Oct.,
1917
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
is removed from t h e funnel, placed in a small platinum crucible, dried a n d ignited. T h e funnel is carefully rinsed with distilled water, t h e rinsings being allowed to r u n into t h e filtrate. After ignition t h e residue is fused with a little iron-free potassium pyrosulfate a n d t h e cake so obtained is dissolved in dilute sulfuric acid. If no residue is left t h e decomposition is complete and t h e two solutions may be combined, and the iron then determined in t h e resulting solution. If dark particles may still be seen, and this will be t h e case if staurolite is present, t h e y are filtered off, ignited a n d fused with iron-free sodium carbonate in a platinum crucible. Lpon treating this fusion with dilute sulfuric acid careful examination should show no black particles a n d after filtering t o remove any insoluble sulfates t h e three filtrates are combined and t h e iron determined in this resulting solution. T h e writer prefers t o reduce t h e iron with stannous chloride and then t o titrate with potassium bichromate, determining t h e end-point electrometrically as suggested by Joel H. Hildebrand,’ a n d for this reason dissolves the fusions in I : I hydrochloric acid instead of sulfuric acid. The exact conditions required b y this method have been studied by Hostetter a n d Roberts of this laboratory, a n d t h e writer wishes t o t h a n k them for the information and assistance t h e y have given him. Other well known methods would probably give equally good results. I n making analyses such as these t h e purity of one’s platinum a n d reagents becomes a question of prime importance. While careful blank determinations will eliminate errors due t o t h e latter they cannot be relied upon in t h e case of t h e former and no iron-bearing platinum may be used. It cannot be too strongly emphasized t h a t no “Analyzed Chemical” can be relied upon without test for work such as this. CONCLUSIONS
Before t h e correct iron content of a sand can be determined t h e sand must be completely decomposed. Simple treatment with hydrofluoric acid and sulfuric acid is not sufficient. Fusion of t h e residue with potassium pyrosulfate must be resorted t o and even subsequent fusion with sodium carbonate in rare cases. GEOPHYSICAL LABORATORY CARNEGIEINSTITUTION OF WASHINGTON WASHINGTON. D. C .
THE FORMATION OF TRI-CALCIC ALUMINATE By EDWARD D. CAMPBELL
Received April 23, 1917
,4s early as 1883 Le Chatelier came t o t h e conclu-
sion t h a t t h e two essential constituents of Portland cement were tri-calcic silicate and tri-calcic aluminate. All efforts t o produce a sound cement of t h e empirical formula x(gCaO.SiOz) y(3CaO.Al203)
+
1
J. A m . C h m . Soc.. 36 (1913). 871.
943
failed, free lime always being found in materials of this composition. Later, Newberry suggested t h a t t h e essential constituents were tri-calcic silicate a n d di-calcic aluminate a n d proposed t h e formula x(gCaO.SiOz) y(2CaO.Al2O3). Even this latter formula gives a mixture almost always containing some free lime, so t h a t in practice i t is customary t o keep t h e lime ratio a little below t h a t called for by t h e Newberry formula in order t o produce a uniformly sound cement. The existence of tri-calcic silicate as first suggested b y Le Chatelier received a strong confirmation from t h e work of A. H. White,’ and in 1915 essentially pure crystals 0 . 0 3 mm. in diameter were described by Shepherd, Rankin a n d Wright.2 Later, by very slowly cooling a solution of di-calcic silicate and calcium oxide in jCa0.3A1203 as solvent, t h e author3 obtained crystals of essentially pure tri-calcic silicate 7 mm. in length. Two facts in connection with tri-calcic silicate should be noted: ( I ) large crystals of tri-calcic silicate can be best obtained b y slowly cooling a solution of di-calcic silicate and calcium oxide in jCa0.3A1~03; ( 2 ) as pointed out by Le Chatelier, when tri-calcic silicate is treated with water, one molecule of calcium oxide readily forms calcic hydroxide, leaving a hydrated di-calcic silicate which gradually undergoes further hydrolysis, These two facts relative t o the formation a n d behavior of tri-calcic silicate would suggest t h e idea t h a t calcium oxide may, under suitable conditions, unite with di-calcic silicate t o form crystals in which t h e calcium oxide would bear a relation t o t h e di-calcic silicate exactly analogous t o t h a t borne by t h e water of crystallization t o t h e hydrated salt with which i t is united. Essentially pure tri-calcic aluminate was prepared a n d its properties described in 1909 by Shepherd, Rankin and Wright.