THE DISSOCIATION EQUILIBRIUM 
 OF KAOLIN 
 
 BY 
 
 CHARLES IMSE ROSE 
 
 THESIS 
 
 FOR THE 
 
 DEGREE OF BAGHELOR OF SGIENGE 
 
 IN 
 
 CHEMICAL ENGINEERING 
 
 COLLEGE OF LIBERAL ARTS AND SCIENCES 
 
 UNIVERSITY OF ILLINOIS 
 
 1922 
 
1922 
 
 Pt72 
 
 UNIVERSITY OF ILLINOIS 
 
 .May.. 20 , 1982... 
 
 THIS IS TO CERTIFY THAT THE THESIS PREPARED UNDER MY SUPERVISION BY 
 
 .....Cha.ri.e8...Jas.g...^p.g.§, 
 
 entitled .TJae...Dis,s.o.c.ia.ti.oii.,E.quiliU.riun:....Qf Ka.olm 
 
 IS APPROVED BY ME AS FULFILLING THIS PART OF THE REQUIREMENTS FOR THE 
 degree of B.a.Gii.elo.r....of > ...,S.c.i.eii.c.e. 
 
 HEAD OF DEPARTMENT OF. .0.6 r^l.G...Eng.ine.e.Mg 
 
Digitized by the Internet Archive 
 in 2015 
 
 https://archive.org/details/dissociationequiOOrose 
 
ACKNOWLEDGMENTS 
 
 /f ik kHr -fc kik 
 
 The writer wishes to express his appreciation of 
 the suggestions and advice that Profe,ssor E.W. Washburn has so 
 kindly given. 
 
 He also wishes to express his thanks for the help 
 rendered by Dr .E.N. Bunting. 
 
 N 
 
 X* & - X- *X* X* Xr X" X* X* X* X - X~ 
 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 / 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
TABLE OF CONTENTS 
 
 Page 
 
 I. INTRODUCTION.. 1 
 
 II. LITERATURE 2 
 
 III . THEORY . . 3 
 
 IV. APPARATUS AND OPERATION 6 
 
 V. RESULTS AND CALCULATIONS 16 
 
 (1) Data 1'roiri Static Method. 19 
 
 (2) Results of Dynamic Method. 20 
 
 (3) Heat of Dissociation 21 
 
 VI. CONCLUSIONS 22 
 
1 
 
 THE DISSOCIATION EQUILIBRIUM OF KAOLIN 
 
 I. INTRODUCTION 
 
 A considerable amount of work has been done in studying the 
 dehydration phenomena of clays, and part of this work has been 
 concerned particularly with the rate of loss or percentage loss of 
 the combined water of the clay at various temperatures. 
 
 The loss of weight of clay samples or the loss of chemically 
 combined water after heating the clay to definite temperatures has 
 been determined for a number of them, but practically nothing has 
 been done to ascertain the tension of the water vapor at those 
 temperatures. With this in mind the problem of finding a method 
 or methods of determining the actual dissociation tension for any 
 temperature was undertaken. 
 
 During the trials a washed North Carolina Kaolin was used 
 
 which is composed for the most part of the mineral kaolinite, 
 
 having the formula: A1 0 . 2SiO . 2H 0 . This clay was not 
 
 2 3 2 2 
 
 analyzed except to determine the average percentage of hygroscopic 
 and combined water. 
 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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 * 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2 . 
 
 II. LITERATURE 
 
 U-.H. Brown and E. T .Montgomery 1 have studied this clay among 
 
 1 
 
 Technologic Paper No- 21. Bureau of 
 Standards. April, 1913 
 
 a number of others, and have determined the percentage loss in weight 
 of the combined water after heating to certain definite temperatures. 
 The graph obtained from their results has been used as an indication 
 of the dissociation tension that might be expected since where 
 their curve shows a relatively large loss of weight at a certain 
 temperature one may be led to believe that the vapor tension will 
 show a relatively large increase, or will be relatively large as 
 compared with the vapor tensions at any lower temperature provided 
 the temperature which produces the fastest rate of dehydration has 
 not been exceeded. 
 
 A thesis along similar lines by Mr.T.K.Chow which is held 
 by this department was occasionally referred to in order to compare 
 values obtained. This particular work has results which are of 
 doubtful worth and no great amount of weight was given to informa- 
 tion obtained from it. 
 
 Suggestions for the apparatus have been found in E. W. Washburn' i 
 . . . 2 
 
 article y and also many have been offered by him. 
 
 2 
 
 Jr. Amer. Ceram. Soc. 37,309 (1915) 
 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
3 
 
 III. THEORY 
 
 Two methods of attaching the problem were suggested, one 
 a static method, and the other a dynamic one. 
 
