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Historical Articles

November, 1953 issue of Plating

 


Question and Answer Session


Presented at the 40th Annual Convention of the American Electroplaters’ Society, June 16, 1953.

Moderator: Dr. Abner Brenner, Baltimore-Washington Branch

Panel: Authors of Educational Session papers

 

CHAIRMAN BRENNER: We are about to begin this Educational Session. I am really gratified to see the wonderful turnout, after your rather hard day of listening to papers.

I would like to introduce the experts this evening; . . . The following people were present on the platform and arose when Dr. Brenner called their names: C. Frederick Paulson, Permutit Company, New York, N. Y.; C. F. Waite, King-Seeley Corporation, Ann Arbor, Mich.; Edwin W. Hoover, Henry Brown, The Udylite Corporation, Detroit, Mich.; Ezra A. Blount, Products Finishing, Cincinnati, Ohio; Edward F. Foley, Enthone, Inc., New Haven, Conn.; P. B. Lonsbury, Walton & Lonsbury, Attleboro, Mass.; A. Korbelak, PLATING, Newark, N. J.; Martin Quaely, Westinghouse Electric Corp., Bloomfield, N. J.; R. Dow, United Chromium, Inc., Detroit, Mich.; Ralph F. Muraca, Lehigh University, Bethlehem, Pa.; Edwin C. Rinker, Sel-Rex Precious Metals, Inc., Belleville, N. J.

CHAIRMAN BRENNER: With a program of this kind, it is necessary to have some rules to give this affair the right atmosphere. There are two rules—one for the corps of experts and one for the audience. The rule for the experts is that in answering questions, they are not permitted to take more time than they did in presenting their papers. The rule for the audience is that they may not ask an expert (if he is one of their business competitors) the composition of any proprietary mixture. This is not because I don’t want you to embarrass them, but you would be wasting your breath.

A gentleman from Westinghouse had some questions about plating on stainless steel.

MR. R. C. WESTPHAL (Westinghouse Electric Corp., Atomic Power Division, Pittsburgh, la.): I am speaking as a customer of chromium plating rather than a plater. We have a critical application for the use of chromium plate as a wearing surface under various wearing conditions on unlubricated surfaces. We require material that has both corrosion resistance and wear resistance. Our problem is: how can we assure ourselves that the chromium plate from various suppliers will have adequate adherence to the base mate rial which in every case is a stainless steel?

Up to the present time we have developed a qualifying test of our own. It is, more or less, a surface wear test under the proposed operating conditions which a prospective supplier must pass in order to plate production work. About ten per cent of the prospective platers generally pass.

CHAIRMAN BRENNER: I am going to give this distinguished panel a chance to volunteer an answer to the question. If no one volunteers, I will ask someone to answer it. (After conferring with the members of the panel): We are not quite sure whether you want a test for adhesion or whether you just want to know where you can get a good job of plating done.

MR. WESTPHAL: Perhaps that is one phase of it— to be able to tell when you have good adhesion. Another problem is—how to specify the conditions and procedure of the plating to the supplier, as is usually done by our concern, which will better guarantee an effective adherent coat.

MR. KORBELAK: As a check on the adherence of the chromium, if the parts are not too large, you might try a thermal cycling test. Such a test would involve heating of the parts to a predetermined temperature with your limit set at a point consistent with the service requirements of the plated coating. Rapid cooling in a solution of dry ice and alcohol or liquid nitrogen would follow the heating operation. Safety measures in such testing should not be overlooked.

MR. LONSBURY: I would have no suggestions other than the Air Force’s specification test which is pretty much destructive and depends upon grinding and extreme bending.

For normal chromium on stainless steel, providing it is clean and not covered with scale, we find two methods suitable—either reverse current etching in sulfuric acid or the one that seems to be preferred by most is reverse current etch in chromic acid solution and then a gradual building up of the plating voltage, almost like chromium over chromium procedure. We get excellent adhesion if we use either procedure. We have done quite a bit of it, too.

CHAIRMAN BRENNER: How do you feel about these answers, Mr. Westphal?

MR. WESTPHAL: The thermal cycling test is one that would lend itself to testing of finished pieces very well; the method of plating as outlined is generally used by both successful and unsuccessful platers, I believe. From my meager knowledge of the situation, there appear to be a great many small detailed steps which must be carried out to assure a good plate and while I mention one or two, that, as far as I know, is not sufficient.

CHAIRMAN BRENNER: I think Mr. Westphal means to intimate that there are so many details that failure to observe any one of then might lead to failure

MR. MORTON SCHWARTZ (Surface Alloys Engineering Co., Los Angeles, Calif.): A rather long, involved discussion on the many aspects of this question could be developed since it involves a complicated situation. Aside from the question of the initial adhesion of the deposit, my experiences indicate that when chromium deposits are used for dry wearing applications, that is, where no lubrication is involved, the whole problem of galling enters the picture.

