Calcined Particles Research Articles

Numerical Study on the Granular Flow and Heat Transfer of a Calcium Looping CO2 Capture System

AbstractThe calcium looping process has become a promising technology for reducing carbon dioxide emissions because of its lower energy consumption compared with other methods. A three‐dimensional multifluid model based on the kinetic theory was employed to study the movement of granules in the calciner. The results demonstrated that an increase in the rotation speed and inclination angle of the calciner led to a decrease in the residence time of the particles. Simultaneously, the probability of the particles being heated was reduced. Insufficiently calcined particles reduce the carbon capture capacity in the next cycle; therefore, suitable operating conditions and mechanism designs are very important.

Synthesis of Spherical Nanostructured g-Al2O3 Particles using Cetyltrimethylammonium Bromide (CTAB) Reverse Micelle Templating

We demonstrated the synthesis of spherical nanostructured g-Al2O3 using reverse micelle templating to enhance the surface area and reactant accessibility. Three different surfactants were used in this study: benzalkonium chloride (BZK), sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB). We obtained spherical nanostructured particles only using CTAB that form a reverse micelle emulsion. The particles have wide size distribution with an average size of 2.54 mm. The spherical particles consist of nanoplate crystallites with size 20-40 nm randomly arranged forming intercrystallite spaces. The crystalline phase of as-synthesized and calcined particles was boehmite and g-Al2O3, respectively as determined by XRD analysis. Here, the preserved particle morphology during boehmite to g-Al2O3 transformation opens a facile route to synthesize g-Al2O3 particles with complex morphology. The specific surface area of synthesized particles is 201 m2/g, which is around five times higher than the conventional g-Al2O3 (Aldrich 544833). Spherical nanostructured g-Al2O3 provides wide potential applications in catalysis due to its high density closed packed structure, large surface area, and high accessibility.

Flame Spray Synthesis of VOPO4 Polymorphs

VOPO4 is a polymorphic compound that exhibits excellent catalytic and electronic properties. Here, formation of different VOPO4 polymorphs two different organic components as precursors is investigated for the first-time using flame spray pyrolysis process as an alternative method to hydrothermal synthesis of VOPO4, the only method currently known for its synthesis. Ammonium based salts of Vanadium and Phosphorous dissolved in aqueous solution were used as precursor for the process. The products from the flame spray process were found to be hollow and amorphous particles in range of 2-10µm with shell thickness in in between 200-300nm. Upon calcination and oxidation, the size of spherical particles grew in diameter and crystallization proceeded. However, the surface of calcined particles showed it was composed of smaller grains in the size range of 0.5-1µm. Finally, the size dependence stability of different polymorph of VOPO4 is discussed as well as the effect of the different precursors used to stabilize Alpha-II and Beta VOPO4 polymorphs.

In-situ synthesis of silica aerogel/polyurethane inorganic-organic hybrid nanocomposite foams: Characterization, cell microstructure and mechanical properties

Silica aerogel nanoparticles have various applications due to their unique properties such as low thermal conductivity, high specific surface area as well as low density. However, due to low mechanical properties of pure silica aerogel, its composite with other materials is used as thermal insulators. In this work, hydrophobic silica aerogel was synthesized using sol-gel as well as solvent substitution methods, and calcined at 200, 300, 400 and 500 °C. In order to improve the mechanical properties, nanocomposites of hydrophobic silica aerogel and polyurethane with 0.5, 1, 3 and 5 wt% of nanoparticle content were prepared. Nanocomposite foams of polyurethane/silica aerogel were prepared with two separate methods: mixing silica aerogel in polyol and mixing those in diisocyanate. Cyclopentane was used as foaming agent. Results of FESEM, BET and water contact angle analysis showed that silica aerogel nanoparticles possess high specific surface area. Furthermore, the calcined particles at 500 °C showed hydrophilic properties. Optical microscopy Images showed that the sample containing 1 wt% of nanoparticles has the lowest cell diameter, highest cell density and narrower cell size distribution due to higher cell nucleation and homogeneity. Moreover, with the increase in nanoparticle content, the cell size distribution was broadened and cell density decreased. Results of scanning electron microscopy (SEM) analysis confirmed that lower contents of hydrophilic nanoparticles in both mixing media leads to more homogeneous and uniform cell microstructure. Results of compression tests showed that in samples with lower cell size and homogenous cell microstructure, the resistance against compression increased and the mechanical properties improved, this was clearly evident in nanocomposite foam containing 1 wt% of silica aerogel.

