US2923620A - Anti-biofouling copper-base alloy - Google Patents

Description

, 2,923,620 ANTI-BIOFQULING COPPER-BASE ALLOY Carl L. Bulow, Trumbull, Conn, assignor to'Bridg eport Brass Company, Bridgeport, Conn., a corporation of Connecticut No Drawing. Original application January 5, 1956, Serial No. 557,441. Divided and this application (Bctober 20, 1958, Serial No. 768,013 r Y 3 Claims. or. 75 -153) This invention relates generally to copper-base alloys and more particularly to crapper-base alloys having superior characteristics with respect to biofouling and corrosion effects. This application is a division of the copending application Serial No. 557,441, filed January 5, 1956, having the same title.

In the classification of copper alloys, the current praetice is to use the term bronze for all copper-base alloys of less than 98% coppercontaining alloying elements other than zinc, and the term brass for all copper-base alloys of copper and zinc in various proportions containing less than 98% copper. Other metals may be present in brass but in such small quantities that their efiect is subordinate to that of zinc. In the present disclosure, where the alloy contains over 98% of copper, it will be identified simply as 98% copper base. 7

Other elements present'in the brass system of alloys are either impurities which were not removed during processing or are those intentionally added for specific purposes. Thus tin is frequently added to copper-zinc systems in varying concentrations to improve its corrosion resistance and to increase its strength and hardness.

Copper base alloys are widely used for the construction of apparatus subjected to corrosive solutions. For example, in the manufacture of condenser and heat exchange tubes, marine hardware and shafts, sheathing, valves and other elements'which come in contact with sea water, it is conventional to make use of copper-zin'c-all'oys such as Muntz metal, Admiralty metal or aluminum brass. Brass is also employed for fresh water supply lines and tank, as well as in industrial and'chemical plant equipment involving exposure to a wide variety of acid and saline solutions. Bronzes are also used under conditions involving corrosivesolutions, aluminum bronze for example being conventionally employed for pfagn blades and silicon bronze for hot water tanks.

Copper-base alloys are susceptible to various types of corrosion which gradually weaken the alloyQandultimate; ly result in service failure. One type of corrosion failure is commonly referred to 'as dezincification. Dezincification occurs due to a complex electrolyticaction giving rise to a gradual removal of the zinc from the surface of the metal and the deposition of a more or less spongy copper in place of the alloy. Such 'cfo'r'rosi'on takesfplace in some instances in a relatively uniform manner over the surface of the brass or bronze tube and at other times in isolated areas where the dezincification is intensified, thereby pitting and eyentuallypenetratingthe,tube wall to produce a leak therein. This intensified-form of corrosion is usually referredtq as Vplug type dezincification. The attack on metal by flowing-water is further augmented by theflturbulence of the liquid, resulting in socalled impingement corrosion. I 7

Conditions conducive to stressedrraabn failure, or as it is more commonly called, season cracking. are the presence of internal stress gradients in are alloy, followed by exposure to ammonia or ammoniacal compounds. Such exposure oc curswhere the copper-base alloy tube i wntact w h urel.ustas..( sshv saRW embY n algal of s i i is a u y, qrmedpn he su rs of the metal. The formation of an organic slime on nietal is generally designated biofouling. As is well known, algae has a high protein content, and upon decomposition thereof ammonia products are released. Hence, a brass tube in natural water is subject to corrosion due to biofouling aswell as the usual corrosion effect resulting from the chemical action of a saline or mineral solution and brass. An extensive discussion ofthe corrosive effect of marine flora and fauna on copper-base alloys may be found in the article of C. L. Bulow, entitled Corrosion and Biofouling of Copper-Base Alloys in Sea Water, appearing in the Transactions of the Electrochemical Society, volume 37,1945, pages 319 to 352. In this article, the testresults are given for a of 240 test pieces of copper alloys of widely variedco 'mposition. These pieces are exposed to clean flowing sea waterfor periods of six to twelve months, duringwhich the water temperature ranges between 2 and 30C. All of the speeirnens were edvered with slime after a few months exposure; I U p p I While it is known to add a small amount of arsenic to a copper alloy to reduce dezincification eifec athe addition of arsenic does not materially inhibitthe formation of algae on the surface of the metal. Indeed, in some instances, arsenic has been found to have the reverse elfe c t and, appears to attract certain forms of marine organisms.

The formation of algae or bacterial slimes on the surface of acopper-base alloy tube not only contributes to- .ward corrosion but also impairs the heat tr'ansfer propbeen necessary to chlorinate the system to retard or'prevent the formation of algae.

Accordingly, it is the principal object of the invention to produce a copper-base alloy which has superior resistance to corrosion and bi'ofdnling effects.

