INDUSTRIAL AND ENGINEERING CHEMISTRY
2124
This value of the total pressure may be compared with the experimental data by interpolating with the Clausius-Clapeyron equation a t 2, = 25%. Temp., OC.
P , Lb./
Sq. In.
160
129
loo
82.5
1417
log P
l/Temp.,OK.
log P
2.110
0.00236 0.00268 0.00282
i:&
1:iC.s
...
P , Lh. / Sq. I n .
...
28.6
...
Similarly, for the vapor composition:
pseudo relative volatility and shows the phenomenon in v, hich all three critical loci coincide, it may be found that, in general, those systems in which the three critical loci coincide give straight-line correlations in the pseudo relative volatility plot. NOMEYCLATURE
L
=
= =
n =
v/v = 459 a12 =
= molal latent heat of compound
L’ LR L‘R
From Figure 12, the ratio of volumes for the standard substance a t the same reduced temperature is obtained from P’R = 0.0168: From Figure 9,
R
P
3.8
= =
=
= =
=
This may be compared with the experimental data by logarithmic interpolation. P , Lb./Sq. In 14.7 28.5 129
yi
70
log
ai
55.3
1.743
48:l
1:&2
log P
log
1,167 1.455 2,110
1: i i 4
~9
...
ti I
53:o
..
= = = = =
= = = =
CONCLUSIONS
I n applying the above plots t o the correlation of vapor-liquid equilibria data of binary systems, no particular difficulty arises in the use of the total pressure plot. However, in the application of the relative volatility plot some choice must be made between either the plot against the reduced pressure of the reference substance or t h a t against volunie ratio of the reference substance (in either case a t the same reduced temperature). I t is recommended that the plot of the logarithm of relative volatility against the logarithm of total pressure of a reference substance a t the same reduced temperature be tried first. If curvature in the critical region is pronounced, then it is suggested that the pseudo relative volatility plot be tlied next. Should this second method fail to eliminate excessive curvature in the critical region, application of the volume ratlo plot can be expected to give a straight-line correlation, as it has in all cases studied. As the system ethanol-water correlates very \yell using the
Vol. 40, No. 11
=
-
molal latent heat of reference substance ( L / T , ) = reducedmolallatent heat (L’/‘T’c) = reduced molal latent heat of refwencr sub. . stance (LI/T,) = reduced molal latent heat of component 1 from solution (L2/T,) = reduced molal latent heat of coniponc~nl 2 from solution total pressure a,t given temperature critical pressure of compound or rnixt,ure total pressure of reference substance ( P / P c ) reduced pressure a t given temperatmure (P’/P‘J = reduced pressure of reference iiubstanw at the same reduced temperature absolute temperature critical t,emperature of compound or mistui~: critical temperature of referenee substance (T/T,) = reduced temperature molal volume of liquid molal volume of vapor mole TOof component 1 in liquid mole of component 2 in liquid mole % of component 1 in vapor mole YOof component 2 in vapor y z z = relative volatility of component 1 (tht. ninre volatile) compared to component 2 zly, 3
LITERATURE CITED
s.,
C a r e y , J. a n d Lewis, IT.K., IXD. P h G . C H E M . , 24, 882 (1932). G o r d o n , D. H., Ibid., 35, 8 5 1 (1943). Griswold, J., Haney, J. D.. a n d Klein, V.A . ,I b i d . , 35, 701 (1943). K a y , W.B., I b i d . , 28, 1014 (1936). Othmer, D. I?.. I b i d . , 32, 841 (1940). Ibid., 34, 1072 (1942). Othmer, D. F., and Gilmont, R . , I b i d . , 3 6 , 8 5 8 (1944). Pitzer, K. S., J . Chem. P h y s . , 7 , 5 8 3 (1939). Sage, B. H., a n d Lacey, IT’. N., Isn. ENG.CHERI., 32,992 (1940). Sage, B. H., R e a m e r , 11. H., Olds, E. H., a n d Lacey, W.N., I b i d . , 34, 1108 (1942). RECEIVED March 31, 1047. Presented before the Division of Industrial and Engineering Chemistry at t h a 111th Meeting of %heAXSRICAXCHEMICAL SOCIETY, Atlantic City, N. J. Previoiis articles of this series have appeared in ISDUWrRI.4L A X D E S C I S i % ~ R I K OC H h h l I S T l t Y : 1940 (P. 841); 1942 (pp. 952 and 1072); 1943 (p. 1269): 1944 ( p p 669 and 858); 1945 (p. 1112); 1046 (pp. 111 and 408); and 1948 (pp. 723, 883, a n d 886).
