ISSN:
1432-2021
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
,
Geosciences
,
Physics
Notes:
Abstract This paper presents the point-defect thermodynamics for fayalite and olivine solid solutions (Fe x Mg1−x )2SiO4. By means of thermogravimetry, the metal-to-oxygen ratio of these silicates has been determined as a function of oxygen potential, compositionx and temperature. Experiments were performed in the range of 1,000° C≦T≦1,280° C and 0.2≦x≦1.0. It is found that V Me ″ , Fe Me · and the associate {Fe′ Si ′ Fe Me · } are the majority defects. With this knowledge it is possible to calculate the nonstoichiometry at given temperature as a function of $$p_{O_2 } $$ and $$a_{SiO_2 } $$ . The cation vacancy concentration shows a $$p_{O_2 }^{1/5} $$ -dependence (forx≧0.2) and increases at givenT and $$p_{O_2 } $$ almost exponentially with compositionx. In the composition range studied here, the silicates show an oxygen excess, and FeO is more soluble in the olivine than SiO2.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01204323
