thermal analysis Flashcards
what is a solid
The molecules, atoms and ions in the solid state are held in close proximity by inter-molecular, inter-atomic, or ionic forces
what is a liquid
The molecules in a liquid have a much greater freedom to move.
what is a gas
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
What may happen to pharmaceutical materials upon heating?
- glass transition
- melting
- boiling
what is Glass transition?
reversible or no?
Glass transition is the transition in amorphous materials from a hard and relatively brittle state into a molten or rubber-like state
yes
what is melting?
reversible?
Melting is a physical process that results in the phase change of a substance from a crystalline solid to a liquid
yes?
what is boiling?
reversible?
Boiling is the rapid vaporisation of a liquid, which occurs when a liquid is heated to its boiling point
yes
what is sublimation?
reversible?
Sublimation is the change from a solid to a gas without entering liquid phase
yes
what is decomposition?
reversible?
Decomposition is the process by which material is broken down into simpler forms of matter.
no
what is denaturation?
reversible?
Denaturation is the structural change of biopolymers that involves the disruption and possible destruction of both the secondary and tertiary structures.
no
what is oxidation ?
reversible?
Oxidation is often the combination of a substance with oxygen
no
what can hot stage microscope do?
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
what is thermogravimetric analysis (TGA)
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
does sample weights change? in glass transition melting boiling and evaporation sublimation decomposition denaturation oxidation
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
what is Differential thermogravimetry (DTG)
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
Applications of thermogravimetry
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
what is exothermic process
involves the giving out of heat
what is endothermic
a process of taking in of heat
what is Differential Scanning Calorimetry (DSC)
The DSC instrument keeps the sample and the inert reference material at the same temperature, whilst the sample is heated or cooled
what is DSC Practicalities?
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 10C 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
what can application of DSC identify?
Melting point Enthalpy Glass transition temperature Polymorphic forms Re-crystallisation phase transformation Purity Miscibility
