MONTHLY REVIEW

Published by the
American Electroplaters Society
Publication and Editorial Office
3040 Diversy Ave., Chicago

VOL. XVII    JUNE, 1930    No. 6

EDITORIAL

RESEARCH—AN AID TO PROGRESS*

A proof of how important research is getting to be in discovering and perfecting new methods lies in the fact that industry, no matter what its field or scale of production can no longer do without its staff of trained experts. Competition is becoming too keen to permit the least slackening of business alertness. Such world famous organizations as the Mellon Institute of Pittsburgh, the Bureau of Standards and Bureau of Mines at Washington, devoted wholly or in part to research, need no introduction. The staffs and equipment maintained for the same purpose by the General Electric and Westinghouse Companies—to mention only two among many—represent an enormous capital investment and loom large as budgetary items. The American Gas Association in the past five years has expended a sum of not less than one hundred thousand dollars annually in this all-important field.

The usefulness of the research specialist may be gaged by his activity in the field of industrial finishing. Paints, lacquers and varnishes are extremely difficult to handle and no single detail contributes more to salability or serviceability than an attractive and durable finish; its problems, however, are manifold, and require endless and thoughtful labor.

A national research organization is in a position to render untold service to the industry it represents. The oft repeated slogan of bygone days that “research is a gamble” and “research—gold brick, or gold bond” is giving way to a brand new trend which may be aptly summed up in the words, “every plant a laboratory.”

*Industrial Gas.

NOTICE TO A. E. S. MEMBERS

If you are going to present a paper at our annual meeting in Washington, kindly boil it down to the FACTS you wish to illustrate for publishing. If necessary have two copies, one to read and one for publishing.

To all members and non-members who contemplate presenting papers to this annual meeting, notice is hereby given that in accord with our Constitution, Part I, Article X, Section 2, papers read before this Society become the property of the Society and can only be released to journals for reprinting 10 days after being published in our Review. This proviso can only be waived by full consent of the Executive Board.

It is hoped that our contributors will observe this rule and request. We fully appreciate the fact that in addressing a body, a lot of superfluities pop up in the impromptu introduction and add value to a lecture, but nothing to an article for publishing. And in past much confusion has come from desire of men reading papers, after it has received approval of A.E.S. in annual meeting, to spread through trade journals, and this is not ethical, according to our ideals.

EXPLANATION OF PLATS

Continued from J. Hay Article Published in May Issue of Review

Please change the part that reads “shows slides from 4 to 26” to read from one to six; and incorporate the new description in place of the old one.

Slide No. 1
Will illustrate the anodes as used in the tables given in the paper in regard to maintenance of the nickel solutions as in No. 1 and No. 4. Shows a nickel anode made by the Mond Nickel Company of the nickel oxide type—99+% pure. This anode was used in solution No. 1 and 2 as per table.

Slide No. 2
Slide No. 2 shows you a 99% plus type depolarized nickel anode. Note the rough structure of this anode. This anode was used in the same solution as slide No. 1 or in other words in solution No. 1 and No. 2. We did not control the boric acid in either of these two solutions.

Slide No. 3
Shows a Mond nickel anode as used in solution table No. 3, with 5 ounces nickel chloride and boric acid control. Note the big improvement in the appearance of the anode. This also is a 99+% anode as in Slide No. 1.

Slide No. 4
Shows the depolarized 99+% nickel anode the same as Slide No. 1. Note the appearance of the anode. .’I his anode has also been used in solution No. 3, as given per table on nickel solutions.

Slide No. 5
Will show you the same anode as in Slide No. 1 which was used in solution No. 4, as per table No. 4, with 11 ounces nickel chloride content and 4 ounces of boric acid.

Slide No. 6
Shows you the same nickel anode as Slide No. 2. This anode was also used in solution No. 4, with 11 ounces nickel chloride and 4 ounces boric acid.

ELECTROPLATING

By F. J. Liscomb Read at Milwaukee Branch Annual Meeting

Electroplating is an art or process whereby a thin, adherent coating of metal can be laid on the surface of another metal by electro-chemical means. That is, with the aid of certain chemicals and a proper current of electricity, a heavy piece or anode of one metal can be gradually dissolved into a solution of chemicals, and is then, by the same current, removed from the chemical bath onto the surface of a cathode. The cathode may be composed of any metal provided its solution pressure is not so great that the cathode metal will spoil the bath by precipitating metal out of the solution and then itself entering the solution.

A simple illustration will suffice to make this point clear.

Let us consider a solution of copper sulphate in water, fitted with anodes. Here we will find that if we provide a cathode of brass with a suitable current density we may deposit on it copper that will be very adherent and of a fine color and texture. However, if we provide a cathode of iron or steel, our results are very different and are far from satisfactory because the iron or steel has a greater affinity for the chemicals of the solution; that is, it has greater solution pressure. Therefore the iron will enter the solution, and, although the copper will be precipitated onto the iron in chemical proportions, the precipitate or deposit will not be adherent because the iron under the copper has been dissolved. If the action is allowed to proceed, all of the copper will be thrown out of the solution and will be replaced by iron, so that finally we will have a solution of iron sulphate instead of copper sulphate. Therefore, as our job requires that this copper deposit be done in an acid bath, because of the beautiful grained surface obtained by this method, we must resort to some process whereby we can treat the iron cathode so that the iron will not come into contact with the acid copper solution. We can overcome our difficult by plating the iron with copper in an alkali bath. This alkali bath will not affect iron as an acid copper bath will. Or, we may nickel plate the iron in a neutral bath, after which the acid copper bath may be used successfully. Zinc also exerts a similar action in both acid and alkali copper baths. Zinc likewise enters a nickel solution.

