SATTWATOR WHERE THE
FELTIS PASSED OVER HEATED ROLLERS AND RECEIVES SUCCEJSlVE DIPPINQS IV HOTASPHALT
.4
DEEPTANK08‘
The ielt ia astrwated with nppioiimatel~twice itr weight of asphalt.
Viscosities of LiquidSolid Systems INFLUENCE OF DISPERSED PARTICLES R. N. TRAXLER, n. E. SCHWEYER, AND L. R. MOFFATT The Barber Company, Inc., Maurer, N. J.
HE properties of systems composed of solid particles dispersed in liquids are of interest because of the widespread use and importance of such mixtures. In the bituminous indutry, for example, pulverulent mineral is frequently added to the bitumen in order to increase its “stability” or resistance to deformation. If the liquid present is viscous, and the concentration of mineral particles is not too great ( I ) data concerning the viscosities of the liquid and of various liquid-solid mixtures can be used to evaluste the “stabilizing effect” of different powders. Most steam- and vacuumrefined asphalts softer than 40 to 50 penetration (100 grams, 5 seconds a t 25” C.) are essentially viscous liquids: that is, their
T
A linear relation exists between the logarithm of the viscosity of viscous mixtures made from a particular liquid and a particular pulverulent solid and the volume per cent of the solid present. An index is given which evaluates the increase in viscosity caused by the addition of different mineral powders. This index measures the percentage increase in viscosity resulting from a one per cent increase in the volume of solid. The stability indices for a number of different powders are given. Further, it is shown that the viscosity of a viscous mixture of a particular Gowder dispersed in a given liquid is inversely proportional t o the average thickness of the films of liquid separating the particles (as measured by the average void diameter). 489
viscosities a t 25’C. do not vary appreciably with tlre applied stress. They have viscosities of the order of 1 0 6 poises or less. Although asphalt of this type and consistency was used in most of the investigations to be described here, some measurements were made with a softer bitumen and R synthetic resin possessing viscosities of t.he order of IO‘ wises. Several methods have Iieen discussed and described recently (4)by means of which the viscosity of highly viscous liquidsandnrixturcsofthem with mineral powders can be rneasured accurately in absolute units at atmospheric teniperatnres. In order to study the efficiency of a yarticular filler in increasing the viscosity of a liquid, it has been found n e c e s s a r y to consider the phase volume
VOL. 29, NO. 5
INDUSTRIAL AND ENGl:NEERING CHEMISTRY
490
"'/VISCI751TY-COMPDSIITION
CURVES
ASPHALT-MINERAL POWDER MIXTURES
1
Constants A and C may be determined by the method of averages for each liquid-solid system and then used to calculate the viscosity a t the various compositions. The agreement between the experimental and calculated viscosities shown in Table I is well within the limits of experimental error.
Stability Index In a given liquid-solid system for which Equation 1 holds, the percentage increase in viscosity caused by an increase in the volume per cent of solid is given by the following equation: "/,increase = 100
i t - - -i
' 100 ('a nL ) =
)
'1' - 1
where 11% and q1are the viscosities of the liquid-solid mixtures at F%and F , volume per cent of powder, respectively, and F, is greater than F,. Percentage change is a function of the slope '4 of Equation 1 becRnse
1
qz/ni = 10"iF? - PI)
F~QUKE 1. INPLUENCE OP DlsPERsEn PART~cLEs ON VI~COSITIES OF Lisnto-Soun SYSTEMS
yo change
Experimental Procedure In studying a filler, four mixtures of the filler and liquid were prepared. Table I gives the volume composition and viscosity data for mixtures of four different fillers and a vacuum-refined Venezuelan asphalt with a Viscosity of 3.18 x lo8 poises a t 25" C. (51 penetration a t 25"C., 100 grams, 5 seconds; 51.7*C. Ring and Ball softening point). The dry powder is thoroughly dispersed in the molten asphalt by hand stirring, and the hot mixture poured into a falling coaxialcylinder viscometer. After the instrument and contents have cooled, excess asphalt is trimmed away and the loaded viscometer is placed in a constant-temperature bath a t 25" C. for one hour before the viscosity is determined.