More particularly, it is an objectof the invention to provide a brass or bronze alloy including an algae inhibiting agent. 1 1 v 7,

Still another object of the invention is to provide a brass or bronzealloy characterized .byareduction in the tendency fdez'ineifi'catio'n, .a reduction in the rate of impingement attack as well as a reduction in the amount ofbiofouling, X

Broadly stateda'jcepper b'aseialloy in a'ccordance with ,the invention further. includesa small amountof mercury, preferably in therangeof ilfilio 1%". More specifically, a brass alloy in iiejmmaneewim. the invention is constituted by copper in the range of approximately 60 to zinc in the range of approximately 15 to 40% and mercury in the range of approximately .001 to 1% 'Due to the volatility of mercury, it cannot readil v f directly introduced into ther nolten brass or bronze since the mercury will quickly vaporize and be driven off. Accordingly, the preferie'dtechnique for forming a copper-base-mercury alloy is by the pr'ocessof amalga ation. In theease 'of brass an amalgam is first produced by treatment of'copper or zinc with a solution of mercury salt under conditions such as to precipitate metallic mercury on the surface ofthe metal. This is accomplished, for example, by soaking smallparticlesor chips of zinc or copper in a mercurous nitrate solution having a small amount "of"'nitric acid added thereto, whereby metallic mercury is precipitated on the surface, of the chips by electrolytic exchange. No electrical, current is required for this purpose.-

The mercury so deposited forms a superficial amalgam on the surface of the chips. The mercury platedchips are washed and dried and the reafter are introduced to the molten-base metal to form the desired alloy. The

iatio br'mereury to copper and zinc may be controlled by the relative amount of chips introduced into the molten metal. Alternatively, the alloy may be formed by the use of zinc, copper, or copper alloy containing a small amount of mercury as a natural impurity or alloying element. The same procedure described hereinabove may be used to introduce mercury into copper-base al loys of the bronze type and in the. other copper-base alloy examples set forth in Table 1 hereinafter.

It has been found that the addition of mercury to copper-base alloys produces a substantial improvement in general corrosion resistance and impingement corrosion towards sea water as well as improved resistance towards dezincification. The inclusion of mercury in brass compositions has been found to have very significantly reduced the extent of biofouling by various marine organisms. Even such alloys as high brass and Admiralty, which are generally subject to biofouling by algae and bacterial slimes, remain very clean vand brassy-bright when incorporating mercury. Residual slime clinging to the surfaces adheres poorly thereto and can be much more readily rinsed from the surface when the alloy includes mercury as disclosed herein.

In Table 1, examples are disclosed of alloys in accordance with the invention, the main constituent of the alloys being set forth in percentage values. In order to provide a basis for comparison of the characteristics of the alloys in accordance with the invention withsimilar alloys in which mercury is absent, Table 1 also includes under each example a conventional mercury-free alloy whose constituents otherwise have about the same relative percentages. Examples D, E, F, G and H are closely related with respect to the relative proportions of copper and zinc, hence these examples are compared with but one similar mercury-free alloy. Examples J .and' K are closely related with respect to the relative proportions of copper and phosphor, hence they are compared with but one similar mercury-free alloy.

Table 1 (in percentages) Example A: Cu 65.03Zn 34.95Hg .04 High brass: Cu 65.92-Zn 34.81-Hg .00

Example B: Cu 60.16Zn 39.83-Hg .07 Muntz metal: Cu 59.75-Zn 40.23--Hg .00

Example C: Cu 71.14Zn 27.84-Sn .96--Hg .05 Admiralty: Cu 71.10-Zn 27.98-Sn .97-Hg .00

Example I: Cu 84.70 Zn 15.29-Hg .008 Red brass: Cu 84.55-Zn 15.44-Hg .00

Example: Cu 99.9P .025-Hg .005 Example K: Cu'99.9-P .038--Hg .010 98% copper base: Cu 99.9-P .008--Hg .000

Example M: Cu 97.84- Si 2.0l-Hg .01 Silicon-bronze: Cu 98.06-Si 1.93Hg .00

Example N: Cu 94.80Al 5.19--Hg .02 Aluminum bronze: Cu 94.97Al 5.02--Hg .00

Example Cu 94.30--Zn .01-Sn 5.36-P .19-Hg .02

Phosphor-bronze: Cu 94.32-Zn .02--Sn In T able 2 below, the rates'of corrosion and the depth of p1tt1ng for the mercury containing Examples A to I versus the related mercury-free alloys are tabulated, the

rates being determined after five years exposure to Atlantic Ocean water. The rates of corrosion tabulated in Table 2 areexpressed in mils per year calculated from the loss in weight and loss tensile strength for these particular alloys. In addition, the depth of pitting or plug type dezincification found in these specimens at the end of five years exposure is also tabulated.