Now that we have taken up briefly the process of electroplating, we ought to know why we electroplate. There are several reasons why we plate baser metals with a more noble metal. They are as follows:

1. To prevent corrosion or rust. Some metals do this better than others; namely, cadmium and zinc.
2. To obtain uniformity of color. For example, an article may be fabricated of several different metals, such as iron, brass lead, etc., and, since there would be several different colors in the finished article, we plate all of the pieces in the article with a metal to give them a uniform color or finish.
3. To beautify a base metal; that is, to make it look like gold or silver or some other finish.
4. To aid in the local carbonizing of steel.
5. Dies and molds and printing plates.

If we disregard corrosion, beauty, and uniformity of color on a manufactured article, and consider the deposit only insofar as the usefulness of the article is concerned, then we need not plate, because a knife will cut no better after being plated, nor will an automobile pull any more freight after this process.

Probably the most extensive use for electroplating is to prevent corrosion or rust. We have learned by experience first, and later proved by science, that if one metal is coated with another there is less tendency for the base metal, steel, to rust or corrode. The question is, what metals should we plate and what metals should we deposit? If we plate steel with cadmium or zinc we prolong the life of the steel at the expense of the zinc or cadmium, as these are corroded instead of the steel, but they afford a great deal of protection because they do not corrode as rapidly as the steel. However, a thin coat of nickel on cast iron would offer little or no protection against corrosion, because, as the iron is porous, the nickel is deposited on a network of interstices, and is therefore not continuous. Thus, there is corrosion of the steel through the nickel. Furthermore, since the nickel is more positive than the iron under these conditions, nickel will actually hasten the corrosion. A light coat of copper on the iron would hasten-corrosion even more than the nickel, because copper is more positive than nickel. Cadmium is the best metal for delaying corrosion, but cadmium is not a satisfactory metal to use where a high-grade finish is desired and where beauty is the main requisite. Therefore, if we use a more electro-positive metal which because of its beauty has little or no rust proofing power, we must resort to a subterfuge and deposit several coatings of this metal, each one processed to remove nodules, etc., or buffed in an endeavor to close up any porous spots in the base metal. By this means we get a continuity of coating through which no moisture or corrosive liquids can penetrate. These several coatings, deposited one over the other, (NI. CU. NI.) must be of considerable thickness to accomplish a rust proofing job.

As cadmium gives the most continuous deposit, a thin deposit of this metal, .00025”, affords considerable protection from corrosion. To get the same protection with zinc we would have to use four times this thickness.

Before we go farther, let us consider the preparation of work to be plated.

Articles to be plated must first be free from scale, grease or other dirt. The method of cleaning varies with the material, which may be:

Hot rolled steel (Heavy scale)—will rot be more than mentioned as the treatment is usually done outside of the plating department.

Bright annealed steel.
Cold rolled steel.
Polished, cold rolled.
Cast iron.

If there is much mineral oil on the surface, it is often safer, as well as more economical, to put the article through a hot, soap-box bath to emulsify the oil and remove it. This is followed by a hot rinse. The article is next put into the electric cleaner tank. In this bath the article is made the cathode and a current of preferably 50 to 75 amperes per square foot is used. This current decomposes the water into its constituent gases; namely, oxygen at the anode and hydrogen at the cathode. There are two reasons for making the article the cathode: First, the gas given off is what is known as a reducing gas, that is, it reduce the oxide to metal; and second, there is twice as much hydrogen liberated as there is oxygen. Therefore, since the electric cleaning process is more of a mechanical action than a chemical action, it follows that with two volumes of gas there will be more mechanical action than if the article is cleaned on the anode. Furthermore, if the article is cleaned on the anode or positive pole, great care must be taken to see that the free cyanide or free caustic content is high enough, for, if it is not, the polished steel will be oxidized instead of cleaned, if sulphates and chlorides of sodium or ammonium are present. The temperature of an electric cleaner solution should be approximately 160° F. If the temperature is higher than this the work dries out before the soap and cleaner can be washed away. The rinse following a cleaner should be warm, because warm water is better qualified to remove cleaner residue than cold water.

After steel has been processed through several cleaners and rinses, the surface becomes slightly oxidized due to the action of air and water. Often this hydroxide of iron accumulates on the surface of the steel in such quantities that it becomes necessary to remove it before placing the article in the plating tank. This is best done by the use of an acid dip which is composed of muriatic acid, usually 20 to 50 per cent acid. The article should then be thoroughly and quickly rinsed at least twice and put in the plating bath without delay. Although acid will do for both steel and brass, in the event that the article is brass a strong cyanide dip is preferable to the acid dip, but cyanide does not help so much on steel.

We are now ready to plate, and, although past experience has shown that the highest state of rust proofing is to be desired, yet, due to production cost and time, it has been found advisable to adopt an arbitrary figure for both the quantity or thickness of the deposit, and the quantity of current necessary to electroplate. It is generally acknowledged that 2/10,000 of an inch in thickness of deposit gives a fair protection. It so happens that 8 to 10 amperes per square foot will give us that thickness of deposit in about 20 minutes. These are simply average figures and may be increased or diminished. In cases where the deposit must be brighter, (less nickel) less current may be used, while, with a suitable solution, much more than 10 amperes per square foot may be successfully used if a heavier deposit, which will of course be less bright, is desired. The deposit can also be increased or diminished by changing the time factor of 20 minutes.

