Suspension Mixing Research Articles

Synthesis and low temperature electrochemical properties of CeO2 and C co-modified Li3V2(PO4)3 cathode materials for lithium-ion batteries

Li3V2(PO4)3/C was prepared as a pristine material by an improved sol-gel method. Then different amounts of CeO2 were employed to modify Li3V2(PO4)3/C cathode materials via a suspension mixing method assisted by polyvinyl alcohol. The 2 wt% CeO2 modified sample (Ce-2) exhibits the best initial charge-discharge performance at −20°C with a specific capacity of 70.4mAhg−1 and 103.3mAhg−1 at 1C in the potential range of 3.0-4.3V and 3.0-4.8V, respectively. The Ce-2 electrode still delivers a stable cycling performance with 95.6 % and 92.7 % capacity retention after 50 cycles even at 5C and at 0°C in the potential range of 3.0-4.3V and 3.0-4.8V, respectively. The electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) measurements indicate that the resistance and polarization of Ce-2 at low temperatures are lower than those of any other samples. In addition, the Ce-2 delivers the highest Li-ion diffusion coefficient derived from PSCA measurement, which further verifies that the electrochemical kinetics of Ce-2 is much more active than that of the pristine sample. The excellent low-temperature performances obtained in this work suggest that CeO2-modified Li3V2(PO4)3/C material is a promising cathode candidate for battery applications at low temperature conditions.

Enhanced low temperature electrochemical performances of LiFePO4/C by surface modification with Ti3SiC2

Ti3SiC2-modified LiFePO4/C cathode materials are prepared via a suspension mixing method followed by heat-treatment at 400 °C. The galvanostatic electrochemical measurements indicate that 4 wt% Ti3SiC2-modified LiFePO4/C exhibits the best electrochemical performances in the voltage range of 2.0–4.2 V. The sample shows the highest initial discharge capacity of 116.0 mAh g−1 at the rate of 0.1 C at −20 °C. And it keeps a capacity retention of 97.0% at 1 C at −10 °C after 100 cycles, higher than 81.2% for LiFePO4/C at the same conditions. Furthermore, Ti3SiC2-modified LiFePO4/C samples deliver lower charge-transfer resistance and higher diffusion coefficient of Li+ compared with the pristine LiFePO4/C, especially the 4 wt% Ti3SiC2-modified LiFePO4/C sample exhibits the lowest charge-transfer resistance and highest diffusion coefficient of Li+ among all the four samples. The improved electrochemical performances can be attributed to the lower charge transfer resistance and higher diffusion coefficient of lithium ions resulted from the modification of appropriate amount of Ti3SiC2. Besides, a series of electrochemical results show that the performances of the electrodes with 10 wt% super-P are superior to those of the electrodes with 5 wt% super-P.

Effects of corn fiber gum (CFG) on the pasting and thermal behaviors of maize starch

Corn fiber gum (CFG) was a novel arabinoxylan hydrocolloid and recent researches showed its considerable potential in food processing. In this study, the interactions of maize starch and CFG were studied. Maize starch/CFG blend gels were prepared from maize starch suspension mixing with 0.1%, 0.25%, 0.5%, 1.0% (w/w) CFG. The pasting and thermal properties, rheological properties, microstructure, leached amylose and swelling power characteristics were evaluated. Compared with the reference, CFG addition lowered peak viscosity and breakdown of the composite system, but increased final viscosity in RVA measurement. The swelling power and the amount of leached amylose of maize starch gels were reduced as the addition concentration of CFG increased. The thermal characteristics of maize starch/CFG mixtures varied insignificantly as determined in DSC heating process. Rheological parameters, such as storage modulus (G’) and loss modulus (G”), of the maize starches were observed to increase when CFG was present, supporting the hypothesis that the interaction between CFG and amylose could happen in the composite system. Confocal laser scanning microscopy (CLSM) confirmed changes in gels microstructure as starch components tended to be inhibited from leaching out of the granules when CFG was added, and the morphology of starch granule was more compact when CFG was added.

