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Marianne Advanced and Applied > Differential Scanning Calorimetry (DSC) > Flashcards

Differential Scanning Calorimetry (DSC) Flashcards

1
Q

What are the basic principles of DSC?

A
  1. Measures the difference in the heat flow (and electrical power)
  2. between the sample and inert reference
  3. as a function of time or temperature.
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2
Q

What are the parameters measured in DSC?

A
  1. Heat capacity Cp
  2. Temperature of transitions
  3. Enthalpy of transitions
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3
Q

What are the units used in DSC?

A

mW = mJ/sec

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4
Q

Of what material is the sample pan made of, and at what temperature?

A
  1. Aluminum
  2. Gold
  3. Glass
  4. Carbon

Aluminum pan used up to 600 C (~ 650 C melts).

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5
Q

What are important properties of the experiment of DSC,mention calibration?

A
  1. Sample is weighed and sealed with a cover.
  2. Purge gases - nitrogen or helium.
  3. Calibration is done by:
    - baseline calibration
    - heat flow calibration: Indium
    - heat capacity calibration: Sapphire
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6
Q

What is an Endothermic Heat Flow, give examples?

A

When heat flows into a sample as a result of an endothermic process, for example:
1. glass transition
2. melting
3. evaporation
Graph: downwards

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7
Q

What is an Exothermic Heat Flow, give examples?

A

When heat flows out of the sample as a result of some exothermic process, for example:
1. crystallization
2. cure
3. oxidation
Graph: upwards

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8
Q

What are the factors affecting DSC measurement?

A
  1. Sample shape (thin for optimisation)
  2. Type of pan
  3. Heating rate
  4. Purge gas
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9
Q

What properties make the ideal purge gas?

A
  1. Dry, inert atmosphere
  2. Ensured even heating
  3. Helps sweep away gases that might be released
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10
Q

What purge gas is used and why?

A

Nitrogen
1. Most common
2. Increases sensitivity
3. Typical flow rate of 50 ml/min

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11
Q

What is calibration of DSC based on?

A

1. Transitions:
- melting (pure metals, In, Sn, Pb)
- polymorphic transitions (KNO3)
2. Enthalpies of high purity metals (In)

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12
Q

What transitions does DSC detect, and explain each.

A
  1. First order transitions (melting and polymorphic changes)
  2. Second order transitions (change in heat capacity)

(no enthalpy change)

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13
Q

How do you calculate the degree of crystallinity of a polymer, and what is the ΔH for a 100% crystalline material?

A

Calculated from enthalpy of melting, with ΔH = 290 J/g.

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14
Q

What is the effect of crystallinity on Tg?

A
  1. Low % amorphous: negligible heat capacity change
  2. 100% amorphous: large heat capacity change
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15
Q

What does the bulk state involve?

A

Both amorphous and crystalline polymers

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16
Q

What is the glass transition temperature (Tg)?

A
  • The temperature at which the polymer softens, changing from a solid ‘glassy’ state to a soft ‘rubbery’ state.
  • Measures changes caused by mass loss.
17
Q

What occurs at the Tg?

A

Sufficient thermal energy is present allowing segments of the main molecular chains to rotate, causing an increase in the free volume of the polymer.

18
Q

What are the factors affecting the Tg?

A
  1. chemical composition and structure
  2. secondary bonding
  3. crosslinking
  4. presence of plasticizers
19
Q

What happens during plasticization of the polymer?

A
  1. Internal stresses are generated
  2. due to the accumulation of water molecules
  3. in the polymeric network.
20
Q

What is the reduction of Tg caused by?

A

The breaking of existing hydrogen bonds by water which facilitates chain rotation.

21
Q

What information do we get from thermal analysis?

A

Changes in material properties as function of temperature.

22
Q

What is the effect of the sample purity on the curves?

A
  1. Peak height is reduced.
  2. Melting occurs over a broader temperature range.
  3. Melting point is lowered.
23
Q

What are necessary properties for a successful DSC experiment?

A
  1. sample weight 1 - 5 mg
  2. Atmosphere N2 (flow rate - 50cm/3min)
  3. Heating rate - 1C/min (slow)
24
Q

What is the procedure of DSC?

A
  1. Weigh sample and seal.
  2. Set temperature program.
  3. After DSC scan measure ΔH.
  4. Select temperature values, calculate partial areas and fraction melted.
    (F=Apartial/Atotal).
25
Q

What is the initial and final temperature of DSC?

A

Initial: 10C below melting T
Final: 20C above melting T

Marianne Advanced and Applied (17 decks)

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