Study of the System Barium Oxide-Aluminum Oxide … · Study of the System Barium Oxide-Aluminum...
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Journal of Research of the National Bureau of Standards Vol. 45, No. 5, November 1950 Research Faper 2149 Study of the System Barium Oxide-Aluminum Oxide-Water at 30° C By Elmer T. Carlson, Thomas J. Chaconas, and Lansing S. Wells A study has been made of the action of water and of barium hydroxide solutions on the following compounds: BaO.Al 2 O 3 , 3BaO.Al 2 O 3 , BaO.Al 2 O 3 .H 2 O," BaO.Al 2 O 3 .2H 2 O, BaO.Al 2 O 3 .4H 2 O, BaO.Al 2 O 3 .7H 2 O, 7BaO.6Al 2 O 3 .36H 2 O, 2BaO.Al 2 O 3 .5H 2 O, and A1 2 O 3 .3H,O. From this, together with a study of precipitation from supersaturated barium aluminate solutions, a diagram of phase equilibria (stable and metastable) at 30° C has been drawn. All the barium aluminates are hydrolyzed by water. The stable solid phases in the system BaO-Al 2 O 3 -H 2 O at 30° C are A1 2 O 3 .3H 2 O (gibbsite), Ba(OH) 2 .8H 2 O, and, over a narrow range, probably 2BaO.Al 2 O 3 .5H 2 O. With the exception of the two lowest hydrates, all the hydrated barium aluminates possess a range of metastable solubility. I. Introduction Although the calcium aluminates, because of their relationship to hydraulic cements, have been the subject of numerous investigations here and elsewhere during recent years, the barium aluminates have been somewhat neglected. The latter, at present, are of limited practical importance. They have been used to some extent in water softening [I], 1 and they may be formed as intermediate products in the conversion of barium minerals to other compounds [2, 3]. It has been shown [4] that BaO.Al 2 O 3 possesses binding properties. Hunt and Temin [5] reported some ex- periments with barium aluminate relative to its suitability as a wall plaster for protection against X-rays, but no details as to preparation or composi- tion of the aluminate were given. Attempts have also been made to prepare barium cement, analogous to portland cement, by substituting barium carbon- ate, in whole or in part, for calcium carbonate in the raw mix. It has recently been reported by Gallo [17] and by Braniski [19] that such substitution is feasible, and that the resulting cement is particularly resistant to sea water and to sulfate waters. The purpose of the present investigation was two- fold. First, to study the hydraLion of the barium aluminates; and second, to discover what analogies, if any, exist between the aluminates of barium, and those of calcium, in the hope thai this might aid in clarifying some 1 aspects of the hvdration of the cal- cium aluminates that are not completely understood. A number of anhydrous barium aluminates are reported in the literal lire, but only three may be considered definitely established, namely, :>Ba().AIX),, BaO.AU);,, and BaO.6Al 4 O 3 [6, 7, 8, 9]. The last is believed to be analogous to /^-alumina |l(), 11], and its exact composition appears lo be somewhat in doubt [8]. ll was not included in the present study. The various barium aluminate hydrates have been described in a previous paper [12]. No evidence of any hydrate more basic than 2BaO.Al 2 O8.5H 2 O was found in the present study, although Beckmann [13] and MaekaWa [14, L5] have reported the preparation of a tribarium aluminate hydrate. Neither optical iii I Hack cis Indicate i in' literature references ai end of this paper. properties nor X-ray diffraction data, however, were given. Malquori [16] has published a phase equi- librium diagram of the system BaO-Al 2 O 3 -H 2 O at 20° C. The present investigation includes a study of the action of water and of barium hydroxide solutions on the various aluminates and a diagram of phase equilibria in the system at 30° C. II. Preparation of Compounds 1. Raw Materials The alumina used in the preparation of the various aluminates was a commercial preparation of gibbsite (AI2O3.3H2O) used in the manufacture of glass. It contained about 0.30 percent of Na 2 O; other impuri- ties were negligible. Barium was obtained in the form of the carbonate, the hydroxide, and (for a few experiments) the nitrate. These were reagent qual- ity chemicals meeting ACS standards. 2. BaO.Al 2 O ;i Barium carbonate and gibbsite were blended in the correct proportions, made up to a thin paste with water containing a few drops of a, dispersing agent, and thoroughly mixed. The paste was then dried and heated in a platinum dish at 1,400° C for 1 hr. The product was shown bv pet rographie examination and X-ray diffraction analysis to be essentially inonobarium aluminate (Ba().AL() :! ). Treatment with hydrochloric acid left a residue amounting to 0.7 percent, probably consisting of corundum. At- tempts to improve the product bv grinding and reheating were unsuccessful. Lower burning tem- peratures were found to be unsatisfactory; for ex- ample, a batch healed for 1 hr at 1,300° had an insoluble residue of N.. r ) percent. 3. 3BaO.ALO :t Tribarium aluminate was prepared in the manner described above for monobariiini aluminate, will) the appropriate change in proportion of raw materials. The mixture was healed in a refractory crucible, as experience showed thai platinum was Strongly 381
Transcript of Study of the System Barium Oxide-Aluminum Oxide … · Study of the System Barium Oxide-Aluminum...
Journal of Research of the National Bureau of Standards Vol. 45, No. 5, November 1950 Research Faper 2149
Study of the System Barium Oxide-AluminumOxide-Water at 30° C
By Elmer T. Carlson, Thomas J. Chaconas, and Lansing S. Wells
A study has been made of the action of water and of barium hydroxide solutionson the following compounds: BaO.Al2O3, 3BaO.Al2O3, BaO.Al2O3.H2O," BaO.Al2O3.2H2O,BaO.Al2O3.4H2O, BaO.Al2O3.7H2O, 7BaO.6Al2O3.36H2O, 2BaO.Al2O3.5H2O, and A12O3.3H,O.From this, together with a study of precipitation from supersaturated barium aluminatesolutions, a diagram of phase equilibria (stable and metastable) at 30° C has been drawn.All the barium aluminates are hydrolyzed by water. The stable solid phases in the systemBaO-Al2O3-H2O at 30° C are A12O3.3H2O (gibbsite), Ba(OH)2.8H2O, and, over a narrowrange, probably 2BaO.Al2O3.5H2O. With the exception of the two lowest hydrates, allthe hydrated barium aluminates possess a range of metastable solubility.
I. Introduction
Although the calcium aluminates, because of theirrelationship to hydraulic cements, have been thesubject of numerous investigations here and elsewhereduring recent years, the barium aluminates have beensomewhat neglected. The latter, at present, are oflimited practical importance. They have been usedto some extent in water softening [I],1 and they maybe formed as intermediate products in the conversionof barium minerals to other compounds [2, 3]. Ithas been shown [4] that BaO.Al2O3 possesses bindingproperties. Hunt and Temin [5] reported some ex-periments with barium aluminate relative to itssuitability as a wall plaster for protection againstX-rays, but no details as to preparation or composi-tion of the aluminate were given. Attempts havealso been made to prepare barium cement, analogousto portland cement, by substituting barium carbon-ate, in whole or in part, for calcium carbonate in theraw mix. It has recently been reported by Gallo[17] and by Braniski [19] that such substitution isfeasible, and that the resulting cement is particularlyresistant to sea water and to sulfate waters.
The purpose of the present investigation was two-fold. First, to study the hydra Lion of the bariumaluminates; and second, to discover what analogies,if any, exist between the aluminates of barium, andthose of calcium, in the hope thai this might aid inclarifying some1 aspects of the hvdration of the cal-cium aluminates that are not completely understood.
A number of anhydrous barium aluminates arereported in the literal lire, but only three may bec o n s i d e r e d de f in i t e ly e s t a b l i s h e d , n a m e l y , :>Ba() .AIX), ,BaO.AU);,, and BaO.6Al4O3 [6, 7, 8, 9]. T h e last isbelieved to be analogous to /^-alumina |l(), 11], andits exact composition appears lo be somewhat indoubt [8]. ll was not included in the present study.
The various barium a lumina te hydra tes have beendescribed in a previous paper [12]. No evidence ofany hydra te more basic than 2BaO.Al2O8.5H2O wasfound in the present study, although Beckmann [13]and MaekaWa [14, L5] have reported the preparat ionof a tribarium a lumina te hydrate. Neither optical
iii I Hack cis Indicate i in' literature references ai end of this paper.
properties nor X-ray diffraction data, however, weregiven. Malquori [16] has published a phase equi-librium diagram of the system BaO-Al2O3-H2O at20° C.
The present investigation includes a study of theaction of water and of barium hydroxide solutionson the various aluminates and a diagram of phaseequilibria in the system at 30° C.
II. Preparation of Compounds
1. Raw Materials
The alumina used in the preparation of the variousaluminates was a commercial preparation of gibbsite(AI2O3.3H2O) used in the manufacture of glass. Itcontained about 0.30 percent of Na2O; other impuri-ties were negligible. Barium was obtained in theform of the carbonate, the hydroxide, and (for a fewexperiments) the nitrate. These were reagent qual-ity chemicals meeting ACS standards.
2. BaO.Al2O;i
Barium carbonate and gibbsite were blended in thecorrect proportions, made up to a thin paste withwater containing a few drops of a, dispersing agent,and thoroughly mixed. The paste was then driedand heated in a platinum dish at 1,400° C for 1 hr.The product was shown bv pet rographie examinationand X-ray diffraction analysis to be essentiallyinonobarium aluminate (Ba().AL():!). Treatmentwith hydrochloric acid left a residue amounting to0.7 percent, probably consisting of corundum. At-tempts to improve the product bv grinding andreheating were unsuccessful. Lower burning tem-peratures were found to be unsatisfactory; for ex-ample, a batch healed for 1 hr at 1,300° had aninsoluble residue of N..r) percent.
3. 3BaO.ALO:t
Tribarium aluminate was prepared in the mannerdescribed above for monobariiini aluminate, will) theappropriate change in proportion of raw materials.The mixture was healed in a refractory crucible, asexperience showed thai platinum was Strongly
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attacked. A temperature of 1,300° was found tobe adequate to reduce the insoluble residue to 0.1percent. For some of the tests, the product wassubsequently fused in an oxygen blast.
4. BaO.Al2O3.H2O
The compound to which the formula BaO.Al2O3.-H2O is assigned was prepared hydrothermally.Gibbsite and barium hydroxide were mixed in therequired proportion, with added water, and placedin platinum dishes that were then stacked in a bomb-type autoclave and heated in an oven at about 260° Cfor 7 days. The product in each of the dishes con-sisted of a hard crust of the desired hydrate sur-rounding a core of softer material. The latter wasshown by X-ray analysis to consist of boehmite(A12O3.H2O). Despite this evidence of the presenceof excess alumina, the molar ratio of BaO to A12O3in the aluminate ranged from 1.10 to 1.14, in agree-ment with the findings previously published [12].It appears likely that the actual formula should be8BaO.7Al2O3.7H2O or 9BaO.8Al2O3.8H2O, but itwould be impossible to establish either formula onthe basis of present data. All preparations of thishydrate, regardless of changes in raw materials andin conditions of heating, have been more or less con-taminated with minute inclusions of some unknownmaterial in the crystals.
5. BaO.Al2O3.2H2O
Monobarium aluminate dihydrate, BaO.Al2O3.-2H2O, was prepared by the method described abovefor BaO.Al2O3.H2O, except that the temperature washeld at about 215° C, and the duration of heatingwas 4 days. The product consisted of well-formedcrystals, ranging up to 3 mm in size. Apparentlythere was a small amount of uncombined alumina,as the molar ratio, BaO :A12O3 :H2O, was found to be0.95:1:1.95, and a slight turbidity remained whenthe crystals were dissolved in hydrochloric acid.
6. BaO.ALO3.4H2O
Several small batches of monobarium aluminatetetrahydrate, Ba,().Al2O:!.4ir2(), prepared by variousmeans, were used in the solubility studies. Somewere prepared by allowing BaO.Al2O3.7H2O to stand,in contact with barium aluminate solution, forseveral months at 30° C. The usual procedure,however, was to raise the temperature to 50° C,whereby the transition period was shortened to afew days. In all eases, the analysis of the productswas xovy close to the theoretical.
