Local solid particle behavior inside the upper zone of a circulating fluidized bed riser

The solid phase behavior is studied in the upper zone of a circulating fluidized bed riser with glass particle of mean diameter 107 μm, using a Phase Doppler Anemometer. Superficial gas velocities U_g > U_c are investigated covering the turbulent and the fast fluidization regimes and this for three static bed heights (H_s = 50 mm, H_s = 100 mm and H_s = 150 mm). The results show that the mean axial particle velocity lateral profile shapes found parabolic for H_s = 50 mm, devolve to a concave shape for H_s = 100 mm and H_s = 150 mm, creating a particles speeding zone between the core and the annulus zones. For both axial and transversal standard deviations of particle velocities in the core region, the values for the three static bed heights unite to form two stages of evolutions with U_g, where the transition velocity between these stages is found associated to the appearing of a significant entrainment of solid particles. At this transition velocity, the transversal movement originally directed toward the center riser, undergo a change toward the wall beginning near the wall and spreading into a large part of the section riser with increasing U_g. A discussion on the boundary between the turbulent and fast fluidization regimes is made based on these results.     

Magnetic properties and transmission electron microscopy studies of Ni nanoparticles encapsulated in carbon nanocages and carbon nanotubes

Three types of carbon nanomaterials, including bamboo-shaped carbon nanotubes with Ni encapsulated and hollow and Ni catalytic particles filled carbon nanocages, have been prepared by methane catalytic decomposition at a relatively low temperature. Transmission electron microscopy observations showed that fascinating fullerene-like Ni–C (graphitic) core–shell nanostructures predominated. Detailed examination of high-resolution transmission electron microscopy showed that the walls of bamboo-shaped carbon nanotubes with quasi-cone catalytic particles encapsulated consisted of oblique graphene planes with respect to the tube axis. The Ni particles encapsulated in the carbon nanocages were larger than that encapsulated in carbon nanotubes, but the diameters of the cores of hollow carbon nanocages were less than that of Ni particles encapsulated in carbon nanotubes, suggesting that the sizes of catalyst particles played an important role during carbon nanomaterial growth. The magnetic properties of the carbon nanomaterials were measured, which showed relatively large coercive force (H_c = 138.4 O_e) and good ferromagnetism (M_r/M_s = 0.325).     

Plastic deformation behaviors and mechanical properties of rolled rings of 20CrMnTi alloy in combined radial and axial ring rolling

In this paper, a new combined radial and axial ring rolling process is proposed, in which a large increase in both the ring diameter and height can be achieved. Using the finite element (FE) method, the plastic deformation behaviors and mechanical properties of the rolled rings of 20CrMnTi alloy in combined radial and axial ring rolling are numerically investigated. It is found that under different axial rolling ratio λ_a and radial rolling ratio λ_r, there are three kinds of plastic deformation behaviors during the process. The first one is that when λ_a = 1 and λ_r > 1, the ring produces the deformation of thickness reduction and diameter expansion and its height basically remains unchanged. The second one is that when λ_a > 1 and λ_r > 1, the ring produces the deformation of thickness reduction, diameter expansion and height increase. The third one is that when λ_a > 1 and λ_r = 1, the ring produces the deformation of thickness reduction, outer diameter constancy and height increase. Owing to these plastic deformation behaviors, the axial and circumferential strain distribution of the rolled rings with the same final geometry is different. To evaluate the mechanical properties of these rolled rings, the compression and tensile tests have been carried out numerically and it is found that the rolled rings with the same final geometry may have different mechanical properties due to the different axial and circumferential strain distribution and the proposed combined radial and axial ring rolling process can thus be adopted to manufacture the rings with the same final geometry but different mechanical properties.     

Investigation on resistance to attrition of coated particles by response surface methodology

The purpose of the present study is to obtain better understanding of the influence of the coating thickness, h, coating formulation, T_g, and fluid bed temperature, T_bed, variables on the resistance to attrition of the coated sodium benzoate reference particles. Three reference coating materials (T_g = 50 – 125 – 150 °C) have been sprayed by using top spray fluid bed coater. Per each coating formulation three different coating levels (h = 1% – 5% – 9% w/w) have been obtained. The coating processes were performed at three different fluid bed temperatures (T_bed = 40 – 55 – 70 °C). The experiments have been designed according to the response surface methodology (RSM). Both single effects and interactions between single effects on the resistance to attrition (response variable) calculated by means of repeated impact tester were evaluated. From statistical analysis, the coating quantity appears to have a predominant effect on the resistance to attrition of the coated particle in these studied ranges of variables. This relationship is linear and positive, which means that an increasing quantity leads to more resistance to attrition. The interaction coating thickness – coating formulation, the interaction between the fluid bed temperature and the coating formulation and the coating formulation as well as the interaction costing thickness – fluid bed temperature were found to be very significant. On the contrary, no direct effect of the fluid bed temperature on the resistance to attrition is detected.     

