Historical Articles

September, 1954 issue of Plating

 

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Nickel Plating From the Sulfamate Bath

Presented at the Forty-First Annual Convention of the American Electroplaters’ Society,
July 13, 1954.

Richard C. Barrett, Barrett Chemical Products Company, Shelton, Connecticut.

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HISTORIC
Nickel plating from sulfamate solutions was first announced in 1938 by Piontellil and Cambri in Italy. Although Piontelli and his co-workers^{2, 3, 4, 5, 6, 7, 8, 9, 10} continued to report regularly upon their progress of plating from sulfamate solutions during the subsequent ten years, the bulk of their research was confined to the development of bath formulae for plating or electrowinning of lead.

Co-incidental with the announcement¹¹ of a commercial source of production of sulfamic acid in this country during the late 1930’s, further interest was aroused domestically and several descriptions only of laboratory interest were published by Choguill,¹² Mathers,¹³ and Forney.¹⁴ In 1940 a patent was issued to Cupery¹⁵ covering the plating of copper, nickel, and lead from sulfamate electrolytes.

During the ensuing ten years after the granting of the Cupery patent, no further published data- upon nickel plating from sulfamate baths appeared on record until 1950 when Barrett¹⁶ described a bath introduced to the electrotype industry late in 1949. As far as is known, this event marked the first reduction to practice in this country of any sulfamate plating bath for the electrodeposition of nickel upon a commercial scale.

Within the five-year period following 1949, more than 60 commercial sulfamate nickel plating baths were installed, comprising more than 50,000 gallons of solution. Such magnitude has made possible the collection of a large backlog of operating performance data, some of which are reported in this paper.

This new activity also encouraged further papers in the technical journals on sulfamate nickel plating as evidenced by the published discussions of Peters,¹⁷ Gurnham,¹⁸ and Barrett.¹⁹ Recently, Diggin²⁰ presented a paper before the Fourth International Conference on Electrodeposition and Metal Finishing at London, in which he describes a nickel sulfamate-chloride bath.

The few references in the literature to sulfamate plating baths, the meager knowledge of the properties of the relatively new sulfamic acid, and the early high cost of the acid combined with a short supply of nickel during the years of World War II and continuing thereafter discouraged active-interest in any new nickel plating process.

Because of many desirable physical properties of nickel deposits plated from sulfamate baths, particularly with reference to low internal stress and the significance of stress upon premature fatigue failure, the aircraft industry as well as others are now actively evaluating the sulfamate nickel plating bath. It is predicted that sulfamate nickel plating will eventually be as common as the familiar Watts nickel.

DESCRIPTION OF SOLUTIONS
Any description of sulfamate plating baths must of necessity start with a description of the unique properties of sulfamic acid and its salts.

Sulfamic acid is a white crystalline inorganic solid, nonhygroscopic and nonvolatile. It may be conveniently handled and stored. In strength and chemical structure it is very similar to sulfuric acid.¹¹

Sulfuric Acid, H2SO4	Sulfamic Acid, HSO3NH2

The substitution of an amino group (NH₂) for one of the hydroxyl (OH) groups of sulfuric acid undoubtedly gives to sulfamic acid many of its unique properties which are reflected in the quality of electrodeposits obtained from its metal salts in solution.

Sulfamic acid is moderately soluble in water, yielding solutions which are highly acid and compare in pH range with those of the three common mineral acids, nitric sulfuric, and hydrochloric (Fig. 1).

The metal salts of sulfamic acid are extremely soluble and in many instances are the most soluble metal salts known (Table I). Nickel sulfamate, Ni(NH₂SO₃)₂, is so soluble that it cannot be successfully re-crystallized from solution. The solubility is many times that of single nickel salts or nickel chloride. Such high solubilities make it possible to build electrolytes with exceptionally high metal content—a desirable condition for high current density operation.

Sulfamic acid is monobasic and will react with metals, metal oxides, or metal carbonates to yield the corresponding metal sulfamate by simple replacement of one hydrogen atom associated with the hydroxyl group. The most common and easiest way of preparing nickel sulfamate is by reaction of a solution of the acid with nickel carbonate:

NiCO₃ + 2NH₂SO₃H Æ Ni(H₂NSO₃)₂ + H₂O + CO₂

Sulfamic acid and its salts slowly hydrolyze in hot solutions (80° C) at low pH to form ammonium acid sulphate. Consequently the preparation of pure nickel sulfamate requires carefully controlled reaction techniques and the presence of suitable inhibitors to prevent hydrolysis. Because of the extreme lability of sulfamate salts to heat, it is virtually impossible to force crystallize or spray dry to produce a solid material which will not assay less than 98-99 percent purity. Such a degree of purity is essential to operation of a sulfamate plating bath at full capabilities.

