T H E HYDROUS OXIDES OF SOME RARER ELEMENTS1 HARRY B. WEISER
AND
W. 0.MILLIGAS
Department of Chemistry, T h e Rice Institute, Houston, Texas March 21, 1998
The composition of the precipitated oxides of aluminum (5, lo), gallium (8), indium (€9,thallium (8), and scandium (14) has been established as a result of x-ray diffraction and isobaric dehydration studies on the several compounds. This paper is concerned with the application of similar methods of investigation to the remaining oxides of Group 111, about which little authentic information \vas available. For the purpose of this summarizing report, the oxides of the metals under consideration will be classified into (a) the aluminum family (gallium, indium, thallium), (b) the scandium family (scandium, yttrium), and (c) the rare earths (neodymium, praseodymium, samarium). EXPERIMENTAL
Following procedures already described (11, 12, 13, 15), dehydration isobars of the several preparations were obtained, taking care to allow sufficient time (days or weeks) for equilibrium to be established a t each temperature point on the isobar. Samples for x-ray diffraction analysis were taken a t various temperatures from separate portions which had been heated in the same way and a t the same time as the weighed samples for dehydration isobars. After sealing (9, 13, 15) in thin tubes of Lindemann glass, the samples were exposed to filtered Cu K, x-radiation in a camera 57.6 mm. in diameter. THE ALUMINUM FAMILY
Previous investigations (8) have shown that precipitated gallium oxide consists of hydrous particles of or-Gaz0s when precipitated rapidly and unaged. The oxide prepared by slow precipitation from ammonium hydroxide solution or after aging may consist of hydrous Ga2O3.HzO. Precipitated indium oxide is hydrous InzOs.3Hz0or In(OH)3. Hydrous thallic oxide prepared by precipitation (6) or by Carnegie’s (2) method (which was said to give a definite trihydrate) shows no indication of Presented a t the Second Annual Symposium of the Division of Physical and Inorganic Chemistry,-A Symposium on the Less Familiar Elements,-held at Cleveland, Ohio, December 27-29, 1937. 673
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HARRY B. WEISER AND W. 0. MILLIGAN
hydrate formation. Dehydration isobars for the various samples are collected in figure 1. The isobar for hydrous thallic oxide is taken from the work of Huttig and Mytyzek (6). X-ray diffraction patterns showing the chemical individuality of the several hydrous oxides and hydrates are given in figures 4, 5 , and 6, respectively. THE SCANDIUM FAMILY
In the preceding paper (14) it was shown that precipitated scandia is the monohydrate Sc203~ & O , corresponding to precipitated alumina, which is y-Al208.HzO. In figure 4 is given a diagram of the x-ray diffraction patterns of Ga2O3 .HzO,Scz08.Hz0,and y-A1203.H20. I t will be noted that
FIG.1. Dehydration isobars for the hydrous oxides and hydrates of gallium, indium, and thallium.
the patterns of the alumina and scandia monohydrates are very similar except for a uniform displacement of the lines. This furnishes additional evidence in support of the chemical individuality of yA1203 "20, even though the dehydration isobar for precipitated alumina is not step curve ( 5 , 12) corresponding to a monohydrate like that of Sc203.HzO (figure 2). No evidence is available concerning the constitution of precipitated yttria, except the observation of Bohm and Niclassen (1) that the freshly precipitated gel is amorphous to x-rays, becoming microcrystalline after prolonged aging. A sample of yttria was prepared by the interaction of solutions of yttrium chloride and ammonium hydroxide a t 25"C., followed by washing with the aid of a centrifuge and air drying. The isobar for
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675
this preparation is a continuous curve (figure 2) with no indication of hydrate formation. In agreement with the results of Bohm and Niclassen, the x-ray diffraction pattern of the freshly formed product consists of two broad diffuse bands (figure 6). Aging experiments have not yet been carried out. THE RARE EARTHS
Damiens (4) claimed that the composition of the precipitated oxides of neodymium, praseodymium, and samarium was represented by the respective formulas Nd~03.3Hz0,Prz03.3Hz0, and SmzOs.3Hz0. Joye and Garnier (7) found that precipitated neodymium oxide retained 3.0, 1.5, and 1.0 moles of water per mole of oxide when the samples were dried
TEMPERATURE - DEGREESc
FIG.2. Dehydration isobars for hydrous scandium oxide monohydrate and yttiium oxide.
a t room temperature, 320"C., and 520"C., respectively. The evidence of Damiens and of Joye and Garnier is not conclusive, since (a) it is not known whether the analyzed products were in equilibrium with a fixed pressure of aqueous vapor a t the temperature of drying, and ( b ) there are not enough data to establish an isobar. In this investigation samples of precipitated neodymium, praseodymium, and samarium oxides were prepared as described above for yttrium oxide. The dehydration isobars for samples precipitated a t 100°C. are given in figure 3. It is apparent that precipitated neodymium and praseodymium oxides consist of the hydrous trihydrate or hydroxide. There is only the slightest indication of a break in the samarium oxide isobar a t thecomposition corresponding to the trihydrate. The neodymium isobar shows some
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HARRY B. WEISER AKD W. 0. MILLIGAN
TEMPERATURE - DEGREES C
FIG.3. Dchydration isobars for the hydrous oxides and hydrates of neodymium, praseodymium, and samarium.
