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Part 2a > thermal analysis > Flashcards

thermal analysis Flashcards

1
Q

what is a solid

A

The molecules, atoms and ions in the solid state are held in close proximity by inter-molecular, inter-atomic, or ionic forces

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2
Q

what is a liquid

A

The molecules in a liquid have a much greater freedom to move.

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3
Q

what is a gas

A

low density
low viscosity
great expansion and contraction with changes in pressure and temperature, the ability to diffuse readily,
and the spontaneous tendency to become distributed uniformly throughout any container

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4
Q

What may happen to pharmaceutical materials upon heating?

A
  • glass transition
  • melting
  • boiling
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5
Q

what is Glass transition?

reversible or no?

A

Glass transition is the transition in amorphous materials from a hard and relatively brittle state into a molten or rubber-like state

yes

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6
Q

what is melting?

reversible?

A

Melting is a physical process that results in the phase change of a substance from a crystalline solid to a liquid
yes?

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7
Q

what is boiling?

reversible?

A

Boiling is the rapid vaporisation of a liquid, which occurs when a liquid is heated to its boiling point

yes

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8
Q

what is sublimation?

reversible?

A

Sublimation is the change from a solid to a gas without entering liquid phase
yes

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9
Q

what is decomposition?

reversible?

A

Decomposition is the process by which material is broken down into simpler forms of matter.
no

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10
Q

what is denaturation?

reversible?

A

Denaturation is the structural change of biopolymers that involves the disruption and possible destruction of both the secondary and tertiary structures.

no

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11
Q

what is oxidation ?

reversible?

A

Oxidation is often the combination of a substance with oxygen
no

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12
Q

what can hot stage microscope do?

A

Use: visualisation of melting and crystallisation
instrumentally study the changes happening with material upon temperature

An optical microscope
A polarising filter - see crystals better
A heating stage - control temp of sample
An optional cooling stage (liquid N2 based)
An optional video camera

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13
Q

what is thermogravimetric analysis (TGA)

A

Sample weight change is measured as a function of temperature

Useful for transformations involving the absorption or evolution of gases from a condensed matter phase

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14
Q 
does sample weights change? 
in glass transition 
melting 
boiling and evaporation 
sublimation 
decomposition 
denaturation
oxidation
A 
in glass transition - no 
melting - no 
boiling and evaporation - decrease 
sublimation - decrease 
decomposition - can decrease if sample is gas or volatile 
denaturation - will not change 
oxidation - will increase
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15
Q

what is Differential thermogravimetry (DTG)

A

Thermal analysis in which the RATE of material weight change upon heating versus temperature is plotted
Used to simplify reading of weight vs temperature thermogram peaks that occur close together
- shows the peaks more clearly

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16
Q

Applications of thermogravimetry

A 
estimation of water content (hydrates)
Residual solvent
study Composition of Multicomponent Systems
 Thermal Stability of Materials
Oxidative Stability of Materials
Estimated Lifetime of a Product
Decomposition Kinetics of Materials
17
Q

what is exothermic process

A

involves the giving out of heat

18
Q

what is endothermic

A

a process of taking in of heat

19
Q

what is Differential Scanning Calorimetry (DSC)

A

The DSC instrument keeps the sample and the inert reference material at the same temperature, whilst the sample is heated or cooled

20
Q

what is DSC Practicalities?

A

A flow of purge gas (e.g. N2) used to provide a dry, inert atmosphere, aid heat flow & carry away gases

Small amounts of sample ~1-5mg for organics, but must weigh accurately

Spread thinly over sample pan to aid heat transfer

Typical scan rate is 10C per minute\Keep the sample pans clean

Normally made of aluminium

So, do not decompose samples in the DSC ! Check with TGA first and stay clear of decomposition temperature

21
Q

what can application of DSC identify?

A 
Melting point
Enthalpy
Glass transition temperature
Polymorphic forms
Re-crystallisation
phase transformation
Purity
Miscibility

Part 2a (12 decks)

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