Thus the heat generated in the system, especially under high bearing loads, may cause the development or enlargement and coalescence of cracks which may result in the lifting of small islands of plate (which, incidentally, may have base metal still adhering to them), causing galling and severe scoring of either or both of the wearing combination.

My suggestion is that you should follow the old adage ”the proof of the pudding is in the eating” in a situation like this. The best inspection or test methods, I believe, are actual performance tests of the parts under the conditions normally employed in use. These tests may or may not be done on a statistical basis, but should be done periodically on parts selected from lots supplied by the plater. Adhesion tests on parts or samples are not sufficient to determine whether or not the parts will function properly. You could be sadly disappointed by operational failures when reliance is put in a single method or test outside of the actual environmental conditions involved.

CHAIRMAN BRENNER: Any other comment on this particular subject? I think Mr. Westphal is learning of some new difficulties and I think maybe he is sorry he brought the question up.

Would someone like to comment on a different subject? Earlier in the program yesterday there was a lot of comment on gold plating. Has the polish been worn off of that subject?

MR. WILLIAM E. TREMBLEY (Texas Instruments, Dallas, Texas): We have a particular problem of brass and copper pieces which are assembled into wave guides for electronic equipment. These particular pieces are silver soldered together. We are experiencing rejections on these pieces sometimes as high as 20 to 50 per cent.

The complexity of these parts is such that it is impossible to fabricate conforming anodes to install within the mechanism itself. Therefore, the coating must be applied to the inside of the compartments by immersion only.

Yesterday, in the discussion on gold plating, nothing was mentioned about cleaning, but we are searching for a method which may in some way alleviate our cleaning troubles and hence reduce our rejections. The main problem we encounter is the burning of the copper and copper alloys. The mixing of these combustion products with the flux used forms a complex mass which is extremely hard to remove.

Do you have anything to suggest: At present we are running the particular pieces through the cleaning cycle five to eight times and still obtaining rejections of a high percentage. We have tried these cleaning cycles as high as 15 times with the same trouble being encountered.

MR. RINKER: It is true that if you use a conventional bath you will get plating by immersion. It is also true that there are many parts of complicated shapes that require auxiliary anodes and I have seen some very remarkable auxiliary anodes. They have taken stainless steel coils and placed them in tubes made of spun glass and inserted them into the intricately shaped tubing and they do a remarkably good job.

As far as cleaning the surfaces, I am a little dubious about the use of bichromate-sulfuric acid pickle as a preliminary bright dip inasmuch as you have a silver soldered assembly. If you can get away with that bright dip and then follow that by a concentrated hydrochloric acid dip, you will have a reasonably clean surface upon which to plate and using flexible anodes you can do a good job of gold plating on the significant surfaces.

MR. TREMBLEY: The cleaning cycle which we are using at present on these pieces is (1) steel cleaner which, is non-smutting on the brass and copper; (2) hydrochloric pickle, about 50 per cent; (3) cold rinse; (4) nitric-chromic pickle (-1 per cent nitric).
We have found a sulfuric-chromic pickle to be extremely undesirable because, although it does a wonderful job on copper and brass, silver chromate films are formed. By the use of a nitric-chromic pickle, we can brighten the silver solder as well as the copper and copper alloys.

Due to the fact that the inside of the piece is completely shielded it is difficult to clean and plate.
We have found that through the use of this chromic-nitric pickle for several cycles the finish is badly etched.

Do you have any suggestion, for a cleaning process

MR. QUAELY I would make one suggestion about combining several solutions. First, use a bright dip of sulfuric-nitric-water for a few seconds; rinse; then use a dilute solution of cyanide followed by thorough rinsing in water.

MR. TREMBLEY: The difficulty with that is when you run through the cycle several times, etching is quite severe.

MR. QUAELY: Why use it six, seven times?

MR. TREMBLEY: You have not seen this piece.

MR. MODJESKA: At the Armour Research Foundation, they have made conforming anodes by use of stainless steel and glass tubing. Now, if you use high frequency superimposition on an electrolytic sulfuric pickle going up to somewhere between 50 and 70 megacycles on the superimposed current with the a.c. slightly less than your d.c., you will clean your parts in one application.

MR. TREMBLEY: How much does it cost?

MR. MODJESKA: The set-up for that type of operation is surprisingly low. Auxiliary alternating current equipment will cost possibly only a couple of hundred dollars. It is done with a very simple condenser frequency oscillator set-up.