Consideration of mean-stress effects on fatigue life of welded magnesium joints by the application of the Smith–Watson–Topper and reference radius concepts

Three types of welded joints have been assessed with regard to their fatigue strength based on the mean-stress damage parameter model according to Smith, Watson, and Topper (P_SWT) and on the reference notch radius concept. These analyses were performed with three different stress ratios, R = −1, R = 0 and R = 0.5, under axial loading. For each stress level, the corresponding Neuber-Hyperbolas, Masing-loops and their maximum stress and maximum strain values were determined in order to calculate damage parameter (P_SWT) values. For a given weld geometry, this damage parameter is able to unify the fatigue results for different R-values within at a tight scatter band and therefore to consider the mean-stress effect. The unification of the results for different weld geometries is performed by applying the reference radii r_ref = 0.05 and r_ref = 1.00 mm as suggested by the IIW-Recommendations.     

Dry separation of particulate iron ore using density-segregation in a gas–solid fluidized bed

A gas–solid fluidized bed has been used to separate particulate iron ore (+250–500 μm in size) by segregating the particles by density. The ore particles were put into a cylindrical column of inner diameter of 100 mm and bed height of 50 mm, and were fluidized at a given air velocity u₀/u_mf = 1.2–3.2 for 10 min. u₀ and u_mf are the superficial air velocity and the minimum fluidization air velocity, respectively. The bulk density of the ore particles after fluidization was measured as a function of height through the bed in 5 mm increments (the 50 mm height was divided into 10 layers) to investigate the density-segregation. The size of the particles in each of the 10 layers was also measured to investigate size-segregation. It was found that both density-segregation and size-segregation occurred as a function of height through the bed after fluidization at u₀/u_mf = 2.0. However, the segregation did not occur near the bottom of the bed for lower u₀/u_mf and did not occur near the top of the bed for larger u₀/u_mf. The origin of the segregation-dependence on the air velocity was discussed considering the air bubbles size and the fluidizing intensity at upper and lower sections of the bed. The Fe content of the 10 layers at u₀/u_mf = 2.0 was measured to calculate the Fe-grade and Fe-recovery. The ore-recovery was also calculated using the weight of ore particles as a function of height through the bed. The feed Fe-grade (before separation) was 52.1 wt%. If the ore particles in the bottom half of the bed were regarded as the product, the Fe-grade was 59.0 wt%, and the Fe-recovery and the ore-recovery were 68.5 wt% and 60.5 wt%, respectively.     

Study on the ITO work function and hole injection barrier at the interface of ITO/a-Si:H(p) in amorphous/crystalline silicon heterojunction solar cells

For this study we focused on the front contact barrier height of HIT (ITO/a-Si:H(p)/a-Si:H(i)/c-Si(n)) solar cell. The ITO films with low resistivity of 1.425 × 10^?4 Ω cm were deposited by pulsed DC magnetron sputtering as a function of substrate temperature (T_s). There were improvement in Φ_ITO from 4.15 to 4.30 eV and delta hole injection barrier from 0 to 0.129 eV for the HIT solar cell. The results show that the high values of Φ_ITO and the delta hole injection barrier at the front interface of ITO/p-layer lead to an increase of open circuit voltage (V_oc), fill factor (FF) and efficiency (η). The performance of HIT device was improved with the increase of T_s and the best photo voltage parameters of the device were found to be V_oc = 635 mV, FF = 0.737 and η = 14.33% for T_s = 200 °C.     

Effect of soil organic matter chemistry on sorption of trinitrotoluene and 2,4-dinitrotoluene