Solid,
Limestonedust
Blsekslata
F 5
io
16 20 5 10
16
ao
Viseasity of Mintue, 9 Erptl. Caled. 4.23 5.06 6.15 7.86 4.05 6.12 8.24
11.0
Filler
4.05 Gray-green 6.05 mlOB 6.31 7.88 4.46 Diatomaceous 6.13 esrth 8.45 11.6
(51
Consequeutly, Equation 2 beconies
composition of the Iiller-liquid system rather than the composition by weight.
Filler
('4
= 100 [ IOW+
- Fd - 1)
(6)
whicli states that the percentage increase in the viscosity of B particular liquid-solid system is constant for a constant increase in the volume per cent of solid. If this increase in volume per cent of solid i s made equal to one (F2 - F, = l), an expression is obt.ained which evaluates the percentage change in viscosity for a one per cent increase in the volume per cent of a particular solid. This expression is a quantitative index of the stabilizing ability of a particular solid and is as folloas:' Btabilitg index (X. 1.) = 100 ( 1 0 A - 1)
(7)
I t is recommended that three or four points 011 the viscositycomposition curve be determined in order to establish accurately the value of A. The stability indices for a number Qf poaders are s h o w in t,hc table which folloas. I
S. I. is readily oaleulated as follow^: S. I.
=
100 (sntiloa oi A
- 1).
Visoosity Of Solid, MiXtU'a, F Erntl. Calod. 5 5.20 8.22 15 12.6 20 21.7 2.4 4.66 4.8 6.46 7.2 8.70 9.6 12.3 10
5.14 8.20 13.1 20.9
4.57 6.34 8.80 12.2
When the data in Table I are plotted on senii-log paper (Figure 1) a linear relation is found to exist between the logarithm of the viscosity and the volume per cent of solid present in visoous mixtures made from a particular liquid and a particular solid. This relation may he expressed as: where
q =
C 10AF
n = viscosity, poises F = volume of solid, yo A , C = constsnts
(1)
LOADED TRlIh
OF
CRUDE ASPA.AIX.\T TRINIDAD LAKE
INDUSTRIAL AND ENGINEERING CHEMISTRY
MAY, 1937
491
DUMPINGTRINIDAD CRUDEASPEALT INTO S T E A MSTILLS FOR REFININQ The refining operation consists chiefly of beating the crude asphalt a t L moderate temperature t o drive off water.
Powder Limeatone Graphite LNebraska) silica [ y a r t s ) Portlan cement Clay
5. I. 4.5 4.5 4.8 5.3 5.7 6.6
Powder Black slate Talc Gray-green mica Diatomaceous earth Wood flour Asbestos
s. I. 6.0 7.1 9.8 15 16 21
The four minerals shown in Table I and Figure 1 were also compounded with (a) a vacuum-refined Venezuelan asphalt with a viscosity of 7.7 X 104 poises a t 25" C. (300 penetration a t 25" C., 100 grams, 5 seconds; 110 secondsfloat a t 65.6' C.) and ( b ) a viscous, nonreactive Bakelite resin possessing a viscosity of 6.9 X 104 poises at 25" C . The viscosities of the mixtures were also determined a t 25" C. Using Equation 7 , the stability indices of the four fillers were calculated as follows : Mineral Filler Limeatone Slfbte Mi08 Diatomaceous earth
Hard Asphalt 4.4 6.4 9.8 14.6
Soft Asphalt 4.2 6.0 9.5 14.7
Bakelite Resin 4.3 6.4 10.2 14.6
These data indicate that the stability index for a pulverulent solid is independent of the nature and viscosity of the liquid present, provided no chemical reaction occurs between the liquid and dispersed solid.