To summarize then:

We must determine what metal is to be plated, and what metal is to be deposited.

Condition of metal to be plated:

Scale, slight scale, cold rolled, oiled, ball burnished, etc.

From their condition determine what type of cleaning is necessary:

Gasoline, soap-soak, electric cleaner, copper cleaner, acid dips, etc.
Suitable rinse tanks.

It is assumed, then, that all of the above conditions have been met, and we now have the plant ready for operation.

We know that it requires a certain current working for a given time to deposit a certain thickness of metal. Since this is so, then, all we would have to do would be to measure up the cathode surface and apply the current for a given time. The result should always be the same and correct. This might be so if the cathode surface was all in one plane. But this is rarely the case, and then too the pH of the solution, which controls the cathode efficiency at least to some extent, must be considered, as well as the contour of the articles being plated. While it is our wish to have all parts equally well plated, yet we find that there is little chance of this, as will be seen in the data contained in this slide. (No. 2 Servis) .

By this graph we can see the extent of the variance. Here are the results of three different tests: The small figure at top center will show how the weighed test pieces were placed in the tank. In between these test pieces several hundred other pieces were hung. The figures on the side are milligrams per piece. The graph lines are labeled “Top,” “Center” and “Bottom” and allude to the position on the spring. It will be seen that the deposit varies from .0100 to .0480 milligrams. Just why this is so is hard to tell unless we consider contacts, but in this slide the graphs are the results of soldered contacts. On heavy bumper bars, radiator shells, and other external parts of an auto, this sane variance exists and is no doubt the reason why some of the work breaks in the salt spray test.

C. F. Burgess showed that the active surface of an anode was the edge. The active surface of a cathode may likewise be said to be the edge; or put it this way, “the near edge,’ (nearest to the anode) and is the place where greatest action or deposit takes place. Hence it is this “near edge” that we find rough deposits, (largest nodules) pits or porous and burned deposits.

Often we find many large plating tanks connected up in multiple without tank rheostats. This would not be so bad providing the same cathode, area, solution, temperature and solution resistivity were all alike.

Slides: Show two lots of nickel solution that were worked in multiple. The metal content of one lot indicates only partial chemical control.

Slide: Shows first a piece of ordinary tin plate. Nickel has been deposited on a similar sheet from three different prepared salts. Worked in series. Note the difference in the size of the grain or nodule. The composition of the salts is not known but directions were followed. All will buff satisfactorily, although one will be better than the other two.
Some pitting slide: Pitting is due to many causes, such as high current density, wrong pH, organic matter in solution, etc. They may all be to blame, but just why a solution will pit in only one area and not throughout the rest of the tank is a mystery.

Slide: We find that only the work on the bottom row of all the racks in the tank has all sorts of imperfections. Above this lower row of pieces the whole batch is free from pitting.

Slide: Shows a roughness, going crosswise of the usual lines, due to polishing. It is thought that this roughness might be due to the adherence of metal bearing dirt to the metal surface and that a deposit of nickel covered the dirt. Several nodules also appear.

Slide: Shows the lower edge of the piece of steel from which these last two micrographs were made. You will admit that there are some pits here, yet only a few pieces in this bath were so marked. The pH If the solution was 5.8. This may have been due to the stratified condition of the solution; i. e., different pH at the bottom of the tank. In other words, the solution had not been sufficiently or frequently stirred.

Stratification of the Solution: Slide: Here we see sodium chloride in water and ammonium chloride in water, each a separate cell, with a nickel anode in each cell connected in series. I he cathode is a fine wire in a small glass tube which is open at both ends in order that it may act as a diaphragm, which allows a small current to pass without stirring the main solution. In the sodium chloride cell the anode goes into the solution momentarily, but is precipitated as nickel hydroxide by the NaOH which is liberated, but in the ammonium chloride solution the anode is dissolved. The solution dissolves the nickel and stratifies the nickel bearing solution which settles in the bottom of the cell. Seemingly the ammonium chloride is split up and the nickel and chlorine unite, the solution becoming green. The slide shows blue. The odor of the ammonia is noticeable. Eventually the nickel chloride strata rises into the zone of the ammonia. This upper strata becomes a deep blue color, showing that the metal does go into the solution and stays there, while in the sodium chloride solution the metal is precipitated. None stays in the solution. If this reaction takes place in a plating solution one can understand why, in the presence of an excess of ammonium chloride, the metal content increased and consequently there is a difference in the pH figure towards 6 or higher. We can also understand why there is much nickel hydrate found in the sludge of mechanical plating barrels in which an excess of sodium chloride, high current densities, and small anode areas prevail. There is a speed limit but we seem to be exceeding it. Further evidence that solutions do become stratified can be seen in the slide.

Slide: Here we see the result of working a brass solution with a copper anode for many hours. Note that the lower edge of the cathode has a different color than the top. The bottom has an all-copper deposit. If this solution had been frequently stirred this difference would not exist.

Slide: Shows one cause of pits or holes in a nickel plated die casting. It has been found that when a tin-bearing die casting is heated by heavy buffing the tin will ooze out. This tin will be wiped away by the buff, leaving a small pin hole which the plating will not fill up or cover. This is often called a pit and perhaps it is, but the plating solution is not to blame for it. The same kind of a hole often appears on highly polished, cold rolled steel, when it is pickled in acid that is too strong.

Slide: Shows the results obtained when a proper current density is used in depositing a metal. In metallizing the flowers and lace the current was low and the deposit smooth.

