Terence E. Warner

Characterization of phosphate sequestration by a lanthanum modified bentonite clay: a solid-state NMR, EXAFS, and PXRD study.

Phosphate (Pi) sequestration by a lanthanum (La) exchanged clay mineral (La-Bentonite), which is extensively used in chemical lake restoration, was investigated on the molecular level using a combination of (31)P and (139)La solid state NMR spectroscopy (SSNMR), extended X-ray absorption spectroscopy (EXAFS), powder X-ray diffraction (PXRD) and sorption studies. (31)P SSNMR show that all Pi was immobilized as rhabdophane (LaPO4·n H2O, n ≤ 3), which was further supported by (139)La SSNMR and EXAFS. However, PXRD results were ambiguous with respect to rhabdophane and monazite (LaPO4). Adsorption studies showed that at dissolved organic carbon (DOC) concentration above ca. 250 μM the binding capacity was only 50% of the theoretical value or even less. No other La or Pi phases were detected by SSNMR and EXAFS indicating the effect of DOC is kinetic. Moreover, (31)P SSNMR showed that rhabdophane formed upon Pi sequestration is in close proximity to the clay matrix.

The role of Aluminium in the synthesis of Mesoporous 4H Silicon Carbide

Aluminium is found to play a key role in the process of forming a mechanically stable and highly porous and granular structure of 4H silicon carbide. The material is prepared by a high temperature reaction of the elemental constituents. The reactions are carried out under different background atmospheres, including nitrogen. Ternary carbides containing Al, Si and N, are formed in the process, and are believed to be responsible for the final outcome of the process, at the highest reaction temperatures, in the form of pure, well-connected grains of 4H-SiC forming a strong and rigid structure with high porosity. The Al containing compounds function as structural promoters for the 4H polytype recrystallization. This is expected - and partly shown - to take place through substitution with 4H-SiC and evaporation of all other constituents during the high temperature sintering step. When extruded into honeycomb structures prior to the sintering process this pure mesoporous SiC final product turns out to be ideal for a combined diesel particulate filter with support for catalysts in the pores.

Copper scandium zirconium phosphate: occupancy of the M1 and M2 sites in the temperature range 100-300 K.

The title compound, with nominal formula Cu(2)ScZr(PO(4))(3), has a beige coloration and displays fast Cu(+) cation conduction at elevated temperatures. It adopts a NASICON-type structure in the space group R3c. The examined crystal was an obverse-reverse twin with approximately equal twin components. The [Sc(III)Zr(IV)(PO(4))(3)](2-) framework is composed of corner-sharing Sc/ZrO(6) octahedra and PO(4) tetrahedra. The Sc and Zr atoms are disordered on one atomic site on a crystallographic threefold axis. The P atom of the phosphate group lies on a crystallographic twofold axis. Nonframework Cu(+) cations occupy three positions. Two of the Cu(+) positions generate an approximately circular distribution around a site of 3 symmetry, referred to as the M1 site in the NASICON-type structure. The other Cu(+) position is situated close to the twofold symmetric M2 site, displaced into a position with a distorted square-based pyramidal coordination geometry. The structure has been determined at 100, 200 and 300 K. Changes in the refined site-occupancy factors of the Cu(+) positions suggest increased mobility of Cu(+) around the circular orbit close to the M1 site at room temperature, but no movement into or out of the M2 site. Free refinement of the Cu site-occupancy factors suggests that the formula of the crystal is Cu(1.92(1))ScZr(PO(4))(3), which is consistent with the low-level presence of Cu(2+) exclusively in the M2 site.

Copper(II) manganese(II) orthophosphate, Cu0.5Mn2.5(PO4)2.

The title compound, Cu(0.5)Mn(2.5)(PO(4))(2), is a copper-manganese phosphate solid solution with the graftonite-type structure, viz. (Mn,Fe,Ca,Mg)(3)(PO(4))(2). The structure has three distinct metal cation sites, two of which are occupied by Mn(II) and one of which accommodates Cu(II). Incorporation of Cu(II) into the structure distorts the coordination geometry of the metal cation site from five-coordinate square-pyramidal towards four-coordinate flattened tetrahedral, and serves to contract the structure principally along the c axis.