thermogaravimetric analysis differential thermal analysis swapnil ppt

a college brief seminar about thermogravimetric analysis(TGA) and differential thermal analysis(DTA)....Swapnil Sanghavi

1. Seminar on
Thermogravimetric analysis (TGA)
And
Differential thermal analysis (DTA)
Presented By:
Swapnil M. Sanghavi
Roll no. 15
M. Pharm.-sem I
Dept. Of Pharmaceutics,
Nootan Pharmacy College, Visnagar.
1Swapnil Roll no. 15 NPC, Visnagar

2. CONTENTS
INTRODUCTION
TYPES
PRINCIPLE & METHODOLOGY
INSTRUMENTATION
FACTORS AFFECTING RESULTS
APPLICATIONS
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3. -CONCERNED WITH AN ANALYSIS OF SAMPLE WEIGHT
CHANGE CURVE.
-INVOLVES CHANGE IN WEIGHT OF A SYSTEM UNDER
EXAMINATION AS THE TEMPERATURE IS INCREASED AT A
PREDETERMINED RATE (PREFERABLY LINEAR)
-USING THERMOBALANCE, CURVE OF WEIGHT CHANGE OF
SAMPLE VS. SAMPLE TEMPERATURE CAN BE OBTAINED
DIRECTLY
-VERY RELIABLE, RUGGED AND VERY ACCURATE
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4. •DYNAMIC TGA: Sample is subjected to
conditions of continuous increase in temperature
usually linear with time
•ISOTHERMAL (STATIC) TGA : Sample is
maintained at a constant temperature for a period
of time during which any changes in weight are
noted
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5. METHODOLOGY
*Described by ‘thermogram’ of calcium oxalate monohydrate
(CaC2O4.H2O)
20
17.5
14
8
w
e
i
g
h
t
Temperature-
Thermogravimetricanalysis of calcium oxalate monohydrate heated at rate of 6̊̊ c/
min
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6. STAGE I: The water of crystallization (or hydration) is lost which corresponds
to 2.46 mg(12.3%) eqlt. to 1 mole of H2O in temp range 100-250 c.
12.3% wt loss corresponds to 12.3% of the original formula wt of
CaCO3H2O(fw=146), hence the product being lost has hasa formula wt of
0.123*146=18, which corresponds to H2O.
STAGE II: 1 mole of carbon monoxide is evolved corresponding to 3.84 mg
(19.2%) in temp. range 400-500 c.
Again, 0.192*146=28, which corresponds to carbon monoxide.
STAGE III : Finally a mole of CO2 is evolved calcium carbonate that
corresponds to 6.02mg (30.1%) in temp range 700-850 c.
The wt loss is 0.301*146= 44, which corresponds to CO2.
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7. INSTRUMENTATION
1)A Recording Balance
2) A Furnace
3) Furnace programmer or controller
4) A Recording Device
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9. RECORDING
BALANCE
Deflection
type
helical
Cantilever
beam
Torsion wire Beam
Null type
RECORDING BALANCE
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10. NULL-POINT TYPE:
Makes use of a sensing element which aptly detects any slightest
deviation of the balance beam & provides the application of
restoring force, directly proportional to the change in weight,
thereby returning the beam to its original null point. The restoring
point is subsequently recorded.
DEFLECTION TYPE:
Essentially based on either a conventional analytical balance
consisting of helical spring, cantilever beam, and strain gauze or a
torsion analytical balance involving the conversion of deviation
directly into a record of wt change
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11. Sample holders:
This is most important in accurate thermogravimetric analysis.
Depending upon the nature of sample, its weight and quantity to
be handled, different size and shape of sample holders known as
crucibles are employed.
These are constructed from various materials like glass, quartz,
aluminium, stainless steel, platinum etc.
These generally are of two types:
(a) Shallow pan for holding samples which eliminates gas, vapours
or volatile matter by diffusion
during heating or.
(b) Deep crucible for general purpose.
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12. Furnace
Must be designed in such a fashion so as to incorporate an appropriate smooth
input thereby maintaining either a fixed temp. or predetermined linear heating
program. (e.g.-6 c/min)
Temperature control is achieved via a thermocouple mounted very close to the
furnace-winding.
Maximum operational temp. may be obtained using different thermocouple
as indicated below:
SR.
NO.
SPECIFICATION MAX. TEMP.
1 Nickel-chrome(nichrome)1100
2 Platinum-rhodium 1450
3 Graphite-tube furnace >1500
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13. Furnace temperature programmer:
o These are the controller which can provide gradual rise of temperature
at a fixed rate.
o This device has a coarse and fine control knobs through which desired
temperature with respect to rate/ time can be obtained.
o This controlling is done by increasing voltage through the heated
element by motor driven variable transformer or by different
thermocouples.
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Factors affecting ThermogravimetricResults:
(I)Instrumental factors:
These include various aspects of instruments like furnace heating (its temperature
and rate), recording of changes on charts (its speed), furnace atmosphere (its rate of
cooling and maintaining temperature), sample holder and its geometry and the
sensitivity of balance
(II)Characteristics of sample:
The important factors about the sample are: weight of sample, particle size of
sample, nature of evolved gas or volatile matter, thermal conductivity of sample and
the heat of decomposition of the reaction.

