April, 1928
I X D C S T R I B L A N D EXGINEERISG CEIEJIISTRY
upper Iimit of speed is approximately 9000 r. p m.; a velocity of 12,000 r. p. m., tested experimentally, proved in most cases no longer economical. Where the highest degree of dispersion is desired it is generally expedient to combine the mechanical action of the
415
colloid mill with chemical influence on the beating process. Peptizers and protective colloids, chosen according to the nature of the material, favor the milling process, without, however, completely eliminating the need of a definite minimum speed of rotation.
Effect of Temperature and Time of Burning upon the Properties of High-Calcium Lime' K. FV. Ray2 and F. C. Mathers ISDIASA USIYERSITY, Broomvcrov Ivn.
Samples of high-calcium limestone were burned at imestigated. Bleininger and COJIPLETE study of temperatures varying from 900" to 1300" C. (1652" to Emley6 give 880" C. (1616' all the factors influenc2372" F , ) , and for periods of time varying from 2 to F.) as the m i n i m u m a n d ing the physical and 10 hours. A portion of each of the quicklimes thus 1300" C. (2372" F.) as the chemical properties of lime is produced was then slaked with sufficient water to m a x i m u m temperature for greatly desired by the indusform a wet putty, while another portion of each was the conversion of high-caltries using arid p r o d u c i n g hydrated to a dry hydrate. These putties and hydrates cium limestone to lime. They lime. It has been Itnown for were then tested to determine the relation of their f o u n d , however, that the some time that the properties rates of settling from water suspension and of their maximum burning temperaof a lime are influenced by the plasticities as measured on the Emley plasticimeter to ture for any l i m e s t o n e is methods of its production, their volumes and their apparent densities. The rates limited by its composition. yet very little work has been of slaking of the original quicklimes were also measured From these investigations done until recently to deteras well as their completeness of hydration. The period it is found that the burning mine this relationship. The of time for the slurry, formed by slaking the quicklime temperature of high-calcium N a t i o n a l Lime Association with excess water, to thicken sufficiently to be used as a limestones for the production has made a study3,' of some finishing coat in plastering was determined for each of lime can be varied from of the properties of the limes lime. From these tests the influence of the temperaabout 900" C. (1652" F.) to produced by its various memture of burning on the quicklimes and hydrates probers, but it has nerer studied 1300" C. (2372" F.). It is duced was determined. k n o w n , however, that the the causes of the differences nrooerties of the lime Drobetween the samdes tested. The literature concerning the effects of different methods duced at 900" C. i l G 2 " F.) aie quite different from tiose of production upon such properties as plasticity, apparent of the lime produced a t 1300" C. (2372" F.). Just what density, time required for the slurry formed by slaking a the-e differences are, however, has never been fully invesquicklime with excess water to become stiff enough to be used tigated. Orton and Peppe17 have investigated the relation as a finishing coat in plastering, etc., is very scanty or en- of the temperature of burning and the rate of slaking, and also the relation of the temperature of burning and the tirely lacking. I n the conversion of limestone into quicklime, t'he nature specific gravity of the quicklime. Their results show that of the stone used and the temperature and t'ime of burning the specific gravity of the quicklime gradually increased are probably the most important factors in determining the from 2.69 for that burned a t 800"C. (1472" F.) to 3.37 for properties of the product. It is well known that limes pro- that burned at 1100" C. (2012" F.), but that it decreased duced at different temperatures from the same stone differ when the lime was formed a t still higher temperatures. illso in properties. If the limestone is calcined a t too high a tem- the time required for the quicklimes to .lake increased from perat'ure, it is usually overburned or "dead-burned," and an 4.5 minutes for that burned at 900" C. (1652" F.) to 11 inferior product very difficult to hydrate is obtained; while minutes for that burned a t 1200" C. (2192" F.) if the stone is calcined a t too low a temperature or for inKnibbs6 states that "the temperature to which a lime has sufficient time, it may be incompletely burned, and upon been heated during calcination influences the character of hydration the central part of each lump may remain as a the hydrate as well as the rate of hydration. The more core or "white-head." Obviously, the correct temperature lightly it is burnt (and the greater the rate of hydration) of lime production lies between these two extremes. the lighter and finer will be the hydrate powder produced. The dissociation pressure of pure calcium carbonate has A lightly burnt lime will produce a very fine hydrate powder been studied by several investigators and a temperature of free from gritty lumps, or, with excess water, a smooth paste, about 898" C. (1648" F.) has been found necessary for a dis- while the same lime overburnt furnishes a heavy, lumpy, sociation pressure of one atmosphere. The temperature hydrate powder and a harsh paste without the unctuous of the burning of limestone to lime has also been quite fully feeling of the paste from the properly burnt lime." Withrow$ has investigated the influence of time and tem1 Received August 4, 1927; resubmitted February 20, 1928. From thesis for degree of doctor of philosophy by K. W.Ray a t Indiana Univerperature of burning of limestone on the rate of set of mortar sity, 1926. and plaster made from the resulting lime. He found that Professor of chemistry, Linfield College, Mchlinnville, Ore.