MR. EDWIN R. BOWERMAN (Sylvania Electric Products, Inc., Flushing, N. Y.): I want to offer first a comment on wave guide plating. The general requirement is that you use a minimum of chemical procedures in cleaning them. The place to build-in the cleaning is from the very beginning of the assembly. If you protect the surfaces from any tarnishing during every single operation, you can go directly into your plating cycle with a minimum of problems. This does call for the cooperation of the manufacturing group, but it represents a standard practice in construction of wave guide equipment. It is very difficult to build wave guide equipment with good operating characteristics if the dimensions on the internal surfaces depart more than a few tenths of a mil from the specifications. Repeated pickling or bright dipping will cause trouble especially at the important joints.
I have a question . . . Several years ago Dr. Stareck made a very interesting proposal that an undercoating of silver be used under nickel in order to obtain good corrosion resistance. We tried the idea in our laboratory and obtained very satisfactory salt corrosion resistance.

Has anybody pursued this matter further and actually put it into commercial application?

DR. STARECK: A couple of years ago we did do some experimental work on combination coatings and I gave a paper on it at that time in which silver was used as a more noble metal. The theory proposed at the time was that if we could get two metals, having either a very small potential between them, or preferably the one underneath being more noble than the surface one; then we could stop corrosion of the base metal. Chromium, however, in its passive condition is very noble and it is impossible to get anything more noble. It can only be approached and silver was one of the metals that was considered for that purpose at the time.

While I still think it has possibilities, as far as I know, no one has used it commercially.

MR. WILLIAM P. INNES (MacDermid, Inc., Taterbury, Conn.): Dr. Brow, would you care to comment on the atmospheric corrosion resistance of copper plus nickel and brass plus nickel, versus all nickel on steel?

DR. BROWN: The relative corrosion protection value of these coatings with a final chromium plate still seems to be a controversial subject. The question is in general: can one substitute say one-half of the nickel thickness by an equal thickness of copper underneath the nickel. There is an excellent paper on this subject by Knapp and Wesley in PLATING (January, 1951). They report on results with panels in an industrial atmosphere. They did not, however, report on results with panels in a marine atmosphere. W. M. Phillips of General Motors Corporation follows the paper by Knapp and Wesley, with a review which is based on inspections of the chromium plated parts of automobiles in parking lots. His results are not in agreement with those of Knapp and Wesley. The chromium plate on cars is washed at least once in a while and also a certain percentage of automobiles are kept in garages over-night during late fall, winter and early spring when corrosion is proceeding at its fastest rate in an industrial atmosphere. This is taken to be the reason that the results of Knapp and Wesley, which indicate that inferior results are obtained by replacing substantial thicknesses of the nickel deposit with a copper undercoat, differ from the results obtained by this inspection of plate on automobiles.

Our results in an industrial atmosphere are similar to those of Knapp and Wesley.

CHAIRMAN BRENNER: These were all on steel?

DR. BROWN: Yes. Of course, thin nickel plate of about 0.3 to 0.5 mil with a final chromium coating on solid yellow brass panels gives quite different results than those obtained with these same thicknesses of nickel on top of copper plated or brass plated steel where the latter coatings on the steel are approximately 1 mil thick. Once the corrosion pit is through the nickel the corrosion of brass or copper proceeds preferentially, and at a faster rate than the nickel in an industrial atmosphere. When the copper or brass plate is perforated then the attack on the steel proceeds at an even faster rate and with greater undermining at the interface of copper and steel than when an equal thickness of nickel is present against the steel. However, with very thick brass or copper or a solid brass or copper panel the corrosion pit also widens and deepens in the brass or copper at the interface with the nickel plate, but at a much slower rate compared to the rate of attack of steel at the interface of copper-iron or brass-iron in an industrial atmosphere.

MR. INNES: How does it stand up in salt-spray?

DR. BROWN: In the salt-spray, unlike an industrial atmosphere, there is little difference in results from substituting say one-half of the nickel thickness by a copper or brass undercoating on steel. One interesting point about salt-spray results with chromium plated nickel coatings on steel is that a cyanide copper strike or a low pH nickel strike tends to give consistently better salt-spray results than when no strike is used. If a very short copper strike is used, for example under one-half minute, and if an acid dip is subsequently used and the transfer time after rinsing is not rapid, rusting will occur in the pores of the thin copper plate before the work is transferred to the nickel bath, which will then result in poor salt-spray results. Therefore, thorough or pressure rinsing without using an acid dip after the copper strike is better practice if the copper strike is very thin and the transfer times are appreciable.

MR. AUSTIN FLETCHER (Enthone, Inc., New Haven, Conn.): Aluminum landing gear, 5 inches in diameter, have to be chromium plated to a thickness of 0.005 inch.