Pure nickel sulfamate (98-99 percent) is supplied as a concentrated solution (48° Be) or as a completely purified and ready-to-operate plating bath with all addition agents present in the proper concentration. Such concentrates made under laboratory control can be stored or operated indefinitely without excessive hydrolysis. A laboratory analysis conducted upon one nickel sulfamate plating bath, which had been in constant daily operation for five years, showed less than 1 percent build up of ammonium acid sulphate.

There is strong evidence to indicate that the sulfamate ion has a tendency to complex metal ions in solution, and it is definitely known that it will form complexes with the sulphate ion,²¹ which interfere with the usual analytical procedure for sulphate by barium precipitation. In a like manner, the conventional Kjeldahl method of analysis for ammonia (ammonium ion) is interfered with by the combined nitrogen in the amide group of the sulfamate ion. Other than -conventional analytical techniques must be used therefore to determine with accuracy the degree of hydrolysis of any sulfamate solution.

Acidic sulfamate salt solutions can be buffered quite well with several of the weak acids such as boric, formic, acetic, citric, lactic, and tartaric. For purposes of nickel plating bath formulation, it is preferred to use the usual concentration of boric acid as an adequate buffer, in the operating pH range of 3.5-4.5 (electrometric).

Sulfamic acid is relatively non-toxic and non-fuming and upon brief contacts with the skin shows no noticeable effect. Sulfamate nickel plating baths are odorless and have no more noticeable effect upon producing skin irritations than do other nickel plating bath formulations of the Watts type. Sulfamic acid is not as corrosive in general to surrounding equipment as either fluoboric or hydrochloric acids.

The basic solution composition for a general purpose sulfamate nickel plating bath which will deposit nickel of medium hardness (250-350 VHN) at low internal stress-is shown in Table II.

The basic solution as given may be prepared from available concentrates of nickel sulfamate by dilution to proper concentration and subsequent purification by the usual high pH and peroxide treatment to remove iron, followed by conventional carbon treatment, filtration, and low current density electrolytic ”dummying” to remove copper, zinc, and other metallics. The wetting-agent and boric acid are then added and pH is adjusted to correct range with careful additions of sulfamic acid. The basic solution is also available as a completely mixed, purified, and ready-to-operate plating bath which constitutes a most convenient and reliable method of starting up a new bath.

The ranges of operating conditions of the basic solution are as follows:

Temperature range—100-140° F
pH range (colormetric)—3.0-5.0
Density (Baumé)—231
Anodes—99 percent plus, rolled de-polarized,
Maximum cathode current density—300 asf at 140° F, 150 asf at 100° F
Agitation—Cathode bar movement or solution circulation
Tank voltage—6-9 volts
Anode efficiency—100 percent
Cathode efficiency—98-100 percent

The average physical properties of nickel deposit from the basic solution are:

Hardness—250-350 VHN
Elongation in 2”—20-30 percent
Tensile strength—90,000 psi
Internal stress (tensile)—500 psi
Color of deposit—White
Appearance of deposit—Semi-matte to lustrous

With slight modifications of both solution composition and/or operating conditions, plus the use of recommended addition agents, the basic sulfamate nickel bath can be adjusted to meet many special requirements of deposits which physical properties demand. Hardness may be increased to 550 VHN, stress can be controlled in the compressive range, tensile strength can be increased, appearance can be semi-bright to full bright and the deposit can have high levelling characteristics for easy buffing.

The sulfamate nickel plating bath possesses pronounced characteristic advantages over other conventional nickel plating solutions, some of which are of such importance to be made the subject of expanded discussion in this paper. Advantages are tabulated as follows:

1. Stress-free deposits (compressive stress deposits easily by the use of stable addition agents).
2. High current density operation at lower tempera-tures.
3. Simplicity of bath composition, control, and maintenance.
4. Low sensitivity to impurities.
5. Nickel deposits of high chemical purity.
6. Wide latitude of operating conditions.
7. Wide range of easily reproducible physical properties of deposit.
8. Improvement to fatigue strength of underlying base metal.
9. Excellent grain structure and ductility.
10. High levelling action for easy buffing.

