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Study of the System Barium Oxide-Aluminum Oxide-Water at 30° C by Elmer T

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Study of the System Barium Oxide-Aluminum Oxide-Water at 30° C by Elmer T 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.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 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-Al2O3-H2O at 30° C are A12O3.3H2O (gibbsite), Ba(OH)2.8H2O, and, over a narrow range, probably 2BaO.Al2O3.5H2O. With the exception of the two lowest hydrates, all the hydrated barium aluminates possess a range of metastable solubility. I. Introduction properties nor X-ray diffraction data, however, were given. Malquori [16] has published a phase equi- Although the calcium aluminates, because of their librium diagram of the system BaO-Al2O3-H2O at relationship to hydraulic cements, have been the 20° C. subject of numerous investigations here and elsewhere The present investigation includes a study of the during recent years, the barium aluminates have been action of water and of barium hydroxide solutions somewhat neglected. The latter, at present, are of on the various aluminates and a diagram of phase limited practical importance. They have been used equilibria in the system at 30° C. to some extent in water softening [I],1 and they may be formed as intermediate products in the conversion II. Preparation of Compounds of barium minerals to other compounds [2, 3]. It has been shown [4] that BaO.Al2O3 possesses binding 1. Raw Materials properties. Hunt and Temin [5] reported some ex- periments with barium aluminate relative to its The alumina used in the preparation of the various suitability as a wall plaster for protection against aluminates was a commercial preparation of gibbsite X-rays, but no details as to preparation or composi- (AI2O3.3H2O) used in the manufacture of glass. It tion of the aluminate were given. Attempts have contained about 0.30 percent of Na2O; other impuri- also been made to prepare barium cement, analogous ties were negligible. Barium was obtained in the to portland cement, by substituting barium carbon- form of the carbonate, the hydroxide, and (for a few ate, in whole or in part, for calcium carbonate in the experiments) the nitrate. These were reagent qual- raw mix. It has recently been reported by Gallo ity chemicals meeting ACS standards. [17] and by Braniski [19] that such substitution is feasible, and that the resulting cement is particularly 2. BaO.Al2O;i resistant to sea water and to sulfate waters. Barium carbonate and gibbsite were blended in the The purpose of the present investigation was two- correct proportions, made up to a thin paste with fold. First, to study the hydra Lion of the barium water containing a few drops of a, dispersing agent, aluminates; and second, to discover what analogies, and thoroughly mixed. The paste was then dried if any, exist between the aluminates of barium, and and heated in a platinum dish at 1,400° C for 1 hr. those of calcium, in the hope thai this might aid in 1 The product was shown bv pet rographie examination clarifying some aspects of the hvdration of the cal- and X-ray diffraction analysis to be essentially cium aluminates that are not completely understood. inonobarium aluminate (Ba().AL():!). Treatment A number of anhydrous barium aluminates are with hydrochloric acid left a residue amounting to reported in the literal lire, but only three may be 0.7 percent, probably consisting of corundum. At- considered definitely established, namely, :>Ba().AIX),, tempts to improve the product bv grinding and BaO.AU);,, and BaO.6Al4O3 [6, 7, 8, 9]. The last is reheating were unsuccessful. Lower burning tem- believed to be analogous to /^-alumina |l(), 11], and peratures were found to be unsatisfactory; for ex- its exact composition appears lo be somewhat in ample, a batch healed for 1 hr at 1,300° had an doubt [8]. ll was not included in the present study. insoluble residue of N..r) percent. The various barium aluminate hydrates have been described in a previous paper [12]. No evidence of 3. 