 The static method consisted of placing the kaolin in a 
 vessel, evacuating the vessel, heating it in a small electric furnace 
 and then measuring the pressure of the water vapor by means of a 
 mercury manometer sealed to the vessel. ( See Fig.1) 
 
 The kaolin was dried before placing it in the vessel so 
 that most of the hygroscopic water would be removed. 
 
 When the apparatus was evacuated the mercury would rise in 
 the long arm of the manometer. Upon heating the kaolin some of the 
 combined water would be liberated, and would develop a pressure 
 dependent upon the temperature to which the clay was heated. This 
 
 pressure would depress the mercury column a definite amount. By 
 noting the difference in height of the mercury column in the two 
 arms of the U tube, and subtracting this difference from the 
 barometric pressure, the pressure of the water vapor above the clay 
 was obtained. 
 
 1’or low pressures a manometer tube was connected to another 
 similar vessel, and by simply noting the difference in height of the 
 mercury columns in the two arms of the manometer, the pressure of the 
 vapor could be ascertained. 
 
 It was assumed that the water would possess a definite 
 vapor tension above the clay at a definite temperature, and that 
 repeated trials would give checji results. 
 
 making a sufficient number of trials at various definite 
 temperatures, it was hoped to obtain values to plot a curve showing 
 

 
 
 
 
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4 . 
 
 the dissociation tension of the clay at various temperatures. 
 
 The idea of the dynamic procedure was to pa3s a measured 
 volume of air over some kaolin which was to be heated in a suitable 
 apparatus, collect the moisture taken up, and then knowing the 
 weight of water vapor in a definite volume of air, the pressure of 
 this water vapor could be found by the use of the gas equation. 
 
 ( See Fig. 2. ) 
 
 It was assumed here also that at any definite temperature 
 the kaolin would have a definite dissociation tension. 
 
 The air in passing over the clay was supposed to take up 
 moisture till the partial pressure of the water vapor in the air 
 was in equiliorium with the clay. Necessarily the partial pressure 
 of the vapor in the entering air would have to be less than the 
 pressure of the water vapor above the clay if the air were to take 
 up any moisture in reaching equilibrium. 
 
 The necessity of passing the air over the clay at such a 
 rate that the equilibrium conditions would not be disturbed to a 
 noticeable extent was realized. The rate of passage of this air 
 would have to be determined by experimentation. 
 
 In order to aid matters it was desired to pass the air 
 through the apparatus in such a manner that the air would pass around 
 small pieces or particles of the kaolin, and not simply pass over 
 a layer of clay spread over the bottom of the apparatus. 
 
 Since any hygroscopic water would interfere seriously 
 with the determination, this was first removed before any data were 
 recorded. 
 

 
 
 
 
 
 
 
 
 
 
 
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 I 
 
 
 
 
 
 
 
 
 
 
 
5 . 
 
 It will be noted in connection with this procedure that 
 the water taken up by the drying tube® need not come from the cls.y 
 entirely, and, in fact, the greater part of the water was contained 
 in the air in the first place, since this would allow equilibrium 
 conditions to be reached in the furnace in less time. 
 

 
 
 
 
 
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 I ■ 
 
IV. APPARATUS AND OPERATION. 
 
 6 . 
 
 The vessel used, in the static method was of hard glass, 
 and the main portion which held the clay was in the shape of a flask 
 with a moderately long neck. To this neck was attached the side- 
 arms for the vacuum pump, and for the manometer to measure the 
 pressure developed. 
 
 The clay was introduced into the flask through a hole in 
 the top of the neck. After placing it in the flask, the top was 
 then sealed off. 
 
 The side-arm for the vacuum pump was provided with two 
 ground glass stop-cocxs, these stop-cocks being about four inches 
 apart. The tops and bottoms of them were sealed with wax when clos 
 after evacuating the bulb. 
 
 The other arm was in the shape of a rough U with the half 
 of the U connected to the flask, the longer. This half was more 
 than long enough to permit mercury to rise in it equal to the 
 barometric height. ( See Fig.l) . 
 
 This apparatus was placed in a small electric resistance 
 furnace, the furnace being of such size that the side-aims projected 
 over the upper edge of it. The top of the neck, and the open 
 
 parts at the top of the furnace were covered with suitable material. 
 The furnace was heated by a current which could be varied to suit 
 one’s needs by the 'manipulati on of a rheostat. Different 
 
 temperatures could thus be obtained. 
 
