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be removed, thorough periodic cleaning may greatly increase the length of service. This is particularly true when solutions of heavy metal salts are in contact with the aluminum. Each cleaning removes the precipitated metal and thus arrests the growth of the small pits which have been induced by electrolytic attack since the last cleaning. In this way the depth of pitting is greatly reduced. On the other hand. cleaning should be avoided when the layer of corrosion prod-
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uct is required to protect the underlying material, as with ammonia and formaldehyde. Aluminum used in contact with foods must be regularly sterilized. Wherever possible this should be done with steam. If a chemical sterilizer containing chlorine has to be used, it should be suitably inhibited. Sodium silicate is frequently a satisfactory inhibitor for such solutions. RECEIYED September 12, 1936.
NEW METALS AND ALLOYS F R O M
LEAD, TIN, ZINC, AND ANTIMONY
T
HE research worker in the base metalslead, tin, zinc, and antimony-is developing new uses for old metals, new alloys for old jobs, new combinations of metals to perform newly created tasks. This paper discusses the alloys based on these metals.
Lead Although new uses have been found for this historic and modern metal, the
COKEPLANT SATURATOR OF STEEL LINEDWITH SHEETLEAD1.25 INCH TEICK (Inset) BEERCAN OF TIX
most important recent developments are in lead alloys. In 1919 it was demonstrated that the addition of a small amount of copper to lead improved lead’s resistance to corrosion by sulfuric acid at elevated temperatures because it tended to offset the deleterious actions of bismuth and antimony. Then tellurium was also shown to improve the behavior of lead under certain laboratory test conditions, but it was not until comparatively recently that the tellurium alloys in use today were developed and commercialized. One of the large l e a d p r o d u c e r s recently introduced to the American market a new type of chemical lead containing not only 0.04 to 0.08 per cent copper but also appro~mately0.02 per cent bismuth. It is claimed that this alloy or new variety of lead can be used for many purposes as satisfactorily as the A. S. T. M. standard chemical lead; in addition, it is said to possess some advantages in mechanical properties. One of the most spectacular recent developments is tellurium lead, which is ordinary lead containing about 0.05 per cent tellurium. It was developed in England and is now extensively used on
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INDUSTRIAL h \ D ENGIAEEKI_\(G CHE\llSTII1
both sides of the Atlantic. This new type of lead exhibits unusual resistance to corrosion by hot concentrated sulfuric acid. Tellurium lead has proved a bocn to numerous users or various types of lead chemical equipment, principally where the previous failures of ordinary lead equipment were due to corrosion fatigue. Tellurium lead has a higher endurance (fatigue) limit than pure lead, and thus longer life and better serrice is expected of it under drastic conditions. An important property of tellurium lead is its capacity for work-hardening. Lead and the ordinary lead alloys are not appreciably hardened or s i renpthened when fabricated by rolling or extrusion. The work-hardening capacity of tellurium lead may easily be demonstrated. Strips of the extruded metal are stamped with letters or numerals so that the strips are considerably distorted. When the strips are pulled in a tensile strength testing machine, fracture occurs, not in the stamped areas but in the blank sections of the strips. As is well known, ordinary extruded lead would, under this treatment, fracture a t the points of deformity. Tellurium lead is being used in the form of sheets, pipe, and other shapes in various industries. One of the large battery makers is using tellurium lead plates in storage batteries of the Plante type. The plates are made by a swaging process, thus utilizing the work-hardening property of the new metal. Tellurium lead is employed abroad for some electric cabk sheathing. Another instance of modern relsearch in lead is the development of three so-called ternary cdloys of lead by the British Non-ferrous Metals Research Ass,ociation. The compositions of these alloys are as follows: Alloy No. 1
2
3
Tin
1:io 0.40
Antimony 0.50
.. ..
