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The health of the components that make up the cables of power lines, and hence their service life, is governed at the micro level by changes in their structure and microstructure. In this paper, the structure and microstructure of aluminum wires of overhead power transmission lines (without a steel core) of different service life from 0 to 62 years have been investigated by quantitative techniques of X-ray diffraction, diffraction of back-scattered electrons, and the densitometric method. Elastoplastic properties of the wires have been tested by the acoustic-resonance method. A decrease in the Al material density Δρ/ρ∼−0.165% was found in the near-surface layer of ∼36 μm depth and in the bulk of the wires with an increase in the service life from 0 to 18 years. The density decrease is associated with the accumulation of microcracks. The following density increase (Δρ/ρ∼−0.06%) in wires with a service life of 62 years is attributed to the formation of ∼0.7 vol.% of crystalline Al oxides in the near-surface layers of the wires. The nature of the change in the elastic modulus, microplastic flow stress, and decrement indicates complex structural changes correlating with the results obtained by diffraction methods.

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Using the method of induced band representations of space groups, we have performed a complete group-theory analysis of electron state symmetries in superlattices grown along the [001] direction. The spin - orbit interaction has been taken into account. The selection rules for both direct and phonon-assisted optical transitions have been derived. Using both the results of our group-theory analysis and data on the various electronic-structure calculations which have appeared in the literature, we predict some variations in the optical transitions when m and/or n are varied. We also propose optical experiments to decide among the numerous and sometimes contradictory results of those band calculations.