INDUSTRIAL A N D ENGINEERING CHE-WISTRY
326
Vol. 21, KO.4
light, and the optical rotation was that observed in a 100mm. tube a t room temperature (18-28” C.) using sodium light. SAMPLE
BOILING RANGE SPECIFIC REFRACTIVEOPTICAL .570 9570 GRAVITY INDEX ROTATION
c.
c.
a-Pinene &Pinene0 Dipentene Terpinolene
155 160.2 174 187
158 163.8 178 189.7
Fenchyl alcohol
200
201.3
a-Terpineol
218
219
0.8625 0.8677 0.8481 0.8744
1.4560 1,4709 1.4743 1.4809
+26.50
+- 1 14. 7. 21
-2 2; 2,
~
( 4 I . Y - L.J
a 1,
0.94 (350 C.) 0.961 (15.6’ C . ) b (m. p. 35’ C.)
1.4626
1.0 (200 C.)
1.4789 (25’ C.)a
0.19 (10% in alc.)
Distilled from gum turpentine. Supercooled.
Experimental
In using the modified Ramsay and Young method for obtaining vapor pressure data on these materials, special precautions had to be taken against contamination from two main sources. One of theee was possible dissolving of foreign matter from the rubber stopper through which the thermometers passed by condensing vapors of the material under test. This source of error was avoided by raising the top of the vapor pressure tube higher above the constant temperature bath. For high-temperature points a wet cloth was wrapped just below the stopper to condense any vapors rising above the mouth of the condenser return tube. The other
source of error was from possible solution by the sample of stopcock grease from the funnel used t o introduce the sample into the vapor pressure apparatus. This was prevented by substituting some of the sample itself for stopcock lubricant. Then, to prevent the thin samples from leaking away under vacuum, an excess of sample was made to flood continuously the outside contact edges of the stopcock. The flooding liquid WRS held in place on absorbent cotton. Details for making the tests are described under Manipulation Details in the previous paper.2 The results are presented in Table I and Figure 1.
The Additive Quality of Oil Absorption’ J. T. Baldwin SANDURACOMPANY, IFC., PAULSBORO. PU’. J.
Determinations of the oil absorption of pigment flocculating or deflocculating I L absorption is genermixtures show that in general oil absorption is additive. action of the liquids4 The ally expressed as the The graph of oil absorption against pigment pergreater the flocculation the number of cubic centicentages in a mixture of pigments is a straight line. greater the liquid absorption, meters of oil or other liquid A slight exception to this is found in mixtures containsince the larger the pigment required to s a t u r a t e 100 ing active pigments such as red lead or zinc oxide. If aggregates the larger is the grams of pigment or filler, and oil absorption is additive, oil absorption is dependent p o r e v o l u m e . Grohn5 has is generally determined by the emphasized the importance Gardner-Coleman methodU2 essentially on the specific surface of the pigment and the interfacial tension or affinity between the pigment of the affinity between the The term “oil absorption’’ and the oil. pigment and the oil, not only h a s been used b o t h a s a in regard t o oil absorption, specific term denoting the absorption of oil, and as a general term denoting the absorp- but also in regard to the character of the paint.5 Blom6 has shown that for mixtures of chrome oxyhydrate tion of any liquid. I n order to avoid confusion, the terms “oil absorption,” “water absorption,” “benzene absorption,” green with barytes or blanc fixe the graph of oil absorption etc., will be used according to the liquid absorbed, and the against the percentage composition of the pigment mixture is a straight line. This means that oil absorption is additive; term “liquid absorption” will be used in the general sense. Gardner2 considers oil absorption to be relative to the spe- that is, the oil absorption of a mixture of pigments is equal to cific surface of the pigment. The fact that the oil absorption the sum of the oil absorptions of the individual quantities of barytes is 13 while that of blanc fixe is 19 shows that the of each pigment. For a binary mixture: specific surface is an important factor. Klumpp3 advances 0, = A 0 a Bob (1) the opinion that oil absorption corresponds with the pore vol- where 0, = oil absorption of mixture A = per cent of pigment A in mixture ume of the closest packing of the pigment after removal of B = per cent of pigment B in mixture the absorbed air. “Pore volume” may be defined as the total 0, = oil absorption of pigment A volume of voids. Klumpp determines the water absorption o b = oil absorption of pigment B of blanc fixe as 110, and the paraffin oil absorption as 200. Such differences in liquid absorption he explains as due to the This fact implies that oil absorption is not dependent on the pore volume, for the pore volume of a mixture of two powders 1 Presented before the Division of Paint and Varnish Chemistry at is seldom equal to the sum of the pore volumes of the two
0
~~
+
the 76th Meeting of the American Chemlcal Society, Swampscott, Mass., September 10 to 14, 1928. * P a i n t Mfrs. Assocn. U. S., Cwc. 86 (1919). I Klumpp, Farben-Zfg., 32, 2306 (1927).
