Abstract: The present invention provides a process for preparing silicon oxide layers on a substrate, and particularly on metal, having improved corrosion-protective properties. This is accomplished by making the silicon oxide protective layer hydrophobic, preferably by incorporating therein hydrophobic organosilicon residues. The protective layers are preferably prepared by vapor deposition in a vessel containing silicon and/or silicon oxides in the gasous form, oxygen, and a organosilicon compound containing at least one hydrophobic group bonded to the silicon.

Abstract: The reflectors, for example for automotive vehicle head lamps are reflectorized by evaporating aluminum thereon in a vacuum vessel at a vacuum of about 10.sup.-7 bar; thereafter, and without removing the reflectors, a gaseous monomer is introduced raising the pressure to about 5 .times. 10.sup.-6 bar to deposit a protective layer by polymerization from the gaseous phase. The monomer gases, preferably, are low molecular weight siloxanes having methyl-, vinyl- or phenyl groups, preferably hexamethyldisiloxane (HMDS), or methyl-, vinyl- or alkoxy silanes, preferably vinyltrimethylsilane (VTMS), polymerization being accelerated and ensured by an electrical discharge generated within the vessel by a heated electron emitter placed at a negative voltage with respect to the reflector blanks. After polymerization, the layer is rendered hydrophilic by treatment with oxygen at a pressure of about 10.sup.-2 to 10.sup.