Synthesis of high purity nickel oxide by a modified sol-gel method

Abstract Nickel oxide (NiO) powder was synthesized by a modified sol-gel method using nickel acetate, citric acid and ethylene glycol as precursors. The synthesized material was thermally annealed at 250 °C for 2 h (pre-calcination step) and at 800 °C for 1 h (calcination). Scanning electron microscopy shows formation of particles with sizes of up to 50 μm after pre-calcination and of ≲ 10 μm after calcination. Nickel, oxygen and carbon were detected by energy dispersive X-ray spectroscopy (EDS) in the pre-calcined material, while only Ni and O were found after the calcination process. X-ray photoelectron spectroscopy (XPS) indicates that the composition of the synthesized nickel oxide is close to stoichiometric. Raman and Fourier transform infrared spectra show only characteristic peaks of nickel oxide. The calcined particles have cubic crystalline structure of NiO as proved by X-ray diffraction (XRD). EDS, XPS, XRD, Raman and FTIR confirmed that high purity nickel oxide was obtained by the proposed low-cost and highly effective method.

Characterization and adsorptive behaviour of snail shell-rice husk (SS-RH) calcined particles (CPs) towards cationic dye

In this study, a low-cost composite adsorbent was prepared from snail shell and rice husk (SS-RH) through calcination for brilliant green dye (BGD) adsorption from aqueous solution. Six two-parameter and three three-parameter isotherm models were used to fit the experimental data by both linear and non-linear regression methods using ten error functions. Linear and non-linear regression analysis coupled with linear and non-linear fit error functions all revealed Langmuir and Sip as two- and three-parameter isotherm models well-fitted for BGD uptake from aqueous solution using calcined particles (CPs) of SS-RH. Chi-square (χ2) error function proved to be the best applicable predictive error function for the two-parameter isotherm study while sum of absolute error (EABS), hybrid functional error (HYBRID) and normalized standard deviation (NSD) are the best error functions for non-linear Redlich-Peterson, Sips and Toth three-parameter isotherm models respectively. Irregular surface texture was observed for the calcined particles of SS-RH as revealed by SEM with BGD filling the opening pores after adsorption. FTIR revealed shift in spectrum broad peaks after adsorption. EDS exhibited active mixed metal oxides formation before adsorption with the observance of weight percent change after adsorption.

Influence of fineness of raw clay and calcination temperature on the performance of calcined clay-limestone blended cements

Workability and strength performance were investigated for blended cements with 35% mass replacement for two calcined clays (mostly containing 2:1 clay minerals) and mixtures with limestone. Raw clays were flash calcined at different temperatures and with different raw meal fineness, but ground to similar 45 μm residues after calcination. The results showed that both calcination temperature and fineness of the raw clay had a noticeable effect on the morphology, kinetics and long-term reaction degree of the resulting calcined particles, which was evident in data on the workability and strength development of the blended cements in mortar. Workability was especially influenced by the calcined clay content and raw clay fineness, to a greater extent when calcined at low temperatures. In contrast, workability progressively improved with the increase of the calcination temperature due to resulting lower specific surface area, as a consequence of increased clay transformation, which gave a spherical shape to some of the calcined clay particles. Strength performance was maximized for finely ground raw clays calcined at temperatures up to 850 °C. Raw clays with higher contents of montmorillonite showed further clay transformation at calcination temperature of 925 °C. These phases reacted more slowly with calcium hydroxide on hydration of a cementitious system than the amorphous phase, resulting in lower performance at 28 days than achieved at optimum calcination temperature, but equivalent performance after 90 days of hydration.

Flexural performance of high strength engineered cementitious composite-steel beam coupling with shrinkage load

With increase of traffic volume, orthotropic steel deck stiffened with a cementitious composite overlay becomes a popular deck type in long-span bridge. In this paper, flexural performance of high strength engineered cementitious composite (HSECC)-steel composite beam, especially the effect of internal curing of HSECC on cracking load, ultimate load, deflection and crack opening under load, is studied by experiments. In the test program, five mixtures of HSECC, including four mixtures internally cured (IC) with pre-wetted calcined particles and one mixture with ordinary curing (OC), are used. The test results show that cracking and ultimate bending load of internally cured HSECC-steel composite beam is greater than that of ordinarily cured composite beam. Deflection at cracking and peak load of internally cured composite beam is larger than that of the beam with ordinarily cured HSECC. Internal curing can also improve the ability of crack opening control after cracking. Reduction on shrinkage stress resulting from shrinkage of the cement composite layer in the structure should be responsible for the positive effect on bending performance of HSECC-steel composite beam.

