Minimum Average Particle Size Research Articles

Structure and Electrochemical Performance of Li[Ni1−x−yCoxMny]O2 [0.025 ≤ x ≤ 0.4, 0.015 ≤ y ≤ 0.25] as Cathodes Compound for Lithium Ion Batteries

Li[Ni(1-x-y)Co(x)Mn(y)]O2 (0.025 < or = x < or = 0.4, 0.015 < or = y < or = 0.25) electrode powders were prepared by a solid-state reaction. The phase purity and R-3m layered structure of the synthesized Li[Ni(1-x-y)Co(x)Mn(y)]O2 materials were confirmed by X-ray diffraction analysis. The particle size of the powder/compounds was decreased with increasing Co and Mn contents to a minimum average particle size of 0.2 approximately 0.3 microm for the LiNi0.35Co0.4Mn0.25O2 powder. A specific capacity of 187 mAh/g was obtained for the LiNi0.35Co0.4Mn0.25O2 electrode with good capacity retention when cycled in the potential region of 3.0-4.6 V with a current density of 20 mA/g at room temperature. Although the structural parameters of the LiNi0.35Co0.4Mn0.25O2 cathode material were similar to those of the LiNil/3CO1/3Mn1/3O2 powder, its specific capacity was higher due to the higher Co contents.

Nanosize Particles of ZrVFe Alloy by Pulsed Laser Ablation in Ethanol

Nanosize powder of ZrVFe alloy has been prepared by a laser ablation method using a ZrVFe alloy as a target material. Ablation of the target alloy was carried out in a liquid container. The laser fluence, energy density at the target surface, was adjusted by manipulating the laser power and focus size to control the ablating conditions. The obtained colloidal dispersions of the nanoparticle were filtered and dried for characterization. The crystal structure of prepared nanoparticles maintained clear crystallinity and was the same as that of the original target alloy by comparison of the X-ray diffraction pattern. The particle sizes were distributed at around 100 nm depending on the used ablation conditions. The minimum average particle size of 71 nm was obtained at the laser fluence of 20.3 J/cm 2 , while the average size was not proportional to the laser fluence. The morphologies and oxidation state of the particle have been discussed for possible use of the ZrVFe powder as a getter material.

Synthesis and microstructureal characterization of nanostructured γ-Ni-Fe powder

The microstructures and their relation to synthesis conditions of nanostructured γ-Ni-Fe alloys, synthesized by a mechano-chemical process, were investigated by using various techniques which include EDS, infrared and optical emission spectroscopy, XRD, TEM, BET and Laser particle analyzer as well as field emission SEM. The results indicate that nanostructured γ-Ni-xFe alloys with x ≈ 32, 46, 55, and 64wt% were successfully synthesized. The impurity contents in these γ-Ni-Fe alloys were very low. Typically, the microstructures of nano γ-Ni-46Fe and their variations with synthesis conditions were focused on. It was documented that γ-Ni-46Fe alloy with a minimum average grain size of 20nm and minimum average particle size ∼70nm can be obtained under specific synthesis conditions. Micro-pore analysis combined with BET and XRD experimental results indicated that the particles usually consisting of less than one hundred grains were actually small (sub-micrometer) polycrystals with no micro-pores within them. Experiments also showed that there were large hard-agglomerates which had an average size of ∼100nm in the nano γ-Ni-46Fe powders obtained at temperatures below 800°C. Above this temperature both the grain growth and the sintering process were significant. Moreover, it was revealed that upon annealing at temperatures below 800°C, the grains of nano γ-Ni-46Fe have an elongated shape with their long axis being in <111> direction and with an aspect ratio of 1.37–1.25. Annealing at temperatures above 800°C caused their grains to change shape gradually to a disk-like form. In addition, the lattice of the nano γ-Ni-46Fe was found to be in a shrunken state with an average grain size of d < 50nm, contradicting results of mechanical alloying by Hays et al. (14).

Structural Refinement of Ag-Fe Blends during High Energy Ball Milling

The effect of high energy ball milling on the structural refinement of the binary system Ag-Fe has been studied by Transmission and Scanning Electron Microscopy, Small Angle Neutron Scattering and Mossbauer spectroscopy. Samples containng 10 wt% of Fe were submitted to high energy ball milling for times up to 50 hours. The process produces a fine dispersion of Fe into the Ag matrix; the size distribution function is quite broad with an average radius of the order of a few nm. The minimum average particle size is obtained after about 10 hours of milling, longer term processing leads to a detectable particle coarsening. TEM analyses give evidence of a well defined orientation relationships between the Fe particles and the Ag matrix. Mossbauer spectroscopy reveals a modification of the hyperfine field experienced by the Fe atoms only for short term milling. On the basis of the experimental results one can assume that the fine dispersion of Fe into the Ag matrix occurs by mutual solubilisation probably induced by plastic shear, followed by fast decomposition by precipitation. After this step, further milling can induce only coarsening of the microstructure.

On the control of crystal size in a semibatch crystallizer

Optimal programming of input flow rate to a solventing-out batch crystallizer was studied to find the maximum or the minimum average particle size while keeping the total amounts of solventing-out agent and crystals constant. For salt-water-ethanol system the maximum difference of average particle size was calculated to be about 20 percent. The difference was confirmed by experiment. The maximum difference was found by model calculation to become very large for a limited range of birth functions.