 To prevent any condensation of water vapor in the apparatu 
 when tne pressure of the vapor in it was greater than the saturation 
 pressure of water vapor at room temperature, a fine wire was 
 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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 , 
 
 . . 
 
 - § 4 # I 
 
 
 
 
 
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7 . 
 
 wrapped about tire exposed arms. This wire extended over that 
 portion of the large U shaped arm not occupied by mercury when 
 pressure would be developed, and also extended up to the first stop- 
 cock on the other arm. The double stop-cock was necessary 
 
 because this warming had a tendency to soften the stop-cock grease, 
 and permit a slow leakage of air into the apparatus when one was 
 used alone. A small current passed through this wire was suffici- 
 ent to warm all parts as much as necessary. 
 
 Temperatures were measured by a thermocouple, and also by 
 an ordinary mercury thermometer, since they rarely exceeded 400 
 degrees Centigrade . 
 
 The diagram shows a sectional view of the apparatus. 
 
 The dynamic apparatus consisted of a fused silica tube 
 about one inch in diameter, and about four feet long. This tube 
 was heated by passing a current through a nichrome ribbon wrapped 
 about it. The coils of the ribbon wera insulated from each other 
 by alundum cement, and the entire heated portion of the tube was 
 surrounded with magnesia pipe covering. 
 
 A wet test meter was used to measure air volumes. The 
 temperature of the air coming from the meter was read by means of a 
 thermometer incorporated in it. 
 

 
 
 
 
 ■ 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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8 . 
 
 When it 7/as desired to reduce the moisture content of this 
 air to such a degree that the vapor pressure of this moisture would 
 be less than that supposed to exist above the clay, the air was 
 passed through a calcium chloride tube. 
 
 Since only three feet of the tube was used as a furnace, 
 it was necessary to warm the exposed ends to prevent any condensa- 
 tion of water vapor in them. The reason for this was similar to 
 that making it necessary to warm the exposed parts of the static 
 apparatus. A fine wire was wrapped about the exposed ends, and a 
 small current passed through it. This current was independent 
 
 of the heating current, and supplied all the heat desired, 
 it was found from experience that a certain amount of heat came from 
 the furnace and xept these ends above room temperature. 
 
 Issuing frcm the furnace, the moisture laden air was 
 passed through a series of six-inch U tubes filled with calcium 
 chloride and provided with ground glass stop-cocks. Three tubes 
 
 were used, and they were found to be sufficient to remove all 
 weighable amounts of water frcm the air. It was also found that 
 calcium chloride was the best agent since the small pieces could 
 be placed in the tubes, and would cane close together, but would 
 nevertheless allow many air passages between them, whereas if 
 sulphuric acid had been used, a certain amount of hydrostatic 
 pressure would have been necessary to pull the air through the tubes, 
 and it was desired to keep the system at atmospheric conditions. 
 
 An attempt was made to saturate small pieces of pumice stone with 
 the acid and then fill the tubes with tn.is, but the acid dripped 
 from the pieces and collected in the bottoms of the tubes, and thus 
 

9 
 
 defeated the purpose of this trial. 
 
 After passing through a stop-cock in the line used to regulate 
 the flow of air, and a guard tube of calcium chloride to prevent 
 any diffusion backwards into the absorption tubes, the air was 
 exhausted either through a water pump, or through an aspirator bottle 
 The stop-cock mentioned was placed in the line at this point in 
 order that all the parts of the apparatus before it would be at 
 atmospheric pressure except for the small pressure of three-twentieths 
 of an inch of water required to operate the meter. By turning the 
 stop-cock the rate of flow could be adjusted, and by watching the 
 hand on the dial of the meter the rate of flow could be measured. 
 
 The pump was a small ordinary water pump, and operated under 
 a constant head. The details of this mechanism are shown in the 
 diagram. It will be noted that air was pulled through the 
 apparatus and not blown through. The water pump was used when a 
 gas meter was available, as there was no other way of measuring air 
 volumes when it was used. 
 
 When a meter was not available, another method of finding 
 the air volumes was employed. This method consisted of using an 
 asnirator bottle to pull the air through the apparatus. uy catch- 
 ing the water coming from the bottle, weighing it, and finding its 
 volume, the volume of the air pulled through could be found. This 
 volume obtained represented a volume of saturated air at the 
 temperature of the water. nnowing the temperature of the water, 
 and its vapor pressure at that temperature, the actual volume of 
 air could be found for dry or otner c ondit ions . The barometric 
 pressure was also needed. 
 

 
 
 
 
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10 . 
 
 It has been noted that a guard tube was used to stop any 
 diffusion backward into the absorption tubes. These guard tubes 
 were placed immediately in front of the pump or aspirator bottle 
 as the case might be. 
 
