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MONTHLY REVIEW

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

VOL. XIV NOVEMBER, 1927 No. 11


NOVEMBER EDITORIAL
Does the plater executive who joins this society for progress of industry, in which he toils for a living, receive any benefit if his idea of joining is just to receive and not to give. Does he ever get “inculcated” with individual responsibility and learn that the medium of exchange is the oldest “success in the world”?

This being a foreman’s executive organization that has provided membership in an associate way for ex-toilers in our vineyards that they might regal in the friendships of their former years, now being beset with desires of men who have nothing to bring to progress of our society except their dues and the gimme thought, that they have discovered certain of their products are of use in this industry and could be more easily introduced though this association, can we keep interest of the pioneer who gives by just increasing our numbers, for pecuniary gain, and will this gain increase our primary ideal education or cause us to deteriorate into a social organization without ideals?

The writer feels that for society to benefit educationally, and industry to benefit progressively irregardless of numbers, we should confine our membership to men who qualify constitutionally and will give and take upon the basis of not who is right but what is right for progress in our advance in electro-deposition of metals.


SOME CONDITIONS ENCOUNTERED IN THE FINISHING OF VARIOUS TYPES OF STEEL PRODUCTS

By W. S. Barrows, Toronto Branch, Past Supreme President

In the preparation of carburized steel for plating we may encounter many conditions of steel which’ are practically unknown to those who handle soft steels only. Not only during the preparatory stages, but during and after plating do these conditions manifest themselves. ‘ Very frequently precautions which are intended to prevent defects’ or to increase the reliability of the steel article, or to beautify the finish, actually decrease the salability of the article.

For instance, a Brinell impression made on a thin carburized steel strip may prove a potential defect, or a high carbon steel article may be rendered unfit for the market by reason of prolonged acid-treatment-during final preparations for electro plating. Trueing carburized steel strips by hammering may produce checks in the steel which will defy detection until the object is polished, cleaned and plated, and platers have been accused of developing these checks by the use of some unnecessary electro-chemical treatment prior to plating, but today the true cause is quite generally known by the technical staffs and as a result the plater now sees less of this class of defect than during former years.

Manufacturers’ identification marks and all similar indentations, whether made during a hot or cold stage in manufacturing may cause cracks and the hardening stresses will reach an abnormal intensity immediately about the - indentations. These cracks-usually extend only to the depth of the thin carburized portion of the object and if an effort is made to break the strip at one of these cracks the steel may break at a point quite distant from the crack and in a perfectly sound region. This fact indicates that the steel may not be damaged by the apparent defect except- with respect to appear-ance, the tough soft interior of the steel lends strength and resistance to breaking strains.

Roughly machined steel frequently proves both expensive and troublesome. One case under my observation is of special interest. A new executive with a mania for-high-speed production was placed in charge of an automatic screw machine department. His tear-off methods were productive of unusually rough pieces which required grinding. A quantity of grinding wheels which formerly sufficed for one year’s supply for the entire plant, was entirely exhausted in two and one-half months by reason of the rough tear-off method of machining. I fail to see the economy in such proceedings. Furthermore, imperfections concealed by rough machining are exceptionally deceptive and may easily lead to failures during subsequent finishing operations or in the active life of the product. Rough machining of steel is simply nothing more or less than pushing a layer of steel before the edge of the tool until the mass of steel can move no farther without breaking, at the breaking point a small gap is formed at right angles to the direction in which the steel object has rotated past the tool. These gaps may, under certain service conditions facilitate the development of very serious cracks during heat treatment and rejections after electroplating.

Grinding is productive of defects which may easily be attributed to some other operation by the inexperienced supervisor. Grinding may soften a hardened surface or it may harden a soft surface. Grinding may actually heat the surface sufficiently to harden under the conductive cooling effect of the mass of steel, in which case small cracks develops and eventually a condition favorable to premature breakage results. A solution of nitric acid diluted to less than 1 per cent acid may be employed to reveal soft spots produced by the grinding of hard surfaces. The article is first polished and then suspended for fifteen or twenty minutes in the dilute acid. The results are very distinct and often really wonderful effects in cluster designs are revealed.

