Static Powder Research Articles

Granule formation mechanisms and morphology from single drop impact on powder beds

Single drops impacting static powder beds were studied to explain the different resulting granule structures. Three chemically similar powders with different physical properties formed static beds with porosities of 0.66–0.69, 0.54, and 0.30–0.35 respectively. Three different binder fluids (distilled water and silicone oils with viscosities of 9.3 and 96 mPa s) were released onto these powder beds from two different heights (0.5 and 30 cm). The initial drop impact, as well as complete penetration of the droplet into the bed, was recorded with a high speed camera. The high speed camera videos were analyzed, and three different granule formation mechanisms were identified: Tunneling, Spreading, and Crater Formation. Tunneling occurred for loose, cohesive powder beds. Powder aggregates were sucked into the drop which then tunneled into the beds. For coarser powders, granules were formed by a Spreading mechanism at a low impact velocity. At a high impact velocity, the drop formed a crater in the bed surface and deformed elastically in the crater, coating the drop in a layer of powder before penetrating into the bed by capillary action. Using all three dimensions of the granule, a new shape factor, the vertical aspect ratio (the ratio of the granule's projected area diameter to its maximum vertical height), was proposed as a more accurate descriptor of granule shape than currently used descriptors such as the horizontal aspect ratio. The different granule shapes observed were explained by the granule formation mechanisms. The Tunneling mechanism always produced round granules, the Spreading mechanism always produced flat disks, and the Crater Formation mechanism produced granules of varying shapes that were dependant on liquid binder properties. The results of this study have important implications for being able to predict granule structure from granule formation mechanisms, and to be able to choose the desired granule properties by operating in the appropriate regime.

Drop impact and agglomeration under static powder bed conditions

AbstractThe influence of impact conditions (reported in terms of Weber and Reynolds numbers) on nucleus formation was studied for single drops striking a static glass bead bed. Results from high speed images showed that the nucleation rate is not influenced by liquid physical properties (density, surface tension, viscosity) for drops that spread significantly (30 < We < 233). Results also showed that nucleus size is determined by how much liquid penetrates into the bed during drop spreading, so does depend on surface tension and liquid density. A corresponding analytical model, derived from first principles, predicts nucleus size to with 1.5% using only liquid physical and powder bed properties, plus the experimentally measured drop spreading behavior. © 2011 American Institute of Chemical Engineers AIChE J, 2012

A solid-state 199Hg NMR study of mercury halides

The principal elements of the 199Hg chemical-shift (CS) tensors of the mercuric halides (HgX 2, X = F, Cl, Br, and I) and the mercurous halides (Hg 2X 2, X = F and Cl) were determined from spectra of static polycrystalline powders and from magic-angle spinning (MAS) spectra. The CS tensors of both HgCl 2 and Hg 2Cl 2 are axially symmetric ( η = 0) within experimental error, differing from literature reports of η = 0.12 and η = 0.14, respectively. The principal elements of the axially symmetric CS tensor in HgBr 2 were also measured using a static sample, and the wideline spectra of HgF 2 and HgI 2 (red polymorph) give chemical-shift tensors that suggest, within experimental error, that the mercury sits in sites of cubic symmetry. The 199Hg CS tensor for Hg 2F 2 is asymmetric. Experiments with static polycrystalline samples may allow the determination of the elements of the 199Hg CS tensors even when MAS fails to completely average the dipolar coupling of the spin-½ 199Hg and the quadrupolar halide nucleus.

Optimized excitation pulses for the acquisition of static NMR powder patterns from half-integer quadrupolar nuclei

Various amplitude- and phase-modulated excitation pulses for the observation of static NMR powder patterns from half-integer quadrupolar nuclei have been generated using the optimal control routines implemented in SIMPSON 2.0. Such pulses are capable of both excitation of the central transition and signal enhancement by population transfer from the satellites. Enhancements in excess of 100% have been achieved for the central transition of the spin-3/2 87Rb nucleus compared with a selective π/2 pulse. These pulses are shown to be relatively insensitive to changes in RF power and transmitter offsets, and can achieve a more uniform signal enhancement than double-frequency sweeps (DFS), resulting in more accurate spectral lineshapes. We also investigate the possibility of “calibration-free” optimized pulses for general use on half-integer quadrupoles with unknown interaction parameters. Such pulses could prove extremely useful for studying low abundance or insensitive nuclei for which experimental optimization of the DFS scheme may be difficult. We demonstrate that a pulse optimized for an arbitrary spin-3/2 system can function well on multiple samples, and can also excite the central transition of higher spin numbers, albeit with a smaller enhancement. The mechanism by which these optimized pulses achieve the signal enhancement is highly complex and, unlike DFS, involves a non-linear excitation of the satellite transition manifold, as well as the generation and manipulation of significant multiple-quantum coherences.