A
Holmes and Fink, Chem. Met. Eng., 27, 347 (1922). 1212 (1922). 'Johnston, J . A m . Chem. Soc., 32, 938 (1910); Mitchell, J . Citem. Soc. (London), 123, 1055 (1923); Smyth and Adams. J . A m . Chem. Soc., 45,1067 (1923). 8
* Holmes, Fink, and Mathers, Ibid., 27,
6 T7at.s. A'al. Lzme Assocn., 9, 68 (1911), Trans. A m . Ceram. Soc., 13. 618 (1911). Ohio Geol. Survey, 4th series, Bull 4, 298 and 316 (1906). * "Lime and Magnesia," p. 110, D. Van Nostrand Co , 1924. Proc. Nat Lime Assocn , 21st Annual Convention (1923), p. 93.
416
INDUSTRIAL AND ENGINEERING CHEMISTRY
BURNING
TEMP.
c.
Vol. 20, No. 4
Table I-Properties of Quicklimes and Hydrates o n Burning Limestone a t Specified Temperatures RATE T E M P . RISE RATE VOLUME VOLUME PLASTICITY OF PLASTICITY OF OF DURING OF OB SETTLED O F DRY PUTTYFROM PUTTY FROM SLAKING SLAKIXG SETTLING HYDRATE HYDRATE QUICKLIME HYDRATE
c.
TIME TO
TH I cK E N H"9A"Y
LIMESTONE B U R N E D 2 HOURS
850
900 950 1000 1050 1100 1150 1200 1250 1300
0.41 0.32 0.18 0.10 0.20 0.30 0.50 0.78 1.25
323 335 340 325 283 280 225 140 132
111 108 112 120 128 132 142 150 120
96 102 109 102 96
320 330 330 340 305 270 253 196 135 118
109 108 109 125 128 136 137 152 140 110
90 102 108 110 102 90 92 72 60 50
88
67 66 61
LIMESTONE BURNED 6 HOURS
850 900 950 1000 1050 1100 1150 1200 1250 1300
1.0 1.0 1.0 1.0 1.2 1.5 3.5 6.0 15.0 33.0
36 41 42 42 42 42 41 38 36 26
0.60 0.35 0.20 0.15 0.15 0.21 0.40 0.70
860
1.0 1.0 1.0 1.0 1.6 2.0 5.0 10.0 20.0 40.0
40 42 42 42 42 42 36 32 24 16
0.32 0.20 0.18 0.15 0.15 0.25 0.50 0.85 1.30 2.30
4.1 4.8 5.4 5.9 6.2 5.3 4.5 4.0 3.5 3.0
0.85
1.40
3.1 3.4 3.6 3.7 4.1 4.8 5.3 6.0 4.5 3.1
LIMESTONE BURNED 10 HOURS
900 950 1000 1050 1100 1150 1200 1250 1300
4.8 5.0 5.5 6.0 5.9 5.0 4.2 3.6 3.2 2.7
a quick-setting lime cannot be obtained by merely controlling the burning conditions. I n general, the time of set increases as the time and temperature of burning increase, except for a slight decrease in time of set for the lime burned a t about 1000" C. (2012' F.). Recently Haslam and HermannlO have studied the effect of the time and temperature of burning on the properties of lime. They used a limestone considered incapable of producing a plastic hydrate and also one giving a plastic hydrate. An optimum temperature and time of burning were found for the production of the most plastic lime from either kind of stone. The rate of reaction of the hydrates with acid, the rate of settling of the hydrate, and the volume of the putty were all found to vary with the plasticity. Increase in fineness of the hydrate particles increased the plasticity of the hydrate. It was the purpose of this work to make a more complete study of the effects of the time and temperature of burning of high-calcium limes. Experimental
The limestone used in this work was from the Salem (oolitic) building stone of Indiana. Its composition was as follows: Per cent ~.
