A solid-state metathesis route to MgSiN2

Nitrides, such as magnesium silicon nitride, hold promise for applications requiring materials with high thermal conductivity. The synthesis of the ternary nitride MgSiN2 is accomplished using SiO2 and Mg3N2 as reactants in a solid-state metathesis (exchange) reaction. This self-propagating reaction is readily initiated when a flame with a temperature > 1100 degrees C is brought into contact with a pressed SiO2/Mg3N2 pellet. By using Mg3N2 in >= 1 M excess, X-ray-pure MgSiN2 can be produced. With lower ratios, elemental silicon forms as an impurity. Increasing the flame initiation temperature to >= 2500 degrees C can also be used to eliminate silicon impurities with the benefit of increasing the crystallinity of the product. The use of other forms of silica as a silicon source provides an inexpensive alternative to produce MgSiN2. A variety of silica sources are examined, including fumed silica, sand, ground quartz, bottle glass, and rice hull ash. Since rice hull ash is an industrial waste product from rice processing, new applications such as in the synthesis of MgSiN2 could prove to be environmentally friendly.