A carburized steel ball cup which was polished and which was thinner at the edge of the axle hole than at the outer circumference proved the source of much trouble by reason of cracks in the face surface of the flange. These cracks could not be detected until after plating. The ball cups were ground on a water grinder before hardening, then after hardening the cups were polished, electro-cleaned and plunged while hot directly- into a 25 per cent solution of sulphuric acid and water, rinsed, and suspended for a few minutes in a cyanide solution, then struck with copper and subsequently nickeled. Investigation proved that rapid grinding, or forcing the grinding beyond the proper cutting limit of the wheel produced very fine cracks. The plunge into the acid solution finished the damage and the nickel deposit magnified the defect to such an extent that the crack was easily detected. The remedy for this condition is obvious.

Forged steel seldom causes the plater much trouble. It is easily prepared and is one of the simplest forms of steel to electro-plate with any metal, a bath of very inferior composition will plate forged steel. But occasionally something happens with plated forged steel which is very interesting and often puzzling to the plater and plant supervisor. A large number of 25 carbon forged steel brackets which were used on a well-known motor car a few years ago were polished, copper plated for 10 minutes in a cyanide copper solution and then heavily brass plated. The brackets were scratch brushed several times during the brass-plating period. After the bracket had remained in storage for several weeks the manufacturer decide to change the shape and size of the bracket and the change necessitated making a weld. Several of the brackets were taken at random from stock and heated to welding temperature. When struck with a hammer while at welding heat the brackets actually disappeared in a shower of sparks which cooled to small sponge like masses of metal. The portion adjacent to the part struck appeared burned, lifeless and very porous. Various methods of heating were tried in an endeavor to avoid ruining the material. Finally the foreman plater was called to the forge department to view the damage and express his opinion. As it was a very simple matter to heat, bend or weld the forging before plating he might naturally be suspicious of some of the finishing treatments and of these the cyanide plating baths might easily prove most powerful.

It is well known that either iron or steel has the property of absorbing hydrogen gas, also cyanide during the electro deposition of either copper or brass from cyanide plating solutions, and especially marked is the absorption when high current densities are employed. In tempered steels this absorption often causes the steel article to break very easily when cold. In forged steels which are not hardened the effect is seldom noticed unless the metal is disturbed while in a highly heated condition and the electro-deposit of copper or brass is intact. The cyanide absorbed during deposition of these coatings and augmented by the evolved hydrogen causes a decided change in the grain structure of the metal base. It assumes a hardness not unlike Bell metal which is composed of 75 per cent copper and 25 per cent tin. This metal when heated to high temperatures and struck a blow with a hammer will fly into powder.

It was found that if the brass plated forgings were heated to a welding heat and allowed to cool slowly and were then reheated, the welding operations could be conducted with absolute freedom from trouble. Some of the brass plated brackets were placed in a cyanide solution as anodes and the brass removed electrolytically and no difficulty was experienced in working the heated metal after the brass coating was removed.

Spot welded steel has given many platers more or less trouble. It is a simple matter to electro plate spot welded steel but often quite difficult to electro plate spot welded steel so that the deposit will remain adherent during a one hour ball burnishing treatment. Sulphuric Acid has been used successfully in some cases, also hot muriatic acid, but if the spot weld is large and the metal thick, necessitating pro- longed contact of the welding copper, or strong current which produces much heat, the condition proves serious. Sulphuric acid of any concentration used at any temperature below 180 degrees Fahrenheit will not prove 100 per cent effective. Pickling followed by some form of frictional treatment is usually successful, but there are cheap lines of goods which can not be treated economically in this manner. Tumbling in water with emery, followed by a 30-second immersion in strong sulphuric acid at a temperature of 160 degrees Fahrenheit proved ineffective on a certain spot welded product which was subsequently ball burnished. Then the following method was tried and found to be 100 per cent reliable.