Slide: There is a contrast here. Too much current was used by the plater, who wished to do in three hours what should have taken at least twenty-four hours.

Slide: While very little is actually known about pitting, there is a suspicion in the minds of some of us who have carried on many years that the generator and the manner of using it are often to blame. The next two slides will in a measure explain this. First we see an early Weston generator which is over fifty years old, having been built in the year 1876. It is a series wound machine. Note the centrifugal mercury field shunt used to prevent a reversal of a field polarity in the event of a sudden stoppage while the plating load was on. The voltage of this machine is 3 to 5, but the amperage is still a problem.

Slide: The next slide shows a recent interpole generator of 6 volts and 10,000 ampere capacity. One does not necessarily have to draw very heavily of his imagination to believe that the early generator, at about half the voltage of the larger machine, could hardly cause much of a pit in a deposit required several hours to make, and which was only .0001” in thickness, while with a larger machine it is possible to lay on a coating of metal ten times as thick in less than one-half an hour. In fact this can be done so rapidly that if the solution is not just right the deposit quickly builds around an air or hydrogen bubble and causes at pit; or perhaps it is the nodule of metal deposited on a particle of conducting debris which causes this pit.

Slide: Shows a section of a Ni elliptic anode (90-92%). The user did not believe in cleaning anodes, and for once we were glad, for by this specimen we were able to determine the actual nickel loss in the nickel scale. It proved to be approximately 2% of the original weight of the anode or 98¢ of every $100.00 worth of nickel anodes.

Alkali Copper solutions: There are several uses for alkali copper solutions. They are used for cleaning and copper plating steel in one operation. There is also light copper plating as a finish only. Then there is the solution used in heat treatment of steel. However, the greatest use for these solutions seems to be as a base on which to deposit a heavy coat of nickel. When used for this purpose it is usually used warm. Its efficiency should be as high as possible and still yield a smooth deposit. One that need not be buffed is preferred. If a copper solution has a cathode efficiency of 50% at a temperature of approximately 110° to 125° F. we may expect to get a good copper deposit, if the current is not too high. The current density will vary with the shape of the article being plated and the distance from the anode. If the efficiency is high because of lack of free cyanide we may expect to find that the deposit (slide) may be covered with a fine powdery deposit. Under the microscope this powder may look like trees. (Slide) If, then, the copper is not buffed, but is nickel plated on top of this moss-like deposit (slide), we may expect a rough nodular deposit of nickel. (Slide) Sometimes the nodule is knocked off and then there is a mark, such as is shown in this slide, where there is a hole down to the steel.

Slide: This slide shows that other solutions act the same way, for here we see the condition in an acid zinc solution deposit where the free acid content was too low, as well as one where the acid content is more correct.

Slide: Shows four cyanide copper solutions which were used in multiple and without rheostats. The bottom lines show the ideal copper and sodium cyanide and sodium carbonate content a glance at the lines will show that the metal content has increased about five times, but the sodium cyanide is not in proportion. The sodium carbonate is several pounds per gallon too much, while the Na₂CO₃ 1OH₂O line seems to follow the other lines. Therefore we must read the right-hand scale, which is in pounds and not ounces. Two ounces should be enough, but here he has forty-eight ounces, or twenty-four times too much. With this condition of solution, under high current densities there is a tendency for some copper to be deposited loosely or in tree-like formation, which may not adhere, and, since the copper is not buffed before nickel plating, these tree-like formations may be dislodged, even after a coat of nickel has been applied, thus leaving a hole or a pit. Fancy what the salt spray test will do here!

Slide: Carbonates in Copper and Zinc Cyanide and Other Alkali Solutions: Sodium carbonate in certain alkali plating solutions has little use except where the cyanide of metals is used, and then in small amounts only. Therefore, we should never add sodium carbonate to a copper or zinc solution, except possibly when the solution is first made. The presence of large quantities of sodium carbonate seemingly does not reduce the resistance of the solution but is said to cause certain roughness of treeing. In the absence of sufficient free cyanide it may be the cause of the heavy, brick-red smut which is often made use of in rose gold and such finishes where a heavy smut is needed. However, in the automotive industries, a bright and smooth as well as a thick deposit, free from trees or nodules, is required, so that nickel may be deposited upon the copper without first buffing the copper. Carbonates accumulate in all cyanide solutions, largely through the decomposition of cyanide by heat or absorption from the air. The odor of ammonia gas arising from a cyanide solution shows that the cyanide is undergoing a change. The partial removal of these carbonates is not difficult. If a solution has a Baumé reading of 30 degrees and a low metal content, there may be as much as 2 pounds of sodium carbonate present. About 75% of this amount can be removed by lowering the temperature to the freezing point of 30 to 32 degrees Fahrenheit. If, however, the Baumé reading is less than 17 degrees there is little possibility of removing any of the carbonates, and in such a solution it is hardly necessary to do so. Hogaboom remarked on the freezing out of carbonates many years ago. He also stated comparatively recently that the carbonates could be partially removed by heat, i. e., by evaporating the solution one-third and then allowing the bath to cool to room temperature, after which the sodium carbonate will separate out in fine crystals. Then the clear solution may be drawn off and the crystals removed. If the freezing goes to zero or lower the yield will be greater, but some of the other ingredients of the bath may also fall. This shows the amount of sodium carbonate frozen out of twenty gallons of an alkali zinc solution, at a temperature of close to zero, which was then allowed to slowly warm up and drain. The 12-inch rule will give you an idea of the volume of the sodium carbonate. The weight was not taken.