3BaO.ALO:t any hydrate more basic than 2BaO.Al2O8.5H2O was found in the present study, although Beckmann [13] Tribarium aluminate was prepared in the manner and MaekaWa [14, L5] have reported the preparation described above for monobariiini aluminate, will) the of a tribarium aluminate hydrate. Neither optical appropriate change in proportion of raw materials. The mixture was healed in a refractory crucible, as iii I Hack cis Indicate i in' literature references ai end of this paper. experience showed thai platinum was Strongly 381 attacked. A temperature of 1,300° was found to from supersaturated solutions. These solutions were be adequate to reduce the insoluble residue to 0.1 prepared in various ways, the most satisfactory being percent. For some of the tests, the product was agitation of anhydrous BaO.Al2O3 with Ba(OH)2 subsequently fused in an oxygen blast. solution for 1 hr, followed by nitration. By this method, solutions containing as high as 35 g of 4. BaO.Al2O3.H2O A12O3 per liter were obtained. Solutions of lower concentration were prepared somewhat more con- The compound to which the formula BaO.Al2O3.- veniently by the action of boiling barium hydroxide H2O is assigned was prepared hydrothermally. solution on gibbsite. Best results were obtained by Gibbsite and barium hydroxide were mixed in the using 75 g of gibbsite, 125 g of Ba(OH)2.8H2O, and 1 required proportion, with added water, and placed liter of water, boiling for 1% hrs, filtering at once, in platinum dishes that were then stacked in a bomb- and allowing to cool. Concentrations ranging from type autoclave and heated in an oven at about 260° C 11 to nearly 19 g of A12O3 per liter were obtained by for 7 days. The product in each of the dishes con- this method. sisted of a hard crust of the desired hydrate sur- The course of precipitation varied somewhat with rounding a core of softer material. The latter was concentration. From highly concentrated solutions, shown by X-ray analysis to consist of boehmite 7BaO.6Al2O3.36H2O began to separate almost at (A12O3.H2O). Despite this evidence of the presence once, while from more dilute solutions the start of of excess alumina, the molar ratio of BaO to A12O3 precipitation was sometimes delayed several days. in the aluminate ranged from 1.10 to 1.14, in agree- After a period ranging from a few days to 4 mos, the ment with the findings previously published [12]. solid phase underwent a transformation to BaO.- It appears likely that the actual formula should be A12O3.7H2O, probably by means of re-solution and 8BaO.7Al2O3.7H2O or 9BaO.8Al2O3.8H2O, but it reprecipitation, as no intermediate forms were would be impossible to establish either formula on observed. This phase change occurred when the the basis of present data. All preparations of this concentration of alumina had been lowered to a hydrate, regardless of changes in raw materials and rather poorly established range indicated by the in conditions of heating, have been more or less con- dotted line in figure 10. 7BaO.6Al2O3.36H2O ap- taminated with minute inclusions of some unknown pears to be progressively more stable as the BaO material in the crystals. concentration is increased. Solutions having initial concentrations below or only slightly above the 5. BaO.Al2O3.2H2O dotted line in figure 10 yielded BaO.Al2O3.7H2O as the primary crystalline phase. Monobarium aluminate dihydrate, BaO.Al2O3.- Considerable work was done in an effort to estab- 2H2O, was prepared by the method described above lish the composition of these hydrates. In the case for BaO.Al2O3.H2O, except that the temperature was of BaO.Al2O3.7H2O, analysis of numerous prepara- held at about 215° C, and the duration of heating tions gave values ranging from 6 to 7 moles of H O was 4 days. The product consisted of well-formed 2 per mole of A12O3. The following experiment crystals, ranging up to 3 mm in size. Apparently throws some light on the question. A preparation of there was a small amount of uncombined alumina, the hydrate was filtered, washed lightly with water, as the molar ratio, BaO :A12O3 :H2O, was found to be and divided into two portions, one of which was 0.95:1:1.95, and a slight turbidity remained when stored in a desiccator over calcium chloride, the the crystals were dissolved in hydrochloric acid. other over a saturated solution of ammonium chloride (relative humidity about 79%). After 11 6. BaO.ALO3.4H2O days, both samples had reached constant weight. The molar ratio H2O:A12O3 was 0.25 in the sample Several small batches of monobarium aluminate dried over calcium chloride, 6.96 in the one dried at tetrahydrate, Ba,().Al2O:!.4ir2(), prepared by various means, were used in the solubility studies. Some the higher humidity. It is inferred that the formula were prepared by allowing BaO.Al2O3.7H2O to stand, is BaO.Al2O3.7H2O, and that 1 molecule of water is in contact with barium aluminate solution, for so loosely bound that it is easily given ofl" in dry air.
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