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CHEMICAL ENGINEERING REVIEWS
Tin and Its Alloys
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T I S >became of its \\-idc use in all fields of industr). continues to attracr the attention of both research svorkers and engineering tec.hnicirns. A ivealth of scientific researches, improvements in processes. and uses relating to tin have been reported in the last 12 months. This revie\\, hoi\.cver, is limited to a n evaluation and interpretation of the major developments. Availability of Tin Little change in the supply picture occurred in 1955 \\-ith the current \\-orld surplus over consumption in the order of 16>000long tons (7.4). There is a steadily rising trend of consumption, but \virh the cessation of United States stockpiling, adequate supplics of tin arc assured for all industrial needs both present and future.
Research Sponsored by Tin Producers T h e International Tin Research Council, financed by the major tin producers of the i\-orld, continues to expand its technical service organizations throughout the world and to vigorous1)- conduct a research program on the technology of tin. T h e annual report of the Council (3B) lists 55 original research papers, booklets or technical articles published by the T i n Research Institute and its associated staffs in 1955. The researches a n d developments of special interest are summarized belolv : A means of assessing the resistance of tinplate to rusting \\.hen exposed to a controlled moist sulfur dioxide atmosphere l r a s developed ( 2 B ) . Repeated ivashing of tinned steel ivith alkaline solutions sho5vs that deterioration in the protective quality of the tin coating results more from enlargement of pores during exposure to the iveather than from dissolution of the tin. Silicate solutions restrain this action ( I B ) . .4preliminary fluxing treatment called
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the '.ciirect c liloride inethod" f t ~ r r i i i ning c a a t iron \\.llicli facilitates the linin? of cast iron bearing shells \vas developed ( 7 B ) . Successful bonding of aluminumtin bearing a!lnys. containing 3rh copp'r and 20c; tin. to steel and their satisfactory s e n i c e in rolling mills and rrolle\. car applications \\-ere obtained (6U 1 , Investigation of the tin-rich end oi die tin-indium equilibrium diagram S ~ O \ V S that rhc soll.ihility of indium in tin is greater than previous investigators have reported. The tin-thallium equilibrium diagram \ v a s found IO be in error; the solid soluhiliry of thallium in rin ma\reach 0.97,a t the eutcctic teinperaturz-a n iniporiniit finding since thallium -:'1 tards the transformation of lvliitc to gr,iy tin ( 3 B ) . Simple proced~iresfor nianufdcturin? chill-cast tin-bronze containing over -'; tin \yere published. Causes of Linsoundness and means of overcoinin: them ark. described ( 9 B ) . Revised methods lor the determination of the thickness of [ i n coatings b!. chemical: \-oluinetric. and coulometric procedures have also Iieen published (70~9).T h e properties. uccurrence. rninin?. smelting. rcfining. and uses for tin and [in allo!-s appear in a n upto-date revie\\- o n tile sullject (.5B). Tlic s!-nhesis nf 60 ne\\- orTanotii1 compounds \vir11 amifungal and biocida! properties is reported (JB). Dioci!.ltin
INDUSTRIAL AND ENGINEERING CHEMISTRY
~ , n y x ) i i n c l s w x k ~ x i dt o t x cKecti\.e stabilizers for poly(vin>-l chloride) plastic; and may also be quite nontoxic (GU). Tiit. use of organotin compounds for the rxatnicnt of rt,arhle fly in cattle and for t h e treatment of \vorms in poultry is increasing (.3B). Ion exchange resins provided a means of measuring the solubility of organotin compounds in seaivarer and for the determiliation of Io\c concentrations of tin l(1 [',I3.'".) (3U). Foundry studies have been conducted leadins to ne\v hear-treatable pe\cter alloys \vith properties that are attractive to manufacturers of peivter\vare (SB). \Vith this material available, modern nontarnishing pe\vter has come into the picture in cver-increasing proportions. (
Modern Nontarnishing Pewter l l o d e r n peivtcr is a tin-base alloy containing approsimately CYGantimony and 1 . j C ; copper. T h e alloying elements are added to increase the hardness and rnec hanical strength T h e nontarnishiriq p ~ ~ ~ p e r tare i e s assured by the complete elimination of lead from the alloy composition. PeLvrer alloys lvith still greater hardness and suitable for rolling and spinning. result from the addition of 2 L ; bismuth or O.lyc silver to the normal ailoy composition ( S B j . . i l l the
R. M. MACINTOSH Tin Research Institute, Inc., Columbus I , Ohio ROBERT A4. MaclNTOSH, Chief Chemical Engineer for the Tin Research Institute, prepared the annual tin review this yeor. Maclntosh i s a graduate o f the Royal Technical College, Glas.;ow, Scotland ( 1 925), and Brooklyn Polylechnic Institute (B.S. in chemistry, 1936). From 1 9 2 6 to 1941 he was Chief Chemist with the Guggenheim Research Laboratories in New York and from 1 9 4 1 to 1949, assistant supervisor in the Analytical and Nonferrous Divisions a t Battelle Memotiol Inslitute. He has been a consultant with the Tin Research Institute, Inc., since 1949; Maclntosh i s a long time member of the American Chemical Society.
