Abstract
The Berkovich indentation loading curves of the initially only extraterrestrial available polymorphs of SiO2 are physically analyzed by applying the now well established FN-h3/2 plots for conical/pyramidal indentations, in view of determining the phase-transition onset forces, indentation energies, and transition energies. Two phase-transitions of synthesized Stishovite yielding 2 polymorphs (one of them is Seifertite) with these properties are characterized. A third post-Stishovite polymorph is safely projected for higher load indentation. Both of them are now available at room temperature on earth for further investigation and the projected third of them is waiting. The published “pop-ins” had to be removed by self-evident repair of the force-depth curve. The meaning of published “pop-ins” is elucidated, apparently for the first time. The reasons for them and their avoidance are manifold. They are not materials’ properties but mechanical artefacts. Published pop-ins are not at all connected to phase-transitions, despite theoretical considerations claiming elastic-plastic conversion at the start of “pop-ins”. Spherical indentation analyses before them are obsolete. Final support is inter alia that one of the two new MgO twinning transitions is within a published “pop-in excursion”. The putting of a pop-in arrow at smooth loading curve without discontinuities is criticized, as the transfer between chemically different phases is neither phase transition nor “pop-in”. The polymorph’s onset forces, their energies and their endo- or exo-thermic phase-transition energies are reported. The development of the Stishovite, post-Stishovite and MgO polymorphs is mechanochemical analyzed. High pressure polymorph energetic properties are important for the earth’s sub mantel investigations and for public safety of technical materials such as MgO for constructions, or covered superalloys for e.g. airplanes, turbines, etc. Breakage and catastrophic cracks are more easily initiated at polymorph interfaces, the onset and transition energies must be above the highest possible mechanical and thermal stress for their being safe.
Highlights
Extraterrestrial materials such as high energy polymorphs of quartz were at first detected in meteorites from Mars and later collected from Moon
A third post-Stishovite polymorph is safely projected for higher load indentation
At every “pop-in” production, the indenter electronics go autonomously in a force hold-mode, while the penetration loop continues in a pseudo creep mode with falsely reporting somehow extrapolated “fake depth” readings until resumption of the loading loop, when too deep penetration depth value readings continue
Summary
High-pressure-high-temperature syntheses are successful in crystallizing sufficiently large single crystals of Stishovite, and Seifertite has been obtained. They are yet the second hardest oxides. Smooth loading curves are necessary before physical (not iterative fitting) analyses are enabled for phase-transition onsets (depth and load), indentation work (Windent), applied work (Wapplied), and transition energy (Wtrans). Such endeavor requires correct calculation, excluding rounding errors with the already long available simple closed formulas. Rethinking of the “pop-in’s” meaning and their removal or avoidance removes the still most complicated common misinterpretations
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