7. BaO.ALO:,.7H,O and 7BaO.6ALOt.36rLO
Monobarium aluminate heptahydrate (BaO.-AL():{.7ILO) and the compound 7Ba().<>AU);(.:;c>II.,Oare close together in composition but quite dissimilarin optical properties. In a previous publication[12], the latter compound was designated 1.1 BaO.-A12()(.('»I\X). They were prepared by precipitation
from supersaturated solutions. These solutions wereprepared in various ways, the most satisfactory beingagitation of anhydrous BaO.Al2O3 with Ba(OH)2solution for 1 hr, followed by nitration. By thismethod, solutions containing as high as 35 g ofA12O3 per liter were obtained. Solutions of lowerconcentration were prepared somewhat more con-veniently by the action of boiling barium hydroxidesolution on gibbsite. Best results were obtained byusing 75 g of gibbsite, 125 g of Ba(OH)2.8H2O, and 1liter of water, boiling for 1% hrs, filtering at once,and allowing to cool. Concentrations ranging from11 to nearly 19 g of A12O3 per liter were obtained bythis method.
The course of precipitation varied somewhat withconcentration. From highly concentrated solutions,7BaO.6Al2O3.36H2O began to separate almost atonce, while from more dilute solutions the start ofprecipitation was sometimes delayed several days.After a period ranging from a few days to 4 mos, thesolid phase underwent a transformation to BaO.-A12O3.7H2O, probably by means of re-solution andreprecipitation, as no intermediate forms wereobserved. This phase change occurred when theconcentration of alumina had been lowered to arather poorly established range indicated by thedotted line in figure 10. 7BaO.6Al2O3.36H2O ap-pears to be progressively more stable as the BaOconcentration is increased. Solutions having initialconcentrations below or only slightly above thedotted line in figure 10 yielded BaO.Al2O3.7H2O asthe primary crystalline phase.
Considerable work was done in an effort to estab-lish the composition of these hydrates. In the caseof BaO.Al2O3.7H2O, analysis of numerous prepara-tions gave values ranging from 6 to 7 moles of H2Oper mole of A12O3. The following experimentthrows some light on the question. A preparation ofthe hydrate was filtered, washed lightly with water,and divided into two portions, one of which wasstored in a desiccator over calcium chloride, theother over a saturated solution of ammoniumchloride (relative humidity about 79%). After 11days, both samples had reached constant weight.The molar ratio H2O:A12O3 was 0.25 in the sampledried over calcium chloride, 6.96 in the one dried atthe higher humidity. It is inferred that the formulais BaO.Al2O3.7H2O, and that 1 molecule of water isso loosely bound that it is easily given ofl" in dry air.The hydrate is completely broken down at 120° 0 [12].
In the ease of the hydrate previously designatedL.lBaO.Al3O8.6H2O[12], the chief uncertainty is inthe ratio of BaO to A12():!. Analysis of numerouspreparations gave ratios ranging from 1.12 to 1.16,with no apparent trend toward higher values fromsolutions richer in BaO (as would be the case if itwere a question of solid solution). On the basisof these analyses the formula 7BaO.(>Al1>O:i.3(>II2Ohas been tentatively assigned to (his compound.
8. 2BaO.ALO:i.5H1,O
The most basic of the barium aluminate hydratesfound iji (his study is 2BaA).Al2Oj.5li2O. Several
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small batches of this were prepared by boiling amixture of gibbsite and barium hydroxide solutionuntil crystallization commenced, then filtering thesolution and concentrating the nitrate by furtherboiling. The compound separated out in coarselycrystalline form and was readily washed by decanta-tion. In all cases the analyses were close to thetheoretical composition. Attempts to prepare amore basic hydrate were unsuccessful.
III. Reactions with Water and with BariumHydroxide Solutions
1. General Procedure
Preliminary experiments were performed to ascer-tain the quantities of the various compounds thatmight be expected to go into solution. A moderateexcess of solid material was then used in subsequentexperiments. The compound being studied wasground, if necessary, to 100-mesh or finer, andplaced in an Erlenmeyer flask of appropriate size,and the flask was then nearly filled with water orwith barium hydroxide solution of the desiredstrength. The flask was then tightly stoppered,shaken frequently until there was no longer anydanger of "setting", and then stored in a cabinetmaintained at 30° C. The cabinet was equippedwith a recording thermometer. No provision wasmade for cooling the air, so that in summer the tem-perature regularly exceeded 30° C. This deviationdid not materially affect the experiments describedbelow but of course could not be tolerated for theequilibrium determinations described in section III,11. Consequently, the latter tests were made duringcooler weather. The normal fluctuation in tempera-ture of the air in the cabinet was about ±0.2° C,but it was undoubtedly much less within the flasks.
The flasks were shaken at intervals. From timeto time, samples of the clear liquid (5 or 10 ml) werepipetted out and analyzed for A12O3 and BaO bystandard analytical methods. Alumina was pre-cipitated by ammonium hydroxide, BaO by sulfuricacid. At the same time, in most cases, a drop of theliquid containing particles of the solid phase orphases present was removed by means of a. smallpipette, placed on a slide, and examined under themicroscope. In this way, phase changes were readilydetected.
In experiments dealing with the anhydrous alumi-nates the reactions were very rapid at first, and theintervals between samplings were too brief to permitclarification by Settling. It. was therefore necessaryto filter off portions of the solutions for analysis.The liquid was filtered through a, fritted glass crucibleby means of suet ion and caught in a small test tubeinside the filter flask. In this way, the solution wasexposed to the air only very briefly, and carbonationwas negligible.
Jn the tables that follow, it will be noted that, thevalues for BaO are given to the nearest tenth of 1percent, although those for A12O,{ are carried tohundredths. Jn the majority of cases this results
in three significant figures, which is believed to bethe limit of precision in sampling with a 10-mlpipette. Initial concentration values enclosed inparentheses were calculated from mixing proportions,rather than determined by analysis.
2. BaO.Al2O3
The results of a series of experiments with mono-barium aluminate (BaO.Al2O3) are given in table 1and figure 1. Experiments 1-1, 1-2, and 1-3 weredesigned to show the action of water on the alumi-nate. To avoid confusion, 1-1 and 1-3 are not in-cluded in figure 1. In experiment 1-1, table 1, 15 gof the dry aluminate was shaken with 300 ml ofwater. The data show that it dissolved ratherrapidly, attaining a concentration of 17.40 g ofA12O3 per liter at 1 hr. This is equivalent to roughly85 percent of the material originally present. Pre-cipitation of amorphous hydrated alumina was ap-preciable at 1 hr, slightly greater at 1 day, and verypronounced at 3 days, as shown by the sharp dropin A12O3 concentration, while the BaO remainedpractically constant.
20 30 40 50 60 70BAO IN SOLUTION, G/ L
90 100
FIOUHE 1. Solubility of BaO.A^Oa in water and in bariumhydroxide solutions at ^o0 C.
For the rest of the experiments, the proportion ofthe anhydrous aluminate was increased to 25 or 30g/300 ml of water (or solution). In No. 1-2, maxi-mum concentration was reached in 1 hr. Theascending curve in figure 1 lias a, slope correspondingclosely to a molar BaO:AM):( ratio of 1:1, and reachesa point, in excess of 36 g of A12O8 per liter. Examina-tion of the table shows that not. one but three separatemaxima, were found, at 1, 2, and 6 hours, respectively.For the sake of clarity some of these points areomitted from the graph in figure I. The concentra-tion fluctuated up and down, ver\ close to the 1:1ratio line, during this period. By way of confirma-
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TABLE 1. Solubility of BaO.Al2O3 in water and in bariumhydroxide solutions at 30° C
TABLE 1. Solubility of BaO.Al2O3 in water and in bariumhydroxide solutions at 30° C—Continued
Time
Concentration ofsolution
AI2O3 BaO
Solid phases present
Experiment 1-1 a
0l h r4hr .1 day3 days14 days1 mo3 mo
glitter0
17.4017.6517.407.304.253.803.40
glitter0
26.527.527.828.027.928.028.2
BaO.AUOs.BaO.Al2OH-hyd. AI2O3.
H y d . AI2O3.Do.D o .D o .D o .
Experiment 1-2
020 min40 min60 min80 min2hr3 h r4 hr__6hr1 day2 days8 days1 mo2 mo.. . . .4 mo __
018.8031.1236.3026.6230.0028.2227.1027.7823.708.027.307.007.105.70
029.047.354.441.046.744.242.543.741.129.232.841.345.145.1
BaO.AhO-,BaO.Al2O3+hyd. AI2O3.
D o .Do.Do.Do.Do.Do.Do.Do.
Hyd . Al2O3+BaO.Al2O3.7H2O.D o .DoDo.
Hyd . AI2O3.
Experiment 1-3 a
040 min50 min60 min70 min80 min90 minKid min2hr3hr .7 h r1 day7 days1 mo4 mo
025. 9027.9026. 7030.8229.5430. 6229.3828.3430. 7028 3616. 767.207.006.10
039.743.040.646.544.145. 544.543.246.845 232.132.541.347.9
BaO AI2O3Do.Do.Do.Do.
BaO.AlaOs+hyd.'AljOa.Do.Do.Do.Do.Do
Hyd. AlaO3+BaO.AbO8.7H2O.Do.D11
Hyd. Al2O3+BaO.Al2O3.4IM>
Experiment 1-4
015 min30 min45 min60 min75 min90 min105 min120 min150min__._190 min280 m i n . . . .:;:;n min390 min1M) min1 day4 days8 days19 days1 mi)•1 mo.3 mo
015.5026. 7033.3035. 4636. HO37. 5037.6036. 9038. 2035. 9633. 5033. 7030. 1020. soL0.808. 058.007. 7H7.757. 657.85
14.736.953.462. 765. 766. 967.967.767.068.965. 163.062. 857. 343. I31.928. 227. 126. 829 345. 757. I
BaO A12O3Do.Do.Do.Do.Do.Do.Do.Do.Do.
BaO.AljOsH 7Ha().6Al2o : i.:!(ill,0.Do.Do.Do.
7BaO.6AljO8.36HaOBaO.AljOs.7HsO.
Do.Do.Do.DoDo.
BaO.AljO8.7H2O 1 hyd. A12O3.
V, \ | i c i i m c n l l-.ri
015 min:'.<> min1 hr2hri hi3 Mayslo ihiysi mo
II16 5026. 4024 5015 soII 3011. 506, 30:: 95
(29. '-'151.766. 260.046. 411 1111 239. 635. 3
Ba( ).AL'():i .
r B a O . 6 A l s O 8 . 3 6 H •<>Do.1 >n1 >oDo.
BaO A.laO 111.0 | hyd. AM >Do.
Time
Concentration ofsolution
AI2O3 BaO
Solid phases present
Experiment 1-6
015 min30 minl h r2hr4hr3 days10 days1 mo
giliter0
18.8426.4917.9013.1012.5010.865.253.81
a/liter(43. 9)70.177.364.355.555.956.252.049.5
BaO.Al2O3.
7BaO.6Al2O3.36H2O.
7BaO.6Al2O3.36H2O.
7BaO.6Al2O3.36H2O+BaO.Al2O3.4H9O.BaO.Al2O3.4H2O.
Do.
Experiment 1-7
015 min30 minl h r2hr4hr3 days10 days1 mo2mo4 mo__ _ .5 mo. _- _
022.8623.0015.7011.8011.4010.344.232.852.772.882.75
(58. 5)89.785.374.067.967.871.956.353.852.552.052.3
BaO.Al2O3.
7BaO.6Al2O3.36H2O.
7BaO.6Al2O3.36H2O.
BaO.Al2O3.4H2O+7BaO.6Al2O3.36H2O.BaO.Al2O3.4H2O+Ba(OH)2.8H2O.
Do.
BaO.Al2O3.4H2O.D o .
