The decrease of depolarization temperature and the improvement of pyroelectric properties by doping Ta in lead-free 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 ceramics

Ta-doped lead-free 0.94NBT-0.06BT-xTa (x=0.0–1.0%) ceramics were synthesized by a conventional solid-state route. XRD shows that the compositions are at a morphotropic phase boundary where rhombohedral and tetragonal phases coexist. The depolarization temperature (T_d) shifted to lower temperature with the increase of Ta content. The pyroelectric coefficient (p) of doped ceramics greatly enhanced compared with undoped material and reached a maximum of 7.14×10⁻⁴ C m⁻² °C⁻¹ at room temperature (RT) and 146.1×10⁻⁴ C m⁻² °C⁻¹ at T_d at x=0.2%. The figure of merits, F_i and F_v, also showed a great improvement from 1.12×10⁻¹⁰ m v⁻¹ and 0.021 m² C⁻¹ at x=0.0 to 2.55×10⁻¹⁰ m v⁻¹ and 0.033 m² C⁻¹ at x=0.2% at RT. Furthermore, F_i and F_v show the huge improvement to 52.2×10⁻¹⁰ m v⁻¹ and 0.48×10⁻¹⁰ m v⁻¹ respectively at T_d at x=0.2%. F_C shows a value between 2.26 and 2.42 ×10⁻⁹ C cm⁻² °C⁻¹ at RT at x=0.2%. The improved pyroelectric properties make NBT-0.06BT-0.002Ta ceramics a promising infrared detector material.     

Relationship between size of oil droplet generated during chemical dispersion of crude oil and energy dissipation rate: Dimensionless,scaling, and experimental analysis

Droplet formation mechanisms during the chemical dispersion of crude oil were investigated using both theoretical and experimental approaches. Dimensionless and force balance analysis identified four distinct regimes of droplet formations. For d>η, d scales either with (ε^?2/5) or (ε^?1/4) or and for d<η, d scales either with (ε^?1/2) or (ε^?1/4) depending on whether the main restoring force against droplet breakage is provided by surface tension or oil viscosity. The symbols d, η, and ε represent the droplet diameter, the Kolmogorov length scale, and energy dissipation rate, respectively. For d>η and <η, the external force, which tries to deform and break the droplet is provided by the pressure difference across the droplet diameter and viscous shear, respectively. Identification of the relationship d～(ε^?1/4) for d<η is a new contribution of this present study. The validity of this relationship was also proven by our experimental observations over a range of physical properties (dynamic viscosity 0.015–8.6 Pa s; oil–water interfacial tension 0.0001–0.015 N/m) and mixing energies (0.00075–0.16 W/kg), similar to those in real environmental settings (e.g., estuary, surface layer of oceans). All these above findings and observations are vital from the stand point of appropriately scaling droplet formation process, during chemical dispersion of crude oil, and in the development of reliable predictive models.     

Impactor designed to increase mass output rate of nanoparticles from a pneumatic nebulizer

A modular impactor was designed to remove large droplets from aerosols generated by a pneumatic nebulizer, the Six-Jet Atomizer from TSI Inc. (Shoreview, MN), with the aim of generating dry nanoparticles. Three interchangeable nozzle heads were designed to provide droplet cutoff diameters of 0.5, 1, and 2 μm at an air flow rate of 8.3×10^?4 m³ s^?1 (50 L min^?1), which corresponds to all six jets of the nebulizer operated at 25 °C and an air pressure of 241 kPa (35 psi). The collection and output characteristics of the 0.5 μm impactor were evaluated from dry particle size distributions produced by nebulizing an aqueous solution with a NaCl mass fraction of 1% both with and without the impactor present. The impactor characteristic cutoff curve was sharp (impactor geometric standard deviation, GSD_imp=1.15–1.19) with a 50% cutoff diameter d₅₀ that ranged from 0.48 μm at 3.0×10^?4 m³ s^?1 to 0.74 μm at 11.7×10^?4 m³ s^?1. The rate of dry NaCl particle generation ranged from 0.5 to 5 g s^?1 (0.04 to 0.4 g day^?1) with mass median diameters MMD_p=80–123 nm and geometric standard deviations GSD_p=1.6–1.8 (depending on flow rate). Anomalous negative impactor efficiencies were observed at flow rates >8.3×10^?4 m³ s^?1 for 100 to 400 nm droplets and at all flow rates for droplets smaller than 100 nm. This phenomenon will be investigated further as a way to increase the generation rate of nanoparticles. A step-by-step procedure is presented for the selection of an appropriate impactor design and operating flow rate for a desired maximum aerosol particle size.     

