Capillary rise properties of porous geopolymers prepared by an extrusion method using polylactic acid (PLA) fibers as the pore formers

The geopolymers were prepared from sodium silicate, metakaolinite, NaOH and H₂O at SiO₂:Al₂O₃:Na₂O:H₂O of 3.66:1:1:x, where x = 8–17, and curing temperatures of 70–110 °C. Since the bending strength of the geopolymers was highest (36 MPa) where H₂O/Al₂O₃ = 9 and the curing temperature = 90 °C, these conditions were adopted. The porous geopolymers were prepared by kneading PLA fibers of 12, 20 and 29 μm diameter into the geopolymer paste, at fiber volumes of 13–28 vol%. The resulting paste was extruded using a domestic extruder, cured at 90 °C for 2 days then dried at the same temperature. The PLA fibers in the composites were removed by alkali treatment and/or heating. The highest capillary rise was achieved in the porous geopolymers containing 28 vol% of 29 μm fibers. The capillary rise of this sample, estimated by the equation of Fries and Dryer¹ was 1125 mm.     

Study of the separation of yeast by microsieves: In situ 3D characterization of the cake using confocal laser scanning microscopy

In situ 3D characterization of Aquamarijn microsieves fouling was achieved using Confocal Laser Scanning Microscopy (CLSM). A filtration chamber allowing direct microscopic observation of microbial cell deposition and cake characterization, specially designed for in situ observations, was used. Fluorescent dyed Saccharomyces cerevisiae yeast suspensions were filtered through 0.8 μm and 2 μm pore diameters silicon nitride microsieves under constant flow rate. The on-line yeasts deposition was recorded and the cake construction was followed layer by layer. Based on the 3D image processing, cake properties (particle arrangement, homogeneity, thickness and porosity). The compressibility of the yeast cake was analyzed. Finally, cake removal efficiency was also studied during microsieve cleaning operation.     

The structure of 1D and 3D CuI nanocrystals grown within 1.5–2.5 nm single wall carbon nanotubes obtained by catalyzed chemical vapor deposition

Catalyzed chemical vapor deposition (CCVD) grown single wall carbon nanotubes (SWCNT) with diameter of D_m = 1.5–2.5 nm were used as templates to host one-dimensional nanocrystals of CuI. The CuI@SWCNT nanocomposite was obtained using capillary filling of preopened SWCNTs by CuI melt at 650 °C. Nanocomposite structural studies were performed on a FEI Titan 60–300 at 80 kV. According to the model and image simulation CuI crystallizes within 1.5–2.0 nm SWCNTs in the form of one-dimensional crystals with zinc blende or rock salt type unit cell connected by [0 0 1] edges and translated along 〈1 1 0〉. Copper cations occupy tetrahedral or octahedral sites in the lattice. In SWCNTs with D_m > 2.0 nm 3DCuI@SWCNTs were generated. The crystals of copper halides exhibit acceptor behavior as supported by Raman spectroscopy.     

Filtration and loading characteristics of granular bed filters

The purpose of this study was to investigate the filtration and loading characteristics of granular bed filters. Stainless steel holders (diameter 71.6 mm, height 70 mm) were fabricated to accommodate 500 g of zirconium oxide (ZrO₂) beads, as the packed media of granular bed. Monodisperse ZrO₂ granules (0.3, 0.8, 2 and 4 mm in diameter) were used to demonstrate the effect of the granule size and packing geometry on both pressure drop and aerosol penetration. From the filter quality perspective, the selection of the ‘best” filter is complicated. Assuming a low face velocity (e.g., 0.58 cm/s), large granule size is more cost-effective because of the higher filter quality factor. The phenomenon implies that the gain in filtration efficiency due to larger surface area (of small granules in the filter) did not compensate for the increase in air resistance. After the cake formation point, the dust cake on glass fiber filter became compressed. This dust cake compaction caused the pressure to drop precipitously and intermittently. In contrast, the rate of increase in pressure drop of the dust cake formed on the granular bed filters decreased with time probably due to the pinhole channels in the increasing mass load. The size and density of the pinholes are determined by the granule size, the face velocity and the size of the challenge aerosols.     

