INDUSTRIAL A N D ENGINEERING CHEMISTRY
Kovember, 1929 l
i
l
l
l
~
l
!
l
1121
l I20
Table V-Effect of Composition of Liquid5 (Volume of silica, 35.9%; volume of liquid, 64.1%;) BUTYL TIME Hours 2 18
Days 2 4
TCRPEX- OELLO-
WATER BUTANOLTOLUEKE TINE
!SOLVE
70
%
3.1 6.3
Trace 7.6
Trace Trace
Trace 2.2
Trace 7.5
7.3 7.3
17.4 22.8 22.8 23.9 23.9 23.9
Trace Trace 2.2 2.2 2.2 2.2
2.2 2.2 2.2 2.2 3.3 3.3
16.0 25.6 25.6 26.6 26.6 26.6
6
7.3
S
7.3 7.3
10 31
5%
%
7.3
Cellosolve. This is shown in another way by Curve No. XI, where the volume of the pigment is constant and the liquid varied from 100 per cent kerosene to 100 per cent linseed oil. Apparently the volume of the settled pigment paste depends on the composition of the liquid. Literature Cited (1) Beakes, IND. ENO. CEEM.,80, 732 (1928).
The Mobility-Concentration Intercept' J. T. Baldwin SANDURA COYPANY, INC., PAULSBORO, h'. J.
Effect of Wetting Power The mobility-concentration curves of castor oil, HE t e r m "mobilityof Vehicle China wood oil, linseed oil, and lubricating oil with concentration i n t e r silica and drop black are studied. The results agree cept" will be used to Since the degree of disperwith Bingham's prediction that the mobility-concendenote the point a t which the sion and the pore space of a tration intercept is independent of the wetting power pigment are dependent on the mobility would become zero of the liquid used, and that the mobility of a pigmentwhen the mobility is plotted w e t t i n g power or adhesion vehicle system i s a linear function of the viscosity of tension of the vehicle, detera g a i n s t the percentage by the vehicle and the concentration of pigment. Thus weight of the pigment in a minations were made using mobility for any concentration of pigment may be p i g m e n t - v e h i c 1e mixture. vehicles of diverse wetting calculated if the viscosity of the vehicle and the moThe word "mobility" is used powers to see if the mobilitybility-concentration intercept are known. Oil abto denote the ability to flow concentration intercept would sorption varies with the wetting power or adhesion tenafter the yield point (mobilbe in any way affected. It is sion of the liquid. ometer intercept) is reached known that the oil absorption and zero mobility then means varies indirectly with the weta state of immobility. This is the reciprocal of 1,he may in ting power of the oil and that mobility is above zero a t the which the paint man uses the word in connection with the ratio of oil to pigment at the oil absorption point, so that mobilometer. The mobilometer intercept is the point a t which variation of the intercept would be expected. Linseed oil, the prolongation of the straight part of the pressure versus the China mood oil, lubricating oil, and castor oil were ground reciprocal of time curve intercepts the pressure axis. in a laboratory edge-runner mill with silica and drop black, The mobility-concentration curves of clay suspended in and the mobility was determined with a Gardner-Parks mobilaqueous media (3) and of lithopone and linseed oil (6) have ometer. The mobility was calculated from the mobilometer been studied by Bingham, who concludes that the mobility readings by the formula: reaches zero a t a finite concentration of pigment which seems 100,000 intimately related to the pore space in the disperse phase, and M = ( w tlW - t M ) that according to this view the mobility-concentration curve tl - t 2 is completely defined by the fluidity of the medium and the where M = mobility pore space of the disperse phase.
T
Presented before the Division of Paint and Varnish Chemistry at the 77th Meeting of the American Chemical Society, Columbus, Ohio, April 29 to May 3, 1929.
