Wide Particle Size Distribution Research Articles

Effects of packing density and water film thickness on the fluidity behaviour of cemented paste backfill

It has been extensively recognized that the water-to-cement (w/c) ratio, solid content, and particle characteristics of tailings have substantial effects on the fluidity behaviour of cemented paste backfill (CPB). However, it is difficult to evaluate the combined effects of these influential factors. To overcome such limitation, packing density and film thickness theories were introduced in this study. A series of fresh CPB mixes with various binder dosages and solid contents were produced for packing density, flow spreading, flow rate and water film thickness (WFT) tests. The obtained results show that the packing density of solid particle (cement and tailings) system decreases with the increase of binder dosage due to the increase in loosening and wedging effect and the decrease in the particle size distribution width. Higher solid content results in an evident decrease in the water film thickness of fresh CPB, while the influence of binder dosage is not clear. For a given range of specific surface area for solid particles, packing density affects the fluidity of fresh CPB through excess water ratio. The flow spread diameter of fresh CPB increases linearly with higher excess water ratio and WFT. It is also found that WFT is the most important parameter that contributes to the fluidity of fresh CPB. These findings have demonstrated that the packing density and WFT can be reliably used for the estimation of the fluidity of fresh CPB.

Study of the discharge behavior of Rosin-Rammler particle-size distributions from hopper by discrete element method: A systematic analysis of mass flow rate, segregation and velocity profiles

In the present work, the discrete element method (DEM) is used to investigate the behaviour of Rosin-Rammler (R-R) particle size distribution (PSD) during hopper discharge. The study attempts to identify mass flow rate (MFR) and segregation as a function of spread parameter (PSD width) and location parameter, which includes detailed analysis of bulk density, segregation and velocity profile of particles. The applicability of the widely used Beverloo correlation for prediction of MFR for studied R-R PSDs is also investigated. The results show that, (1) MFR increases as PSD width (at fixed location parameter) increases, whereas MFR decreases with increase in location parameter at fixed PSD width; (2) the studied R-R PSDs exhibit a monotonic trend of flow bulk density and MFR with respect to PSD width and location parameter; (3) the effect of PSD width on overall segregation is found to be more than the location parameter; (4) the velocity profiles for considered R-R PSDs vary along the height of hopper, but remain uniform in shape and follow a pure parabolic increase from the hopper wall; (5) DEM flow rate prediction shows a good agreement with the Beverloo correlation by applying the concept of flow bulk density.

Dynamic susceptibility of a concentrated ferrofluid: The role of interparticle interactions.

The dynamic susceptibility of concentrated ferrofluids of magnetite-kerosene type is studied experimentally to clarify the effect of interparticle interactions on the magnetization reversal dynamics and the ferrofluid relaxation time spectrum. We synthesize six ferrofluid samples, four of which have the same wide particle size distribution with a high (more than 2kT) average energy of magnetic dipole interactions. These samples differ in particle concentration and dynamic viscosity. The two remaining samples have a lower content of large particles and a moderate energy of magnetic dipole interactions. For all samples, we measure the dynamic susceptibility in the weak probing field at frequencies up to 160kHz and the field amplitude dependence of the susceptibility at a frequency of 27kHz. The results show that the susceptibility dispersion at frequencies up to 10kHz is due to the rotational diffusion of colloidal particles and aggregates. Steric and hydrodynamic interparticle interactions are the main reason for the strong concentration dependence of the viscosity and so they also strongly influence the frequency dependence of the susceptibility. The influence of van der Waals and magnetic dipole interactions on the susceptibility is manifested indirectly, through the formation of multiparticle clusters. The contribution of clusters to the low-frequency susceptibility reaches 80%. Their large sizes (about 100 nm) shift the dispersion region to frequencies of 1-100Hz, depending on the temperature and particle concentration. Experiments at 27kHz demonstrate the increase in the dynamic susceptibility with increasing field amplitude. This growth is unexpected since all spectral amplitudes in the Debye function expansion of the dynamic susceptibility decrease monotonically with increasing field. To clarify the situation, the auxiliary problem of the magnetodynamics of a uniaxial particle in the alternating field is solved numerically. The Fokker-Planck-Brown rotational diffusion equation is used. It is shown that an increase in the field amplitude reduces the anisotropy barrier and the Néel relaxation time of particles and increases the dynamic susceptibility by one to two orders of magnitude compared to the weak-field limit. The calculation results are in qualitative agreement with the experimental data and allow us to propose a consistent interpretation of these data. We find that the increase in dynamic susceptibility with increasing amplitude is observed when two necessary conditions are met: (i) The suspension viscosity and the field frequency are high enough to cause the blocking of the rotational degrees of freedom of particles and aggregates and (ii) particles with a large magnetic anisotropy are present in the ferrofluid.