Assessment of thermal conductivity as a function of porosity in bread dough during proving

During the proving process, yeast fermentation in the aqueous phase of dough produces carbon dioxide which diffuses through the aqueous phase to the gas cell nuclei entrapped during dough mixing. CO₂ evaporates to generate within gas cell nuclei an excess pressure that provides the driving force for dough expansion. As a result, the void fraction of the dough increases and thermal conductivity decreases. These two properties are of considerable interest because of their technological significance in breadmaking (specific volume and processing times). The aim of the present study was therefore to investigate experimentally the thermal conductivity and porosity evolutions of bread dough during the proving process. Apparent density and thermal conductivity of fermenting dough were experimentally determined as a function of fermentation time using the line-heat source probe and image analysis methods, respectively. Thermal conductivity values were observed in the range of 0.36–0.12 W m^?1 K^?1 and values of void fraction air between 6 and 78% at proving conditions of 35 °C and 95% HR for 100 min of fermentation time. According to experimental data, relationship between thermal conductivity λ and porosity ? could be adequately described by a nonlinear equation: λ(?) = 0.421–0.134?–0.219?^0.5.     

Supercritical CO2 extraction of omega-3 rich oil from Sacha inchi (Plukenetia volubilis L.) seeds

Supercritical carbon dioxide (SC-CO₂) was employed to extract omega-3 rich oil from Sacha inchi (Plukenetia volubilis L.) seeds and partially defatted cake. For ground seeds, the supercritical extraction was carried out at temperatures of 40, 50 and 60 °C and pressures of 300 and 400 bar, and for the cold pressed partially defatted cake, the extraction was carried out with 300 bar at 40 °C and with 400 bar at 60 °C. The global extraction yields (X₀), oil solubility, fatty acid composition of the oil and tocopherol content were determined. The seed samples used in this work contained 54.3% oil, of which 50.5% was linoleinc acid (ω-3). The maximum extraction recovery for the seeds as 92% at 400 bar and 60 °C, but on one occasion a recovery of 99.1% oil was obtained when cold pressed extraction was employed, followed by supercritical extraction at 400 bar and 60 °C. A high tocopherol content of about 2–3 g/kg of oil was obtained.     

Clarification of red raspberry juice using microfiltration with gas backwashing: A viable strategy to maximize permeate flux and minimize a loss of anthocyanins

Red raspberry (Rubus idaeus) juice was produced by maceration of raspberry pulp at 50 °C for 2 h using 400 mg kg^?1 Klerzyme^®150 enzymatic pectolitic preparation followed by raw juice clarification with gelatin and bentonite or cross-flow membrane filtration. A minimal loss of anthocyanins from 630 to 540 mg l^?1 was obtained when the juice was clarified using a ceramic multichannel microfilter (MF) with a pore size of 0.2 μm. A light transmission at 625 nm in MF permeate was above 85% and the residual pectin (900 mg l^?1) was completely removed. During ultrafiltration through ceramic or polysulfone membranes with a molecular weight cut-off of 30–300 kDa, the content of anthocyanins was reduced to 220–370 mg l^?1, but a light transmission at 625 nm was as high as 96%. The permeate flux in MF was maintained at high values above 170 l m^?2 h^?1 at 3 bar for more than 2 h by backwashing the membrane with a compressed air every 6 min for 1 min. The cake compression at high pressures was avoided by short filtration times between backwashing.     