The spot welded parts were taken directly from the welder, placed on racks and given one minute in an electro-cleaning solution made from one of the well-known prepared compounds. Then momentarily immersed in a 25 per cent solution of sulphuric acid and water, rinsed and given a 10 second immersion in a solution composed of Nitric Acid 3 parts, Muriatic Acid 2 parts and Water 5 parts, then thoroughly rinsed in cold water, swilled in a cyanide solution (8-oz. per gallon), to remove the yellow discoloration caused by the Nitric Acid Mixture, then rinsed and passed through a 2 per cent Muriatic Acid solution to acidulate the surface of the metal, rinsed again in cold running water and placed in a-nickel bath and plated with a current density of 10 amperes per square foot for one hour. . The spot welded product which was treated as described withstood unusually long burnishing treatment and severe hammering, bending and twisting tests.

Various types of nickel solutions were used during the experimental period. A solution of Nickel Sulphate and Magnesium Sulphate gave splendid deposits, while a solution of Nickel Ammonium Sulphate, Nickel Sulphate and Ammonium Chloride produced 80 per cent failures repeatedly. Spot welded parts which were given the Nitric Acid treatment were successfully plated in any one of the various Nickel baths employed. The Nitric Acid mixture heretofore mentioned may also be employed to good advantage on wire goods which by reason of their shape, size or lack of rigidity are not easily tumbled. A strong solution or a prolonged immersion is not advisable. The volume of solution should be sufficiently large enough to permit of reasonable use without becoming heated to any appreciable extent.

Tempered steels, carburized steels and some forms of special steel alloys often present very interesting problems during the fabrication of a product which finally receives a protective or decorative finish at the hands of the electroplater and it behooves the plater to be alert as the average plant executive makes no discrimination between soft steels and high carbon steels with respect to electro-plating or the preparatory treatment.


Progress Report

THE SPOTTING-OUT OF SULFIDE FINISHES

By W. P. Barrows
(Research Associate of the American Electroplaters’ Society at the Bureau of Standards.)

I. Introduction
During the past two years the American Electroplaters’ Society has collected a research fund, based principally upon three-year subscriptions, usually of $50.00 per annum, from manufacturers and from branches of the Electroplaters’ Society. Up to date about $7,000 has been collected, of which about $2,501 was received from manufacturers of builders’ hardware for the specific purpose of studying “spotting-out.” This problem was therefore undertaken first. As funds permit, other phases of electroplating will be investigated.

The study of spotting-out was started on January 15th, 1927, by W. P. Barrows, formerly a member of the Bureau staff. Visits were made to numerous plants during February, April and August, and information and samples were obtained. Laboratory studies have been conducted upon the causes and remedies of one type of this defect. This report is a brief summary of the principal facts and conclusions thus far derived from this investigation. The facts are definite, at least for the conditions employed; but the conclusions are necessarily tentative, as new facts that may be subsequently learned in the laboratory or plant may modify these conclusions. Pending further work that is in progress, no definite recommendations are warranted.

II. Types of Spotting-out
At least two types of spotting-out may be distinguished. The first kind, which will be referred to as “crystal spots,” occurs on “oxidized,” or more strictly speaking “sulfide” finishes. These spots have a “dendritic” (tree-like) structure, that is easily recognized, especially with a lens or microscope. These form the principal subject of this report. The other type may be referred to as “stain spots,” as they consist of irregular discolored areas, that are most likely to be formed on cast metals. These will be studied later.

III. Formation of Crystal Spots
In order to obtain definite and reproducible data on the factors involved in the formation of these spots, methods of accelerating the spotting-out were first developed. In general these involved the storage of the specimens in a confined space (usually a glass desiccator) in the presence of some accelerating agent such as sulfur, rubber, or certain types of -paper. By placing in the same vessel samples that had been subjected to different treatments, and noting the time required for spots to appear, the effects of such factors as cleaning, plating, rinsing, coloring and lacquering, were determined. By-varying the atmosphere in the different desiccators, the effects of storage conditions could be compared.

The time required for the appearance of crystal spots that could be detected with the unaided eye, varied greatly in different experiments, but was roughly reproducible. Thus under the most accelerated conditions, e. g. with sulfur or rubber present, such spots were observable in from one to three days. Conditions less favorable for spotting, such as in the presence of certain papers, caused the spots to appear in from one to four weeks. Whenever it is stated that no spotting occurred, this means that no spots could be detected in periods from three to six months.