‘ Some of t h e properties of tricalcic aluminate were described in I g I j by Rankin a n d Wright5 as follows: “This compound occurs in equant colorless grains 0 . I mm. and less in diameter, often hexagonal or rectangular in outline, with indications of imperfect cleavage after the octahedron or rhombicdodecahedron, crystal system, isometric; refractive index, Nna = I . 7 1 * o OOI ; hardness, 6 ; fracture, conchoidal; luster, vitreous. Occasionally faint gray interference colors were observed and were evidently due to strain.” The experimental d a t a from which Shepherd, Rankin and Wright drew their conclusions are shown in t h e accompanying diagram taken from t h e two publications mentioned. This diagram assumes t h a t tricalcic aluminate, composed of 37.78 per cent A1203 and 6 2 . 2 2 per cent CaO, is a stable phase in all mixtures containing less t h a n j 2 . 2 per cent A1203 and a t all temperatures u p t o its melting point, I j35 O * j ” , a t which point i t “dissociates into CaO a n d liquid.’’ It is stated t h a t because of t h e dissociation a t t h e melting point into CaO and liquid, pure tri-calcic aluminate is
+
1 THISJOURNAL, 1 (1909). 5 . * A m . J. Scr., 39 (191J), 1 ; 29 (1909), 293. J THIS JOURNAL, 6 (1914), 706. 4 Am. J. Sci., 28 (1909). 293. 6 I b t d . , 39 (1915), 1.
,
944'
TB% J O U R N A L OF I N D U S T R I A L A N D E R G I N E E R I N G C H E M I S T R Y
"best obtained by.crystallization from glass of its own composition' at a temperature below 1535'. It forms with the compound gCa0.3Ali03 (a eutectic mixture of the composition CaO 50, A1203 so), which nielts at 1395' * 5'. It does not form a eutectic with CaO; but the composition CaO j g , A1203 41 is the quadruple (invariant) point at which these two compounds are stable in contact with liquid and vapor, the equilibrium temperature being 1535 '." T h e preparation of t h e pure tri-calcic aluminate is described in 1909, as follows: "In order to prepare the pure compound 3CaO.Al203, it is necessary to bake the charge a long time at about 1400". This allows diffusion to occur with the elimination of the excess of CaO and 3Ca0.jAlzOs. Experimentally, we found that t h e 37.78 per cent charge held z I days at 1400' was free of the excess phases. Similarly, the compositions 35 per cent, 34 per cent and 3 2 per cent of when merely fused and crystallized, without the long exposure, show 3CaO.Al203 with CaO and gCa0.3A1203,but were transformed into CaO and 3CaO.ALOa by heating at 1400' for the same length of time. In order to accelerate the reaction we took the previously fused charges and ground them to a fine powder before starting the heat treatment. Such cases as this are not uncommm in silicate melts and the investigator must bear them constantly in mind or he will be led far astray."
Vol. p, No.
IO
if t h e tri-calcic aluminate is regarded as a definite phase stable at all temperatures u p t o 1535'. T h e work is based on t h e conception t h a t gCa0.3A1203 is a solvent in which CaO is soluble, t h e concentration being a function of t h e temperature, a n d t h a t t h e limit of solubility of CaO at temperatures below 1535" is when there are about four molecules of CaO t o one of jCa0.3A1203, t h a t is, when a n empirical formula corresponding t o t h a t of t h e tri-calcic aluminate has been reached. Under this conception t h e melting point of t h e jCa0.3AI203 would be lowered by t h e solution of CaO from 1455 t o 1395O, a t which point C in t h e diagram (Fig. I ) would represent t h e eutectic solution of CaO in gCa0.3A1203. With increase in concentration of CaO t h e melting point would rise along t h e line C B A . If a mixture of t h e empirical formula 4CaO A1203 were heated well above 1535' C. and then cooled slowly enough t o allow a n approach t o chemical equilibrium, t h e resulting material must, if tri-calcic aluminate is a stable phase, consist of crystals or grains of CaO with 3Ca0.AlzOs. This is indicated in t h e diagram since such a mixture would come in t h e field M L N , being well t o t h e left of L N .
