Temperature dependence of internal mechanical losses of gypsum stone with complex composition and structure

Abstract

Experimental studies of the temperature dependence of internal mechanical losses in terms of Q−1 in the range from 25 to 120 °C used gypsum stone specimens from the Novomoskovskoye deposit (Tula region, Russia). This investigation is important to determine optimal modes of heat treatment of gypsum stone to obtain construction gypsum. The specimens were cylinders 40 mm in diameter and 75 mm in length with piezoelectric transducers at the ends. They included three types of rocks: gypsum, flint, and thin coal interlayers. The groups included specimens consisting of gypsum without flint layers, two layers consisting of a gypsum layer at one end and a flint layer at the other, and three layers with a flint layer in the middle part of the specimen. Losses Q–1 were determined as f0/(fmax – fmin), where fmax and fmin were frequencies at the level of 1/√2 of the maximum amplitude of sample longitudinal oscillations at the resonance frequency f0. In the temperature range up to 80 °C, the loss Q–1 increased monotonically, while the resonance frequency f0 decreased. There were two maxima of Q–1 and f0 at 85 and 110 °C. The phase transitions of gypsum from dihydrate to hemihydrates (α- and β-hemihydrates) and then to the anhydrous state (dehydrate) caused these maxima.