The effect of annealing on electrical properties of fluorinated amorphous carbon films

Fluorinated amorphous carbon (a–C:F) films have been deposited by electron cyclotron resonance chemical vapor deposition (ECR–CVD) at room temperature using C₄F₈ and CH₄ as precursor gases. The chemical compositions and electrical properties of a–C:F films have been studied by X-ray photoelectron spectroscopy (XPS), capacitance–voltage (C–V) and current-voltage (I–V) measurements. The results show that C–CF_x and C–C species of a–C:F films increase and fluorine content decreases after annealing. The dielectric constant of the annealed a–C:F films increases as a result of enhancement of film density and reduction of electronic polarization. The densities of fixed charges and interface states decrease from 1.6 × 10¹⁰ cm^− 2 and (5–9) × 10¹¹ eV^− 1 cm^− 2 to 3.2 × 10⁹ cm^− 2 and (4–6) × 10¹¹ eV^− 1 cm^− 2 respectively when a–C:F films are annealed at 300 °C. The magnitude of C–V hysteresis decreases due to reduced dangling bonds at the a–C:F/Si interfaces after heat treatment. The conduction of a–C:F films shows ohmic behavior at lower electric fields and is explained by Poole–Frankel (PF) mechanism at higher electric fields. The PF current increases indicative of reduced trap energy when a–C:F films are subjected to higher annealing temperatures.     

Solid-state synthesis and spark plasma sintering of submicron BaYxZr1 − xO3 − x/2 (x = 0, 0.08 and 0.16) ceramics

Fine powders (particle size of 100–200 nm) of BaY_xZr_1 − xO_3 − x/2 (x = 0, 0.08, 0.16) were produced by solid-state reaction at 1000–1050 °C using nanocrystalline ZrO₂ and BaCO₃ raw materials. The powders were densified by means of the spark plasma sintering process resulting in dense and homogeneous submicron microstructures. Near full density ceramics with grain size < 300 nm were obtained by sintering at 1600 °C for 1–5 min.     

Low-temperature sintering and electrical properties of (K,Na)NbO3 based lead-free ceramics with high Curie temperature

Lead-free ceramics (1 ? x)(K_0.48Na_0.52)NbO₃–(x/5.15)K_2.9Li_1.95Nb_5.15O_15.3 (x = 0.3–0.6, KNN–KLN100x) were prepared by conventional sintering technique at a low temperature of 960 °C. The effects of KLN contents on microstructure, dielectric, and piezoelectric properties were investigated. After the addition of KLN, the sintering performance and Curie temperature of the ceramics were markedly improved. The ceramics with x = 0.3 exhibited very good piezoelectric properties: d₃₃ = 138 pC/N, k_p = 45.03%, T_c = 495 °C, the dielectric constant at room temperature ?_r (RT) = 478 and the maximum dielectric constant ?_r (max) = 5067. These results indicated that the KNN–KLN100x lead-free ceramics sintered at low temperatures are promising for high temperature piezoelectric applications.     

A wall-coated catalytic capillary microreactor for the direct formation of hydrogen peroxide

The direct formation of hydrogen peroxide from H₂ and O₂ was successfully carried out in a capillary microreactor at room temperature and atmospheric pressure. A key element in sustaining the activity of the catalyst is the incarceration of the palladium nanoparticles in a cross-linkable amphiphilic polystyrene-based polymer, prepared following the protocol of Kobayashi [R. Akiyama, S. Kobayashi, J. Am. Chem. Soc. 125 (2003) 3412–3413]. The immobilization effectively reduced the leaching of palladium under acidic conditions. Applying the catalyst as a coating on the inner walls of a capillary enabled the sustained production of 1.1% hydrogen peroxide over at least 11 days. The highest catalyst utilization in a 2 mm capillary reactor was 0.54 mol_H2O2/h g_Pd. When the inner diameter of the reactor capillary was reduced to 530 μm, the rate was enhanced fourfold to 2.28 mol_H2O2/h g_Pd corresponding to a turnover frequency of 0.067 s^?1.     

