ACTION OF ANTIFOULING PAINTS Solubility and Rate of Solution of Cuprous Oxide in Sea Water JOHX D. FERRY1 AND D-AYTON E. C.4RRI'I"I' Woods Hole Oceanographic I n s t i t u t i o n , W o o d s H o l e , .Mass.
T
HE effective supprerT h e solubilitj of cuprous oxide, the most c*ornrnoiil> tion, the solution \vas i'orcwi sion of marine growth+ used antifouling toxic, has been meawred i n oxygen-free nut through a sealed-in sinsea water. It is proportional to the hjdrogen ion concentered glass filter by applying by a n antifouling paint is tration and agree4 with calculations from thermod) namic nitrogen presRure, anti samassociated with the dissolution of a toxic substance data, assuming that the disqol\ed copper elists as the coniples were collected for analyfrom the paint into sea plex ions CuC12- and CuC13--. The rate of solution of his. The pH was quickly cuprous oxide in sodium chloride-nitrateborate buffers measured with a Beckman water. For paints containing eopper compounds as is proportional to the hydrogen ion coriceiitratiori and is a glass electrode. ;ifter cxlinear function of the square of the chloride ion concentoxics, the leaching rate powre t o the air, the cutration at constant ionic strength. I t is concluded that must exceed about 10 microprous copper in solution brthe dissolution occurs principall? by a process whose rate grams of copper per sq. cm. came oxidized to the cupricdetermining step is the formation of CuC12-, together w ith of paint surface per day to form, and was partially rea small contribution from a process w hich does not iniolie Drevent the attachment and precipitated as a mixture of growth of fouling organchloride ions. basic cupric carbonate and isms (5). On this basis oxychloride (5). Any such t h e ideal copper antifouling precipitate was redissolved by addiug citric acid, a i d the copper content was determined paint is one whose surface can steadily release toxic over a very long period a t a rate which is somewhat greater than the critical colorimetrically with sodium diethyl dithiocarbamate (2, 6 ) . value (to provide a reasonable factor of dafet,y) but not ( w e s Further details in procedure for s t w d different series of w l u bilitp measurements follow: sively greater (to prevent 'wastage of toxic). The design of a paint to approach this ideal depcnds upon tlie SERIES 1. The sea wat,er \vas deaerated t ~ yevacuat 1 and 3 were measured in normal sea water a t several different temperatures from 0 " t o 36.5' C. Several conditions of agitation were also employed; the rates of aolution obtained a t rat not attained a maximum rate of solution u r i t l v i , r h nio-t vifilc,iit conditions of agitntioii employptl. By adjusting t h e conditions of agitation and the area of exposed wlutcl, the effect of diffusion on the solutioii iate c a n he eitliixt. i~liniiiiatctlor made prccloniinnnt. Coating 1 pi~uvidc~il a 1ai.g~ :+wa of c ~ s p o dcuprous oside. and coating? 2 aiitl 3 ~nial1c.rarczi-, p ~ unit r of panel surface. Subsequent,measurement.- n-ere niatlc. uritlcr three different conditions: ( a ) with coating 2 or 3 , at liigli agitation, where the effect of diffusion is eliminated; ( b ) Tvitli mating 1! at high agitation, where the effect of diffu>ioii i; slight : fc) with coating 1, a t low agitation, Tvhcre the effect of diffuqioii prctlominates.
Vol. 38, No. 6
0.083 0.225
18 2C :30 .>
0.300
o.-1on ~~~~
Coating 1 measurpd 17.1 19.8 39.8 qO.0 ,0.2 ~~
~~
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