Abstract: Method for producing nano- to micro-scale particles of a material by homogeneous thermal decomposition or reduction of a reactant gas (12) containing the material, whereby the method comprises the steps of supplying the reactant gas (12) to a reaction chamber (16) of a reactor via at least one inlet, and a) heating the reactant gas (12) to a temperature sufficient for thermal decomposition or reduction of the reactant gas (12) to take place inside the reaction chamber (16), or b) confining a temperature dependent reaction or reaction sequence involving a plurality of reactants inside the reaction chamber (16). The method comprises the step of supplying a primary gas (22) through a porous membrane (20) constituting at least part of at least one wall of the reaction chamber (16) to provide a protective inert gas boundary to minimize or prevent the deposition of the material on the porous membrane (20).