The procedure after cleaning is a zincate dip followed by a chromium bath with the current on and the temperature at 70° F. The chromium bath temperature is raised in one hour from 70° to 120° F and plating continues for an additional nine hours. After plating the deposit is ground to specification. Somewhere along the line due to this temperature change, they think, or due to the grinding method, the chromium seems to separate.

Does anybody think it might be this raise in temperature or grinding operation that is causing the trouble?

MR. LONSBURY: I would very much mistrust any qualities of the starting deposit. At low temperatures chromium is not very strong—it is fragile. Elevating the temperature while plating is not harmful.

MR. SCHWARTZ (Los Angeles): Do they put the part in the chromium solution when the solution is at 70° F and commence plating; then as they continue plating, they increase the temperature of that particular bath—is that the procedure?

MR. FLETCHER: That is right.

MR. SCHWARTZ: There is a publication, I don’t know whether it is French or German, in which that type of solution is proposed as a chromium strike. The part is immersed into a chromium bath at room temperature, given a strike, and transferred to a standard chromium plating solution. The practice you described seemed to me to be impractical production since ”down-time” for cooling is involved after each load is plated. If they want to use that particular procedure, they should try using a strike solution at that temperature and then transfer to a conventional chromium bath.

CHAIRMAN BRENNER: Is this primarily a problem of adhesion?

MR. ROBERT B. GOODSELL (Enthone, Inc., New Haven, Conn.): This particular case happened to be on 72 S aluminum. The manufacturer uses a conventional 33 ounce per gallon chromium plating bath. I had loaned them a copy of Proceedings in which Dr. Brenner’s paper appeared on ”Physical Properties of Deposited Chromium”, and I must admit that they got a lot out of it, and were really interested in going into its fine points. Here is what they brought out— they got the impression that at 70° F you would get a matte, hard, more or less brittle type deposit. Am I correct there?

CHAIRMAN BRENNER: Yes.

MR. GOODSELL: The problem seems to be this, then: they have spent a lot of money to equip tanks with cooling coils and it takes time to cool them down to 70° F. They start off plating at 2 amps/sq in and maintain that current density throughout the entire time of ten hours.

What they are running into occasionally in the grinding operation are cracks. It seems like a laminated type deposit where chromium is peeling on chromium. When they grind these parts down to around 0.005, which is the finish, are they getting into this hard, brittle deposit and is that causing the cracking of the deposit? In other words, the efficiency of the bath is far greater at the lower temperatures than it is at the higher temperatures, so in the first hour, we will say, of deposit, they are getting a brittle deposit and when they grind down to this point, that is causing this flaking.

CHAIRMAN BRENNER: I don’t think that could be quite the answer. All chromium is brittle—there must be other factors involved. I am not sure that those conditions you mention were ever set forth to be good plating conditions. Would someone who has had more recent data like to answer?

MR. LONSBURY: I think that there is very possibly a mushy, fragile deposit to start with.

DR. HAROLD J. WIESNER (Bendix Aviation Corporation, South Bend, Ind.): We have been performing this same operation in our plant for the last two or three years.

CHAIRMAN BRENNER: You mean this low temperature plating?

DR. WIESNER: Yes. As a matter of fact, these people are subcontractors of ours. We have not experienced this same trouble.

CHAIRMAN BRENNER: Do you think the data in our paper on chromium plating is at fault?

DR. WIESNER: I would rather suspect that if they are getting a double plating effect that there might be something like an operator removing the part, checking it and not using sufficient care in returning the piece to the bath. At least some type of current interruption is indicated. The indications are, in all the work that we have done, that the temperature, particularly in the small baths which they use, would rise within the first hour to the correct operating conditions. In which case the plating thickness would be less than what they would be grinding off. Therefore I am sure that if they are having this flaking appearance or double plating or whatever the problem is, that it is not due to the cycle which has been described. I repeat again, we have used the method for the past two or three years and have not experienced that type of trouble.

CHAIRMAN BRENNER: I am glad to know that. Could you give us any reason why these conditions are used? I think we are all a little curious as to why you used them.

DR. WIESNER: The basic reason is to obtain maximum adhesion. If a conventional zincate dip is used, followed by plating in a warm chromium bath, the tendency is for rapid dissolution of the zincate film with a high probability of poor adhesion. This is particularly true on large pieces such as those in question, since the time required to get the pieces in the bath is great. However, if you use a cold chromium solution and start the piece in this chromium solution with the current on, you can get a sufficiently good adhesion to meet all the requirements. Our experience in general has been that this procedure is much more to be desired than that using a zincate, for example, copper strike followed by a chromium.

The adhesion results that we get by using this technique will meet all the requirements.