8
&A HzO
%Ol
-it0
GALOJHZO
0
I
2
3
4
FIG.
5
E C M
FIG.5
4
FIG 6
FIG 4. X-ray diffiaction patterns for the trlhydrates of the oxides of Indium, neodymium, and praseodgmlum FIG 5 X-ray diffraction patterns for the hydrous monohydrates of the oxides of aluminum, scandium, and gallium FIG 6 X-ray diffractlon patterns for the hydrous oxldes of yttrium, samarium, and gallium
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indication and the praseodymium isobar a slight indication of the formation of monohydrate a t temperatures around 400°C. X-ray diffraction patterns of Ndz03.3Hz0 are given in figure 5. These patterns are distinct from the patterns of the respective anhydrous oxides. There is some indication of a new crystalline phase in the x-radiograms of samples of neodymium oxide dehydrated a t temperatures around 400" to 500°C. These new diffraction lines are distinct from the lines of the trihydrate or anhydrous oxide. This evidence supports the suggestion that a monohydrate of neodymium oxide may exist. The x-ray diffraction pattern of precipitated samarium oxide consists of one, or possibly two, very broad, diffuse bands. In the absence of a definite break in the dehydration isobar and a well-defined x-radiogram, the present authors prefer to consider this material to be hydrous samarium oxide, and not a definite hydrate or hydroxide. SUMMARY
The following is a brief summary of the results of this paper: 1. But few early studies have been made of the hydrous oxides and hydrous hydrates of the Group 111metals other than aluminum. In this report the composition of the hydrous oxides and hydrous hydrates of gallium, indium, thallium, scandium, yttrium, neodymium, praseodymium, and samarium have been investigated from the standpoint of their dehydration isobars and x-ray diffraction patterns. 2. The dehydration isobars have been obtained under conditions that ensure the establishment of equilibrium at each point of the isobar. 3. Samples for x-ray diffraction examination were removed and sealed in thin tubes of Lindemann glass under conditions that ensure neither loss nor gain of water vapor. 4. The precipitated oxides of indium, neodymium, and praseodymium consist of the hydrous trihydrates or hydroxides. 5 . The precipitated oxides of gallium (when formed slowly or aged) and of scandium are hydrous monohydrates. 6. The precipitated oxides of thallium, gallium (when formed rapidly or unaged), yttrium, and samarium show no indication of hydrate formation. These precipitated gels should be considered as hydrous oxides of the respective metals. REFERENCES (1) BOHMAND KICLASBEN: Z. anorg. allgem. Chem. 132, 1 (1924). (2) CARNEGIE:Chem. News 60, 113 (1889). (3) CROOKES:Phil. Trans. 209A, 15 (1908). (4) DARIIENS: Ann. chim. 191 10, 181 (1918). (5) FRICKE A N D H ~ T T I Gin : Handbuch der allgemeinen Chemie, Vol. I S , pp. 57-106. Akademische Verlagsgesellsrhaft, Leipzig (1937).
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(6) HUTTIGAND MYTYZEK: Z. anorg. allgem. Chem. 192, 187 (1930). JOYE AND GARNIER: Compt. rend. 164, 510 (1912). MILLIGAN AND WEISER: J. Am. Chem. SOC.69, 1670 (1937). MILLIGAN AND WEISER: J. Phys. Chem. 41, 1029 (1937). WEISER: Inorganic Colloid Chemistry, Vol. 11, pp. 90-100. John Wiley and Sons, Inc., New York City (1935). (11) WEISERAND MILLIGAN: J. Phys. Chem. 38,513 (1934). (12) WEISER AND MILLIGAN: J. Phys. Chem. 38, 1175 (1934). (13) WEISERANDMILLIGAN: J. Am. Chem. SOC.69, 1457 (1937). J. Phys. Chem. 42, 669 (1938). (14) W E I S E R AND MILLIGAN: (15) WEISER, MILLIGAN, AND EKHOLM: J. Am. Chem. SOC.68, 1262 (1936).
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