•
PRODUCTION
Alloy Coating Gains Momentum Tenacious nickel-phosphorus clloy coatings move in on electroplated nickel, will coat many materials JNI ICKEL-PHOSPHORUS alloys have
un-
usual corrosion resistance. And they coat mild steel and other materials uniformly besides. Engineers attending the chemical industry corrosion conference at Wrightsville, N . C , sponsored by International Nickel, w e r e told t h a t tests indicate t h e coatings to b e more resistant than electroplated nickel. T w o systems shown t h e engineers differ in application methods a n d chemical composition. But both h a v e low porosity and good corrosion resistance. T h e y also have properties t h a t suit them for some specific applications. From an economic standpoint, these coatings cost more initially. But longterm advantages suggest t h a t they will take over a big p a r t of the electroplating business—especially where complex shapes are involved.
• M e t a l s Aren't All. A highly adherent coating, developed b y General American Transportation's Kanigen D i vision, contains about 9 1 % nickel a n d 9% phosphorus. T h e s e coatings c a n b e deposited o n properly prepared surfaces of wrought iron, cast iron, steel (including stainless), a n d most of t h e iron, copper, a n d aluminum alloys. I n addition t o metals, you can coat plastics, glass, a n d ceramics a n d also use t h e coating as a base for electroplating. Parts t o be plated a r e immersed in a hot buffered solution of nickel chloride a n d sodium hypophosphite. Plating occurs at a uniform rate of about 0.001 inches p e r hour. T h e total thickness d e p e n d s o n time—the general practical limit, though, is 5 mils. Infinite "throwing power" makes t h e process ideally suitable for plating irregular or complicated pieces, while very large vessels can be handled simply b y filling
t h e m with t h e solution a n d maintaining t h e temperature at 2 1 0 ° F . for the p r o p e r time. Although t h e as-plated hardness of t h e coating is 48 o n t h e Rockwell C scale, specimens don't flake or chip w h e n drawn t o the tensile limit. However, some microscopic cracking does occur when p l a t e d bars a r e bent through 180 degrees. If you w a n t a m o r e ductile coating, you can get it by making t h e heat treatment longer. On t h e other h a n d , you can develop hardnesses t o 70 by short heat treatments. H i g h levels of adhesion a n d hardness a r e particularly useful in applications w h e r e resistance to corrosion a n d abrasion a r e required, as in ice-making machines a n d screw conveyors. Tank cars with 3 mils of Kanigen have shown excellent resistance t o 50 t o 7 4 % caustic, carbon disulfide, and ethylene oxide d u r i n g tests of eight to 10 months, says C h a r l e s Sanborn of Inco. A similarly t r e a t e d ammonia flash tank has b e e n in service for a year with no evidence of corrosion. Industrial applications a r e many: atomic energy, chemical manufacture, printing, petroleum processing, a n d a host of others. Corrosion resistance is a major factor in a number of uses: valves, p i p e , fittings, p u m p s , heat transfer surfaces. Probably t h e most important application is to prevent iron contamination in such articles as
T w o nickel—phosphorus coatings appear t o h a v e greater corrosion resistance than electroplated nickel. H e r e , a worker checks some Niphos-clad t u b i n g preparatory to firing 68
C&EN
OCT.
14,
1957
L a r g e vessels c a n be Kanigen-lined b y filling t h e m
screw conveyors, food handling equip ment, reaction vessels, a n d the like. • W e l d i n g Is α Success. Niphos is the other nickel-phosphorus coating (C&EN, Aug. 1 9 , p a g e 7 0 ) . Devel oped b y N e w York Testing Labora tories and licensed t o T u b e Reducing Corp., the coating contains 9 8 % nickel and 2 % phosphorus. Pieces being coated with Niphos are processed in a reducing furnace at 1650° F . An important feature of this coating material is its behavior at temperatures in t h e range of stress relieving a n d welding operations. In m a n y cases oxide coating c a n b e r e d u c e d during normal stress relieving treatments. Brazing of coated surfaces requires no special techniques—the coating itself is a brazing material. Welding attempts have been quite successful, particularly with type 312 stainless steel, since the coating does n o t peel away from t h e wreld joint in the heat-affected zones. Most test results for t h e t w o alloy coatings show they are a great deal alike in t h a t they are durable and uni form. So selection of o n e process in preference to t h e other d e p e n d s mostly on the economics of individual applica tions. Niphos i s relatively simple t o apply. But if large e q u i p m e n t has t o be plated the cost of reducing vessels may b e prohibitive. Kanigen plating requires a little more application equip ment b u t heat treatment is usually unnecessary. •
can you ^"MiuiniinniîiïïHMÏPPPMPPMfPi^ use this CORROSION INHIBITOR? PQ Sodium Silicate deposits a thin film on metal surfaces which protects them against corrosive attack. For example, a drop of sodium silicate (ratio Na 2 0:3.3Si02) s t o p s the attack o n aluminum by many alkalis. As shown above, the evolution of gas on the surface of aluminum in the sodium carbonate solution (left) ceases when PQ Silicate is added. Popular household detergents, industrial and metal cleaners use PQ Silicates for this valuable property. Protection against corrosion in water systems is obtained with 28 parts per million o f Ν (1:3.22 SiO*,) Silicate. (Dosage reduced by 50% after protection established.) We will b e glad to discuss how PQ Silicates' protective action can help you. Know how PQ Soluble Silicates can help solve a problem in your operations. Ask to be placed on the mailing list of Silicate Pys & Q"s. Edited monthly for quick reference on silicate developments and research.
PQ
PHILADELPHIA QUARTZ COMPANY with solution and holding the temperature at 210° F . H e r e , a vessel gets coated
Soluble Silicates
Sodium Silicate; Sodium Metasilicate; Sodium Sesquisilicate; Sodium Orthosilicate; Potassium Silicate
1162PUBLIC LEDGER BLDG., PHILADELPHIA 6, PA. Associates: Thila. Quartz Co. of Calif., Berkeley, Calif. ; National Silicates Limited, Toronto, Canada
OCT.
14, 1957
C&EN
69
