Silicon Monoxide - Formation of SiO

Formation of SiO

The first precise report on the formation of SiO was in 1887 by the chemist Charles F. Maybery (1850–1927) at the Case School of Applied Science in Cleveland. Maybery claimed that SiO formed as an amorphous greenish-yellow substance with a vitreous luster when silica was reduced with charcoal in the absence of metals in an electric furnace. The substance was always found at the interface between the charcoal and silica particles. By investigating some of the chemical properties of the substance, its specific gravity, and a combustion analysis, Maybery deduced that the substance must be SiO. The equation representing the partial chemical reduction of SiO2 with C can be represented as:

Complete reduction of SiO2 with twice the amount of carbon yields elemental silicon and twice the amount of carbon monoxide. In 1890, the German chemist Clemens Winkler (the discoverer of germanium) was the first to attempt to synthesize SiO by heating silicon dioxide with silicon in a combustion furnace.

However, Winkler was not able to produce the monoxide since the temperature of the mixture was only around 1000°C. The experiment was repeated in 1905 by Henry Noel Potter (1869–1942), a Westinghouse engineer. Using an electric furnace, Potter was able to attain a temperature of 1700°C and observe the generation of SiO. Potter also investigated the properties and applications of the solid form of SiO.

Because of the volatility of SiO, silica can be removed from ores or minerals by heating them with silicon to produce gaseous SiO in this manner. However, due to the difficulties associated with accurately measuring its vapor pressure and because of the dependency on the specifics of the experimental design, various values have been reported in the literature for the vapor pressure of SiO (g). For the pSiO above molten silicon in a quartz (SiO2) crucible at the melting point of silicon, one study yielded a value of 0.002 atm. For the direct vaporization of pure, amorphous SiO solid, 0.001 atm has been reported. For a coating system, at the phase boundary between SiO2 and a silicide, 0.01 atm was reported.

Silica itself, or refractories containing SiO2, can be reduced with H2 or CO at high temperatures, e.g.:

As the SiO product volatilizes off (is removed), the equilibrium shifts to the right, resulting in the continued consumption of SiO2. Based on the dependence of the rate of silica weight loss on the gas flow rate normal to the interface, the rate of this reduction appears to be controlled by convective diffusion or mass transfer from the reacting surface.

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