INDUSTRIAL AND E\ GIKEERIIC G CHEMISTRY
DECEAIBEH, 1936
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surface is corrosion resistant even with veneers as thin as 0.001 inch, although t h e usual ratio of precious to base metal is 1 to 10. This development of a method for covering a base metal with a highly corrosion-resistant material makes the precious metals available for large equipment where extreme resistance to corrosion is required, and a t a relatively moderate cost.
Bibliography (1) (2) (3) (4) (5)
(6) (7) (8)
Courtesy, H a n d v & Harman
A
SHEET O F P U R E SILVER,
59
x
62.5
INCHES IN SIZE
(9) (10) (11) (12) (13)
Balke, C. W., IND.EICG.CHEY.,27, 1166 (1935). Can. Chem. M e t . , March, 1934, 65. Carter, F. E., Chem. & M e t . Eng., 36, 553 (1929). Carter, F. E., Trans. Am. Inst. Chem. Engrs., 31, 459 (1935,. Downs, E., Chem. Age (London), April 6, 1935, 21. I n d . Chem., 1934, 427. Jones, C. H., Chem. & M e t . Eng., 36, 551 (1929). Lee, J. A, paper presented before Intern. Chem. Eng. Congr , June, 1936. McDonald, D., Chem. Age (London), Feb. 14, 1931, 142. Pope, Frederick, Met. & Chem. Eng., 15, 690 (1916). Rogers, B. A., Ihid., 41, 631 (1934). Schoonover, I. C., Ihid., 41, 545 (1934). Thews, Chem. Fabrik, 1930, 49.
RECEIVED October 9, 1936.
An important use for t h e platinum has been developed in the glass industry; t h e old trouble of t h e serious attack on t h e refractory pouring dies by t h e molten glass has been eliminated by covering t h e refractory with platinum-rhodium alloys. Both platinum and platinum-rhodium alloys have proved satisfactory for use in resistance furnaces where temperatures of 1300" C. or higher are encountered. Platinum-iridium alloy anodes are used in certain electrochemical processes.
Tantalum T h e chemical and physical properties of t h e metal, tantalum, make i t extremely interesting as a material of construction for equipment; Balke has treated t h e subject at length ( I ) before. B y far the greatest interest in tantalum results from its resistance t o acid corrosion. It is resistant to t h e attack of hydrochldric and nitric acids, aqua regia, and wet or d r y chlorine a t ordinary temperatures. Although it is not corroded by dilute sulfuric acid a t ordinary temperatures, it appears to be slowly attacked by boiling, concentrated sulfuric acid. Solutions of caustic alkalies do not corrode the metal easily. Hydrofluoric acid seems t o be t h e only chemical that will attack it. Under certain conditions i t may be deteriorated a t ordinary temperatures by hydrogen gas liberated in t h e nascent condition in contact with t h e metal. Tantalum can absorb a large volume of hydrogen, producing a brittle hydride. At elevated temperatures it also combines readily with nitrogen and oxygen. T h e metal is capable of being drawn, stamped, hammered, formed, or welded without introducing strain areas. It can be hardened through a wide range without losing a n y resistance to chemical attack. B u t i t cannot be cast,
Plating Base Metals with Precious Metals Among t h e most interesting of t h e recent developments are precious-clad metals and plated surfaces. These applications of t h e most expensive metals will no doubt be further utilized by t h e process industries in t h e future. Advances have been made in t h e technic of plating platinum, rhodium, and palladium. T h e Chemical Exposition in New York last fall exhibited for t h e iirst time gold, silver, platinum, and other precious metals clad on nickel, brass, copper, and steel bases. Layers of t h e precious and base metal are welded together and rolled or drawn to finished dimensions. T h e
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Discussion R. H. LEACH Handy & Harman, Bridgeport, Conn.
