English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Zendy Open

Presents the pdf analysis as premium feature

PDF Analysis

Insights

Presents the summarisation as premium feature

Summarisation

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the zaia usage as premium feature

ZAIA

Zendy Tools

Zendy Plus

Presents the access of premium content as premium feature

Premium Content

The structure of dolomite, CaMg(CO3)2, was determined from 298 to 1466 K at a constant pressure of about 3 GPa using in situ synchrotron X-ray diffraction data to investigate the state of disorder. An order parameter s, defined as 2 xCa - 1, varies from s = 1 (where xCa = 1) for a completely ordered dolomite to s = 0 (where xCa = 0.5) for a completely disordered dolomite. On heating, there is no measured change in s until the temperature is high enough to cause exchange of Ca 2+  and Mg 2+  cations. Significant disorder began to occur at about 1234 K [s = 0.83(1)] and increases along a smooth pathway to T = 1466 K [s = 0.12(5)]. The R3 - ↔ R3 - c transition in dolomite is described by a modified Bragg-Williams thermodynamic model with the following molar free energy of disorder, G̅ d  (T; s) = RT c [1 - s 2  + 1/2 a(s 4  - 1) - (T/T c ) {2 ln2 - (1+s) ln(1 + s) - (1 - s) ln(1 - s)}]. Using T c  = 1466 K and a = -0.29, this model provides an excellent agreement with experimental data. Moreover, the maximum enthalpy of disorder, H̅ d (s = 0) = RTc(1 - 1/2 a) ~ 14 kJ/mol, agrees with published calorimetric data. A thermodynamic description of the aragonite + magnesite ↔ dolomite reaction boundary is also presented and it reproduces the main qualitative features correctly.

Cation disorder in dolomite, CaMg(CO 3 ) 2 , and its influence on the aragonite + magnesite ↔ dolomite reaction boundary