4
5 6
Klumpp, Farben-Zrg., 33, 1044 (1928). Grohn, Ibid.,33, 1660 (1928). Blom, I b i d . . 33, 1970 (1928).
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327
powders. The fine particles of one powder may adhere to the coarser particles of the other powder, or fit into the interstices between the larger particles. Absorption Determinations with Several Pigment Mixtures and Linseed Oil
'
To investigate further this additive quality of oil absorption, the writer made a series of absorption determinations with several pigment, mixtures and linseed oil. The results are given in Table I and Figures 1 to 5 as indicated below. Silica and drop black were used in the first determination. (Figure 1) Silica particles contrast sharply with those of drop black in size, shape, and surface-energy characteristics. The calculated oil absorptions are found from Equation 1. Prussian blue and barytes (Figure 2) were mixed and the results together with those for the silica-drop black mixture show conformity with the additive rule of Equation 1. Red lead and asbestine (Figure 3) were used in order to determine what effect a soap-forming pigment might have on the oil absorption of a pigment mixture. I n this case there is a decided deviation of the actual values from the calculated values, which is apparently due to the soap-forming properties of the red lead. Soaps generally lower the absorption, so that this explanation seems logical. The effective absorption by asbestine is the absorption by the asbestine if the additive rule is met and the absorption by the red lead is constant. It may be found graphically by projecting a straight line from the 100 per cent red-lead point through the point for a mixture to the 100 per cent asbestine axis, which it intersects a t the effective absorption value. The lower line in Figure 3 illustrates this. Or Equation 1 may be solved for the absorption of asbestine using the observed values for the absorp tion by the mixture. The effective absorption of red lead may be calculated in a similar manner, but since it is more reasonable to assume a constant value for the absorption of the red lead than for the asbestine, the effective absorption of the asbestine is the more interesting. The effective absorption, being a projection, is not very accurate, but it is a measure of the maximum degree to which the absorption of either pigment may have been lowered. I n the determinations made with a red lead and silica mixture (Figure 4) a deviation from the calculated values similar to that shown in the preceding experiment confirms the opinTable I-Absorption Determinations with Various Pigment Mixtures and Linseed Oil
COMPOSITION OF MIXTURE Silica Per cent
100 75 50 25
Drop black
Per cent 25 50 75
100 Barytes ~. 100 75 50 25 Red lead 100 75 50 25 Red lead 100
75 50 25
Zinc oxide 100 75 50 25
OIL ABSORPTION5 Found Calculated Cc./IOO g . b Cc./lOO R. 26.15 34,25 33.71 41.50 41.33 49.45 48.92 56.50
EFFECTIVE ABSORPTION OF
INERT
Cc./lOO E .