The first appearance of spots was no necessary indication that the samples then had such an unsatisfactory surface as to be objectionable commercially. The rate at which the spots increased both in size and number determined the time when they could be classed as commercially unacceptable.

The experiments thus far conducted have yielded the following facts and tentative conclusions:

(1) Crystal spots occur only on finishes that contain sulfur, such as the “oxidized” finishes on copper or brass; and the black nickel finish containing sulfur.

(2) These spots do not appear on bright or relieved parts of the copper or brass unless some sulfide is still present, e. g. if it has been incompletely relieved.

(3) Crystal spots appear only on sulfide finishes that have been lacquered. Unlacquered specimens may tarnish, but do not spot out.

(4) Sulfide finishes on surfaces plated with copper or brass, show just the same tendency to spot out as those produced directly on solid copper or brass.

(5) The composition of the base metal beneath the plated surface has no effect on the tendency to form crystal spots. (The rusting of a steel base through pores in a plated coating, represents a form of stain spots, and should not be confused with the crystal spots.)

(6) The alkaline cleaners, acid dips, plating solutions, or coloring solutions used in preparing the finish, have no necessary relation to crystal spots. These also form as readily on copper that has been “oxidized” with hydrogen sulfide, without coming in contact with any liquid except water.

(7) Powdered sulfur, and rubber such as rubber bands which contain free sulfur, when in contact with the lacquered, “oxidized” metal, markedly accelerate crystal spotting. This is a convenient method of producing such spots. Sulfur vapor accelerates the spotting, approximately in proportion to its concentration Hydrogen sulfide also accelerates the spotting but less so than does free sulphur. Sulfur dioxide does not produce spots, but causes etching and tarnishing, especially at high humidities.

(8) Some kinds of paper used for wrapping undoubtedly accelerate the spotting, but to a less degree than do sulfur or hydrogen sulfide. Experiments are in progress to determine whether the effects of such papers are due to their possible sulfur content or to physical properties such as a permeability.
(9) Variation of the humidity from zero to 90 per cent in the desiccators, had little effect upon the accelerating action of sulfur on spotting out. Further studies will be needed to fully explain the fact that more spotting out is observed in the plants in the hot, humid months.

(10) Sulfide finishes exhibit a definite, but less marked, tendency to spot out even in the absence of external sulfur or other accelerating agencies. At ordinary temperature (70 to 90 deg. F.) this tendency of the finishes to spot out of themselves is less at high humidities (90 per cent) than at moderate humidities (50 to 70 per cent).

(11) The presence of air is apparently necessary for the production of these crystal spots. Specimens in a vacuum in close contact with sulfur, showed no such spots, though the sulfur attacked the finish where the lacquer was scratched or broken. Presumably the oxygen of the air is the active constituent in causing the crystal spots. It is well known that lacquer coatings are not impervious to oxygen or other gases.

(12) If both sulfur and oxygen are necessary for the crystal spots, it is not surprising that they may form when no other external accelerating agent such as sulfur is present; as the coating contains the sulfur, and air may pass through the lacquer.

(13) Sulfide finishes with several coats of lacquer show some decreased tendency toward spotting, but the improvement is hardly sufficient to warrant the increased expense.

(14) Efforts were made to decrease the spotting-out by preparing lacquers containing such oils as bodied linseed, tung, fish and mineral oils. Lacquers containing bodied lin seed oil greatly decrease the tendency toward spotting-out, but unfortunately they increase the tendency of the finish to tarnish, especially at high humidities. Their use can not therefore be recommended.

IV. Possible Remedies
From the above facts it appears that it may be possible to prevent or at least reduce the tendency for crystal spotting, by (a) excluding sulfur from the finish itself; (b) excluding sulfur or injurious sulfur compounds from the surroundings; and (c) excluding air or oxygen from the finish. Of these, (a) would involve changes in manufacturing processes, which while possible, might involve great expense and delay. Remedy (b) may be accomplished by keeping the articles during manufacture, storage and transportation, away from sulfur, hydrogen sulfide, rubber, or other materials that may yield sulfur or volatile sulfides. Course (c) might be carried out by treating the surface so as to produce a film more impervious to air than the lacquer film. Experiments that are now in progress indicate that if even a very thin film of a grease such as petrolatum is applied to the lacquered surface the tendency to crystal spotting is decreased.

