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Brittle gold-about alloys-Phase Diagrams


#1
    One thing which seems to have been overlooked in this
discussion is the crystallography of the metals. In any metal which
has been cast at some time there is a crystalline structure which,
depending upon the amount it has been worked since casting and the
various component parts of it, will be more or less permeable to
gases and liquids. Unless the alloy is at the 'eutectic', the point
at which the amounts of the constituent parts exactly dissolve in
one another, there will be a surplus of one or more metals which
will crystallise out separately and simply form a 'mixture' in the
'alloy'. These crystals will be available to be attacked by
anything which can get to them. 

Artisans This is a major simplification of that is most
easily discussed using Phase Diagrams and that if used will lead to
major errors. Using what I have in the way of phase diagrams for
systems of interest to you: There is usually a solid solution made
when one element(A) is added to another(B). This can range from.very
little to total solubility examples of each would be Ag-Fe and
Ag-Au. With larger quantities of A than the solubility limit you
will have a second phase present which can simplistically be a
different crystal structure, an intermetallic compound or a solid
solution of B in A (actually there are a very wide range of
possibilities. For example with Ag-Cu there is limited solubility of
Cu in Ag at lower temperatures but up to about 8% at temperatures
near the melting temperature. Keeping this in a supersaturated
solution is the reason that you quench sterling when annealing. The
primarily copper phase if precipitated out will significantly
increase the strength of the sterling. An example of more complex
behavior would silver with lead or tin.

I have made these comments in the hope that I will cause at least
some of you to study Phase Diagrams. You would find this very
useful in your metal jewelry pursuits jim (James ME Wallbridge P.
Eng.) Libertarian, Metallurgist, Wood & Metal Worker, Fly Fisher,
Resident of Calgary, Canada’s new head office location of choice.
Permission is hereby given to use any or all herein, as
an attributed quote, unless the body of the message states otherwise.