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USGS1964

Crystal chemistry and structure refinement of five hydrated calcium borates

The crystal structures of the five known members of the series Ca 2 B 6 O 11 ·xH 2 O (x = 1, 5, 5, 7, 9, and 13) have been refined by full-matrix least-squares techniques, yielding bond distances and angles with standard errors of less than 0·01 Å and 0·5°, respectively. The results illustrate the crystal chemical principles that govern the structures of hydrated borate compounds. The importance of hydrogen bonding in the ferroelectric transition of colemanite is confirmed by more accurate proton assignments.

Journal of Inorganic and Nuclear Chemistry↗
USGS1960

The crystal structure of cesium biuranyl trisulphate, Cs2(UO2)2(SO4)3

The crystal structure of the new compound Cs(UO 2 ) 2 (SO 4 ) 3 has been determined by X-ray diffraction methods. The compound is tetragonal, space group P 4 2 1 m "> P42 1 m ( D 2 d 3 ), with a = 9·62 ± 0·02, c = 8·13 ± 0·01 A ̊ "> c = 8·13 ± 0·01Å , and Z = 2; s.g. (calc.) = 4·80 ± 0·03, s.g. (obs.) = 4·74 ± 0·05. The compound forms plates parallel to (001) bounded by the form (110). Intensity data were obtained from Buerger precession photographs of the ( hk 0) and (0 kl ) reciprocal lattice nets. No corrections for absorption were made. The co-ordinates of the U and Cs atoms were obtained by interpretation of the Patterson projections normal to (001) and (100) and a plausible structure was derived from electron density projections. The final parameters of the structure were determined from subtraction electron density maps, least squares analysis of the structure factors, and spatial considerations. The compound has a layer structure consisting of (UO 2 ) 2 (SO 4 ) 3 ] n 2 n − sheets paralle to (001), tied together by cesium ions. The UO 2 2+ group is co-ordinated by five sulphate oxygens which form a nearly plane pentagon approximately normal to the uranyl axis. The Cs 2 atom is co-ordinated by twelve oxygen atoms and the Cs 1 atom by eight oxygen atoms. X-ray and optical data are also given for the compound Rb 2 UO 2 (SO 4 ) 2 ·2H 2 O.

Journal of Inorganic and Nuclear Chemistry↗
USGS1964

The system K2Mg2(SO4)3 (langbeinite)-K2Ca2(SO4)3 (calcium-langbeinite)

The join between the compositions K 2 Mg 2 (SO 4 ) 3 and K 2 Ca 2 (SO 4 ) 3 was studied by means of high-temperature equilibrium quenching techniques and by means of a heating stage mounted on an X-ray diffractometer. Complete solid solution exists in the system, but at 25°C members of the solid solution series are isometric only in the composition range 0–73·5 wt. per cent K 2 Ca 2 (SO 4 ) 3 . At compositions richer in K 2 Ca 2 (SO 4 ) 3 than 73·5 wt. per cent, members of the series are optically biaxial. At higher temperatures members of the solid solution series are isometric at successively more calcium-rich compositions and pure K 2 Ca 2 (SO 4 ) 3 is isometric above about 200 ± 2°C. The system is not binary, as mixtures richer in K 2 Ca 2 (SO 4 ) 3 than 42 wt. per cent decompose with the formation of liquid and CaSO 4 .

Journal of Inorganic and Nuclear Chemistry↗
USGS1965

The binary system K2SO4CaSO4

The binary system K 2 SO 4 CaSO 4 was studied by means of heating-cooling curves, differential thermal analysis, high-temperature quenching technique and by means of a heating stage mounted on an X-ray diffractometer. Compositions and quench products were identified optically and by X-ray. Limited solid solution of CaSO 4 in K 2 SO 4 was found. There is a eutectic at 875°C and 34 wt. per cent CaSO 4 . Calcium langbeinite melts incongruently at 1011°C. The melting-point of CaSO 4 (1462°C) was determined by the quenching technique using sealed platinum tubes. The only intermediate crystalline phase found in the system is K 2 SO 4 ·2CaSO 4 (calcium langbeinite).

Journal of Inorganic and Nuclear Chemistry↗
USGS1967

The ternary system K2SO4 MgSO4 CaSO4

Melting and subsolidus relations in the system K 2 SO 4 MgSO 4 CaSO 4 were studied using heating-cooling curves, differential thermal analysis, optics, X-ray diffraction at room and high temperatures and by quenching techniques. Previous investigators were unable to study the binary MgSO 4 CaSO 4 system and the adjacent area in the ternary system because of the decomposition of MgSO 4 and CaSO 4 at high temperatures. This problem was partly overcome by a novel sealed-tube quenching method, by hydrothermal synthesis, and by long-time heating in the solidus. As a result of this study, we found: (1) a new compound, CaSO 4 ·3MgSO 4 (m.p. 1201°C) with a field extending into the ternary system; (2) a high temperature form of MgSO 4 with a sluggishly reversible inversion. An X-ray diffraction pattern for this polymorphic form is given; (3) the inversion of β-CaSO 4 (anhydrite) to α-CaSO 4 at 1195°C, in agreement with grahmann ; (1) (4) the melting point of MgSO 4 is 1136°C and that of CaSO 4 is 1462°C (using sealed tube methods to prevent decomposition of the sulphates); (5) calcium langbeinite (K 2 SO 4 ·2CaSO 4 ) is the only compound in the K 2 SO 4 CaSO 4 binary system. This resolved discrepancies in the results of previous investigators; (6) a continuous solid solution series between congruently melting K 2 SOP 4 ·2MgSO 4 (langbeinite) and incongruently melting K 2 SO 4 ·2CaSO 4 (calcium langbeinite); (7) the liquidus in the ternary system consists of primary phase fields of K 2 SO 4 , MgSO 4 , CaSO 4 , langbeinite-calcium langbeinite solid solution, and CaSO 4 ·3MgSO 4 . The CaSO 4 field extends over a large portion of the system. Previously reported fields for the compounds (K 2 SO 4 ·MgSO 4 ·nCaSO 4 ), K 2 SO 4 ·3CaSO 4 and K 2 SO 4 ·CaSO 4 were not found; (8) a minimum in the ternary system at: 740°C, 25% MgSO 4 , 6% CaSO 4 , 69% K 2 SO 4 ; and ternary eutectics at 882°C, 49% MgSO 4 , 19% CaSO 4 , 32% K 2 SO 4 ; and 880°, 67·5% MgSO 4 , 5% CaSO 4 , 27·5% K 2 SO 4 .

Journal of Inorganic and Nuclear Chemistry↗