Efficiency of Cyanide Copper Solution: Slide: Take two new solutions, one composed of 50 grams of copper cyanide and 85 grams of sodium cyanide per liter, and the other made up with 50 grams of copper carbonate and 100 grams of sodium cyanide and 2 copper solution which were old. All four solutions were fitted with weighed copper anodes and sheet tin cathodes and connected in series with a copper coulometer. The coulometer was kept at room temperature, while the copper solutions were heated to around 120 degrees F. and worked for one hour at an A. C. D. Of approximately 8 amperes per square foot. When the electrodes were weighed it was found that the anodes had worked at 100% efficiency, while the two new solutions and cathodes had worked at 17% efficiency for the copper cyanide with 3.3 ounces of free cyanide. The deposit blistered and was a very dark color. The copper carbonate solution cathode showed a 32% efficiency, while the two old and dense solution worked at 67% and 57% cathode efficiency, according to the quantity of free cyanide present. Of course there was more metal deposited by the old solution, but the deposit was more rough and nodular than that obtained by the new solutions. Believing that the temperature had considerable to do with the cathode efficiency, as well as the free cyanide, another run was made, but only with the two new solutions and at a temperature of 165 degrees F. instead of 120 degrees as before. To our surprise the efficiency of the copper cyanide solution jumped from 17% up to 84%, while the efficiency of the copper carbonate solution went from 32% to 96%. This latter solution gave a good red metallic color and a smoother deposit. The color from the copper cyanide solution was much improved and there were no blisters. Therefore, from these figures we learn that sometimes when a copper solution yields a blistered deposit, heating the solution to a higher degree will cause a better efficiency and a better deposit. Since it is known that high cathode efficiency and current density tend to yield a faulty, heavy deposit (loose and nodular), there seems to be no reason why a satisfactory heavy deposit cannot be obtained from the same solution if a low current density is used. Of course this will take time. You have noticed that all of the copper anodes dissolved at an efficiency of 100%, while the cathode efficiency varied from 17% to 96%. There is, then, a tendency for the metal content of the solution to increase in proportion to the difference between the anode and cathode efficiency. Where the solutions are large and are worked heavy this increase in metal content must be considered seriously, and some method must be employed to overcome this condition, other than running it into the sewer.

The Bureau of Standards: Has shown that nickel plating solutions may not contain more than 5/100 of 1% of zinc, or 3/100 of 1% of copper. Nickel salts seldom contain even this much, but frequently much zinc gets into a plating solution because the plater or helper uses galvanized pails or tubs in making the solution. When an excess of zinc does get into the solutions, frequently the deposit of nickel will be both black and white with zebra-like markings. See slide.

CADMIUM PLATING

Read at 1929 Annual Meeting (Philadelphia Branch)

MR. CLAYTON M. HOFF: Friends, I think I have disposed of one of the old idioms. I had been invited twice, but personally couldn’t accept at the time, and the old saying was that what happens twice happens three times. Well, it didn’t.

In order that we may make this talk rather brief, I want to outline to you the various points that I expect to cover.

Outline

1. Growth of Cadmium Plating.
2. Variety of Applications.
3. Composition of Plating Bath.
4. Formation and Removal of Carbonates.
5. Anode Design.
6. Computing size of Equipment—

a—Still Plating.
b—Barrell Plating.
c—Mechanical Conveyor.

7. Calculation of Costs.
8. Commercial Consideration.
9. Value of Efficiency.

1. The Growth of Cadmium Plating

In a little over one decade the use of Cadmium for rust protection in this country has grown from almost nothing to a point where considerably over one hundred thousand pounds of Cadmium are consumed monthly for this purpose.
It is estimated that over nine million square feet of surface or more than twenty million pounds of iron and steel are protected against rust by Cadmium each month.

Although Cadmium may have displaced, to a slight extent, other methods of rust protection, the increase in its use is due chiefly to the increase in the demand and a demand for increased rust protection. Due to its chemical and physical properties Cadmium has the advantage of combining rust protection with good appearance. These facts, together with the advantages of obtaining a satisfactory degree of rust protection with relatively thin deposits have been chiefly responsible for the increased use of Cadmium.

2. Variety of Applications

Cadmium always has been and is at present applied chiefly for rust protection. There has been much written and much more said both for and against Cadmium in regard to its merits as a rust protective plate. We shall summarize our conclusions as follows:

a. Cadmium provides for a given thickness of deposit, a greater - protection than does other metals used for rust protection.

b. Cadmium is especially resistant to salt water corrosion.

c. Cadmium combines rust protection with an attractive appearance and desirable color.

d. Cadmium when properly deposited is very ductile and adherent.

e. Cadmium possesses desirable electrical and physical properties.

f. There are many applications where Cadmium is more suitable, more desirable and more economical to apply than any other material.

g. The success in the use of Cadmium depends upon a correct knowledge of its properties and the limits of its method of application.

Aside from the foregoing we shall not comment in the use of Cadmium for rust protection but believe it will be of interest to note other applications of electro-deposited Cadmium.

Because it approaches in color aluminum and chromium, Cadmium is used on small parts in contact with or in proximity to these metals on automobiles, airplanes, engines, marine-craft, and utensils. Polished Cadmium is not so different from a chromium plate and the fact that small work is not successfully plated with chromium in barrel plating but quite readily plated thus with Cadmium makes it advantageous to use Cadmium in such parts.

Cadmium is used in ornamental work, as a substitute for silver, as a base for other finishes such as: Flemish Iron, Oxidized Copper, etc. In many cases in order to obtain strength and economy in construction it has been found desirable to replace copper, brass or bronze with steel or iron, protecting it with Cadmium and finishing thereafter.