Effect of milling techniques on the particle characteristics of conductive Pr-substituted YBa2Cu3O7-y compound

In this work, the effects of milling techniques on Pr-substituted YBa2Cu3O7-y (YPrBCO) particles were investigated. The Pr-substituted YBa2Cu3O7-y powders were prepared by solid-state reaction method. The stoichiometric mixtures of Y2O3, BaCO3, CuO and Pr6O11 starting powders were calcined at 880 °C for 12 h in air to form respective compounds. The resulting products were milled for 4 – 12 h using the conventional ball milling technique and for 4 h using the high-energy planetary ball milling method. The phase and structure identification of powders were characterized by X-ray diffraction (XRD) technique. The microstructure and chemical composition were studied using scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDS). The XRD patterns indicated that the pure phase of YPrBCO powders was obtained. For this material system, the conventional ball mill technique gave particles having a relatively wide particle size distribution with a maximum size of ~2 μm regardless of milling time. In contrast, the narrower particle size distribution was observed for the YPrBCO powder obtained from the high-speed ball milling method and the largest particle size did not exceed 100 nm. These results showed that the powder produced by the high-speed ball milling technique could have a potential use in colloidal solution for printed thermoelectric film.

The Effect of Hydrothermal Dewatering Temperature on Hydro-Char Obtained from Oily Scum

Oily scum was treated by hydrothermal dewatering (HTD) under 120-240°C. The changes of surface characteristics and physico-chemical structure of oily scum were investigated and the effect of temperature on the properties of the hydro-char obtained from oily scum was analyzed through different characterization techniques. Results show that the moisture content of HTD treated hydro-char decreases as the temperature increases, which implies that the oily scum can be dewatered and upgraded through HTD method. The morphologies of the HTD pretreated oily scum present less oil content, smaller particle size, and become darker. As the reactor temperature increases from 120 to 240°C during the HTD process, the moisture content of hydro-char obtained decreases from 35.51 to 11.31%, while the liquid content and hydro-char content increase from 58.53 to 79.76% and from 2.50 to 5.29%, respectively, and the released gas content slightly varies in the range of 3.14 - 4.31%. The breaking and gathering effects of the HTD upgrading on oily scum result in a wide particle size distribution of products, which indicates that the overall structure of raw oily scum has been destroyed. With the increase of HTD temperature, the shorten vibration of methylene groups in hydro-char products is weakened.

Facile preparation and characterization of lanthanum oxide powders by the calcination of lanthanum carbonate hydrate in microwave field

Micron-sized lanthanum oxide powders are prepared by the calcination of lanthanum carbonate hydrate in microwave field. The decomposition process of lanthanum carbonate hydrate was analyzed by TG-DSC and indicates the reaction undergoes three stages, resulting in the generation of lanthanum oxide at 770 °C. For microwave assisted calcination, XRD patterns demonstrate that hexagonal La2O3 structure is initially formed after calcination at 650 °C for 2 h, and FT-IR analyses confirm the decomposition of precursor is complete after calcination at 750 °C for 2 h. SEM investigations reveal that 800 °C is the optimal calcination temperature to generate La2O3 powders with uniform morphologies. In comparison, conventionally calcination experiments are carried out in electrical furnace. Both XRD and FT-IR analyses are in consistence with TG-DSC, which indicate the temperature required for fully decomposition of lanthanum carbonate hydrate by conventional heating is higher than that of microwave heating. SEM images present irregular morphologies and wide particle size distribution of conventionally prepared samples. All the techniques are utilized to prove the feasibility of decomposing La2(CO3)3 to generate La2O3 in microwave field and highlight the advantages of microwave heating.