Two kinds of composite films: Graphene oxide/carbon nanotube film and graphene oxide/activated carbon film via a self-assemble preparation process

Two kinds of free-standing composite films, including graphene oxide and activated carbon film as well as graphene oxide and carbon nanotube film, were fabricated through a simple suspension mixing and then natural deposition process. The films were characterized by various measurement techniques in detail. The results show that the composite films without any treatment almost still remain the original properties of the corresponding precursors, and exhibit loose structure, which can be easily broken in water; whereas after treated at 200 °C in air, the films become relatively more dense, and even if immersed into concentrated strong alkali or acid for five days, they still keep the film-morphologies, but regretfully, they show obvious brittleness and slight hydrophilicity. As soon as the treated films are performed in high concentrated strong alkali for about one day, their brittleness and wettability can be improved and became good flexibility and complete hydrophilicity.

Synthesis and characterization of terbium-doped SrSnO3 pigments

Present work contains results related to the synthesis of new ceramic pigments based on strontium stannate in which a part of tin ions was substituted by terbium ions. The pigments of general formula SrSn1−xTbxO3, where x=0–0.5, were synthesized by solid state reaction and by suspension mixing of initial reagents. The samples were characterized by X-ray diffraction analysis, colouristic analysis, lightfastness, scanning electron microscopy and particle size analysis. Single phase powders which were prepared by solid state reaction at the temperature of 1400°C have a perovskite orthorhombic crystal structure and an increasing content of terbium causes a shift of the diffraction lines and an expansion of the unit cell. Mechanoactivation and the subsequent calcination at the temperature 1500°C can be suggested as the preferable method for obtaining the pigments with the most interesting colour properties and with the highest light stability. Strontium stannate pigments doped by terbium were characterized with interesting light yellow colour. Formula SrSn0.5Tb0.5O3 presents a composition of the sample with the best colour properties. A technological use of the pigments was tested by application into an organic binder system and high temperature ceramic glazes.

Biochemical Engineering Parameters for Hydrometallurgical Processes: Steps towards a Deeper Understanding

Increasing interest in biomining process and the demand for better performance of the process has led to a new insight toward the mining technologies. From an engineering point of view, the complex network of biochemical reactions encompassed in biomining would best be performed in reactors which allow a good control of the significant variables, resulting in a better performance. The subprocesses are in equilibrium when the rate of particular metal ion; for example, iron turnover between the mineral and the bacteria, is balanced. The primary focus is directed towards improved bioprocess kinetics of the first two subprocesses of chemical reaction of the metal ion with the mineral and later bacterial oxidation. These subprocesses are linked by the redox potential and controlled by maintenance of an adequate solids suspension, dilution rate, and uniform mixing which are optimised in bioreactors during mining operations. Rate equations based on redox potential such as ferric/ferrous-iron ratio have been used to describe the kinetics of these subprocesses. This paper reviews the basis of process design for biomining process with emphasis on engineering parameters. It is concluded that the better understanding of these engineering parameters will make biomining processes more robust and further help in establishing it as a promising and economically feasible option over other hydrometallurgical processes worldwide.

High pressure gas separation performance of mixed-matrix polymer membranes containing mesoporous Fe(BTC)

Mixed-matrix membranes (MMMs), filled with inorganic particles, provide a means to improve the gas separation performance of polymeric membranes. In this work, MMMs containing the mesoporous metal organic framework (MOF) Fe(BTC) in a Matrimid®-PI matrix were characterized in terms of their carbon dioxide (CO2) and methane (CH4) separation performance at low and high pressures. Physical properties (density, thermal degradation, and glass transition) of Fe(BTC) and prepared MMMs were analyzed. An optimized priming and suspension mixing protocol resulted in a homogeneous distribution of MOF particles in the Matrimid®-PI matrix, as observed by scanning electron microscopy (SEM). Experimental results showed decreased thermal degradation but increased membrane density and glass transition with increased Fe(BTC) loading, as well as improvement in CO2 permeability and CO2/CH4 selectivity. At high pressures, the native Matrimid®-PI membrane showed typical plasticization behavior, but as the MOF loading increased gas transport properties seem to be controlled by MOF particles leading to reduced plasticization tendencies. The favorable performance of MOF containing membranes can be attributed to the strong increase in the sorption capacity and chain rigidity by the Fe(BTC) particles which suppressed plasticization. At a mixed gas feed pressure of 40bar, MMMs with 30wt% MOF showed a CO2/CH4 selectivity increase of 62% compared to the native Matrimid®-PI membrane, while the permeability was about 30% higher than that of native polymer.