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EXPERIMENTAL
I600
1
T h e materials used were strictly C . P. calcium carbonate a n d t h e purest available alumina containing b y analysis 99.60 per cent Al2O3. These materials were thoroughly dried a n d mixtures were made b y accurately weighing out in t h e proportion of four CaC03 t o one of A1203. Enough of t h e mixture was weighed out for each experiment t o give approximately 60 g. of fused material. T h e mixture was first placed in portions in a covered cylindrical platinum crucible 48 mm. in diameter a n d 5 7 mm. deep and ignited over night at a temperature between 1100 a n d 1150' C. in order t o drive off carbon dioxide and reduce t h e bulk of t h e mixture. T h e covered crucible was then heated in t h e same furnace a n d in substantially t h e same manner as t h a t employed in t h e preparation of synthetic celite a n d large crystals oE tri-calcic silicate already referred to. A mixture of t h e empirical formula 4CaO A1208 would contain 68.06 per cent CaO with 31.94 per cent A1203. I n t h e first experiment a mixture of t h e above composition was placed in t h e covered platinum crucible and heated over night by means of a MBker burner. T h e temperature was measured as in our previous work b y means of a standardized platinum rhodium thermocouple, t h e bead of which was within z or 3 mm. oE t h e crucible containing t h e material under treatment. In t h e morning, blast was p u t on a n d t h e temperature, which was about 1150' at t h e s t a r t , was increased until t h e thermocouple indicated a little above 1600' C., at which temperature it was held within less t h a n 5' for one a n d one-half hours. After holding a t 1600' t h e temperature was lowered a t t h e rate of 2 j ' per hour during seven hours, or until i t h a d dropped t o 1425' when t h e gas was turned off and t h e furnace allowed t o cool over night. During t h e entire seven hours of cooling, with t h e exception of one instance when t h e temperature was 4' lower
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I I
FIG.I
T h e object of t h e research herein described, t h e laboratory work of which was carried out b y G. W. Blanco, M.S., a n d B. A. Standerline, M.S., was t o determine whether tri-calcic aluminate must be considered as a stable phase in t h e strict sense of t h e word in which it is employed in t h e phase rule, or whether regarding it either as a saturated solid solution of CaO in gCa0.3A1203, or else gCa0.3AlzOa with four molecules of CaO of crystallization, may not be in closer accord with t h e experimental facts t h a n
Oct.,
1qrj
T E E J O U R N A L OF I N D U S T K I A L A N D ENGINEERING CHEMISTRY
than t h a t aimed at, t h e therrnocouplc indicated a t the end of each hour t h a t t h e desired temperature had been reached within .'2 In order to remove t h e material, which had apparently been thoroughly liquefied, from t h e crucible, i t was necessary t o break it into a number of pieces by means of a small.chise1. A micro section of this "GI"mixture magnified 100 diameters is shown in Fig. TI. This section clearly shows a n apparently cellular structure, t h e cells hcing occupied by crystals or grains of calcium oxide, while the cell walls constitute t h e magma from which t h e crystals or grains of cai'cinm oxide have separated. Another mixture, "G-3," of t h e same composition as t h e preceding, was prepared b y essentially the same method. The same r a t e of cooling froin 1600" was used, t h e only difference being t h a t t h e h e a t was turned off after 6 hrs., t h a t is, when t h e temperature had lowered t o 1 4 j o o instead.of 1425'.
945
a t which temperature i t was first held for four hours.
It was then increased during one hour t o 142j0,
a t which temperature it was held constant for another 4 hrs., or, in all, 9 hrs. An examination, of t h e material after cooling over night showed little or no s h sorption by t h e magnesia discs. A second heating of t h e same piece was then carried out in subst.antial1y t h e same manner a s in t h e preceding experiment, except t h a t t h e temperature after heating over night was raised quickly until t h e thermocouple in t h e annular space indicated 1463' C. It was then held between 1460 and 1465' for 4 hrs., raised during t h e next hour a b o u t 1o0, then held 4 hrs. longer between 1 4 7 5 a n d 1480' after which the furnace was again allowed to cool over night. A distinct, b u t not considerable, absorption was found. I n making a n absorption of t h e fluid constituent of "G-3'3 a slight moclification of t h e method was used. In addition t o t h e thermocouple in t h e annuiar space a second standardized thermocouple was introduced, t h e bead of this latter being placed inside t h e magnesia cylindcr and testing directly an t h e magnesia disc supporting t h e piece under treatment. f n this way t h e exact temperature of t h e pie& itself and t h e absorbing disc could be measured. In this absorption after preheating over nigh* a s usual, blast was p u t 'on a n d t h e temperature raised until t h e thermocouple in t h e annular space indicated rqjo", a t which .time t h e inner couple in contact with t h e absorption disc and piece under treatment was 1438' C. During t h e next 8'/* hrs. the temperature of t h e inner couple was between 1438 and 1446" except for a short time en i t reached 14 j o O C. During most of t h e -time e temperature of t h e thermocouple in t h e annular space indicated a temperature from 17 to z s 0 higher a t recorded b y t h e inner couple. An exn of t h e material after cooling showed t h a t a piece weighing j:. 