Mixed high temperatures lead

Close to the critical point, the density changes, as does the viscosity, and, in the case of water, the dielectric constant. Whereas subcritical water is insoluble for nonpolar organic substances, overcritical water can be used like a nonaqueous solvent [76]. The pressure and temperature can be adjusted to set optimal properties of water for the reaction. This makes it possible to use overcritical water, which can be mixed with liquid fuels, for desulfurization. The free radicals, which appear more frequently at high temperatures, lead to the splitting of the sulfur compounds and the formation of hydrogen sulfide [77]. 

In some locations, high-temperature fluids undergo considerable subsurfece mixing with relatively fresh seawater. This leads to precipitation of the less soluble iron and copper sulfides within the conduits. The fluids discharging into the ocean generally have temperatures less than 400°C and are milky white because of zinc sulfide precipitates. These white smokers also build chimneys, some of which are as much as 13 m high. Because of their lower temperatures, white smokers are typically encrusted with worm... 

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