Iron and aluminum oxides (A1r03 and FerOa) Silica (SiOz) Magnesium carbonate (MgCOa) Calcium carbonate (CaCOs)
0.35 1.02 0.10 98.46 TOTAL99.93
The stone was a soft, porous, high-calcium limestone of uniform texture and composition. In preparation for use, the stone was crushed in a laboratory stone breaker of the Blake type and was then screened. The pieces 6 to 12 mm. to inch) in size were used, and the fines were discarded. The broken and screened stone was allowed to dry at room temperature and was then burned in fie-clay crucibles holding 500 grams of the stone, except that a t 1100"C. (2012"F.) and abovegraphite crucibles were used. The burning was done in a gas-fired furnace. The temperature was measured with a platinum-rhodium pyrometer. The pyrometer tube was inserted through a hole in the side of the 1 o I n d . Eng. Chem., 18, 960 (1926).
3.4 3.8 . . ~ 3.8 4.3 4.9 5.0 5.8 5.1 5.0 2.9
335
110
100
340 .~.
115 ..
108.. _
340 330 303 240 149 123 124 108
120 128 125 142 144 145 130 110
110 110 108
96 84
67 48 45
furnace and on through a hole in the side of the crucible to the charge of lime. Samples of thelimestone were burned at the temperatures for the periods indicated in Table I. The samples of stone were placed in the hot furnace, and the time was measured from the time the crucible was placed in the furnace until it was removed. About 2 hours were required for the crucible and contents to come to the temperature of the furnace. The burned samples, after cooling in air, were transferred to tightly closed glass-stoppered bottles, where they were preserved until used for testing. The following tests were applied. RATE OF SLAKING-The method employed for testing the rate of slaking was similar to that used by White and True.ll Ten grams of the lime ground to 20 mesh were added to 50 cc. of water a t 25' C. (77" F.) in a pint Dewar tube. The lime was vigorously stirred with a Centigrade thermometer and the temperature was read every 30 seconds. The time required for the slaking was taken as the time in minutes from the addition of the lime until the maximum temperature was reached. The rate of slaking of the quicklime when ground to 100 mesh did not appreciably differ" from the rate of slaking of the same sample when ground to only 20 mesh by this method of testing. A rough idea of the completeness of hydration of the various samples was gained by noting the maximum temperature reached during the slaking. However, a sensitive thermometer was not used, neither was a correction made for the heat lost during the determination. This loss probably never amounted to more than a degree or two. RATE OF SEmLIm-The method of Holmes, Fink, and Mathers was employed.4 Seven and one-half grams of the 20-mesh lime were carefully slaked to produce a putty of normal consistency. The amount of water required in the slaking was usually about 20 cc. After standing 24 hours the putty was transferred to a 100-cc. cylinder of 23 mm. (0.90 inch) internal diameter and water was added to bring the volume to about 75 cc. The cylinder was then shaken to disintegrate and to disperse the lime, after which sufficient water was added to make 100 cc. and the cylinder was again shaken until uniform mixing was obtained. It was then allowed to stand without disturbance. The position of the 11 I n d .