Blue 25 50 75 100 Asbestine 25 50 75
13.25 36.00 58.75 81.85 104.25
36.01 58.75 81.51
9.50 11.90 17.00 23.30
16.58 20.05 23.35
19.1 24.5 28.0
14.20 17.82 21.99
16.7 21.3 25.3
100 Silica
30.60
25 50 75 100
11.30 15.40 21.50
o m
26,15
Barytes
29.90 25.35 25.73 12.0 21.20 21.57 12.5 75 16.46 17.40 12.0 100 13.25 The experimental error in determining absorptions varies from 0.1 to 0.5 cc. according to the pigment and vehicle used. b Cubic centimeters of oil per 100 grams of pigment. 25 50
ion that the deviation is due to soap formation rather than to change in pore volume. With a mixture of French-process zinc oxide and barytes (Figure 5), the variations from the calculated values are small, but the largest variation is when the barytes content is 75 per cent. This contrasts with the case when red lead is used, when the largest variation was with a red-lead content of 75 per cent, and may indicate that lead soaps diffuse more slowly through the oil than the zinc soaps. Inasmuch as zinc oxide does not form soaps with linseed oil so rapidly as red lead, this is probably the reason the absorption curve in Figure 5 does not sag so much as those of Figures 3 and 4. Deviations from Additive Rule
This contrasting behavior of the zinc and lead soaps indicates that with linseed oil and zinc oxide the limiting factor in regard to the absorption curve is the amount of soap formed, whereas with linseed oil and red lead it is the rate of diffusion of the soap through the oil to the surface of the inert pigment. In other words, zinc soaps diffuse rapidly in linseed oil but form slowly, and lead soaps form rapidly from red lead but diffuse slowly. If fatty acids were added to linseed oil, we would expect that more zinc soap might be formed and the zinc oxide-barytes absorption curve would be lowered. But we would not expect the red-lead absorption curve to be lowered, since the amount of soap formed is not the limiting factor. To test this theory, zinc oxide and barytes (Table I1 and Figure 6) and red lead and asbestine (Table I1 and Figure 7) were used with linseed oil to which had been added 10 per cent of linseed oil fatty acids. The results show that the absorp tion curve of the zinc oxide mixture was slightly lowered, while that of red lead was raised (compare data for same mixtures in Tables I and 11). The raising of the latter may be due to a lessening of the diffusion rate of the soap. The increase in oil absorption of the asbestine and zinc oxide when used with the fatty acid mixture may be caused by a decreased
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fusion of soaps in vehicles, and the relative cohesion between the particles of different pigments. With inert materials the additive quality of oil absorption is exact enough to permit its use as a method of quantitative analysis of binary powder mixtures, when the absorptions of the individual components of the mixture are known. Relation between Specific Surface of Pigment and Interfacial Tension between Pigment and Oil
g ZINC onm. 0
26
00
16
loo
affinity between the pigment and the vehicle (see Equation 2), while the lowering of the absorption for red lead and barytes may be due to increased affinity. Table 11-Absorption Determinations w i t h P i g m e n t Mixtures a n d Linseed Oil P l u s Linseed Oil F a t t y Acids EFFECTIVE ABSORPTION COMPOSITION os MIXTURE OIL ABSORPTION Zinc oxide Barytes Found Calculated OF INERT Cc./lOO g. Cc./lOO g. Cc./lOO E. Per cent Per cent 32.50 100 27.00 27.03 75 25 10.6 21.70 21.55 10.9 50 50 6.8 14.07 16.07 25 75 100 10.60
8.90
12.60 17.25 24.25 31.40
14.48
20.16 25.77
23.7 25.6 29.4
The additive quality of oil absorption indicates that oil absorption is a function of powder surface area. The variation in liquid absorption of the same powder with variation in the liquids absorbed proves that the affinity between the powder and the liquid is an important factor in determining the liquid absorption. Assuming that the powder surface and the affinity between the powder and the liquid are the controlling factors governing liquid absorption, an attempt was made to find the mathematical relation between these quantities. The only specific data available on the affinity between a solid and a liquid were those of Bartell and Osterhof' giving the adhesion tensions of silica and carbon black for several liquids. Adhesion tension is equal to the difference between the surface tension of a solid and the interfacial tension between the solid and the liquid. It is not a measure of wettability as the paint man sees wettability. What the paint man calls "wettability" is the ability of a liquid to displace air from a pigment. Adhesion tension measures the ability of one liquid to displace another from a pigment or powder. The adhesion tension of benzene and silica is about the same as that of water and carbon black, but in the language of the paint man benzene wets silica much better than water wets carbon black.