Microwave synthesis of Y2O3:Eu3+ nanophosphors: A study on the influence of dopant concentration and calcination temperature on structural and photoluminescence properties

Red fluorescent emitting monodispersed spherical Y2O3 nanophosphors with different Eu3+ doping concentrations (0–13mol%) are synthesized by a novel microwave assisted urea precipitation, which is recognized as a green, fast and reproducible synthesis method. The effect of Eu3+ doping and calcination temperature on the structural characteristics and luminescence properties of particles is investigated in detail. The as prepared powders have (Y,Eu)(OH)(CO3) structure which converts to Y2O3:Eu3+ from 500°C and become crystalline at higher temperatures. The crystallite size of nanophosphors increased from 15nm to 25nm as the calcination temperature increased from 700°C to 1050°C. The efficient incorporation of Eu3+ ions in cubic Y2O3 host matrix is confirmed by the calculated X-ray Powder diffraction (XRPD) structural parameters. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) micrographs show that the as obtained and calcined particles are spherical, monodispersed and non-agglomerated. The overall size of particles increases from 61±8nm to 86±9nm by increasing Eu3+ concentration from 0mol% to 13mol%. High resolution TEM revealed polycrystalline nature of calcined particles. The particles exhibit a strong red emission under ultraviolet (UV) excitation. The photoluminescence (PL) intensity of the peaks increases proportionally with Eu3+ concentration and the calcination temperature with no luminescence quenching phenomenon observed even for Y2O3:13%Eu3+. The fluorescent emission properties combined with the monodispersity and narrow size distribution characteristics make the Y2O3:Eu3+ heavy metal free nanophosphors applicable in fluorescence cell imaging and as fluorescence biolabels.

The investigation of different particle size magnesium-doped zinc oxide (Zn0.92Mg0.08O) nanoparticles on the lubrication behavior of paraffin oil

Magnesium-doped zinc oxide (Zn0.92Mg0.08O) (ZMO) nanoparticles of 23 nm particle size have been synthesized by auto-combustion method. The variation in particle size of these nanoparticles has been performed by their further calcination at 800 and 1000 °C for 2 h and the corresponding calcined particles are designated as ZMO-1 and ZMO-2, respectively. The nanoparticles have been characterized by powder-XRD, scanning electron microscopy (SEM), energy dispersive X-ray and transmission electron microscope. The effect of particle size on the antiwear lubrication behavior of paraffin base oil has been investigated on four-ball lubricant tester. The tribological tests of these nanoparticles as antiwear additives have been studied at an optimized concentration (0.5 %w/v) by varying load for 30 min test duration and by varying the test durations at 392 N load. Various tribological parameters such as mean wear scar diameter, friction coefficient (µ), mean wear volume, running-in and steady-state wear rates show that these nanoparticles act as efficient antiwear additives and possess high load-carrying ability. From these tribological tests it has been observed that the lubrication behavior of studied nanoparticles is strongly size-dependent. The best tribological behavior is shown by nanoparticles of the smallest size, ZMO. Being sulfur, halogen and phosphorous free, ZMO nanoparticles have potential to be used as low SAPS lubricant additives. The SEM and atomic force microscopy analysis of the worn surfaces lubricated with ZMO nanoparticles at 392 N applied load for 60 min test duration show drastic decrease in surface roughness. The values of surface roughness of different additives are in good agreement with their observed tribological behavior.

Green Synthesis of Y2O3:Eu3+ Nanocrystals for Bioimaging

ABSTRACTRare earth (e.g., Eu, Er, Yb, Tm) doped Y2O3 nanocrystals are promising fluorescent bioimaging agents which can overcome well known problems of currently used organic dyes like photobleaching, phototoxicity, and light scattering. Furthermore, the alternative quantum dots (QDs) composed of heavy metals (e.g., CdSe) possess inherently low biocompatibility due to the heavy metal content. In the present work, monodisperse spherical Y2O3:Eu3+ nanocrystals were successfully synthesized by microwave assisted urea precipitation method followed by thermochemical treatment. This is a green, fast and reproducible synthesis method, which is surfactant and hazardous precursors free. The as prepared particles were non-aggregated, spherical particles with a narrow size distribution. The calcined particles have a polycrystalline structure preserving the monodispersity and the spherical morphology of the as prepared particles. After calcination of Y(OH)CO3:Eu3+ precursors at 900°C for 2 hours, a highly crystalline cubic Y2O3 structure was obtained. The Y2O3:Eu3+ spherical particles showed a strong red emission peak at 613nm due to the 5D0–7F2 forced electric dipole transition of Eu3+ ions under UV excitation (235 nm) as revealed by the photoluminescence analysis (PL). The effect of reaction time on size and photoluminescence properties of calcined particles and also the effect of reaction temperature and pressure on the size and the yield of the precipitation process have been studied. The intense red fluorescent emission, excellent stability and potential low toxicity make these QDs promising for applications in bio-related areas such as fluorescence cell imaging or fluorescence bio labels.