V. Future Plans
Further experiments will be conducted in the laboratory to check the above conclusions, and especially the feasibility and value of various possible remedies. Arrangements will then be made for a number of plants to try under commercial conditions the most promising procedures. It will therefore be at least a few months before definite recommendations can be made.

As soon as feasible a study of the stain spots will be undertaken.


ZINC COATING OF IRON AND STEEL

By Willard M. Scott

Presented at the American Electroplaters Convention at - Newark, N. J., June 30, 1926.

Zinc Plating
The annual loss due to corrosive influences on wrought steel and alloys of steel amounts to millions of dollars. It goes without saying that this tremendous-economic waste can be reduced considerably by employing protective coatings which prevent the action of corrosive elements and thereby prolong the useful life of the material. The importance, therefore, of employing some protective coating need hardly be stressed.

There are numerous ways to coat wrought steel or its alloys, but so far experience has shown that electroplating methods give most satisfactory protection against corrosion. This paper will deal with zinc plating, its operation, and its means of control.

Different Methods of Applying Zinc as a Protective Coating Against Corrosion
There are several methods or processes for applying zinc on wrought steel or its alloys. Among these is the “hot dip” process, which consists simply of immersing the object to be coated in a molten mass of zinc. This method in the trades is called “hot galvanizing.” In this method, the operation is a very tedious one and great care must be exercised so that injury will not result to the workmen, and that great losses may not be incurred by volatilization of the zinc. Another method of applying zinc on steel parts is by means of the sherardizing process, which consists in heating zinc dust until the zinc vaporizes and adheres to the metals or metallic parts.

Recently a method was put into practice about 12 years ago utilizing the idea of spraying molten zinc by means of a gun. This process, however, does not offer very satisfactory coatings for protection against corrosion, but does offer very useful means for covering up defects on electroplated parts which otherwise would be rejected on account of black spots created by unavoidable causes.

Electro-galvanizing unquestionably offers the best protective coating against corrosive elements. The remaining part of this discussion will deal chiefly with this latter method without burdening you with many details concerning the advantages of this process, but rather imparting some practical information about its operation and definite means of obtaining successful results.

Different Types of Solution Used in Electro-Galvanizing
There are virtually two types of solution used in zinc electroplating of ?steel parts. The so-called “acid-zinc” and the cyanide solutions are most widely used. Both solutions are extensively employed in industrial work, each having advantages and disadvantages with which the electro-plater should become acquainted.

The sulphate process is generally termed the zinc-acid solution, and is used principally for cast iron and barrel plating.. The ingredients of this solution are zinc sulphate, ammonium chloride and sodium acetate, with the addition of sulphuric acid. The zinc sulphate determines the metal concentration; the ammonium chloride assists conductivity; sodium acetate acidifies. The ammonium chloride and sulphuric acid consume the zinc from the anodes. It cannot be overstressed that the acidity of the bath should be maintained constant. Care must be exercised not to allow too much free sulphuric acid in the solution because it acts always on the anodes, whether the solution is in operation or not. This tends to accentuate the zinc content and requires more acid to adjust the higher concentration. Figuratively speaking, the sodium acetate acts as a buffer. Now if a reasonable amount of sulphuric acid is added, it combines with the sodium acetate and liberates acetic acid, and in this manner the solution can be maintained constant. It so happens that the concentration of sodium acetate can be great without harming the deposit, so there is no danger if the excess of sodium acetate is added to the solution.

Zinc Cyanide Solutions
Zinc cyanide is used for work that requires a tenacious deposit to withstand severe corrosive effects. From actual physical and chemical tests we found that this deposit will stand up better than any other coating. There are, of course, many complicated formulas for making up this type of a solution, but the very best results invariably follow from the more simple formulas. It is always wise to know the action of every ingredient that enters into a solution, and the less complicated a solution is, the easier it is for the electro plater to determine the cause of his troubles, if he experiences any, and quickly overcome them.

