One or more coating precursors are selected from metal or silicon compounds at a temperature above their melting points but substantially below their standard vaporization temperature, thereby causing the coating precursors to be in the form of a liquid. A vaporization chamber has a structure for continually injecting the liquid coating precursor into the chamber to produce a vapor. A seal-less, magnetically driven portion rotates a structure for distributing the liquid coating precursor in the vaporization chamber. In one embodiment, a barrier gas is injected adjacent the chamber at a velocity greater than the diffusion velocity of the vapor to prevent the vapor from communicating with the magnetically driven portion. In another embodiment, a first portion of the magnetically driven portion is connected to a structure for distributing the liquid coating precursor in the vaporization chamber. The second portion, located adjacent the first portion, but outside the vaporization chamber, magnetically couples with and rotates the first portion.