Eng. Chem., 17, 520 (1925).
April, 1928
INDUSTRIAL AND ENGINEERING CHEMISTRY
top of the lime suspension was read a t intervals of 5 minutes. The entire set of readings was necessary to give a complete record of the rate of settling, but in order to shorten the description the rate of settling was taken as the number of cubic centimeters settled per minute until the volume occupied by the suspension was 50 cc. Therefore, the rate of settling equals 50/X where X is the time in minutes required for the suspension to settle to the 50-cc. mark. This value can be expressed without giving the table of settling, and it offers a convenient unit for comparison, but it is not entirely satisfactory since it takes no account of the rate of settling after the 50-cc. mark is passed. However, Holmes. Fink, and Mathers4 have shown that the portion of the settling curve above the 50-cc. mark clearly represents the settling rate, and that the last portion of the settling curve represents the thickening or dewatering effect. APPARENTDENsITY-The apparent density of the dry hydrate formed by hydrating the 20-mesh quicklime in an atmosphere of steam was taken by means of a Scott’s volumeter, which is similar to the instruments used in the paint industries for determining the apparent density of dry paint pigments. It consisted of a 40-mesh sieve fixed above a series of glass baffle plates in such a way that any powder slowly stirred through the sieve was deflected by the plates several times as it fell into the measuring cup below. The measuring cup was of 1 cubic inch (16.38 cc.) capacity. The sieve and baffle plates served to disintegrate any lumps or clusters of particles so that the fine powder fell into the cup under uniform conditions. When the cup was full it was leveled by scraping off with a steel spatula all excess material extending above its edges, and the exact cubic inch of material so obtained was weighed. Usually, the average of three determinations was taken as the apparent density of the hydrate. From the apparent density, the approximate volume of loose hydrate which was formed from each gram of the quicklime Fas calculated from the formula V =
Time R e q u l r e d t o Reach Maximum Temperature Qulckllme Slaked fo Wet Putty Fzq. I
16.38/0.75cl, where J’ = Tolume of hydrate produced from 1 gram of quicklime, and d = the apparent density of the hydrate formed, expressed in grams per cubic inch; 16.38 the conversion factor of cubic inches to cubic centimeters; and 0.75 the average weight of lime in grams required to form.1 gram of hydrate. The volume of the wet suspension formed from 1 gram of lime was calculated by dividing the final volume of the settled hydrate obtained in the rate of settling tests by 7.5, the weight of quicklime used. TIMEREQUIRED FOR STIFFENING-There seemed to be no standard method for determining the time required for a putty formed when a quicklime was slaked with excess of
417
water to thicken sufficiently to be used directly as a finishing coat in plastering. Several methods were tried and from these the following method was adopted: Sufficient quicklime was taken to form slightly more than 40 cc. of putty after it had settled. This weight varied with differently treated samples but was about 15 grams. The weight required was calculated from the volume of the hydrate formed from 1 gram of quicklime as described above. This calculated weight of 20-mesh quicklime was added to 75 cc. of water in a 200-cc. beaker and the mixture was stirred until slaking was complete. After cooling, this lime suspension was poured into a wax cylinder 3.05 em. (1.19 inches) inside diameter and 10 cm. (3.93 inches) in height. These cylinders were made by lowering a Nessler tube full of cold water into a bath of melted paraffin and then removing the tube to cool. This process was repeated until the solidified wax was of sufficient thickness. A small hole was then punched through the wax to the glass, the glass cylinder was filled with hot water, and the paraffin tube was slipped off. The hole was filled by plunging the end of the cooled wax cylinder into the melted wax for an instant. After the lime suspension had stood in these wax cylinders for 24 hours, the tops were cut off 3.8 em. (1.5 inches) from the bottom by means of a saw, thus allowing the surplus water and the small amount of the hydrate which was above this position to drain off. These cups were then allowed to stand a t room temperature until the lime putty would support a weight of 200 grams applied upon a flat-bottomed glass rod 6.5 mm. (0.25 inch) in diameter. The number of hours required for the sample to come to this consistency was taken as the time required for stiffening. The value of this method was qualitatively checked by testing two samples of quicklime whose “hodability” or rates of thickening were known from commercial practice. Sample A was so slow to thicken, or its “hodability” was so poor as to make it unfit for commercial use. The “hodability” of sample B was good. When these samples
Fig. 3
were tested by the above method, sample A required 118 hours to stiffen while sample B stiffened to the same degree of firmness in 85 hours. PLASmcITY-Both the putty formed by slaking the 20mesh quicklime with sufficient water to give a wet putty and the putty made by soaking the dry hydrate in water were tested for plasticity. The dry hydrate was produced by hydrating 80 grams of powdered quicklime (20-mesh) with 50 cc. of water and stirring while the reaction was taking place. The plasticity was measured by the Emley plasticimeter12 using plates of 25 per cent porosity.
