Structure-design strategy of 0–3 type (Bi0.32Sr0.42Na0.20)TiO3/MgO composite to boost energy storage density,efficiency and charge-discharge performance

A novel 0–3 type (Bi_0.32Sr_0.42Na_0.20)TiO₃/MgO composite is investigated in this work, which possesses a high stored energy storage density w_s˜2.50 J/cm³, recoverable energy storage density W_R˜2.09 J/cm³ with high efficiency η˜84% under low electric field (20 kV/mm). The excellent performance is owning to the increase of breakdown strength (BDS) value and the intrinsic mechanism for enhanced BDS value by MgO incorporation is disclosed by numerical simulations (COMSOL). Moreover, the studied composite exhibits excellent charge-discharge performance, the current density (C_D) and power density (P_D) are 1671 A/cm² and 150 MW/cm³, respectively, which are much superior to that of other ceramics. Besides, most of the stored energy is discharged within ˜0.15 μs via charge-discharge tests. This work not only provides a novel technique to designing bismuth-based ceramic capacitors with simultaneously high W_d, η and excellent charge-discharge performance, but also deepens the understandings of the role for the metallic oxide in the composite.     

Scaling laws and internal structure for characterizing electrospun poly[(R)-3-hydroxybutyrate] fibers

Using chloroform/dimethylformamide (CF/DMF) co-solvent, electrospinning of poly[(R)-3-hydroxybutyrate] (PHB) solutions was carried out at ambient temperature. The effects of the applied voltage (V), flow-rate (Q), and solution viscoelastic properties on the Taylor cone, electrified jet, and fiber morphology were investigated. In addition, the electric field developed by the needle-plate electrode configuration was calculated using a finite element analysis to reveal the tip-to-collector (H) effect. Among the processing parameters (V, Q and H), it was found that Q played a key role in determining the jet diameter (d_j) and electrospun fiber diameter (d_f), and scaling laws existed between them, i.e., d_j-Q^0.61 and d_f-Q^0.33. The diameter reduction ratios of D_o/d_j (D_o is the needle diameter) and d_j/d_f were measured as 50-120 and 5-10, respectively; it suggested that major jet stretching took place in the straight electrified jet region, and further chain orientation could be gained by the subsequent process of jet whipping. By changing PHB concentrations from 5 to 15 wt%, the solution viscosity (η_o) was increased from 100 to 4900 cP, whereas the surface tension and solution conductivity remained unchanged; it provided a good model solution to exclusively reveal the η_o effect on the electrospinning process. Our results showed that the η_o-dependence of d_j and d_f also followed simple scaling laws: d_j-η_o^0.06, and d_f-η_o^0.39, with a prefactor depending on the processing variables, mainly the flow-rate. Regardless of the PHB concentrations used, the obtained PHB fibers showed a similar crystallinity fraction of ca. 0.63 and possession of major α-crystals together with a small amount of β-crystals with zigzag chain conformation.     

Physicochemical studies of globular proteins—Bovine serum albumin,egg albumin,and lysozyme—In some aqueous iodide salts solutions of IA group and cetyltrimethyl ammonium bromide systems

Densities (ρ, kg m^?3), and viscosities (η, 0.1 kg m^?1 s^?1) of Bovine Serum Albumin (BSA), Egg Albumin, and Lysozyme in aqueous iodide salts of lithium, sodium, and potassium, along with cationic surfactant‐cetyltrimethyl ammonium bromide (CTAB) were measured at a temperature of 303.15 K. The 0.0010–0.0018 g %, w/v of each protein at an interval of 0.0002 mol L^?1 in 0.2, 0.4, and 0.8 millimol L^?1 of salt and CTAB are studied. Data are used for apparent molar volumes (V_?, 10^?6 m³ mol^?1) and intrinsic viscosities ([η], dL kg^?1), respectively. Data are regressed and extrapolated to zero concentrations for ρ⁰, η⁰, and limiting values and S_d, S_η and S_V corresponding slopes for protein–salt structural interactions. With size of cations, the densities decrease as CTAB > LiI > NaI > KI and increase with salts concentrations, with salts the densities are as Lysozyme > BSA > Egg Albumin, viscosities and V_? as BSA > Egg–Albumin > Lysozyme. The ρ and η values with CTAB higher and [η] are lower and converse at around 0.4 mmol L^?1 salt and is effective for greater stability of proteins. The [η] in CTAB are higher than other salts and decreases with size of cations with stronger intermolecular forces. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Active single basin solar still with a sensible storage medium