Action of Antifouling Paints EFFECT OF NONTOXIC PIGMENTS ON THE PERFORMANCE OF AXTIFOULING PAINTS BOSTWICII; H. ICETCHUNI AND JOHN C. AYERS Woods Hole Oceanographic Institution, F’oods Hole, Muss.
REVIOUS papers of this series (3-6) have discussed the properties of toxic pigments and of paint matrices which are important in formulating antifouling paints. The effects of adding nontoxic pigments to paints formulated both with soluble and insoluble matrices are described here. The use of a nontoxic pigment introduces a third related variable in the paint tomposition. Any variation in one of the components, matrix, toxic pigment, or nontoxic pigment, must be compensated by a related variation of one or both of the other components. For expqrimental purposes it is convenient to maintain either the weight or the volume occupied by the toxic pigment constant so that comparisons between paints may be
made. The nontoxic pigment is, then, substituted for an equal weight or volume of the matrix. I t has been shown by Young, Schneider, and Seagreri (8) that the substitution of a nontoxic pigment for an equal weight of vehicle improves the antifouling effectiveness of a copper paint. This effect was attributed to an increase in the permeability of the paint film. The authors of the present paper found results with paint3 compounded with insoluble matrices confirm these observations. However, the increase in the availability of toxic is attributed to the increase in the volume which it occupies in the paint film when the nontoxic pigment is substituted in this u-ay. As has been shown by Ferry and Ketchum ( d ) , the
November 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY
The irdusion of nontoxic pigments in antifouling paints formulated with insoluble matrices does not affect the leaching rates or fouling resistance provided the proportion, by volume, of the toxic pigment in the dry paint film is greater than the minimum critical value. In paints formulated with a soluble matrix, on the other hand, the introduction of a nontoxic pigment results in higher leaching rates at equal toxic volume fractions. Above a minimum critical toxic volume fraction, however, the fouling resistance is satisfactory regardless of the presence or absence of the nontoxic pigment. Variations in the total pigment volume fraction from 0.12 to 0.24 had little or no effect on the physical performance of these paint films when exposed in the sea. In the design of antifouling paints, therefore, it is necessary to determine first the critical toxic volume fraction required to give satisfactory antifouling performance. The total pigment volume can then be varied at will by the substitution of nontoxic pigments for an equal volume of matrix to obtain the most satisfactory paint.
probability of continuous contact of toxic particles increases, with a consequent increase Fn the leaching rate, as the volume occupied by the toxic in the paint increases. This is a purely geometrical effect which does not imply any change in the structure of the film or the manner of arrangement of the particles within it. MATERIALS AND METHODS
The Vinylite paints used in this investigation were compounded with materials supplied by the Bakelite Corporation-namely, cuprous oxide (electrolytic), polyvinyl chloride-acetate (Vinylite ,VYHH), and Celite. The varnish vehicle paints were supplied by Richard J. Eckart of the Sapolin Company, Inc. The varnish vehicle has the following composition: 26 lb. 75 Ib. 3 gal. 3 gal. 101/2 gal. 7 gal.
