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fluidization Process of passing gas through loose, fine-grained particles causing the mixture to flow like a liquid; this facilitates mixing and chemical reaction. The faster the gas flows the more the mixture expands and movement increases. A bubble phase may form which travels upwards until all the solid particles are transported by the gas. Fluidization is used in coal-fired power stations and may occur naturally in volcanic eruptions producing pyroclastic flows and surges. It is the phenomenon which enables pyroclastic flows to travel distances in excess of 100 km and to surmount topographic obstacles hundreds of metres high.