Control and maintenance has been reduced to a minimum in the sulfamate nickel plating bath. Because of the simplicity of the bath composition, in which the sole nickel salt comprises more than 90 percent of the dissolved solids, routine analysis need be no more complicated than the taking of a hydrometer reading. The accompanying chart (Fig. 2) indicates the relationship between specific gravity or degrees Baumé at 70° F and nickel metal concentration at specified boric acid content.

Boric acid control is not critical and it is sufficient to analyze for this constituent only at monthly intervals, using standard analytical methods for the determination of boric acid. The pH should be checked periodically, preferably daily, with any good color comparator or electric pH meter. In normal operation, pH tends to rise slowly with use and may be adjusted quickly with small additions of sulfamic acid.

The sulfamate nickel plating bath has a very low sensitivity to contamination, in many instances tolerating much higher amounts of metallic and organic impurities than other conventional nickel plating baths. Good engineering practice is to provide for solution circulation with continuous electrolytic purification at low current density either in compartmented tanks or separate cells, in lieu of which to ”dummy” periodically during shut-down time. In applications involving extra heavy deposits, continuous filtration is advised. Activated carbon should not be used as it will remove the organic wetting agent or stress reducer (SNSR). Severe cases of organic pollution can be removed by the usual activated carbon treatment along with subsequent replenishment of the addition agents removed.

Sulfamate nickel plating solutions can be used with any equipment normally used with high chloride Watts’ nickel solutions, providing however that lead be excluded from contact with the solution. Lead sulfamate is very soluble, and lead must not, therefore, be used for heating coils and thermostat control bulbs.

Anodes must be of 99 percent plus purity and rolled depolarized or electrolytic sheet and should be bagged, preferably with Vinyon type bags. Anode corrosion is 100 percent without the need for chloride-ion to promote corrosion. Although other investigators of nickel sulfamate plating solutions have advocated use of chlorides in their bath composition, it is considered highly undesirable because chlorides promote excessively stressed deposits.

STRESS AND ITS CONTROL
Many- industries in recent years have used electroplating processes as engineering tools to solve production problems rather than merely as a means to obtaining a decorative finish. A few examples are: electroforming of complicated shapes (wave guides); salvage of worn or mis-machined parts by heavy build-up of deposits; hard cladding of soft metals for abrasion resistance; manufacture of phonograph record stampers and printing plates; reproduction of surfaces such as human skin texture in prosthetics for artificial limbs and-for grain of simulated leathers; electroforming of denture models; production of finely perforated screen cloth; heavy cladding of pipe, chemical reaction vessels, and storage tanks. The literature is replete with references to such engineered applications of heavy nickel plating.

It has been common knowledge for years that in general nickel deposits have been plagued with high values of internal tensile stress which have been recorded as much as 60,000 psi from all chloride and high chloride Watts’ baths.

Many authors have discussed in detail the importance of stress effects upon the quality of electroplating and within recent years have described several instruments for accurately measuring the stress of a deposit. ^{22, 23, 24, 25, 26} Excessively high stresses can cause peeling, cracking, crazing, warping, blistering, distortion, shrinkage, and even complete destruction and failure of plated metals either as structural units or as protective coatings.

Not only do highly tensile stressed plated coatings fail within themselves, but they also induce premature fatigue failure of the underlying base metal upon which they are laid down. The aspects of fatigue failure caused by electroplating has become a major problem with the aircraft industry where premature failures cannot be tolerated at any cost. These same stresses can also lead to the phenomenon known as ”stress corrosion” which accelerates corrosion failures of many articles having decorative plate such as automobile bumpers and bumper guards.

Early in 1947 the author initiated research to discover a nickel plating bath which might produce nickel deposits low in stress without the use of certain organic addition agents. Hundreds of stress measurements were made on over 1,000 different nickel plating baths during a two-year period. The only bath which showed a pronounced decrease in stress of all those tested was the basic sulfamate nickel formula.

Plotted curves showing the relation of stress to current density are shown in accompanying graphs (Figs. 3, 4 and 5) and indicate the true stress of deposits made both from the basic sulfamate nickel bath as well as baths containing organic stress reducing agents (SNSR). The dashed line curve in Fig. 3 is replotted from data given by Diggin20 and is included for purposes of comparing sulfamate baths operating with chlorides as opposed to those without chlorides.