TIN AND ITS ALLOYS alloys listed in the report have been adopted for commercial use. A collection of modern nontarnishing pewter articles obtained from manufacturers all over the world was assembled by the Institute for exhibition in the Jvorld's principal cities. T h e "Pewter of Today" exhibit consists of over 1000 pieces and has been vieired by several thousand visitors in London, Slunich, Dusseldorf, T h e Hague, Brussels, and Paris (2C-5C, 7 C ) . This exhibit (rill be shown to the public in the principal cities of the United States during the period of August 1956 to March 1957 (2C)' \Vorking Xvith a soft, pliable metal s u c h as pewter, hard when cast but ductile for hammering, is a satisfying hobby for young and old. Instructions for modeling in pewter sheet have appeared in the literature ( 6 C ) . T h e simple instructions include raising and stretching the sheet. staining and mounting the speciiriens without the use of expensive tools. T h e casting of handles in metal and rubber molds and soldering the casrings to shaped pieces have been adequatc.Iy covered (7C).
ne\\. techniques has been patented ( 7 3 0 , 7 5 0 ) . T h e diffusion of silver into sheet copper during soldering is affected by temperature, time? and by the flux used ( 7 0 ) .
Solders and Fluxes Some ~ v o r khas been done on solders for heat-rcsisrant applications. Solder compositions. methods of using them, and the resulting strength of tlie joints are given ( ? E ) . Binary and ternary alloys of cadmium. zinc, lead \\-it11 tin, and the influence of copper and silver additions to these alloys has been investigated for special and demanding applications i i E ) .
New flux compositions continue to zippear in the literature. A flux based 011 aluminum chloride, zinc chloride, and sodium chloride is recommended for aluminum ( S E ) . Aluminum chloride is also favored as the activator in mixtures of rosin, glycerol monochlorhydrin, and diethylene gl>,colfor tlie soft soldeiing of heav)- metals ( 3 E ) . The hydrochlorides of aryl biguanides mixed \rith rosin, \vaxes or high-boiling organic liquids have good fluxing action and may be used on electrical assemblies \\-ithour removal of the flus residue ( 7 E j . .\ solid flus composition \\-liich may be cast in molds contains rrichloronaphthalene ( 4 0 5 ) . rosin ( 2 j r ; ) , vaseline (20yc)! and lithium chloride (1 !yc) ( / E ) . Fluxes
Soldering Techniques hIany innovations and advances have been made in soldering practices. Tough soldering jobs on ceramics, titanium. stainless steel, and aluminum have been made easy by using a n abrasive \\.heel loaded kvith solder and operated a t variable speed to coat the metals \vithout a flux (5D.720). T h e critical factors, from a rnetallurgical viewpoint, for successful soldering ( 3 0 ) and eight different techniques to improve soldered assemblies are garnered from industrial experiences ( 7 7 0 ) . Joint strength and joint quality have received considerable attention (0-0,SD, JJD, 2 7 0 ) . Soldering by resistance heating is favored over conduction for three reasons-f,r example. improved joint qualit), increased operator safety, and loirer costs ( 9 0 ) . T h e soldering of printed circuits and a mechanism for automatic dipping of printed circuit assemblies is illustrated ( 7 0 , 3D! 2 2 0 ) . T h e prevention of soldering troubles in making electrical circuits has been covered ( 7 6 0 ) . An automatic soldering machine, so designed to leave the operator's hands free: has appeared on the market ( 7 0 0 ) . T h e joining of difficult-to-solder metals such as stainless steel ( 7 9 0 ) :aluminum ( 7 8 0 , 250),and titanium ( 2 0 ) has been simplified. Soldering outdoors requires special equipment and techniques and these have been covered ( 2 0 0 ) . Induction soldering should not be overlooked if high-speed production is needed ( 7 7 0 , 2 3 0 , 2 4 0 ) . T h e soldering of cans by
Courtesy Amp'ex Division, Chrysler Corp.
