f 1^ T 1 COMPOSITION ANO COMPARISON OF ZINC i:i^i:CTROPLATING SOLUTIONS BY JOHN ELDER FYRON THESIS FOR THK DEOREE OF BACHELOR OF SCIENCE IN CHEMICAL ENGLVEKRINO COLLEGE OF LIBERAL ARTS AND SCIENCES UNIVERSITY OF ILLINOIS 1917 UNIVERSITY OF ILLINOIS ^~^hr%..f?<^. ^..t., i9r..7 THIS IS TO CERTIFY THAT THE THESIS PREPARED UNDER MY SUPERVISION BY ^^.€r«S^ S ENTITLED A .£n:<Z:>rr.. IS APPROVED BY ME AS FULFILLING THIS PART OF THE REQUIREMENTS FOR THE DEGREE OF. ( J Instructor in Charge Approved : HEAD OF DEPARTMENT OF. tyy^-if '> c:' /-» UlUC TABLJS OF CuJilTiillirS Introduction page 1, I, CoiEinerolal zinc electro-plating solutions 1. II# Comparison of methods for zinc-plating 2. Ill, History 3. Experimental 6, I. Analysis (a) Qualitative 6, fb) Quantitative 8, fc) Table I - Results of Qualitative Analysis 7. (d) Table II - Results of Quantitative Analysis 11, (e) Table III - Distribution of Sulfates IE, (f ) Table IV - Composition of Lleaker Solution IE. II, Plating Tests 15, (a) Specifications for Commercial Plating - Table VI — 15, (b) Method of Conducting Tests 15, (e) Table VIII - Results of Plating Tests 18. (d) Discussion of Results 19, Summary Eo, References El. Digitized by the Internet Archive in 2013 http://archive.org/details/compositioncompaOOpyro - 1 INTRODUCTION There is apparently a real need for a good, effective, but oheap, zino eleotro-plat ing solution for ccmrr.eroial work, for despite the number of formulas to be found in the Journals and the number of commercial solutions on the market, there is only one which the large users of zinc-plating Solutions agree is sat- isfactory in every respect. This is the solution which was put on the market in 1905 by the Meaker Co., of Chicago. The ma- kers have not patented the formula, but have managed to keep its composition a secret, in spite of the many attempts, which have been made at various times by different users, to analyze it. Some of the advantages claimed for this solution are that it gives a good, fine-grained, well-adhering coating of zinc on iron and steel; it is neutral, efficient, and self-sustaining, all that is necessary to keep it in continuous operation being the occasional addition of sulfuric acid, and during the course of a year, the addition of ten per cent of fresh solution to the bath, (The necessity for the latter seems to be a question with the users. ) Moreover, it is claimed that it can be oper- ated successfully using as high a current density as 60 amperes per square foot of cathode surface, which is m:uch higher than can be used with other solutions. This is a great advantage, as it means that the same thickness of deposit can be obtained in fif- teen minutes with this solution as that obtained in an hour and forty-five minutes with a Solution where the current density is limited to ten amperes per square foot. The only objection to the Lieaker solution is the price. 2 It sells for Eore than other solutions, but since no other plat- ing bath will give good results, there is no difficulty in selling it. Undoubtedly a large part of tiie material in the solution has been added, not because it is necessary to insure good op- eration, but merely to prevent analysis. Accordingly, it was decided to analy25e the solution, so far as possible, and using the same electrolyte as that found by analysis to be the basis of the Meaker solution, try the effect of several addition agent* The chief use for zinc-plating is in the deposition of a thin layer of the metal on iron and steel to protect them from corrosion* Zinc has the advantage over tin for this purpose in that it is electro-positive to iron (+,493 to -.16)' so that in case a part of the iron becoires exposed and wet, zinc tends to dissolve in place of the iron. The coating of zinc may be applied to the metal either el- ect rolytically or by one of the many so called hot processes, such as dipping, sherardizing , spraying, etc. The dipping m^e- thod, or some modification of it, is probably the most generally used, but, while the zinc thus deposited is generally brighter and more pleasing in appearance than that deposited elect roly- tically, it has been shown that the latter protects the iron much more thoroughly. The excessive amount of zinc required by the hot galvaniz- ing industry in the early days led to the adoption of means for smoothing or wiping the deposit in order not only to save the 3 zlno, but also to secure a smoother and more uniform coating. This, however, is only possible v;ith sheets, wire, and a fev/ pro ducts which can be passed continuously through the bath« The wiping is held by some authorities to constitute a serious ob- jection to the hot-galvanizing process, in that it is said to de crease