Microstructure studies of periodic layers phenomenon in Mg/SiO₂ diffusion couples in the temperature range of 673-873 K

Scientific problem of this study is related to the intriguing phenomenon of periodic layered structure formation in Mg/SiO₂ diffusion couple. Such morphology comprises a regular array of alternating layers (single or double phase), which are periodic in space and time. The Mg/SiO₂ diffusion couples composed of the high purity Mg and SiO₂ end-members were heated up to the appropriate temperature and for different times under protective argon atmosphere. In order to reveal the possible influence of external stresses on the phenomenon of periodic layers creation two instruments were used. At first, the differential scanning calorimeter (DSC) was applied, where the high vapour pressure of magnesium allowed obtain the sample without use of any external pressure. At second, in the thermomechanical analyzer, which allowed precisely setting of the clamping force. Application of SiO₂ as amorphous and single crystal was used to find the possible correlation between the layer frequency and crystallographic orientation. The microstructure evolution regarding the displacement reaction in the Mg/SiO₂ system was established in the temperature range of 673-873 K. Measurements of the composition of created layers and determination of their morphology using structural investigation in SEM was followed by the determination of reaction product thickness, bands amount and width. It was followed by their examination under transmission electron microscope. Finally, the phase composition results of the produced periodic layers were correlated with the Mg-Si-O equilibrium phase diagram.

Acknowledgments

The research was financed by the National Science Centre, Poland under the project No. 2014/15/B/ST8/00195.