Enhancement of pyroelectric properties of lead-free 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 ceramics by La doping

Lead-free 0.94NBT-0.06BT-xLa ceramics at x = 0.0–1.0 (%) were synthesized by a conventional solid-state route. XRD shows that the compositions are at a morphotropic phase boundary where rhombohedral and tetragonal phases coexist. With increasing La³⁺ content pyroelectric coefficient (p) and figures of merits greatly increase; however, the depolarization temperature (T_d) decreases. p is 7.24 × 10⁻⁴C m⁻² °C⁻¹ at RT at x = 0.5% and 105.4 × 10⁻⁴C.m^−2 °C⁻¹ at T_d at x = 0.2%. F_i and F_v show improvements at RT from 1.12 (x = 0%) to 2.65 (x10 ⁻¹⁰ m v⁻¹) (x = 0.5%) and from 0.021 to 0.048 (m².C⁻¹) respectively. F_i and F_v show a huge increase to 37.6 × 10⁻¹⁰ m v⁻¹ and 0.56 m² C⁻¹ respectively at T_d at x = 0.2%. F_C shows values of 2.10, 2.89, and 2.98 (x10⁻⁹C cm⁻² °C⁻¹) at RT at 33, 100 and 1000 (Hz) respectively. Giant pyroelectric properties make NBT-0.06BT-xLa at x = 0.2% and 0.5% promising materials for many pyroelectric applications.     

Working mechanism of methyl hydroxyethyl cellulose (MHEC) as water retention agent

The working mechanism of methyl hydroxyethyl cellulose, MHEC (M_w = 2.5 · 10⁵ g/mol, DS_methyl = 1.81, MS_hydroxyethyl = 0.15) as water retention agent in cement was investigated. First, the hydrocolloid was characterized and its performance as non-ionic water retention agent was determined employing the filter paper test. Also, water sorption and swelling of individual MHEC fibers under conditions of different humidities were monitored by ESEM imaging. Second, its working mechanism was established. It was found that at low dosages, MHEC achieves water retention by intramolecular sorption of water and concomitant swelling while at higher dosages, MHEC molecules agglomerate into large hydrocolloidal microgel particles (d > 1 μm) which effectively plug the pores in the mortar matrix. MHEC association was evidenced by an exponential increase in solution viscosity as concentration rises, a strong increase in the hydrodynamic diameter of solved MHEC molecules, and a noticeable reduction of surface tension.     

Characteristics of droplets generated by bubble bursting from chromic acid solutions

The effects of electrolyte concentration and gas flow rate on the characteristics of droplets generated from bubbles bursting on the surface of CrO₃ solution were studied with an experimental bubbling system. The experimental conditions included two electrolyte concentrations, 125 and 250 g l^-1 of CrO₃, and three flow rates of sparging air in the range of 4–8 l min^-1. A cascade impactor collected droplet samples for chemical analysis. A laser aerosol spectrophotometer and an aerodynamic particle sizer were employed simultaneously to measure the number concentration and size distribution of the droplets. A layer of foam formed on the liquid surface under all experimental conditions studied except at the gas flow rate of 4 l min^-1 in 125 g l^-1 CrO₃ solution. Foams had a significant effect on the characteristics of droplets generated from bursting bubbles. At identical gas flow rate and electrolyte concentration, the formation of foams led to a reduction in number concentration of droplets larger than 10 μm in aerodynamic diameter and a lower concentration of airborne Cr(VI). In the ranges of gas flow rate and electrolyte concentration tested, the results showed that the airborne Cr(VI) mass concentration increased significantly with gas flow rate and slightly with electrolyte concentration in the presence of foams. The results obtained in the present study should have applications in the emission control of Cr(VI)-containing droplets in chromium electroplating processes.     

Application of Box–Behnken design and response surface methodology for modeling of some Turkish coals

The aim of our research was to apply Box–Behnken experimental design and response surface methodology for modeling of some Turkish coals. As a base for this study, standard Bond grindability tests were initially done and Bond work indexes (W_i) values were calculated for three Turkish coals. The Box–Behnken experimental design was used to provide data for modeling and the variables of model were Bond work index, grinding time and ball diameter of mill. Coal grinding tests were performed changing these three variables for three size fractions of coals (−3350 + 1700 μm, −1700 + 710 μm and −710 μm).Using these sets of experimental data obtained by mathematical software package (MATLAB 7.1), mathematical models were then developed to show the effect of each parameter and their interactions on product 80% passing size (d₈₀). Predicted values of d₈₀ obtained using model equations were in good agreement with the experimental values of d₈₀ (R² value of 0.96 for −3350 + 1700 μm, R² value of 0.98 for −1700 + 710 μm and R² value of 0.94 for −710 μm). This study proved that Box–Behnken design and response surface methodology could efficiently be applied for modeling of grinding of some Turkish coals.     