MR. LONSBURY: Have you tried starting the plating at the standard conditions, 120 or 133° F?

DR. WIESNER: Some work was done starting the bath at 120-130°. Adhesion results were very poor because of the fact that the zincate film dissolves very rapidly under those conditions.

MR. LONSBURY: I have not plated too much chromium directly on aluminum and certainly not .010 inch thickness of chromium. Still, I have applied 0.002 inch directly to the zincate coat with apparently good adhesion and apparently the zincate surface was not removed. We did have voltage applied before putting the pieces in the chromium bath.

DR. WIESNER: What type of adhesion test do you employ—what do you consider good adhesion?

MR. LONSBURY: Well, this unfortunately was cast material where we didn’t have the privilege of using any destructive test, and it did not have to be ground. But, there were times when we bad a lack of proper ,,wards and there was a considerable build-up of corners—probably built to 0.006 inch or 0.008 inch and we ground those off on the standard polishing wheel, which does give quite a beating to the piece. Beyond that we didn’t have ay adhesion tests.

DR. WIESNER: These pieces must be subjected to a bend test, crushing test, actually to the point where it fractures the part and still doesn’t flake. We have other parts which are small—an aluminum cylinder— in which case we simply sandblast the pieces, put them in the chromium tank. Simply sandblasting the pieces then putting them right in the tank will give fair adhesion, but on aircraft parts adhesion requirements are much more rigid.

MR. FRANK PASSAL (United Chromium, Inc., Detroit, Mich.): There is a procedure where chromium can be deposited from a bath at elevated temperature, using a cleaning procedure which involves a special zincate film. During this procedure, zincate film is dissolved so that in effect you get direct deposition of chromium on aluminum. The adhesion tests re have made have involved deposits of anywhere from 10 to 20 mils of chromium directly on aluminum. Such deposits have been subjected to alternate heating and cooling cycles and also honing.

The exact procedure in the process is subject to patent application and will be issued very shortly. If anyone is interested in the details of this procedure, especially if it involved defense work, we will be glad to give them the information on it.

DR. L. E. LANCY (Ellwood City, Pa.): I would like to make a comment to a previous question regarding the separation of chromium deposits. When starting the deposition at 70° F the full 2 amp/sq in current density could not be applied because it would be too high at such a temperature. Most likely the temperature and current is stepped up gradually. It could very possibly be that at some point the rate of current is too low for deposition to be maintained for the temperature at that particular time. Thus one can easily imagine a situation where deposition is started again, the new deposit not adhering to the previous chrome layer.

MR. LAWRENCE J. DURNEY (Enthone Inc., New Haven, Conn.): In a previous connection, we had a similar experience with deposits of this type. Deposits, however, were on steel and at normal current densities. We did nevertheless encounter the same condition described, in which a separation of the plate, apparently due to lamination, occurred in the grinding process. The thicknesses involved were much the same, 0.015 inch to 0.018 inch of chromium on the diameter, later being ground to a coating of 0.010 inch. Microscopic examination gave no indication of any lamination in the plate. Failures were traced to high contact temperatures and shear stresses set up in the grinding operations. By using a diamond wheel dressed with rather more than the usual frequency and replacing the soluble oil type lubricant with a solution of 1/2 oz/gal of sodium bicarbonate, we were able to reduce the contact temperature of the grinding operation. This, in turn, eliminated the problem of plate separation.

MR. GOODSELL: Where can we obtain information on the proper technique in grinding hard chromium?

MR. INNES: There are three factors involved here: (1) 2 amp/sq in at 70° F, particularly at sharp edges, would give you a burn and increasing the current density as the temperature goes up or plating at the same current density would cause laminations. I think that point is a possibility.

(2) We have noticed, particularly in zincate films, that when the lack of adherence is suspected, local heating is the best method of blistering the electrodeposit. If they are getting local heating due to grinding, they might expect failure of adhesion. However, (3) a good zincate film on properly cleaned metal should withstand a fairly high temperature—about 850° F. I would recommend for this job that a nickel strike be employed prior to a conventional chromium plate.

MR. JULIUS TERES (U. S. Air Force, Wright Patterson Air Force Base, Ohio): I have a question for the experts.
During the War, on certain electronic applications, ”whiskering” on cadmium as experienced. Has any one done any work on tin-cadmium or tin-zinc alloy and what experience was shown for that particular type of application?

DR. LANCY: As far as I know, ”whiskering” was never noticed with any alloys; it was always the pure metals which appeared to grow whiskers.

CHAIRMAN BRENNER: Of course, they lad not plated those alloys at that time. Someone said the Bell Telephone Company may have done some work on this.

