Arrangement Of Primary Particles Research Articles

Manipulating the crystal plane angle within the primary particle arrangement for the radial ordered structure in a Ni-rich cathode

The geometric structure and arrangement of primary particles are of great significance for fine control of the radial structure in a Ni-rich cathode.

Persistent and partially mobile oxygen vacancies in Li-rich layered oxides

Increasing the energy density of layered oxide battery electrodes is challenging as accessing high states of delithiation often triggers voltage degradation and oxygen release. Here we utilize transmission-based X-ray absorption spectromicroscopy and ptychography on mechanically cross-sectioned Li1.18–xNi0.21Mn0.53Co0.08O2–δ electrodes to quantitatively profile the oxygen deficiency over cycling at the nanoscale. The oxygen deficiency penetrates into the bulk of individual primary particles (~200 nm) and is well-described by oxygen vacancy diffusion. Using an array of characterization techniques, we demonstrate that, surprisingly, bulk oxygen vacancies that persist within the native layered phase are indeed responsible for the observed spectroscopic changes. We additionally show that the arrangement of primary particles within secondary particles (~5 μm) causes considerable heterogeneity in the extent of oxygen release between primary particles. Our work merges an ensemble of length-spanning characterization methods and informs promising approaches to mitigate the deleterious effects of oxygen release in lithium-ion battery electrodes. Oxygen release in Li-rich layered oxides is of both fundamental and practical interest in batteries, but a varied mechanistic understanding exists. Here the authors evaluate the extent of oxygen release over extended cycles and present a comprehensive picture of the phenomenon that unifies the current explanations.

Spectral induced polarization of clay-oxide hybrid particles

The properties of clays and oxides govern many environmental processes, consequently, ongoing effort is invested in developing non-destructive, in-situ analytical tools that reflect these properties. Herein, the physicochemical properties of montmorillonite (MMT) and iron-oxide coated montmorillonite (FeOx-MMT) were characterized using common analytical techniques, and the results were compared to spectral induced polarization (SIP) measurements. FeOx-MMT particles showed a lower CEC, higher pH dependency of the surface charge, and lower suspension stability. Also, the size of the primary particles increased following iron-oxide deposition. SIP measurements over a range of salinities showed that the effective polarization length of the clays was in the order of several microns, suggesting the measurements of aggregates (not primary particles). Moreover, FeOx-MMT particles were more compact than MMT, and their size decreased with increasing salinity due to compaction of the EDL and arrangement of primary particles in the aggregate. The SIP-response to pH changes agreed with zeta potential measurements; at low pH values, MMT exhibited higher polarization due to the higher CEC. However, at a high pH, the differences diminish due to deprotonation of the Fe-OH surface groups. These findings suggest that SIP is a sensitive method that can detect changes in the surface chemistry of soil particles.

Settling velocities of multifractal flocs formed in chemical coagulation process

A number of different flocculation mechanisms are involved in the formation of chemical coagulation flocs. Consequently, two flocs with the same size may have been formed by different mechanisms of aggregation and therefore have different arrangement of primary particles. As a result, two flocs with the same size may have different masses or mass distributions and therefore, different settling velocities. Although the correct estimation of the floc mass and density is critical for the development of the floc settling model, none of the suggested floc settling models incorporate the information on mass distribution and variable density of flocs. A probability-based method is used to determine the floc fractal dimensions on floc images. The results demonstrated that flocs formed in lime softening coagulation are multifractal. The multifractal spectra indicated the existence of a multiple fractal dimensions as opposed to the unique box-counting dimension which is a morphology-based fractal dimensions typically introduced into the Stokes' Law. These fractal dimensions may provide information on the flocs' aggregation mechanism, floc's structure, and the distribution of mass inside the floc. More research is required to investigate how to utilize the information obtained from the multifractal spectra to incorporate the variable floc density and nonhomogeneous mass distribution of flocs into the floc settling models.

Relations between the texture of silica aerogels and their preparation

The effect of the preparation conditions on the morphology (Brunauer, Emmett and Teller surface area, micro-, meso- and macroporosity, fractal dimension) of silica aerogels is presented. Solutions of tetramethyloxysilane (TMOS) in methanol were used for the sol-gel reactions. The parameters were volume fraction of TMOS, pH of the medium and hypercritical drying method (methanol or CO 2). Adsorption of different gases was used for the characterization of the size and arrangement of primary particles at the molecular scale and thermoporometry gave information on the arrangement of primary particles into aggregates.

Influence of Soil Structure on Water Relations in Low Humic Latosols: II. Water Movement

AbstractExperiments were carried out to study the effect of two aspects of structure, macrofabric (arrangement of peds) and microfabric (arrangement of primary particles within the ped), on water movement. Two latosolic soils of nearly similar composition and varying greatly in soil fabric were used. Capillary conductivity of the soils and their water‐stable aggregates were obtained. The results showed that the effect of macrofabric on water movement was more pronounced in the lowtension range (0–0.2 bar). Identical flow rates were obtained for the same size water stable aggregates of both soils, suggesting that intra‐ped pores did not significantly contribute to water flow in this tension range. It was suggested, however, that microfabric might influence fluid flow properties in the high tension range.