Formation Of Magnesium Silicide Research Articles

Formation of Magnesium Silicide in bulk diffusion couples

Formation of Magnesium Silicide in binary Mg/Si diffusion couples and in reactions of Mg with Silicon Dioxide was investigated. The position of the Kirkendall marker plane inside the reaction zone of the bulk diffusion couples revealed that at 500 °C, Mg is virtually the only mobile species in the Mg2Si intermetallic compound. Such diffusion behaviour was rationalized using crystallographic information about anti-fluorite structure of the Mg2Si phase. Using general relations between integrated diffusion coefficient for a stoichiometric compound, tracer diffusivities of the components and data on thermodynamic stability of the phases involved in the interaction, the tracer diffusion coefficient DMg⁎ in the Mg2Si was derived.During diffusion-controlled interaction of Mg with Silicon Oxide, the Mg2Si intermetallic is formed within the transition zone microstructure as a continuous phase with the periodically arranged bands of MgO-particles embedded in the matrix phase. In the case of bulk Mg/quartz-SiO2 couples annealed at 500 °C, MgSiO3 and Mg2SiO4 silicates are also found in the reaction zone next to the SiO2-substrate. This can be explained with the help of the equilibrium Mg–Si–O phase diagram. However, no formation of Magnesium Silicates was observed in diffusion-controlled reactions between Mg and fused (amorphous) Silica.At the early stages of the interaction in bulk Mg/SiO2 couples, the situation was found to be different. No quasi-binary compounds MgSiO3 and Mg2SiO4 were detected in the diffusion zone after reaction of Mg with monocrystalline SiO2 as well as fused Silica at 550 °C. In both cases, the layer adjoining the SiO2-substrate is Magnesium Oxide.The formation of periodic layered morphology is considered to be a manifestation of the Kirkendall effect accompanying reactive phase formation in the solid state. The suggested mechanism is operative when the components have distinctly different mobilities in adjacent reaction product layers.

Pulsed nanosecond annealing of magnesium-implanted silicon

Single-crystalline silicon is implanted by magnesium ions at room temperature and then subjected to pulsed ion-beam annealing. The surface morphology, crystallinity, and optical properties of the implanted silicon are studied before and after annealing. It is shown that ion implantation makes a near-surface layer of silicon about 0.1 m thick amorphous. Pulsed nanosecond ion-beam annealing results in silicon recrystallization and the formation of crystalline magnesium silicide precipitates. Optimal values of the implantation dose and pulse energy density for the formation of magnesium silicide precipitates in the near-surface layer of silicon are found.

Solid-state synthesis of Mg2Si via short-duration ball-milling and low-temperature annealing

In this work, a short duration ball-milling of elemental Mg and Si followed by a thermal treatment is suggested in order to synthesize magnesium silicide via solid-state reaction. The formation of magnesium silicide was studied in terms of its structure and thermal characteristics by powder X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy and differential scanning calorimetry. Pure Mg2Si was formed after short milling and heating at temperatures as low as 280°C. Differential scanning calorimetry analysis was performed to study the kinetics of the reaction. The activation energy of the reaction was calculated using the Ozawa–Flynn–Wall and Friedman methods. The thermoelectric properties suggested semiconducting behavior whereas thermal conductivity values of highly dense hot-pressed pellets are consistent with the literature.

A SEED OF SOLAR FORSTERITE AND POSSIBLE NEW EVOLUTIONAL SCENARIO OF COSMIC SILICATES

Laboratory experiments suggest that magnesium silicide (Mg2Si) grains could be produced in the hydrogen dominant gas outflow from evolved stars in addition to amorphous oxide minerals. If the magnesium silicide grains were incorporated into the primitive solar nebula, the magnesium silicide would easily become forsterite (Mg2SiO4) by oxidation as it reacted with the relatively oxygen-rich, solar composition gas. This hypothesis can explain the existence of abundant forsterite grains with solar oxygen composition in meteorites, i.e., magnesium silicide could be the precursor of much of the forsterite found in our solar system. In addition, if a significant fraction of the solar forsterite is derived from magnesium silicide, it could explain the apparent low abundance of presolar forsterite. Furthermore, the lower degree of crystallinity observed in silicates formed in outflows of lower mass-loss-rate stars might be caused by the formation of magnesium silicide in this relatively hydrogen-rich environment.

Formation of Magnesium Silicide by Mechanical Alloying

Elemental Mg and Si powders were mechanically alloyed in a planetary ball mill. The formation of magnesium silicide as well as the formation of magnesium oxide and hydride in the milled powders was studied in detail by X-ray diffraction and scanning differential calorimetry. It was found that direct formation of the magnesium silicide, Mg2Si, occurred after 10 hours of milling and the content of Mg2Si increased with increasing the milling duration. The activation energy for the formation of Mg2Si was calculated by the Kissinger approach to be 215 kJ/mol. Besides oxidizing and hydrizing of Mg by decomposed organic additives during mechanical alloying, an increased contamination of powders from steel and alumina milling tools with increasing milling duration was detected. A short milling duration followed by a thermal treatment was thus suggested to synthesize magnesium silicide.