Historical Articles

December, 1953 issue of Plating

 

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Progress Report on Development of a New Accelerated Corrosion Test

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Presented at the 40th Annual Convention of the American Electroplaters’ Society, June 18, 1953.

W.L. Pinner, Manager, Process Development Division, Houdaille-Hershey Corporation, Detroit, Michigan.

This project had its inception in growing dissatisfaction with the salt-spray test as a means of evaluating the serviceability of decorative plated coatings. Industry has recognized the difficulty of duplicating results from one salt-spray box to another, as apparently there are unrecognized factors which cause wide variation in results. Additionally the salt-spray test, as presently used, does not duplicate the types of failure encountered in actual service and it is obviously desirable that an accelerated test should accomplish this.

In 1951 a group, under the Chairmanship of Mr. F. L. LaQue, was appointed by the Research Committee to determine the advisability of action. The report of this Advisory Committee has been published in PLATING1. For easy reference a few pertinent passages of it are reviewed as follows:

committees, there is as yet no project director, as such, nor is there an undergraduate Fellow carrying out the experimental work. The purpose of the Project is so important and the need for speedy action is so acute that activities are being contributed by several companies, whose representatives form the project committee. Appended to this report is a list of fifteen top-flight technical men, representing thirteen companies participating in the actual work. These men form the Project Committee, agree upon the course of action, and then see to it that the actions required are carried out in their respective plants and laboratories.

Project 15 is unique in that its support, financially, is very largely derived from the companies that its committee members represent, inasmuch as the expense for carrying out the work would be far beyond a sum appropriate to be expended from the limited fund available from the Research Committee. It is pertinent to mention that this expense in no single instance has affected the support which these companies other wise provide to the Research Committee for its other; activities. The organizations involved and their representatives are more than glad to contribute their time and expense, with the hope that results from the project will be forthcoming at as early a date as possible.

In keeping with the recommendations of the Advisory Committee, Project 15 has accepted as its three principal starting assignments; first, the design, fabrication and service exposure of plated parts; second the gathering of pertinent data on conditions thought to contribute to the deterioration of plated coatings, and third the carrying out of exploratory accelerated corrosion tests in order to select qualitatively those which appear to have merit and which should be investigated quantitatively at a later date.

While the Advisory Committee suggested the studying of the performance of decorative plated coatings over steel, the project committee agreed that these studies should be supplemented by similar ones involving such coatings on diecast parts. Service tests are therefore planned on both materials and, for purpose of illustrating the extent of the cooperative effort, the assignments involved in this phase of the program shall be listed.

First of all it is pertinent to mention that the designed test parts will resemble front license plates and will be exposed on the front license plate brackets of cars in Detroit, there, very fortunately, being no numbered plates required in this location in the state of Michigan.

For the handling of the diecast parts the following assignments were made and are partially completed: General Motors Corporation agreed to furnish the diecast dies, cast the parts and store the dies for future use. Packard Motor Car Company agreed to polish the parting line and buff the parts ready for plating. Doehler-Jarvis Company is to inspect the parts, plate them with an appropriate copper-nickel-chromium plate and package them for shipment. Chrysler Corporation will store excess parts not in use and will attend to the installation of them on’ taxicabs and other test cars.

As for the handling of the steel parts the following should be noted: Hudson Motor Car Company designed and furnished the necessary dies; Kaiser-Frazer Corporation furnished the raw material, formed the parts and assembled the necessary brackets by projection welding; and the Udylite Corporation agreed to polish the steel and round the edges preparatory for plating and to store the parts.

Two types of plating will be applied to the steel parts, one consisting of straight nickel followed by chromium, the other consisting of a combination copper-nickel plate followed by chromium. The Electric Auto-Lite Company will nickel plate, buff and chromium plate part of the steel pieces. The Ford Motor Company will copper plate, buff, bright nickel and chromium plate the other part of the steel pieces. Chrysler will store excess parts not in use and attend to their installation on mobile test sites. The entire committee will attend to the inspection, photographing and carrying out of any laboratory work involved in connection with the exposure specimens. As one her necessary assignment, the Udylite Corporation has made an extensive study of racking methods necessary for the production of a tapered section plate as recommended by the Advisory Committee.

It may be reported that this phase of the program ‘is well under way, with virtual assurance that the parts ‘ill be ready for exposure prior to the Winter months ‘of 1953-1954.

