July, 1946
I N D U S T’R I A L A N D E N G I N E E R I N G C H E M I S T R Y
cause the same coating was employed; the opposing forces were. on the one hand, attraction between the paint system and the substrate and, on t h e other hand, difference between the osmotic pressures of the internal solution and t,he external solution (immersion bath). This osmotic pressure gradient was greatest when the barh contained distilled water, and blistering resulted in all cases. It was smallest when the bath had a n osmotic pressure of 30 stmosphercs, and no significant blistering was observed in ,any caw. The osmotic pressure of tlie bath solutions just able to prevent blistering of the paint system used in t h e w tests on the four different substrate materials, therefore, may serve as a relative measure of the attractive forces between the paint system and the substrates employed. (This assumes t h a t t h e substrate does not influence the internal osmotic pressure of the blisten, P B . ) MECHANISM O F PROCESS
Tile preceding analysis of forces involved in blistering assumed that some water had reached the coating-substrate interface; no mention was made, however, of t h e mechanism of this process. T h e observations made in the’eourse of this investigation furnish a n adequate explanation of t h e forces causing transfer of water through t,he face of t h e film, hut fail t o explain why, under certain conditions, water passes entirely through t h e film and btxcomes concentrated in blisters a t the interface. Since a definite force exists, which is represented in niogt cases by a n wcaping tendency gradient drawing water into the coating, a still greater force ivould seem t o be required t o draw it o u t again into blisters at the interface wit+ the substrate, especially since the forces of adhesion must also be overcome in the process. Horvever, it is possible t h a t the blisters do not form exactly a t the interface, but t h a t a thin, perhaps monomolecular layer of the coating remain. attached t o the substrate. I n this case absorbed \vater would not have t o leave the coating t o cause blistering. It is likely t h a t the concentration of dissolved film substance in the absorbed n.ater xould increase &s water m o w s from the facv of
699
the film toivard the layer next t o the subdtmte. This concectration gradient should keep the water moving through tlie film t o tlie intvrface, or t o the last layer next t o t h e interface. There it should form blisters as ,soon as tho pressure becomes high enough to overcome the cohesivc strrngth a t the interface between monomolecular layer ant1 film. This assumption, however, makes it mow difficult t o unilcrstand \Thy there are .such marked differences in blistering propertics of a given coating tcm on different substrate materials, unlcw it is a s s u n i d that the character of this monornolccular layer is grr,atly motlificd by the nature of tlic .substratum. ACKNOW’LEDG11EST
This work was conducted at the request of and tinder conrrart with thc Bureau of Ships, S a v y Depart,ment. Tlie assistance of the head and various membcrh of ti;e Rosearcli Section, Bureau of Ships, and permission by the S a v y Department t o publish the results of this investigation, are gratefully acknowlvdged. We also thank W.hI. Peirce and D . 1,. Gamble, as well as other members of the Technical Department of The S e i v Jerst’y Zinc Company, for their constant interest and advice, and C. L. Blose, L. H. Farbcr, and H. E. Green for carrying out most of the experimental work. LITERATURE CITED ( 1 ) A m . Soc. for Testing Slaterial.;, Standards, Suec. D714-43T, pp. 1559-62 (1944). (2) Handbook of Cheiiiistry and P h y s i c s . p..1207, Clcveland. Chem.
liuhber Pub. Co., 1942. (3) I f l i d . , p. 1655. (4) International Critical Tahles. Yol. 111, p , % S i (1928). (5) Kittelberger, If-. W., ISD. Exti. CHEM., 34, 943-8 (1942). (6) L o n r y , H . H . , and I,ii:lt. i ’ a r n i - h , and I’lustics Chemistry a t the 109th \leetirig of t h e . i \ i E H i C . * s CIIF.\IIC.AL SOCIETY A ,t l n n t l c C i t y , S . J.
ACTION OF ANTIFOULING PAINTS Solubilities of Antifouling Toxics in Sea Water JOHX D. FERRY’ AND GORDOS A. RILEY r o o d s Hole Oceanographic I n s t i t u t i o n , IPbods H o l e , Mass. T h e solubilities i n sea water of iarious copper arid mercur> compounds which have been proposed as antifouling toxics coier a \cry wide range, from l o p 3 to oier lo5micrograms of metal per cc. Cuprous oxide, the toxic which has been nio4t widely used, has a solubility of 5 . & micrograms of copper per CC., high enough to be effectiie but not jo high that its leaching rate from antifouling paints i h too difficult to control.
T h e solubility and rate of solutiori of c u p r o u , ~oxitlr in >(saivater wcre reported in thc first paper of this series (.5). Altliough no other toxic substance has bcen .
