Thermal Analysis

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Nomenclature of Thermal Analysis

- Thermal analysis is a group of techniques that study the properties of materials as they change with temperature

- Gives properties like Enthalpy, Thermal capacity, Mass change, Co-efficient of thermal expansion….

- For studying reactions in solid state, thermal degradation reactions, phase transitions….

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Techniques• Thermal Gravimetric Analysis (TGA): mass

– Weight Loss due to decomposition– Differential Thermogravimetric Analysis (DTG)

• Differential Scanning Calorimetric (DSC): ΔH– Heat flow during Transitions

• Thermal Mechanical Analysis (TMA): deformation/dimension– Thermal Expansion Coefficient

• Temperature Programmed Desorption (TPD): evolved gas– Temperature at which gas is desorbed from (catalyst) surface

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Principle

• Sample is heated at a constant heating rate

• Sample’s property is measured– Weight TGA– Size TMA– Heat Flow DSC– Gas evolved TPD

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Thermo Gravimetric Analysis (TGA)

• Constant Heating Rate– Heating Rate (°C/min)

• Data – Weight vs Time– Weight vs Temp

• TGA curve gives information on:– Change in sample composition– Thermal stability

Sample amount: 5-20 mg

Heating rate: 1-100 °C/min

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TGA: Decomposition of CaC2O4.H2O

- H2O

- CO

- CO2

Air, 10 K/min

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TGA: Phenomena causing Δm

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TGA: Applications

• Characterizing Thermal stability, Material purity, humidity determination

• Examination of Corrosion studies

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TGA/MS (Mass Spectrometry)• MS characterizes substances by identifying and

measuring intensity of fragment ions of different mass-to-charge ratio (m/z)

• Incoming gas molecules are first ionized and then separated according to their m/z

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Factors affecting TG curve

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Differential Scanning Calorimetry (DSC)• A Calorimeter measures heat into or out of a sample• A Differential Calorimeter measures the heat of a

sample relative to a reference• A Differential Scanning Calorimeter does the above

with a temperature or time scans

• Operates by comparing the heat transfer to the sample pan with the heat transfer to a reference pan

• Separate heaters heat pans at same rate• Sample pan with material will take more heat to keep T

of sample pan increasing at the same rate as reference pan

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DSC, Heat Capacity

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DSC: Principle of Operation

Tf

Timeor Tr

Heat flow (mW)

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-10DSC signal, Φ

Peak integral -> ∆H

∆H

TemperatureTr

Ts

Tf

Time

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DSC cell

Sample pan (Al / Cu / Au)

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Sample Preparation: Shape

• Keep sample as thin as possible (to minimize thermal gradient)

• Cover as much of the pan bottom as possible• Sample should be cut rather than crush

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DSC Thermogram: Typical Transitions

Exo

Endo

Glass transition Crystallization Melting

Endo

a polymer

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• To characterize polymers, organic chemicals, inorganics

• Tg, melting, crystallization, onset of oxidation and heat capacity

DSC: Applications