Noi plot ted m figure 1.
tion of this unexpected finding, the experiment wasrepeated, with samples taken at shorter intervals(experiment No. 1-3 in table 1). This time fourmaxima were found, at 50, 70, and 90 min., and 3hr, respectively, and again the concentration variedup and down along the 1:1 line. Although the actualmechanism of this process could not be determined,a partial explanation may be advanced. When theanhydrous aluminate is agitated with water it dis-solves rapidly at first, but the rate of solution de-creases as the concent rat ion rises and the amount ofundissolved solid diminishes. Precipitation of a newsolid phase, or phases, commences as soon as a suffi-ciently high concentration has been reached andproceeds at an increasing rate for some time. Even-tually the point is reached at which the two processesof solution and precipitation are equal. For somereason, in these experiments, they failed to remainin balance; instead, first, one and then the other pre-dominated. The fact thai the concentration moveddownward as well as upward along the 1:1 ratio lines u g g e s t s t h a t t h e p r e c i p i t a t i n g p h a s e mus t h a v e beenB a ( ) . A U ) : i . 7 l l j ( ) . N o n e of t h i s p h a s e w a s a c t u a l l yo b s e r v e d a t t h i s s t a g e , but t h e u n d i s s o l v e d g r a i n s ofB a ( ) . A U ) : , w e r e seen t o be c o a t e d w i t h a t h i n l a y e rof e x t r e m e l y line b i ref r ingent , c r y s t a l s , too s m a l l fori d e n t i f i c a t i o n . It. is a s s u m e d tha t these w e r eBaO.Al2O3.7H2O. The subsequent departure fromt h e I : I l i n e is re f lec t ed in a n i n c r e a s e in t h e p r o p o r t i onof h y d r a t e d A U ) : , in t h e p r e c i p i t a t e . T h e s u d d e nb r e a k in t h e d i r e c t i o n o f h i g h B a O i n d i c a t e s t h a ts o m e of t h e p r e c i p i t a t e d B a ( ) . A I , ( ) , . 7 l I X ) h a s b e e nhydrolyzed, with precipitation of hydra ted Al,(){.T h i s p r o c e s s c o n t i n u e d for 2 m o o r l o n g e r u n t i l n oB a O . A l 2 O 3 . 7 H 2 O r e m a i n e d . T h e final v e r t i c a l p o r -t i o n o f t h e c u r v e i n d i c a t e s t h a t A U ) : 1 w a s s t i l l c o m i n g
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out of solution when the experiment was terminated.Experiments 1-4 to 1-7 in this series were designed
to determine the action of barium hydroxide solu-tions on monobarium aluminate. By referring tothe table and the figure it may be seen that thealuminate went into solution in the 1:1 molar ratioin all cases, and that the first new phase to be pre-cipitated was 7BaO.6Al2O3.36H2O. This compound,because of its needle-like crystalline habit, formed avoluminous precipitate with the result that thecontents of the flasks acquired a thick, mushyconsistency. In their subsequent behavior, thesepreparations differed. In experiment 1-4, the pre-cipitate was transformed to BaO.Al2O3.7H2O within1 day. This, in turn, showed evidence of hydrolysisafter 3 mos. It may be noted parenthetically, thatin this experiment, as in 1-2, more than one maximumwas observed, also that some of the points in thetable have been omitted from the graph for thesake of clarity. In 1-5 and 1-6, the precipitate wastransformed to BaO.ALO3.4H2O, without inter-mediate formation of the heptahydrate. There isalso evidence of a shift in concentration of thesolution in the direction of increasing BaO, corres-ponding to the liberation of excess BaO as the7:6:36 hydrate was converted to the 1:1:4. Experi-ment 1-7 followed a similar course, but with the addi-tion of another precipitated phase, Ba(OH)28H2O,first noted after 10 days. The curve in this caseshifts toward the left, as would be expected.
A close study of the curves in figure 1 revealsthat the ascending branch does not indicate a molar-ratio of exactly 1:1, although it is very close to thatvalue in the case of No. 1-2. The others becomeprogressively steeper as we go toward the high BaOside of the diagram, reaching the BaO:Al2O3 ratioof 0.91:1 for No. 1-7. This is due to the fact thaithe samples for- analysis were measured volumetric-ally, and that no correction was made for theincrease in volume of the barium hydroxide solutionresulting from addition of the solid aluminate. Thisincrease was found to be of the right order of magni-tude to account for the departures from the theo-retical 1:1 slope.
The process of solution to form a supersaturatedsolution, followed by precipitation of a differentsolid phase, is characteristic of binding agents, suchas portland cement and gypsum plaster. Other
|4] have reported that monobariumcapable of setting, and this fact wasring the course of the present study,aluminate was mixed with sufficient
water to make it workable, molded into a briquet,and allowed to stand in a moist closet. A moderateamount of heat was evolved shortly after molding.Alter r> hr, the briquet was lirm enough to heremoved from the mold. After standing moist,overnight and then being allowed to dry, the speci-men was quite hard, hut did not have enough strengthto permit an actual test to he made. The materialexpanded ahout, 10 percent during setting. The set.product contained considerable isotropic material,
investigatorsaluminate isconfirmed d>Some of the
probably hydrated alumina. X-ray analysis2 showedthe presence of a small amount of BaO.Al2O3.7H2O.These observations, together with the fact that theset material is readily attacked by water, make itappear unlikely that monobarium aluminate, initself, would have any value as a cementitiousmaterial.
3. 3BaO.Al2O3
Tribarium aluminate, 3BaO.Al2O3, reacts violentlywith water with the evolution of considerable heat.The course of solution and precipitation when 50 gof this compound was shaken with 300 ml of wateris shown in figure 2 and table 2. It may be seenthat the maximum concentration was reached in 4min. At this time, barium hydroxide (Ba(0H)2.8H2O) precipitated out, followed shortly by
10 20 30 40 50 60 70BAO IN SOLUTION, G/L
90 100
FIGURE 2. Solubility of 3BaO.Al2O3 in water at 30° C.
7BaO.6Al2O3.36H2O. Eventually, the predominantsolid phase was found to be 2BaO.Al2O3.5H2O in avery finely divided form not hitherto observed.These results were confirmed by two similar experi-ments, in one of which the tribarium aluminatepreviously had been heated to the fusion point andreground. The results differed in minor details, butwere in essential agreement. The fused materialreacted slightly less rapidly than did the anhydrousaluminate burned at 1 ,:>00°.
TABLE 2. Solubility of 3BaO.AlaO3 in water at 80° C
'rime
ConciMitnitimiof solution
AhOi BaO
Solid phases present
Experiment 2-1
minmin ,mintirLay
HID.mo.
glitter0
20. 0021.9020.0412.60io.;i.r)3. i.r.3, io
(//liter0
91.395. 191.666. 1(12. 2
47.8-17.2
3BaO.AljO8.
3BaO.AlaOH Ba(OH)j.8HsO.
7BaO.6AljOj.36HjO I Ba(OH)2.8H»O.7BaO.6AljOa.36Hj0 h2BaO.AlaOj.6HjO.
1 x raj diffraction patterns referred to In this paper were made by BarbaraSullivan, of the Constitution and M Icrostructure Section of i his Bureau,
385
8 12 I 6 20 24 28 32 36 40 44 4 8 52 56 60 64 68 70
BAO IN SOLUTION, G/L
FIGURE 3. Solubility of BaO.Al2O3.H2O in water and inJ>ariumrjiydroxide solutions at 30° C.
Inasmuch as the solution of this aluminate in waterrapidly reaches a concentration at which bariumhydroxide is precipitated, it appeared that little couldbe learned by studying its reaction with bariumhydroxide solutions; hence no tests of this kind weremade.
The capacity of tribarium aluminate for absorbingmoisture is illustrated by the following experiment.A 5-g sample of the freshly burned aluminate wasplaced in a crucible and confined over water in acovered glass jar at room temperature and weighedat intervals. In 6 days it took up moisture equiva-lent to 13 moles of H2O per mole of 3BaO.Al2O3.From then on the increase in weight proceeded moreslowly, but when the test was terminated at the endof 5 mo, the total water that had been taken up wasequivalent to 43 moles of H2O per mole of 3BaO.-A12O3. This is considerably more than would berequired to hydrolyze the compound completely toBa(OH)2.8H2O and A12O3.3H2O.
4. BaO.Al2O3.H2O
A series of three tests was made with Ba().Al2O3.-H3O, using puce water and half-saturated andsaturated solutions of barium hydroxide. The re-sults are given in table 3 and plotted in figure 3.Ten grams of the crystalline hydrate, ground topass a No. LOO sieve, was added to 200 ml of solution.The rate of solution is seen to be relatively slow.After 5 days, the material in No. 3-] bad been con-verted to hydrated alumina, and the others to7BaO.6Al2O;i.3()H2(). Further phase changes oc-curred On longer standing, as indicated in the table,and it- may be assumed that if the mixtures had beenkept still longer their behavior would have beenessentially similar to that described below for solu-tions of comparable concentrations.
TABLE 3. Solubility of BaO.Al2O3.H2O in water and bariumhydroxide solutions at 80° C.
Time
Concentration ofsolution
AI2O3 BaO
Solid phases present
Experiment 3-1
05hr.__-5 days.13 days24 days1 mo. .2 mo...3 m o -
05hr.._-5 days.13 days2i days1 mo...2mo.--3 mo...
06 tirr> days13 days24 daysI Mill2 mo. . .3 mo. .
glliterV)
3.857.506.674.854.133.603.45
gjliter
7.122.529.329.329.329.329.3
Ba0.A1203.n~20.BaO.Al2O3.H2O+hyd. AI2O3.Hydrated AI2O3.
Do.Do.Do.Do.Do.
Experiment 3-2
03.27
11.459.207.757.487.307.30
(23)28.843.842.640.340.339.941.0
Bao.Aloo3.H2o.
7BaO.6AhO3.36HjO.BaO.AhO3.7H2O.
Do.BaO.AljO8.7HjO+BaO.A]jO8.4HjO.
Do.Do.
Experiment 3-3
02.85
L0.3310. 83
7. <i.ri
li. (II1. 10
3.85
(46)51.66 6 . r>86. 262.760.156.255.2
flao.Aho3.n2o.
7BaO.6AljOa.36H2O.7BaO.6AhOs.36HiO (-BaO.AhOs.4HsO.BaO.AliO8.4HaO.
Do.Do.
O + hyd. A18O3.
5. BaO.ALO,.2H,O
A series of three experiments parallel to those*described in the previous section was made with thedihydrate. The results are shown in table 4 andfio-iire 4. Again we find that the rate of solution
386
1
-
-
-
1 1
rf
/
1 1
1 1
/
<*
^ ^
1 1
i \/ \
/
^ - - ^
1 ! 1
1 1 1 1 1
4-1
/
1 1 1 / 1 !
1 1 1 1 1 1 1 1 1 I
4-2
A
1 1 1 1 1 1 I I ! l /
1 1 1 1 I 1 1 1 1 1 1
4 - 3
/ "
1 1 1 I 1 1 1 1 1 1 !
8 -
6 -
4 h
8 12 16 2 0 24 4 8 52 56 6 028 32 36 40 44
BAO IN SOLUTION, G/L
FIOTJRE 4. Solubility of BaO.Al2O3.2H2O in water and in barium hydroxide solutions at 30° C
64 68 70
was relatively slow, and that the sample mixed withpure water eventually precipitated hydrated alumina.Sample 4-2, however, went into solution slowly, andno new phase was observed until after 2 mo hadelapsed. Then the tetrahydrate appeared, andgradually increased at the expense of the dihydrate.Sample No. 4-3 dissolved somewhat more rapidly,and the original material had all disappeared within1 mo, with precipitation of the tetrahydrate. Asmall amount of hydrated alumina was observedat the later ages in experiments 4-2 and 4-3.
