Improved procedures for the laboratory study of high-temperature viscoelastic relaxation

Several aspects of the experimental procedure used in our laboratory for the study of high-temperature viscoelastic relaxation in geological and ceramic materials have been critically examined and refined. Most importantly, we have newly quantified a contribution to the torsional compliance of the specimen assembly from the interfaces between the metal foil and alumina torsion rod at each end of the specimen. We demonstrate that this extraneous contribution to the apparent compliance of the specimen can be removed by subtraction of the torsional compliance of a foil-bearing reference assembly similarly containing two alumina-foil interfaces. This new strategy along with other improvements including the modelling of drift in transducer sensitivity, suppression of background creep, minimising the aliasing of high-frequency noise, and allowance for the viscoelastic behaviour of the alumina control specimen, promise more accurate determination of the dispersion and attenuation associated with pronounced high-temperature viscoelastic relaxation. Correction of previously published data for fine-to-medium grained polycrystalline olivine for the interfacial compliance suggests somewhat milder frequency and temperature dependence of Q^-1 than previously reported and substantially stronger grain size sensitivity.