Preparation of Plate‐Like Sodium Niobate Particles by Hydrothermal Method

Sodium niobate NaNbO3 hydrate (NN‐hydrate) particles with a plate‐like morphology were prepared at 140°C for 2 h in 12 mol/L of NaOH by the hydrothermal method. Bar‐like Na8Nb6O19·13H2O particles were synthesized at as low as 100°C for 2 h. This work demonstrates that by carefully optimizing the reaction condition, we can selectively fabricate niobate structures, including the bar‐like, plate‐like, fibers and cube particles through a direct reaction between NaOH solution and Nb2O5. It was found that Nb6O198− formed was an important premise for formation of the NN‐hydrate, and lower [OH–] was not favorable in preparing the NN‐hydrate as there was an optimum [OH−]. Through researching effects of the reaction temperature, time, concentration of NaOH, and content of Nb2O5 on the NN‐hydrate structure and evolution, the formation mechanism from solid reactants to the intermediate were investigated. After calcining at 800°C, the synthesized NN‐hydrate particles made a phase almost transform to the perovskite NaNbO3, and the morphology of these calcined particles was still plate‐like.

Application of TXRF for burn leach test of TRISO coated UO2 particles

A Total Reflection X-Ray Fluorescence (TXRF) methodology, employing burn-leach test, was developed to assess the quality of SiC layer in tristructural isotropic (TRISO) coated UO2 particles prepared in BARC. The coated particles were heated at 1,123 K for about 96 h to constant weight. The calcined particles, thus obtained, were then heated in suprapure concentrated nitric acid. The supernatant was analysed for trace elements by TXRF. No uranium was detected in this supernatant solution. The study demonstrates the good quality of SiC layer and applicability of TXRF for burn leach test of TRISO coated UO2 particles prepared.

Silver nanoparticle-containing submicron-in-size mesoporous silica-based systems for iodine entrapment and immobilization from gas phase

Submicron-in-size silica particles with controllable morphology, particle size and mesoporosity, have been prepared under basic conditions making use of cationic alkyltrimethylammonium surfactants (CnTAB, n=12,16,18) as porogens. Gaseous nitrogen adsorption, XRD and TEM experiments revealed quasi-spherical homodispersed objects possessing regular mesopores of the MCM-41 type; lengthening of the hydrophobic tail of the template resulted in smaller particles with greater intraparticle pores. The aggregation and sintering of individual silica particles during the calcination step led to the formation of particle clusters comprising interparticle voids, as evidenced by the 129Xe NMR and TEM studies. The calcined particles were subsequently loaded with metallic silver. The measurements of iodine adsorption onto Ag-functionalized materials from the gas phase were supplemented by XRD, SEM/EDX, and TGA/DTA studies. It was demonstrated that the functionalized silica retained much gaseous iodine in an irreversible manner, mainly as an ‘interfacial’ AgI. The best compromise between the textural parameters and the post-synthesis functionalization was obtained for the large-pore silica templated with C18TAB. Indications about the presence of silver metal nanoparticles, displaying certain heterogeneity in size and shape, within the pores of this sample were given based on the analysis of 129Xe NMR spectra supplemented by UV–Visible absorption spectra and powder XRD patterns in the wide-angle region. The material can be recommended for the entrapment and immobilization of radioactive iodine in the nuclear industry since it guarantees that the adsorbed pollutant is primarily localized within the material pores and is thermally stable up to 800K in air.

Experimental Investigations on Deposit Formation by Recarbonation on External Heat Exchanger Surfaces in Oxyfuel CFB Boilers

Applying the oxyfuel process to the circulating fluidized bed technology, one of the major process concerns is the possible deposit formation on the immersed surfaces of the external heat exchangers caused by the recarbonation of unused calcined desulphurization sorbent (CaO). This paper presents first results from experiments carried out under air- and oxyfuel atmospheres in a lab-scale BFB of calcined limestone with an in-bed cooled deposition probe. It was found, that under oxyfuel conditions, the strong recarbonation of calcined particles on the cool surface lead to hard and stable carbonate depositions.

