A reactor for producing particles in a precipitation process, comprising: a housing defining a reaction chamber; a stator assembly including two or more stators in the reaction chamber; a rotor assembly including three or more rotors in the reaction chamber, the rotor assembly configured for rotation about an axis of rotation relative to the stator assembly; a first inlet to supply a first reactant material to the reaction chamber at a first radial location; a second inlet to supply a second reactant material to the reaction chamber at a second radial location different from the first radial location, wherein the first and second reactant materials react to produce precipitation of particles in the reaction chamber; and an outlet to supply the particles formed in the reaction chamber; and wherein the stator assembly includes at least a first stator and a second stator, wherein the rotor assembly includes at least a first rotor, a second rotor and a third rotor, wherein the first inlet is positioned to supply the first reactant material to the reaction chamber upstream of the first rotor, and wherein the second inlet is positioned to supply the second reactant material to the reaction chamber in a region of the second stator, and includes a plurality of openings in the second stator, said openings being in communication with the reaction chamber and spaced from an axis of rotation of the rotor assembly, and wherein the second stator includes a plurality of circumferentially spaced teeth and wherein the openings are located radially inwardly of the teeth and in radial alignment with the teeth rather than in alignment with spaces between the teeth. a housing defining a reaction chamber; a stator assembly including two or more stators in the reaction chamber; a rotor assembly including three or more rotors in the reaction chamber, the rotor assembly configured for rotation about an axis of rotation relative to the stator assembly; a first inlet to supply a first reactant material to the reaction chamber at a first radial location; a second inlet to supply a second reactant material to the reaction chamber at a second radial location different from the first radial location, wherein the first and second reactant materials react to produce precipitation of particles in the reaction chamber; and an outlet to supply the particles formed in the reaction chamber; and wherein the stator assembly includes at least a first stator and a second stator, wherein the rotor assembly includes at least a first rotor, a second rotor and a third rotor, wherein the first inlet is positioned to supply the first reactant material to the reaction chamber upstream of the first rotor, and wherein the second inlet is positioned to supply the second reactant material to the reaction chamber in a region of the second stator, and includes a plurality of openings in the second stator, said openings being in communication with the reaction chamber and spaced from an axis of rotation of the rotor assembly, and wherein the second stator includes a plurality of circumferentially spaced teeth and wherein the openings are located radially inwardly of the teeth and in radial alignment with the teeth rather than in alignment with spaces between the teeth.