Transcript
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)
0
-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
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