A s ma l l w e i g h t o f the sample is recommended using a small weight eliminates the existence of temperature gradient throughout the sample. Particle size of the sample: The particle size of the sample should be small and u n i f o rm. T h e u s e o f l a r g e par t i c l e o r c r y s t a l may result in apparent, very rapid weight l o s s d u ri ng h e a ti n g . 2 5

25. O ther fa c to r s af f ecting T G A cu r v e: S a mp l e h o l d e r H e a t o f r e a c tion C o mp a c tne s s of s a mp l e P r e v i o u s h i s t o ry of t h e s a mp l e

26. A d v antages of T G A: A relatively small set of data is to be treated. Continuous recording of weight loss as a function of temperature ensures Equal weightage to examination over the whole r a nge o f s tu d y . As a single sample is analyzed over the whole range of temperature, the variation in the value of the kinetic parameters, if a n y , w i l l b e i n d i c a te d .

27. Limita t ions of T G A: The Chemical or physical changes which are not accompanied by the change in mass on heating are not indicated in thermo- gravimetric analysis. During TGA, Pure fusion reaction, crystalline transition, glass transition, crystallization and solid state reaction with no volatile product would not be indicated because they provide no c h a nge i n ma s s of th e s p e c i me n .

28. A p pli c ations of T G A: From TGA, we can determine the purity and thermal stability of both primary a nd s e c o n d a ry s t a n d a rd. Determination of the composition of complex mixture and decomposition of complex OR composition of complex systems. For studying the sublimation b e h a v i o ur o f v a ri o u s s u b s t a n c e s . TGA i s u s e d to s t u dy t h e k i n e t i c s o f the r e a c tion ra t e c o n s t a nt. The effect of reactive or corrosive a t m o s p h e re on m a ter i a l s .

29. A na l y s i s of th e do s a g e f o rm. Used in the study of catalyst: The change in the chemical states of the catalyst may be studied by TGA techniques. (Zn- ZnCrO4) Zinc-Zinc chromate is used as the catalyst in the s y nt h e s i s of m e than o l . Oxid a tive s t a b i l i t y of m a ter i a l s . E s tim ated l i f e time of a p r o d u c t. Moisture and volatiles contents on materials. T G A i s o f ten u s e d to meas u re r e s i d u a l solvents and moisture, but can also be used to determine solubility of p h a rm a c e u tic a l m a ter i a l s i n s o l v e nt s .