TABLE 4. Solubility of BaO.Al2O3.2H2O in water and inbarium hydroxide solutions at 30° C
Time
Concentrationof solution
B a O
Solid phases present
Experiment 4-1
05 hr..._5 day8.13 days24 days1 mo_.-2 mo..-3 mo. . .I IMII
0 __ .5hr_...5 days.13 days24 days1 mo2 mo:; innI 1110
0 . .:, in.;. daysL3 days24 days1 mo2 mo:: moI mil
OlUter03.003. .r,r,4.583.252.752.402.402.28
g/liter0
0.610.820.120.720.820.720.920.8
Ba0.Als0J.2II20.Do.Do
BaO.AljOs.2H2O+hyd. AI2O3.Bydrated AljQs.
Do.Do.Do.Do.
Experiment 4-2
03. 054.456.307.407.757.857.004.1S
(23)28.5:«). s::::. 835.335. 936.036, :>33.9
BaO.AljO».2HjO.Do.Do.Do.Do.Do.
BaO.AljOj.2HjO hBaO.Al2O3.4H2O.Do.
HaO.Al-On.'lIhO+hyd. AI2O3.
Experiment 4-3
03. 436, 737 r,S7 256.324.884.078. 78
(46)51.766. l68, 768. 157.1M i l63. '.163. 2
It l ( ) . A hDo.Do.Do,
BaO.Al3Os.4H2O ! BaO.AljOs.2HsO.BaO.AlsOs.4HsO,BaO.AliOs.4HsO I-liyd. AlsOs,
Do.
BaO.AlsOs.4HsOH byd. AhOu.
6. BaO.Al2O3.4H2O
Preliminary e x p e r i m e n t s showed t h a tBaO.Al2O3.4H2O, unlike the compounds previouslydiscussed, exists as a stable or metastable phase inthe system BaO-Al2O3-H2O at room temperature.A larger number of mixtures was therefore made, inorder to ascertain the location of the solubility curve.The results obtained with this hydrate are given intable 5 and plotted in figure 5. The rate of solutionof this hydrate was relatively slow. The sample incontact with distilled water showed evidence ofhydrolysis at 1 day, and hydrated alumina wasobserved after 2 days. After about a month, all ofthe BaO was in solution. Precipitation of hydratedalumina continued, accompanied by a drop in con-centration of alumina in solution.
TABLE 5. Solubility of BaO.Al2O3.4H2O in water and inbarium hydroxide solutions at 30° C
Time
Concentrationof solution
AI2O3 BaO
Solid phases present «•
Experiment fi-l
01 day2 days5 days12 days19 days26 days40 days2 mo3 mo1 mo•ri mo7 mo
glitter01.051.732.002.402.502.482.051.981.901.701.551.40
glitter02.35.18.5
12.414, 615.115. fi18, 815.715.114.914.6
BaO.Al2O3.4H2O.Do.
BaO.AljOs.4HsO+hyd. AI2O3.Do.
BaO.AlsOs.4HsO+hyd AljOj.Ilvd. AlsOs.
Do.Do.Do.Do.Do.
Experiment 5-2
01 day2 days5 days12 days19 days26 days40 days2 moi mo1 mo5 mo7 mo9 mo
00.301.151.702.733.003.032. HI2 SI)3.002 HO2. 702. <i02.00
(7.6)H. :;9.5
10.311.9
12! 613.514.617 119.421.223. -122. i)
Hil().Al2()a.41I2O.Do.Do.
HiiO.Al2O3.4U2O I hyd. A.1JOJ.
BaO.AlsOs.4HsO 1 byd. AlsOs.Do.Do.Do.D oDo.D o
11 v<i- AI2O3.1)0.
387
5-6
I
5 -7
y i I / I
5-8 5-9 5-106> <&>
1/ 1 1 I4 8 52 56 602 8 32 36 40 4 4
BAO IN SOLUTION, G/L
FIGURE 5. Solubility of BaO.Al2O3.4H2O in water and in barium hydroxide solutions at 30° C.
6 4 68 70
TABLE 5. Solubility of BaO.Al2O3.4H2O in water and in TABLE 5. Solubility of BaO.Al2O3.4H2O in water and inbarium hydroxide solutions at 30° C—Continued barium hydroxide solutions at 30° C—Continued
Time
Concentrationof solution
AI2O3 B a O
Solid phases present
Experiment 5-3
01 day . .6 days.IS days1 mo2 mo__3 mo. . .4 mo.. .5 mo8 mo.. .14 mo._
glliter00.671.752.402.602.852.872.852.752.902.51
glliter(13.3)14.515.917.017.517.617.517.617.717.918.5
Ba0.Ab03.4H20.Do.Do.Do.Do.
BaO.AhO3.4H2O+hyd. AI2O3Do.Do.Do.Do.
Hyd. AI2O3.
Experiment 5-4
01 day__6 days.15 days1 mo.. .2 mo.. .3 mo.. .4 mo.. .5 mo.. .8 mo.. .14 mo
00.641.652.502.752.802.822.822.752.852.85
(17.7)19.020. 121.622.022.022.122.022.021.822. 0
Ba0.A1203.4H20.Do.Do.Do.Do.
BaO.Al2O3.4n2O+liyd. AI2O3.Do.Do.Do.
BaO.AljOj.4HjO+hyd. AM);,.
Experiment .r>-.r>
01 d a y . . .2 days12 daysI'.i days•.T, days:!!! days•10 days2 mo .3 mo4 mo. ..6 mo7 i n n
00.862.002. 352. cr.2.772. 902.953.002.802.902. 832 . .H.r,
(22.7)23.8
25.926. 126. 52<i. 821;. 726. :i:><;. 626. 12:,. x25.9
Ba0.A1203.4HJ0.Do.Do.Do.Do.
BaO.AMh.ilbO I hyd. AM),.Do.Do.Do.Do.Do.
BaO.AlaOj.4HjO I hyd. AM>,.Do.
Kxpeiimeni C d
0I dayli days16 days1 mo2 mo:; mo
0
0.731.922. 702. 7.r>2. 7.r>2 . 7 7
(27.9)28. 8:!(;.::31.631.631. (i31. fl
B a O . A l j O s . H I •<>.
Do.Do.Do.Do.
BaO.AljO8.4HsO I hyd. AM), .Do.
Time
Concentrationof solution
AI2O3 BaOSolid phases present
Experiment 5-7
01 day6 days15 days1 mo2 mo3 mo
glliter00.651.742.602.702.682.75
g/liter(37.2)37.939.140.540.840.740.7
Ba0.A1203.4H20.Do.Do.Do.Do.
BaO.Al2O3.4H2O+hyd. AI2O3.Do.
Experiment 5-8
01 dayli days15 days1 mo2 mo3 mo..4 mo5 mo
00.732.002.702.752.752.702.802.75
(41.7)a 40. 7
44.445.345. (i45.545.445.345.0
Ba0.A1203.4H20.
Ba0.A1203.4H20.Do.Do.
BaO.Al2O3.4H2O+hyd. AI2O3.Do.Do.Do.
Experiment 6 9
01 day6 days15 days1 mo ..2 mo...3 mo..
00.812. 002.702.802.702.75
(46. 5)"42.0a 47. 8
49.850.149. c.i49. 9
BaO.Al2O3.4H2O.
BaO.Al2O3.4H2O+Ba(()lI)j.slI().Do.Do.Do.Do.
Experiment 5 10
0I day7 days16 days1 1110 „2 mo
:t mo1 mo
00. '.!<;2.202. 902. 702. (IS
2.862. 7S
a (52.0)»42. 2»50.1
62. 763. 3WA. 1
63. 754.0
BaO.AljOj.4HjO.
+ (<) 11)2.SIM).Do.Do.
M i i O . A I 2 O 3 . 4 H 2 O I B a ( ( ) I I ) j , s l l , ( > I h y d .AljOs.
Do.Do.
•Prepared when room temperature was below :to", resulting in some precipita-tion 01 Haioil b.siijO which [('dissolved very slowly. These, points aro notplotted in figure 6.
lii test No. .r)-2, the material appeared to dissolvecongruently :>t lirst, but hydrated alumina was ob-served niter 5 days . After about, a month, maximumconcentration of AI2O;( in solution was a t t a ined .Thereafter, BaO continued to dissolve, Leaving aresidue of hydrated alumina. In many cases theOriginal form of the crystals was maintained, butthe gradual disappearance of birefringence and the
388
loss of transparency gave evidence of the decom-position. After 7 mo none of the original crystallinematerial was observed.
All of the other samples went into solution in amolar ratio of 1:1 (BaO:Al2O3), attaining an ap-parently stable condition of equilibrium. Neverthe-less, hydrated alumina appeared eventually in all theflasks, indicating progressive hydrolysis. As wouldbe expected, this reaction occurred more rapidly inthe less basic solutions, but it was apparent even inthose in contact with solid barium hydroxide. Thiswill be discussed further in section III, 13.
7. BaO.Al2O3.7H2OAlthough less stable than the tetrahydrate, the
heptahydrate lasts long enough to permit a deter-mination of its metastable solubility, and numeroustests were made for this purpose. The results ob-tained from some of these are given in table 6 andfigure 6. In water (No. 6-1) this compound hy-TABLE 6. Solubility of BaO.Al2O3.7H2O in water and in
barivm hydroxide solutions at 30°C
Time
Concentrationof solution
AI2O3 BaO
Solid phases present
Experiment 6-1
030 niin2hr___17 h r . . .2 days5days_13 days2 m o . .3 m o . . .6 Hid
0II) min1 day . .2 days.4 days.7 daysKi days1 mo . . .2 mo . . .3 mo . . .I mo
g/liter
1.822.802.603.302.311.901.631.4S1.30
glliter
2.744.14(i. 37
17.217.317.117.216.315.7
BaO.Alo03 .7H().Do.Do.
BaO.Al2O3.7H2O+hyd. AI2O3.Hyd. AI2O3.
Do.Do.Do.Do.Do.
Experiment fi '1
04.206.607. 107. 467.427.003.602.852.552. 45
9.715.419.119.519.820.227. 3•27. 627.827.427.8
Bao.AlJO3.7H2o.Do.Do.Do.Do.
E y d . A.I2O8.Do.Do.Do.Do.
TABLE 6. Solubility of BaO.Al2O3.7H2O in water andbarium hydroxide solutions at 30°C—Continued
Time
Concentrationof solution
AI2O3 BaOSolid phases present
Experiment 6-3
010 min1 h r . . . _1 day4 days13 days1 mo2 mo3 mo4 mo
015 min1 day2 days6 days15 days2 mo3 mo
g\Hter05.155.756.807.007.157.167. 053.703.27
g\lite.r18.525.426.127.527.428.327.829.633.033.0
Ba0.A1203.7H20.Do.Do.Do.Do.
BaO.Al2O3.7H2O+hyd. A12O3.
Hyd. AI2O3.Do.
Experiment 6-4
02.704.356.656.707.457.287.25
25.328.330.233.633.534.534.534.3
BaO.Al2O3.7H2O.
BaO.Al2O3.7H2O+hyd. AI2O3.Do.
BaO.AbO3 .7H2O+hyd. Al2O3+BaO.Al2Os.4H2O.
Experiment 6-5
010 minlhr___1 day . .6 days.15 days1 m o . . .3 m o . .
05 days.1 mo2 mo. . .3 mo . . .4 mo. . .5 mo . . .6 mo . . .
0l h r . . .1 day . .6 days.15 days.1 mo4 mo
05.646.427.457.557.357.707.20
32.339.240.941.641.341.241.541.6
BaO.Al2O3.7II2O.Do.Do.Do.Do. '
BaO.AbO3.7H2O.BaO.Al2O3.7H2O+BaO.Al2O3.4H2O.
Experiment 6-6
06.707.1(17.307.147.007.007.08
(40. 0)49.750.150.550.550.250.350. 2
Ba0.A1203.7H20.Do.Do.Do.Do.Do.Do.Do.
Experiment 6-7
04.351.867.227.757. Ill)7.60
47.152.052.754. I55.155. 154. 5
Ba0.A1208.7H20.Do.Do.Do.Do.Do.Do.