Cadmium is electrically a good conductor compared to steel or iron and its use in connection with high frequency currents is a valuable one.

The low melting point of Cadmium while limiting the use of this metal in one direction proves an advantage where soldering is required, for example, in electrical and radio work.

Considerable experimental work has been done in the use of Cadmium on automobile cylinder heads, tops of pistons, etc., for the prevention of the adherence or formation of carbon. The results of our tests indicated that while Cadmium did not prevent the formation of carbon it did cause such deposits as were-formed to be quite soft and easily removable. These results although interesting, did not have any practical application for at about the same time as these tests were being completed improvements were made in engine designs and in fuels that eliminated most of the carbon formation.

This metal has long been used as a constituent of bearing metal but its use alone as an anti-friction medium was not enjoyed until tests were made by Cadmium plating the leaves of the springs used for support of automobile bodies. Some of the better cars are thus equipped at present, Cadmium acting as a lubricant or anti-friction medium, as a rust preventive and indirectly prevents squeaking and, according to the manufacturers, provides excellent riding qualities.

3. The Composition of Plating Bath

This is perhaps the most important factor to consider in connection with Cadmium Plating for it is this that determines the efficiency, stability, throwing power and electrical properties of the plating solutions, as well as the brightness, ductility, porosity, and hardness of the deposited Cadmium and the design of the Anode and to some extent the design of the plating equipment.

Some of the recent research work on this subject has been very well described by Mr. L. R. Westbrook in his paper “The Electroplating of Cadmium from Cyanide Baths” which was presented at the Fifty-fifth General Meeting of the American Electro-chemical Society, May 28, 1929.

This work consisted essentially of studying the effect of the variation of the amounts of the different ingredients composing a Cadmium plating bath, the trying out of new and different ingredients and addition agents and of different metallic brightness.

In the experimental work the baths have been judged by the character of deposit produced, the electrical properties of the solution and the behavior of the bath under conditions of continuous or intermittent operation over an extended period of time. The plates were examined for adhesion, ductility, uniformity, physical structure and appearance as a finish. Under electrical properties of the solution were included the range of cathode current densities over which bright plates could be secured, the cathode metal current efficiencies at various current densities, conductivity, comparative throwing power, and electrode polarization. Cathode metal current efficiency measurements were based on data obtained with a copper coulometer in series with the experimental bath, and a Haring cell was used to determine conductivity, comparative throwing power and electrode polarization.

For commercial operation it is desirable to have a plating bath that will function to give a satisfactory deposit with maximum uniformity and efficiency under a wide variation in operating conditions. This involves high conductivity and throwing power, with ability to produce a bright and satisfactory plate over a wide range of cathode current densities at high efficiency. Also the bath should be self-sustaining, or not subject to appreciable variations in composition due to continued use. Hence while Cadmium can be deposited from a simple solution of cadmium cyanide in excess sodium cyanide, the above requirements necessitate the presence of other constituents, as well as a proper balance of the bath composition.

The baths with which this paper is concerned may be considered to be made up of the ingredients shown in the following table, within the practical range of concentrations there indicated.

By eliminating the material whose effects were undesirable or inappreciable the following remained as essential ingredients:

Sodium cadmium cyanide NaCd (CN)₃
Sodium cyanide Na CN
Sodium hydroxide Na ON
Sodium sulfate Na₂SO₄
Metallic brightens (Ni) in small amounts.
An organic addition agent.

Confining our attention to these ingredients a study was again made of the results of varying the amount of each one without and with some variations in the others. The results were briefly as follows:

Increasing the cadmium concentration results in increasing the cathode current efficiency, conductivity, throwing power, maximum cathode current density permissible, smoothness and fineness of grain size of plate and stability of the bath under continual operation.

Increasing the free sodium cyanide constituent of the baths increases the anode current efficiency, decreases the cathode current efficiency and tends to produce smoother and brighter deposits.

An increase of sodium hydroxide results in increased cathode current efficiency, conductivity, anode polarization, brightness of deposit, especially at low current densities and ductility of deposit. It is evident that the free sodium cyanide and the sodium hydroxide act to neutralize the undesirable effects of each other while still retaining their beneficial properties.

Variations in the concentration of sodium sulfate have little effect on the electrochemical properties of a plating bath. It is used, however, because practical operation has shown the baths containing it to be more stable and operate more uniformly.

Of the metals tried for brightness only nickel, cobalt, and copper Hg proved advantageous. Of these nickel alone did not plate out with Cadmium at normal current densities and was, moreover, more effective than cobalt or copper Hg. The effect of small amounts of nickel in the bath was to produce a smoother, brighter, denser, and more ductile plate of Cadmium. It also increases the range of cathode current densities over which a satisfactory plate can be secured by raising the limiting maximum cathode current density.

An organic addition agent is necessary to secure the physical characteristics essential for rust protection and finish. Of the organic agents Tried, gulac and Turkon Oil produced the most satisfactory results and have the advantage that the amounts used can be varied over a wide range in the recommended bath without producing a noticeable change in the character of the deposit. An insufficient amount results of course in a dull or matte appearance of the plate while an excess may produce a harder and sometimes brittle deposit.

The tests for metallic brightness disclosed facts that many metals act very detrimentally, producing dark, spongy or non-adherent deposits. The metals with which we have worked can be roughly classified as follows:

Nickel, cobalt and copper Hg are beneficial, in proper amounts.

Aluminum, zinc, iron and the alkali-earth metals are ordinarily inert.