Experimental investigation of sealing ability of lost circulation materials using the test apparatus with long fracture slot

Lost circulation in fractured formations is a major challenge. The addition of conventional lost circulation materials (LCMs) to drilling fluids is the main method to control loss. The seal integrity is affected by different properties of LCMs. Plugging apparatus with slot is extensively used to evaluate sealing performance of the selected LCMs. In general, the fracture in the formation has depths, and the drilling fluids loss far into the formation. A LCM test apparatus with long fracture slot was introduced in this paper. The main objective of this work is to study the effect of LCM type, concentration and particle size distribution on the seal integrity with long fracture slot. The breaking pressure, fluid loss values, position and thickness of plugging zone are the parameters for evaluating LCM performance. Optical microscopy and scanning electron microscopy were used to observe the arrangement and microstructure of the seal. We can better understand the sealing mechanisms in long fracture by analyzing the cell pressure and fluid loss vs. time plot and the seal structure. Results showed that increasing the LCMs stiffness resulted in higher breaking pressure. There is a critical maximum concentration at which LCM will bridging and filling set at the fracture entrance and no tight seal barrier inside the fracture. Loss effect was beneficial to form thicker plugging zone inside the fracture. Suitable wide particle size distribution of LCM formed thick plugging zone inside the fracture. Multi-layer seal barrier can withstand the external load together, resulted in high seal integrities. The addition of fibrous materials in particles resulted in higher breaking pressure and lower fluid loss.

Influence of size-induced segregation on the biomass gasification in bubbling fluidized bed with continuous lognormal particle size distribution

Via the multiphase particle-in-cell approach, the biomass gasification in a three-dimensional bubbling fluidized bed with sand material of wide particle size distribution (PSD) is numerically simulated. The gas and solid motion are solved by treating the gas as the continuum medium in the Eulerian framework and numerical parcel in the Lagrangian framework, respectively. After validating the numerical results with experimental data, the radial and axial segregation induced by the wide PSD and chemical reactions, combined with the particle-scale information of both particle type (e.g., temperature, heat transfer coefficient, constituent mass fraction, and solid residence time) are discussed. The results demonstrate that obvious radial and axial segregation impact the spatial distribution of temperature and heat transfer of both particle types. The skewed distribution of the residence time of biomass particles is obtained. Biomass particles exiting the bed behave with large carbon content. PSD width exerts an evident influence on the spatial distribution of heat transfer coefficient, mass, and constituent content of biomass particles. Enlarging the PSD width enhances the gasification performance of biomass particles with the reduced mass and increased residence time for biomass particles in the bed, and the reduced char residual in the biomass particles lost. The results obtained in this work provide new insights regarding the presence of the radial and axial segregation induced by the wide size distribution and chemical reactions, which can be beneficial for the scale-up and the in-depth understanding of the fundamental mechanisms for the gasification process in this kind of reactor.

Wetting Transition from Lotus Leaf to Rose Petal using Modified Fly Ash

AbstractWe present a facile and scalable approach to develop lotus leaf as well rose petal like superhydrophobic surfaces using fly ash (an industrial waste obtained from the burning of coal). To achieve this, as‐obtained fly ash powder with wide particle size distribution (FA) was processed through sedimentation technique to obtain fly ash powder with narrower particle size distribution (FAS) and modified with two different concentrations of stearic acid (SA) and treated at two different temperatures – one each below and above melting point of SA. All samples showed superhydrophobicity, where, the water contact angle (WCA) increased with an increase in the amount of stearic acid and modification temperature. Interestingly, the water droplets roll‐off from the modified FA surfaces at a small tilting angle of 5° similar to the lotus leaf, whereas, the modified FAS surfaces exhibited high adhesion for water droplets even when inverted, as in case of the rose petal. It was seen that drying at temperature lower than melting temperature of stearic acid introduced additional roughness, yet the WCA decreased. This is investigated to understand the effect of topology and substrate nature on WCA in different wetting states.

Thermal Plasma Synthesis of Zirconia Powder and Preparation of Premixed Ca-Doped Zirconia

A novel study about the synthesis of zirconia and calcia-stabilized zirconia powders were carried out by DC thermal plasma starting from cheap precursors as the carbonates. Different operational parameters were investigated to explore the effects of the process conditions, such as the plasma torch power and the gas flow rate on the composition and the morphology of the powders. The products phase changes from a metastable tetragonal to monoclinic/tetragonal mixture. Basically a main tetragonal phase was obtained at low torch power (7 kW) while the amount of monoclinic phase linearly rises with the power, up to 66 wt% at 26 kW of plasma power and high gas flow rate. The gas flow rate also affects the shape and the size of the powder, where high values reduce powder aggregation and enhance the spherical shape. The best results were achieved at 22 kW of plasma power and high gas flow rate, with powders of roundness about 79% and a wide particle size distribution. Adding the calcium carbonate to the zirconium carbonate (corresponding to 8 wt% CaO in the final mixture), the plasma treatment mainly produces a tetragonal phase zirconia, that at 1400 °C in furnace changes in a stable cubic phase. These powders could be made suitable for further industrial applications after proper treatments.