time for plunger t o fall, in seconds pressure on plunger, in grams Subscripts 1 and 2 represent runs in which the time is appreciably longer in 1 than in 2. t = w =
IhTDUSTRIA.LA N D E S ~ I S E E R I S GCHEMISTRY
1122 X o f e on Derit'aiion of Equalion 1-From flow ( 4 ) c =
where
Ringham's equation of plastic
(F - n u l
(2)
viscous deformation F shearing force .f = yield value u = mobility Y = distance between shearing planes ZI
= =
Since in the same instrument r is constant, it may be discarded for relative measurements. Solving (2) for u, I'
11
=
F-f
.(3)
f for a capillary according to Bingham (2) can be calculated from the relation,
the edge-runner mill showed a fairly uniform intercept, there must be a yariable ot'her than viscosity which affects the fineness of grinding, and that variable is the pressure, rate of shear, or angle of shear which the mortar had and the edgerunner mill did not have. At a critical viscosity or wettability this shear factor may assume unusual import,ance. The mobility-concentration intercept evident'ly has possibilities as a method of studying grinding action. Table I-Mobility-Concentration I n t e r c e p t s of Mixtures C o n t a i n i n g Vehicles of Varying W e t t i n g Power VEHICLE PIGMENTMOBILITYIKTERCEPT Per cent SILICA A S PIGMENT
China wood oil
66,7 50.0 66.7 50.0 30.0 64.0 49.0 66.7 54.5 66.7 49.0
Linseed oil where w1 and wz are the rate3 of flow at the shears F1 and F,. Since with the mobilometer the time consumed for the fall of the plunger is i n d i r e c t l y proportional to the rate of flow, if 1 is the time in seconds for the fall, It = 1//1, etc. The shearing force with the mobilometer is 28, the weight on the plunger plus the weight of the plunger, so that ci' = F. Then (4) becomes
Lubricating oil Castor oil Linseed oil
111 CBmR
OIL
OIL
21 LWRICATIXC
131 CAI;:*
141 L l x = D
WOOD
OIL
OIL
Substituting in (a), 1L =
-1.1
100.000
=
(i.
71'111
11
-
"">
t
11
12
The 100,000 is used arbitrarily to increase the ease of handling of M.
Table I shows the results. Figures 1 and 2 show that these oils gave practically the same mobility intercepts regardless of wetting power: 72 per cent for silica and 54 per cent for drop black, or 47.6 per cent for silica and 29.6 per cent for drop black by volume. Lubricating oil varies somewhat from these figures, and this may be due to the high ratio of yield point to mobility, which makes the determination of the mobility less accurate. Effect of Method of Grinding
Linseed oil and China wood oil were ground with silica in a mortar and the mobility was determined in a modified
Bingham-Murray plastometer of the suction type. The same proportioned mixtures and also using castor oil were then ground in the edge-runner mill just as had been the mixtures which were run on the mobilometer. The results (Table I1 and Figures 3 and 4) show that the mill-ground materials give the same intercept within experimental limits with the capillary plastometer as with the mobilometer, but that there is a large difference between the mortar-ground and millground China wood oil-silica mixtures. The intercept for the former is 78 per cent and for the latter 72 per cent. The closeness of the mortar-ground linseed oil-silica intercept to the mill-ground intercept in contrast to the disparity with the China wood oil-silica composition may mean that the more yiscous the vehicle the greater is the degree of dispersion possible by grinding. However, since the mixtures ground on
4.35 17.5 16.3 81 171 12,5 51.7 1.47 4.83 13.7 51.7
72.5
71 60
72 72.8
D R O P BL.4CK h S P I G M E N T
China wood oil Castor oil Linseed oil Lubricating oil
Multiplying both numerator and denominator by 111%
Yo]. 21, KO.1 1
50 0 43 2 34 2 44 6 35 7 45.4 40.7 37.0 44.5 36.0 29.0
3 75 9 4 18 2 2 2 4 2R 32.3 44.4 57.2 28.6 38.5 64.5
cj4 0
54 0 -54.0 5 7 , .i
Effect of Rate of Shear
If the intercept is a measure of pore volume, then with the use of a vehicle having a high specific gravity a lower intercept would be expected, but the intercept expressed on a volume basis should remain constant. Glycerol and silica w e r e ground and determinations of mobility made with a capill a r y plastometer and w i t h a MacMichael v i s c o m e t e r . (Table 111) The intercept is lower than would be expected, being a t 40 per cent by volume contrasted with 47.6 per cent when oils were used. This is probably because of the difficulty in wetting the silica with the glycerol-that is, the wettability is a t such a point that the amount and method of grinding are limiting factors controlling the intercept. The difference in intercepts as determined by the MacMichael instrument and the capillary plastometer may be due to the different rates of shear. Oil Absorption-Mobility Concentration Relationships
In terms of oil absorption-i. e., cubic centimeters of oil per 100 grams of pigment-the mobility-concentration intercept of silica would be 31, and of drop black 87. These figures, in comparison with the linseed oil absorption of silica of 22.5 and of drop black of 47, are decidedly above the amounts of vehicle necessary to secure a paste. Therefore, it seems likely that a t very low mobilitieq and high concentrations of pigment
ISDUSTRIAL A N D EXGIiVEERIAVG CHEMISTRY
Soveniber, 1929
the mobility-concentration relationship is not linear but curves off to a point approaching the oil absorption. The high yield values (mobilometer intercepts) and low mobilities of this region of the curve make it difficult to study with a suction plastometer. Since some types of commercial paints leave filnis containing concentrations of pigment which would he in the region of curvature, this region is of conqiderable interebt. of M e t h o d of Grinding on Mobility-Concentration Intercept of Silica-Vehicle Mixtures VI1IICI.I. PICMEKT ~ I O B I L I TIY \TERLPPT Per cent
Table 11-Effect
(rROl.\I)
China wood oil
Linseed oil
65.0 18.5 66.7 50.0 66.7 50.0
3 57 8.2R 2.1 5 6 5.27 25.5
66 7
5 89 33 0 1 05
50 0 60 0 0 0 66 7 18.1 0.0 66.7 54.2
Castor oil China wood oil Linseed oil
--,,
IU MORTAR
-
.)
