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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 OF
T
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.
ILVDUSTRlAL AND EAVGISEERIiVG CHEMISTRY
1126
1-01, 21,
so.11
FIGURE 5
0
10.
20'
3s
.w' co' rmw r n s t n m ~ cLND
40'
DISTANCE
w
90'
iud
since ignition loss persists in appreciable amount to within 5 feet of the kiln front, whereas the lime free to recombine becomes very low several feet farther back. The effects of a change in firing conditions are illustrated by Figure 5. Results obtained in the preheating zone are little different from those in Figure 4. Subsequent calcination is slower and recombination of the lime is not completed, producing an unsatisfactory clinker. Under these conditions the recombination of the lime appears t o be the slow process, lagging behind the calcination of the calcium carbonate. Since rotary kilns vary in design or dimensions, and operating conditions may differ, the results given above serve only to illustrate the use of the method. The curves given may only be considered representative of the specific con-
ditions prevailing. The method would seem, however, to be capable of yielding interesting and valuable results regarding the influence of the various factors involved in kiln operation. Acknowledgment
John Treanor, president of the Riverside Cement Company, and Earle JIacDonald, general superintendent, have given their hearty support and cofiperation in this investigation. Literature Cited (1) Lerch and Bogue, IND. ENG CHEX.,18, 739 (1928). (2) Steinour and Woods, Rock Pvoducl?, 33, 74 (1929)
Reduction of Tricalcium Phosphate b y Carbon Effect of Silica and Alumina on the Reaction1 K. D. Jacob, D. S. Reynolds, and W. L. Hill FERTILIZER AND FIXSD NITROGEN IKVESTIGATIONS, B ~ R E AOF U CHEMISTRY A N D SOILS, WASHINGTOY, D. C.
I
T HAS been known for many years that the rate of re- calcium phosphate and coke with silica and alumina. Ross, duction of tricalcium phosphate by carbon is increased Mehring, arid Jones (27) conducted a rather extensive series of by the presence of silica. This discovery is usually attrib- experiments on mixtures of phosphate rock and carbon with uted to Wohler (37) in 1829, but the credit actually belong. silica and with potash silicates, under closely controlled to Berthier ( I ) , who published a short paper on the subject in conditions. While the last mentioned investigations brought 1826. The process was first applied to the conimercial out some interesting facts regarding the reduction of phoso rock, conclusions as to the individual effect of silica on manufacture of phosphorus in 1890 by Readman ( H ) ,~ ~ hphate used an electric furnace. the reaction cannot be drawn from the results because of the During the past fifteen years considerable work has heen presence of appreciable quantities of alumina and other imdone on the preparation of phosphoric acid by smelting purities in the materials used. A study of the factors affecting the reduction of pure trimixtures of phosphate rock, silica, and carbon in a reducing atmosphere, oxidizing the evolved phosphorus to phosphorus calcium phosphate by pure carbon has been reported in a pentoxide, and finally recovering the latter as orthophos- recent paper by Jacob and Reynolds (I 1 ) . The present inphoric acid by absorption in water, or by means of the electro- vestigation was undertaken to determine the effect of silica and alumina on the reaction. static precipitator. The literature (5,26,3Zt o 36) contains the results of a nuinMaterials ber of semi-commercial investigations on different phases of the process, but these have been directed principally towards the TRICAI,CIUU PHOSPHATE AXD CAnBox-These materials solution of various mechanical difficulties, and the chemical were the same as were used in a previous investigation (11). side of thc process seems t o have received comparatively The variety of carbon qpecified as carbon flour? was used in all little attention in the way of thorough laboratory investi- the experiments. gations. Waggaman, Easterwood, and Turley (34) report the SILICA-A commercial grade of quartz flour was treated on results of a few iaboratory experiments on mixtures of tri2 This material was obtained from the National Carbon Co , Cleveland, 1
Received May 7, 1929.
Ohio
