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PM2A Autumn Amy L > Thermal Analysis > Flashcards

Thermal Analysis Flashcards

1
Q

What is thermal analysis?

A

Studies the effect of temperature on the behaviour of samples

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2
Q

What does thermal analysis study?

A

State changes (i.e. melting, boiling)
Degradation profiles
Complex chemical phenomena

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3
Q

List 3 recoverable thermal events

A

Phase transition
Desolvation
Glass transition

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4
Q

List the 4 phase transitions which are recoverable thermal events

A

Melting = transition of a solid to a liquid under the application of heat
Vaporisation (evaporation) = transition of a liquid to a gas under the application of heat
Sublimation = transition from a solid to a gas without entering a liquid phase
Deposition = transition from a gas to a solid without entering a liquid phase

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5
Q

Define: Desolvation

A

The removal of solvent from a material under the application of heat
Dehydration when the solvent is water

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6
Q

Define: Glass transition

A

Transition of amorphous materials from a hard and brittle state into a soft and flexible state under the application of heat

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7
Q

List 3 non-recoverable thermal events

A

Decomposition
Denaturation
Oxidation

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8
Q

Define: Decomposition

A

The breakdown of a product into, usually simpler, chemical products under the application of heat

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9
Q

Define: Denaturation

A

The structural change of proteins that involves the disruption and possible destruction of both the secondary and tertiary structures

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10
Q

Define: Oxidation

A

The reaction of a substance with oxygen, under the application of heat

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11
Q

What is hot stage microscopy and what is it used for?

A

Samples are heated through a pre-set heating programme and visualised through polarises, which assist in contrast
It can determine phase transition temperatures

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12
Q

What is thermogravimetric analysis (TGA)?

A

Thermal analysis in which the rate of material weight change change upon heating vs temperature is plotted
Temperature is varied in a controlled manner

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13
Q

Which thermal events cause a weight change of the sample according to thermogravimetric analysis (TGA)?

A

Vaporisation
Sublimation
Desolvation
(Decomposition)

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14
Q

Which thermal events do NOT cause a weight change of the sample according to thermogravimetric (TGA)?

A

Glass transition (Tg)
Melting (Tm)
(Decomposition)

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15
Q

What is the formula that predicts mass loss by desolvation during thermogravimetric analysis?

A

FORMULA

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16
Q

List 3 instrumental factors which can affect TGA curves

A

Heating rate = quicker heating rates give higher degradation temperatures
Furnace atmosphere = inert atmosphere prevents oxidation
Material and geometry of pans = surface area and conductivty

17
Q

List 5 sample factors which can affect TGA curves

A

Mass = small mass changes may be difficult to detect
Particle size = reactive surface area increases at smaller particle size
Samples pre-treatment = crystalline vs amorphous
Packing = compressed samples affect thermal conductivity and combustion
Thermal conductivity = transfer of heat

18
Q

List 3 applications of TGA

A

Solvent content
Estimates lifetime of a product
Decomposition kinetics of materials

19
Q

Define: Endothermic

A

A process that involves taking in heat from its environment

20
Q

Define: Exothermic

A

A process that involves giving out heat to its environment

21
Q

What is the formula to calculate free energy change?

A

FORMULA

22
Q

Define the terms of the free energy change formula

A

(triangle) G = free energy change
(triangle) H = enthalpy change
T = temperature
(triangle) S = entropy change

23
Q

What is the relevance of the (triangle)H value in the free energy change formula?

A

If (triangle) H 0 = endothermic

24
Q

Define: Crystallisation temperature (Tc)

A

The temperature at which a solid crystalises into an ordered form, under the application of heat

25
Q

Define: Melting temperature (Tm)

A

The temperature at which a solid transforms to a liquid, under the application of heat

26
Q

What is the purpose of differential scanning calorimetry (DSC)?

A

When a material undergoes a change in physical state or when it reacts chemically, heat is absorbed (endo) or liberated (exo)
The DSC instrument keeps the sample and the inert reference material at the same temperature (triangle T = 0), whilst the sample is heated or cooled
The energy required to maintain (triangle)T = 0 is measured and therefore gives heat measurements directly

27
Q

How are the temperature changes associated with a thermal event found from DSC?

A

Take the peak value/centre of the curve

28
Q

How are heats (or enthalpies) of thermal events found from DSC?

A

Look at the area under the curve

29
Q

Explain the method of DSC

A

A flow of purge gas (N2) is used to provide a dry, inert atmosphere, aid heat flow and carry away gases
Small amounts of sample (1-5mg)
Spread thinly over sample pan to aid heat transfer
Pans normally made of aluminium

PM2A Autumn Amy L (7 decks)

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