The sorption of organic contaminants in soil is mainly attributed to the soil organic matter (SOM) content. However, recent studies have highlighted the fact that it is not the total carbon content of the organic matter, but its chemical structure which have a profound effect on the sorption of organic contaminants. In the present study sorption of two nitroaromatic contaminants viz. trinitrotoluene (TNT) and 2,4-dinitrotoluene (2,4-DNT) was studied in different SOM fractions viz. a commercial humic acid, commercial lignin and humic acid and humin extracted from a compost. ¹³C-DP/MAS NMR studies indicated that the structural composition of the organic carbon in different SOM fractions was different. The order of sorption of the nitroaromatics in the different sorbents was: humic acid-commercial > humic acid-compost > humin ～ lignin. Among the aliphatic and aromatic carbon fractions (representing bulk of SOM matrix), adsorption parameter K_f(1/n) for nitroaromatics sorption correlated well with the aliphatic carbon (r = 0.791 for TNT and 0.829 for 2,4-DNT) than the aromatic carbon (r = 0.634 for TNT and r = 0.616 for 2,4-DNT). However, among carbon containing functional groups, carbonyl carbon showed strong positive correlation with sorption of TNT (r = 0.991) and 2,4-DNT (r = 0.967) while O-alkyl carbon showed negative correlation (r = 0.832 for TNT and r = 0.828 for 2,4-DNT). The study indicates that aliphatic domains in the SOM significantly affect the non-specific sorption of both the nitroaromatic contaminants.     

Size and shape influence of luminescent orthovanadate nanoparticles on their accumulation in nuclear compartments of rat hepatocytes

In this paper the process of nonfunctionalized negatively charged orthovanadate nanoparticle accumulation and redistribution in cells dependent on their shape and size was investigated. Aqueous colloidal solutions of nReVO₄:Eu^3 + (Re = Gd, Y, La) luminescent nanocrystals of different sizes and shapes have been synthesized. The average sizes of spherical particles were 2, 20, and 300 nm, of spindle-like particles – 22 × 6.3 nm, and of rod-like particles – 57 × 4.4 nm. Luminescence of nReVO₄:Eu^3 + nanocrystals was effectively excited by UV and visible irradiation. By means of luminescence microscopy and luminescence microspectroscopy, it has been revealed that spherical nanocrystals with an average diameter of 2 nm tend to accumulate mainly in the rat hepatocyte nuclei in situ and also in the isolated nuclei of these cells. An additional experiment has shown that nanoparticles reveal tropism to nuclear structural components. The penetration into nuclei does not require any modifications of the surface of nanoparticle and is governed by the shape and size of nanoparticle and also is determined by the cellular type.     

Microwave dielectric ceramics in (Ca1− xBax)(Zn1 / 3Nb2 / 3)O3 system

(Ca_1−xBa_x)(Zn_1 / 3Nb_2 / 3)O₃ (x = 0–1.0) microwave dielectric ceramics were prepared and investigated. The Ba(Zn_1 / 3Nb_2 / 3)O₃-based solid solution was observed for x = 0.9, and the compositions with x = 0.1–0.7 resulted in the mixture of two phases. Dielectric constant ε_r and temperature coefficient of resonant frequency τ_f of the present ceramics varied anomalously and reached their maximum at x = 0.7–0.9, and these phenomena were originated from the partial substitution of small Ca²⁺ ions for larger Ba²⁺ at A-site. On the other hand, a good combination of microwave dielectric properties (ε_r = 36, Qf = 16,170 GHz, τ_f = − 12 ppm/°C) were obtained at x = 0.1, while the decreased Qf value was observed in other compositions.     

Improvement of dry float–sink separation of smaller sized spheres by reducing the fluidized bed height

In this study, the influence of the fluidized bed height on the float–sink of different sized spheres in a gas–solid fluidized bed was investigated. Fluidized beds with heights h = 200, 150, 100 and 50 mm were prepared using a cylindrical column of inner diameter = 290 mm and a mixture of zircon sand and iron powder as the fluidized medium. Float–sink experiments were carried out using density adjusted spheres of diameter D_sp = 40, 30, 20 and 10 mm. It was found that the float–sink performance at D_sp ?20 mm is not affected by the height of the bed, and the sharpness of separation (the density range where spheres neither float nor sink completely) is less than or equal to 200 kg/m³. In the case of D_sp = 10 mm, the sharpness of separation is a larger value (1100 kg/m³ at h = 200 mm), whereas it decreases with decreasing h and is 400 kg/m³ at h = 50 mm. The fluctuation of the surface height of the fluidized bed was visually recorded. The fluctuation is reduced by reducing h. The fluctuation vs. h correlates with the sharpness of separation at D_sp = 10 mm vs. h. These results indicate that the dry float–sink separation of smaller sized spheres is improved as the fluctuation of fluidized bed surface is decreased by reducing the fluidized bed height.     