BR-254 (phenolic resin) Cumar V-21/1 (cumarone resin) Linseed oil Wolin (Zapon K, a wood oil substitute) Solvesso 2
High flash naphtha Trace of driers
The soluble matrix paints were modifications of Navy Specification 52-P-61paints formulated and supplied by the Mare Island Naval Shipyard. The leaching rates were determined by the standardized technique described in a previous paper ( 7 ) . The exposures for fouling tests were made at Miami Beach, Fla., by Charles M. Weiss. VINYLITE PAINTS
The leaching rates, during exposure in the sea, of a series of paints containing various amounts of cuprous oxide in Vinylite are given in Table I. Three paints in which Celite has been
VOLUME
2125
FRACTION CUzO
Figure 1. Total Amount of Copper Lost from Vinylite Paints Plotted against Volume Fraction of Cuprous Oxide in Paint 0 0
Paints that contain only cuprous oxide Paints that also c o n t a i n Celite
substituted for an equal weight of Vinylite are included. Comparison of the paints containing the same weight percentage of cuprous oxide shows that this substitution of Celite has appreciably increased the leaching rates. The volume fraction occupied by the toxic pigment is also included in Table I. The substitution of Celite for a n equal weight of Vinylite results in a n increase in the proportion by volume of the toxic pigment in the dry. paint film. For example, the volume fractionb of the toxic in the two paints containing 70% cuprous oxide by weight are 0.33 for the paint with toxic alone, and 0.40 for the paint which also contains Celite. When the total amount of copper lost from the paints between the 8th and 24th weeks is plotted against the volume fraction of cuprous oxide, as in Figure 1, it is found that the availability of the toxic is directly related t o the volume fraction of the toxic, and appears to be largely independent of the presence of Celite in the formulation. The solution of copper from cuprous oxide paints made with a Vinylite vehicle depends upon the continuous contact of toxic particles. T o obtain adequate contact the volume fraction occupied by the toxic must exceed 0.3 (4). The usefulness of Celite in improving the leaching rates of these paints appears to be related to the change in the volume fraction occupied by the toxic. The increase of this fraction results, when Celite is substituted for a n equal weight of matrix, because the Celite is denser, and thus occupies less space than the equal weight of Vinylite which i t replaces. VARNISH VEHICLE PAINTS
TABLE I. LEACHING RATESOF PAINTB CONTAINING VARIOUS AMOUNTS O F CUPROUS OXIDE AND CELITE I N VINYLITE
The effect of nontoxic pigments on the availability of both cuprous oxide and metallic copper flake from a varnish vehicle Copper Leaching Rates after ~~~~~~$paint of short oil length has been studied. It is necessary to Soaking, Weeks Mg./Sq. know the minimum loading for both toxic pigments in this 8 12 16 20 24 Cm,b vehicle in order to evaluate the effects of the nontoxic pigment. 61 29 20 14 2.7 80 20 .. 0.45 39 23 17 11 2.1 The results of a n experiment performed to determinc this mini30 70 7 .. 0.33 9 16 5 0.9 mum loading are shown in Table 11. Cuprous oxide must occupy 60 40 .. 0.24 2 1 .. .. 0.1 60 40 .. 0.12 2 1 .. .. 0.1 a volume fraction greater than 0.35 in order to permit the release 15 70 15 0.40 33 17 10 8 1.5 20 60 20 0.30 6 16 10 5 0.8 of the toxic pigment at a n adequate rate to prevent fouling. This 25 25 50 3 0.22 7 6 2 0.4 loading is somewhat greater than t h a t which was found prea The following bulking values were used in computing the volume viously for Vinylite vehicles (4). When metallic copper is used fraction: Cur0 Grade 1, 0.0209 gal./Ib., Vinylite, VYHH 0.098 gal./lb. and Celite 0.052 gal./lb. as the pigment a toxic volume fraction of 0.20 or greater is adeb Calculated bv integration of leachinn rate-time curve. assunling a linear change between each pair of measurements. quate. The effectiveness of metallic flake pigments at lower loadings than are required for cuprous oxide has also been obPaint Composition Weight, % cuzo VinylVolume ite CuzO Celite Fraction= 10 90 ,. 0.65
INDUSTRIAL AND ENGINEERING CHEMISTRY
2126
Tovic Composition Weight Yolume % fraction'"
.
Copper Leaching Rates, ?/Sa. Cm./Day after: ~0 mo. 1 mo. 2 mo. 3 ~ n o . 4 mo. .-
j b Rh
n I.
