| dc.description.abstract |
<p>Laboratory tests on microscale are reported in which amorphous silica grains were
compressed in a liquid environment, namely in solutions with different silica ion
concentrations for up to four weeks. Such an arrangement represents an idealized representation
of two sand grains. The grain surfaces and asperities were examined in Scanning Electron
Microscopy (SEM) and Atomic Force Microscopy (AFM) for fractures, silica polymer growth,
and polymer strength. Single chains of silica polymers are found to have a failure
pulling force of 330 - 450 nN. </p><p>A chain of observations are reported for the
first time, using Pneumatic Grain Indenter and Grain Indenter-Puller apparatuses,
confirming a long-existing hypothesis that a stressed contact with microcracks generates
dissolved silica in the contact (asperity) vicinity, which eventually polymerizes,
forming a structure between the grains on a timescale in the order of weeks. Such
structure exhibits intergranular tensile force of 1 - 1.5 mN when aged in solutions
containing silica ion concentrations of 200- to 500 ppm. Stress appears to accelerate
the generation of silica polymers around stressed contact regions, so does mica-silica
contacts. The magnitude of intergranular tensile force is 2 to 3 times greater than
that of water capillary effect between grains.</p>
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