I I 1/ I 1 / ( 1 1 / 1 I I I I12 I 6 2 0 2 4 4 8 5 2 56 6028 32 36 10 44
BAO IN SOLUTION, G/L
FIGURE (>. Solubility 0/ BaO.AI2():i-7Jl1!() in water and, in barium hydroxide solutions at 80° C,
6 4 6 8 70
HO7N77 5( 389
drolyzed rapidly, with precipitation of hydratedalumina. The approximately horizontal portion ofthe curve indicates that solution and precipitationproceeded simultaneously until the hydrate wasexhausted.
In experiment 6-2, the least basic of the bariumhydroxide solutions used, hydrolysis was not appar-ent until after 7 days. The concentration, mean-while, had remained approximately constant forseveral days, and this concentration was taken asthe metastable solubility of BaO.Al2O3.7H2O at thispoint. The subsequent behavior of the mixture wassimilar to that of 6-1. Experiment 6-3 followed thepattern of 6-2, except that the hydrolysis in thiscase did not proceed rapidly until after 2 mo. Allthe mixtures in the more basic region reached acondition of equilibrium that persisted until theexperiment was terminated. It will be shown below,however, that this equilibrium is actually metastable,and that BaO.Al2O3.7H2O is not the final reactionproduct.
8. 7BaO.6Al2O3.36H2OThe results of experiments with 7BaO.6Al2O3.36H2O
are given in table 7 and figure 7. In general, thiscompound behaves much as does the heptahydrate,but it is more soluble and considerably less stable.In experiment 7-1, the hydrate dissolved almostcompletely in water within 10 min, with simultaneousprecipitation of amorphous hydrated alumina. Thelatter process continued at a diminishing rate, andequilibrium was not reached even after severalmonths. In 7-2 the hydrolysis was much slower,and some of the original hydrate was still presentafter 4 days. At 8 days, however, the remainder ofthe hydrate was found to have been transformedinto BaO.Al2O3.7H2O. The latter phase soon dis-appeared, and for some time the precipitation ofalumina continued, as evidenced by the verticalportion of the curve. At 3 mo., BaO.Al2O3.4H2()was first observed as a solid phase, and there is anaccompanying break in the curve toward the left.
1.4-
TABLE 7. Solubility of 7BaO.6Al2O3.36H2O in water and inbarium hydroxide solutions at 80° C
Time
Concentration ofsolution
AI2O3 BaO
Solid phases present
Experiment 7-1
010 min__2hrlday__.2 days. .9 days..19 days.1 mo2 mo3 mo4 mo5 mo7 mo
g/liter08.809.309.306.603.803.002.752.432.352.201.951.95
g/liter0
16.617.519.419.419.419.119.018.618.618.818.518.4
7Ba0.6Al203.36HoO.7BaO.6A]2O3.36H2O+hyd. AI2O3.Hyd. AI0O3.
Do.Do.Do.Do.Do.Do.Do.Do.Do.Do.
Experiment 7-2
0
2hr1 day___4 days__8 days_ _18 days.1 mo2 mo. _. _3 mo4 mo5 mo7 mo
09.40
11.4011.8010.869.006.605.404.353. 753.553. 303.00
7.824.7
29.529.629.829.429.528.5"28.029.129.028.8
7BaO.6Al2O3.36H2O.
7BaO.6Al2O3.36H2O+hyd. AI2O3.Do.Do.
BaO.Al2O3.7H2O+hyd. AI2O3.Hyd. AI2O3.
Do.Do.
Hyd. Al2O3+BaO.Al2O3.4H2O (trace).Do.Do.
Hyd. AI2O3.
Experiment 7-3
010 minlhr1 day.__2 da\s5 days..14 days.1 mo2 mo3 mo1 mo6 mo
06.348.90
12.1012.2012.007.937.056. 755. 004. 303. 95
15.225.729.234.3:i.rK 236.734. I36.641.842.342. 141.7
7BaO.6Al2O3.36H2O.Do.1)0.1)0.Do.
BaO.Al2O3.7H2O+hyd. AI2O3.Do.
Hyd. AbOs+BaO.AljOs.iHsO (trace).Do.Do.Do.
1 2 1 6 4 8 52 56 6 028 32 36 40 44BAO IN SOLUTION, G/L
FIGURE 7. Solubility of 7BaO.6AljOa.36HjO in water and in barium hydroxide solutions at :so° C.
6 4 68 70
390
TABLE 7. Solubility of 7BaO.6Al2O3.36H2O in water and inbarium hydroxide solutions at 80°C—Continued
Time
Concentration ofsolution
AI2O3 BaO
Solid phases present
Experiment 7-4
010 min.2hr1 day__.4 days..18 days1 mo2 mo3 mo... .6 mo7 mo
010 min_1 hr1 day__.2 days_.5 days..14 days1 mo2 mo.. .4 mo
010 min.lhr..i1 day__2 days.5 days15 days1 mo—2 mo.. .4 mo.--
010 i i i i n30 min1 day. .2 days5 days9 days.1 mo.. .2 mo...3 mo.. .4 mo.. .5 mo. . .
01 daj1 days7 days
10 days17 <l:i.\ SI UK)3 mil1 Hid
g/liter08.208.909.60
11.148.307.807.456.803.903.65
glitter23.036.036.839.342.137.437.636.135.931.631.4
7BaO.6Al2O3.36H2O.
7BaO.6Al2O3.36H2O.Do.
BaO.Al2O3.7H2O+BaO.Al2O3.4H2O.Do.
BaO.Al2O3.4H2O+hyd. A12O3.Do.Do.Do.
Experiment 7-5
07.709.76
11.6011.2611.4011.107.656.957.05
28.740.643.746.446.847.346.642.841.842.1
7BaO.6Al2O3.36H2O.Do.Do.Do.Do.
BaO.Al2O3.7II2O.Do.Do.
BaO.Al2O3.7H2O+BaO.Al2O3.4H2O.
Experiment 7-6
07.109.36
10.8010.9010.8411.007.957.357.20
37.846.549.052.652.752.952.748.848.447.8
7BaO.Al2O3.36H2O.Do.Do.Do.Do.
7BaO.Al2O3.36H2O+BaO.Al2O3.7H2O.BaO.Al2O3.7H2O.
Do.Do.
Experiment 7-7
08.509.609.909.809.708.204.383.703. 603. 373. 15
4.5. 355.866.156. 557. 057.358.552.961.451.461. 150. 5
7BaO.6AlsOs.36H2O.Do.Do.Do.Do.
7BaO.i)AI2O: t.:wiT2O+Ba0.Al20s.4H20Do.
BaO.AhO8.4HsO.BaO.AljOs.4H2O+hyd. AI2O3.
Do.Do.Do.
Experiment 7-8
(110.(1110. 1010.20
8. 907. 1(16. L84.401. If.
51.564.265. 766. 1
65.062. (i.r>H. (157. 5.ri7. 3
7B: iO .6Al 2 O 3 . 36H2( ) .7Ha() .6Al 2 ( ) 3 .3( i I l2( ) I l ( a (OI I K M I ,< >
Do,7H:iO.6Al2O:i.:i<ill2O+BaO.Al2O:i.4H2O
I Ba (oii). ' .siii 'O.BaO.AhO8.4H2O I Ba(OH)a.8HjO
Do.Do.Do.Do.
Mixtures in the more basic region reached a maxi-mum concentration that persisted long enough (5 toif) days) to permit the plotting of an approximatemetastable solubility curve in this range. The dataand curve for experiment 7-3 show that it resembled7-2, except thai in the more basic solution the inter-mediate phase, BaO.Al2O3.7H2O, persisted longer.Experiment 7-3 shows another peculiarity in thai the
heptahydrate formed was subsequently hydrolyzed,with a corresponding increase in basicity of the solu-tion. Experiments 7-4, 7-5, and 7-6, in solutionsprogressively more basic, are characterized bygreater stability of the intermediate phase,BaO.Al2O3.7H2O, and by a decrease in the amount ofliydrated alumina precipitated. In 7-7 and 7-8. theheptahydrate no longer appears as an intermediatephase, the original hydrate being transformeddirectly into the tetrahydrate. In 7-8, Ba(OH)2.8H2Oalso appears as a solid phase. The reverse kink in thecurve for this mixture reflects a temporary failureof the temperature control, which permitted the tem-perature to fall about 1 deg, resulting in precipitationof more barium hydroxide.
9. 2BaO.Al2O3.5H2OResults of so lubi l i ty exper iments wi th
2BaO.AL2O3.5H2O are given in table 8 and figure 8.This hydrate dissolved in water without any precipi-tation at first, so that the molar ratio of BaO to A12O3in solution remained approximately 2:1. Precipita-tion of hydrated alumina was first observed after 26days. The remaining crystalline material thereuponwent into solution as alumina continued to separateout.TABLE 8. Solubility of 2BaO.Al2O3.5H2O in water and in
barium hydroxide solutions at 30° C—Continued
Time
Concentrationof solution
A12O3 BaO
Solid phases present
Experiment 8-1
01 day5 days12 days..19 days-20 days.33 days40 days2 mo3 mo4 mo6 moIII mo
glitter03.425.055. 506.106.155.601. 553.402.702.552.151.87
glitter0
10.4
16.818.419.720.820.921.120.620. 620.319.9
2BaO.AhO3.5H2O.
2BaO.Al2O3.5H2O.Do.Do.
2liaO.Al2O3..riII2O+liyd. AhOs.Hyd. AI2O3.
Hyd. AI2O3.Do.Do.Do.Do.
Experimenl 8-2
0.l d a y . . .r> days12 daysi«.i days26 days33 days40 days2 mil3 mo4 mo8 moIII III:.
(8.5)14.9
20.321.922. (i23.124 324. !24. 224.22:!. 623. 5
2BaO.AljO3.6H2O.
2HaO.Al2O3.5ihODo.Do.
2BfiO.AljOi.5H2O+hyd.Do.
2HaO.AI,.O:1..r.ll;O | hyd.
Ilyd. AI2O3.Do.Do.Do.
Experiment 8-3
01 :l:i\5 daysL2 days111 days26 days33 days40 days2 mo3 Hill
i mo0 mo
(11.85:;. 201 (10
l . 7 ( i
5. (to5. 15
5. 255. L25.30B L5
( 1 7 . ( 1 )
23.0
20.331.232. 032. 332. 932. 132. 832. 532, 0
2BaO.Al2Oa.6H2O ' hyd. AljOa.Do.Do.Do.Do.
2BaO.AljO3.6H2O I hyd. AIJOJ.Do.Do.Do.
391
8 I 2 16 2 0 24 4 8 5 2 5 6 6 028 32 36 40 44
BAO IN SOLUTION, G/L
FIGURE 8. Solubility of 2BaO.Al2O3.5H2O in water and in barium hydroxide solutions at 30° C.
6 4 6 8 70
TABLE 8. Solubility of 2BaO.Al2O3.5H2O in water and inbarium hydroxide solutions at 30° C—Continued
Time
Concentrationof solution
BaO
Solid phases present
Experiment 8-4
01 day2 days5 days12 days19 days20 days40 diiys2mo3 mo1 mo•r> mo
(//liter01.702.452.853.804.204.304.154.254.404.204.05
g/liter(25. 7)30.732.534.036.737.837.838.038.137.937.337. 6
2BaO.Al2O3.5H2O.Do.
2BaO.Al2O3.5II2O+hyd. AI2O3.Do.
2BaO.Al2O3.5H2O+liyd. A12O3.Do.Do.Do.Do.
Experiment 8-5
09 days22 days:Sfi days2 mo:i mo4 mo5 rno
0X 40:i. 40:(. do:i. 253.353.35:\. 40
(34. 2)42.5•v.i. 6
i:(. <i43.543. 143.814.0
2BaO.AhO3.5HsO.2BaO.Al2O;i.5II2<H hyd. A12O3.
Do.Do.Do.Do.Do.Do.
Experiment 8 9
09 days22 days'M\ days2 mo3 mo4 mor, mo
03.303. 02:i. 202.903.022.992.95
(39. 9)47.0is. 0is. 2IS. 247.848.2IS. 1
2Ba0.Al20;t..r)ll2O.