Size distribution and sites of origin of droplets expelled from the human respiratory tract during expiratory activities

A new expiratory droplet investigation system (EDIS) was used to conduct the most comprehensive program of study to date, of the dilution corrected droplet size distributions produced during different respiratory activities.Distinct physiological processes were responsible for specific size distribution modes. The majority of particles for all activities were produced in one or more modes, with diameters below 0.8 μm at average concentrations up to 0.75 cm^?3. These particles occurred at varying concentrations, during all respiratory activities, including normal breathing. A second mode at 1.8 μm was produced during all activities, but at lower concentrations of up to 0.14 cm^?3.Speech produced additional particles in modes near 3.5 and 5 μm. These two modes became most pronounced during sustained vocalization, producing average concentrations of 0.04 and 0.16 cm^?3, respectively, suggesting that the aerosolization of secretions lubricating the vocal chords is a major source of droplets in terms of number.For the entire size range examined of 0.3–20 μm, average particle number concentrations produced during exhalation ranged from 0.1 cm^?3 for breathing to 1.1 cm^?3 for sustained vocalization.Non-equilibrium droplet evaporation was not detectable for particles between 0.5 and 20 μm, implying that evaporation to the equilibrium droplet size occurred within 0.8 s.     

Micromoulding of PZT film structures using electrohydrodynamic atomization mould filling

In this work, electrohydrodynamic atomization combined with a photolithography polymeric micromoulding technique was used to form PZT ceramic structures. PZT thick film structures consisting of squares and rectangles of various sizes and separations were produced and used to evaluate the process. An expansion effect of approximately 10 μm on the ceramic structure width relative to the 200 μm wide mould design was observed. The minimum continuous gap between features achieved using this process was 13.5 μm, and the smallest regular PZT square structure obtainable was 106 μm in width. A sloping side wall of the PZT structures caused by the shielding of the photoresist mould was also observed in the process. The resulting PZT structures had a homogenous microstructure and exhibited a relative permittivity of 250, d_33, f of 67 pCN^?1 and remnant polarisation of 8.8 μC/cm².     

Notable grain-size dependence of converse piezoelectric effect in BaTiO3 ceramics

Converse piezoelectric effect is of critical importance to device applications like actuators, but no systematical investigation concerning the influence of microstructure on it has been reported for BaTiO₃ ceramics so far. Piezoelectric and ferroelectric properties were inclusively investigated for a group of BaTiO₃ ceramics that are fabricated through solid-state reaction route and show various average grain sizes in this study. It was found that the piezoelectric properties of these BaTiO₃ ceramics display significant grain-size dependences. The direct piezoelectric coefficient d₃₃ increases with decreasing the average grain size (GS) from 170 pC/N at 40 μm, reaches a maximum value of 413 pC/N at 1.2 μm, and then decreases with a further reduction of GS. Converse piezoelectric effect was characterized by measurement of unipolar strain versus electric field (S–E) curve, and the converse piezoelectric coefficient d₃₃*(E) was quantitatively calculated from the slope of S–E curve at relatively large E. Interestingly, d₃₃*(E) is nearly twice as large as d₃₃ and shows a quite similar trend of change with GS to d₃₃. It increases largely from 350 pm/V to 870 pm/V when reducing the GS value from 40 μm to 1.2 μm, and then decreases to 480 pm/V with the further GS reduction to 0.7 μm. Meanwhile, the remanent polarization P_r shows an increase with the decreasing of GS, reaches a maximum at 3.3 μm, and then decreases with the further GS reduction. Domain structure is considered to play an essential role in determining the notable grain-size dependence of converse piezoelectric effect.     