Table 2 7 Alloy Weight 1 Tensile Pitting 3 Strength 2 Example A (Hg .04%) 0.18 0 25 7. 2 High Brass (Hg nil) 0. 53 0 78 10.0 (p L) Example B (Hg .07%) 0.66. 2. 60 0.0 Muntz Metal (Hg nil).. 2.70 4 8. 35 0. 0

Example 0 (Hg 05%).- .32 .30 3.0 Admiralty (Hg nil) 37 36 14. 0 (p.t.d.)

.26 .37 3.8 16 28 7. 9 26 47 0. 8 28 l3 0. 8 23 23 5. 3 26 68 13. 5 (p.t.d.)

Example I (Hg .008%) 45 .49 7.6 Red Brass (Hg nil) .44 .45 11.5

Example I (Hg .005) .50 60 7. 0 Example K (Hg .010)..- 48 74 7. 0 98% Copper Base (Hg ni 46 53 9. 5

Example M (Hg .010) 40 41 10.0 Silicon-Bronze (Hg nil) .37 49 17.0

Example N (Hg .02) 18 59 1. 7 Aluminum-Bronze (Hg nil) .33 1.44 p 3.5

Example 0 (Hg .0 .43 .25 7.5 Phosphor-Bronze (Hg nil) .44 .54 11.0

Norm-All values are the average of six or more tests.

Table 3 Rate of Impingement Corrosion in mils per year Alloy Example A (Hg 04%) High Brass (Hg nil) Example B (Hg 07%) Muntz Metal (Hg nil) Example 0 (Hg 05%) Admiralty (Hg m'l) Example 1) (Hg .10%) Example E (Hg 06%)-- Example F (Hg 004%). Example G (Hg 008%)- Example H (Hg 04%) 10/30 Brass (Hg nil) Example I (1507 .0087) Red Brass 1351111 Example I 0 Example K 98% Copper Base Example M SiliconBronze Example N Aluminum-Br e Example O Phosphor-Bronze- To demonstrate more specifically the effectiveness of mercury as a dezincification inhibitor in brasses, Table 4 presents data showing the improved resistance to dezincification by brasses containing mercury versus mercury-free brasses. In a 1.0% cupric chloride solution, the loss in weight for mercury-containing and mercuryfree brass is not substantially difierent, but the loss in tensile strength, which is due to dezincification, is markedly altered by the presence of mercury. This diiference is brought out through the use of a ratio of rate of corrosion based on loss in tensile strength to the rate of corrosion based on loss in weight. When this ratio approaches unity (1.0) uniform corrosion free from dezincification is indicated. The data in Table 4 reveals that mercury in brass does act to a considerable degree as an efiective inhibitor of dezincification.

Table 4 Data showing improved resistance to dezincification by brasses containing mercury versus mercury-free brasses in 1% cupric chloride solution (78 day test):

The data in the above tables indicate that the addition of mercury to high brass, Muntz metal and 70/30 brass results in a substantial improvement in general corrosion resistance towards sea water. Brass alloys also have improved resistance towards dezincification. The addition of mercury to Admiralty metal improves the resistance of this alloy towards dezincification and impingement corrosion. In the cases of Phosphor bronze and silicon bronze, the addition of mercury results in some improvement in general corrosion resistance; that is to say, the corrosion is more uniform and somewhat lower. Adding mercury to these alloys also improves the impingement corrosion resistance. The addition of mercury to the copper base metal and red brass gives rise to more uniform general corrosion, although at a slightly higher rate. The addition of mercury to aluminum bronze produces a substantial improvement in general corrosion, impingement corrosion and corrosion pitting. Thus, in all instances, a beneficial effect is obtained.

Having thus set forth the nature of the invention, What is claimed is:

1. A corrosion-resistant copper base alloy adapted for exposure to corrosive solutions and consisting essentially of approximately 99% of copper, approximately .025% of phosphorous and mercury in an amount not exceeding 1% and notless than .001%.

2. A corrosion-resistant silicon-bronze alloy adapted for exposure to corrosive solutions and consisting essentially of approximately 98% of copper, approximately 1.9% of silicon and mercury in an amount not exceeding 1% and not less than 001%.

3. A corrosion-resistant aluminum-bronze alloy adapted for exposure to corrosive solutions and consisting essentially of approximately 94% of copper, approximately 5% of aluminum and mercury not in excess of 1% and not less than .001%.

References Cited in the file of this patent UNITED STATES PATENTS 2,270,660 Misfeldt Jan. 20, 1942 2,381,219 Le Baron Aug. 7, 1945 2,400,566 Misfeldt May 21, 1946

Claims (1)

1. A CORROSION-RESISTANT COPPER BASE ALLOY ADAPTED FOR EXPOSURE TO CORROSIVE SOLUTION AND CONSISTING ESSENTIALLY OF APPROXIMATELY 99% OF COOPER, APPROXIMATELY .025% OF PHOSPHOROUS AND MERCURY IN AN AMOUNT NOT EXCEEDING 1% AND NOT LESS THAN .001%.