Transient mathematical models are presented for an active single basin solar still (ASS) with and without a sensible storage material under the basin liner of the still. Sand is used as a storage material due to its availability. The flowing water temperature is assumed to vary with time and space coordinates. Analytical expressions are obtained for various temperatures of the still elements as well as for the temperature of sand. The performance of the still with and without storage is investigated by computer simulation using the climatic conditions of Jeddah (lat. 21° 42′ N, long. 39° 11′ E), Saudi Arabia. Effects of mass flow rate and thickness of the flowing water for different masses of the storage material on the daylight P_dl, overnight P_on and daily productivity P_d and efficiency η_d of the still are studied. The dependence of P_d and η_d on the thickness and thermal conductivity of the basin liner material is also investigated. It is found that P_d and η_d decrease as the mass of the storage material increases, due to the increased heat capacity of the storage material. Furthermore, P_d and η_d are found to decrease with increasing thermal conductivity of the basin linear material. Therefore, it is advisable to fabricate basin liners of ASS from cheap insulating materials such as glass and mica with an optimum thickness of 3 mm. On a summer day, a value of P_d of 4.005 (kg/m² day) with a daily efficiency of 37.8% has been obtained using 10 kg of sand compared to 2.852 (kg/m² day) with a daily efficiency of 27% when the still is used without storage. The annual average of daily productivity of the still with storage is found to be 23.8% higher than that when it is used without storage.     

Characterization of floc size, strength and structure under various coagulation mechanisms

Flocs generated by various coagulation mechanisms exhibit different size, strength and structure. The properties and fractal dimensions of flocs formed under three common coagulation mechanisms, i.e. charge neutralization, sweep and bridging, were investigated at various hydraulic conditions. The results showed that the floc size decreased with the increasing average velocity gradient G and the stable floc size exponent γ was of the following hierarchy: charge neutralization (0.6107) > sweep (0.5618) > bridging (0.3674). Furthermore, fractal dimensions of flocs were the highest when formed by sweep and the lowest when generated by bridging flocculation. The mass fractal dimensions measured by light scattering were between 2.0 and 3.0 and the floc strength was between 0.01 and 0.58 N m^− 2. An intrinsic unity of the relationship among floc size, fractal dimensions, floc strength under the three coagulation mechanisms was demonstrated.     

The effect of ball size on mill performance

The specific rates of breakage of particles in a tumbling ball mill are described by the equation S_i = ax^α_i(Q(z), where Q(z) is the probability function which ranges from 1 to 0 as particle size increases. This equation produces a maximum in S, and the particle size of the maximum is related to ball diameter by x_m = k₁d². The variation of a with ball diameter was found to be of the form a = k₂/d^1.5. Both k₁ and k₂ vary with mill diameter, and simple power laws have been assumed, k₁ ∝ D^0.1, k₂ ∝ D^0.6. If it is also assumed that the mean overall values of S_i for a mixture of balls is the weighted mean of S_i values for each ball size, equations are derived for calculating this mean value. As an example, the results are used in a mill simulation to show the quantitative effect of different ball mixes in a two-compartment cement mill versus a uniform mix over the whole mill.     