Cadmium 0 25 0 25 0.15
Lead Remainder Remainder Remainder
Sheet and pipe made in these alloys, although stiffer than ordinary lead, are easily handled and can readily be welded and soldered. The alloys do not appear to be sufficiently resistant to corrosion to warrant their extensive use in the chemical industries. Their superior tensile strength obviously deserves consideration, but as yet these ternary alloys have not been widely adorted in this country. The addition of calcium to lead produces valuable alloys, particularly for the bearing met:il field. One important example is a bearing metal containing about 97.5 per cent lead which is hardened with small amounts of calcium and other elements. This alloy is being used in increasing quantities each year. One of its outstanding characteristics is a higher initial melting point than that of the lead-and-tin base bearing metals customarily used. It has been said that bearing linings made of this alloy can actually smoke, owing to lubrication failure, and thus raise a danger signal which may save costly bearing or shaft repairs. As is well known, most of the commoner bearing alloys, under similar conditions, will melt before the “smoking” temperature is reached. For telephone cable sheathing an alloy containing 0.03 to 0.04 per cent calcium has been proposed. When the sheathing is properly manufactured, such an alloy has good strength and a relatively high endurance h i t . For ordinary atmospheric exposure the alloy is reported to have corrosion resistance equal to that of lead or the 1 per cent antimonial lead frequently used as cable sheathing. The constitution diagram of the lead-calcium alloys was carefully determined by one of the large industrial laboratories. At 0.1 per cent calcium a peritectic reaction with lead occurs. The solubility of calcium in lead diminishes from this point to about 0.01 per cent calcium a t room temperature. Accordingly, the alloys containing sniall amounts of calcium are susceptible to precipitation-hardening, or may exhibit age-hardening. It was demonstrated several ye:w ago that antimony-lead
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Lead is prominently used i n the heavy chemical industry and i n other lines. When alloyed with a few hundredths per cent tellurium, it meets drastic conditions successfully. Improved mechanical properties augment good corrosion resistance, producing a superior material of construction. Lead alloyed with antimony (up to 28 per cent, commonly with about 6 per cent) is used i n appreciable quantities o n account of its physical properties. A lead alloy containing 1 per cent silver and another with 7 per cent tin are used for special purposes. Pure tin is used with chemicals because of its corrosion resistance and nontoxic nature. Zinc-coated metals and die-casting alloys are used despite somewhat limited corrosion resistance.
alloys, containing about 10 per cent antimony, were not entirely satisfactory for use as grids in storage batteries. Some of the antimony enters the electrolyte and tends to a partial self-discharge of the battery when idle. This disadvantage, however, has not seriously affected the usefulness of storage batteries for automobile starting and lighting. Sound reasoning and actual experiment have shown that a lead alloy containing 0.1 per cent calcium can be used for storage battery grids, largely eliminating the self-discharge which occurs when an antimonial alloy is used. Obviously the use of the new alloy will be followed with interest, even though there is some uncertainty as to the likelihood of its use in automobile starter batteries of the Faur6 type. Such thin grids are difficult to cast and must be given a heat treatment in order to impart to them the strength of the antimonial grids now in use. Lead has indirectly been associated with chromium plating for 10 years or more. In some of the earliest plating equipment, lead tank linings functioned not only to hold the electrolyte but also to act as insoluble anodes. In a small percentage of the chromium plating installations, there has been some drastic corrosion of the lead tank linings or anodes. After experimenting with a wide variety of lead alloys, i t was shown that a 7 per cent tin-93 per cent lead alloy could be satisfactorily used for tank linings, heating coils, and anodes. This alloy has come into use because it does not appear to require frequent periodic anodic treatments in order to prevent serious corrosion. Heretofore, 6 per cent antimonial lead had been used with considerable success, but the anodic treatments appeared advisable. The addition of 1 per cent silver t o lead forms an insoluble anode which is very desirable in the production of highpurity commercial zinc (99.97 per cent). The adoption of the alloy contributed materially in reducing the lead content of the electrolytically refined zinc to about one-tenth of the amount formerly contained in the ordinary electrolytic product. Antimonial lead, commonly called “hard lead,” is a popular alloy. It is widely used in the construction industry for rooiing, gutters, leaders, finials, and mullions; it is employed by rayon manufacturers for pump bodies, valves, and other items of equipment; various chemical industries use hard
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INDUSTRIAL AYD ENGINEERIXG CHEMISTRY
lead for tank linings and coils. The antimonial content of the lead depends upon the use to which the metal is put, the percentage ranging from 6 per cent or lower for rolled sheet for linings and roofing to 28 per cent for special nozzles used in a rayon plant in Europe. There are some installations of antimonial lead alloys of ordinary compositions plus about one-hundredth as much tellurium. Some success has been claimed for them. Several years ago, the BullardDunn p r o c e s s of c o m b i n i n g pickling and coating was developed. By this method electrolytic pickling is accomplished, and simultaneously a thin fdm of lead or tin is deposited upon the clean iron or steel surface. Thus the metal is p r o t e c t e d against subsequent rusting.