MR. R. A. EHRHARDT (Bell Telephone Laboratories, Murray Hill, N. J.): As far as I know, practically everything will grow whiskers under ideal conditions. However, I think it is probable that the purer metals are more likely to grow whiskers than the less noble metals. Work is still in progress and no report on it can be given at this time.

CHAIRMAN BRENNER: Have you any explanation of this particular phenomena? ‘

MR. EHRHARDT: No, none that we can report.

MR. A. G. SPINDLER (Evansville Plating Works, Evansville, Ind.): Would black chromium over bright nickel or white brass produce a black finish?

MR. QUAELY: I have not tried it over polished or bright nickel surfaces. Black chromium has been tried on various types of brass and black finishes were obtained in all cases. -

MR. SPINDLER: Did you put black chromium over white nickel?

MR. QUAELY: I have not tried that.

MR. SPINDLER: Do you think it has possibilities?

MR. QUAELY: It should be all right. The only trouble we had was plating directly on aluminum and some of the high manganese alloys.

MR. W. B. STEPHENSON, JR.: (General Electric Company, Evendale, Ohio): In the plating of electroless nickel, what concentrations of the side reaction products such as phosphate or neutralized hydrochloric acid will cause the plating action to cease? Is there any regeneration process to reactivate the solution,

CHAIRMAN BRENNER: As to your first question: the reaction products are phosphites which build-up in concentration with no particular effect. For example, we have taken a new bath, added 100 g/l of sodium phosphite and found very little effect. It is possible that phosphite might increase the phosphorous content in the deposit or might slow down the rate of deposition, but there seems to be no considerable deleterious effect.

The acid concentration is rather critical because unless one keeps the pH in the best range, the deposits become poor in quality. Too, I think the rate of deposition would fall off at the higher acidities, but as I have not experimented in that range, this is conjecture.

MR. STEPHENSON: As the acid is neutralized by the addition of sodium hydroxide, will the resulting salt build-up finally stop the reaction?

CHAIRMAN BRENNER: No. Only minor effects as I have just mentioned.
If you add nickel as nickel chloride, then sodium chloride will accumulate in the bath. I don’t believe this will have much effect. In answer to one of your questions, I don’t know of a satisfactory way of eliminating the phosphite from solution economically. We have tried to do this by ordinary precipitation methods. It is possible that ion-exchange methods might serve, but the value of the materials in the solution is so small it does not seem worthwhile. There are only a few cents’ worth of chemicals in the solution, so it is really better to throw it away.

MR. RALPH D. WYSONG (Studebaker Corporation, South Bend, Ind.): Are there any data on corrosion resistance of electroless nickel?

CHAIRMAN BRENNER: The only data we have ace on salt-spray tests which we ran. We found the coatings were similar to ordinary nickel coatings in protective value.

MR. WYSONG: In your paper of 1946 you stated that the coating contains nickel phosphide, and as the solution ages there is a build up of the phosphide’. To what per cent can the phosphide be increased without a deterioration of the coating’ and does a old solution produce a coating having less resistance to corrosion?

CHAIRMAN BRENNER: I think not. The corrosion resistance of the deposit would increase as the amount of phosphorous in the coating increased, because nickel phosphide has very much more resistance to chemical attack than pure nickel. We have electrodeposited the same type of alloy from similar solutions except using phosphite instead of hypophosphite. Nickel phosphide alloy is quite resistant to chemical attack. For instance, after immersion in cold hydrochloric acid along with pure nickel deposits, the alloy will still be there long after the ordinary nickel has dissolved.

MR. WYSONG: You made a statement on the increase in chlorides and possible decrease in pH. We have been using a solution for quite some time now and once in a while we run into corrosion, red rust on the surface. It is over a chromium alloy steel. We run into most corrosion on the surface of the coating within six to eight hours after plating. Could it be that the pH is off?

CHAIRMAN BRENNER: I do not know the answer.

MR. WYSONG: The coating is 0.0003 inch to 0.()004 inch thick.

CHAIRMAN BRENNER: Unless you didn’t get adequate coverage. If the surface were not catalytic all over you might not get deposition of the electroless deposit.

MR. STEPHENSON: We have found in our work that the salt-spray resistance of electroless nickel is about equal to that of electroplated nickel, if the electroless nickel has been heat-treated. Usually we heat-treat around 500° for about an hour.

The gentleman who spoke of the blush rusting might find his trouble being in the surface condition of the metal. If it has been heat-treated and has scale on it which has not been perfectly removed, he might find that he has a different surface before plating. This might give him a different character of plate.

MR. RAYMOND F. VINES (Dentists Supply Company, York, Pa.): What are the disadvantages of very low and very high carbonate contents in gold, silver and copper cyanide baths?

MR. MODJESKA: The same objections to carbonates in base metal solutions (less noble metal solutions) apply to precious metals.