The synthesis of nanocrystalline YIG in an ammonium nitrate melt

Yttrium iron garnet particles were synthesized in two different ways: first, in an ammonium nitrate melt (ANM) and second, via a solid-state reaction (SSR) route. The structural and magnetic properties of the samples were compared using XRD, SEM and dc magnetization measurements. It was observed for the ANM technique that the phase formation of YIG starts at 1000 °C and then develops with increasing temperature and sintering times. The saturation magnetization, M_s, increases sharply with increasing annealing temperature and then saturates at around 23 emu g^?1 above 1100 °C, while the coercivity decreases due to the increasing particle size. An almost single-phase sample was obtained through ANM route by annealing for 2 h at 1300 °C, after which the YIG fraction in the SSR sample was only 0.34, with M_s = 7.08 emu g^?1. The average particle sizes of the ANM samples were calculated using experimentally determined M_s values. It appeared that they vary from the sub-micron to the micron range, depending on the sintering temperature, and this coincides with the values determined from the SEM micrographs. These samples have homogeneous structures, small grains, good magnetic properties, and do not contain massive agglomerates. Therefore, the synthesis of YIG via the ANM technique represents another alternative to the SSR route.     

Effect of BaCu(B2O5) on the sintering temperature and microwave dielectric properties of BaO–Ln2O3–TiO2 (Ln = Sm,Nd) ceramics

BaCu(B₂O₅) (BCB) ceramic powder was used to decrease the sintering temperatures of BaSm₂Ti₄O₁₂ (BST) and BaNd₂Ti₅O₁₄ (BNT) ceramics. The sintering temperature of the BST and BNT ceramics was reduced from approximately 1350 °C to 850 °C by the addition of BCB. The bulk density of the specimens increased and reached the saturated value with increasing BCB content. The variation of the dielectric constant (ɛ_r) was similar to that of the bulk density and, thus, the relative density plays an important role in determining the ɛ_r value of the specimens. The Q-value initially increased with the addition of BCB but decreased considerably when a large amount of BCB was added because of the presence of the liquid phase. Good microwave dielectric properties of Qxf = 4500 GHz, ɛ_r = 60 and τ_f = −30 ppm/°C were obtained for the 16.0 mol% BCB-added BST ceramics sintered at 875 °C for 2 h.     

Fatigue of 2024-T351 aluminium alloy at different load ratios up to 1010 cycles

Fatigue properties of 2024-T351 aluminium alloy are investigated in the high cycle fatigue (HCF) and very high cycle fatigue (VHCF) regime. Endurance tests are performed with ultrasonic equipment at 20 kHz cycling frequency at load ratios of R = −1, R = 0.1 and R = 0.5 up to 10¹⁰ cycles. Additional servo-hydraulic tests between 8 and 10 Hz at R = 0.1 show no frequency influence on fatigue lifetimes. Linear lines in double logarithmic S–N plots are used to approximate data. Slope exponents of approximation lines increase with increasing numbers of cycles for all load ratios. Failures above 5 × 10⁹ cycles (R = −1 and R = 0.1) or 10¹⁰ cycles (R = 0.5) occur, and no fatigue limit is found. Fatigue cracks leading to failures above 10⁹ cycles are initiated at the surface or slightly below at broken constituent particles or at agglomerations of fractured particles, which are probably Al₇Cu₂(Fe, Mn). Specimens stressed with more than 10¹⁰ cycles at R = −1 without failure show several cracks starting at constituent particles. Maximum crack lengths are 30 μm, which is considerably below grain size.     

Effect of V2O5 additive to 0.4SrTiO3–0.6La(Mg0.5Ti0.5)O3 ceramics on sintering behavior and microwave dielectric properties

The effect of V₂O₅ addition on the microwave dielectric properties and the microstructures of 0.4SrTiO₃–0.6La(Mg_0.5Ti_0.5)O₃ ceramics sintered for 5 h at different sintering temperature were investigated systematically. It was found that the sintering temperature was effectively lowered about 200 °C by increasing V₂O₅ addition content. The grain sizes, bulk density as well as microwave dielectric properties were greatly dependent on sintering temperature and V₂O₅ content. The 4ST–6LMT ceramics with 0.25% V₂O₅ sintered at 1400 °C for 5 h in air exhibited optimum microwave dielectric properties of ɛ_r = 50.7, Q × f = 15049.6 GHz, T_f = −1.7 ppm/°C.     