Tin The ubiquitous tin can represents the widest use of this metal, although the tin content of the container is small. Despite almost universal satisfaction with the tin can for food and drink, it has been r e c o g n i z e d that common sheet tin (tinned iron) has some i m p e r f e c t i o n s or STRIPSOF LEADWHICH “breaks” in the tin coating. To remedy this situation, the InterWERE STAMPEDAND THEN PULLEDIN A national Tin Research and DeTENSILETESTINQ MAvel0 pm en t C o u n c i l recently CHINE TO NEAR THE recommended that ordinary hot BREAKINQ POINT dip-coated tinned iron could be The tellurium lead (left) wae work-hardened by thestampimproved by following the hot dip ing and tends to break at c o a t i n g w i t h an electroplated eome other location whereas the other lead (rikht) was coating. This new process may weakened by the stamping and tends to break in suoh a be widely employed. The eleclooality. trolytic deposit is extremely thin and the additional cost should not be excessive. In addition to the bearings metals, mentioned under the discussion of lead, we must necessarily include tin alloys. Because modern industry and transportation demand so much from bearing metals-higher speeds, heavier loads, longer service, etc.-it is natural that these alloys should be given close study. Regular tin-base babbitt metal can be considerably strengthened by the addition of 1 per cent cadmium. Automotive engineers hare lately been concerned over the corrosion of some bearing metals by oils used to lubricate motor car engines. In England the problem has been attacked by introducing tin soaps in the lubricating oils, to forestall the breakdown of the lubricants which is apt t o result in the corrosion. Tin has recently been used in large quantities in pewter ware. The layman is apt to conclude that, since pewter is rather ductile and easily shaped and worked, it must contain much lead. He might be surprised to learn that modern pewter contains no lead whatsoever. Recent research indicates that pewter composed of 5 per cent antimony and 95 per cent tin alloy is superior to the common alloy which contains about 2 per cent copper, 6 per cent antimony, and
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92 per cent tin. A further proposed combination i. 5 per cent silver and 95 per cent tin. The widespread use of chromium plating has brought tin (as a constituent of bronze) into this field. Commercial methods have recently been developed in which bronze coatings are electrodeposited on steel, thus producing an undercoat for chromium plating. Wider use of the new bronze plating is expected. The intensive development work in new applications for tin will lead to a better understanding of the uses of this metal and Ehould rewlt in new tin products. Zinc
Zinc-coated iron or steel (usually called “galvanized iron”) is employed in large tonnages for structural purposes. Most of the applications of this material are so well known as t o need no mention here. However, in certain industries employing chemical processes which induce or are accompanied by conditions of high humidity, heavy zinc coatings of the modern type are useful for structural steel or iron members in order t o avoid the destructive effects of rust. The mechanical weakness of pure sheet zinc has been recognized in recent years and has led to the development of a strong zinc alloy, containing about 98 per cent zinc with small amounts of cadmium, copper, and magnesium. This material is marketed as corrugated roofing sheet. The use of this newer sheet has, in some instances, proved more economical than zinc-coated steel for roofing purposes. One of the large steel concerns has recently developed a new type of zinc-coated steel wire. The coating, consisting of electrodeposited high-purity zinc, is applied and then the n-ire is treated mechanically to give it a uniform and smooth surface. This product is expected to be more serviceable than ordinary galvanized iron or steel wire. About twenty years ago zinc base die-casting alloys were not particularly popular, possibly because failures of the castings were not uncommon. A thorough study during recent years, however, showed that the failures of the early castings were traceable to one or both of the following causes: Intercrystalline corrosion occurs when the zinc-aluminum (with or without copper) alloys contain appreciable amounts of impurities, such as lead and tin. The other cause of failure was associated with a phase change in the constitution of the metal. Today, zinc base alloy die castings are used in enormous quantities. The success of these alloys is due in part to the high-purity zinc (99.97 per cent) now on the market and to research work, partly sponsored by the American Society for Testing Materials. Antimony
Some of the newer uses of antimony have necessarily been discussed previously under the topics of lead and tin, since the principal use of metallic antimony is in the form of lead and tin base alloys-antimonial lead, bearing metals, and type metals. The use of antimony as a coating has been discussed but as yet does not seem important. Metallic antimony is used, in small tonnage, as an insoluble electrode in the determination of hydrogen ion concentration of solutions.