15. Applications of Thermogravimetry
o Determining the purity and thermal stability of both primary and
secondary standards.
o Investigating the correct drying temperatures and the suitability of
various weighing forms for gravimetric analysis
o Direct application to analytical problems
o Determining the composition of alloys and mixtures.
Thermogravimetryis a valuable technique for assessing the purity of
materials
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16. o Analytical reagents, especially those used in titrimetricanalysis as primary
standards, e.g. Na2CO3, KHP have been examined.
Many primary standards absorb appreciable amounts of water when exposed
to moist atmospheres.
TG data can show the extent of this absorption, hence the most suitable
drying temperature for a given reagent may be determined.
o The thermal stability of EDTA as the free acid and also as the more widely
used disodium salt. Na2EDTA .2H2O has been reported.
According to that the dehydration of the disodium salt commences at
between 110 and 125 c , which confirmed the view that Na2EDTA.2H2O could be
safety heated to constant weight at 80 C.
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17. o Thermogravimetrymay be used to determine the composition of binary
mixtures.
E.g. for Ca and strontium binary mixture. Here the decomposition
temperature for CaCO3 is 650 to 850 C.
Where for strontium carbonate the decomposition temperature is 950 to 1150C.
Both carbonates decompose to their oxides with the evolution of carbon
dioxide.
Hence the amount of calcium and strontium present in a mixture may be
calculated from the weight losses due to the evolution of carbon dioxide at the
lower and higher temperature ranges respectively.
o This method can also be extended to the analysis of a three component
mixtures.
o The most important applications of thermogravimetryis in examining the
thermal stability of polymers.
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18. References
1)Instrumental Methods of Chemical Analysis
B.K.Sharma
Page No. –m-308
2)Pharmaceutical Drug Analysis
AshutoshKar
Page No. -194
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19. CONTENTS
Theory
Instrumentation
Methodology
Application
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20. THEORY
The difference of temp. under estimation & a thermally inert reference material is
continuously recorded as a function of furnace temp. in DTA.
The measurement of changes in heat content is carried out by heating the two
material at elevated temp. or cooling to subnormal temp. at a predetermined rate.
The thermal effect may either be endothermic or exothermic and are caused by
physical phenomena such as fusion, crystalline structure inversion, boiling,
vapourisation, sublimation or others. Some enthalpiceffect are also caused by
chemical reaction. In this manner, endo-and exothermal bands and peaks
appearing on thermogramgive info, regarding the detection of enthalpicchanges.
The range of phenomena measurable during a DTA-run is much larger than in a
TGA-run.
TGA & DTA are complementary techniques, because the information obtained by
the application of one approach is often enhanced by the application of other
method.
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METHODOLOGY
A.Insert a very thin thermocouple into a disposable sample tube 2mm in
diameter and containing 0.1-10 mg of sample.
B.Another identical tube is either kept empty or filled with reference substance,
such as quartz, sand, alumina or alundumpowder.
C.The two tubes are simultaneously inserted into a sample block and
subsequently heated(or cooled) at uniform predetermined programmed rate.
And
D.DTA-being a dynamic process, it is extremely imp that all aspects of the
technique must be thoroughly standardized so as to obtain reproducible
results. Such aspects are,
-pretreatment of specimen, -particle size & packing of specimen, -dilution of
the specimen, -nature of inert diluent, -crystalline substances must be
powdered and sieved thru 100 mesh sieve, -micelle size is critical for colloidal
particle and –adequate control of atmosphere.