d8.2 71 5
70
>
70 0
R O 1.63
72 0
i o
22 1
8.9
71.0
33.3
Tahle Ill-Mobility-Concentration Intercept of Glycerol-Silica as D e t e r m i n e d b y Two [ n s t r u m e n t s PIGMENT MOBILITY ISTERCEPT P C R CENT
MACYICHAEL
11.1 18.9 50.0
19.6 39.5 0.0
63.0
C . I P I L L A R Y PLASTO."IETER
49.ti 39.5 0.0
1.32 2.74 8.0
38.7
Hardy aiid Sottagtl (6) have shown that when steel is joined to steel and copper to copper with the same adhesive the joint between the steel surfaces is the stronger. but when -tee1 is joined to copper the strength of the joint which breaks close to the copper surface is the mean of the strength of the steel and copper joints instead of being the strength of the weaker joint. This made theni of the oDinion that the att r a c t i v e force of the steel must extend t h r o u g h the layer of adhesive so as to affect t h e s t r e n g t h of the joint at the copper surface. When pigment parti131 cles are brought in close I '\\ contact as they are at high concentrations. they inay exert their attraction through their vehicle upon each other so as to form a structure. The structure would be such that the particles would exs b c c ercise a minimum attractive force. rearrangIng them and causing a decrease in the mobility. This ma;. explain the probable curvature of the mobility-concentration relationship at high pigment concentrations. For the concentrations of pigment in which the mobility relationship is linear, the niobility for any concentration of pigment may be calculated: 1,
X
=
WZ.V
m - I
17)
1123
where M = mobility a t Y per cent of pigment concentration m = mobility of vehicle I = intercept S a f e on Derioalion of Equation 7-Since the relation between A! and N is linear with intercepts on both the .Vf and x axes, it is obvious that the case is a standard one of the form as
+ by + c = 0
This becomes 1.1f
+ mv
(SI
- I m = (1
Solving for .M, ms
-11 = m
--
(7)
I
I t is also possible to solve this relationship for I and thus determine the intercept with o n l y o n e run on the plastometer or mobilo n i e t e r provided the iiiobility of the liquid is known. Table IV, showing a c o r r e s p o n d e n c e bet w e e n oil absorption and yield point, illustrates the influence of wettability or adhesion tension on the degree of dispersion. The less the oil absorption the greater is the wettabilityand theless the yield point. Yield point and oil absomtion then arc measures of the degree of dispersion, but the mobility-coricentration curve measures the rate of change of mobility with change in concentration and thus is entirely independent of the degree of dispersion or yield point. The fact that the mobility-concentration relation is linear nieans that the di+ persing power of the pigment is constant regardless of what that dispersing power is but when that dispersing power is changed by the cohesion between the particle.. the relation becomes curved. Table IV-Relation
b e t w e e n Oil Absorption a n d Yield P o i n t SILICA" DROPBLACK" OIL Yield Oil Yield Oil point b absorbed point absorbed Jfobtlometer-gramc Mobilomeler-grams Linseed 55 22.3 200 47 China wood 103 25.0 Castor 135 27.5 Lubricating 700 28.5 900 54 a All oil and silica mixtures contained 66 per cent silica and all droii black mixtures, 44 per cent drop black b Yield point is equivalent of mohilometer Intercept, and IS not true yield point
;;: E
Very fine grinding in a viscous vehicle may subdivide the pigment into a state that is finer than natural, while coarse grinding in a viscous vehicle may result in failure to separate some of the pigment particles as finely as is natural. The film of air around the particles and the ability of the vehicle to replace the air would be importslit factors in defining t h(, effectiveness of the grinding. This natural equilibrium or state of dispersion of the pigment for which the mobility-concentration intercept nieasurethe pore space is apparently a function of the cohesion between the pigment particles. This cohesion depends, not only on the chemical structure, but also on the size and shape of the particles, since this defines the effectiveness of the field< of attraction between the particles. There exists an approviniate relation between a d h e h i
1124
INDUSTRIAL AND ENGINEERING CHEMISTRY
tension and oil absorption (I), and as the pigment-oil mass obtained a t the end point of the oil absorption test is not much above zero mobility, the intercept was calculated in oil absorption terms (cubic centimeters of oil per 100 grams of pigment) and the adhesion tension corresponding to those terms was postulated as an approximate measure of cohesion. For silica this was 60 dynes per square centimeter, for drop b l a c k 45 dynes per square c e n t i m e t e r , and for lampblack 71 dynes per s q u a r e c e n t i m e t e r . These figures indicate that lampblack is harder to deflocculate than drop b l a c k o w i n g to its higher cohesion, which of course is a well-known fact. The difference bet w e e n the adhesion tension and the cohesion should represent the d i s p e r s i n g p o w e r of a liquid. The natural state of dispersion in which the mobility-concentration intercept represents a pigment is dependent on the cohesive properties of the pigment. Therefore, we should expect a tendency for pigments to settle to a cake with a pigment concentration similar to that a t the mobility-concentration intercept. However, as the adhesion tension of the liquid in which the pigment is suspended in-
Vol. 21, No. 11
creases, so will the percentage of pigment in the cake increase as a result of finer dispersion. Chemical changes and adsorption going on in a paint may alter the adhesion tension and the cohesion, thus raising and lowering the mobility as well as the yield point. If the yield point changes without change in the mobility, altering of the adhesion tension alone would be suspected, or if the mobilityconcentration intercept changed without change of yield value, alteration of cohesion would be probably alone the cause.