Bronze powder filters VOL. 48, NO. 9, P A R T II
SEPTEMBER 1956
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MATERIALS OF CONSTRUCTION containing zinc chloride, stannous chloride, ammonium chloride, lead chloride, and lithium chloride are recommended for applying a lead coating to iron, cast iron, and copper alloys ( 6 E ) . Practical suggestions governing the use of fluxes and for the removal of flux residues to ensure good joints are summarized ( 3 5 ) .
Other Tin-Containing Materials
A heat-treatable zirconium-tin-molybdenum alloy is readily rolled at 1300" C. and has four times the creep strength of pure zirconium ( I F ) . An improved dental amalgam containing silver 60Yc, tin 79%, copper 3%$ and zinc ?cc has a short settinq time: high hardness, and controlled expansion after mising with mercury ''5F '. Tin-base alloys make efl'ective tips for ball point pens. T h e tips are die cast a t hiqh speed, lvith high dimensional accuracy and high fluidity. Separate machining operations are avoided (7F). T h e low melting poin: of tinbase alloys permits casting in inexpensive foundry equipment. Molds can be paper m2ch&, plaster, \vood. or rubber as well as metal. Casting procedures for bearing alloys. peivter, jeivelry, and organ pipes are illustrated ( 7 C ) . T h e tone of an organ pipe is governed by the tin content of the metal used. A description of organ pipe manufacturing includes casting spotted metal (tin-lead), shaping. joining, bending: and tapering the sheet (6F). 'Additions of approximately 0.7500 copper reduce segregation in lead-tinantimony alloys and give a more uniform cast structure in heavy bearings (4F). New developments in collapsible tube packaging have become necessary because of the neiv "il-onder" drugs (ZF, 3F).
find new industrial uses (7G: 8G, 78G) and the process has been estended to the plating of \\.ire \\here the value of escellent shelf life and solderability can be utilized (76G). T h e practical applications and procedures for the tin-nickel electroplate have been recorded l\-ith an increasing number of com.mercia1 installations reported ( 7 X , 77G, ,?7G].Additional theories on the complesing of the Huoride ion in tin-nickel plating have been published ( 6 G ) . Tin-lead plating has been given recent attention with respect to the relation of plating conditions on the composition of the deposit (32:7G. 3 G . 27G). The plating of a n alloy of 11"; tin, 7yGantiman!-: 82% lead as an overlay bearingsurface for aircraft parts has been described as a successful operation (25G). Bath compositions and operating conditions for electroplating bearing shells \vith tin, lead? and indium have been reported ( I S G ) . The engineer is often faced u i t h the problem of selecting a plated coating with specific properties. This selection can be simplified if the results of cornparative tests on the finishes are rc.
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(24G). Immersion tinning by chemical displacement has been successfully applied to aluminum castings (32G) and to other metals ( 7JG). .inodic oxidation of tinplated steel ha3 replaced the thermal oxidation of bakery pans and tinlvare-the so-called burninq-in process (29G). A brightenin5 agent for the T i n (11)-sulfuric acid electrolyte is based on n-octyl sulfate pius pyroligneous tars obtained from the clistillation of saccharides (TOG. 17G).
