Co3 Phase Research Articles

Disordered Crystal Structure and Anomalously High Solubility of Radium Carbonate.

Radium-226 carbonate was synthesized from radium-barium sulfate (226Ra0.76Ba0.24SO4) at room temperature and characterized by X-ray powder diffraction (XRPD) and extended X-ray absorption fine structure (EXAFS) techniques. XRPD revealed that fractional crystallization occurred and that two phases were formed─the major Ra-rich phase, Ra(Ba)CO3, and a minor Ba-rich phase, Ba(Ra)CO3, crystallizing in the orthorhombic space group Pnma (no. 62) that is isostructural with witherite (BaCO3) but with slightly larger unit cell dimensions. Direct-space ab initio modeling shows that the carbonate oxygens in the major Ra(Ba)CO3 phase are highly disordered. The solubility of the synthesized major Ra(Ba)CO3 phase was studied from under- and oversaturation at 25.1 °C as a function of ionic strength using NaCl as the supporting electrolyte. It was found that the decimal logarithm of the solubility product of Ra(Ba)CO3 at zero ionic strength (log10 Ksp0) is -7.5(1) (2σ) (s = 0.05 g·L-1). This is significantly higher than the log10 Ksp0 of witherite of -8.56 (s = 0.01 g·L-1), supporting the disordered nature of the major Ra(Ba)CO3 phase. The limited co-precipitation of Ra2+ within witherite, the significantly higher solubility of pure RaCO3 compared to witherite, and thermodynamic modeling show that the results obtained in this work for the major Ra(Ba)CO3 phase are also applicable to pure RaCO3. The refinement of the EXAFS data reveals that radium is coordinated by nine oxygens in a broad bond distance distribution with a mean Ra-O bond distance of 2.885(3) Å (1σ). The Ra-O bond distance gives an ionic radius of Ra2+ in a 9-fold coordination of 1.545(6) Å (1σ).

A novel constructed carbonate-mineralized functional bacterial consortium for high-efficiency cadmium biomineralization

A stable, urease-producing consortium (UPC) was constructed for high-efficiency cadmium (Cd) ion mineralization via a short-term and efficient acclimation process (five acclimation transfers). 16S rRNA gene high-throughput sequencing and quantitative polymerase chain reaction (qPCR) analyses of the urease subunit C (ureC) gene suggested that the three functional genera, all belonging to the phylum Firmicutes, rapidly increased during the process and finally composed the UPC (70.22–75.41 % of Sporosarcina, 13.83–20.66 % of norank_f_Bacillaceae, and 5.91–13.69 % of unclassified_f_Bacillaceae). The UPC exhibited good adaptability to a wide range of environmental conditions (a pH range of 4.0–11.0, temperature range of 10−45 °C, and Cd concentration range of 0−200 mg L−1). After 8 h of incubation, 92.87 % of Cd at an initial concentration of 100 mg L−1 was mineralized by UPC, exhibiting a great improvement as compared to the first acclimated consortium (C-1). Furthermore, although the acclimated consortium had been successively transferred 21 times, the Cd biomineralization efficiency remained stable, and this was consistent with the observed stable microbial community structure. X-ray diffraction (XRD) spectra revealed that Cd was mineralized in a (Ca0.67, Cd0.33)CO3 phase. This research obtained a promising microbial resource for the biomineralization of Cd or other hazardous heavy metal contaminants.

Phase relations in the system FeCO3-CaCO3 at 6 GPa and 900-1700 C and its relation to the system CaCO3-FeCO3-MgCO3

The subsolidus and melting phase relations in the CaCO 3 -siderite system have been studied in multianvil experiments using graphite capsules at pressure of 6 GPa and temperatures of 900-1700 °C. At low temperatures, the presence of ankerite splits the system into two partial binaries: siderite + ankerite at 900 °C and ankerite + aragonite up to 1000 °C. Extrapolated solvus curves intersect near 50 mol% just below 900 °C. At 1100 and 1200 °C, the components appear to form single-phase solid solutions with space group symmetry R 3 c , while CaCO 3 maintains aragonite structure up to 1600 °C and 6 GPa. The FeCO 3 solubility in aragonite does not exceed 1.0 and 3.5 mol% at 900-1000 and 1600 °C, respectively. An increase of FeCO 3 content above the solubility limit at T > 1000 °C, leads to composition-induced phase transition in CaCO 3 from aragonite, Pmcn , to calcite, R 3 c , structure, i.e., the presence of FeCO 3 widens the calcite stability field down to the P-T conditions of sub-cratonic mantle. The siderite-CaCO3 diagram resembles a minimum type of solid solutions. The melting loop for the FeCO 3 -CaCO 3 join extends from 1580 °C (FeCO 3 ) to 1670 °C (CaCO 3 ) through a liquidus minimum near 1280 ± 20 °C and 56 ± 3 mol% CaCO 3 . At X (Ca) = 0-30 mol%, 6 GPa and 1500-1700 °C, siderite melts and dissolves incongruently according to the reaction: siderite = liquid + fluid. The apparent temperature and X (Ca) range of siderite incongruent dissolution would be determined by the solubility of molecular CO 2 in (Fe,Ca)CO 3 melt. The compositions of carbonate crystals and melts from the experiments in the low-alkali carbonated eclogite (Hammouda 2003; Yaxley and Brey 2004) and peridotite (Dasgupta and Hirschmann 2007; Brey et al. 2008) systems are broadly consistent with the topology of the melting loop in the CaCO 3 - MgCO 3 -FeCO 3 system at 6 GPa pressure: a Ca-rich dolomite-ankerite melt coexists with Mg-Fe-calcite in eclogites at CaO/MgO > 1 and Mg-dolomite melt coexists with magnesite in peridotites at CaO/MgO < 1. However, in fact, the compositions of near solidus peridotite-derived melts and carbonates are more magnesian than predicted from the (Ca,Mg,Fe)CO3 phase relations.