Surfactant-free synthesis and electromagnetic properties of Co–Ni–B composite particles

The Co–Ni–B composite particles with different mol ratio of Co to Ni were composited of spheres, spheres in-pair, hierarchical assemblies of dentrites, which were surfactant-free synthesized by chemical reduction method in aqueous solution. The complex permeability of the Co–Ni–B composite particles indicated reverse resonant peak at the frequency range of 8–16 GHz, where the complex permittivity showed the positive resonant peak and the μ_r″ of particles showed negative values, caused by the transformation between electric and magnetic energy. The imaginary parts of relative permeability (μ_r″) of Co–Ni–B composite particles indicated one broad resonant peak over the 2–8 GHz range for the high effective anisotropy. A slight decrease in complex permittivity resulted in an excellent impedance matching property. The Co–Ni–B composite alloy particles with mol ratio of 7:3 exhibited reflection loss less than ?20 dB in frequency range of 4.0–14.5 GHz for the absorber thickness of 1.1–3.2 mm, and an optimal RL of ?32.4 dB was obtained at 12.8 GHz with thickness of 1.2 mm. The broadest bandwidth of reflection loss less than ?10 dB from 13.0 to 17.0 GHz, covering almost the whole Ku-band, was obtained for a thickness of 1.1 mm layer.     

La and Co substituted M-type barium ferrites processed by sol–gel combustion synthesis

The flake-like Ba_1−xLa_xCo_xFe_12−xO₁₉ (x = 0.0–0.4) were synthesized using sol–gel combustion synthesis process followed by the thermal insulation process and heating treatment. The synthesis process was investigated and the structure details, morphology, and magnetic properties were evaluated. TG/DTA was used to investigate the formation mechanism and to identify the thermal insulation temperature at 400 °C followed by the heat treatment temperature at 1200 °C. XRD patterns demonstrated that the unit cell volume and particle size decreased with the increase of the substitution content. The typical particles size was in the range of 1–2 μm in the planar dimension whilst the thickness was in the range of 200–500 nm. It was found from the VSM graphs that the saturation magnetizations M_s reached a maximum of 68.15 emu g⁻¹ at x = 0.3 and then decreases to 64.72 emu g⁻¹ at x = 0.3 whilst the coercivity H_c sustained decreases from 2190.70 to 1181.07 Oe g⁻¹ with substitution content increased from 0 to 0.4.     

Low temperature sintering and microwave dielectric properties of Ba4Sm9.33Ti18O54 ceramics

The effect of BaCu(B₂O₅) (BCB) on the sinterability, microstructure and microwave dielectric properties of Ba₄Sm_9.33Ti₁₈O₅₄ (BST) has been investigated. Dilatometric measurements reveal that the sintering temperature of BST can be reduced by the addition of BCB. Microstructural analysis shows abnormal grain growth with large amount of BCB. A ceramic composite with Q × f = 4000 GHz, ?_r = 52 and τ_f = ?29 ppm/°C which can be sintered at 950 °C is obtained when 10 wt% BCB is added to BST. EDS analysis shows that the composite is chemically compatible with silver.     

Diffusion of a line vortex in a second grade fluid embedded in a stagnation point flow

The diffusion of a line vortex embedded in a radially inward axisymmetric stagnation point flow for a second grade fluid is considered. This flow is the diffusion of a line vortex for a second grade fluid when a stagnation point flow is superimposed. The velocity field is in the form of υ_r = −αr, υ_θ = υ(r, t), υ_z = 2αz, where r, θ, z are cylindrical polar coordinates and α is a constant related to the inward flow. An exact solution of the governing equation is given. It is found that for small values of the time the solution approaches the diffusion of a line vortex in a second grade fluid and for large values of the time the solution tends to the flow of a line vortex in a second grade fluid embedded in a radially inward axisymmetric stagnation point flow.     

Effect of B2O3 and CuO additives on the sintering temperature and microwave dielectric properties of Ba(Mg1/3Nb2/3)O3 ceramics

B₂O₃ added Ba(Mg_1/3Nb_2/3)O₃ (BBMN) ceramics cannot be sintered below 930 °C. However, when CuO was added to them, they were sintered even at 850 °C. The amount of the Ba₂B₂O₅ second phase, which was formed in the BBMN ceramics decreased with the addition of CuO. Therefore, the CuO additive is considered to react with the B₂O₃ inhibiting the reaction between B₂O₃ and BaO. A dense microstructure without pores developed with the addition of a small amount of CuO. The bulk density, dielectric constant (ɛ_r) and Q-value increased with the addition of CuO, but decreased when a large amount of CuO was added. Excellent microwave dielectric properties were obtained for the Ba(Mg_1/3Nb_2/3)O₃ + 2.0 mol% B₂O₃ + 10.0 mol% CuO ceramic sintered at 875 °C for 2 h, with values Q_xf = 21 500 GHz, ɛ_r = 31 and temperature coefficient of resonance frequency (τ_f) = 21.3 ppm/°C.