2BaO.AljOj.5HjO+hyd. A1SO8Do.Do.Do.Do.Do.Do.
Kxperimorii s 7
II'.) days22 days
:tr> days2 mo3 mo<l IIKI
(12. 703.00
3.052.782. 852. HO
46. 650. I
" 1 7 . 0
51.561.752. I52. 3
2BaO.AljOj.5HjO.2BaO.AljOs.5HsO I Ba(OH)j.8HjO.2BaO.AljOj.5HjO+Ba(OH)j.8HjO I hyd.
AljOg.Do.Do.Do.
2BaO.AljO8.5HjO I hyd. AhOj.Kxprrimrnf S s
12 days22 daysiili days2 1110 . . . . .
3 mo4 rno.
02. HI)2. KX
;t. 052. SI)2.702. 75
(49.4)52. 7
• . |K. 1
5 2 , '•>- M l . II
53 753, 7
2BaO.AljOs.5HjO.
2BaO.AljOj.5HjO I Ba(OH)j.8HjO I hyd.MJOJ.
Do.Do.Do.Do
• Fluctuations in BaO concentration reflect temporary (allure <>r temperaturecontrol.
In barium hydroxide solutions, the course of solu-tion was similar, but the original hydrate appearedto be more stable as the concentration of bariumhydroxide increased. Although small amounts ofhydratod alumina were formed in all cases, much ofthe crystalline material remained even after 5 mo,except in 8-2, the least basic of these mixtures.
10. Precipitation From Supersaturated Solutions
In any study of phase equilibria in aqueous solu-tions, it is desirable to approach equilibrium fromboth sides, that is, from supersaturation as well asundersaturation. This is particularly true whenreactions are slow and when metastable phases maybe formed. In the present study, it was found thatprecipitation from supersaturated solution gaveresults that were not always reproducible and thatoften were difficult to interpret. This phase of theinvestigation, the first actually to be undertaken,yielded information vital to an understanding of thevarious solid phases and their formation, but it didnot furnish a clear picture of the equilibrium rela-tionships in the system. The solubility experimentsdescribed in the preceding sections proved to beessential to a clarification of these relationships.
Supersa tura ted solutions for the precipitation ex-periments were prepared as described in section II,7. These were kept in the 'M)° C cabinet with oc-casional shaking, and samples of the solutions werepipetted out from time to t ime for analysis. Smallsamples of the solid phases that precipitated werealso taken for microscopic examinat ion. Ou t ol alarge number of such solutions prepared at varioustimes, a, few have been selected as typical of thegroup, and the results are presented in table 9 andfigure 9.
Examination of the curve for Experiment 0-1shows that the precipitation followed a straight line,a s i d e from s l ight irregularit ies t h a t m a y be a t t r i b -u t e d to e x p e r i m e n t a l e r r o r s . T h e last t w o a n a l y s e si n d i c a t e a s l ight but, de f in i t e shift t o w a r d a l owerc o n c e n t r a t i o n of B a O . T h i s is probably d u e t oc r y s t a l l i z a t i o n of Ba( ( ) I I ) 2 . 8H 2 O on t h e wall of ( h eflask a b o v e t h e level of t h e Liquid, a p h e n o m e n o no b s e r v e d in a n u m b e r of t h e Masks a f t e r s t a n d i n g for
392
TABLE 9. Precipitation from supersaturated barium aluminatesolutions at 30° C
TABLE 9. Precipitation from supersaturated barium aluminatesolutions at 30° C—Continued
Time
Concentration ofsolution
A12OS BaO
Solid phases present
Experiment 9-1
01 day__2 days_5 days.13 days20 days29 days47 days2mo_._3 mo___4 mo. . .6 mo.__
01 day__2 days.5 days _13 days20 days29 days47 days2 mo_ .3 mo. . .4 mo. . .6 mo . . .
01 day . .2 days5 days.13 days20 (lays47 days2 mo-__3 mo—4 mo. . .6 mo. . .7 mo8 mo. . .
05 mo. . .7 mo. . .9 mo—12 moi . r i I I K Il.s mo
(//liter17.8016.388.085.583.903.503.453.202.952.652.452.45
glitter27.827.126.125.825.526.026.126.025.825.624.824.7
None.Hyd. AI2O3.
Do.Do.Do.Do.Do.Do.Do.Do.Do.Do.
Experiment 9-2
19.2418.9217.669.126.705.605.004.403.933.503.303.10
35.634. 934.932.232.533.633.733.733.833.433.132.8
None.Hyd. AI2O3.
Do.Hyd. Al2O3+BaO.Al2O3.7H2O.
Do.Hyd. AI2O3.
Do.Do.Do.Do.Do.Do.
Experiment 9-3
19.4019.3414.3610.168.147.707.467.326. 866. 807.007.107.25
43.843.536.630.828.027. (i26. 926. 725.725.625.438.842.9
None.7BaO.fiAl2O3.36H2O.7BaO.6Al2O:i.36H2O+BaO.Al2O3.7H2O.BaO.Al2O3.7H2O.BaO.Al2O3.7H2O+hyd. A12O3.
Do.Do.Do.Do.Do.Do.
I ' A p c i i i i i c n l 9-4
14.107.486. 604.664. 053.403.20
37.830. 737. I37. 136. (.i36. 836. 5
None.BaO.Al2O3.7H2O.Hyd. AhOs.
Do.Do.Do.Do.
Experiment 0-5
01 day2 days.5 days13 days20 days17 days2 Mid:! moA IIKIli mo
01 das1 days7 days11 days1'., days2 mo7 mo11 mo15 mois mo
glitter•21). Of
10 3(111.900. 207. 407. 307. 107.057.237. 257 .12
(j Ilitcr51.551.0t o . .r>36. 834.634. 233.833. 633. 633. 532. (.i
N (7BaO.6AljO8.36HjO.7BaO.6AljOj.36HjO I BaO.AljO8.7HjO.BaO.AljOs.7HjO.
Do.Do.Do.Do.Do.Do.Do.
Experiment 9 6
17.6517.3913.2911 1110.788. 757. 437.24.',. 183.863.40
51.751. 143. .r>40. 242. 639. 138. 036. 647.445. 214.5
None.7 l t ; i ( ) . r , A I .< > , . : » , ! | , ( ) .
Do.Do.
BaO.AljOj.7HjO,Do.Do.Do.
BaO.AljOj.4HjO I hyd. A.ljOaDo.Do.
Time
0 . .1 day2 days . . . ._5 days . . _ _9 days . . .15 days . . .20 days47 days2 mo
Concentration ofsolution
A12O3
gjltter20.2016.4613.4211.308.477.907.307.007.00
BaO
Solid phases present
Experiment 9-7
glitter59.454.249.547.244.543.342.441.841.4
None.7BaO.6Al2O3.36H2O.
Do.7BaO.6Al2O3.36H2O+BaO.Al2O3.7H2O.BaO.Al2O3.7H2O.
Do.DO.Do.D o .
Experiment 9-8
01 day2 days.5 days . . .9 days . . .13 days20 days . . .47 days . . .2 mo
17.7417. 5215.2811. 228.707.747.607.307.05
64 362.759.854.351.750.049.749.348.5
None.7BaO.6Al2O3.36H2O.
D o .7BaO.6Al2O3.36Il20+BaO.Al203.7H20.BaO.Al2O3.7H2O.
Do.Do.Do.Do.
Experiment 9-9
06 days. .
10 days3mo7 mo .11 mo ._13 mo15 mo .
14.16
11.447.684.003.383.303.30
59.2
54.950.344.143.243.243.2
None.Ba0.Al203.7H20+7Ba0.6Al203.3fiH20
(slight amt.).BaO.Al2O3.7H2O.BaO.Al2O3.7H2O+BaO.Al2O3.4H2O.BaO.Al2O3.4H2O4hyd. A12O3.
Do.Do.Do.
Experiment 9-10
05 mo7 mo9 mo12 irio15 mo18 mo
11.107.806.005.204.324.003 . 7 5
60.855. 953.852.551.350.550. 4
None.BaO.Al2O3.7H2O+BaO.Al2O3.4H2<).Ba().Al2O3.4H2O+hyd. A12O3.
Do.Do.Do.Do.
Experiment 9-11
010 daysI mo2 m o3 mo
12. 1011. 7.r>8. ou(i. 004.85
(IS. 1(17. 663.259.358. 0
Ba(OH)2.8H2O.
Ba(OI 1)2.8I [2O+BaO.Al2O3.4112O.
Ba(OH)2.8II2O+BaO.Al2O3.4H2O.
several months. Disregarding these two points,the average slope of the Line indicates :i molar ratio,Ba():Al2()3 0.10:1, in the precipitate. Analysis ofthe precipitate after 7 mo gave a molar ratio,BaO:Al2O3:H?O 0.07:1:3.27.
T h e p r e c i p i t a t e w a s b u l k y , a n d u n d e r t h e m i c r o -scope appeared as extremely line, irregular, Lsotropicgrains, with refractive index about L.57, close to themedian index of gibbsite (A12O3.3H3O). The X-raydiffraction pattern showed the stronger lines ofgibbsite, superimposed on a broad hand indicativeof amorphous material. It is inferred that theprecipitate originally was amorphous, and thatcrystallization to gibbsite occurred progressively onaging. 'The BaO present may he assumed to headsorbed.
Experiment 9-2 followed a similar course, exceptthat a small amount of BaO.AlaO3.7H2O appeared asan intermediate product and persisted for several
393
16 2 0 44 4 8 52
FlfiURK 9.
2 8 32 3 6 4 0BAO IN SOLUTION, G/L
Precipitation from supersaturated barium aluminate solutions at 30
56 6 0 64 6 8 70
C.
days. Its subsequent re-solution is reflected in aninflection toward the ri<z;ht in the curve.
Solutions more basic than No. 9-2 behaveddifferently. Experiments 9-3, 9-5, 9-6, 9-7, and 9-8precipitated 7BaO.6Al2O3.36H2O as the initial solidphase, followed by simultaneous disappearance ofIbis phase and precipitation of BaO.Al2O3.7H2O. In9-4, 9-9, and 9-10, the l a t t e r hydrate was the initialphase to separa te out . It will be noted t h a t in thislat ter group the initial concentrat ion of Al2O;t wasbelow 15 g/liter in each case. No. 9-6 is exceptionalin that the inversion from 7BaO.(iAl2O : j.:WlI2O toBaO.AI2O : j.7lI2O was accompanied by an abruptchange in direction of the concentration curve.For some unknown reason, the other members of I beseries failed to show this break, though 9-7 and 9-8do show a more gradual change in slope, which maybe attr ibuted to the same reaction.
Experimeni 9-4 is of interest in t ha i it, exhibitscomplete hydrolysis of the BaO.Al2Os.7H2O first,formed, with a corresponding change in concentrationof the solution. The same is true of No. 9-3, except-thai in this case the hydrolosis was still incompletewhen the experiment was terminated after s tnos.Experimeni 9-6 underwent an analogous change inconcentration, but in this case BaO.Al2O3.4H2O wasprecipitated along with the alumina. In 9-9 and 9-10these tWO phases were also coprecipilal ed, but. thehydrated a lumina was present only in small amount,
insufficient to cause any deflection of the concentra-tion curve. Experiments 9-3, 9-5, 9-7, and 9-8 ap-pear to have reached equilibrium at about 7 ^ of A12O3per liter, but it will be noted that these experimentswere terminated after 7 mos or less. This group wasstarted as the investigation was nearing completion,and their study was necessarily abbreviated. Itshould be clear from the previous discussion, how-ever, that this apparent equilibrium is metastable,and it may reasonably be assumed that on longerstanding, this group would have behaved as did theother members of the series.
Experiment 9-1 1 contained an excess of Ba(OH)2.-8II2() present, as a solid phase. The first new phaseobserved was BaO.Al2O3.4H2O, rather than t-hehepta-hydrate. It is worthy of note that even in contact,with excess barium hydroxide, the hydrate that- wasfirst- precipitated was a, tnonobarium compound.