It has been found that without any carbonate present the deposit has a tendency to be more granular. That follows whether we have used a strike or whether we have gone into a bath with our work cathodic prior to its entry into solution. The apparent desirable minimum of carbonate in both gold and silver has been in the neighborhood of 15 grams per liter.

We ran test panels, as I mentioned, and when less than 10 g/l of carbonate were present in either the potassium or the sodium formulations in gold and silver baths, we did start out with a granular deposit. At 15 g/l and up to 30 and 40 g/l, we did have better smoothening. At high concentrations, say, 8, 10, 12 ounces per gallon, then we noticed an increase in polarization, a decrease in cathode efficiency, and particularly in the case of gold, a greater tendency toward sponginess.

It is only recently that heavy deposits of gold have been plated continuously. Many reports, particularly those older than the past ten years, show that; for heavy deposits of gold the article should be plated for one quarter of the time, brushed, put back in the tank, etc.

We can follow the trend from intermittent, additive plating to the present continuous plating with closer control of our plating solutions and we find when the carbonate concentration’ increases we tend toward sponginess which definitely requires smoothing and brushing. During the War, in the silver plating of bearings it was observed that high carbonates made for a more porous deposit which did not machine satisfactorily. Frequently, the operator of the tank laid the blame to lack of adequate filtration, solution insufficiently cleaned, though the trouble was traced to high concentrations of carbonate.

Back to peacetime operations: We have definitely shown in decorative silver that high carbonates will favor the tendency for that bugaboo of the plater, spotting out.

MR. QUENTIN O. SHOCKLEY (Allison Division, General Motors Corporation, Indianapolis, Ind.): In regard to this carbonate damage to silver solutions, we thought during World War II that we should treat solutions when they reached 90 to 100 g/l potassium carbonate. Since the War, due to economy measures, we have backed off somewhat from our treatment process, and with soluble anodes, we have successfully operated silver solutions with potassium carbonate as high as 250 g/l; so we are somewhat confused by this reported tendency of having a more porous plate with high carbonate content. Frankly, we cannot go that high when we use insoluble anodes, since we do experience more porous deposits. Apparently, this reported porosity is related to polarization of the ‘anode and poor corrosion of the anodes, allowing particles of silver to come off the anode, and subsequently to be deposited at the cathode. We believe this can be caused by high carbonate concentration; however, our most serious difficulties are caused by crystals of potassium carbonate precipitating when the potassium carbonate concentration rises above approximately 200 g/l.

In connection with high carbonate, I would like to comment on the proposal of using carbides to remove carbonates from silver solutions. We tested this in our laboratories and it looked promising. We then went to one of the country’s leading manufacturers of bottled: gas equipment and asked them to quote on a carbide generator in which we intended to use the silver solutions with high carbonate content in place of water, discarding the acetylene gas and the carbonate precipitate. They took the proposal under advisement and in a week or two came back saying they didn’t want anything to do with it. Their laboratory told them there was danger of a formation of silver acetylides and that they knew copper acetylides to be spontaneously explosive and that it was theoretically possible silver acetylides would do the same thing; therefore, they didn’t want anything to do with such an installation.

CHAIRMAN BRENNER: That’s the first time I ever heard of someone who did not want to sell his products.

MR. JOHN W. HOLLAND (Arvin Industries, Columbus, Ind.): Does the black chromium process as described in this morning’s session have any possibilities as a black finish on metal furniture? If so, would it be economical?

MR. QUAELY: We have not considered thus far the use of black chromium for its decorative properties although it is quite possible that it could be used for such. However, with the high current density that is used and the large size of your furniture, you would have a problem on generator capacity.

DR. E. B. SAUBESTRE (Sylvania Electric Products, Flushing, N. Y.): Mr. Modjeska gave a review this afternoon on recommended carbonate removal methods and after looking at them, I feel the majority of them are rather unsuitable for tin plating baths. Do you have any recommendations there?

MR. MODJESKA: We prepared both potassium and sodium stannate baths in our work, but unfortunately while we can show very satisfactorily quantitative precipitation of the carbonate, the tin comes out, too.

DR. ALLAN A. JANS (American Optical Company, Buffalo, N. Y.): Mr. Quaely, how large a piece have you actually turned black and how long does it take to get a good optical black finish?

MR. QUAELY: We have coated some objects such as cylindrical anodes for electron tubes, about 1 inches in diameter, about 4 inches long. A real black coating, quite thick was obtained. We plated for five minutes, which was more than enough inside of a minute it was black all over.