49
23
".--
0,115
229
lis
25 36
7b R b
4 b 25
*
3b
46
7 b
Followinm bulking values were used in computing volume fraction: C u ? O , Grade-2, 0.0197,gal./lb., Cu 0.015 gal./lb., varnishsolids 0.111 gal./lb. b Paint fouled at this time when exposed a t Miaml Beach, Fls. a
served wibh other types of vehicles. It is suggested that the explanation may depend upon the geometric arrangement of the pigment particles. The cuprous oxide paints may be described as "cannon ball'' struchres in x-hich one particle is piled upon another, roughly like the familiar structure of a pile of cannon balls. The pigment in the copper flake paints, on the ot'her hand, may be arranged like a '(house of cards." The latter arrangement would provide continuous contact with a lonw pigment, volume than the former. In order to study the effect of nontoxic pigments on the availability of toxic in this vehicle, china clay was added in graded amounts. The volume fraction occupied by the toxic pigment was kept constant, in all of the paints a t 0.30. This is in contrast t o the previously described experiment \There the weight proportion n-as kept const,ant,with a resuliing increase in toxic volume fractions. The results of this experiment, are presented in Tahle 111. The paint containing cuprous oxide a t a volume fraction of 0.30 gave inadequate leaching rates (Table 11): and the substitution of as much as 235% nontoxic pigment for an equal volume of matrix did not improve this formulation. The substitution of nontoxic pigments for part of the matrix of the nletallic copper paints, likewise, had no substantial effect on t,he leaching rate. For this vehicle, as well as for Vinylite paints, the leaching rates are related to the toxic volume fraction, and are not increased, at constant' toxic volume, by the addition of nontoxic pigments. The same toxic volume fract,ion is obtained Ivith a lower weight percentage of toxic in those paints containing t,he nontoxic pigment. Thus, for cuprous oxide, the paint containing 23.3y0 inert pigment by weight required only 58.7% cuprous oxide to give the same re1at)ive toxic volume, leaching rates, and fouling
TABLE 111. EFFECTOF SCBSTITUTISG CHINACLAY FOR
AP;
EQUALT T O L 7 X E O F M.4TRIX O S COPPER LEACHIKG RATESO F VARNISHVEHICLEPAISTB CONTAIUIUG A TOXIC T'OLVME FRACTION OF 0.30" Weight CompositionbToxic Inert % Toxic 7'
c 11
0
5 10 15
77 74 72 69 67
Leaching nates T i S q . Cm.jDay after: 0 mo. 1 1x10. 2 mo. 3 mo. 4 mo.
226 218 200 235 242
27 44 24 27
22
19
$: 01
28
SOLUBLE MATRIX PAINTS
The effect of nontoxic pigments in paints formulated with a soluble matrix ( 6 ) was studied by the addition of diat'ornaceous silica to modifications of Navy Specification 52-P-61 formulation. The matrix of this paint consists of 6476 rosin, 327, Hcrcolgn, and 4V0 Pliolite by weight,. Three series were made in which the total pigment volume fract'ions mere 0.12, 0.18, and 0.24. In each series the total pigment volume was obtained using various proportions of cuprous oxide and Celite. The average leaching rates between the second and sixt,h months of exposure, and the fouling resistance and physical condition of t,he paint film after seven months of exposure are plotted in Figure 2 against the volume fraction of cuprous oxide. The leaching rates of the paints were related t o the volume of cuprous oxide, as would be expected, but in contrast to the behavior of the insoluble matrix paints, they did not depend upon the toxic volume fraction alone. They v,-ere greater for the paint's with t'he higher total pigment volume when compared 011 equivalent cuprous osidc volumes. On the basis of t,he simplified theory of the action of thcse paints presented previously ( 6 ) , the rate of loss of cuprous oxide should be related to the pa,int composition as follom:
L1
=
Kz WIL2 U'Z
20
0
LEACHING R A T E S
W
04
o"\
too.
@ p a
Z
8
50.
$
0
Q
PAINT
a 0 0 0 FlLV
0
CONDITION
d 01
VOLUME
20 16
15 18 19 19 25 24 18 16 a Bulking value of ehina clay i> 0.046 gd./lb. Other bulkin2 values used are given in Table 11. b Varnish solids make up remainder of dr>- film. Paint fouled a t this time when exposed a t Miami Beach, Fla. 20 23
effectiveness as the paint containing 70% by neight of toxic and no inert. Similarly, 67"c metallic copper, when combined with 19% nontoxic pigment, was found equivalent to 777, metallic copper when used alone. Kithin limits, therefore, a nontoxic pigment may be substituted for an equal volume of matrix without detriment to the antii'oulirig effectiveness of the formulation. This reduces the weight fraction of toxic pigment required in the dry film.