In conformance with the suggestion of the Advisory Committee, it is presently planned that the test panels will have a total thickness of metallic coating varying from about 0.0004 inch, at one end, to 0.0016 inch at the other end. In the foregoing it will have been noticed that the steel parts will be coated with two types of coating, one being all-nickel and the other being a’ combination of copper-nickel. It is important to mention that the variations in thickness and the use of different types of coatings is definitely not designed to compare the serviceability of the plate as a function of these factors, because such matters do not fall within the scope of this project. Rather the purpose of variations in thickness is to provide coatings which will fail at early dates and at dates after longer periods of exposure. The different types of coatings were selected because these are in widespread use in industry. It is necessary to remember that the entire purpose of this phase of the program is to obtain the types of deterioration which occur under known conditions, so that efforts may be made later to obtain exactly these same kinds of deterioration by accelerated means.

Presently it is planned to provide about 1000 panels of each of the three categories. While the exact distribution has not been arrived at, it is probable that not more than one-half of each kind will be subjected to service exposure. The balance of the panels will be carefully stored to be used at a later date in experimental work, when accelerated means wilt be sought which will duplicate the exact types of service failures.

The second phase of the program involves the gathering of all pertinent data which are known, or suspected, to contribute to the deterioration of plated coatings. The most pertinent data will, of course, be gathered during the time of exposure of the test panels. However, prior to that; time, the Project is obtaining data ‘and to this end it has enlisted the cooperation of certain departments of the’ city of Detroit, of which there may be mentioned, for example, the Weather Bureau and the Department of Parks and Boulevards, the latter of which will keep the Project supplied with information regarding the amount and locations of materials used for de-icing streets. Additionally the Project is maintaining liaison with certain groups which have allied interests and it may point, for example, to a recent attendance at a Joint Industry Conference which considered details of a Detroit area air pollution study. Furthermore, the Project has drawn on information already in the files of certain committee members, who have for considerable periods of time gathered information on various factors in the air and on the city streets, all thought to contribute to the general picture. Still further, certain committee members have arranged the installation of collector bottles, mounted on automobiles, for the collection of street and air contaminants so as to determine the percentage and kinds of ingredients which may be picked up on automobile parts and thus cause corrosion to occur.

The third phase of the program involves the carrying out of exploratory accelerated corrosion tests in order, at a later date, to select those which appear to merit further investigation. The committee recognizes that a great number of factors are involved in the mechanics by which corrosion occurs on plated parts. These are numerous and, to mention a few, the committee will take due recognition of the effect of abrasion from dirt particles, salt, moisture, and high acid content of slush on the street following a snowfall or any condition leading to ice formation. The committee recognizes that in the air, rainfall itself is damaging, especially the first part of a rainfall, which in scouring the air carries down considerable quantities of corrosive chemicals.

As the first step in this part of the program, various committee members volunteered the use of various types of testing equipment, including humidity cabinets, intermittent immersion test equipment, cold cabinets, salt spray boxes, total immersion tanks and other similar equipment. There followed the appointment-of a subcommittee which solicited ideas from all of the members of the main committee as to the types of test which should be preliminarily looked at. The ideas accepted by the subcommittee and subsequently specifically assigned to committee members for experimental investigation are listed as follows:

1. The carrying out of tests at temperatures lower than those normally used in salt-spray tests and approaching the temperatures likely to prevail when roads are treated with salt during winter months when- corrosion is believed to be most severe. This should include admission of corrosive gases such as sulfur dioxide which change in solubility with temperature.

2. The continuous immersion of test specimens in solutions made up to represent what might be encountered in service.

3. Tests in which the specimens would be immersed in solutions of appropriate composition and then exposed to a humid atmosphere with or without the admission of corrosive gases in a cycle of immersion and atmospheric exposure.

4. Tests in which the specimens first would be chilled, then sprayed with an appropriate solution simulating early rain containing dust in suspension and then returned to the chilling chamber for further exposure.

5. Modifications of the standard and acetic acid modified salt-spray test, such as:

(a) Intermittent operation
(b) Substitution of oxygen or carbon dioxide, or both, for air in the spray
(c) Adjustment of pH by acids other than acetic e. g., sulfurous

6. Addition to the test environment of solid particles such as ash, dust and soot (carbon).

7. Use of a gelatin film as a reservoir of corrosive media, but especially as a means of holding solid particles and corrosion products in contact with the metal while it is being subjected to attack in a spray or other corrosive environment.

8. Expose specimens to a moist atmosphere carrying sooty smoke from a high sulfur fuel (coal or gas) so that surfaces will become contaminated followed by further exposure to a moist atmosphere.

9. Explore effects of temperature between freezing point and some higher temperature on the galvanic potential relationships amongst basis and coating metals.