** This plasticimeter is described in Bur. Sfandards, Tech. P a p n 169.
I N D U S T R I A L A N D ENGIhTEEEIA7GCHEMISTRY
418
OTHER PRoPERTIEs-color, hardness, and texture of the quicklime and hydrates were not measured, but were qualitatively observed in all cases. ERRORIN EXPERIMENTAL WoRK-The experimental error in this work was fairly large. The temperature of the lime a t the top of the crucible was about 50" C. (90" F.) lower than that at the bottom. For this reason the lower half of the lime sample burned at one temperature was mixed with the upper half of the lime sample from the crucible burned a t a higher temperature to obtain the sample for
Fig. 4
950" C. (1742" F.) were incompletely changed to lime and therefore did not completely slake. Slaking seemed to be practically complete for all quicklimes burned a t 900-1100" C. (1652-2012" F.) regardless of the time of burning. However, above 1100" C. (2012" F.) the higher the temperature and the longer the period of burning the more incompletely did the quicklimes slake. RATE OF SETTLISG-Figure 3 shows the relation of the temperature of burning of the limestone t o the rate of settling of the suspension formed when the quicklime was slaked
Fig 5
testing. I n this way the sample having the average properties of the lime burned a t the desired temperature was obtained. Also in those cases where the samples were burned for periods of 5 or 10 hours the temperature of the furnace varied sometimes as much as 25" C. (45" F.). Moveover, the properties of the lime seemed to be modified by the conditions of hydration as well as by the conditions of burning. I n several cases the properties of the wet putty made direct from the quicklime were quite different from those of the dry hydrate produced from the same quicklime. Thus, i t seems probable that the most plastic wet putty, as well as the most plastic dry hydrate, should come from quicklimes burned at the same temperature provided the conditions of hydration do not modify their properties. But the quicklime giving the most plastic hydrate was burned a t about 200" C. (320" F.) higher temperature than was the quicklime giving the most plastic wet putty. However, the results obtained in this work show clearly the general effects of the temperature and the time of burning on the various properties of the lime produced. The stone burned a t 850" C. (1562" F.) was too incompletely decomposed, when burned for less than 5 hours, to be tested, since very little of it hydrated, and also the samples burned a t 900" C (1652" F.) contained a fairly large amount of carbon dioxide. This probably influenced the results to some extent. Results
RATEOF SLAKING-The rate of slaking is greater the lower the temperature a t which the lime is produced. This is shown in Figure 1. The samples burned at 1000" C. (1832" F.) and below reacted with water with great violence. The limes formed a t temperatures of 1000" C. (1832" F.) to 1150" C. (2102" F.) were still very active. As the temperature of burning was increased the rates of slaking decreased until the limes formed a t 1300" C. (2372" F.) were very inactive and required a long period of time to hydrate. The completeness of slaking as judged by the total rise in temperature is shown in Figure 2. All limestones burned for less than 10 hours at temperatures below
Vol. 20, No. 4
Fig. 6
