Investigation of CO2 insertion into lanthanide amides, alkoxides, and mixed amide/alkoxides

A novel set of lanthanide (Ln) alkoxycarbonates, [Ln(μ-CO2-DBP)(DBP)2]2 where Ln = lanthanide; and DBP = OC6H3-2,6-C(CH3)3, were isolated from a systematic study of the insertion of CO2(g) (referred to as CO2) into the Ln-O bonds of a series of new lanthanide alkoxides, Ln(OR)3. This study was undertaken to determine if the deleterious metal carbonate [M(CO3)y] formation that promotes higher thermal budgets during processing could be avoided. While processing controls can reduce the formation of the M(CO3)y phases, this is not always effective, and preventing the formation of these phases is of interest. Since CO2 insertion into transition metal alkoxides has been extensively studied and many structures reported, this research focused on CO2 insertion into the less-studied Ln-O bonds of Ln(OR)3. Initially a series of lanthanide amides [Ln(NR2)3 where R = SiMe3 and Ln = Ce (1), Sm (2), Dy (3), Yb (4), and Lu (5)] were synthesized following established routes.4-6 Subsequent conversion of the Ln(NR2)3 species into a series of Ln(OR)3 was achieved by an amide/alcohol exchange route resulting in Ln(DBP)3 (Ln = Ce (6), Sm (7), Dy (8), Yb (9), and Lu (10); DBP = 2,6-di-tert-butylphenoxide).7, 8 Once isolated, CO2 at low pressure (\u3c5 psig) and ambient temperature was introduced to the Ln(OR)3 species to form a novel family of lanthanide alkoxycarbonate compounds identified as [Ln(\xb5- O2C-DBP)(DBP)2]2 (Ln = Ce (11), Sm (12), Dy (13), Yb (14), and Lu (15)). Surprisingly, CO2 did not insert into all of the Ln-O bonds, indicating that this process might be more controllable than initially expected. Higher-pressure CO2 experiments yielded the same carbonate compounds. Further manipulation of the ligand set, as a means to control CO2 insertion, was explored by using a mixed amide/alkoxide precursor generated in situ. This resulted in the formation of an unusual complex, Sm4(μ-CO3)2μ-O)2(DBP)4(THF)2(μ-DBP) (16). From this fundamental study, it has been shown that the ligand may be able to impact the degree of CO2 insertion into Ln-O bonds. The synthesis and characterization of 1 - 16, as well as future implications of this work, will be discussed in detail

Fabrication of large-volume, low-cost ceramic lanthanum halide scintillators for gamma ray detection : final report for DHS/DNDO/TRDD project TA-01-SL01.

This project uses advanced ceramic processes to fabricate large, optical-quality, polycrystalline lanthanum halide scintillators to replace small single crystals produced by the conventional Bridgman growth method. The new approach not only removes the size constraint imposed by the growth method, but also offers the potential advantages of both reducing manufacturing cost and increasing production rate. The project goal is to fabricate dense lanthanum halide ceramics with a preferred crystal orientation by applying texture engineering and solid-state conversion to reduce the thermal mechanical stress in the ceramic and minimize scintillation light scattering at grain boundaries. Ultimately, this method could deliver the sought-after high sensitivity and <3% energy resolution at 662 keV of lanthanum halide scintillators and unleash their full potential for advanced gamma ray detection, enabling rapid identification of radioactive materials in a variety of practical applications. This report documents processing details from powder synthesis, seed particle growth, to final densification and texture development of cerium doped lanthanum bromide (LaBr{sub 3}:Ce{sup +3}) ceramics. This investigation demonstrated that: (1) A rapid, flexible, cost efficient synthesis method of anhydrous lanthanum halides and their solid solutions was developed. Several batches of ultrafine LaBr{sub 3}:Ce{sup +3} powder, free of oxyhalide, were produced by a rigorously controlled process. (2) Micron size ({approx} 5 {micro}m), platelet shape LaBr{sub 3} seed particles of high purity can be synthesized by a vapor phase transport process. (3) High aspect-ratio seed particles can be effectively aligned in the shear direction in the ceramic matrix, using a rotational shear-forming process. (4) Small size, highly translucent LaBr{sub 3} (0.25-inch diameter, 0.08-inch thick) samples were successfully fabricated by the equal channel angular consolidation process. (5) Large size, high density, translucent LaBr{sub 3} ceramics samples (3-inch diameter, > 1/8-inch thick) were fabricated by hot pressing, demonstrating the superior manufacturability of the ceramic approach over single crystal growth methods in terms of size capability and cost. (6) Despite all these advances, evidence has shown that LaBr{sub 3} is thermally unstable at temperatures required for the densification process. This is particularly true for material near the surface where lattice defects and color centers can be created as bromine becomes volatile at high temperatures. Consequently, after densification these samples made using chemically prepared ultrafine powders turned black. An additional thermal treatment in a flowing bromine condition proved able to reduce the darkness of the surface layer for these densified samples. These observations demonstrated that although finer ceramic powders are desirable for densification due to a stronger driving force from their large surface areas, the same desirable factor can lead to lattice defects and color centers when these powders are densified at higher temperatures where material near the surface becomes thermally unstable

CSI: Dognapping workshop : an outreach experiment designed to produce students that are hooked on science.

The CSI: Dognapping Workshop is a culmination of the more than 65 Sandian staff and intern volunteers dedication to exciting and encouraging the next generation of scientific leaders. This 2 hour workshop used a 'theatrical play' and 'hands on' activities that was fun, exciting and challenging for 3rd-5th graders while meeting science curriculum standards. In addition, new pedagogical methods were developed in order to introduce nanotechnology to the public. Survey analysis indicated that the workshop had an overall improvement and positive impact on helping the students to understand concepts from materials science and chemistry as well as increased our interaction with the K-5 community. Anecdotal analyses showed that this simple exercise will have far reaching impact with the results necessary to maintain the United States as the scientific leader in the world. This experience led to the initiation of over 100 Official Junior Scientists

2-(Hydroxymethyl)pyridinium chloride

In the title molecular salt, C6H8NO+·Cl−, the packing is consolidated by N—H...Cl and O—H...Cl hydrogen bonds, resulting in the formation of [010] chains of alternating cations and anions

Probing the structure, stability and hydrogen storage properties of calcium dodecahydro-closo-dodecaborate

Calcium borohydride can reversibly store up to 9.6 wt% hydrogen; however, the material displays poor cyclability, generally associated with the formation of stable intermediate species. In an effort to understand the role of such intermediates on the hydrogen storage properties of Ca(BH_4)_2, calcium dodecahydro-closo-dodecaborate was isolated and characterized by diffraction and spectroscopic techniques. The crystal structure of CaB_(12)H_(12) was determined from powder XRD data and confirmed by DFT and neutron vibrational spectroscopy studies. Attempts to dehydrogenate/hydrogenate mixtures of CaB_(12)H_(12) and CaH_2 were made under conditions known to favor partial reversibility in calcium borohydride. However, up to 670 K no notable formation of Ca(BH_4)_2 (during hydrogenation) or CaB_6 (during dehydrogenation) occurred. It was demonstrated that the stability of CaB_(12)H_(12) can be significantly altered using CaH_2 as a destabilizing agent to favor the hydrogen release