Metal treatment – Compositions – Heat treating
Patent
1989-12-14
1991-11-05
Dean, R.
Metal treatment
Compositions
Heat treating
148 1, 204164, 427 38, C23F 1500
Patent
active
050629000
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a process for improving the corrosion resistance of metallic materials such as stainless steel, ordinary steel, weakly alloyed steels, carbon steels, heat treatable steels, refractory steels, nickel based and cobalt based alloys, aluminium and its alloys, titanium and its alloys, zirconium and its alloys, zinc and its alloys, copper and its alloys.
The surface treatment of metallic materials has been carried out up until now by standard chemical reactions (oxidation, reduction conversion treatments).
Furthermore subjecting the surface of metallic materials to a surface treatment by plasma in an atmosphere composed of a rare gas such as argon, is known. With such a treatment the negatively polarised surface of the metallic material is bombarded with ions such as Ar.sup.+, which causes a tearing off of the surface atoms and a preferential erosion and leads to a very high reactivity vis-a-vis the atmosphere and to an increase in roughness.
It has now been found that if the neutral monotomic gas is replaced by certain types of molecular gas, oxidants or reducers, it is possible, with a surface treatment by plasma at a low temperature (that is to say at ambient temperature), to improve the corrosion resistance of metallic materials.
Consequently a subject of the present invention is a process to improve the corrosion resistance of a metallic material, characterised in that the cold metallic material is subjected to a surface treatment by plasma at a low temperature, at a pressure from 1 to 10.sup.3 Pa, in an atmosphere comprising at least one gas chosen from the following: oxygen, ozone, nitrogen, hydrogen, air, carbon dioxide, carbon monoxide, the nitrogen oxides, water, combustion gases and mixtures of these with a neutral gas.
Plasma at low temperature or `cold` plasma generally refers to plasma obtained by luminescent discharge in a low pressure atmosphere (less than 10.sup.3 Pa) atmosphere. The discharge is obtained in an enclosure between an anode and the negatively polarised metallic material which serves as a cathode. The metallic material to be treated is maintained at a `cold` temperature, that is to say in practice its temperature is maintained at less than 100.degree. C. This can be achieved using a cathode and an anode cooled by a circulation of water.
Under the influence of the electric field, the molecules of the gas are dissociated, excited or ionised; in the electric discharge thus created, a low energy plasma sweeps the surface of the material and the various gaseous types react with the surface atoms according to their chemical affinity. A large number of elements disappear from the treated surface according to whether the gases are oxidants or reducers. After treatment, the surface is generally passive vis-a-vis the atmosphere, that is to say, standard pollution elements C, S, P, O . . . .
One of the most interesting characteristics of cleaning by molecular plasma is that it does not change the surface roughness of the material even on coatings with a low softening point given the temperature of the plasma. In effect there is no erosion with a molecular gas, whereas erosion is significant with rare gases.
The reaction products, for the most part, certainly in the gaseous form, are evacuated by pumping and the others, which are positively charged can be redeposited on the cathode, for example calcium, but without however interfering with the surface.
In the present invention neutral gas denotes a rare gas such as argon, neon and helium.
Gaseous atmospheres that are particularly suitable are N.sub.2 /O.sub.2, mixtures, including air, carbon dioxide, N.sub.2 /H.sub.2, H.sub.2 /Ar.
Treatment time can be from approximately 1 second to 10 minutes. Advantageous operating voltages are between 100 and 5,000 V.
It is certain that the results previously indicated can be obtained by electric or electromagnetic fields generated by standard techniques for `cold` plasma usually used for physical deposits in the vapour phase (magnetron, ion or electron guns, standard ionic dep
REFERENCES:
patent: 4509451 (1985-09-01), Collins et al.
Chemical Abstracts, vol. 99, No. 8, Aug. 1983, p. 214, No. 57309f.
Chemical Abstracts, vol. 96, No. 16, Apr. 1982, p. 283, No. 127177a.
Chemical Abstracts, vol. 97, No. 10, Sep. 1982, p. 298, No. 770342.
Berneron Roger
de Gelis Pierre
Dean R.
Institut de Recherches de la Siderurgie Francaise
Koehler Robert R.
LandOfFree
Process for the improvement of the corrosion resistance of metal does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for the improvement of the corrosion resistance of metal, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for the improvement of the corrosion resistance of metal will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-496530