Relation between Viscosity of Liquid-Solid Mixtures and Film Thickness of Liquid A study of the stabilizing effects of various kinds of mineral powders on liquids raises the question as to what property of the pulverulent solid is the determining factor in causing the increase in viscosity as more of the powder is added. The physical properties of twenty-three mineral powders were determined and the viscosities of mixtures made by combining them with different asphalts were measured. These studies have led to the conclusion that the viscosities of mixtures of a particular liquid and solid are inversely proportional to the average void diameter of the dispersed solid a t the percentage of voids represented by the rolume per cent of liquid present in the mixture, that is:
~ n ,= C / d (8) where vrn = viscosity of mixture at 25" C., poises d = av. void diameter of powder as present in mixture,
microns C = a constant for a particular liquid and a particular solid
The validity of Equation 8 is illustrated by the data in Table 11. The California asphalt was vacuum-distilled and had a viscosity of 3.22 X loe poises a t 25" C. (55 penetration a t 25OC., 100grams, 5 seconds; 47.2" C. Ring and Ball softening point), the Venezuelan asphalt was vacuum-refined and had a viscosity of 3.18 X loe poises a t 25" C. (51 penetration a t 25"C., 100 grams, 5 seconds; 51.7" C. Ring and Ball softening point), The average void diameters were calculated by the equation (6) where
log d = mB f b d = av. void diameter, microns B = per cent voids
(9)
m, b = constants
TABLE11. CORRELATION OF VISCOSITIES OF MIXTURES WITH AVERAUE POREDIAMETERS Mineral Powder
Red slate
Trap rock
Limestone
Silica
Solid, F
Viscosity of Mixtme, qm Poises X
Av. Pore Diam., d
Vol. % 10-6 California Asphalt 10 5.14 15 6.35 20 7.85 25 9.70 30 12.0 10 4.95 20 7.69 30 12.0 Venezuelan Asphalt 5 4.05 10 5.05 15 0.31 20 7.88 10 5.25 15 6.80 19 8.36 23.8 10.7
rlmd
-
Microns
4.31 3.46 2.78 2.24 1.80 12.8 8.27 5.34
22.1 22.0 21.8 21.7 21.6 63.3 63.6 64.1
16.5 13.2 10.1 8.55 9.91 7.96 6.40 5.42
66.8 66.7 63.7 67.4 52.0 54.1 53.5 58.0
C
492
INDUSTRIAL AND ENGINEERING CHEMISTRY
By means of Equation 9 it is possible to calculate the average void diameter of certain compacted powders over a wide range of void contents after having determined experimentally the relation a t some convenient void content. As pointed out previously ( 2 ) , Equation 9, with a value for slope m of 0.019, will hold for a large number of mineral powders. However, for powders with unusual particle shapes or nonuniformity of particle shape, it is necessary to determine experimentally the average void diameter a t different void contents. Further, it is admitted that the relation given by Equation 9 does not hold for very low void contents since the plot of log d vs. per cent voids must curve in the region of very low per cent voids in order to pass through the origin. But, in the work discussed here, we are not interested in mixtures where the volume per cent of liquid is very low because such systems are non-Newtonian or plastic. The value for C of Equation 8 for seventeen of twenty-three mineral powders (thirty-two of forty-four liquid-solid combinations) studied showed an average deviation of less than 6 per cent when the average void diameters of the powders as present in the mixtures were calculated by means of Equation 9; twenty combinations showed less than 2 per cent deviation. An average deviation of 6 per cent is considered satisfactory because of the experimental error encountered in measuring the void content and permeability (void diameter) of the compacted powder and the viscosities of the asphalt and mixtures. Of the six mineral powders (used in twelve combinations) that gave an average deviation for G greater than 6 per cent, all had unusual particle shapes or showed irregularity of particle shape (3) as measured by the ratio of the three axial
VOL. 29, NO. 5
lengths. Since Equation 9 did not hold for these powders, experimental data a t various degrees of compaction had to be obtained and values for the average void diameter of the powder? as present in the mixtures, interpolated from the curve for per cent voids us. void diameter. When these interpolated values for d were used in Equation 8, the deviation of C for a particular liquid with a given solid for all combinations was less than 6 per cent. The data obtained from a study of forty-four combinations of different liquids and mineral powders indicate that the absolute viscosity of any system is inversely proportional to the average void diameter of the pulverulent solid as present in the mixture. The average void diameter is a secondary property of a pulverulent solid and is influenced by such primary properties as particle size, particle size distribution, particle shape, and regularity of particle shape. Consequently, these primary properties of the powder will indirectly influence the viscosity of liquid-solid mixtures through their effect on the average void diameter.
