Barium coordination polymers based on fluorinated and fluorine-free benzene-dicarboxylates: Mechanochemical synthesis and spectroscopic characterization

A series of new Ba-based coordination polymers (CPs) were mechanochemically synthesized by milling Ba-hydroxide samples with perfluorinated and fluorine-free benzene-dicarboxylic acids, including tetrafluoroisophthalic acid (H₂mBDC-F₄), tetrafluorophthalic acid (H₂oBDC-F₄), isophthalic acid (H₂mBDC) and phthalic acid (H₂oBDC). The new fluorinated CPs: [Ba(mBDC-F₄)·0.5H₂O] (1) and [Ba(oBDC-F₄)·1.5H₂O] (2) are compared to their nonfluorinated counterparts: [Ba(mBDC)·2.5H₂O] (3), and [Ba(oBDC)·1H₂O] (4). These materials are thoroughly characterized using powder X-ray diffraction. The products obtained by milling are all hydrated but vary in their water contents. Compositions and local structures are investigated by elemental analysis, thermal analysis, MAS NMR and attenuated total reflection-infrared spectroscopy. These materials exhibit high thermal stabilities but small surface areas that remain unchanged even after thermal treatments.     

Investigations of gas and particle dynamics in first generation needle-free drug delivery devices

Abstract. Transdermal powdered drug delivery involves the propulsion of solid drug particles into the skin by means of high-speed gas-particle flow. The fluid dynamics of this technology have been investigated in devices consisting of a convergent-divergent nozzle located downstream of a bursting membrane, which serves both to initiate gas flow (functioning as the diaphragm of a shock tube) and to retain the drug particles before actuation. Pressure surveys of flow in devices with contoured nozzles of relatively low exit-to-throat area ratio and a conical nozzle of higher area ratio have indicated a starting process of approximately 200 s typical duration, followed by a quasi-steady supersonic flow. The velocity of drug particles exiting the contoured nozzles was measured at up to 1050 m/s, indicating that particle acceleration took place primarily in the quasi-steady flow. In the conical nozzle, which had larger exit area ratio, the quasi-steady nozzle flow was found to be overexpanded, resulting in a shock system within the nozzle. Particles were typically delivered by these nozzles at 400 m/s, suggesting that the starting process and the quasi-steady shock processed flow are both responsible for acceleration of the particle payload. The larger exit area of the conical nozzle tested enables drug delivery over a larger target disc, which may be advantageous. Received 12 March 2000 / Accepted 8 June 2000     

Leakage of nuclear material powder from pressure container through a small orifice

Because of the radioactivity and toxic nature of nuclear materials, their containment within oxide matrices, encased in sealed containers, has been proposed as a suitable means for storage and transportation. However, container failures because of cracks or small orifices present a major leakage risk for nuclear materials, consequently posing a significant hazard to the environment and human beings. In this study, terbium oxide powder was used as a nuclear material representative to examine the leakage of nuclear material powder through orifices located at the base of a pressure container. The dependence of the orifice diameter, the powder layer thickness, and the internal pressure of the container on the leakage mechanism and amount was examined. A simplified model correlating the dependence of the above-mentioned parameters to determine the utmost leakage amount was also developed based on the present results. The leakage of the nuclear material powder was assessed by measuring its concentration using an optical particle counter. The diameter of the orifice determined the powder leakage mechanism, which in turn influenced the amount of leakage produced. Comparison studies showed that unlike the changes in the differential pressure, the volume of the container has little effect on the leakage amount. Under sufficiently high internal pressures, the oxide powder can be released as a fine aerosol. The work is not only crucial from the nuclear safety aspect, but is also beneficial for the safe application of powder and nanoparticles.     

