Difference between revisions of "Pseudo phase diagram"
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Revision as of 08:43, 20 December 2015
Pseudo phase diagrams are phase diagrams for the visualisation of advanced mechanosynthesized materials.
Due to the very different character of mechanosynthesis compared to thermodynamic synthesis routes pseudo phase diagrams have a very different character than conventional phase diagrams and break many rules (which often are mistakenly believed to be unbreakable).
"pseudo" since the structure of the material at a specific point in the diagram is not defined by the thermodynamic history of the material but by the way it was mechanosynthesized. There are lots of special positions in the diagram that arise due to the specific chosen crystal structure and chequerboard pattern.
Differences between conventional and pseudo phasediagrams
In conventional phase diagrams there are regions of configurations that are reachable via thermodynamic processes and regions which are not. The accessible regions often are continuous. This becomes visible in stoichiometies that contain decimal marks - this is called a mixing series.
In pseudo phase diagrams for the visualisation of mechanoysnthesized materials only a few of the simplest stoichiometric fractions are of concern leaving only a few dots in the phase diagram. Many of those dots may be in regions that are in the thermodynamically forbidden areas! Please recall that diamondoid materials by definition do (for all practical purposes) not diffuse at their usage temperature. A good example may be lonsdaleite (hexagonal diamond) which is hard to access thermodynamically (almost forbidden area) and would like to change to graphite. But it can't since it is deeply frozen at room temperature.
By purely thermodynamic processes it is also often not possible to exactly hit the simple-fraction-stoichiomtey-points in the allowed regions when looking at a small enough randomly cropped out test-volume. (Note that a small test-volume requires a high degree of order to meet the fraction). This is the especially the case when very similar elements (or isotopes) are included.
Applicability on binary compounds
Pseudo phase diagrams are good for orientation what kind of low level metamaterials can be built with binary diamondoid compounds.
An example of such an pseudo phase diagram would be a square with CO2 (upper left) SiO2 (upper right) beta-C3N4 (lower left) Si3N4 (lower right) as their "end members". (solid CO2 is likely to be explosive but with a sufficient number of C atoms substituted with Si atoms it will be stable - it may be possible to draft a forbidden zone around the solid CO2 corner). In this specific diagram from top to bottom from oxides to nitrides the crystal structure must change significantly (due to the changing valence number) making a less continuous transition.
[todo: add existing images of such diagrams]