Kinetic model of nucleation and growth in silicate melts: Implications for igneous textures and their quantitative description

We present a new high-resolution numerical model for the simulation of crystallization and texture evolution using arbitrary rates of crystal nucleation and growth. The algorithm models single or multiphase solidification in a three-dimensional domain and 17 simulations using constant, linearly increasing, exponential, and Gaussian functions for the rates of nucleation and growth yield equigranular to seriate textures. Conventional crystal size distributions of all textures are nearly linear to concave-down (previously interpreted as formed by equilibration coarsening), and identical distribution patterns can result from multiple non-unique combinations of nucleation and growth rates. The clustering index is always a non-monotonous function, which initially increases then decreases with increasing crystal fraction. For texture from random homogeneous nucleation the index is substantially lower than previous predictions based on a random sphere distribution line, hence, natural samples interpreted as clustered now have greater degrees of randomness or ordering. The average number of contact neighbors and the average neighbor distance of a crystal depend linearly on crystal size, but one of the two remains insensitive to nucleation and growth kinetics and represents potential indicator of other crystallization processes than random nucleation and crystal growth. Simultaneous comparison of size, spatial and clustering patterns and of their departures from expected values are suggested to allow for separation of effects of crystallization kinetics, melt–mineral mechanical interactions, suspension mixing, or postcrystallization re-equilibration and coarsening on natural igneous rocks.

Gelcasting of alumina suspension using gellan gum as gelling agent

As one of the excellent colloidal ceramic forming methods for fabricating complex shaped ceramic components, gelcasting has been extensively investigated in the past two decades. In this article, a novel nontoxic system for gelcasting of ceramics was investigated using gellan gum as gelling agent. The rheological and gelling properties of gellan gum solutions with different types of cations and different concentrations of divalent magnesium ions were studied. Influences of concentration of gellan gum and solid loading of alumina suspension on the rheological properties and gelling properties of alumina suspension were investigated. The rheological properties of concentrated alumina suspension mixing with gellan gum and magnesium chloride were evaluated. Dense ceramics prepared by gellan gum gelation showed homogeneous microstructure and good mechanical properties.

Synthesis and properties of inorganic pigments based on pyrochlore compounds with different lanthanides

For the last few decades the attention to the ecological problems, which primarily concerns the pigmentary field of research, constantly increased. So we have prepared new ecological pure thermally stable inorganic pigments with yellow, orange and red colours based on pyrochlore structure. The series of pigments have been prepared by two different methods (namely by solid state reaction and suspension mixing of raw materials). The goal was to develop conditions for the synthesis of this type of pigments and to determine the influence of the lanthanides (Ln = Dy, Ho, Er, Tm, Yb and Lu) and preparation methods on the colouring effect and properties of oxides based on Ln–Zr–V. All prepared pigments were applied into organic matrix in mass tone. The compounds were evaluated from the standpoint of their structure, thermal stability, colour properties and particle size distribution. Obtained results indicated that these pigments can provide rich yellow and orange hues.

Enhanced electrochemical performance of LiFePO4/C cathode material modified with highly conductive TiN

Highly conductive titanium nitride (TiN) modified LiFePO4/C powders have been prepared via a suspension mixing process followed by heat treatment at 60°C. The structures and compositions of LiFePO4 samples modified with TiN are characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It is found that nano-sized TiN particles together with the amorphous carbon layer form an integrated network on the surface of LiFePO4. Galvanostatic charge/discharge test indicates that TiN modification is effective to improve the discharge capacity and cycle performance, especially at high rates. Electrochemical impedance spectroscopy (EIS) and potential step chronoamperometry (PSCA) measurements prove that the co-coating layer of C and TiN dramatically alleviates the charge transfer impedance and enhances the Li-ion diffusion coefficient, respectively. The sample with 5wt.% TiN exhibits the best electrochemical performance among several samples investigated in this work.