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INSTRUMENTATION
1)Sample holder with built-in
thermocouple assembly
2)Flow-control system
3)Furnace assembly
4)Preamplifier & Recorder
5)Furnace power programmer
and controller

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(1)Sample Holders:
Both metallic as well as non-metallic materials are employed for the fabrication
of sample holders.
Metallic materials generally include nickel, stainless steel, platinum and its
alloys.
Non-metallic material generally includes glass, vitreous silica or sintered
alumina.
Metallic holders give rise to sharp endothermsand flat endotherms.
On the other hand non-metallic holders yield relatively sharp endothermsand
flat exotherms.

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o In DTA apparatus, one always prefers a tubular furnace.
o This is constructed with an appropriate material (wire or ribbon) wound on a
refractory tube.
o Such furnaces possess the desired characteristics for good temperature
regulation and programming.
o These are fairly inexpensive. Generally, the choice of the resistance material as
well that of refractory is decided from the intended maximum temperature of
operation and gaseous environments.
(2)Furnace:

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Temp. controller
In order to control temperature, the three basic elements are required.
-Theses are sensor, control element and heater.
On-off Control-In this device, if the sensor-signal indicates the temperature
has become greater than the set point, the heater is immediately cut off.
Not used in DTA.
Proportional control –In on-off controllers there occurs fluctuatationsof
temperature around the set value. These can be minimized if the heat input to
the system is progressively reduced as the temperature approaches the desired
value. Such a controller that anticipates the approach to the set value is known as
a proportional controller.

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(4) Recorders –
In thermo analytical studies, the signal obtained from the
sensors can be recorded in which the signal trace is
produced on paper or film, by ink, heating stylus, electric
writing or optical beam.
There are two types of recording devices similar to the TG.-
one is deflection type and
other is null type.

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APPLICATION
(a) Identification of substances –We know that the DTA curve for two
substances is not identical. Therefore, these serve as finger prints for
various substances. Particularly, DTA has become an established
technique for the identification of clays.
(b) Identification of products –When a substance reacts with another
substance, the products is identified by their specific DTA curves.
Therefore, this technique has been termed ‘reaction DTA’.
(c) Melting points –As melting points can be easily determined by DTA, it
means that this technique can be used as a direct check of the purity of
the compound.
(d) Quantitative Analysis –We know that the area of DTA peak is
proportional to the total heat of reaction and hence to the weight of the
sample. Therefore, the quantitative analysis is possible with the help of
standard curves of peak area vs. weight.
(e) Quality control –DTA technique has been widely used for the quality
control of a large number of substances like
cement, glass, soil, catalysts, textiles, explosives, resins etc.

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References
1)Instrumental Methods of Chemical Analysis
B.K.Sharma
Page No. –m-318
2)Pharmaceutical Drug Analysis
AshutoshKar
Page No. -198

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What the caterpillar calls the end, Butterfly calls it the beginning