10. Explore effect of addition of wetting agent to favor penetration of corrosive media into fine pores or cracks.

11. Examine coated specimens with respect to the amount of current required to prevent corrosion in an appropriate testing solution such as sodium sulfate adjusted to proper pH or in a solution collected from Detroit streets after treatment with salt in winter or simulation of this.

12. Miscellaneous proposals

(a) Eliminate positional effects in spray boxes by moving specimens or nozzles, or both.
(b) Investigate effects of oxidizing agents other than air in promoting breakdown of coatings in appropriate media.
(c) Investigate water-line effects in connection with immersion tests.

Some results from the preliminary investigations already have been made available in reports which would require many additional pages to cover. These results would more appropriately be contained in detail in the Project progress reports, normally published in PLATING. It is sufficient to say that the experimental work thus far has eliminated certain chemicals found in the atmosphere or on the streets and at the same time has definitely assigned corrosion of plated parts to certain other chemicals which through their existence in road dirt or in the air can cause corrosion. Illustrative of the type of test which is being carried out, a section of a report of one committee member is quoted as follows:

"Tests were conducted on 4 x 6 inch plated panels (0.001 inch nickel over NAX steel polished to 10 profilometer) with solutions thought to represent a possible early rain in a mingled industrial atmosphere. An extension of this work concerned the corrosive nature of chemicals of several types on nickel electrodeposits.

A synthetic industrial water wash was made of ingredients commonly regarded as atmospheric contaminants. The mixture was composed of ammonium chloride (0.020 g/l), sodium sulfite (0.020 g/l), ammonium nitrate (0.020 g/l), zinc oxide (0.020 g/l) and powdered pumice (0.020 g/l). It is recognized that fumes of some of these salts cannot be washed out of air with any degree of effectiveness but might be carried as precipitants in showers.

This ‘early rain’ when applied to chilled panels and stored in an ice box with occasional removal to the outside to permit condensation did not show any evidence of attack on nickel coatings. Contrariwise, other panels, placed in a humidity box, 100 per cent at 100° F, showed rapid rusting at isolated points. It was realized that not all ingredients of the ‘early rain’ necessarily contributed to this corrosive effect and the constituents were checked individually. Panels, bordered with a thin coating of silicone lubricant or a line drawn by a grease pencil to permit retention of fluid,’ were flooded with aqueous solutions of varying concentrations and allowed; to stand at room temperature. Solutions of 1 g/l of sodium sulfite and ammonium chloride rapidly perforated the nickel coatings and in 14 hours caused extreme rusting. The corrosive action present in the early rain was therefore assigned to the ammonium chloride and the sodium sulfite.

A number of other common industrial salts then were tried in much the same manner, with individual panels being subdivided to eliminate plating variations. Table I lists the results obtained.

It can be reported that each corrosive salt is different in its mode of destruction and has a different optimum of physical conditions under which it is most effective as an agent of nickel corrosion. Inhibition of a corrosive ion by another is possible. Wetting agents seem to be effective in reducing even the electrolytic corrosion of nickel, especially at low potentials (less than 0.5 volts).

TABLE I. RESULTS OF CORROSION TESTS USING COMMON INDUSTRIAL SALTS* Nickel chloride—very severe perforation at room temperature Sodium metabisulfite—solution of plate accompanied by perforation Sodium tartrate—no effect Sodium chloride—mild perforation at strong concentrations (20 g/l) Potassium pyrosulfate—extreme solution of nickel, very fine perforation Potassium iodide—strong attack on the nickel at many small points without perforation Potassium iodide plus ammonium chloride—acts as potassium iodide alone Ammonium sulfate—attack only when dried and placed in humidity chamber, strong perforation Sodium acetate—no attack under any test condition *NOTE: By perforation is meant spots of red rust.

The conclusion is that some chemicals that are present and are washed out of industrial atmospheres are so corrosive to nickel that they cannot be satisfactorily used to test the value of nickel plates other than in regard to the efficacy of thickness as a means of preventing penetration to the base metal. The effects of inhibitory ions and physical conditions point to causes of irregularity in salt spray results without regard to the possibility of highly corrosive contaminants such as the sulfite anion and ammonium cation.”

As noted in the foregoing, detailed information on the preliminary tests may be published at a later date, as seems advisable and at the discretion of the Research Committee.

The purpose of this report has been to outline the types of programs in progress and generally to report the status of the Project. The committee would welcome suggestions from any of the Society membership as to further types of accelerated tests which might be considered.

This report is rendered on behalf of the Project 15 Committee by its Chairman.

REFERENCE CITED

1. Plating 39, 65 (1952).