THERMOGRAVIMETRIC THERMOGRAVIMETRIC ANALYSISANALYSIS

PURUSHOTHABIRAMI

ASHIQARUL

What is TGA ?

Process which measures the weight loss(or weight gain) of a sample material as a function of temperature

PRINCIPLE• As materials are heated they loose

weight from a simple process such as drying or from chemical reactions that liberate gases .

TGA-Principle of Operation

• A sample of the test material is placed into a platinum cup that is supported on, or suspended from an analytical balance located outside the furnace chamber.

• The balance is zeroed, and the sample cup is heated according to a predetermined thermal cycle.

TGA-Principle of Operation• The balance sends the weight signal to the

computer for storage, along with the sample temperature and the elapsed time.

• The TGA curve plots the TGA signal, converted to percent weight change on the Y-axis against the reference material temperature on the X-axis.

METHODOLOGY

TGA-Basic Diagram

• The analyzer usually consists of a high-precision balance with a pan (generally platinum) loaded with the sample.

• The pan is placed in a small electrically heated oven with a thermocouple to accurately measure the temperature.

• The atmosphere may be purged with an inert gas to prevent oxidation or other undesired reactions.

• A computer is used to control the instrument.

Methodology

• Analysis is carried out by raising the temperature gradually and plotting weight against temperature.

• The temperature in many testing methods routinely reaches 1000°C or greater, but the oven is greatly insulated.

• After the data is obtained, curve smoothing and other operations may be done such as to find the exact points of inflection.

Methodology

• A method known as hi-res TGA is often employed to obtain greater accuracy in areas where the derivative curve peaks.

• In this method, temperature increase slows as weight loss increases.

• This is done so that the exact temperature at which a peak occurs can be more accurately identified.

Methodology

• Several modern TGA devices can vent burnoff to a fourier-transform infrared spectrophotometer to analyze composition.

• Fourier transform infrared (FTIR) spectroscopy is a measurement technique for collecting infrared spectra.

• Instead of recording the amount of energy absorbed when the frequency of the infra-red light is varied , the IR light is guided through an interferometer.

Methodology

Methodology

• After passing through the sample, the measured signal is the interferogram.

• Performing a Fourier transform on this signal data results in a spectrum identical to that from conventional (dispersive) infrared spectroscopy.

Processes Requiring TGA

• Drying• Structural Water Release• Structural Decomposition• Carbonate Decomposition• Gas Evolution• Sulphur Oxidation• Fluoride Oxidation• Re-hydration

Temperature Ranges

• Room Temperature to 1,200°C Kanthal wire wound heating element

• Room Temperature to 1,600°C Platinum alloy wire wound heating element Silicon Carbide heating element

• Room Temperature to 1,700°C Molybdenum Disilicide heating elements

Areas of ApplicationTGA is commonly employed in Research and Testing

• Characteristics of materials such as polymers,• Degradation temperatures, • Absorbed moisture content of materials, • Level of inorganic and organic components in

materials, • Decomposition points of explosives,and solvent

residues. • Corrosion kinetics in high temperature oxidation.

Examplesof

TGA-Report

Precipitated Zr5O8(SO4)2*15 H2O

Analysis of Filtrate from Precipitation

• Precipitation• 5ZrOCl2 + 2H2SO4 + xH2O

Zr5O8(SO4)2*15 H2O (s) + 10 HCl

• Decomposition• Zr5O8(SO4)2*15 H2O (s)

Zr5O8(SO4)2*14 H2O (s) + H2O (v)

• Zr5O8(SO4)2 5 ZrO2 (s) +2 SO2 (v)

15 H2O Water Loss Wt. Loss % loss1 18.0152 1.7215732 36.0304 3.4431463 54.0456 5.1647194 72.0608 6.8862925 90.076 8.6078656 108.0912 10.329447 126.1064 12.051018 144.1216 13.772589 162.1368 15.49416

10 180.152 17.2157311 198.1672 18.937312 216.1824 20.6588713 234.1976 22.3804514 252.2128 24.1020215 270.228 25.82359

SO2 1 64.0588 31.94522 128.1176 38.0668

TGA in Black & WhiteTGA in Black & White

REFERENCESREFERENCES

• Brochure of Orton .• Lecture notes of Terry A. Ring, Chemical

Engineering, University of Utah.• HKUST• Wikipedia.• Advt. of TA Instruments in youtube.com

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