Arsenic, antimony, tin, lead and silver are detrimental, arsenic being the worst offender.

As a result of these tests, in which the effects of varying the different ingredients were recorded, chartered and studied it was possible to formulate a bath in which all the ingredients were present in their most desirable amounts. Two typical formulae for Cadmium Plating Baths are as follows:

Properties (applicable to both baths), at room temperature.

4. Formation and Removal of Carbonates

Sodium carbonate accumulates in cyanide plating baths during use from two sources: absorption of carbon-dioxide from the air and hydrolysis and oxidation of the sodium cyanide.

Fortunately sodium carbonate in itself has little effect on the electrical properties of the bath or on the character of the deposit unless present in unusually large quantities. The results in a laboratory test indicated that amounts up to ten per cent had little effect on the appearance of the plate or on the electrical properties of the bath while on commercial baths this limit appeared to be lower about six to seven per cent or about ten ounces per gallon. It is, of course, assumed that the proper proportions of sodium cyanide and sodium hydroxide are maintained.

The chief objection to the formation of sodium carbonate is the fact that proportional amounts of sodium cyanide and sodium hydroxide are in effect removed from the bath, and must be replaced to maintain a normal bath composition. If these ingredients are not replaced the result is lowered conductivity and throwing power, increased anode polarization and defective deposits.

Another objection to the presence of large amounts of carbonates is that it brings the solution nearer its saturation point so that crystallization occurs if the temperature of the bath is appreciably below normal.

The rate of carbonate formation is decreased by the use of adequate Cadmium Anode surface, avoiding the use of insoluble anodes and elevated temperatures. A rise in bath temperature should be avoided as this rapidly accelerates the hydrolysis and oxidation of sodium cyanide.

It is obvious that high anode and cathode current efficiencies reduce the formation of carbonate, that a high inductivity prevents excessive heating of the bath and that high concentration of sodium cyanide tends to decrease hydrolysis. All these factors have been taken into consideration in preparing the formula for a Cadmium plating bath. The mechanical loss of solution, with replacement, though small, tends to decrease the rate of carbonate formation. It is interesting to note the results of commercial operation. Of the hundreds of baths of the recommended composition, some of which have been in almost continuous operation for six or more years, only one has required treatment for the removal of carbonates, and this bath, due to the peculiar character of the work, was operated with insoluble anodes carrying one-half of the total current used for plating. Proper treatment for removal of the carbonate reduced it to approximately two per cent or a little more than three ounces per gallon. This plating bath had been in operation for more than three years before the carbonate content became objectionable.

Considerable experimental work has been done on removal of carbonates from Cadmium Plating Baths. Among the materials tried out are calcium cyanide, barium cyanide, calcium cyanide and lime. Calcium cyanide, theoretically the best material to use was found unsatisfactory for the reason that it could not be obtained commercially in sufficient purity. Calcium carbide is the most objectionable impurity forming acetylene. Furthermore, calcium cyanide is so readily hydrolyzed that it will liberate HCN in contact with atmospheric moisture.

Barium cyanide is very expensive and furthermore is impractical because it precipitates the sulfates along with the carbonates, in fact the sulfate is more insoluble than the carbonate. Calcium cyanide reacts very slowly with sodium carbonate in such a bath and furthermore hydrolyzes to a considerable extent liberating ammonia in objectionable quantities.

Treatment with lime was found the most suitable and economical. The results of our experiments indicated that if the plating bath containing carbonates was treated with a ten per cent excess of freshly slaked lime, agitating thoroughly for 24 hours at room temperature or for 3 to 4 hours at around 180° F. the carbonate content could be reduced to about 2 per cent or 3.2 per gallon. For the most economical recovery filtration should be employed for removing the solution from the precipitate. This lime treatment does not appreciably affect the sulfate content of the bath or the cyanide. It does, on the other hand, produce sodium hydroxide which ingredient, of course, had been reduced by carbonation.

5. Anode Design

As previously stated the bath composition is a determining factor in anode design.

If the bath is designed to have a cathode current efficiency of 96 per cent or over it is essential that the anode current efficiency be approximately the same in order that the Cadmium component of the bath remain constant. An efficiency of 96 per cent is obtained at the cathode with a current density of about 30 amp./sq. ft. and the same at the anode with a current density of about 20 amp. per sq. ft. It is obvious then that if insoluble anode surface is used, the overall anode current efficiency is decreased below that of the cathode and by continual operation more cadmium is removed from the bath than is dissolved. It is essential then that if the bath is to be self-maintaining that no insoluble anode surface be employed. This is the basic principle to be considered in the design of an anode to be used with high current efficiency baths.

An anode meeting this requirement is one in which the Cadmium metal is cast around a centrally placed rod or strap of steel which acts as a support for the anode and which in most cases permits all the Cadmium to be dissolved therefrom without scrap or loss.

It has been our experience that in still plating and in mechanical conveyors that to provide the maximum uniformity of Cadmium in the plated work, it is desirable to have the length of the anodes such that the bottom thereof is a little higher than the bottom of the work, the tops of both being just below the surface of the solution.

In mechanical barrel plating it is desirable to have the anode close to the revolving barrel and of such shape that it is approximately concentric therewith so that the Cadmium is dissolved uniformly therefrom.

6. Computations of size of Equipment

In order to intelligently determine the size or capacity of plating equipment required it is essential to know the thickness of deposit required and the approximate area to be plated.