with excess water. The limes prepared by burning the limestones a t 1000-1100" C. (1832-2012" F.) gave very slow settling suspensions. The limes prepared by burning the limestones at temperatures below 950" C. (1742" F.) usually contained some undecomposed calcium carbonate and this caused the suspensions to settle more rapidly. I n the cases of burning below 950" C. (1742" F.) the lower the temperature and the shorter the time of burning the greater was the amount of undecomposed calcium carbonate, consequently the greater were the rates of settling of the suspended hydrates. Limes burned a t temperatures above 1100" C. (2012" F.) also had increased rates of settling, and the higher the temperature a t which the stones were calcined the greater were the rates of settling of the suspended hydrates. The rates of settling of all the hydrates formed by hydrating the quicklimes to dry hydrates were very great. The quicklimes burned at low temperatures hydrated very rapidly, and the hydrates formed from them were coarse and sandy and settled very rapidly. The quicklimes formed a t 11001250" C. (2012-2282" F.) hydrated more slowly and gave finer and smoother hydrates that settled much more slowly. The quicklimes burned a t 1250-1300" C. (2282-2372' F.) gave coarse hydrates, as was to be expected from the compact and semifused condition of the quicklimes. APPARENT DENSITYAND VOLUMINOUSNESS OF HYDRATESThe voluminousness of the hydrates seems to be closely related to the rates of settling of the hydrates. Finely dispersed hydrates occupy the greatest volumes, while the coarse and sandy hydrates occupied the smallest volumes. Thus the slow-settling suspensions produced from the quicklimes burned a t 950-1100" C. (1742-2012" F.) by slaking to wet putties occupied the greatest volumes, while the fast-settling hydrates from the inactive limes burned at 1250-1300" C. (2282-2372' F.) occupy the least volumes. The relation of the temperatures of burning of the limestones to the volumes of the settled suspensions formed by slaking the quicklimes with excess water is shown in Figure 4. I n the hydration of the quicklimes to a dry hydrate, however, those quicklimes burned at 1050-1200" C. (1922-2192' F.) gave the largest volumes of hydrate (Figure 5). The quicklimes
April, 1928
I-VDUSTRIAL A N D ENGINEERING CHEMISTRY
419
Conclusions
burned below this temperature hydrated so rapidly that the hydration could not be properly controlled, and coarse hydrates of small volumes and high apparentdensities were obtained. ~l~~ the partly overburned quicklinles formed a t 1250-1300" C. (2282-2372' F.) gave coarse, dense hydra@ of small volumes and large apparent densities. pLASTICITy-All samples of quicklimes burned at ternperaturesbelow 11000 c. (20120 F.) and slaked with water to wet putties gave plastic putties. The quicklimes burned at 11500 c. (21020 F,) and above gave less putties, and the higher the temperature of the burning the less plastic were the putties formed (Figure 6). All of the very active quicMimes gave plastic putties when slaked with excess water, while the inactive quicklimes gave non-plastic putties. The non-plastic putties were always coarser and more sandy than the plastic putties. The plasticities of the putties from the dry hydrates were very different from the plasticities of the putties from the wet hydrates. This is shown in Figure 7. When the quicklimes were hydrated to a dry hydrate and the dry hydrate \vas made into a putty, the plasticities of the putties formed from the quicklimes burned at 1100-1250" C. (2012-2282' F.) were greater than when the quicklimes were burned either below or above these temperatures. The plasticities of the putties from the dry hydrates were nearly proportional to the rates of settling of these hydrates. The finer and softer hydrates gave the more plastic putties. RATE OF THICKENING OF SLuRRY-The rates a t which the slurry thickened after the quicklimes were slaked with excess water were inversely proportional to the voluminousness of the settled suspensions. The slurries formed from the quicklimes burned a t 1000-1150" C. (1832-2102" F.) were the last to thicken, while the slurries from the quicklimes burned a t 1200-1300' C. (2192-2372' F.) were the first t o thicken (Figure 8). The incompletely burned quicklimes formed a t 850-950" C. (1562-1742' F.) gave slurries that were intermediate in their rates of thickening.