0580 g. lost by absorption 0 . 8 7 7 9 g. or 17.3 per cent. rtions of t h e magnesia disc showing absorbed ial were dissolved a n d t h e weight of AlzOa a n d 0 determined, a n d t h e per cent of these constituents in t h e absorbed material calculated. These analyses showed t h a t t h e material absorbed in t h e second experiment from t h e "G-I" contained Ala08 n o . 11-G-I x 100 D I A M B I K R S 4 7 . 7 6 a n d CaO 52.24, while t h a t from t h e "G-3" In order t o remove any component of t h e "GI" gave AlzOs 4 7 . 2 4 a n d CaO 5 2 . 7 6 per cent. material which might he liquid below I j , j j o C. t h e Since t h e temperature readings of t h e two thermosame method of procedure was followed as t h e one couples in t h e third absorption showed t h a t t h e thermoused t o remove t h e fluid constituent of synthetic couple in t h e annular space indicates from 17 t o 2 j o cellite from t h e crystals of tri-calcic silicate. A piece higher temperature t h a n t h a t actually existing a t t h e of t h e "G-I" mixture was placed on two discs and sur- point where t h e piece under treatment is located, it rounded by a low cylinder of pure MgO, t h e cylinder would be evident t h a t , i n t h e first absorption experibeing covered with a third disc of t h e same material. ment during t h e 4 hrs. t h e thermocouple recorded The tiiermoconple used t o record the temperature was 1400' in the annular space, t h e material under treatplaced in t h e annular space around t h e stack a n d was ment must have been below t h e melting point of t h e two mm. of t h e cylinder surrounding t h e piece under eutectic (1395' * j 9 ) , while during t h e last four treatment. I n making the absorption t h e furnace hours when t h e couple in t h e annular space recorded was allowed t o heat over night in order t o bring t h e 142j0 t h e material itself must have been very close temperature t o a little above I X O O " C. Blast was p u t t o 1400' or t h a t temperature which is most favorable on in t h e morning a n d t h e temperature raised until to t h e crystallization of tri-calcic aluminate. The the thermocouple in t h e annular space indicated 1400°, f a c t t h a t any absorption was found on t h e second treat-
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y ment of this same piece of material would indicate the difficulty of converting the 5Ca0.3A1203 into tricalcic aluminate, even in the presence of a large excess of CaO. Tri-calcic aluminate seems t o be best formed when the 5Ca0.3A1203 is held for a very long time in contact with CaO a t a temperature just above the melting point of t h e eutectic solution of CaO (139g’), b u t below t h e melting point of the pure 5Ca0.3A1203 (1455’). Under these conditions, if tri-calcic aluminate is either a metastable saturated solid solution of CaO in gCa0.3A1203 or is gCa0.3Al2O3 with four molecules of CaO of crystallization, it would gradually form and separate or crystallize from t h e still fluid solution until in time saturation of t h e whole of t h e gCa0.3Al203 had taken place. The entire mass would thus be converted into tri-calcic aluminate, unless there were present a n amount of CaO in excess of what would be required t o form tri-calcic aluminate with all of t h e Alz03. If t h e problem is considered as a simple study of t h e solubility of CaO in gCa0.3A1203 we would then regard a mixture having t h e empirical formula 4CaO A1203 a t 1600’ as a saturated fluid solution of CaO in 5CaO.3Al2O3 with some undissolved crystals or grains of CaO in suspension. On cooling such a solution a t the rate of 25’ per hour, since t h e solubility of the CaO in gCa0.3Al203 is a function of the temperature, t h e grains or crystals of CaO in suspension would gradually grow a t t h e expense of t h e dissolved CaO, so t h a t a t any time during t h e cooling period down t o the solidifying point of the eutectic solution the mass would consist of crystals or grains of CaO in a matrix made up of a solution of CaO in gCa0.3A1203 saturated a t t h e temperature a t which the material is held. Since t h e separation of tri-calcic aluminate seems t o require t h a t the solution of CaO in gCa0.3AlzO3 be slightly supersaturated and held a t a constant temperature for a very long time, and since t h e “ G - I ” and “G-3” mixtures were in a supersaturated state below the melting point of tri-calcic aluminate for three hours only, comparatively little tri-calcic aluminate would separate. Three hours compared with twenty-one days is a short time, but even in three hours some tri-calcic aluminate might be expected t o be found if a careful petrographic examination of the material were made. The composition of t h e liquid drawn off from “G-3” a t temperatures between 1438 and 1446’ agrees, as closely as experimental work could be expected, with t h a t of a solution having t h e same melting point as shown in t h e diagram in Plate I.
