NOVELTY - A system for preparing silicon tetrafluoride by the thermal decomposition of alkali or alkaline earth-metal fluorosilicate comprises fluidized bed reactor (1) comprising a reaction chamber (10) for thermal decomposition of fluorosilicate into silicon tetrafluoride gas (16) and alkali or alkaline earth-metal fluoride; heater apparatus in thermal communication with reaction chamber; and exhaust gas treatment system for treating gases discharged from the fluidized bed reactor, the exhaust gas treatment system comprising a particulate separator in fluid communication with fluidized bed.    USE - As a system for preparing silicon tetrafluoride (claimed), used as a precursor in the production of silane for production of polycrystalline silicon which is used to produce semiconductors and solar cells; also used for ion implantation, plasma deposition of fluorinated silica and as a metal silicide etch.    ADVANTAGE - The system transfers heat efficiently to the fluorosilicate material and that produce by-products that can suitably be recycled. The fluidized bed reactors provide high mass transfer and heat transfer rates between decomposing fluorosilicate particles and the gas phase which enhances the decomposition rate of the fluorosilicate particles.    DETAILED DESCRIPTION - A system for preparing silicon tetrafluoride by the thermal decomposition of alkali or alkaline earth-metal fluorosilicate comprises fluidized bed reactor (1) comprising a reaction chamber (10) for thermal decomposition of fluorosilicate into silicon tetrafluoride gas (16) and alkali or alkaline earth-metal fluoride; heater apparatus in thermal communication with reaction chamber; and exhaust gas treatment system for treating gases discharged from the fluidized bed reactor, the exhaust gas treatment system comprising a particulate separator in fluid communication with fluidized bed reactor for removing alkali or alkaline earth-metal fluoride from gases discharged from fluidized bed reactor.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic of a fluidized bed reactor.    Fluidized bed reactor (1)    Distribution unit (2)    Fluidizing gas (5)    Reaction chamber (10)    Withdrawal tube (12)    Fluoride residue storage (15)    Silicon tetrafluoride gas (16)