1-Differences in the temperatures of the burning of limestones to limes cause differences in the properties of the limes 2-Differences in the lengths of time of burning of limestones to limes cause only minor differences in the properties of the limes formed. I n general, increasing the time of burning from 2 hours to 10 hours has about the Same effect as that of increasing the temperature of burning about 50" C. F*)3-verY active1 quick-slaking limes are Prepared by burning a t low temperatures. Inactive and slow-slaking limes are Produced when the limestones are burned at high $emperatures. The optimum temperatures seem to be 10001100" C. (1832-2012' F.). 4-When the quicklimes are slaked with excess water to lvet hydrates, both the hydrates from theincompletely burned stones and those from the stones burned at high temperatures have high rates of settling in water suspensions. The hydrates from the stones burned a t intermediate temperatures have low rates of settling5-All the hydrates made from the quicklimes with only sufficientwater to give dry hydrates have high rates of settling from water suspensions. However, the slowest settling hydrates are obtained from the quicklimes burned at 11001250" C. (1832-2282' F.). The hydrates from the quicklimes burned a t either lower or higher temperatures than these are coarse and sandy and settle more rapidly. 6-The volume of settled suspension, and of the dry hydrate that is formed from a unit of quicklime, is nearly inversely proportional to its rate of settling. Those quicklimes giving voluminous hydrates give slow-settling suspensions, while the quicklimes that give coarse and compact hydrates give fast-settling suspensions. 7-The plasticities of the hydrates formed by slaking the quicklimes directly to wet putties are greatest for those hydrates from the quicklimes burned U a t low or intermediate temperatures. Burning a lime at high temperatures 0 3 1300 72 6 (1200-1300" C. or 2192-2372" F.) decreases the plasticity of the putty 5 1200 made from it. 9 8-The plasticity of the putty made 3 012 by soaking the dry hydrate in water e is, in most cases, much less than that 1 P of the putty made by the direct slakga 1000 932 ing of the quicklime to a wet putty. E 9-The plasticities of the putties fi 400 made by soaking the dry hydrate in water are greatest when the dry hy/IO /20 130 /40 /50 /60 40 60 80 /00 /PO drates are made from the quicklimes flaJf+Y y p . 3 j r o m hydruote Rate 01thrchening rn h o u r s a burned at 1100-1250" C. (1832-2282" F.). The hydrates from quicklimes f% 7 fig. b burned at temperatures either below The two most important factors in the speed of thickening or above these give less plastic putties. of a putty are the voluminousness of the putty and the 10-The time required for the stiffening or thickening amount of retarded hydration that takes place after the of the slurries formed by slaking the quicklimes with excess putty has been formed. The voluminousness of the putty water is greatest when the slurries are formed from quickdetermines the amount of water that a lime will retain as a limes burned a t intermediate temperatures (1000-1150" C. putty. Limes that are incompletely burned give hydrates cr 1832-2102' F,). Quicklimesburned at temperatures above of small volume and form putties that thicken rapidly owing this give slurries that thicken much more rapidly. Incomto the small amount of water that must be lost by evapora- pletely burned limes also give slurries that have medium tion or taken up by hydration. Limes burned at very high high rates of thickening. temperatures give hydrates of small volume which continue -~ their hydration during the period of soaking. These limes The American Refractories Institute has issued Technical give putties that thicken very rapidly, not only because of Bulletin No, 19, by M, c, Booze, on ,,Heat Penetration in Rethe small amount of water that they retain, but also because fractories.)j copies can be had by addressing the Institute, this water is taken up by the continued hydration of the putty. Oliver Bldg , Pittsburgh, Pa.
e
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5
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