Achieving high comprehensive energy storage properties of BNT-based ceramics via multiscale regulation

It is difficult to obtain high polarization strength and high breakdown strength synchronously, resulting in the drawback of lower energy storage density, which inhibits commercial application of energy storage materials. We have successfully prepared (1-x)(0.93Bi_0.5Na_0.5TiO₃-0.07CaSnO₃)-xSrTiO₃ (BNT–CS–xST) ceramics by solid-state method. The presence of polymorphic nanodomains and the large electric displacement generated by the high charge Sr²⁺-Sr²⁺ ion pairs help to delay saturation polarization (P_m ∼ 48.64 μC/cm² at 315 kV/cm). In addition, the breakdown field strength (E_b) is increased by grain refinement and increasing the band gap. It is noteworthy that a high recoverable energy storage density (W_rec = 4.2 J/cm³) and a great efficiency (η = 88%) were achieved simultaneously in BNT–CS–0.5ST ceramic. Moreover, excellent charge-discharge performance was also achieved, with a discharge energy density W_d of 2.2 J/cm³, a current density C_D of 1724 A/cm² and a power density P_D of 250 MW/cm³. The study demonstrates that the great potential of BNT–CS–xST ceramics in power storage devices and provides an effective strategy for designing ceramics dielectric capacitors with excellent performance.     

Effects of phase behavior on mutual diffusion at polymer layers interface

Using oscillation mode of rheology and theoretical calculation, we have observed for the first time the crossover of mutual diffusion coefficient, D_m, from high to low temperatures at the multiple layers interface of polymer films. A model which reflects a more realistic terminal state has been proposed to fairly fit the experimental data, by which the mutual diffusion coefficient D_m can be determined. It is substantially found that the diffusion keeps proceeding for the multilayer system at the temperature lower than the critical temperature due to the requirement of a period of time for binodal compositions to reach. Moreover, it is found that the apparent activation energy, E_d, derived from the Arrhenius relation of D_m versus 1/T, increases surprisingly when the welding temperature is below 150 °C, which relates closely to the effects of the phase behavior occurring in the two-phase region of the blend.     

Fractal analysis of morphology of PE/PA blends: Composition

Composition effect on the phase morphology in polyethylene (PE) with polyamide (PA) blends was investigated by pattern analysis of scanning electron micrographs. The average diameter denoted as d_g is defined to discuss the morphology of the blends and further, different fractal dimensions, D_M and D_N, were introduced to characterize the phase morphology. Scale function S_N(r) and S_M(r) are defined to study the selfsimilarity of the phase morphology. The plots of S_N(r)/S_N(r)m (the maximum of S_N(r)) versus r/rm (the maximum of r) and S_M(r)/S_M(r)m (the maximum of S_M(r)) versus r/rm showed the selfsimilar formation of the phase pattern. Furthermore, we calculated the fractal dimension D of different PE/PA blends. The results showed that the fractal dimension was an effective parameter to describe the spacial distribution of dispersed particles. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

High thermal stability of energy storage density and large strain improvement of lead-free Bi0.5(Na0.40K0.10)TiO3 piezoelectric ceramics doped with La and Zr

Properties of lead-free Bi_0.5-xLa_xNa_0.40K_0.10Ti_0.98Zr_0.02O₃ (x?=?0.000–0.040) ceramics were investigated. All ceramics have a pure perovskite structure. A high energy storage density (～1.00?J/cm³) at room temperature (RT) is noted for the x?=?0.030 sample, while x?=?0.020 and 0.040 samples have very high thermal stability of energy storage density of ～3% (at 75–150?°C). Furthermore, the x?=?0.030 and 0.040 samples have the highest energy storage efficiency (η) value of 94% at 125?°C with high thermal stability (η?=?84–95% at 25–150?°C). The x?=?0.005 sample has high electric field-induced strain (S_max?=?0.42%) and high normalized strain coefficient (d^*₃₃?=?S_max/E_max?=?700?pm/V) with large improvements (～200% and 163% for S_max and d^*₃₃, respectively), as compared to the based composition. This ceramic system has potentials for piezoelectric and/or energy storage density applications.     

Polymer rheology: Influence of molecular weight and polydispersity

Literature data on the non-Newtonian flow of bulk polymer and of polymer solutions are correlated on the basis of a four-parameter equation, η = η_∞ + (η₀ ? η_∞)/[1 + (τD)^m], η being the viscosity at shear rate D, and η₀ and η_∞ limiting values at D = 0 and D = ∞, respectively. The parameters η₀, η_∞, and τ all show dependence on molecular weight, and in general there is good correlation between τ and η₀. There is evidence that τ is related to a molecular weight higher than the weight-average. The exponent m shows dependence on molecular weight distribution and approaches an upper limit of unity for a monodisperse linear polymer. For linear unblended polymers it may be expressed empirically by m = (M?_n/M?_w)^1/5.     