Incomplete double frequency sweeps to select small quadrupolar coupling static powder patterns

Difference spectra based on the magnitude of the quadrupolar coupling of a site has been observed under static conditions utilizing a double frequency sweep pulse sequence to enhance the central transition of a small electric field gradient (EFG) environment. Through the use of convergent sweeps that only cover the inner satellite transitions of the smaller EFG site, an echo spectrum results that favors the smaller site, which can then be used in conjunction with normal echo spectra to create a difference spectrum that consists primarily of the smaller site. The simplification of the static lineshape data permits simulation for the extraction of chemical shift anisotropy (CSA) information for the site. The method is demonstrated using 93Nb NMR for samples with multiple niobium environments due to mixtures of compounds, MgNb 2O 6/LiNbO 3, or due to crystallographic structure, KCa 2Nb 3O 10.

Static solid-state 14N NMR and computational studies of nitrogen EFG tensors in some crystalline amino acids

The recently reported direct enhancement of integer spin magnetization (DEISM) methodology for signal enhancement in solid-state NMR of integer spins has been used to obtain static (14)N powder patterns from alpha-glycine, L-leucine and L-proline in relatively short experimental times at 9.4 T, allowing accurate determination of the quadrupolar parameters. Proton decoupling and deuteration of the nitrogen sites were used to reduce the (1)H-(14)N dipolar contribution to the transverse relaxation time allowing more echoes to be acquired per scan. In addition, ab initio calculations using molecular clusters (Gaussian 03) and the full crystal lattice (CASTEP) have been employed to confirm these results, to obtain the orientation of the electric field gradient (EFG) tensors in the molecular frame, and also to correctly assign the two sets of parameters for L-leucine. The (14)N EFG tensor is shown to be highly sensitive to the surrounding environment, particularly to nearby hydrogen bonding.

Effect of production parameters on the properties of IN 718 superalloy by three-dimensional printing

Three-dimensional printing is a rapid prototyping process in which powdered materials are deposited in layers and selectively joined with binder from an ink-jet style print head. By this method, three-dimensional objects are created directly from their computer-aided design models. This process consists of a moving print head spreading liquid binder through nozzles on a stationary powder bed for fabrication of green parts using computer-aided design data in a layer-wise manner. This process provides the possibility of direct manufacturing of high performance components. In this study production of full-density three-dimensional superalloy parts by three-dimensional printing with a single sintering step was aimed. For this purpose, Inconel 718 superalloy powders were used. Various shaped parts were produced with 100–200 μm layer thicknesses and then sintered at 1260–1300 °C temperatures. Densities of these samples were measured and microstructural evaluations were made.

High‐precision measurement of internuclear distances using solid‐state NMR

AbstractToday, nuclear magnetic resonance (NMR) is among the most efficient tools in structural studies. Measurement of interatomic distances is the most common way of determining high‐resolution structures of molecules using NMR techniques. In this article, we describe NMR techniques for static powder samples, based on a two‐dimensional single‐echo scheme, enhanced with adiabatic cross‐polarization. They can significantly increase the accuracy of measuring internuclear distances and turn NMR into a high‐precision crystallographic technique, complementing the X‐ray, and neutron‐scattering methods. Experimental examples are presented for intramolecular CN and CC distances in α‐crystalline form of glycine. © 2008 Wiley Periodicals, Inc. Concepts Magn Reson Part A 32A: 56–67, 2008.

Determination of chemical shift anisotropies of unresolved carbonyl sites by C-α detection under magic-angle spinning

We demonstrate that the static powder pattern line shape of chemical shift anisotropy (CSA) can be obtained for unresolved carbonyl sites of polypeptides under magic-angle spinning. The CSA interaction is first recoupled at the carbonyl site. The phase factors associated with the CSA recoupling are then transferred to the adjacent α carbon by an isotropic polarization transfer based on scalar spin–spin coupling. Because α carbons of polypeptides are usually better resolved, we can then obtain the CSA static powder pattern line shapes of the carbonyl sites after Fourier transformation in the second dimension. We validate our approach experimentally by measurements on [U– 13C, 15N]- l-alanine, [U– 13C, 15N]- l-valine and prion fibrils with uniform 13C and 15N labels on selected residues.

Physical Characterization of Component Particles Included in Dry Powder Inhalers. II. Dynamic Characteristics

Characteristics of particles included in dry powder inhalers is extended from our previous report (in this journal) to include properties related to their dynamic performance. The performance of dry powder aerosols for pulmonary delivery is known to depend on fluidization and dispersion which reflects particle interactions in static powder beds. Since the solid state, surface/interfacial chemistry and static bulk properties were assessed previously, it remains to describe dynamic performance with a view to interpreting the integrated database. These studies result in complex data matrices from which correlations between specific properties and performance may be deduced. Lactose particles were characterized in terms of their dynamic flow, powder and aerosol electrostatics, and aerodynamic performance with respect to albuterol aerosol dispersion. There were clear correlations between flow properties and aerosol dispersion that would allow selection of lactose particles for formulation. Moreover, these properties can be related to data reported earlier on the morphological and surface properties of the carrier lactose particles. The proposed series of analytical approaches to the evaluation of powders for inclusion in aerosol products has merit and may be the basis for screening and ultimately predicting particle performance with a view to formulation optimization.