Obtaining a Material Based on β-SiC and Carbon Fibers Using an Electric Arc Technique

Abstract—A method is presented for obtaining a material consisting mainly of carbon fibers with a graphite-like structure (Cfib) and a cubic phase of silicon carbide β–SiC using a DC arc plasma. The developed method of synthesis is characterized by a number of advantages, such as no protective gases required, easy implementation, and short duration of the operating cycle in the system (for several seconds). Judging by the data of scanning electron microscopy, the obtained silicon carbide crystals have a typical regular facetting and are characterized by a wide particle size distribution ranging from a size less than 1 μm to tens of microns. The silicon carbide crystals grow on the surface of carbon fibers, whereas their average size exhibits a decrease upon approaching the interface between the surface of graphite fiber and silicon carbide.

Optimization of rice bread formulation by mixture design and relationship of bread quality to flour and dough attributes

The bread making aptitude of five rice flours (native and gelatinized) and five gluten substitutes (GS) were prior tested and the best ingredients for mixture design were set. Native flour with a wide distribution of particle size, xanthan gum (XG), guar gum (GG) and sodium alginate (SA) were selected due to their good performance. The effect of formulation on bread volume (BV), cell area fraction (CAF) of breadcrumb and dough rheology was determined by using a simplex centroid mixture design with constrain (2.1 g of GS/100 g of flour). A significant effect of formulation on viscoelasticity of dough was observed. A non-linear relationship between BV and dough viscosity was found with maximum BV at 60000 Pa⋅s. The optimum formulation, from XG to GG mass ratio of 0.71, yields maximum values of BV (4.07 ml/g of flour) and CAF (29%); optimum bread presented good textural attributes and a slightly toasted crust.

General analytical solution to coagulation problem with homogeneous collision kernel

Since the pioneering work of Lee was published, the log-normal moment method (LNMM) has been applied in order to obtain approximate analytical solutions to the coagulation problem with several different types of collision kernels. In this study, the coagulation problem with an arbitrary homogeneous collision kernel is solved using LNMM. The new analytical solution is used to analyze the ways in which the error of the log-normal analytical solution varies depending on the functional form of the collision kernels, which could not be discussed in detail with the previous individual analytical solutions for specific collision kernels. The log-normal analytical solution tends to underestimate the particle size distribution width due to the symmetric assumption, leading to the underestimation of the polydispersity effect. This increases the error of the analytical solution as the particle size dependency of the collision kernel increases.

Synthesis and Evaluation of Novel Iridium Ruthenium Oxide Catalysts Supported on Reduced Graphene Oxide for Oxygen Evolution Reaction