X-ray diffraction and vibrational data for a series of triphosphates type MIINa3P3O10.12H2O (MII = Cu,Ni and Mg) and their anhydrous forms MIINa3P3O10

Chemical preparation methods, X-ray diffraction and vibrational data are reported for six triphosphates type M^IINa₃P₃O₁₀.12H₂O (M^II = Cu, Ni and Mg) and their anhydrous forms M^IINa₃P₃O₁₀. These condensed phosphates are respectively, CuNa₃P₃O₁₀.12H₂O, MgNa₃P₃O₁₀.12H₂O, NiNa₃P₃O₁₀.12H₂O, CuNa₃P₃O₁₀, NiNa₃P₃O₁₀ and MgNa₃P₃O₁₀. The hydrate triphosphates were prepared by the method of ion-exchange resin, where as their anhydrous forms were prepared by total thermal dehydration of M^IINa₃P₃O₁₀.12H₂O (M^II = Cu, Ni and Mg).CuNa₃P₃O₁₀.12H₂O, MgNa₃P₃O₁₀.12H₂O and NiNa₃P₃O₁₀.12H₂O are isotypic, and crystallize in the monoclinic system, space group is P2₁/n, Z = 4, the unit-cell parameters are: CuNa3P3O10.12H2O, a = 15.052(8) Å, b = 9.234(3) Å,c = 14.767(8) Å and β = 90.03(5)°. MgNa3P3O10.12H2O: a = 15.049(1) (1) Å, b = 9.245(4) Å, c = 14 0.722(3) (2) Å and β = 90.00(5)°.NiNa₃P₃O₁₀.12H₂O: a = 15.010(1) Å, b = 9.208(4) Å, c = 14.710(2) Å and β = 90.00(5)°.The anhydrous forms CuNa₃P₃O₁₀, MgNa₃P₃O₁₀ and NiNa₃P₃O₁₀ crystallize in the monoclinic system, space group is P2₁/n, Z = 4, the unit-cell parameters are: CuNa₃P₃O₁₀, a = 12.464(0) Å, b = 8.437(7) Å, c = 12.083(1) Å and β = 109.77(8) °; MgNa₃P₃O₁₀: a = 11.931(4) (1) Å, b = 12.912(2) Å, c = 10.057(0) Å and β = 113.83(2)° and NiNa₃P₃O₁₀: a = 12.686(8)Å, b = 9.271(2) (4) Å, c = 11.440(3) Å and β = 102,95(5)°.     

氟化镁钡粉体制备方法研究进展

氟化镁钡（BaMgF₄）材料不仅拥有铁电性、光学性、多铁性等优良性能,而且作为氟化物,它也具备声子能量低、发光效率高、化学稳定性好等优势,近年来已被广泛用作固态激光材料和稀土离子的发光基质。但是,获得尺寸、形貌合适的纯相纳米级氟化镁钡粉体材料仍然是其制备过程中需要解决的关键问题。本文重点对国内外关于氟化镁钡粉体材料的制备方法进行了总结,从原料、氟化剂、反应条件等方面详细介绍了每种方法在应用过程中不断改进和完善之处,综合比较分析了不同制备工艺的特点和局限性,为今后高性能氟化镁钡粉体材料的制备及应用提供参考。     

Thermoelectric and structural properties of a new Chevrel phase: Ti0.3Mo5RuSe8

The new Chevrel phase Ti_0.3Mo₅RuSe₈ has been synthesized and characterized by quantitative microprobe analysis, powder X-ray diffraction, and high-temperature thermoelectric properties measurements. The thermoelectric properties of this compound are compared to the previously reported data for other related Chevrel phases. We report also the results of Rietveld analysis of powder X-ray diffraction data for Ti_0.3Mo₅RuSe₈. This compound adopts the rhombohedral Chevrel phase structure (space group , Z=3) with hexagonal lattice constants a=9.75430(25) Å and c=10.79064(40) Å. The low level of incorporation and low scattering power of Ti precluded the identification of the Ti positions, and Rietveld refinement was carried out only for the Mo₅RuSe₈ framework of Ti_0.3Mo₅RuSe₈ (R_p=10.5%, R_wp=14.6%). Rietveld analysis was also used to refine the structure of the unfilled phase Mo₅RuSe₈ (, Z=3, a=9.63994(8) Å, c=10.97191(11) Å, R_p=8.0%, R_wp=10.5%). Comparisons between the two structures are made.     