All stress measurements were made with a Brenner-Senderoff Spiral Contractometer, an instrument admirably suited to accurate checking upon values of stress in plated coatings and which has been thoroughly described previously.27 Because stress varies with thickness, all measurements were taken at the uniform plated thickness of 0.0006 inch as determined by ampere minutes of plating time and checked for accuracy periodically with Magne-gage readings.

Variations in temperature, pH, and nickel metal content of the bath caused corresponding variations in recorded stress values. Except for the extremes of minimum and maximum, the stress variations were insignificant or within the experimental error of measurement.

In general the effects of all of the bath variables upon stress can be summarized in the following manner:

pH—Stress has slight minimum at pH 4.0. Increases slowly at lower pH values and sharply at values above 6.0.

Metal content—No appreciable effect upon stress.

Temperature—Stress decreases with increase of bath temperature and increases with drop in temperature, usually not more than a total of plus or minus 5,000 psi for the extremes.

Chlorides—Stress rises sharply and linearly with increasing chloride content; approximately 3,000 psi for each 10 percent increase of chloride as nickel chloride.

Current density—Stress increases gradually with increase of current density.

Agitation—Agitation reduces the rate of increase of stress with increase of current density.

Boric acid—No appreciable effect upon stress within the range of 2.0-5.0 oz/gal.

Wetting agent—Acts slightly as stress reducer.

In those applications where deposits having specified stress values must be maintained under close production control, it is strongly recommended that some type of stress measuring instrument such as the spiral contractometer be used daily. The use of such an instrument for daily control purposes becomes quite simple once a specific helix has been calibrated in arbitrary units for the particular control range. It is not even necessary to strike the helix in Wood’s nickel or copper plate in those instances where it is used to measure comprehensive stress as the nickel will not exfoliate from the stainless steel.

The stress reducer (SNSR) used in the sulfamate nickel bath to produce compressive stressed deposits is completely stable over long periods of bath operation and is lost only gradually through drag-out and codeposition. There being no chemical analytical control for this material, it is necessary to control the effects of this addition agent with a stress measuring instrument.

HIGH CURRENT DENSITY OPERATION AT LOW TEMPERATURE
In certain types of electroforming operations, it is necessary to plate upon temperature sensitive materials such as wax, plastic, and low fusing point alloys, and in most cases the base material must be removed later by melting out, preferably in hot water or hot ail.

Heretofore, nickel plating bath formulae suitable for plating at room- temperatures and having reasonably good stress characteristics have been those containing ammonium salts and, because of high pH operation, have been limited to current densities usually under 15 asf.

The sulfamate nickel bath can be successfully used at maximum current densities of 60-75 asf at temperatures ranging from 80-100° F, giving approximately a fourfold or better increase in speed. Previously cited references^{16, 17, 18,19} have indicated how this higher speed at low temperatures helped immeasurably to correct production bottlenecks in the electrotyping industry.

Additionally, it is well known that hardness of nickel deposits increase with decreased bath operating temperature. Sulfamate nickel baths can be operated as hard nickel baths at 90-100° F with but a slight sacrifice in limiting current density.

IMPROVEMENT OF FATIGUE STRENGTH OF UNDERLYING BASE METAL
It has been demonstrated that plated coatings of tensile stress cause premature fatigue failures in the base metals upon the plated coating’s failure from stress cracking.^{28, 29} Since the majority of fatigue failures originate at the surface, any weakness of a surface condition can be detrimental to life under fatigue conditions.

The aircraft industry in particular is very concerned with effects of plated coatings upon reduction of fatigue strength of steel and aluminum alloys.

Unpublished data have indicated that Watts nickel plating baths giving deposits with high tensile stress can cause as much as 46 percent reduction in fatigue strength of underlying steel, whereas nickel deposited in compression causes no reduction and in some instances slight (5-7 percent) gains in fatigue strength.
Almen,29 has shown conclusively that fatigue fractures cannot originate and cracks cannot propagate in compressively stressed material and that tensile stressed surfaces as thin as 0.0003 inch can be seriously considered a threat to early failure of a part.

Sulfamate nickel plating has been tested thoroughly over a period of two years by two major aircraft engine producers and has been found acceptable for plating parts without endangering their fatigue resistance. In certain cases, heavy nickel plate under compression has been used to increase materially fatigue life by protection of surfaces from nicks, scratches, or dents which might rapidly lead to fatigue failure. Two examples of such application is protection of the leading edges of propeller blades and jet engine compressor blades from small stone abrasions with heavy cladding of hard nickel under 2,500,000 psi compressive stress.