4b Xb
17
Vol. 40, No. 11
F R A C T I O N OF
TOTAL PIGMENT VOLUME'O:.24,
0 2
CU20
1 8 , 8 = 12
Figure 2. Leaching Rates, Fouling Resistance, a n d Paint Film Condition Plotted against Yolume Fraction of Cuprous Oxide in Paint Paints contain various proportion3 of cuprous oxide and of Cslite in a matrix consisting of rosin, Hercolyn, and Pliolite
November 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY
2127
or better after seven months’ exposure a t Miami Beach, Fla. COMPOSITION, LEACHING RATES,AND CALCULATED This may be considered the critical volume loading for these MATRIXSOLCTION RATES paints. Nine of these paints contained various amounts of (Paints formulated with a matrix of rosin, Hercolyn, and Pliolite containing nontoxic pigment; three contained only the toxic pigment. various proportions of CuzO and Celite) The physical condition of the paint film showed little relation Composition of Paintsa Average Calculated to the cuprous oxide volume, or to the presence of the nontoxic Volume Fraction !VeXht Leaching Loss of Celite CunO Matrix Cui0 Matrix Rate, CuzO Matrix (Rz) pigment. There was a slight tendency for the paints containing 6.7 9.8 0.88 0.44 0.56 0 0.12 the loyest total pigment volume to give somewhat poorer results 6.5 12.1 0.88 0.37 0.60 0.024 0.096 than the others. 7.0 14.9 0.33 0.62 0.08 0.88 0.04 5.6 . 16.2 0.88 0.26 0.66 0.06 0.06 The type of nontoxic pigment may be more important than 4.8 19.9 0.18 0.04 0.88 0.70 0.08 4.1 14.0 0.006 0.024 0.88 0.12 0.73 the amount used in a soluble matrix paint. Babel ( 2 ) has ob12.2 0.44 12.7 0 0.18 0.82 0.56 tained different results depending upon the type of nontoxic 15.1 0.48 12.4 0.036 0.144 0.82 0.48 pigment used. The effect of substituting various pigments for 17.1 0 . 5 0 12.1 0.06 0.12 0.82 0.43 23.2 0.55 11.8 0.34 0.09 0.82 0.09 the Celite in Navy Specification 52-P-61 paint is shown in Table 9.0 25.8 0.82 0.25 0.59 0.12 0.06 0.144 0.036 0.82 0.16 7.0 33.6 V. All the paints gave satisfactory fouling resistance for six 0.63 21 . o 14.8 months a t Miami Beach, Fla., with the exception of the one 0 0.24 0.76 0.65 0.35 16.6 15.2 0.048 0.192 0.76 0.56 0.39 containing precipitated chalk. Only three paints, however, 0.08 0.16 0.50 0.42 17.1 18.9 0.76 0.12 0.12 0.76 0.41 0.45 16,5 23.7 were rated better t h a n 90% in both fouling resistance and paint 0.50 13.1 28.6 0.16 0..08 0.76 0.30 film condition at this time. These three contained asbestine, 0.192 0.048 0.76 0.20 7.0 24.8 0.54 Venetian red, and barytes as the nontoxic pigment. a Folioiring bulking values were used in computing volume fraction of
TABLE IV.
’
these paints: C u i 0 0.0197 gal./lb., Celite 0.060 gal./lb., matrix solids 0.113 gal./lb.