Ultrahigh-Field Solid-State 59Co NMR Studies of Co(C2B9H11)2- and Co(C5H5)2+ Salts

Cobalt-59 NMR spectra of stationary powder samples of salts containing Co(C2B9H11)2- and Co(C5H5)2+ have been acquired at 21.14 T using single-echo stepped-frequency experiments. The resulting central transition, mI = 1/2 ↔ mI = −1/2, line shapes span more than 2.0 MHz and are dominated by the second-order quadrupolar interaction. Analysis of the spectra leads to CQ values of ca. 163 MHz for both ions, among the largest 59Co CQ values reported. In addition, 59Co chemical shift anisotropies are significant for Co(C2B9H11)2- and Co(C5H5)2+, with values of 4500−4700 and 5650 ppm, respectively. Isotropic 59Co chemical shifts for the cobalticarborane anion are unavailable from NMR measurements of solution samples, probably because of the extremely short relaxation times anticipated for this complex.

Constant-time method for measuring inter-nuclear distances in static powders

We present a constant-time modification of a single-echo 2D technique for measuring the constants of spin–spin interaction between heteronuclei in static powder samples. Compared to the sequence with variable echo time, the new scheme provides higher resolution. Another important improvement is a possibility to eliminate the central peak from a natural-abundance matrix. The experimental results are presented for glycine-[ 13C α, 15N] and glycine-[ 13C′, 15N].

Cation doping and oxygen content dependence of magnetic properties in single layered La 0.5Sr 1.5MnO 4 manganite

The magnetic properties of single layered La 0.5Sr 1.5Mn 0.95 B 0.05O 4 ( B=Mn, Ru, Co and Ni) manganites are analysed by static magnetization and neutron powder diffraction measurements. Charge ordering (CO) at around 240 K and antiferromagnetic (AFM) ordering at temperatures lower than 110 K, observed in the pure compound, are hindered by both cation doping and oxygen content variation. A spin glass behavior with a common freezing temperature characterizes the doped samples. Argon and oxygen annealing seems to hinder the CO and AFM ordering which in turn becomes field dependent.

Powder specific active dispersion for generation of pharmaceutical aerosols

Dry powder inhalers are increasingly employed to deliver pharmaceutical aerosols. Efficient mechanisms of particle dispersion are central to their success in disease therapy. Creation of a powder aerosol requires the input of energy to transition the static powder bed into an entrained aerosol. The purpose of this study was to investigate the effects of input of vibrational energy into a powder on aerosol entrainment. Rotating drum characterization of powder flow was performed on lactose and maltodextrin excipients blended with albuterol sulfate. Dispersion experiments were conducted using an entrainment tube and a vibration actuator, vibrational energy input being derived from analysis of powder flow data from rotating drum analysis. Results of analysis of the rotating drum data showed that with increasing rotational speed powders reached a constant state of fluidization with a mean avalanche time dependent on the powder. Dispersion experiments demonstrated that the input of vibrational energy increased the dose emission while the input of frequencies specific to the powders improved the reproducibility. Frequency analysis of the vibration signals indicated that the reproducibility was determined by the bandwidth of the signal. This work suggests that an ability to tailor energy input to match the flow properties of a given powder formulation may significantly improve reproducibility of dose delivery from active dry powder inhalers.

Solid‐State NMR and EXAFS Spectroscopic Characterization of Polycrystalline Copper(I) O,O′‐Dialkyldithiophosphate Cluster Compounds: Formation of Copper(I) O,O′‐Diisobutyldithiophosphate Compounds on the Surface of Synthetic Chalcocite

A number of polycrystalline copper(I) O,O'-dialkyldithiophosphate cluster compounds with Cu4, Cu6, and Cu8 cores were synthesized and characterized by using extended X-ray absorption fine-structure (EXAFS) spectroscopy. The structural relationship of these compounds is discussed. The polycrystalline copper(I) O,O'-diisobutyldithiophosphate cluster compounds, [Cu8{S2P(OiBu)2}6(S)] and [Cu6{S2P(OiBu)2}6], were also characterized by using 31P CP/MAS NMR (CP = cross polarization, MAS = magic-angle spinning) and static 65Cu NMR spectroscopies (at different magnetic fields) and powder X-ray diffraction (XRD) analysis. Comparative analyses of the 31P chemical-shift tensor, and the 65Cu chemical shift and quadrupolar-splitting parameters, estimated from the experimental NMR spectra of the polycrystalline copper(I) cluster compounds, are presented. The adsorption mechanism of the potassium O,O'-diisobutyldithiophosphate collector, K[S2P(OiBu)2], at the surface of synthetic chalcocite (Cu2S) was studied by means of solid-state 31P CP/MAS NMR spectroscopy and scanning electron microscopy (SEM). 31P NMR resonance lines from collector-treated chalcocite surfaces were assigned to a mixture of [Cu8{S2P(OiBu)2}6(S)] and [Cu6{S2P(OiBu)2}6] compounds.