Tungsten carbide precursors as an example for influence of a binder on the particle formation in the nanosecond laser ablation of powdered materials

A study of LA-ICP-MS analysis of pressed powdered tungsten carbide precursors was performed to show the advantages and problems of nanosecond laser ablation of matrix-unified samples. Five samples with different compositions were pressed into pellets both with silver powder as a binder serving to keep the matrix unified, and without any binder. The laser ablation was performed by nanosecond Nd:YAG laser working at 213 nm.The particle formation during ablation of both sets of pellets was studied using an optical aerosol spectrometer allowing the measurement of particle concentration in two size ranges (10-250 nm and 0.25-17 μm) and particle size distribution in the range of 0.25-17 μm. Additionally, the structure of the laser-generated particles was studied after their collection on a filter using a scanning electron microscope (SEM) and the particle chemical composition was determined by an energy dispersive X-ray spectroscope (EDS).The matrix effect was proved to be reduced using the same silver powdered binder for pellet preparation in the case of the laser ablation of powdered materials.The LA-ICP-MS signal dependence on the element content present in the material showed an improved correlation for Co, Ti, Ta and Nb of the matrix-unified samples compared to the non-matrix-unified pellets. In the case of W, the ICP-MS signal of matrix-unified pellets was influenced by the changes in the particle formation.     

Synthesis and structural characterization of Al4SiC4-homeotypic aluminum silicon oxycarbide, [Al4.4Si0.6][O1.0C2.0]C

A new quaternary layered oxycarbide, [Al_4.39(5)Si_0.61(5)]_Σ5[O_1.00(2)C_2.00(2)]_Σ3C, has been synthesized and characterized by X-ray powder diffraction, transmission electron microscopy and energy dispersive X-ray spectroscopy (EDX). The title compound was found to be hexagonal with space group P6₃/mmc, Z=2, and unit-cell dimensions a=0.32783(1) nm, c=2.16674(7) nm and V=0.20167(1) nm³. The atom ratios Al:Si were determined by EDX, and the initial structural model was derived by the direct methods. The final structural model showed the positional disordering of one of the three types of Al/Si sites. The maximum-entropy methods-based pattern fitting (MPF) method was used to confirm the validity of the split-atom model, in which conventional structure bias caused by assuming intensity partitioning was minimized. The reliability indices calculated from the MPF were R_wp=3.73% (S=1.20), R_p=2.94%, R_B=1.04% and R_F=0.81%. The crystal was an inversion twin. Each twin-related individual was isostructural with Al₄SiC₄ (space group P6₃mc, Z=2).     

Structural and stability characteristics of agglomerated clusters

We investigated the cohesion of agglomerates formed by sticking two fractal clusters, each cluster having been previously generated by particle aggregation on a 3D lattice. The degree of cohesion of an agglomerate of a given configuration was defined by the number of connections simultaneously established on the two stuck clusters. All the possible nonoverlapping configurations were investigated and the corresponding porosity and brittleness as well as the pore volume and connection frequencies were determined. The numerical study showed the greater internal cohesion of agglomerates issued from sticking of reaction-limited aggregation (RLA) clusters compared to that of diffusion-limited-aggregation (DLA) clusters. DLA and RLA agglomerates presented continuously decreasing pore volume frequency curves, the latter agglomerates being characterised by a greater frequency of large pores. Comparison with typical controlled fragmentation experiments showed the number of connections to be the prevailing factor in the cohesion of aggregates formed in aqueous suspensions under various conditions. Received: 25 January 2001 Accepted: 16 May 2001     

Ternary and quaternary layered nitride halides, Ca2N(X,X′) (X,X′=Cl, Br, I): Evolution of structure with composition

The quaternary systems Ca-N-Cl-Br and Ca-N-Br-I have been investigated resulting in the synthesis of a number of new layered nitride mixed halides. The evolution of structure with composition has been investigated by powder X-ray and powder neutron diffraction techniques. A continuous solid solution exists between Ca₂NCl and Ca₂NBr with intermediate compounds adopting the same anti- α-NaFeO₂ structure (rhombohedral space group ) as the ternary end members. A phase transition occurs in the Ca₂NBr_1−yI_y system between y=0.7 and y=0.8 corresponding to a switch from cubic close packing to hexagonal close packing of metal-nitrogen layers and corresponding adoption of the anti-β-RbScO₂ (filled anti-CdI₂) structure (hexagonal space group P6₃/mmc). While nitride and halide anions occupy distinct crystallographic sites, there is no ordering of halides in quaternary materials irrespective of stoichiometry or structure type. All the nitride halides show temperature independent paramagnetic behaviour between 2 and 300 K.