The basis of this calculation is the time and current required to deposit a definite thickness or amount of Cadmium, which, of course, is nothing more or less than the electrochemical equivalent of Cadmium multiplied by the efficiency of the process. This can be calculated or obtained from tables already prepared.

If we assume for example that a deposit of .0003"-180 amp. is desired we find or can calculate that 30 amp. flowing for about 6 min. at about 100 per cent efficiency will deposit .216 oz. of Cadmium or on one square foot of surface a thickness of .0003". Twenty amperes for 9 min. will, of course, neglecting current efficiency do the same.

Then in a still plating tank if we allow, for example, 4 min. for loading and unloading it, and a plating time of 6 min. we have a cycle of 10 minutes or six changes or loads per hour. Then, for example, if we have 6000 sq. ft. of work to plate in a day’s time of 10 hours or 600 sq. ft. per hour, we would have for each load 100 sq. ft. the work on one load would occupy a space in the tank about 5 x 10. The character of the work will determine to some extent the dimensions of the tank, sufficient space being provided between the racks so that they do not overlap. For uniform work a tank 14 ft. long, 6 ft. deep, and 21/2 ft. wide would be sufficient to accommodate the aforementioned work.

The generator size is determined by the current that is required for plating and cleaning (if electrolytic cleaning is used). One hundred square feet of work at one load at 30 amps. per sq. ft. would require a capacity of 3000 amperes and allowing one-half of this for electrolytic cleaning a total capacity of 4500 amperes at 6 volts would be required.

For efficient solutions such as described about two amperes per gallon are allowable for continuous operations in still plating without heating of the solution. This would indicate a solution volume of 1500 gallons which checks approximately with our estimated dimensions which show: 14 x 6 x 2 1/2 = 210 cu. ft. x 7.5 = 1575 gallons completely filled or approximately 1500 gallons at a working level.

The calculations for a mechanical conveyor equipment are similar with the exception that the time allowed for loading and unloading (for example 4 min. in the foregoing case) may be eliminated or greatly decreased for the equipment may be operated at almost full capacity all the time. The generator size may therefore be decreased somewhat.

In mechanical barrel plating the same principle applies. Using our previous example assuming, however, that we have 600 sq. ft. per hour of small work instead of large pieces to plate. Assuming the same thickness of deposit which will require 180 ampere minutes per sq. ft. or 3 ampere hours per sq. ft. we have required (00 x 3 or 1800 ampere hours per hour; which if the plant is operated continuously for the required period would require a generator of 1800 ampere capacity at the voltage required by the equipment.

If we use a plating barrel operating at 300 amperes we would require six such barrels operating continuously, each barrel plating 100 sq. ft. per hour. Different equipment will accommodate different loads but in all probability such a barrel should have 50 sq. ft. per load with two loads per hour. Inasmuch as some time is lost in loading and unloading the regular practice would be to employ two additional barrels keeping in actual continual operation. 1\ plating barrel equipment accommodating 300 amperes should have from 100-150 gallons capacity for proper operation in the recommended bath.

7. Calculation of Plating Costs

For convenience the costs of Cadmium plating may be divided as follows:

Labor
Overhead
Metal Solution
Power

Some costs are calculated per price, some on units of weight or that it is difficult to provide any exact outline that will be adaptable to all, products or conditions.

There are some facts that are of interest however, though obvious, one that the labor and direct overhead in plating bear a reciprocal relation to each other. By the use of more mechanical equipment for handling purposes the overhead is increased and the labor decreased and vice versa, and the other that the ratio of surface to weight of the work plated has a special significance when we are plating with a relatively high price metal.

It is this factor which frequently determines what material can be most economically used for rust protection.

8. Commercial Consideration

We do not believe that determining the factors which constitute an efficient plating bath for Cadmium is in itself sufficient.

It is also desirable that all the ingredients be, if possible, provided in dry form to reduce shipping costs, furnished as one compound to avoid chances of mistakes in making up a plating bath, and that maintenances of the solution be simplified as much as possible.

Convenience and safety in handling the materials for the plating lath should also be given considerations.

9. Value of Efficiency

It would seem perhaps that too great an emphasis has been placed on high current efficiencies. The question might be appropriately raised, why work for high current efficiencies when electric power cost is the smallest item in plating cost.
If power costs alone were to be considered it might be amiss to emphasize current efficiencies. However, there are other and more significant factors to consider. It is not the-current that we use that counts so much as the current we lose. Every bit of current that is not used in carrying metal from the anode into the solution tends to create an oxidizing action at the surface of the anode with the result that some of the sodium cyanide of the bath is converted to carbonate. This increase in carbonate in turn tends, through increasing the resistance of the bath and the anode polarization, toward a further increase in the carbonate content, thus establishing what is termed a “vicious cycle.”

At the same time if the cathode current efficiency is not decreased the bath is depleted in cadmium content with the result that the character of the deposit suffers.

To recondition or maintain such a bath requires the frequent additions of not only sodium cyanide but cadmium in the form of a salt or compound which as we know is more costly than metallic cadmium and introduces another negative radical which tends to accumulate with undesirable results.

By employing high current efficiencies not only are economies effected in power and in chemicals but the maintenance of the solution is greatly simplified.

Interpolations to Mr. Hoff’s Paper

Page 1. (1) I say “rust protection.” I wish we could say rust proofing, but there is no such thing as absolutely rust proofing yet, so we will limit ourselves to rust protection, which is a much better experiment.

Page 8. (2) I might at this time mention the fact, or show you some photographs representing the different deposits obtained with different mixtures of the bath. Unfortunately, we haven’t a blackboard here, but we can pass these