Collaboration with NASA

Claes HedbergProfessor Claes Hedberg of the PDRL is currently viting at NASA Ames Research Center (Moffet Field, Mountain View, California) for some months for the project "Manipulating the Toughness of Rocks Through Electric Potentials"

Project info

Rocks in the Earth crust contain – in their minerals – previously unrecognized defects, which release electronic charge carriers when the rocks are mechanically stressed. These charge carriers are defect electrons in the oxygen anion sublattice, O– in a matrix of O2–, known as positive holes. These charge carriers have some truly amazing properties. They can flow out of the stressed volume and spread into the surrounding unstressed rocks. Important to this project is the fact that the wave function associated with these positive holes appears to be highly delocalized, meaning that hundreds of their O2– neighbors loose some of their electron density. This in turn must affect the bond strength between anions and cations, and thereby affect many fundamental physical properties of the rocks, including their volume and their mechanical strength. This is a quantum mechanical effect, which has far-reaching theoretical and practical implications.

We have conducted three sets of experiments using high intensity ultrasound waves to activate positive hole charge carriers in a gabbro, a typical rock from deep in the crust:

  • Measure the bending of a cantilevered rock beam;
  • Measure the stiffness of the rock in three-point bending experiments;
  • Measure the volume expansion when positive holes are activated.

In cases 1 and 2 we have been able to show that the effect exists and is measurable. In particular, in case 2 we have demonstrated a decrease on the order of 10-15% in the flexure module. In case 3 we have received credible evidence that the rock volume does increase. More experiments are warranted to determine the magnitude of the effect.

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