Literature Cited (1) Traxler, R.N.,IND. ENQ.CHIOM., Anal. Ed., 8,185 (1936). (2) Traxler,R.N., and Baum, L. A. H.,PhysiCs, 7,9 (1936). ENG. (3) Traxler, R. N.,Baum, L. A. H., and Pittman, C. U., IND. CHEM.,Anal. Ed., 5,165 (1933). (4) Traxler, R. N., and Schweyer, H. E., Proc. Am. Soc. Testing Materials, 36,11,518 (1936). RECEIVED Ootober 29,1936. Presented before the Division of Colloid Chemistry &tthe 92nd Meeting of the American Chemical Society, Pittsburgh, Pa., September 7 t o 11, 1936.
Thermochemical Examination of Nitrocellulose P. R. MILUS E. I. du Pont de Nemours & Company, Inc., Wilmington, Del.
S
INCE discrepancies exist in the published values for the heats of formation of nitrocelluloses of various nitrogen contents, thermochemical constants calculated from these data are not very reliable where accuracy is essential. Numerous calorimetric determinations,, gas analyses, and calculations of the equation of decompositlon and temperature of explosion were made on nitrocelluloses of 12.62 to 13.45 per cent nitrogen content. The heat of explosion and gas analysis data, together with the most recent data on the heats of formation of the gases formed by the explosive decomposition, were used to calculate the heats of formation of these nitrocelluloses. The heat of formation can be expressed by the following formula:
F, = K," - El, where F, = heat of formation, C, K," = sum of heats of formation of products of explosion, C* E, = heat of explosion, C,
Materials and Apparatus The nitrocelluloses, of 12.62 to 13.45 per cent nitrogen content, used in these experiments were of regular plant manufacture. The nitrogen content was determined by the du Pont nitrometer
method and is reproducible by 10.02 per cent nitrogen. Each sample was dried 24 hours at 40" to 50' C. and 2 hours at 100" C. to ensure complete dryness. The calorific value or heat of explosion, &, was determined in a calibrated calorimetric apparatus. The bomb (Fi ure 1) of 35cc. capacity was charged with 3.4 grams of nitrocelfulose. Ignition was obtained from a &volt storage battery usin 0 10 ram of nitrocellulose as a primer charge. This corresponfs tb a foading density of 0.1. The temperature rise, 3.5' to 5.0' C., was measured by means of a Beckman type thermometer. The permanent gas volume was measured by allowing it to exDand into an evacuated calibrated system. The increase in prkssure was noted and the gas calculated to cubic centimeters per gram at standard temperature and pressure. The water roduced was expelled from the bomb by heating it to 5 0 4 0 " and the vapors were absorbed by calcium chloride contained in a U-tube and calculated to cubic centimeters per gram (gaseous) S. T. P. Analysis of the permanent gases, which consisted of carbon dioxide, carbon monoxide, methane, hydrogen, and nitrogen, was made by means of a gas analysis apparatus according to standard procedure for gasesof this type.
8,
The results thus obtained--&, permanent gas volume, gaseous water, and gas composition-were used to calculate the equation of decomposition and the Centigrade temperature of explosion for nitrocelluloses of 12.62 to 13.45 per cent nitrogen content (Table I). -
