Aluminium artefacts

By altering the pH of the solution, it may be possible to dissolve out the chlorides without corroding the metal. This is achieved by the formation of a thin, passive film, approximately 10 nm thick on the exposed uncorroded metal. The pH required to passivate any given metal or alloy can be determined by inspection of the relevant E-pH diagram. For wrought iron, a passive film will form above a pH value of 9.5. This would be a disaster for aluminium artefacts... 

Pressure build-up in an inappropriately chosen pan is a frequent cause of difficulties. It is important to determine whether the sample needs to be rim in a hermetically sealed pan or not dry samples imhkely to evolve significant amounts of volatiles below decomposition do not need to be sealed. Yet if run in a hermetically sealed pan then pressure will build up inside the pan as it is heated. Many hermetically sealed aluminium pans cannot withstand high internal pressure and will deform (not necessarily visible) and result in potential artefacts in the trace as heat transfer to the sample changes. Ultimately sample leakage and bursting can occur, which usually results in contamination of the analyser. The best solution for such systems is to work with crimped pans that do not seal, or use hds with holes in. If not available then it may be best to pierce the pan hd before encapsulation so that pressure does not build up. Sometimes one hole will block with sample (particularly if a hole is made after loading the sample) and back pressure will force sample out of the pan giving more artefacts, so it is better to have more than one hole in the lid. 

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