Structure and density of deposits formed on filter fibers by inertial particle deposition and bounce

The morphology and packing density of particle deposits formed by accumulation on thin steel fibers suspended in an aerosol stream were studied by confocal microscopy. Measurements were made with electrically neutral polystyrene spheres (d_P=1.3, 2.0, 2.6 and 5.2 μm) as a function of flow velocity (v=0.7–5 m/s) and fiber diameters (d_F=8 and 30 μm). Deposition under these conditions was dominated by inertia (Stokes number St=0.3–9), interception (interception parameter R=0.04–0.35) and particle bounce, with a negligible contribution from diffusion.The experiments show a systematic transition of deposit morphologies with a newly introduced particle bounce parameter β～St/R, where St and R are based on the diameter d_F of the bare fiber. Compact, forward facing deposit structures dominate in case of significant particle bounce (i.e. for β>β?, where β* represents the critical conditions for the onset of bounce on the bare fiber). Dendritic structures with pronounced sideways branching are formed at β<β*. R is of relatively little influence as an independent parameter, probably because interception occurs mostly on preexisting deposit structures with dimensions in the order of d_P.The mean porosity ε of the deposit structures was determined on the basis of contour measurements by confocal microscopy, in combination with data on the accumulated particle volume per unit fiber length (known accurately from a previous paper by Kasper, Schollmeier, Meyer, and Hoferer (2009). Once noticeable deposits had formed, ε was found to attain stable values between 0.80 at d_P=1.3 μm and 0.55 at d_p=5.2 μm.     

Effects of thickness on structures and electrical properties of K0.5Na0.5NbO3 thick films derived from polyvinylpyrrolidone-modified chemical solution

Lead-free ferroelectric K_0.5Na_0.5NbO₃ (KNN) films with different thicknesses were prepared by polyvinylpyrrolidone (PVP)-modified chemical solution deposition (CSD) method. The KNN films with thickness up to 4.9 μm were obtained by repeating deposition-heating process. All KNN thick films exhibit single perovskite phase and stronger (1 1 0) peak when annealed at 650 °C. The variation of dielectric constant with thickness indicates that there exists a critical thickness for the dielectric constant in the KNN films which should lie in 1.3–2.5 μm. The similar trend is observed for the ferroelectric and piezoelectric properties of KNN films. Both the remnant polarization P_r and the piezoelectric coefficient d₃₃ of KNN thick films increase with the film thickness and become saturated after the critical thickness.     

Characterization of expiration air jets and droplet size distributions immediately at the mouth opening

Size distributions of expiratory droplets expelled during coughing and speaking and the velocities of the expiration air jets of healthy volunteers were measured. Droplet size was measured using the interferometric Mie imaging (IMI) technique while the particle image velocimetry (PIV) technique was used for measuring air velocity. These techniques allowed measurements in close proximity to the mouth and avoided air sampling losses. The average expiration air velocity was 11.7 m/s for coughing and 3.9 m/s for speaking. Under the experimental setting, evaporation and condensation effects had negligible impact on the measured droplet size. The geometric mean diameter of droplets from coughing was 13.5 μm and it was 16.0 μm for speaking (counting 1–100). The estimated total number of droplets expelled ranged from 947 to 2085 per cough and 112–6720 for speaking. The estimated droplet concentrations for coughing ranged from 2.4 to 5.2 cm^?3 per cough and 0.004–0.223 cm^?3 for speaking.     

Supercritical CO2 based processing of amorphous fluoropolymer Teflon-AF: Surfactant-free dispersions and superhydrophobic films

We report the application of a modified RESS process to create and collect in high yield nanoparticles of an amorphous fluoropolymer, Teflon-AF1600. The nanoparticles with diameters ranging from 10 to 100 nm can be synthesized from polymer solutions in supercritical CO₂ at 300 bar and 60 °C. The nanoparticles are collected by formation of dry ice in a liquid nitrogen-cooled trap. Nanoparticles embedded in dry-ice can be dispersed in organic solvents (acetone, ethanol, and n-heptane) creating surfactant-free dispersions. When dispersed in water, the nanoparticles self-assemble at the air–water interface forming a mechanically robust, superhydrophobic film. The film can support large water droplets (up to volume 250 μL) without breaking and is impermeable to water. The films cast from dispersions as well as those lifted-off water surface, are highly porous and superhydrophobic in nature (water contact angle θ_adv = 162°). This work demonstrates the utility of supercritical fluids based processing of fluoropolymers.     

Fabrication and characterization of reaction-bonded silicon carbide with poly(methyl methacrylate) as pore-forming agent