Surface structure and oxidation reactivity of oil sand coke particles

Fractions of particles of varying mean diameter were isolated from coke obtained from the fluid coking of Athabasca bitumen. Correlations were established between the rate of oxygen sorption and the apparent surface area as measured by carbon dioxide adsorption. The rate of oxygen sorption, r₀, could be related to particle radius, R, by the equation: r₀ ∝ R^{D − 3} over a range of particle size where D is the fractal dimension of the coke. The existence of such correlations may be related to the iterative processes which form the particles.     

Melting parameters of poly(glycolic acid)

Equilibrium melting temperature T_m⁰, heat of fusion ΔH_f, and entropy of fusion ΔS_f of poly(glycolic acid) (PGA) was determined by using Clapeyron-Clausius equation. Equilibrium melting temperature T_m⁰ was 504.6 K which was determined by Hoffman-Weeks plots. The pressure dependence of T_m⁰ was determined by high pressure DTA up to 150 MPa. Volume change ΔV_f at melting was determined by using dilatometer. Heat of fusion in PGA was 183.2 (J g⁻¹), which is very close to the value reported by Chujo et al. who determined it by using T_m depression in copolymer with poly(lactic acid). ΔS_f of PGA was 0.363 (J g⁻¹ K⁻¹), which is about twice that of PLA, and the reason was discussed on the basis of the elastic modulus below T_m.     

Electronic thermal conductivity and thermopower of armchair graphene nanoribbons

A theoretical investigation of the diffusion contribution to thermopower, S_d, and the electronic thermal conductivity, κ_e, of semiconducting armchair graphene nanoribbons (GNRs) is made for T ⩽ 300 K. Considering the electrons to be scattered by edge roughness, impurities and deformation-potential coupled acoustic phonons and optical phonons, expressions for S_d and κ_e are obtained. Numerical calculations of S_d and κ_e, as functions of temperature and linear carrier density, bring out the relative importance of the contributing scattering mechanisms. A GNR of width 5 nm, supporting an electron density 2 × 10⁸ m⁻¹, is found to exhibit room temperature values of S_d and κ_e as 42 μV/K and 26.5 W/mK, respectively. A decrease in armchair GNR width, is found to enhance S_d and reduce κ_e. The effect of varying the electron density is to increase their magnitude when Fermi energy moves into the second subband. An analysis of thermopower and thermal conductivity data in clean armchair GNR samples will enable better understanding of the electron–phonon interaction.     

Turbulent transition in impactor jets and its effects on impactor resolution

A review of a number of widely used impactors suggests that the poorer performance often seen in some of the stages is due to the onset of turbulence in the jet at too large values of either the Reynolds number Re, or the nozzle-to-collector distance L. This phenomenon is studied here by measuring the collection efficiency versus Stokes number curves η(S) of a low-pressure thin-plate-orifice impactor as a function of Re and L (measured in units of the orifice diameter d_n). A drastic broadening of the η(S) curve is observed in the vicinity of a critical Reynolds number $\text{Re}{}^1\text{(L/d}{}_{\mathrm{<mtext>n</mtext>}}\text{)}$. $\text{Re}{}^1$ increases at diminishing L/d_n, taking values near 800 and 400 for L/d_n of 3.1 and 4, respectively. No transition is seen at L/d_n=1 or 2, even at Re as high as 2700. This transition in the jet modifies both the high and the low S tails of the η(S) curve. It should be distinguished from a previously studied turbulent transition of the boundary layer near the collector plate, which arises at much larger Reynolds numbers, changes only the low Stokes number tail of the η(S) curves and disappears when using small collector plates. A specialized experimental apparatus is used to provide an initial jet with very low turbulence level, as well as to isolate incipient turbulence effects from other mechanisms leading to broadening of the η(S) curves. The particles are brought very close to the axis via aerodynamic focusing, while particle capture by Brownian diffusion is offset with a repulsive electric field. Free-stream turbulence ahead of the impactor nozzle is eliminated by passing only a small fraction of the flow through the critical orifice and the focusing lenses. The remaining gas required to attain jet Reynolds numbers up to 3700 is introduced laminarly and axisymmetrically as sheath air through an outer porous wall right before the impactor nozzle. At Re in the range of a few tens, a strong increase of the critical Stokes number with increasing L/d_n is observed.     