Efficient orientational averaging by the extension of Lebedev grids via regularized octahedral symmetry expansion

Gaussian spherical quadrature methods in the guise of the Lebedev sampling grids are highly efficient for some orientational (“powder”) averaging problems in solid state NMR. However, their applicability is currently restricted, as the sets of orientations are derived analytically and because they are not well adapted to simulate the broad peakshapes encountered, for example, in the NMR on static powders or on half-integer quadrupolar spins subject to second order quadrupolar interactions under magic-angle spinning conditions. We remedy these problems by (i) introducing the recursive procedure regularized octahedral symmetry expansion (ROSE), to which any existing Lebedev set may be subjected. Each recursive step gives a 9-fold enlarged set of orientations. (ii) We demonstrate that ROSE-expanded grids, in conjunction with spectral interpolation, is well suited for calculating broad peakshapes. These advances combine into the apparently most efficient general-purpose two-angle orientational averaging technique proposed to date for solid state NMR applications.

Static and dynamic compaction of ceramic powders

The static and dynamic compaction of ceramic powders was investigated experimentally using a high-pressure friction-compensated press to achieve static stresses of 1.6 GPa and with a novel gas gun setup to stresses of 5.9 GPa for a tungsten carbide powder. Experiments were performed in the partial compaction region to nearly full compaction. The effects of variables including initial density, particle size distribution, particle morphology, and loading path were investigated in the static experiments. Only particle morphology was found to significantly affect the compaction response. Post-test examination of the powder reveals fracture of the grains as well as breaking at particle edges. In dynamic experiments, steady structured compaction waves traveling at very low velocities were observed. The strain rate within the compaction waves was found to scale nearly linearly with the shock stress, in contrast with many fully dense materials where strain rate scales with stress to the fourth power. Similar scaling is found for data from the literature on TiO 2 powder. The dynamic response of WC powder is found to be significantly stiffer than the static response, probably because deformation in the dynamic case is confined to the relatively narrow compaction wave front. Comparison of new static powder compaction results with shock data from the literature for SiO 2 also reveals a stiffer dynamic response.

Accurate measurement of C13–N15 distances with solid-state NMR

Solid-state NMR technique for measuring distances between heteronuclei in static powder samples is described. It is based on a two-dimensional single-echo scheme enhanced with adiabatic cross polarization. As an example, the results for intramolecular distances in α-crystalline form of glycine are presented. The measured NMR distances Cα13–N15 and C′13–N15 are 1.496±0.002 and 2.50±0.02Å, respectively.

Sequence of phase equilibrium states in the Dy-Mn-O system during thermal dissociation of the DyMn2O5 compound

The phase equilibria attained in the Dy-Mn-O system during step-by-step removal of oxygen from the DyMn2O5 compound are investigated using the static method (vacuum circulation setup, T = 725−950°C) and X-ray powder diffraction analysis of quenched solid phases. It is found that dissociation of DyMn2O5 proceeds in three stages. The temperature dependences of the equilibrium oxygen pressure for the revealed phase equilibria are determined experimentally. The changes in the standard thermodynamic functions of the reactions of dissociation and formation of DyMn2O5 and DyMnO3 from the oxides are calculated.

未燃チャーと微粉コークスの高炉内挙動の同時解析

A mathematical model of blast furnace operation, which is able to estimate the behaviors of the unburned char and the fine coke simultaneously, has been developed. The model based on the multi-fluid theory treats dynamic powders that are moving entrained by the gas stream as individual phases and static powders as solid components. The former takes conservation equations of momentum, thermal energy, chemical species and continuity. The latter takes only mass balance equations of chemical species, and shares fields of flow and temperature with the other solid components, such as lump coke, sinter, and so on. In the simulations, the unburned char is derived from the pulverized coal injected from the tuyere, and there is no difference in model treatment between the unburned char and the pulverized coal. The fine coke is generated uniformly in the raceway region from the coke particles, and the generation rate is determined by a kinetic treatment. The simulation of the blast furnace operation by this model revealed that the unburned char and the fine coke having different diameters and densities show different flow patterns especially in the cohesive zone and deadman. Consequently these two powders formed different areas of accumulation and reactions while large amount of powders were deposited in the deadman zone regardless of difference in flow patterns.