Home > THERMAL ANALYSIS OF METAL IMPREGNATED SOL-GEL ALUMINA GRANULES
THERMAL ANALYSIS
OF METAL IMPREGNATED SOL-GEL ALUMINA GRANULES.
Thermal analysis is measurement and interpretation of the relationship between the physical/chemical properties of sample and temperature. Temperature of sample is controlled in a predetermined way-either by continuously increasing or decreasing the temperature at constant rate (linear heating or cooling) or by carrying out a series of determinations at different temperatures (Isothermal measurements).
Thermal analysis is a good tool to measure thermal decomposition of solids and liquids, solid-solid and solid-gas chemical reactions and phase transitions. Thermal analysis is done using various methods and these methods are distinguished from one another by the property by which they are measured.
The parameter (temperature)
for calcination process of sol-gel alumina granules is optimized using
DTA and TGA.
THERMOGRAVIMETRIC ANALYSIS (TGA)
TGA is the branch of thermal
analysis which examines the change in mass of a sample as a function
of temperature. The change in mass is observed due to the
evolution of gases from the sample. Nitrogen gas is used here.
Figure 1: Thermogravimetric analyzer (TA-2050)
Figure
2: Blow-up of sample loader
Precise measurement of weight change of solid is useful to determine sample purity, water, organic content and for study of decomposition reactions.
Data from TGA-2050 was acquired using the following procedure.
Equilibrate at 30C.
Ramp 10C/min to 500C.
Isothermal for 1 min (Maintains temperature at 500C for 1 min).
Ramp 10C/min to 30C.
Isothermal for 1 min (Maintains temperature at 30C for 1 min).
Data storage: On.
The above method was saved.
As temperature of sample
was raised, chemical reactions occurred resulting in change of sample
weight. Change in weight was measured as a function of temperature.
The following trend is observed.
dm
Temperature
Figure 3: General trend of sample in TGA (weight change versus temperature)
TGA curve provides information
about thermal stability of initial sample, intermediate compounds formed
and also that of residue.
DIFFERENTIAL THERMAL ANALYSIS (DTA)
DTA involves heating of sample and reference under identical conditions, while recording temperature difference between sample and reference. This differential temperature is then plotted against time or temperature. DTA determines the precise temperature at which reaction takes place or identifies phase change.
The DTA used here is DTA-50.
DTA-50 consists of an insulated chamber (furnace) containing a reference
pan, sample, heater and two thermocouples.
Figure 4:
Differential Thermal An
alyser (DTA-50)
Reference Sample Heating Coil
Gas Thermocouples
Figure 5: Schematic Diagram of DTA
Following procedure was used to acquire data from DTA-50.
Turn on the DTA-50 and then the TA-60WS.
Press
Click the TA-60WS icon the computer screen and select DTA-50, TA-60 Ch.1 (detects the signal).
Interpretation of data obtained from DTA-50.
Temperature of both sample and reference were raised slowly from room temperature to 475C using furnace heater.
The reference has no phase transitions within the heating range and was heated linearly.
Temperature
Time
Figure 6: Temperature versus time showing no transition
in reference temperature
The baseline of DTA curve exhibited discontinuity at transition temperature that is the temperature of sample deviated from temperature of reference. This te
mperature difference was detected, amplified and recorded as a peak.
Temperature
Figure 7: Temperature versus time showing phase transitions of
a sample
The peak lower than baseline represents melting transition and peak above baseline represents glass transition.
For all the granules with different compositions of metal the following similar trend was observe
d. At 100
C a peak (arrow pointed upwards in figure was observed. This peak represents removal of water from the granules. The incomplete peak at 475
C indicates that melting point of granules is greater than 475
C, showing that granules can be calcined
at 450
C.
Temperature
Figure 8: Temperature versus time graph showing variation in temperature profile
of sol-gel alumina granules.
CONCLUSION
DTA compares the difference between sample and reference as a function of temperature resulting in values of phase transition temperature. TGA compares the mass change of sample as a function of temperature giving the sublimation temperature. Thus with DTA and TGA the metal impregnated sol-gel alumina granules could be calcined at 450C.
REFERENCES
http://www.users.globalnet.co.uk/~dmprice
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