Rheological properties of iron oxide particle suspensions

Viscosities of γ-Fe₂O₃ dispersions in epoxy resin, phenol resin, and polyvinyl butyral solutions are measured at shear rate D from 19.2 to 384 sec^?1. Volume fraction of γ-Fe₂O₃ in these dispersions ranges from about 0.002 to 0.03. The concentration dependence of relative viscosity η/η_s is closely represented by the Mooney equation. From this equation, intrinsic viscosity [η] of suspensions is found to decrease from 46.1 at D = 19.2sec^?1 to 14 at D = 384 sec^?1 for epoxy resin solution. The high [η] value indicates the existence of flocs containing immobilized liquid. By increasing the shear rate, the average floc size is reduced to point where at an infinite shear rate, only small clusters or possibly particles remain. Of the three polymers, the lowest [η] value is obtained in the dispersion of the phenol resin solution.     

Fractal Dimensions of Simulated and Real Fat Crystal Networks in 3D Space

The microstructure of fat crystal networks is closely related to rheological properties of fat products, and thus is of particular interest to food scientists. The fractal dimensions of fat crystal networks calculated by microscopy methods such as box-counting, D _b, particle-counting, D _f, and mass fractal dimension, D _m, have been extensively employed to quantify the microstructure of fats. This work revealed the microstructural basis of D _b, D _f, and D _m in 3D space through both computer simulation and experiments on the high melting fraction of milk fat crystal networks. Similar to our previous simulation study on the fractal dimensions of fat crystal networks in 2D space, D _b is sensitive to crystal size, area fraction, and not sensitive to distribution orderliness of crystals, which is the percentage of evenly distributed fat crystals within the simulated fat crystal networks. D _f and D _m were not affected by any of the microstructural factors studied in the simulation.     

Fractal characteristic of three Chinese coals

Experimental and theoretical investigation about coal/char structure is presented. Surface structures of parent coal and char with different burn-off ratios were analyzed. We introduced the fractal theory into Scanning Electron Microscopy image analysis and utilize the particle surface fractal dimension (D_ps) to quantitatively describe the surface character of coal/char particles. D_ps of three Chinese coals reach their maximum in the 35-45 wt% char burn-off interval and then decrease with increasing carbon burn-off ratio. The inner-pore information of coal/char particles was determined by N₂ isotherm adsorption/desorption. Using fractal BET model, internal surface fractal dimension (D_s) of coal/char particles was calculated. The D_s change trend of three Chinese coals is similar to their S_BET development. It means the D_s can quantitatively describe the inner pore structure character of coal/char particles.     

Enhanced energy storage properties of Bi(Ni2/3Nb1/6Ta1/6)O3–NaNbO3 solid solution lead-free ceramics

Sodium niobate energy storage ceramics with good environmental performance are widely used in electric power conversion and pulse power system, large energy storage density and high efficiency, huge power density and charge and discharge faster. In this work, (1-x)NaNbO₃-xBi(Ni_2/3Nb_1/6Ta_1/6)O₃ [(1-x)NN-xBNNT] (0.12 ≤ x ≤ 0.18) ceramics system were prepared by solid state reaction method. By introducing Bi(Ni_2/3Nb_1/6Ta_1/6)O₃ (BNNT), a relaxation strategy was constructed, which significantly improved the energy storage properties of NaNbO₃ (NN) based ceramics. Finally, comparatively high recoverable energy density (W_rec) of 3.43 J/cm³ and large energy storage efficiency (η) of 83.3% were obtained in 0.86NN-0.14BNNT ceramics. Besides discharge energy density (W_d) of 0.69 J/cm³, ultra fast charge-discharge rate (t_0.9) of 55 ns, the power density (P_D) of 70.66 MW/cm³ and the current density (C_D) of 883.23 A/cm² were also observed in ceramic.