.
Conclusions
1-The mobility-concentration intercept is independent of the wetting power of the vehicle, but is dependent on the grinding conditions. 2-The intercept is probably a measure of the pore volume of the pigment in a state of dispersion determined by its own characteristics of cohesion. 3-The mobility-concentration relation is linear except in regions of pigment concentration approximate to the oil absorption. I n these regions the cohesion forces residual in the pigment probably become more active, thus producing curvature. 4-The wetting power of the vehicle is a very important factor in determining the dispersion of the pigment and consequently the yield point or shape of the plasticity curve. This means that, for the same pigment mixed with a series of vehicles, the yield point will tend to vary directly with the oil absorption. Literature Cited (1) (2) (3) (4) (5) (6)
Baldwin, IKD.ENG.CHEW,21, 326 (1929). Bingham, “Fluidity and Plasticity,” p. 219 (1922). Bingham, Ibid., p. 221 (1922). Bogue, “Colloidal Behavior,” p. 432 (1924). Bogue, Ibid., 441 (1924). Hardy and Nottage, Proc. Roy. SOC.(London), llOA, 62 (1926).
A Method of Studying the Reactions in a Portland Cement Kiln’ William N. Lacey and Hubert Woods CALIFORNIA INSTITUTE
T
OF
TECHNOLOGY, PASADENA, AND RIWRSIDECEMENT CO., h
S ANQELES,CALIF.
H E material entering the rotary kiln for burning Port- 2CaO.SiOn are the most desirable ones in the cement from land cement consists of a finely ground mechanical the viewpoint of strength development. The formation of mixture of limestone and clay, or of chemically similar 3CaO.Si02 is the most difficult to carry to completion. In a materials. As the charge travels forward through the kiln mix carrying a higher percentage of CaO it is necessary t o i t is gradually raised in temperature, absorbing heat from the heat the charge to a higher temperature and perhaps hold it hot gases traveling in a countercurrent. During this process there for a longer time in order to insure completeness of the following changes occur in the order named: (1) evapora- reaction. If this is not accomplished, some uncombined caltion of free moisture; (2) removal of combined water from cium oxide will be left in the product. This is undesirable, hydrous clay; (3) removal of carbon dioxide from magnesium not only because it results in a smaller percentage of 3Ca0.carbonate; (4) removal of carbon dioxide from calcium SOz, but also because the free lime, when present in any carbonate; (5) reaction of calcium oxide with clay t o form large extent, causes unsoundness in the cement. Since the chemist is interested in these processes of pro4Ca0.A1203.Fe203, 3CaO.Al203, and 2Ca0.Si02; (6) reaction of remaining CaO with 2CaO.Si02 t o form 3Ca0.Si02. duction and recombination of calcium oxide in the kiln charge, These steps undoubtedly overlap, and two or more may be the percentage of free lime present a t various stages of the process affords a means of following the course of these reacproceeding simultaneously a t a given point in the kiln. The last three reactions are probably of greatest interest tions. A method of determining uncombined calcium oxide to the chemist who is concerned with conditions of operation has been described by Lerch and Bogue (2, b) which has proved of the burning process. The compounds 3Ca0.Si02 and very satisfactory for this purpose. The method depends upon a titration of the lime with ammonium acetate in absolute 1 Received June 17, 1929. Presented at the meeting of the Pacific alcohol solutions, calcium acetate and ammonia being formed Division of the American Association for the Advancement of Science, and the latter removed by heating, allowing the use of phenolRerkeley, Calif., June 19 to 22, 1929.