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Vol. 9, No.
IO
LOW TEMPERATURE DISTILLATION OF LIGNITE COAL By H. K. BENSONAND L. L. DAVIS Received August 6, 1917
The use of lignite coal for t h e production of paraffin and illuminating oils by destructive distillation has been developed t o a considerable extent in the SaxoniaThuringia lignite belt of Germany.l For this purpose soft, friable “wax coals” were distilled a t about 200’ C. under a slight vacuum for 24 hours, yielding the following products: tar, 6 t o 8 per cent; coke, 3 2 t o 36 per cent; t a r water, 46 t o 5 0 per cent; and gas, I O t o 1 2 per cent. From t h e distillation and refining of t h e crude oils were obtained a light lignite oil (“benzin”), distilling under 150’ C., with a specific gravity of 0.780 t o 0.810 and a flash point of 2 5 t o 30’ C . ; a burning oil (“solarol”), boiling below 250’ C., with a specific gravity of 0.825 t o 0.830 and a flash point of 50’ C.; a solvent oil (“putzol”) boiling up t o 280’ C., with a specific gravity 0.850 t o 0.860 and flash point, 100’ C.; together with paraffin oil, soft and hard paraffin and creosote oil. Ammonia may be recovered from t h e t a r water, though it is generally used directly as a fertilizer. The coke does not “cake” as does t h a t of ordinary coking coals, but shrinks slightly during distillation and is generally briquetted for use as a fuel. I n 1908, 1 2 factories, employing 1 2 2 1 workmen, were engaged in refining lignite oils.2 Inasmuch as a large portion of the coals of Washington and of t h e West‘in general are of a lignite character a study of a representative Washington lignite coal was made t o determine t h e yield of oil from the coal and t h e relation of t h e temperature of distillation t o t h e nature of t h e products obtained. DESCRIPTION
OF THE SAMPLE
The coal used was a representative sample of black lignite from t h e Hannaford No. I Mine, Tono, Washington. It is black in color, with a brown streak, is slightly banded in structure and breaks with a conchoidal fracture. The coal slacks on exposure t o air, but may be shipped some distance without weathering if placed in closed cars. The only use made of t h e coal a t t h e present time is as a steam coal in specially designed locomotives. The proximate analysis of the coal is given in Table I : TABLS~-PERCENTAGE COMPOSITION OF TONO LIGNITE CAR SAMPLE LABORATORY 474, 75) SAMPLE PERCENTAGES: As Received Air Dry Pure Coal Air Dry Moisture.. ............ 2 0 . 2 14.5 . . . . . . 12.3 Volatiles. 31.5 33.5 44.0 40.8
(U.5‘. Geol. Survey, Bull.
.............
Fixed . . . . . . . .......... Ash., . . . . . . . . . . 3 89 . 94 Sulfur. . . . . . . . . . . . . . . . . 0 . 5 2 Nitrogen.. . . . . . . . . . . . 1.06 B t. u . . . . . . . . . . . . . . . . 9.280
4 93..095 0.56 1.14 9,940
5. 6. ..0. . . 0.73 -1.49 13,000
3 79 . 81 0.3 1.60 9,650
CONCLUSIONS
I-A binary system of CaO and A1203 containing more t h a n 4 7 . 8 per cent ca0 should be regarded as a study in solubility of CaO in gCa0.3A1203. 11-Tri-calcic aluminate should be regarded either as a metastable saturated solid solution of CaO in jCa0.3A1203, or as gCa0.3A1203 with four molecules of CaO of crystallization, rather t h a n as a stable phase in t h e strict sense of the word. UNIVERSITY
OF
MICHIGAN,ANN ARBOR
APPARATUS U S E D
The retort used in distilling t h e coal was constructed as in Fig. I. A piece of standard black 3-in. pipe ( A ) 18 in. long was closed a t one end with a cap and a t the other with a companion flange and blind flange. The blind flange was bolted t o the face with t w o 1 Dammer, “Handbuch, der Chemiscben Technologie,” 4, 135-148; Ludwig Medicus, “Lehrbuch der Chemischen Technologie,” 965-977; Fischer, “Handbuch der Chemischen Technologie.” 141-153. 2 Z. angew. Chem., 1909, 2072.