Microstructure of bilayer manganite PrCa2Mn2O7 showing charge/orbital ordering

The microstructure of the charge/orbital ordering Ruddleden-Popper phase PrCa2Mn2O7 was studied by transmission electron microscopy along both the [001] and the [110] orientation. Three coexisting charge/orbital ordering phases CO1, CO2, and CO3 were observed along the [001] orientation at room temperature. Different from the one-dimensional modulation in the CO1 and CO2 phase, the CO3 phase is characterized by two sets of mutually perpendicular structural modulations. From [110] high angle annular dark field-scanning transmission electron microscopy, we found that the Pr atoms locate in-between the bilayer MnO6 octahedra, which is different from the previous reports.

Effect of Mg-doping on pyrolysis evolution and phase constitutes of Ba0.7Sr0.3TiO3 (BST) system derived from sol-gel

Gels and powders of dielectric Ba0.7Sr0.3(Ti1-xMgx)O3 (BST) were prepared by sol-gel technique. Effect of Mg-doping of on the pyrolysis evolution and phase constitutes of BSTs was investigated using DSC-TG and XRD. Results show that Mg-doping leads to a remarkable change of crystallizing process of BSTs from a double phase-transformation of non-doping sample into a single phase-transformation and quickens the crystallizing reaction of formation of BST perovskite. The maximum Mg-doping level should be less than x = 0.15 in Ba0.7Sr0.3 (Ti1-xMgx)O3 system. The amount of (Ba,Sr)CO3 phase in the BST powders increases considerably with the Mg-doping level, indicating Mg atoms should occupy the A positions of ABO3 structure of BST, instead of the B position.

Magnetic characterization of the (Zr,Sm)Co3 phase in Sm(CoFeCuZr)z magnets

Magnets with composition Sm(CobalFe0.2Cu0.1Zrx)8 (x=0;0.02;0.04;0.06,0.08) were studied using x-ray diffraction Rietveld analysis. In addition to the majority 2:17 and 1:5 phases, the magnets present a rhombohedral (SmZr)1(CoFeCu)3 (PuNi3 structure) phase, whose volume fraction increases with Zr addition. Higher Zr contents decrease coercivity and lead to the appearance of impurity phases such as 6:23 (Th6Mn23 structure), 2:7R (Gd2Co7 structure), and 5:19R (Ce5Co19 structure) in the magnets. The 1:3R phase was reproduced in a Fe57-doped sample of Sm0.33Zr0.67Co3 and its Mössbauer spectra, at several temperatures, were adjusted using four sextets and a nonmagnetic doublet. The beneficial effect of small additions of Zr on the coercivity of the magnets is discussed.

The (SmZr)Co$_3$Phase in Sm(CoFeCuZr)$_rm z$Magnets

Detailed microstructural characterization of magnets and homogenized as-cast alloys, which included X-ray diffraction Rietveld analysis, has indicated that the so-called platelet or lamellae phase is (SmZr) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> (CoFeCu) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> with the PuNi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> structure and lattice parameters a~0.5 nm and c~2.4 nm. The structural and magnetic properties of the (SmZr)Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> phase were investigated. The microstructure shows two phases differing in their Zr/Sm ratio. Magnetization curves for the samples (Sm <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.33</sub> Zr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.67</sub> )Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , (Sm <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.33</sub> Zr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.67</sub> )Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2.97</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.03</sub> , and (Sm <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.67</sub> Zr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.33</sub> )Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> are consistent with the two-phase microstructure observed. Room temperature coercivity values of these samples are low (ap1 kOe.)

Mg,Al layered double hydroxides with intercalated indomethacin: Synthesis, characterization, and pharmacological study

Magnesium aluminium layered double hydroxides (LDH) with a molar Mg/Al ratio of 2.0 have been prepared with intercalated indomethacin following two routes: reconstruction from a previously calcined Mg2Al–CO3 LDH, and coprecipitation from the corresponding chlorides. The solids have been characterized by powder X‐ray diffraction, FTIR, and 13C CP/MAS NMR spectroscopies and thermal stability (differential thermal analysis and thermogravimetric analysis). Intercalation of the drug is attained by both routes; however, while coprecipitation leads to a single layered structure, contamination with another layered MgAl–CO3 phase occurs by the reconstruction method. The amount of drug intercalated, as well as the heigth of the gallery, are larger by the coprecipitation than by the reconstruction one. The data obtained support a somewhat tilted, upwards orientation of the drug molecules forming an interdigited bilayer, in the case of the sample prepared by coprecipitation, with the carboxylate groups pointing towards the hydroxyl layers. However, in the case of the sample prepared by reconstruction, the molecules are forming a tilted, upwards monolayer. The solids prepared are stable up to 250°C. Pharmacological studies in vivo show that intercalation of the drug in the LDH reduces the ulcerating damage of the drug. © 2004 Wiley‐Liss, Inc. and the American Pharmacists Association J Pharm Sci 93: 1649–1658, 2004