As for larger sections, we did some on sheet cylinders, too. We did not have occasion to plate large, odd-sized pieces. We tried something in the nature of 4 inches in diameter, by 6 inches in width, and in all cases we were able to obtain eve coatings, that is, even to the eye and jet black all over. We have not gone into any larger sizes.

MR. CHARLES LEVY (Watertown Arsenal, Watertown, Mass.): Can anyone offer information on electroplating on titanium with any metal and particularly with chromium?

MR. KORBELAK: So little work was done in our studies of adherent plated coatings on titanium that the negative results that were obtained offer little in the way of information for others to follow.

MR. FLOYD MICKELSON (Motorola Radio, Chicago, Ill.): Does anyone know of a good reliable method of passivating 416 stainless steel? We have been having trouble with our passivating, using the conventional 20 per cent to 30 per cent nitric acid. Soon after the parts are out of the bath they rust.

MR. JANS: The Army has adopted one method—they do not passivate.

CHAIRMAN BRENNER: Are you satisfied with that lack of answer?

MR. MICKELSON: That is exactly the answer I wanted.

MR. WALTER DENNEY (Belmont Casket Company, Columbus, Ohio): We do decorative plating, most of it is silver, and before the War we had times when our silver was perfect, and again it would spot out within 12 to 24 hours after a piece was lacquered. After the War I thought we got away from that when I changed the arrangement of the-tanks. I got some new hot water tanks, got a glass tank, and thought we had the best thing. Things went well for about a month and then the spotting started again. Usually the spotting happens when it starts to rain, when there is a lot of moisture in the air. A couple of years ago I put in a hot cyanide tank—that has a lot of fumes. Whether these fumes and the moisture in the air cause this spotting, I don’t know. I have tried every way and contacted quite a few people to find out what I should do. I made acid dips, -I used sulfuric acid. After we come from the silver tank, we go into the catch tanks, then into a cold water rinse and then into a sulfuric acid dip (it has about 10 per-cent sulfuric). After it is dry, it is scratch brushed and lacquered. The next day when we go to assemble it, it is spotted, so we have to do this all over.

I wonder if there is anyone here who has an answer.

CHAIRMAN BRENNER: Isn’t this rather a question for the Weather Bureau?

MR. DENNEY: We have a pretty good weatherman in Columbus, but I don’t think he could help.

CHAIRMAN BRENNER: This is spotting out under lacquer?

MR. DENNY: When I wash the lacquer from silver I have been using a 5 inch pumice stone. Usually when we run a color job, we shine it up with the same kind of brush wheel, with just plain water and never have any of that spotting. But anything that has a matte finish spots out with a brown spot. Washing the parts, then a cyanide dip removes the spotting.

MR. MODJESKA: Bureau of Standards Report, 1928, gave some data on this problem.

CHAIRMAN BRENNER I think that study showed some of the symptoms—I think it was sulfur but I don’t think it was a complete answer.

MR. MODJESKA: I think I am correct in the year— 1928, that the Bureau of Standards report referred to the spotting out problem. That problem is not limited to cast hardware; I think you will find a great, sympathetic group among the lamp manufacturers and the picture frame manufacturers.

One of the suggested treatments has been a dichromate dip. I believe the concentrations employed have been in the neighborhood of 16 oz/gal, either sodium dichromate or chromic acid with a trace of sulfuric, and that definitely has seemed to prevent the formation of black spots. But, unfortunately, we tend to get a pink film, so the follow-through on that was to go through the chromic acid, then follow it with a dilute sulfuric dip; thus far we have not had any repetition of the trouble, but I certainly would not want to offer that as a panacea. It has worked in the cases we have tried, but we are far from accepting it as the cure-all.

MR. FRED FULFORTH (Philadelphia Branch, A.E.S. Educational Sessions Chairman): Before Dr. Brenner brings this meeting to a close, I would like to thank, on behalf of the Philadelphia Branch, all the ‘members of the audience who have attended this Question Period tonight. It was questionable whether we should attempt it or not, but I am happy we did as we have a large number present—128 and 14 experts.

CHAIRMAN BRENNER: I think the experts up here certainly should be congratulated on the very skillful way in which they have answered all these questions from the audience. On the other hand, I think the audience should be commended on the very patient way they have listened to the answers.

DR. BROWN: On the last problem, I think it might be worthwhile to try this experiment and check the results by comparison tests in a humidity cabinet or even in a salt-spray. It is an old idea. Use about 34 oz/gal of chromic acid or bichromate in the final hot water rinse before drying and lacquering the clean buffed or satin-finished brass, silver or copper surfaces. Bichromate or chromic acid dips even when giving invisible films tend to retard white corrosion of zinc and to slow-up the tarnishing of silver, brass and copper from sulfide and ammonia fumes. The chromate film also improves the adhesion of the lacquer.



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