Recently, environmental issues such as global warming and depletion of fossil fuels have become important topic, and progress toward sustainable societies with renewable energies such as solar and wind energy is a critical issue to overcome the social problems. Conversion of surplus energies to hydrogen via water electrolysis has attracted attention as energy storage method to utilize renewable energies effectively. However, activity, durability, and cost of catalysts are insufficient for practical application in water electrolysis systems due to high over-potential and low kinetics of electrode reactions, especially, oxygen evolution reaction (OER) on the anode [1-2] for polymer electrolyte water electrolyzer (PEWE). Iridium oxide (IrO2) particles have been used as anode catalysts, because of its high activity and durability for OER. However, decreasing iridium loading amount is required to reduce catalyst cost. In a previous study, we have successfully synthesized novel IrO2 nanoparticle catalyst supported on carbon nanotubes with large surface area of IrO2 catalyst to improved OER activity [3]. For further improvement of OER activity, increasing the specific activity of the catalyst for OER is required. One of the approaches to improve catalytic activity is formation of alloy of iridium with other metals with high activity, such as ruthenium. In the present study, we have synthesized novel alloy nanoparticle catalysts, IrRuOx, supported on the reduced graphene oxide (rGO), as active catalysts for OER. The IrRuOx / rGO catalyst was characterized and evaluated in catalytic activity for OER in sulfuric acid solution.The IrRuOx / rGO catalyst was synthesized by hydrothermal method. Briefly, required amount of metal complexes, H2IrCl6 and RuCl3, and graphene oxide (GO) prepared by modified Hummers’ method were dispersed in ethanol/water mixture and the mixture was heated at 80˚C for 6 h. Then, the mixture was heated at 150˚C in hydrothermal autoclave for 4 h to form IrRuOx nanoparticles. The IrRuOx / rGO catalysts were characterized by transmission electron microscopy (TEM), energy dispersed X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and electrochemical methods. The OER activity of the IrRuOx / rGO was examined in 0.5 M H2SO4 solution by linear sweep voltammetry (LSV) using a rotating disk electrode (RDE) system. A TEM image of the Ir0.7Ru0.3Ox / rGO catalyst is shown in Figure 1. The Ir0.7Ru0.3Ox nanoparticles with wide particle size distribution were dispersed on the surface of rGO substrate. An average size of the nanoparticles was 1.9 ± 0.8 nm. The loading amount of the Ir0.7Ru0.3Ox catalyst is estimated to be approximately 23.9 wt% by EDX measurements. In addition, the EDX analysis reveals that the ratio of Ir to Ru of the IrRuOx nanoparticles is proportional to the ratio of starting materials, H2IrCl6 and RuCl3. The XRD patterns of the IrRuOx / rGO catalysts with different Ir/Ru ratio are shown in Figure 2. The XRD data shows the (200) peak of IrRuOx is shifted to small angle and became broader with increasing Ir ratio of the catalysts. Furthermore, the XPS results of the IrRuOx / rGO catalysts showed binding energy of Ir 4f peak was shifted to a lower energy state with increasing the ratio of Ru. The XRD and XPS data suggest that nanoparticles of the catalyst form alloy of RuO2 and IrO2. In addition, the shift of the binding energy of Ir 4f peak reflects the modification of the electronic state of Ir, which affects the catalytic activity for OER, by alloy formation with Ru atom. Figure 3 shows linear sweep voltammogram of the IrRuOx / rGO catalyst obtained in 0.5 M H2SO4 solution. Electrochemical measurement reveals activity of the IrRuOx / rGO catalyst for OER is higher than that of the IrO2 / rGO catalyst, especially, onset potential of the reaction is 68 mV lower than that on the IrO2 / rGO catalyst. High activity of the IrRuOx / rGO catalyst indicates that alloying IrO2 with RuO2 improves the catalytic activity for OER. In summary, we successfully prepared the alloy catalysts of IrO2 and RuO2 supported on rGO substrate, and the IrRuOx / rGO catalysts can be a promising candidate as anode for water electrolysis. Acknowledgements This work was supported by JSPS KAKENHI Grant number 17K05969.

Identification of the initial particle size distribution for coal combustion simulations

AbstractPulverized coal generally features wide particle‐size distributions (PSD). How to set an initial PSD in coal combustion simulation remains an open question. To answer this, the Gaussian‐quadrature theory was applied to provide a discrete reconstruction of the PSD described by Rosin‐Rammler and Upper‐Limit functions. From the perspective of the moments of PSD, a theoretical analysis was conducted for mass, momentum, and energy exchange terms between gas and particle phases in pulverized coal jet flame. The analysis presented that the first, the second and the third moments of PSD were the most important to capture the flame ignition behavior. The large eddy simulations showed that the proposed method with two or more particle sizes could provide good predictions of flame ignition distances. And Sauter mean diameter (D32) could represent the complete PSD when predicting the ignition behavior of pulverized coal jet flame.

Benzyl alcohol oxidation with Pd-Zn/TiO2: computational and experimental studies

ABSTRACT Pd–Zn/TiO2 catalysts containing 1 wt% total metal loading, but with different Pd to Zn ratios, were prepared using a modified impregnation method and tested in the solvent-free aerobic oxidation of benzyl alcohol. The catalyst with the higher Pd content exhibited an enhanced activity for benzyl alcohol oxidation. However, the selectivity to benzaldehyde was significantly improved with increasing presence of Zn. The effect of reduction temperature on catalyst activity was investigated for the catalyst having a Pd to Zn metal molar ratio of 9:1. It was found that lower reduction temperature leads to the formation of PdZn nanoparticles with a wide particle size distribution. In contrast, smaller PdZn particles were formed upon catalyst reduction at higher temperatures. Computational studies were performed to compare the adsorption energies of benzyl alcohol and the reaction products (benzaldehyde and toluene) on PdZn surfaces to understand the oxidation mechanism and further explain the correlation between the catalyst composition and its activity.