Effects of colloidal silica suspension mixing on porosity of phosphate-bonded investments after setting and heating processes

A numerical simulation model, which was based on the setting and heating reactions of the binder phase of phosphate-bonded investment compacts, was developed to compute the porosities of set and burnout compacts. Densities and concentrations of microsilica particles in dilute suspension were measured and input into the simulation model. Validity of the model was confirmed by experimental results, that is, colloidal silica suspensions were prepared using different silica concentrations and mixed with investment powders. Porosities of these set and burnout compacts were experimentally measured. Effects of these factors on the porosity of compacts were examined using the developed simulation model: liquid/powder (L/P) ratio, concentration of microsilica particles in colloidal silica suspension, and ratio of binder component (NH₄H₂PO₄) in investment powder. It was concluded that numerical simulation is a viable tool for dental materials research.

La0.6Sr0.4CoO3−δ modified LiFePO4/C composite cathodes with improved electrochemical performances

LiFePO4/C particles were coated with highly conductive La0.6Sr0.4CoO3−δ (LSC) via a suspension mixing method followed by heat-treating. The effects of LSC coating were studied by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), galvanostatic charge/discharge test, electrochemical impedance spectroscopy (EIS), potential step chronoamperometry (PSCA) and cyclic voltammetry (CV). The results of HRTEM and XRD showed that the incomplete carbon network could be repaired by nanometer-sized LSC while the co-coated composite retained the structure of LiFePO4. Electrochemical test results indicated that LSC coating could significantly improve the electrochemical performances at high charge/discharge rates. The 4wt.% LSC-coated LiFePO4/C sample exhibited the best electrochemical performance with discharge capacities of 136, 125 and 96mAhg−1 at the rates of 1, 2 and 5C, respectively. These data were much higher than those of the uncoated sample. This improvement could be mainly attributed to the lower charge transfer resistance and higher diffusion coefficients of Li+ ions resulted from the higher conductivity of LSC and the faster kinetic process between the LSC/LiFePO4 interfaces.

Study of ceramic pigments based on Er2Ce2−x Mo x O7

This contribution is focused on the synthesis, characterization and optical properties of new inorganic pigments which are environment friendly and can substitute some toxic metals in interesting colour compounds. Pyrochlores belong to the group of high-temperature pigments, and are a variety of actual and potential applications for several materials. Examples include catalysts, thermal barrier coatings, solid electrolytes, nuclear waste forms and host materials for luminescence centers. The pigments were prepared by the solid state reaction and also by method of suspension mixing of materials in the series with increasing content of molybdenum. The pigments were applied into organic matrix and ceramic glaze. The colour properties of these applications were investigated depending on content of Mo, method of preparation and temperature of calcination (1350–1550 °C after step 50 °C). The optimum conditions for their synthesis were determined. The pigments were evaluated from standpoint of their structure, colour and particle sizes. Characterization of Er2Ce2−xMoxO7 pigments (x = 0.1, 0.3, 0.5 and 0.7) suggests that they have a potential to be alternative yellow or orange colourants for paints, plastics, ceramics and building materials.

Ti3SiC2 Modified LiFePO4/C Cathode Materials with Improved Electrochemical Performance

LiFePO4/C was modified with highly conductive nanolaminated Ti3SiC2 via a suspension mixing method followed by heat-treatment at 400°C. The samples of pristine LiFePO4/C and Ti3SiC2-modified LiFePO4/C were characterized by X-ray diffraction (XRD), Raman spectroscopy, high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), galvanostatic charge/discharge test, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and potential step chronoamperometry (PSCA). It was found that a Ti3SiC2-based conducting network characterized by a “plane-to-point” conducting mode was constituted in the LiFePO4/C cathode. Electrochemical test results indicated that the addition of Ti3SiC2 not only improved the discharge capacity at high rates, but also enhanced the electrochemical reversibility. It also alleviated the charge transfer impedance and facilitated the diffusion of lithium ion. The 4 wt% Ti3SiC2-modified LiFePO4/C sample exhibited the best electrochemical performance. For example, the sample provided higher capacities of 140.4 and 101.2 mAh g−1 than those of pristine sample (121.0 and 63.4 mAh g−1) at 1 C and 5 C, respectively.

