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Evolution of microstructure and elastic wave velocities in dehydrated gypsum samples
Author(s) -
Milsch Harald,
Priegnitz Mike
Publication year - 2012
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2012gl053674
Subject(s) - porosity , gypsum , microstructure , mineralogy , hemihydrate , dehydration , geology , mineral , materials science , composite material , chemistry , geotechnical engineering , metallurgy , biochemistry
We report on changes in P and S‐wave velocities and rock microstructure induced by devolatilization reactions using gypsum as a reference analog material. Cylindrical samples of natural alabaster were dehydrated in air, at ambient pressure, and temperatures between 378 and 423 K. Dehydration did not proceed homogeneously but via a reaction front moving sample inwards separating an outer highly porous rim from the remaining gypsum which, above approximately 393 (±5) K, concurrently decomposed into hemihydrate. Overall porosity was observed to continuously increase with reaction progress from approximately 2% for fully hydrated samples to 30% for completely dehydrated ones. Concurrently, P and S‐wave velocities linearly decreased with porosity from 5.2 and 2.7 km/s to 1.0 and 0.7 km/s, respectively. It is concluded that a linearized empirical Raymer‐type model extended by a critical porosity term and based on the respective time dependent mineral and pore volumes reasonably replicates the P and S‐wave data in relation to reaction progress and porosity.