Synthesis of Strontium Hexaferrite Using D-Fructose as a Fuel

Strontium hexaferrite (SrFe12O19) powder was synthesized by sol-gel based combustion technique. In this technique, strontium and iron nitrates were used as the source nitrates and D-fructose as the fuel. The phase formation, thermal properties, particle morphology and surface morphology of the sintered pellets were analyzed by X-ray diffraction (XRD), thermogravimetry/differential thermal analysis (TG-DTA) and high-resolution scanning electron microscope (HR-SEM). Crystalline particles obtained by the calcinations of the precursor powder at 900°C, showed the crystalline diffraction pattern with the corresponding major angles, 30.41°, 31.02°, 32.37°, 34.24°, 35.81°, 37.21°, 40.47° and 42.60° respectively. HR-SEM studies have revealed that the structure of calcined particles is a mixed hexagonal and nearly plate like hexagonal, and the surface of the sintered pellets results in hexagonal structure with good magnetic properties.

Soft Solution Processing for the Synthesis of Alumina Nanoparticles in the Presence of Glucose

Alumina nanoparticles were synthesized following hydrothermal process at 170°C for 6 h, using glucose and other water‐based precursor materials. The uncalcined and calcined (550°–1200°C) particles were characterized by differential thermal analysis, thermogravimetry, Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD), and multipoint Brunauer–Emmett–Teller (BET) surface area. The microstructures of the calcined (at 550°C) particles were examined by field‐emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). XRD and FTIR studies revealed that gamma‐alumina (γ‐Al2O3) persisted up to 1000°C followed by the appearance of alpha‐alumina (α‐Al2O3) at 1200°C. BET surface area analysis confirmed that the specific surface area of γ‐Al2O3 was higher compared with α‐Al2O3. Because of particle agglomeration, the crystallite sizes obtained by the BET method showed larger values than those determined by the XRD method for the samples calcined at 550°–1200°C. For 550°C‐treated sample, FESEM micrograph showed the aggregated particles of size 20–80 nm, while TEM image of the same sample revealed a particle size of 5–10 nm.

Synthesis and Characterization of Uniform Fine Particles of Iron(III) Hydroxide/Oxide

AbstractIron(III) hydroxide was precipitated from the homogeneous solutions, containing variuos amounts of iron(III) nitrate, potassium sulfate, and urea, by heating at 85 °C for different periods of time (5‐30 min). The precipitated solids were either in the form of gel or dispersed particles of different shapes and sizes, depending upon the composition of the reactant mixtures. The as‐prepared solids were amorphous in nature and were formulated as Fe(OH)3.H2O. On calcinations at 800 °C for 1 h, the latter converted into crystalline compound, composed of α‐Fe2O3 (hematite). The calcined particles retained the original features of their precursors to a maximum extent.

Preparation of La1 − x − yCaxSryCrO3 with High-Density Structural Phase Transition and Electrical Conduction Properties

Combining simultaneous substitution of Ca and Sr for the La site in and pulverization of calcined particles with planet-type yttria-stabilized ball mill , ceramics with sintering density of more than 93% were successfully prepared. Not only sintering properties but also structural phase transition behavior, such as temperature, variation of enthalpy, and entropy, of could be controlled by alkaline earth composition. The variation of the transition behavior on Sr content could be fairly explained with the model, assuming that the phase with high crystal symmetry has high thermodynamic stability, i.e., low standard Gibbs energy of formation. Because not only has high sintering properties but also no structural phase transition between room temperature to solid oxide fuel cell (SOFC) operation and equal electrical conductivity to that of , which was reported to be a promising material for SOFC interconnectors, it can be expected that is a superior candidate to as interconnector material for SOFCs.

Monodisperse spherical mesoporous Eu-doped TiO2 phosphor particles and the luminescence properties

Monodisperse spherical and mesoporous Eu-doped TiO2 phosphor particles were prepared by nonionic surfactant-assisted soft-chemistry method. It is shown that the phosphor particles possess submicron diameter of about 250nm and narrow size distribution. Under ultraviolet irradiation the particles show characteristic luminescence corresponding to D05-Fj7 of Eu3+. Especially, the calcined particles consisted of mesopores and semicrystalline framework shows the strongest photoluminescence compared to the amorphous particles without annealing and the completely crystalline particles annealed at higher temperature. This is attributed to the energy transfer from titania nanocrystallite to Eu3+ ions dispersed in glassy amorphous titania region.