In the zinc cyanide work which we have done, we found that the following formula gives the best results: zinc cyanide, sodium cyanide and sodium hydroxide. The zinc cyanide in this formula determines the metal concentration. The sodium cyanide assists in conductivity, while the sodium hydroxide aids in throwing power of the solution. The last mentioned chemicals also act on the anodes, and if they are present in excessive amounts it tends to insulate the anodes and reduces the current efficiency so that the plating becomes difficult if not very troublesome. So sodium cyanide may be said to act as a replenishing agent by increasing the conductivity.

It is very important for the electro plater to be able to control the uniformity of this solution, and such electrical instruments should be provided to keep this solution constant.

If troubles are encountered on difficult parts which require plating in deep recesses and the like, it is good practice to add more sodium hydroxide which invariably will cure the trouble.

If, on the other hand, simple parts such as iron sheets of a definite known area, are plated, the sodium cyanide solution can be maintained constant by frequently measuring the amperage and voltage of the solution.

The Importance of Check Analysis and Current Control
It is the general practice that if one method of control is employed, it is not necessary to use the other, but this has its disadvantages which are too numerous to mention here. The science of electro plating has passed the rule of thumb stage. Scientific methods of control are practiced which tend to reduce the troublesome influences that the electro plater experiences. It is agreed that reasonable control can be maintained by either the chemical analysis method or by current control, but the maximum efficiency of electro deposition can be maintained only by the use of both.

Analytical Control of Cyanide Solution
It is essential in zinc cyanide plating to control the amount of free cyanide sometimes called “uncombined sodium cyanide.” It is know that zinc cyanide is insoluble in water but is soluble in sodium cyanide, but it will dissolve only a certain amount and the excess that remains over is sodium cyanide and the restrictiqn of this free cyanide to a minimum amount is very important. Zinc cyanide will also dissolve in sodium hydroxide up to a certain point. Beyond this amount an excess of sodium hydroxide will cause free caustic to be present in the solution. The electro plater must exercise great care to see that the amount of free cyanide is not too great otherwise brittle and blistery deposits will result. The exact amount of free cyanide or free caustic cannot be specified here because this is dependent on the nature of the work and the type of solution used.

If, however, an excess of free cyanide is present, and is causing brittle and blistery deposits which chip and render the coating uneven, this excess can be reduced by adding .8 ounces of zinc cyanide for one ounce of free sodium cyanide that is present in the solution. The exact amount of free sodium cyanide can of course always be determined by analysis.

In using the cyanide method of electro plating the solution should remain at room temperature and the current density should not exceed the limits of 19 to 30 amperes per square foot.

In complicated designs where plating is required to reach deep recesses, it is best to use concentrated solution to obtain the desired throwing power with a 19-ampere per sq. ft. current. It is important to bear in mind that the anode surface should never be greater than the cathode area, and anodes about 1 1/2 in. square will be found more suitable than anodes having a greater width, in a still bath.

Specification Requirements Covering Zinc Plating
Strictly speaking we do not have any definite specifications for determining the characteristics of zinc plating for iron and steel. For many years we used the salt spray method and the Preese tests for determining the uniformity and resistance of the deposit under the corrosive agents.

Recently, however, a movement has been started by the American Engineering Standards Committee and sponsored by the American Society for Testing Materials, to draw up standard specifications for zinc coatings on iron and steel. The work of this committee includes drawing up a large number of requirements covering hot galvanizing, sherardizing, electro plating, spraying and other methods of coating iron and steel with zinc. The work of this committee is not completed but is progressing rapidly and the outcome of their work will no doubt be of great value to the electroplating trade.


IS THE CATHODE LIKE AN ELECTRO-MAGNET

This paper is based on the Aatomic theory and the magnetic effect of the electrolyte on the cathode surface when an electric current is passed through the electrolyte.

Now the first question: What is an atom? Science teaches us that an atom is the smallest particle into which matter can be divided by chemical separation. It is still further explained that the atom is composed of very much smaller particles of matter called electrons which have a positive and negative charge (North and South pole).

