Abstract: The invention relates to an orifice chamber (18) designed to expand a gas, in particular intended for a fluid catalytic cracking unit, said orifice chamber comprising the following elements: a chamber (181) having an axis (X), an inlet duct (182) that opens into the chamber (181), an outlet duct (183) located on the opposite side from the inlet duct following said axis (X), and a plurality of internal plates (184) positioned crosswise to the axis (X) inside the chamber at a distance from one another along the axis (X), each internal plate (184) being provided with a plurality of through-orifices (185), characterized in that at least the plurality of internal plates is made of a ceramic material.