To be sure that tAAese deviations from the a' litive rule were not caused by the method by which the pigments were mixed, determinations of oil absorption were made after the red lead and asbestine had been thoroughly mixed in the dry state, and also by adding the second ingredient of the mixture after the first ingredient had been saturated with oil. N o difference in the results was found. Table 111-Absorption Determinations w i t h Red Lead-Asbestine Mixture in Lubricating Oil COMPOSITlON OF MIXTURE OILABSORPTION Found Calculated Asbestine Red lead CC./IOO C C . / l O O g. P e r cent Per cent . .E. 100 12.45 19.57 20.84 75 25 29.22 50 50 29.75 37.61 25 75 36.50 100 46.50
A mineral lubricating oil was used with red lead and asbestine, with the result,s shown in Table I11 and Figure 8. The irregular variations between the actual and calculated values mayebe due to tendencies of the asbestine and red lead to cohere. The absorptions of both the red lead and asbestine are higher with the mineral oil than with linseed oil, indicating that the mineral oil does not have such good wetting qualities. It is probable that the less the wetting power of the liquid, the more effective the cohesion between the powder particles becomes, and the d o r e marked will be the irregularities from the additive rule of oil absorption. Comparison of Table I11 with the figures for the same mixture in Table I shows that the mineral oil does not produce a sag in the absorption curve as does linseed oil, which supports the assumption that the sag is produced by soap formation. Value of Oil Absorption Curves
The study of the oil absorption curves of pigment mixtures in various vehicles should be helpful in estimating the relative activity of pigments, and of vedicles, the relative rate of dif-
ma.
8.
With the liquids for which % UBVSIhT Bartell and Osterhof had de*' " " lm termined adhesion tensions with silica and carbon black, liquid absorptions were taken with 300-mesh pulverized sand, carbon black, and drop black. The results are given in Table IV. The liquid absorptions of volatile liquids were determined in a bottle instead of in the usual open vessel. Table IV-Relation
LIQUID Water Aniline Hexane Benzene Carbon tetrachloride Decalin a-Bromonaphthalene
between Absorption Adhesion T e n s i o n a n d Liquid
SILICA Adhesion Liquid tension absorption Dynes/ Cc./lOO g. sq. cm. 82.82 26.80 82.00 29.80 42.13 43.07 52.43 38.40 40.69
49.50
41.92
38.50
CARBON BLACK DROPBLACK Adhesion Liquid Liquid tension absorption absorption Dynes/ Cc./lOO g. Cc./lOO g. sq. cm. 54.74 330 98.25 80.32 60.51 73.50 69.93 317 81.08 238 73.70 89.45 76.38
217 257
~~
7
Bartell and Osterhof, IND. END. CHRM.,19, 1277
(1927).
67.90 69.75
IND USTRIAL A N D ENGINEERING CHEMISTRY
April, 1929
The logarithms of the adhesion tensions plotted against the logarithms of the absorptions approximated a straight line, Figures 9, 10, and 11. The tangent of the slope of the line for silica was -0.733; for drop black, -0.725; and for carbon black, -0.790. These lines represent equations of the form: L = S/A“ (2) where L is the liquid absorption, S is a surface constant depending upon the effective surface of the powder, A is the adhesion tension, and n is a constant (approximately 0.75). 5c
4I
1c
3:
X
25 5
