Adhesion At Crystalline Interfaces In Rock

The objective was to ascertain the magnitude of forces responsible for coherency of rock by quantifying the strength of the attractive forces operating between minerals in rock. These forces oppose stresses set up in various rock gragmentation processes, hence strength measurements of these forces might prove useful in designing more efficient rock fragmentation methods. Methods were developed for estimating strength of intergranular adhesion in rock. Examination of bicrystals broken at the crystalline interfaces reveals that bonds responsible for this adhesion operate only over a portion of the interfacial area. This work demonstrated that strength tests can be conducted on small selected areas, i.e., grain boundaries in rock. This permits a determination of small scale zones of strength or weakness which may be related to the overall strength of the rock.

A direct method has been developed for estimating the strength of intergranular adhesion in rock. It involves the separation of a bicrystal from the rock and a determination of the tensile strength at the solid-solid interface. This technique has been successfully applied to the study of quartz-feldspar interfaces separated from pegmatites, graphic granite, and the Rockville granite yielding average tensile strengths of 5.86, 8.62, and 10.65 MN/msq (850, 1,250, and 1,524 psi) respectively. The data generated by this technique indicate that the members of these bicrystals are strongly adhernet. Examination of bicrystals broken at the crystalline interfaces indicates that the bonds responsible for this adhesion operate only over a protion of the interfacial area. The significance of this work is that it demonstrates that tensile strength tests can be conducted on small selected areas, e.g. grain boundaries in rock. This permits a determination of small scale zones of strength or weakness which may be related to the overall strength of the rock. Selected area microindentation hardness testing has also been performed to probe hardness variations near phase boundaries.

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