The results of the above experiments and of an u m b e r of o t h e r s i n v o l v i n g p r e c i p i t a t i o n f r o m s u p e r -s a t u r a t e d s o l u t i o n m a y b e g e n e r a l i z e d a s f o l l o w s : ( I )Solutions containing less than 36 g of BaO per liter(approximately) precipitate amorphous hydratedalumina, together with some adsorbed BaO. Therate of precipitation from the more concentrated solu-tions is fairly rapid, but from solutions less concen-trated it may be extremely slow. The s table productis gibbsite. (2) Solutions containing more than 36 gof BaO per liter (approximately) precipitate one of
394
the hydrated barium aluminates. In this more basicregion the concentration of alumina determines whichaluminate precipitates first. Above 15 g of A12O3per liter (very roughly) the first phase to appear is7BaO.6Al2O3.36H2O; below that concentration theinitial solid phase is BaO.Al2O3.7H2O. (3) 7BaO.6A12O3.36H2O is relatively unstable and soon dis-appears with the formation of either hydratedalumina, BaO.Al2O3.7H2O, or BaO.Al2O3.4H2O, de-pending on the concentration of BaO in the solution.(4) BaO.Al2O3.7H2O is metastable and eventually dis-appears with formation of either hydrated alumina orBaO.Al2O3.4H2O or both.
11. Phase equilibria in the system BaO-Al2O3-H2Oat 30° C
From the data given in the preceding sections, it ispossible to construct the greater part of the phaseequilibrium diagram for the system BaO-Al2O3-H2Oat 30° C. The equilibrium concentrations and thecorresponding solid phases are listed in table 10.In order to complete the diagram, it was necessaryto study the solubilities of two additional compounds,namely, gibbsite (A12O3.3H2O) and barium hydroxideoctahydrate (Ba(OH)2.8H2O). Gibbsite was treatedwith barium hydroxide solutions in the mannerpreviously described in connection with the alumi-nates. Analyses were made at intervals for a periodof 8 to 9 mos, at the end of which time the concen-trations had remained substantially constant for3 mos. The barium hydroxide curve was establishedin part by experiments described above. Twoadditional points were obtained by determining thesolubility of recrystallized barium hydroxide octa-hydrate in water and in a barium aluminate solutioncontaining 1.42 g of A12O3 per liter. In these experi-ments equilibrium was attained quickly, but becauseof the high temperature coefficient of solubility andthe lack of high-precision temperature control itwas necessary to make repeated analyses and useaverage values. The equilibrium data obtainedin these two series of experiments ace included intable 10.
TABLE JO. Concentration of barium illuminate, solutions instable or metastable, equilibrium with solid phases at 30° C
TABLE 10. Concentration of barium aluminate solutions instable or metastable equilibrium with solid phases at 30° C—-Continued
E icperi-mi'iil
in 2HI 3
I
6-2..5-3..5-4..5-5..5-6..
( ' ( i n c c i i l r a -i ion of solu-
tion
AI2O3 BaO
glitter0. 20
. 39
.70
.881. IK;1. inL. 682.002. 682. 693. (in
3.002, 832. 792 '.in2, 71
U/lilrr4.89.7
14.219.023. 929. I34.238. 844.749. 668. I
12.517.622.026. 131.6
Solid phases preseni
A.hO8.3Ha0
MJO>.3HJO I Ba(OH)a.8HaO...
BaO. UaOa.4HjO I hyd. AUO3-.dodododo
I )ired ion of approachto equilibrium
From undersaturation.Do.Do.Do.Do.Do.Do.Do.DoDo.Do.
I).,.Do.Do.Do.Do.
Experi-ment
10-2110-2210-235-79-9. _ .5-8.5-910-12...
8-38-48-58-68-78-810-13 _
6-210-149-36-39-49-56-49-610-156-59-710-1610-24.__9-86-610-256-710-1710-18...
7-2
7-37-47-57-6._..
7-77-8
H)-19__10-20
Concentra-tion of solu-
tion
AI2O3
(//liter3.113 083.252 683.332.742.742.86
5.204 203.352 952.802.752.70
7 447.426 897.127 487.207 337 247.207 457 107.166.957.327 107.167.787 657.80
11. SO
12.2011 1411.6011.00
9. 9010. 20
(0)1 42
B a O
gl liter33.335 237.540 743.245.449.955.6
32.437 843.648 152.053.755.4
20 022.825 627.830 733.334 436 637.341 441 943.646.349.250 354 255.357.762. 2
29.5
35.242 146.452.7
:>(•>. 566.1
62.954 1
Solid phases present
BaO.Al2C3.4H2O+hyd. A12O3-.dododo
. . . . dodo
BaO.Al2O3.4H2OBaO.Al2O3.4H2O +Ba (OH)2.
8H2O
2BaO. AI2O3.5H2O +hyd. AI2O3.dododododo ..
2BaO. A12O3. 5H2O + Ba(() H)».8H2O.
BaO.AbO3.7H2O. do . .
dodo .dodo -dododo .-dododo ..dodododo .
. dodo
BaO. A12O3. 7H2O +Ba(OH)2.8H2O.
7BaO . 6 AI2O3 . 36H2O +hyd.A12O3.
7BaO.6Al2O3.36HaOdo
. d o . . .7BaO . 6AI2O3 . 36HaO + B a O .
AliOa.7HaO.7BaO.6AlaO8.36HaO7Bii() . 6AI2O3 . 36H2O | BaO.
Al2O3.4H2O+Ba(OH)2.8H2O .
Ba(OH)a.8HaO...do
Direction of approachto equilibrium
From supersaturation.Do.Do.
From undersaturation.From supersaturation.From undersaturation.
Do.Do.
Do.Do.Do.Do.Do.Do.Do.
Do.Do.
From supersaturation.From undersaturation.From supersaturation.
Do.From undersaturation.From supersaturation.From undersaturation.
Do.From supersaturation.From undersaturation.From supersaturation.
Do.From undersaturation.From supersaturation.From undersaturation.d
o
0
do
c
Do.
Do.Do.
Do.Do.
Also included are a number of points representingequilibrium (metastable) approached from supersat-uration rather than undersaturation. These pointsare shown as filled triangles in figure 10, in order todistinguish them from the others. It. will be notedthat there is fair agreement between the two methodsof approach in the case of Ba().AlL>():!.7llX). In thecase of the t etrah yd rate, however, the values ob-tained from the precipitation experiments are erraticand are generally higher than those obtained fromsolution experiments. The reason for this is notknown. No corresponding figures are given for7BaX).C>AL():i.:Wl L(), as there was no arrest in con-centra t ion during precipitation in this range. Fur-ther, there are no precipitation data for 2BaO.Al2O8.-ML.O because this phase was not obtained by precipi-tat ion at 30°.
No attempt was made to determine the solubilitycurve of amorphous hydra ted a lumina, part ly be-cause it is difficult to prepare this material free ofinterfering ions, and partly because it was believed
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14
12
10
5 6 60 64 6 8 70
FIGURE 10.
B A O IN S O L U T I O N , G / L
Concentration of barium aluminate solutions in stable or metastable equilibrium with solid phases at 30° C.
Symbols represent solid phases present, as follows: ©,7BaO.6Al2O3.36H2O; V, T , BaO.Al2O3.7H2O; A, A, BaO.Al2O3.4H2O; * , 2BaO.Al2O3.5H2O; O. AI2O3.3H2O(gibbsite); D, Ba(OH)2.8H2O. Combination of two symbols indicates coexistence of two solid phases. Filled triangles represent equilibrium approached fromsupersaturation. Other points represent equilibrium approached from undersaturation.
that such a curve would be dependent on the modeof preparation, hence not very significant. No testswere made with any of the crystalline forms of hy-drated alumina other than gibbsite, and, as men-tioned above, no work was done on the compoundBaO.6Al2O3.
Solubility curves for BaO.Al2O3.H2O and BaO.-A12O3.2H26 are likewise missing. As shown in sec-tion III, 4 and III, 5, these hydrates, both of whichwere prepared hydrothermally, are unstable in con-tact with barium hydroxide solutions at 30° C, andhence cannot be said to possess solubility curves atthis temperature.
Figure 10 is the phase equilibrium diagram of thesystem BaO-Al2O3-H2O at 30° C, complete except asnoted above. The stable phases are gibbsite andbarium hydroxide octahydrate, and possibly, overa narrow range, 2BaO.Al2O8.5H2O or BaO.Al2O3.-III,(). The other phases for which curves are shownare metastable throughout their entire range. Nev-ertheless, because of I he slowness of transition fromone phase to another, it is possible to trace a definitesolubility curve for each of the solid phases, except7 B a O . 6 A l 2 O 8 . 3 6 H 2 O a n d a m o r p h o u s h y d r a t e d a l u -m i n a . A d o l l e d CUTVe h a s been d r a w n to r e p r e s e n tt h e a p p r o x i m a t e s o l u b i l i t i e s of t h e f o r m e r .
It is a p p a r e n t f rom figure 10 t h a t ( h e r e is s o m eu n c e r t a i n t y a s to w h a t is t h e s t a b l e solid p h a s e o v e ra s h o r t range (50 to 56 g of B a O per l i t e r , a p p r o x i -m a t e l y ) . O n t h e bas i s of t h e d a t a g i v e n , it a p p e a r st h a t t h e r e is a point at 2.8 g of A U ) : , a n d ,r>2.0 g ofBaO per literal which gibbsite and 2BaO.Al2O8.5H2Oare in equilibrium, and another point at 2.7 g ofAM)-, and 55.6 g of BaO per liter at which 2BaO.-A l 2 O 8 . 5 H a O a n d ' B a ( O H ) 3 . 8 H 2 O a r e t h e s t a b l e s o l i dphases. I low ever, t he solubilil ies of the I liree alumi-nous phases are so close together in this area, andthe reactions leading to equilibrium are so slow, that
the stability relations here indicated cannot be con-sidered definitely established. Additional experi-ments a few degrees above and below 30° C mightassist in clarifying (he question.
12. Equilibria at Other Temperatures
A few experiments were conducted at temperaturesother than 30° C. In particular, sufficient work wasdone on the solubilities of BaO.Al2O3.7H2O andBa(OH)2.8H2O at 25° C to establish at least a portionof the curves for these compounds. As might beexpected, they are parallel to the curves at 30° C,but at lower concentrations. The solubility ofBa(OII)2.8H2O was found to be equivalent to 42.7 gof B a O per l iter at 2 5 ° C, a n d the point a t w h i c h t h etwo solid phases coexist was placed approximatelyat 6.8 g of Al-O, and 52.0 g of BaO per liter. Thesolubility of Ba(OII),.SlU) at 50° C, expressed interms of BaO, was found to be about 102 g/liter.This figure is not exact, as the temperature controlwas probably no closer than 1 (leg, but is givenmerely to indicate the magnitude of the temperaturecoefficient of solubility. At this temperature BaO.-ALO,.7II,() is rapidly converted to BaO.Al2O8,4H2O.N o equ i l ibr ium m e a s u r e m e n t s we re m a d e for t h elet i a h y d r a t e at t e m p e r a t u r e s o t h e r t h a n 3 0 ° C .
As m e n t i o n e d in t h e i n t r o d u c t i o n , a d i a g r a m ofp h a s e equ i l i b r i a in t h i s s y s t e m a t 2 0 " (• h a s beenp u b l i s h e d by M a l q u o r i [16]. W i t h d u e a l l o w a n c elor t h e difference in t e m p e r a t u r e , it sti l l is difficultt o r e c o n c i l e h i s d i a g r a m w i t h t h a t g i v e n i n f i g u r e 1 0 .I n p a r t i c u l a r , M a l q u o r i s h o w s o n l y t w o b a r i u m
a l u m i n a t e h y d r a t e s , 2 B a O . A I , ( ):;.r>l \ , i ) a n d o n e t h a th e d e s i g n a t e s B a ( ) . A l , ( ) ; ; . ( i l 1 , 6 . T h e l a t t e r , w h i c hw e m a y a s s u m e t o b e i d e n t i c a l w i t h t h e c o m p o u n dr e f e r r e d t o h e r e i n a s t h e h e p t a h y d r a t e , i s i n d i c a t e dt o b e t h e s t a b l e p h a s e a l o n g a c u r v e e x t e n d i n g a p p r O X -
396
imately from 2 g of A12O3 and 12 g of BaO to 6 g ofA12O3 and 22 g of BaO per liter. This is considerablyabove the curve shown in figure 10 for gibbsite(AI2O3.3H2O), and the latter very probably wouldbe found to have a lower solubility at 20° than at30°. It is believed, therefore, that Malquori's curvedoes not represent stable equilibrium.