PHYSICAL PROPERTIES
Deposits from sulfamate nickel plating baths have in general a very fine grain structure, and as a result the deposits are very smooth and ductile and have a slight sheen in appearance. The color is much whiter than any deposits from baths containing chlorides and indicates a higher purity of nickel without chlorine inclusion.

Tensile strengths range from 60,000 psi to 130,000 psi, depending upon the conditions under which a bath is operated. Correspondingly, ductility ranges from 30 percent elongation in 2 inches to a low of 6 percent elongation at a hardness of 550VHN.

Hardness can be controlled in the range of 200 VHN to 550 VHN with reproducibility by use of recommended addition agents and shifting of operating conditions. High pH and low temperature operation of the basic bath will produce the hardest deposits without appreciable stress.

A complete resume with collected data will be made the subject of a later paper upon the physical properties of sulfamate nickel deposits.

Sulfamate nickel deposited under compressive stress and with certain addition agents will have very good levelling power. Brush surface analyzer measurements have indicated a reduction in surface roughness from 120 microinches RMS to 7 microinches RMS for a deposit 0.0015 inches thick. The need to buff this smooth, relatively hard nickel coating is reduced considerably by such levelling action.

ACKNOWLEDGMENTS
In conclusion, the author wishes to acknowledge and thank the many people who have helped to contribute some of the data used in this paper: Mr. Earl Brodhag and Mr. Robert Ruddock for tensile strength, elongation, and other physical property measurements; Mr. I. Friedman of Curtiss-Wright Aeronautical for stress data; Mr. Moeller of Pratt & Whitney aircraft for fatigue measurements; and the E. I. DuPont de Nemours & Co: for use of their charts and data on sulfamic acid.

References

1. L. Cambri & R. Piontelli, Rend. reale ist. Lamb 72, 128 (1938).
2. L. Cambri & R. Piontelli, Ital. patent 268,824, (1938).
3. R. Piontelli, Chimico e industrla (Milan), 22, 65 (1940).
4. R. Piontelli, Ital. patents 381,860 (1940); 388,932 (1941).
5. R. Piontelli, Ric. Sci. Ital., 11, 246 (1940).
6. R. Piontelli, ibid. 12, 1196 (1941).
7. R. Piontelli & G. F. Patuzzi, Metallurgia Italiana, 34, 215 (1942).
8. R. Piontelli, Korr. Metallsch., 19,110 (1943).
9. R. Piontelli, 3rd International Conference on Electrodeposition, London, 1947.
10. R. Piontelli, J. Electrochem. Soc., 94, 106 (1948).
11. M. E. Cupery, Ind. Eng. Chem. 30, 320 (1938).
12. H. S. Chogtull, C. A., 34, 5351 (1940); Trans. Kansas Acad. Sci., 42, 213 (1939).
13. F. C. Mathers & R. B. Forney, Trans. Elect. Chem. Soc., 78, 420 (1940).
14. R. B. Forney & F. C. Mathers, Trans. Elect. Chem. Soc., 76, 371 (1939).
15. M. E. Cupery, U. S. Patent 2,318,592 (May 11, 1943).
16. R. C. Barrett, Electrotypers & Stereotypers Bull., 36, 55 (1950).
17. E. I. Peters, ibid., 38, 96 (1952). -
18. C. F. Gurnham, Product FinishinB, 18, 54 (1953).
19. R. C. Barrett, panel discussion, Electrotypers & Stereotypers Mag., June 1954.
20. M. B. Diggin, Fourth International Conference on Electrodeposition, London, 1954.
21. E. Divers & T. Haga, J. Chem. Soc., 69, 1634-54 (1896).
22. G. G. Stoney, Proc. Royal Soc. (London) A82, 172 (1909)-.
23. B. Martin, Proc. Amer. Ej lectroplaters Soc., p. 206 (1944).
24. W. Phillips & F. L. Clifton, Proc. Amer. Electroplaters’ Soc., 34, 97 (1947).
25. K. G. Soderberg & A. K. Graham, ibid., 74 (1947).
26. A. Brenner & S. Senderoff, J. Research Bur. Stds., 42, 89 (1949).
27. A. Brenner & S. Senderoff, Proc. Amer. Electroplaters Soc., 35, 53 (1948).
28. R. J. Love, Monograph 1403, Inst. of Metals Monograph & Report series .13, (1953).
29. J. O. Almen, Product Engineering, 22, 101 (Mar. 1951).