the lasting qualities of the coating, while if the wiping is not employed, the expense of the galvanizing is enormously in creased and some grades of product cannot be subsequently man- ufactured in suitable finished formi Moreover, the losses due to the formation of dross and skimmings also increase the cost of the process. Although the Sherardizing procesl, which consists in heat- ing the articles to be coated in zinc dust, has been widely ex- ploited in this country since its introduction in 1904, it has not come into extensive commercial service* The coating form- ed by this process is rich in iron and not altogether pleasing in appearance. Moreover, the process does not lend itself well to continuous operation, i. e. , goods cannot be cleaned and gal- vanized in continuous process. Articles which require bending after galvanizing cannot be given continuous coatings by not processes with any certainty that such coatings will adhere and withstand bending operations without cracking. Moreover, with hot processes, the thickness of the deposit cannot be regulated to any extent, while with the electrolytic method, the thickness of the deposit can be reg- ulated very exactly. Although the galvanizing process probably had its origin about 1820, it is not until 1829 that we find any miention of 4 electro-galvanizing. In that year Dr. Jno. Revere, of Jiiew York brought before the Lyoemr of Natural history, of that city, sam- ples of ziiio ooated spikes and small plates attached to wood, the v/hole having been exposed to the action of sea water since 1827. Revere was convinced that the coating of zinc formed an excellent protection for iron articles* The mention of eleotro- ohem.ical term.s in Revere's work indicates that the coating was accom.plished by electro-galvanizing methods. However, the first patents relating to this process were not issued until 1852, 5 when Wall patented a solution for "electrically depositing zinc upon iron by means of Voltaic batteries." Other early patents show that the problem: of electro-galvanizing received consider- able study. However, the extensive u.se oi electro-galvanizing in the early days was not practicable owing to the limited current av- ailable from batteries. Electro-plating reciuires the use of an electric generator supplying current of high amperage at low voltage, and it has required many years to develop this type of generator and give it a fair degree of efficiency. The poss- ibilities of electro-galvanizing have therefore been unapprec- iated until recent times* After the invention of the generator there was a revival cf interest in electro-galvanizing, as is shovm "by the numher of patent! issued and the number of form.ulas for zinc plating sol- utions that appeared in the journals. Between 1880 and 1903 there were forty-nine patents, mainly for solutions, issued in England, France, Germany and the United States. In these sol- utions, the zinc salts most generally used for the electrolyte i 5 are the sulfate and tue ohlorlde, the greatest range of dlffer- enoe being in the addition agents suggested* Of these agents for improving the quality of the deposit and 8 9 lasting qualities of the solution, colloids and glucosides seem to "be mose generally accepted as satisfactory, although in going through the journals for the last fiftenn years one finds no less than forty different suhstances, varying in composition from the sirple salts of sodium, aluminium, etc., to the most com.plex organic compounds 10 Watts and Shape seem to have heen the only ones to m.ake a system.atic study of various addition agentsi They tried out forty-two different substances , using a "bath containing twenty- five percent zinc sulfate and one gram per liter of an organic comipound* ah ircn cathode s.nd zinc anode were used, the bath being kept at 2£° C. , and current passed for two hours at a cur- rent density of 1«1 amperes per square decimeter of cathode sur- face. Of the substances tested, beta-napthol and pyrogallol gave results which coFipared miost favorably with those obtained from Meaker solution under the same conditions. 6 EXPEHIMEIITAl. I, Analysis, Qualitative. The Meaker ziiac-plating solution is a clear cclorless sol- ution* ijn standing, brov/n, spongy particles similar to tlie material deposited by iron water, separate out. The solution is very faintly acid to litniusi li A qualitative analysis^was made of the solid material obtained by evaporation of the Meaker solution, for the metals and aoids« 2. Jl liter of the-J4eaker solution was distilled, the dis- tillation being continued until the residue remaining in the flask began to char* The greater part of the distillate oame over at 100°C, , and was plain water.