DISCUSSION
in which L1 is the rate of loss of cuprous oxide, R2 the intrinsic rate of solution of the matrix, v z the volume fraction occupied by the matrix, and wi and w pare, respectively, the weight fractions of cuprous oxide and matrix. The value of Rs calculated from this equation should be the same for all paints, since no changes in matrix composition were made. As shown in Table IV, the calculated values of Rg tend to increase as the nontoxic pigment or the total pigment volume increases. The simplified theory is, therefore, not adequate to explain these results. Alexander and Benemelis ( 1 ) report improvement of similar paints by the introduction of inert pigments. They suggest that increased porosity of the film may be responsible for the beneficial effects of the inert pigment. The observed results could also be explained as a n effect of surface deposits if they accumulated to a greater extent on the paints u hich contain the greater amounts of cuprous oxide. These deposits have been shown to depress the copper leaching rate ( 4 ) . The fouling resistance of the paints was related solely to the volume fraction of cuprous oxide in the paint film, and was independent of the total pigment volume and of the presence or absence of the nontoxic pigment. This result is in contrast to the leaching behavior described above. Four of the paints containing the lowest total pigment volume had fouling resistance ratings of 80% or greater, although their average copper leaching rates were lower than the usual critical value-ranging from 5.0 t o 6.4 micrograms of copper per square centimeter per day. There is no apparent reason why these paints should be more effective than other paints with similar leaching rates. The remaining paints showed the expected correlation between leaching rates and fouling resistance. The twelve paints which contained cuprous oxide volume fractions of 0.08 or more gave fouling resistance ratings of 89%
TABLE V. EFFECT OF SUBSTITUTIXG PIGMENTS FOR CELITEON FOULING RESISTANCE AND PHYSICAL CONDITION OF ANTIFOCLIKG PAINT FILMAFTER EXPOSURE Fouling Resistance, Pigment Used Celite Asbestine Venetian red Indian red Zinc oxide Barytes Pptd. chalk
Paint Condition,
%
%
90 93
85 100 90 89 88 90 84
100
100 100 95 50
These experiments show that the presence or absence of a nontoxic pigment in paints made with insoluble matri-es has n o effect on the antifouling performance providcd the proportion, by volume, of the toxic pigment in the dry paint is maintained constant. The results can be explained on the basis of continuous contact of toxic particles. It seems, therefore, uunecessary to postulate that the increase in permeability of these films influcnccs their antifouling effectiveness. I n the design of antifouling paints formulated with an insoluble matrix it is necessary to first determine the toxic volume loading required t o give adequate toxic release. For Vinylite, Knyliterosin, and short oil varnish vehicles, for example, toxic volume fraction of cuprous oxide required is from 0.3 to 0.36. The total pigment volume loading t o give the desired physical properties can then be studied by substituting various amounts of nontoxic pigment for equal volumes of matrix. This leaves the toxic volume fraction unchanged, so that equivalent antifouling results from all paints of the series may be expected. I n soluble matrix paints, the presence of the nontoxic pigment results in somewhat higher leaching rates a t equal toxic volume fractions. The fouling resistance of the paints and their physical performance during exposure in the sea appear to be independent of the presence of nontoxic pigment. Above a certain toxic pigment volume, which may be expected to vary depending on the composition of the matrix, all paints give satisfactory fouling performance regardless of the presence of nontoxic pigments. The authors’ experiments indicate that satisfactory results may be obtained with a variety of pigment volumes. LITERATURE CITED
Alexander, A. L., and Benemelis, R. L., in press. Babel, V. S., Oficial Digest Federation Paint & Varnish Production Clubs, No. 240 (1944). Ferry, J. D., and Carritt, D. E , IND. ENG.CHEM, 38, 612-17 (1946). Ferry, J. D., and Ketchum, B. H., I b i d . , 38, 806-10 (1946). Ferry, J. D., and Riley, G. A., Ibid., 38, 699-701 (1946). Ketchum, B. H., Ferry, J. D., and Burns, A. E , Jr , Z b i d , 38, 931-6 (1946). Kctchum, B. H., Ferry, J. D., Redfield, A . C., and Burns, A. E., Jr., Ibid., 37,456-60 (1945). Young, G. E., Sohneider, W. K., and Seagren, C. IT’., I b i d . , 36, 1130-2 (1944). RECEIVEDAugust 2, 1947. Contribution No, 399 of the Woods Hole Oceanographic Institution. The experiments were conducted under contract with the Bureau of Ships, N a v y Department, which has given permission for their publication. The opinions presented here are those of the authors and do not necessarily reflect the official opinion of the Navy Department or the naval service a t large.