Influence of Ball-milling on Sintered Body Density of Fine Tungsten Powder

The fine pure tungsten powder with a BET particle size of 0.14 μm was prepared by sol spray drying-calcination-hydrogen reduction process. The influences of ball-milling ways (dry-milling and wet-milling) on the tungsten powder morphology and powder formability were investigated. The changes of pure tungsten properties with sample size (small samples with a thickness of 2.5mm and big samples with a thickness of 2cm) were explored. In addition, the variation of microstructure and grain size with different ball milling way and sample size was studied in detail. Results show that both dry-milling and wet-milling have a great improvement in powder formability. The densities of dry-milling sintered bodies are obviously higher than that of wet-milling bodies. At the same time, the density distribution of dry-milling sintered bodies is more uniform in big samples. The wet-milling powder has a wider particle size distribution and a strong activation effect, thus the wet-milling powder sintered body has a coarser grain.

Microencapsulation of Purple-Fleshed Sweet Potato Anthocyanins with Chitosan-Sodium Tripolyphosphate by Using Emulsification-Crosslinking Technique

Anthocyanins extracted from purple-fleshed sweet potato were encapsulated using emulsification-crosslinking technique with chitosan acted as polymer and sodium tripolyphosphate as cross-linker. The parameters influencing microencapsulation were investigated i.e. stirring intensity and polymer concentration, pH of polymer and crosslinker solution, and also ratio of anthocyanins extract (core) to polymer concentration by characterizing the properties of obtained microcapsules. Stirring intensity of 1600 rpm achieved microcapsules with smaller mean diameter, narrower particle size distribution, and greater encapsulation efficiency than that of 1200 rpm for each similar polymer concentration. The research revealed that pH of 3.0 gave the greatest encapsulation efficiency and antioxidant activity of microcapsules. However, the different of mean diameter and particle size distribution of microcapsules for all of pH solution variation was not significant. Ratio of anthocyanins extract to polymer concentration 75% (w/w) possessed the greatest encapsulation efficiency, the biggest mean diameter and the widest particle size distribution between all of ratio variation. Meanwhile, ratio of 150% was selected for further analysis (microstructure and FT-IR) because it gave narrower particle size distribution and smaller mean diameter with its encapsulation efficiency was only little different from others ratio. Microstructure analysis by SEM revealed sphere and irregular microparticles. FT-IR analysis revealed that that there was bonding and interaction among anthocyanin, chitosan, and tripolyphosphate ion.

Kinetics of Overlapping Precipitation and Particle Size Distribution of Ni3Al Phase

The precipitation kinetics of overlapping process from nucleation and growth to coarsening of the γ′(Ni3Al) phase in Ni–Al alloys are investigated quantitatively by using the interface diffusion-controlled phase field model. It is found that the time exponent of average particles radius of the γ′ phase is about 1/3 at the growth and coarsening stage, while the exponent is smaller than 1/3 at the later steady-state coarsening stage. The decrease rate of the number density of the γ′ phase is larger at the steady-state coarsening than that of the growth and coarsening stage. The particle size distribution (PSD) is widened at the nucleation and growth stage, then is narrowed at the growth and coarsening stage, and becomes wide again at the steady-state coarsening stage; the width of PSDs obtained by the quantitative calculation is greater than 0.215 proposed by the LSW theory. Moreover, the position of the PSDs peak moves from 1.0 of the normalized radius at the nucleation and growth stage to less than 1.0 of the growth and coarsening stage, and then moves back to 1.0 at steady-state coarsening stage. The non-monotonically variation of kinetics of the γ′ phase during the precipitation process are reasonable and theoretically significant for the kinetics evolution.

Effect of the CoFe2O4 initial particle size when sintered by microwave on the microstructural, dielectric, and magnetic properties

AbstractThe particle size of CoFe2O4 powders (average particle size of 350 nm) was reduced to 50 nm by high‐energy milling. In this paper, special attention was given for analyzing the densification and grain growth of both particle sizes (350 and 50 nm) subject to ultrafast sintering assays using microwave sintering and their effect on the magnetic and electric properties. The results indicated that the grain growth was 10 times higher for the nanoparticle system, reaching similar sizes of ~1 μm in both cases after sintering. The relative density values were higher (95%) in the nanoparticle system due to the wide distribution of particle sizes generated in the grinding process. Qualitatively inferred microscopy analysis showed high sinterability of fine particles with a narrow distribution of grain size when subjected to ultrafast firing processes. Magnetization measurements at room temperature clearly show the reduction of Hc with increasing grain size. Electric resistivity, dielectric constant (ε′), and dielectric loss tangent (tan δ) were measured as a function of frequency at room temperature. The low values of dielectric constant (ε′) and dielectric loss (tan δ) in the low frequency range, shown for all samples sintered by microwave, prove the excellent uniformity in the microstructure.