Tinplate, Cans, and Packaging IVorld tinplate production continues to make n n v records Lt-ith tinplate shipments of 7,000,000 tons in 1955 ( 2 H ) . .A neiv tin mill a t Ijmuiden (Holland; is no\v in production (76H). T h e modern processes of tinplate manufacture ( 7 H . 8H, 72H) and the plans for expansion--\\-orld tinplate potential-have been revie\ved ( 9 H ) . Further development of radian1 gas-fired panels for reflowing electrolytically deposited tin has resulted in improved brightness (3H). 1Ietallurgical factors affecting the qualit), of cans have been appraised ( 7 . i H ) and the appearance of stria in hot dip coatings has been studied (4"). Inorganic protective films and acid and sulfur-resisting lacquers have been revieu.ed and appraised for the internal protection of tinplate food containers
(6H). T h e fields of application for electrolytic and hot-dipped tinplate have been discussed by Lewis with respect to draiving, shearing, M-elding, and lacquering
Electroplating T h e trend in electroplating practice is toward a wider use of alloy plating ( 3 G ) . I n previous vears new tin-allo). electroplates have been reported in this revie\v. These tin-alloy electroplates have passed through the trial periods of testing and appraisal and a great number of papers have appeared describing the industrial applicatiom and practical uses of these finishes (73G. 75G). Bronze plating as a n undercoat for chromium plating has been given still more attention (4G, 5G, 9G, 30G). Lt'hite bronze plating baths and techniques have been improved and this coating is meeting with considerable success in the plating of tableware and for decorative uses (79G-27G. 23G, 30G). Tin-zinc plating (80 : 20) continues to
liably reporred. Factors influencing shell life are discussed and types of coatinqs best fitted for manufactured products are suggested (22G). T h e importance of designing for plating is emphasized. T?-pes of coatings available, and specifications for utilizing coatings xvith good throtving poiver have been recordcd
(73H). .A tinning oil containing mineral oil, 5 to 10% palm oil, and 0.75 to 2% stannous chloride has been advocated as a substitute for palm oil (?If). Other substitute tinning oils have been suggested
(7H).
Courtesy David Brown Foundries Co., Sheffield, England
Contrast in bronze castings A worm g e a r blank, 1 4 f e e t in diameter, a n d a 3-inch thrust washer
INDUSTRIAL AND ENGINEERING CHEMISTRY
T h e Seattle Fisher); Technological Laboratory: after a 10-year trial period, concludes that fish frozen and stored in evacuated tin cans have a much longer storage life than xvhen packaged in other \vays ( 7 4 " ) . T h e canning of carbonated beverages continues to advance. T h e development of a "corrosivity tester" for estimating shelf life has eliminated some of the problems in this field ( 7 0 H , 1 7 H ) . T h e mechanism and case histories of rusting of cans are discussed with suggestions on protective packaging (77H).
TIN A N D ITS ALLOYS Corrosion Research Tests on the corrosion behavior of tinplate for packaging purposes are reported (5i) and observations are made that carmelization products in fruits may act as accelerators of corrosion ( 3 ) . T h e elimination of corrosion in soft drink cans is claimed by adding 10 to 50 p.p.m. of a n enzyme called D e e 0 :-/i). T h e specific action of various vegetables, fruits, meats! a n d fish on the can is described, as \vel1 as the effect of dissolved tin and iron on the taste of the canned goods ( 2 ) . T h e rate of corrosion of tinned steel specimens immersed in solutions of sodium hydroxide, carbonate, and phosphate is recorded. T h e effect of adding sodium sulfite or hypochlorite is also reported (7Bi. T h e character and speed of attack on tinned surfaces are discussed. Hydrazine or sodium chromate are suggested as corrosion inhibitors. Sodium alky! sulfate detergents induce corrosion on tin sheets (6i.Si,, A molten alloy of 527, bismuth, 3Zyc lead, and 1
