Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Forming nonmetal coating using specified waveform other than...
Reexamination Certificate
2001-06-15
2004-07-06
King, Roy (Department: 1742)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Forming nonmetal coating using specified waveform other than...
C205S215000, C205S220000, C205S223000, C205S333000
Reexamination Certificate
active
06758956
ABSTRACT:
The invention comprises a method for the darkening of a surface layer of a piece of material containing zinc during which the piece of material is oxidized in a dip bath which contains a hydrous solution of a hydroxide and a nitrate, a piece of material treated by such a method, and also the electrolytes for the realization of the method the methods for pretreatment of the pieces of material.
Generally, for the darkening of material surfaces containing zinc, the method known as “blackening by chromating” has been used so far. This method uses the highly reactive molecule of Cr
6
which is, however, according to the most recent findings, strongly detrimental to health.
A less harmful method for the darkening of pure zinc surfaces is described in the scientific paper “production of a protective and decorative coating on zinc by alternating-current treatment at 50 Hz in alkaline solutions” by M. Al. Encheva, published in the J. Appl. Chem. of the USSR 45.318 (1972). In this paper, a dip bath for the darkening of surfaces made of zinc is presented which contains as an electrolyte, within the scope of anodic oxidation, hydrous solutions of NaOH and NaNO
3
. This scientific paper is focussed both on the improvement of corrosion resistance of pieces of material with a zinc-coated surface, and on the appearance of the surface-treated pieces of material, especially their transformation.
The quoted paper only mentions rough and wide ranges of parameter for the treatment process, not indicating any details, however, of homogeneity and uniformity of the darkened surfaces. not indicating any details, however, of homogeneity and uniformity of the darkened surfaces. A further development of the familiar method is described, regarding its application on solar collectors, in the published study “Optimization and Microstructural Analysis of Black-Zinc-Coated Aluminium Solar Collector Coatings” by S. N. Patei et al., published in “Thin Solid Firms”, 113 (1984), p. 47).
In EP 0 339 578 A1, a process for the production of black-coated steel strips is described which consists of an electrolyte treatment in a dipping bath containing from 75 to 200 g/l of a compound selected from among the group comprising hydroxides, sulphates and chlorides of sodium, potassium or nickel. Preferably, the dip bath contains nitrate ions in a quantity from 2 to 100 g/l. For the anodic oxidation used for this process, current densities within the range from 30 to 200 A/cm
2
are used. This process is preferably operated with alternating current. The dipping bath must absolutely contain both an inhibitor substance and a complex-forming one.
FR 2758339 A describes a method for anti-corrosion treatment of metallic workpieces, in particular ferruginous ones. The dip bath used for electrolysis contains between 300 to 700 g/l of alkali hydroxides, between 20 and 50 g/l alkali nitrates and/or nitrites, between 40 to 100 g/l borax, and between 10 to 40 g/l tensides, the dipping bath bring maintained at a temperature within the range from 110 to 130° C.
The scientific paper by Fry H.E.A. with the title “The Anodic Oxidation of zinc and a Method of Altering the Characteristics of the Anodic Films”, published in “Journal of the Electrochemical Society”, volume 106, No. 7, July 1959, pages . . . 606-611, equally describes methods of anodic oxidation of zinc. Black coatings have been achieved by anodizing zinc in a sodium hydroxide solution with a current density of about 200 mA/cm
2
. Dark layers were apparent in case of dip bath solutions containing sodium carbonate and sodium hydroxide, if low anode potentials were used. All samples were immersed into the bath for 15 seconds without voltage and prior to feeding the potential.
From this starting point, the invention is based on the purpose to develop processes for the darkening of a surface layer of a piece of material containing zinc in such a way that all treated surfaces show increased homogeneity adhesion and uniformity, and also to provide the respective piece of material having such properties, and also the electrolytes for the execution of such processes.
The requirement is met by a method according to claim 1. The dip bath solution preferably contains an alkali salt or ammonium salt from among the group comprising phosphates, acetates, carbonates, sulphates, exalates, citrates and borates of alkali metal or ammonium.
If these process parameters are maintained, the result is the homogenous darkening of the surface layers of the surfaces of those pieces of material which contain zinc from a dark gray colour to black, leading also to an excellent homogeneity of the surface layer. It should be emphasized that it is a comparatively low current density which will lead to the desired colour changes of the surface layers, quite contrary to the method described in the scientific paper.
The method is characterized by the piece of material being immersed into the dip bath of a device which is equipped with, at least, two electrodes for anodic oxidation, the alternating or direct voltage being fed to the electrodes prior to immersion of the piece of material into the bath, and only then the piece of material will be immersed into the bath while maintaining the voltage which should initially be 8 volts for alternating current and initially 20 volts for direct current with an electrode spacing of 3 cm. When the piece of material is immersed, first a high current will flow between the electrodes. After the expiry of a period of a few seconds after immersion of the piece of material, the current density required for this method should be adjusted by reducing the voltage. Such a method will essentially contribute to the homogeneity of the darkened surface layer. It is important to provide of a minimum current flowing during immersion of the piece of material for the purpose of improvement of homogeneity.
Appropriate pieces of material could be all suitable substrates which are coated with a zinc layer whose surface has been treated, and also pure zinc. Instead of pure zinc, you could use a zinc alloy presenting, in relation to the dry layer, a high content of zinc, e.g. a minimum of 50 percent in weight. Additionally, it is possible to apply a pure zinc layer, or a zinc alloy layer by any other method to a substrate, such as vapor deposition processes like PVD and CVD, hot dip galvanizing and all methods for mechanical surfacing of such layers. In individual cases, mat zinc-coated or bright galvanized steel sheets may be used. Possible zinc alloys may be, among others, Zn/Fe, Zn/Ni, Zn/Fe/Co, Zn/Co, Zn/Al, Zn/Sn, Zn/Mn.
Titanium may be used as the opposite electrode for the piece of material to be treated. Other materials could also be used for the electrodes if the required current density is adapted accordingly. Other possible materials for the opposite electrode are precious metals, stainless steel, tantalum, graphite.
The pH value should preferably be adjusted by means of the respective concentration of NaOH or KOH. The pH value will be finally decisive, while, for providing the OH′ groups, it is also possible to use amines or other organic bases, soluble potassiums (sodium silicates, potassium silicates, lithium polysilicates), amino hydrosilicones, basified titanic acid esters (silica esters) in single or combined form. Optionally, zirconium compounds which are made available/resembling? (for) groups similar to OH′ may be used [Sense? Translator's remark].
For acceleration of the treatment process, the pH value should be higher than 13. This is also applicable for all methods relating to the invention which are described later on. In this case, . . . anodic oxidation may be processed over a treatment period of from 1 second to 10 minutes until the surface layer has darkened.
The method can optionally be carried out with direct voltage or alternating voltage. Generally, for operation with direct current, lower current densities will be required for achieving darkening of the surface layer.
When operating the process with direct voltage, the temp
Kruse Thomas
Meisterjahn Peter
Ewald Dorken AG
King Roy
Leader William T.
Snell & Wilmer LLP
LandOfFree
Method for darkening a superficial layer which contains zinc... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for darkening a superficial layer which contains zinc..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for darkening a superficial layer which contains zinc... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3205232