13. Effect of Impurities
As is well known, barium hydroxide solutionsrapidly absorb carbon dioxide from the air, withthe formation of barium carbonate. Preliminaryexperiments indicated that this reaction would notseriously affect the results obtained in this study.The carbonate formed is practically insoluble inbarium hydroxide, and thus would be expected tohave no effect on equilibrium relations. Samplesfor analysis generally were taken with a pipette,leaving little chance for carbonation during sampling.Any carbonate formed on the microscope slide wasreadily distinguished from other phases by its highbirefringence. Periodic opening of flasks for sam-pling resulted in visible carbonation, but the totalamount was negligible, as evidenced by the constancyof concentration of the solution after attainment ofequilibrium.
More serious contamination was introduced bythe solvent action of the barium hydroxide solutionson the glass containers. In order to estimate theextent of the attack, a large number of silica deter-minations were made on reaction mixtures that hadstood for varying periods of time. The amount ofsilica found in solution was invariably small, usuallyabout 2 or 3 mg/liter. The amount of silica in thesolid residue, however, was considerable in flasksthat had been standing a long time, but there wasno apparent uniformity as to amount. For examplethe molar ratio of SiO2 to ALO:! was found to be 0.03in Ihr precipitate from one solution (not listedabove), and 0.84 in the precipitate from another ofvery nearly the same concentration. Both hadstood 2 yr, and in both cases the total quantity ofsolid was slight, having precipitated from relativelydilute solution. In most cases the amount of pre-cipitate was much greater and the percentage ofSi()2 correspondingly smaller. For example, theresidue from mixture 0-1, filtered off after (i mo,contained 0.01 mole of Si()L, per mole of AU) : ; . Thesilica was found to be present in the amorphousphase, not in tire crystalline BaX).AU) : ;.4l \A), whichwas in mos t cases the other phase present in theprecipi ta te after long s tanding . This was shown ina number of cases by separat ion of the precipitateinto line and coarse fractions, followed by analysisof each. This fact may be significant in connectionwith the observed presence of the amorphous phasein even the most basic mixtures , in the region wherethe equilibrium d iagram indicates that: one of theCrystalline hydrates should be the stable phase. It,is probable that in this case the observed amorphousm a t e r i a l ( a l w a y s s m a l l in a m o u n t ) is e i t h e r abarium silicate hydrate or a, barium aluminosilicat e.hydrate, in either case relatively insoluble.
The presence of silica in the precipitate is positiveevidence of the solvent action of the solutions on theglass containers. It must be assumed, therefore,that the other constituents of the glass, chiefly sodaand boron trioxide, likewise were present as contami-nants. No tests, however, were made for theseconstituents. It is reasonable to suppose that thesoda would remain in solution and that it mighttherefore have some effect on the equilibriumconcentrations. From the fact that no progressivechange in equilibrium concentration with time wasobserved, it is believed that this factor was of negli-gible significance.
IV. Comparison of Barium and CalciumAluminates
It was brought out in section III, 2 that anhydrousmonobarium aluminate possesses the property ofsetting to a hard mass after being mixed with water.The same phenomenon was observed with anhydroustribarium aluminate as well. It was also shown thatboth of these compounds, when mixed with water,form solutions that are highly supersaturated withrespect to certain hydrated products. This is inagreement with the well-known theory of Le Chatelier[18] that "the crystallization which accompanies theset of all of the bodies hardening upon contact withwater results from the previous production of asupersaturated solution". Le Chatelier and laterinvestigators have shown that this is true of thecalcium aluminates, so that in this respect it may besaid that there is a similarity in behavior between thealuminates of barium and of calcium. There is afurther similarity in that both 3BaO.Al2Ou and3CaO.Al2O3 react very vigorously with water,whereas the corresponding 1 : 1 aluminates reactmuch more slowly. Beyond this, however, it isimmediately apparent that the aluminates of bariumare quite different from those of calcium. Theformer are much more soluble and form an entirelydifferent series of hydra t ion products. As is wellknown, the calcium a luminates produce an isometrichydra te , 3CaO.Al2Oa.6H2O, as well as a crystall ineproduct consisting of hexagonal plates in which theratio of CaO to Al_.():i is either 2 : 1 or 4 : 1 or anintermediate1 value. Neither type of product wasobserved with the bar ium aluminates . These, on (IK1,o ther hand, yield a, series of hydra te s in which theratio of BaO to AU) : i is 1:1, or nearly so, togetherwith a single more basic hydrate, 2BaO.Al2Os.5H2O,w h i c h i n n o w a y r e s e m b l e s t h e d i c a l c i u m a l u m i n a t ehydrate. Only in the least basic region of the phased i a g r a m a r e t h e s y s t e m s B a ( ) - A U ) : t - I I 2 O a n d C a O -Alj();.-I I_.() s i m i l a r . H e r e , o v e r a s h o r t r a n g e in t h el a t t e r s y s t e m , a n d o v e r a m u c h l o n g e r r a n g e in t h ef o r m e r , g i b b s i t e is t h e s t a b l e so l id p h a s e .
V. SummaryOn the basis of the exper iments described above,
and subject to the experimental condit ions, thefollowing conclusions are presented:
1. Monobar ium a luminate is hydroly/.ed by water ,with precipitation of hydra t ed a lumina.
397
2. Monobarium aluminate dissolves in bariumhydroxide solutions with precipitation first of7BaO.6Al2O3.36H2O, subsequently of BaO.Al2O3.-7H2O in the less basic and BaO.Al2O3.4H2O in themore basic solutions.
3. Tribarium aluminate is rapidly hydrolyzed bywater, with precipitation of Ba(OH)2.8H2O, BaO.-A12O3.7H2O, and, subsequently, 2BaO.Al2O3.5H2O.
4. All the hydrated barium aluminates dissolve inwater and are hydrolyzed, with precipitation ofhydrated alumina.
5. The hydrated barium aluminates dissolve inbarium hydroxide solutions with eventual precipita-tion of the equilibrium solid phases, but frequentlywith preliminary separation of metastable inter-mediate solid phases.
6. The stable solid phases in the system BaO-Al2O3-H2O at 30° C are: (a) gibbsite (Ai2O3.3H2O) over arange from approximately zero concentration toabout 52 g of BaO and 2.8 g of A12O3 per liter; (b)Ba(OH)2.8H2O from 52.9 g of BaO and zero A12O3to about 55.5 g of BaO and 2.7 g of A12O3 per liter;(c) probably 2BaO.Al2O3.5H2O (but possibly BaO.-A12O3.4H2O or gibbsite) over the short range from52 BaO and 2.8 A12O3 to 55.5 BaO and 2.7 A12O3.
7. 7BaO.6Al2O3.36H2O is a metastable phase, notsufficiently stable to permit an accurate determina-tion of its solubility.
8. BaO.Al2O3.7H2O is also metastable, but it mayexist in contact with solution for several months.
9. BaO.Al2O3.4H2O is likewise metastable over thegreater part, if not all, of its range, but its stabilityis greater than that of the higher hydrates.
10. 2BaO.Al2O3.5H2O resembles BaO.Al2O3.4H2Oin its degree of stability in the metastable range.
11. No hydrate more basic than 2BaO.Al2O3.5H2Owas found.
VI. References[1] R. Stumper, Chimie & industrie 22, 1067 to 83 (1929).[2] G. Grube and G. Heintz, Z. Electrochem. 41, 797 (1935).[3] K. Akiyama, Z. Kajima, and H. Aiba, J. Soc. Chem. Ind.
(Japan) 41, 218 (1938), and 43, 145 (1939); abstr. inChem Abstr. 33, 325 and 7497 (1939).
[4] V. F. Zhuravlev, Tsement 1939, No. 8, 41; abstract inChem. Abstr. 35, 595 (1941).
[5] F. L. Hunt and M. Temin, Radiology (Feb. 1927).[6] G. W. Morey, U. S. Patent 1,688,054 (1928).[7] H. V. Wartenburg and H. J. Reusch, Z. anorg. allgem.
Chem. 207, 1 (1932).[8] S. Wallmark and A. Westgren, Arkiv. Kemi, Mineral,
Geol. 12B, No. 35 (1937).[91 N. A. Toropov, Compt. rend. acad. sci. URSS 1935, 150.
[10] N. A. Toropov and M. M. Stukalova, Compt. rend.acad. sci. URSS, 24, 459 (1939).
[11] N. A. Toropov and M. M. Stukalova, Compt rend.acad. sci. URSS, 27, 974 (1940).
[12] E. T. Carlson and L. S. Wells, J. Research NBS 41, 103(1948) RP1908.
[13] E. Beckman, J. prakt. Chem. [2] 26, 385 and 474; 27, 126(1883).
[14] G. Maekawa, J. Soc. Chem. Ind. (Japan) 44, 912 (1941);abstr. in Chem. Abstr. 42, 2536 (1948).
[15] G. Maekawa, J. Soc. Chem. Ind. (Japan) 45, 130 (14)42).[161 G. Malquori, Gazz. chim. ital. 56, 51 (1926).[17] G. Gallo, Ind. ital. del cemento 17, 123 (1947).[18] H. Le Chatelier, Experimental researches on the constitu-
tion of hydraulic mortars (1887) (Translated by J. L.Mack, 1905).
[19] A. Braniski, Rev. materiaux construction trav. publ.(Ed. C), No. 404, 154 (1949).
WASHINGTON, June 2, 1950.
Journal of Research of the National Bureau of Standards Vol. 45, No. 5, November 1950 Research Paper 2150
Permeability of Glass Wool and Other Highly PorousMedia'
By Arthur S. IberallAn elementary treatment is developed for the permeability of fibrous materials of
high porosities, based on the drag of fche individual filaments. It is believed Unit I lie sametreatment is valid for other highly porous media,. A brief historical review is given oftheories relating I he permeability to the s t ructure of porous media. The applicability ofthe currently accepted permeability theory, based on the hydraulic radius, only to media,of low porosities is discussed. Both approaches may be extended to pennii approximatecorrelat ion for i n t e r m e d i a t e porosi t ies . Fo r f ib rous m a t e r i a l s of h igh p o r o s i t y , it, is s h o w nthai the efleei of fluid inertia results iii a permeability thai varies wilh How even ai lowReynolds Dumber. 'The permeability to gaseous flow is also shown to vary with the abso-lute gas pressure. This variation is appreciable when the molecular mean free path is ofthe same order of magnitude as the separation between filaments or particles in the medium.Data suitable for the design of linear flowmeters utilizing fibrous materials of high porosityare given, including da,I a, on I he useful porositv range of fibrous media.
I. I n t r o d u c t i o n
During the war there arose a need in the Bureau ofAeronautics, Department of the Navy, for rapidprocurement of equipment suitable for field tests ofdiluter-demand oxygen regulator's, winch are used
by flight personnel ;ti high altitudes. Duo to dilli-culties in procurement, and certain disadvantagesin the convenient use of commercially availableflowmeters for (lie measurement of gaseous How, the
S ( ) l development of a suitable flowmeter was undertaken.After some preliminary consideration, efforts werecentered on the development of ;i constant-resistanceflowmeter utilizing a porous medium ;is the flow-
i nia paper is a 11Njavj i >epari men! |t hi' e n d 0 1 i i i is p a p e r
iretical abstract ol a report i" fche Bureau of Aeronautics,Figures In brackets Indicate i he literature references at
398