Reaction-bonded silicon carbide (RBSC) ceramics were prepared by liquid silicon infiltration at 1600 °C using a carbon biscuit. The green body was made by slip casting a stabilized carbon powder slurry, followed by pyrolysis in a vacuum furnace at 1000 °C for 2 h; the density of the biscuit (ρ_b) was controlled using poly(methyl methacrylate) (PMMA) powder as pore former in mass proportion from 30% to 50% in 5 percentage point intervals. The particle size of the PMMA had significant effects on the microstructure, distribution of residual silicon, and the mechanical properties of the ceramic. For 40 mass% PMMA with d₅₀=1.17 μm and d₅₀=0.51 μm, ρ_b was 0.81 and 0.82 g/mL, with corresponding biscuit porosities of 51% and 50%, which gave peak values of both RBSC ceramic density of 3.07 and 3.10 g/mL, and flexural strength of 741 and 794 MPa, respectively. XRD analysis showed that the main phase was β-SiC, with a small quantity of α-SiC. Using PMMA with d₅₀=0.51 μm, a small quantity of residual Si was well dispersed with grain size <1 μm. “Black core” residual carbon in the RBSC was successfully avoided when ρ_b≤0.82 g/mL (mass proportion PMMA≥35%). PMMA as pore former favored the elimination of the detrimental black core and the preparation of dense RBSC with good mechanical properties.     

A comparative structural study of ternary graphite intercalation compounds containing alkali metals and linear or branched amines

New donor-type ternary graphite intercalation compounds (GICs) containing alkali metals and branched amines are prepared by direct reaction of graphite with the alkali metal and amine. The new GICs include M(iC3)_0.4C_15–18 (M = Li, Na; iC3 = iso-propylamine; d_i = 0.76 nm) with a monolayer intercalate arrangement; and Na(sC4)_1.6C₁₈ (sC4 = sec-butylamine; d_i = 1.34 nm) and Na(iC4)_2.0C₂₈ (iC4 = iso-butylamine; d_i = 1.28 nm) with bilayer arrangements. Li-sC4-GIC and K-iC3-GIC are not formed using this reaction chemistry. M-iC3-GICs show galleries expanded by 0.06 nm more than that for M(nC3)_0.7–0.8C₁₆ (M = Li, Na; nC3 = n-propylamine). Unlike the case of rigid-sheet hosts where branched amines intercalate at a lower rate and with lower amine content, M-sC4-GICs and M-iC4-GICs readily form intercalate bilayers.     

Sintering of nanocrystalline Ta2O5 and ZrO2 films compared to that of TiO2 films

Thin (d = 60 nm/140 nm) nanocrystalline Ta₂O₅ and ZrO₂ films were deposited onto SiO₂ flakes, using a liquid route synthesis. Their sintering behaviour was characterized and compared to that of the corresponding powders and the known equivalent TiO₂ film in terms of grain size, grain growth and layer porosity. The effect of the substrate was noticeable on crystallisation process but not on grain growth. The sintering behaviour was actually dictated by the initial size and the packing of the precipitated grains related to the synthesis of the film.     

Mathematical models for kinetics of batchwise hydrogenation of shale oil

Hydrogenation of shale oil in a batch autoclave is described by a second order kinetic equation depending on the hydrogen current concentration (H) and on the current value of a total characteristic of the oil (x_i), both approaching to their equilibrium levels (H_∞, x_i∞). Algorithms are proposed to estimate the values of hydrogenation rate coefficient (k) and H_∞ from the plot of decrease in hydrogen concentration in time versus H at isothermal conditions. A new concept “specific change of the characteristic” (β_i = dx_i / dH) is introduced to handle various x_i (oil yield, viscosity, density, iodine number, and yield of the fraction 200–275 °C).The equilibrium constants (K_i) and β_i for the characteristics are estimated on the basis of experimental results. The temperature-dependencies for k, K_i and β_i are determined. A scheme is proposed to predict current values of H and x_i for different H₀, T_max and oil mass under isothermal and non-isothermal conditions.The model deduced and the coefficients and constants found can be applied for quantitative evaluation of catalysts and initial oils for hydrogenation.     

Low shear compounding process for thermoplastic fabrication of ferroelectric lead-free fibres

The thermoplastic ceramic extrusion process involves the shaping of a polymer highly filled with inorganic powder, the so-called ceramic–thermoplastic feedstock. The limitation faced with the process is the amount of raw material required to produce the feedstock. Depending on the density and desired volume of the materials used, the typical amount of ceramic powder required is a minimum of ∼100 g. The validation of a low shear feedstock preparation method against a standard high shear mixing method occurred. Microstructure investigation and single electromechanical fibre characterization of low shear produced KNN (d₃₃ – 49 pC/N; P_r – 3.7 μC/cm³) and PZT (d₃₃ – 392 pC/N; P_r – 32.4 μC/cm³) fibres, in terms of PE, SE loops and d₃₃ measurements, demonstrating the reproducibility of the results when compared to a standard ceramic–thermoplastic high shear mixing process. The repeatability of the measurements showed the proposed procedure to be robust, validating the new compounding method for wide-scale use.