T
HE reticence of those who have found silver most suit'able for certain chemical processes, to publish information regarding its advantages makes the presentation of specific data extremely difficult and tends to impose on any potential user the task of making independent and, in some cases, comparatively expensive tests. As Lee states, silver alloys have had a limited use but it is the pure metal or fine silver which is most important. While it is true that the first cost may seem to be comparatively high, the salvage values are correspondingly large and this must be taken into consideration in any fair appraisal of the net cost. The ages old concept that silver is a precious metal and one that must be conserved seems to inhibit a rational analysis of the actual cost of using it. Modern electrolytic silver refineries produce a high grade of pure or fine silver, and manufacturers are prepared to supply silver sheet and tubing in size and gage comparable to those obtainable in copper, brass, and other nonferrous metals and alloys. Furthermore, methods for fabricating equipment have been developed during recent years to a degree that ensures a satisfactory job whether the apparatus is made entirely of silver, with a silver lining, or of a bimetal or duplex plate. While it is true that the choice of the three types of linings-namely, electroplated, removable, or duplex metalwill depend upon several factors, it does not seem amiss to repeat that the last type is available in sizes suitable for the manufacture of large pieces of equipment. Silver-clad steel, for example, has the advantages of the strength of the steel and the corrosion resistance of silver. The cost is dependent upon the thickness of the silver required to meet any specific condition, but in any case the initial investment would be materially reduced. The silver cladding has been subjected to successive reductions by rolling and will have, therefore, the same protective properties against corrosion as any sheet of rolled silver. Short-time tests on the strength of iine silver at elevated temperatures indicate that at 600' F. the strength is approximately two-thirds that of annealed fine silver or about 15,000 pounds per square inch; at 800" F. the strength is about 12,000 pounds
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I\DUSTKlAL AND ENGINEEHIUG CHE\fISTRY
per square inch, and at 1000” F. about 8000 pounds per square inch or only about one-third of annealed fine silver. It would be of interest to have information regarding long-time tests, but, in general, the indications are that the st>rengtha t elevated temperatures is comparat’ively low and the use of a silver lining or silver-clad base metal would be necessary if the strength was an important consideration. Silver alloys such as silver solders show less reduction in strength at elevated temperatures. As an example, tests on silver-soldered joints with copper tubing and bronze fittings showed that at 425“ F. there was no evidence of creep in the soldered joints when the loading was considerably in excess of the creep limits on t,he extra heavy copper tubing.
YOL. 28, N O . 12
In recent years there has been much interest in the bactericidal propertips of silver. Much research work has been done and this particular property should be of interest to chemists in the food, wine, and fruit juice industries. The increase in the use of silver in chemical plants during recent years is the best evidence that, in spite of its cost, there are many applications where its use is justified. I t also seems probable that further cooperation between producers of silver and engineers responsible for development of equipment in chemical industries would bring ahout the development of new uses. RECEIVED October 9, 1936.
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Discussion C. L. MANTELL P r a t t Institute, Brooklyn, N. Y. ITH increasing attent’ion being given to electrical heating and its applicat,ion to the chemical processing industries, heating elements as materials of construction should be studied. In this field the nickel-chromium alloys, particularly those of nominal composition 80 nickel-20 chromium, 60 nickel-15 chromium with the balance iron, and 30 nickel-20 chromium with the balance iron, all wit,h additions in small amounts of alloying and modifying agents, have been widely accepted and applied. These alloys are discussed as materials of construction in a recent paper [Trans. EZecfroche?n.SOC.,68, 29-42 (1935) 1. I am somewhat surprised that Lee has found uses for silver equipment in tanneries. Either this is an unusual tannery or else Lee’s “chemical engineering index of penetration” in tanneries has risen remarkably high from his last survey. If the tanners
are beginning to use silver equipment, there is hope that the average tannery may become a part of the chemical industries. In connection with tin as a material of construction, particularly from the viewpoint of corrosion, reference should be made to a paper on “Corrosion of Tin and Its Alloys” (Trans. Am. Inst. ,Mining M e t . Engrs., Inst. Metale Div., 1929, 111-48) as well as t,o the A. C. S. Monograph 51 on “Tin,” published in 1929. For a number of severe service applications where metals and alloys have fallen down on the job, manufactured carbon has given satisfactory performance. The article on “Carbon: a Neglected Material of Construction for Reaction Equipment” should be thought-provoking [IND.ENG.CHEM..24, 1255-9 (1932) 1. RECEIVED October 9, 1936.
FILTERPRESSWITH 43
ALLOY PLATES. EACH PLATE wEIGHS 85 POUNDS
Courtray, Aluminum Company of America