 The furnace was heated by a current which could be varied 
 as desired. ±>y using several different currents in a preliminary 
 test, the temperatures corresponding to them were found. From 
 these values a, graph was plotted and enabled one to find a current 
 that would give a desired temperature. Direct current was used 
 to avoid variations. 
 
 The temperature of the furnace was measured by means of 
 a thermocouple. To test the heating of the furnace the hot 
 junction of the couple was moved along the heated portion of the 
 tube, and the results noted. It was found that the furnace was 
 heated uniformly. 
 
 The apparatus was tested for leaks by evacuating it, and 
 then sealing it while heated. No leaks were observed. All 
 joints were sealed or wired or both, and rubber stoppers and tubing 
 were used to make connections. 
 
 In later determi nations it was found necessary to intro- 
 duce a capillary in the line between the exit of the furnace and 
 the first absorption tube. This capillary was used to prevent 
 diffusion of water vapor from the heated clay into the tubes with- 
 out having air carry it. 
 
 Before loading the furnace the clay was made into small 
 pellets composed of two-thirds ordinary clay, and one-third clay 
 which had been dehydrated by heating for one hundred hours in a 
 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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11 . 
 
 high vacuum. These pellets were broken into small pieces prelim- 
 inary to pushing them into the furnace, but were not broken into 
 small particles. They were then pushed into the furnace, and 
 filled the heated portion to within too or three inches of each end 
 of it. This insured the clay being heated uniformly. The pur- 
 pose of this breaking of the pellets was to provide as much surface 
 as possible, and to allow the air to circulate around the small 
 pieces instead of simply over them. Since the pieces were 
 irregular there were many small openings that the air could pass 
 through. Had the furnace been filled with the fine particles 
 
 it would have been completely stopped up, or if a less amount had 
 been used then a layer would have formed at the bottom of the tube 
 and the air would have passed over the clay. 
 
 Before collecting any moisture or measuring any air 
 passing through the furnace the apparatus was allowed to come to a 
 constant temperature. After this haa been attained the absorption 
 tuoes were placed in the line. These tubes were previously 
 connected togetner by small pieces of rubber tubing which were 
 wired fast to the side-arms. Then all joints were sealed and in- 
 spected, the stop-cocks on the calcium chloride tuoes were opened* 
 The regulating stop-cock was opened a slight amount, and air was 
 slowly drawn through the apparatus. The opening ol the main 
 
 s t op - c o c had to be adjusted for each run. 
 
 The data necessary were the air volume and its temperature 
 
 when issuing from the meter, the weight of the water taken up by 
 the calcium chloride tubes, the barometric pressure, r.nd the 
 

 
 
 
 
 
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12 . 
 
 temperature of the furnace. 
 
 \ 
 
Dynamic Apparatus 
 

 
 
 
 
 
16 
 
 V- RESULTS MU CALCULATIONS 
 
 The static method showed that the kaolin adsorbs a large 
 amount of air which is given off slowly when the clay is heated, and 
 which seriously interferes with the measurement of the vapor pressure. 
 Its presence was detected in the apparatus by observing that when 
 the manometer tube was at room temperature there was no condensation 
 of water vapor on the inside walls, of the tube though the pressure 
 measured was far in excess of that allowed for saturation pressure 
 of water vapor in air for the same temperature. There were no 
 leaks in the apparatus when these observations were made. The 
 air is held tenaciously by the clay, and is only removed after a 
 long period of heating in the exhausted vessel. When all of the 
 air was removed most of the water of the clay had been removed, and 
 no reliable results could be obtained. 
 
 Due to factors mentioned above, and also the development of 
 leaks in the apparatus occasionally but at an important time, no 
 results of any value were obtained with the static apparatus with 
 the open manometer tube. 
 
 I’or low pressures the closed manometer tube apparatus was 
 used, and some check results were obtained over a moderate range of 
 temperatures. These results were obtained after cooling and 
 heating several times, and after all air had been removed from the 
 clay. The mass of clay used with this particular piece of 
 
 apparatus was considerably less than in the case of the other piece. 
 (See Graph II). I'rom the data obtained from this test another 
 
 curve was plotted as shown in Graph III. 
 

 
 
 
 
 
 
 
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 . 
 
 
 
 
 
 
 
 
 
 
 
 . 
 
 
 
 
 
 
 
 
 
 
 
 •• 
 
 
 
 
340 
 
 320 
 
 t i 
 
 300 g 
 
 •H 
 -P 
 £ 
 0) 
 o 
 
 280 
 
 260 
 
 CO 
 0) 
 0) 
 h 
 W 
 0) 
 
 240 « 
 «» 
 
 p 
 
 -Hlfn 
 
 0) 
 
 ft. 
 