The second question: What is the magnetic effect of the electrolyte on the cathode? The answer to this is that wherever there is a current of electricity there must also be a stream of magnetic lines of force. These lines of force always lie at right angles to the current that produces it. The current passing through the plating bath from the anode to the cathode produces this. Fundamental principles of electro chemistry teach us that a plating bath is composed of Ions which are the constituents into which the combination present in the solution, are decomposed by the electric current and carried to the cathode and anode. The Ions separated at the cathode are called cathodeions, and the Ions separated at the anode are called anodeions. The electric current passing through the electrolyte causes the positive anodeions to move to the cathode and the negative cathodeions to move to the anode.

This would indicate that there would be an endless stream of positive and negative Ions passing back and forth through the solution; thus the movement of the Ions as the theory goes would make it appear that there is an alternating current passing through the plating bath where the fact is that we use a constant direct current to electrolize the plating bath. Taking for granted that these laws and principles of electro chemistry are correct, I might say, that to the average plater the movement of the positive and negative Ions passing back and forth in a solution is not clear, hence my question, is the cathode like an electro-magnet?

In comparing the cathode with an electro-magnet, we will first define what an electro-magnet is. An electro magnet is a bar of iron or steel which has been magnetized by an electric current passing through a wire coiled about the iron, and possessing the property of attracting to itself particles of electrical conductors. Magnetism is preserved only as long as the current is flowing through its coil. This leads to the theory that the atoms, or we might say the metallic conductors in the plating bath which surrounds the cathode, have the same magnetic effect on the cathode that the coil of wire has on an iron core. The magnetism of the cathode ceases as soon as the current stops flowing.

The electro technical man: His theory that a cathode is like an electro-magnet is based on the Laws of Actions between electric currents, which is, that unlike poles attract each other, and like poles repel each other. Conductors carrying currents attract or repel each other or tend to, because of the magnetic fields or lines of force that are generated around the conductors by the action of the currents. The anode and cathode being conductors will cause the current or magnetic lines of force to flow at right angles through the plating bath which is, the same as a magnetic field, causing the anode to repel or give off, and the cathode to attract or take on the metallic contents as well as all of the other electro chemical conductors that you have in the plating bath is composed of atoms.

Each atom is of itself a minute magnet and has a North and South pole. When the solution is at rest and the current is cut off, these minute magnets lie in every which way, so that their North and South poles oppose and annul one another. As soon as you send a current through the plating lath these minute magnets will line up their field in one direction again so that their poles will attract one another. The new arrangement is due to the fact that each one of the atoms is polarized, or has acquired magnetic qualities.

In the plating bath the current enters through the anode which makes it the North pole.

The electro motive force causes the atoms that have been in a corrosive state on the surface of the anode caused by the actions of whatever corrosive agent you have in the plating bath to travel from the anode toward the South pole, the cathode, which in turn attracts the North pole of the atoms causing crystals to form, or in other words, your deposit of metal which ever it might be, the velocity with which the atoms move towards the cathode depends upon the voltage or pressure that is applied to the current. This also brings up the theory that the gas given off at the cathode is caused by the velocity with which the atoms strike the cathode combined with the electro thermal effect of the electric current on the cathode.

When an electric current passes through the cathode, it will become heated to a small extent on account of the resistance of the cathode itself. For example, if you have a large cathode in your plating bath, and you are using we will say about ten amperes to the square foot, there might be very little gas developed at the cathode, but if you replace this large cathode with a smaller one using the same amount of amperes on the smaller cathode the gas developed will be much greater unless you reduce the current. The higher the electric current used the stronger will be the thermal effect. This seems to be more pronounced in cyanide and alkali solutions. A good example of thermal effect is if you will place a pan of water on a flame you notice that when the pan begins to get warm there will be small bubbles collecting on the bottom of the pan. When the heat gets too strong, the bubbles will burst and rise to the top in the form of a gas. When too strong of an electric current is passed through the plating bath the thermal effect will cause the plating bath to heat up. This might be called hysteresis of the bath.

Hysteresis may be thought of as a lot of molecular frictions. In some plating baths it takes more electrical energy to keep the minute atoms in their magnetic lines of axis and in some plating baths it does not require so much electrical energy. Hence wherever there is power or work there will also be heat.

In concluding this paper, the writer would welcome any criticism that might be made to the theory of this paper, is the cathode like an electro-magnet, or is it not?

FRANK HORATH, St. Louis Branch, A. E. S.


 

 



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