Discussion

MR. EDWIN R. BOWERMAN (Sylvania Electric Products, Flushing, N.- Y.): Can electroformed printing plates be prepared consistently that have a hardness of 625 Vickers plus or minus 50? If so, what modification of bath would be required?

MR. BARRETT: 625 Vickers is a little high. We can consistently hold 550 to 575 Vickers. The modifications necessary to achieve that hardness are the use of an organic addition agent that is perfectly stable and a change in the operating conditions. We generally shift to a high pH operating range and low temperature.

MR. ARMAND G. CHARRON (Texas Instruments, Inc., Dallas, Texas): In plating aluminum parts, do you put this sulfamate nickel over the aluminum or is the conventional method of plating aluminum used?

MR. BARRETT: We use the conventional method of plating, using a zincate treatment. We do know of -one particular job, preparing plates for selenium rectifiers, where laying sulfamate nickel directly on aluminum without zincate is used.

MR. CHARRON: Do you think you could also use this one-step method when either vapor blast or mechanical blast is employed?

MR. BARRETT: In the particular case mentioned, a vapor or mechanical blast is used. The interlocking surface condition helps to keep the nickel in place as well as the compressive stress of the nickel which makes it lay down as well.

MR. CHARRON: Do you feel it is sufficient?

MR. BARRETT: It is, in this particular case, but that is only a thin coating. I would not recommend it for thick coatings.

MR. A. D. SQUITERO (Hanson-Van Winkle-Munning Company, Matawan, N. J.): Was the chloride curve, shown by the dotted line, primarily on the tensile side?

MR. BARRETT: Yes.

MR. SQUITERO: Then-you feel that the additions of chloride will always produce a deposit tensile in stress?

MR. BARRETT: Very definitely.

MR. SQUITERO: Can your process continuously produce a deposit in compressive stress in the presence of chlorides?

MR. BARRETT: Only in the presence of organic addition agents. Without their presence, tensile stress increases about 3000 psi for each 10 percent increase of chloride content.

MR. SQUITERO: What are your objections to the use of chlorides?

MR. BARRETT: Chlorides raise the tensile stress of nickel deposits in direct proportion to their concentration. This is approximately 3000 psi for each 10 percent increase of chloride as nickel chloride.

MR. SIDNEY WEISMAN (Curtiss Wright Corporation, Caldwell, N. J.): You showed a slide-near the end of your lecture on the application of nickel to aluminum inducer blades. A great many requests have been made by our engineering department to use various types of coatings on aluminum and magnesium in order to reduce wear on certain parts in our propeller assemblies.

In contacting men who were influential in developing and applying the methods for plating magnesium and aluminum, recommendations were made that thick coatings of chromium or nickel should not be plated on parts used in high stress applications. You mentioned that there was an application of approximately 0.015 inch of nickel, which is a relatively thick coating. We have been reluctant to suggest the plating of thick nickel or chromium coatings on some of our aluminum or magnesium parts for the reason that we have experienced chipping and plating separation from parts subjected to operation under conditions of stress. I would like to have your opinion on this point.

MR. BARRETT: If nickel is laid down in compressive stress, a crack can neither originate nor propagate in the compressive surface. That is an established fact. To protect the sensitive surfaces of some metals like aluminum, the aircraft industry is now using fairly thick, hard nickel coatings. In fact, one aircraft company has put as much as 0.030 inch of hard nickel on the leading edge of propeller blades and have increased the life span of those blades from 100 to 400 hours.

MR. WEISMAN: Is it true that the basic preparation of the aluminum or the magnesium will represent the final adherence factor? In other words, if you have a zinc immersion method for preparing your metals, is it true that the final strength will be governed by the strength of that particular intermediate coating?

MR. BARRETT: Yes, that would definitely determine final adherence. Parts are bake tested in an oven for an hour at approximately 250° to determine adherence.

MR. WEISMAN: Have you had any experience in the use of sulfamic acid in the plating of titanium?

MR. BARRETT: No.

MR. A. ADAMS (Armalite Company, Ltd., Toronto, Ontario, Canada): Most patents now in effect on bright nickel solutions mention their use in sulfamate nickel solutions. Have you tried any of the major brighteners in your sulfamate solution? If so, how did the results compare to Watts type bright nickel solution?

MR. BARRETT: Our laboratory has developed a bright nickel sulfamate bath with compressive stress that will be announced very soon. It is more stable than a Watts type solution.

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