 200 | 
 
 e-i 
 
 180 
 
 220 
 
 160 
 
 140 
 
 Graph II 
 
 Pressure-Temperature Curve 
 
 8 
 
 Vapor Pressure in mm. of Mercury, 
 10 12 14 16 
 
 18 
 

 
 
 
 
Curve from Van’t Hoff equation. 
 
 0017 . C018 .0019 Wlm .0071 .007 
 

 
 
 
19 . 
 
 D ata fr om Stat i c Metho d, 
 
 Temperature Degrees Pressure of vapor 
 
 Centigrade in mm. lie r cur y 
 
 145 
 
 9.0 
 
 190 
 
 10.5 
 
 235 
 
 13.5 
 
 260 
 
 14.0 
 
 275 
 
 16,0 
 
 300 
 
 X 7 .0 
 
 The dynamic method was not influenced by adsorbed air. 
 
 This method snowed tnat tne clay was very slow in approaching 
 equilibrium as did the static method. 
 
 When air was passed through the apparatus slowly, about 
 two-tenths of a cubic foot per twenty-four hours, water vapor from 
 the furnace diffused over into the absorption tubes, and thus 
 made the results high. When air was passed through too quickly 
 the equilibrium was disturbed, and a low value for the pressure 
 was always certain to be the result. This diffusion was prevented 
 in the last part of the work by introducing a short piece of 
 capillary tubing in the line between the end of the furnace and the 
 absorption tubes. 
 
 Although adsorbed air did not influence the results here, 
 check results could not be obtained although the manipulations 
 carried out in each test at the same temperature were exactly 
 alike* Care was taken to see that any hygroscopic water was re- 
 

 
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20 . 
 
 moved before any run was made, and that the clay in the furnace 
 was net dehydrated. When any clay became dehydrated it was removed 
 and replaced by other material . 
 
 Results of Dynamic Method 
 
 Temperature Degrees Pressure of Vapor 
 
 Centigrad e mm. of Llercurv 
 
 317 
 
 9.39 
 
 320 
 
 7.96 
 
 433 
 
 93.26 
 
 200 
 
 3.69 
 
 175 
 
 1.47 
 
 293 
 
 7.06 
 
 297 
 
 7.04 
 
 320 
 
 7.49 
 
 322 
 
 13.18 
 
 322 
 
 2.80 
 
 352 
 
 12.93 
 
 322 
 
 15.61 
 
 322 
 
 5.7 
 
 347 
 
 3.14 
 
 The volume and temperature of the air were known, and by 
 subtracting the saturation pressure of water vapor in air from the 
 barometric reading, the pressure of the air was found. Using 
 these three quantities in the gas equation, gave the moles of air. 
 The moles of water could be found from the gain in weight of the 
 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
21 . 
 
 absorption tubes. We had then that : 
 
 ptr n : P : : N : N y air from which the pressure of the 
 
 n 2° HO H 2° 
 
 2 
 
 water vapor could be found. 
 
 H e at of Di ssociation. - The heat of dissociation for one 
 mole of water was found by the use of the formula: 
 
 log 
 
 P 
 
 H 
 
 R 
 
 f-1 - ... A— ) 
 
 V * h ) 
 
 where the pressures and temperatures used were those obtained from 
 the static method det erminations . 
 
 p =9.0 
 1 
 
 p = 17 
 2 
 
 T = 145 + 273 = 418° 
 1 
 
 T = 300 + 273 = 573° 
 2 
 
 log 9.0 
 
 = -0.5353 
 
 e 1,7 
 1 =0.00239 
 
 1 =0.00174 
 
 T 
 
 2 
 
 (1 - 1 ) =-0.00065 
 
 T T 
 
 2 1 
 
 H 
 
 .0*0353 = p 
 
 1.985 
 
 ( -0.00065) 
 
 H = 1940 calories per mole H 0 
 P 2 
 
 H = 1940 = 107.8 calories per gin. HO 
 
 p 18 2 
 

22 . 
 
 VI. CONCLUSIONS 
 
 Since the values obtained by the static method could 
 be reproduced, they may be taken as approaching the correct values. 
 
 Results from the dynamic method are low in comparison 
 v/ith those obtained by the static procedure, as might be expected. 
 The highest value given by the dynamic method would be the nearest 
 to the correct value, and even then might be considerable short 
 of it . 
 

 
 
 
 
 
 
 
 
 
 
 
 
 
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