Improved electrochemical performance of La0.7Sr0.3MnO3 and carbon co-coated LiFePO4 synthesized by freeze-drying process

Abstract Carbon coated LiFePO 4 particles were first synthesized by sol–gel and freeze-drying method. These particles were then coated with La 0.7 Sr 0.3 MnO 3 nanolayer by a suspension mixing process. The La 0.7 Sr 0.3 MnO 3 and carbon co-coated LiFePO 4 particles were calcined at 400 °C for 2 h in a reducing atmosphere (5% of hydrogen in nitrogen). Nanolayer structured La 0.7 Sr 0.3 MnO 3 together with the amorphous carbon layer forms an integrate network arranged on the bare surface of LiFePO 4 as corroborated by high-resolution transmission electron microscopy. X-ray diffraction results proved that the co-coated composite still retained the structure of the LiFePO 4 substrate. The twin coatings can remarkably improve the electrochemical performance at high charge/discharge rates. This improvement may be attributed to the lower charge transfer resistance and higher electronic conductivity resulted from the twin nanolayer coatings compared with the carbon coated LiFePO 4 .

Comments on "Suspension Mixing Tank - Design Heuristic"

The study deals with analysis of the process characteristics of agitated system with a pitched blade impeller and radial baffles (impeller power input and impeller pumping capacity) under turbulent regime of flow of agitated batch. Original experimental data are compared with results of CFD simulation in a pilot plant mixing system published in literature.

Suspension Mixing Tank - Design Heuristic

The design of suspension mixing tanks is often embedded in empiricism due to insufficient understanding of the hydrodynamics of dense solid-liquid interaction. This is particularly limiting during the design of mixing tanks or batch reactor for expensive high quality products in the fine chemicals, biological and pharmaceutical processing industries. In this paper, a computational fluid dynamics (CFD)-assisted design approach has been employed to study the effectiveness of mixing tank geometrical configurations to suspend particles. Ten crucial variables were investigated and the effects of changing the value of these variables were documented. In addition, a multivariable study involving these ten variables was also conducted to investigate the most important variables among them. Finally, by capturing the essence of the results, a design heuristic was developed which can be applied across the process industry.

Measuring Flow Velocity in Pulp Suspension Mixing Using Ultrasonic Doppler Velocimetry

Ultrasonic Doppler velocimetry (UDV), a non-invasive fluid flow measurement technique suitable for use in opaque systems, was used to measure pulp suspension flow velocity in a rectangular 1 : 11-scale agitated pulp stock chest. The flow characteristics of a Maxflo impeller were measured as a function of fibre mass concentration, fibre type and impeller speed. Using the velocity profiles measured, the impeller pumping rate and flow number were calculated as a function of suspension yield stress (itself a function of fibre mass concentration and fibre type). The flow number was found to decrease as the suspension yield strength increased. For example, when the mass concentration of a hardwood pulp was increased from 0% (water) to 3.3%, the flow number decreased from 0.64 to 0.43. UDV was also used to identify regions of poor mixing by measuring flow profiles at critical locations within the vessel. This study also demonstrates the ability of UDV to measure the cavern size of the pulp suspension during agitation.

A multi-scale assessment of Pb(II) sorption on dolomite

Macroscopic sorption studies indicated that Pb sorption capacity was independent of pH over the pH range 5–7, while sorption as a function of reaction time up to two weeks for systems with no bulk precipitate phases showed continuous Pb uptake on dolomite. This could be due to diffusion of Pb into the micropores of dolomite as well as an increase in surface sites caused by particle size reduction during suspension mixing. Normalized XANES spectra for systems undersaturated with respect to Pb carbonate precipitates resembled the spectrum of Pb4(OH)4+4, suggesting that Pb is mainly coordinated to dolomite as an inner-sphere surface complex. On the other hand, the XANES spectrum for 10−3 M Pb at 1 atm CO2(g) in a 2 M Mg(NO3)2 background electrolyte solution resembled that of cerussite, while a sample at 5×10−4 M Pb in equilibrium with air and 2 M Mg(NO3)2 resembled that of hydrocerussite. EXAFS analyses of sorption samples in chloride solutions showed that there were only first-shell contributions under 1 atm CO2(g), while higher shell contributions from Ca/Mg were seen at 10−3.42 atm CO2(g). On the other hand, EXAFS samples prepared in nitrate solutions showed noticeable differences in speciation under different reaction conditions—from outer-sphere surface complexes at low Pb concentrations and pH, to inner-sphere surface complexes at moderate Pb concentrations and neutral pH, to the formation of Pb carbonate precipitates at the highest Pb loadings.