Preparation of (0 2 0)-oriented BaTi2O5 thick films and their dielectric responses

Barium dititanate (BaTi₂O₅) thick films were prepared on a Pt-coated Si substrate by laser chemical vapor deposition, and ac electric responses of (0 2 0)-oriented BaTi₂O₅ films were investigated using several equivalent electric circuit models. BaTi₂O₅ films in a single phase were obtained at a Ti/Ba molar ratio (m_Ti/Ba) of 1.72–1.74 and deposition temperature (T_dep) of 908–1065 K as well as m_Ti/Ba = 1.95 and T_dep = 914–953 K. (0 2 0)-oriented BaTi₂O₅ films were obtained at m_Ti/Ba = 1.72–1.74 and T_dep = 989–1051 K. BaTi₂O₅ films had columnar grains, and the deposition rate reached 93 μm h^?1. The maximum relative permittivity of the (0 2 0)-oriented BaTi₂O₅ film prepared at T_dep = 989 K was 653 at 759 K. The model of an equivalent circuit involving a parallel combination of a resistor, a capacitor, and a constant phase element well fitted the frequency dependence of the interrelated ac electrical responses of the impedance, electric modulus, and admittance of (0 2 0)-oriented BaTi₂O₅ films.     

The effect of the hydrothermal synthesis variables on barium titanate powders

In this work, the influence of (a) Ba excess in the starting hydrothermal mixture with TiO₂, (b) hydrothermal reaction temperature, and (c) washing cycles on the hydrothermal synthesis of barium titanate (BaTiO₃) were investigated to assess their relative contributions to the final characteristics of the sintered oxide. BaTiO₃ cake was prepared by hydrothermal synthesis at 150 °C and 180 °C using BaOH₂·8H₂O and TiO₂·xH₂O as starting hydrothermal mixture with an excess of Barium (+1 Ba mol% and +2 Ba mol%). The obtained BaTiO₃ cake was washed several times from 0 to 14 (W_n<15) using simple de-ionized water and then sintered at 1120 °C for 3 h. All considered hydrothermal syntheses variables strongly contribute to the final characteristics of the sintered BaTiO₃ powders in terms of Ba²⁺/Ti⁴⁺ molar ratio, crystalline structure and mean particle size. In particular, it is clear from these experiments that the removal of the unfavorable barium salts from BaTiO₃ cake by long washing cycles before final calcination is a critical step in the hydrothermal synthesis of BaTiO₃.     

Experimental and modelled efficiencies during the filtration of a liquid aerosol with a fibrous medium

The aim of this study was to determine and model efficiency during the filtration of a liquid aerosol through a fibrous filter. A series of experiments demonstrated that liquid particle filtration is different from solid particle filtration in that a drainage state appears, characterized by a constant pressure drop at the end of filter clogging. Moreover, during filter clogging, the number efficiency presents a minimum level for particles close to 100 nm in diameter (the most penetrating particle size). The results also reveal that during filter clogging there is a decrease in the medium's performance for particles smaller than 100 nm and an increase in efficiency for particles with a diameter >200 nm. Both effects are induced by the amount of liquid collected in the medium. Finally, a model is proposed to describe filter efficiency during clogging with a liquid aerosol.     

Ionic conductivity across the disorder–order phase transition in the SmO1.5–CeO2 system

Samples of Sm_xCe_1 ? xO_2 ? δ (0.05 ≤ x ≤ 0.55) were prepared by solid-state reactions and the disorder–order phase transition and grain ionic conductivity were investigated using XRD and ac impedance spectroscopy technique, respectively. For 0 ≤ x ≤ 0.35 the material has a fluorite structure and gradually stabilizes into a C-type rare-earth structure at 0.40 ≤ x ≤ 0.55 because of oxygen-vacancy ordering. The highest grain ionic conductivity observed is 0.0565(37) S cm^?1 at 700 °C for Sm_0.20Ce_0.80O_2 ? δ with an associated activation energy (E_A) of 0.791(7) eV. The slopes for E_A and pre-exponential factor change during phase transition and the conductivity decreases monotonically. Upon comparison of the E_A between the SmO_1.5–CeO₂ and NdO_1.5–CeO₂ systems, it is seen E_A for the SmO_1.5–CeO₂ system is lower than NdO_1.5–CeO₂ system at compositions with less than 25% trivalent rare earth element while higher E_A is observed for the SmO_1.5–CeO₂ system at Nd/Sm concentrations above 25%.     

Combustion synthesis and characterization of LSCF-based materials as cathode of intermediate temperature solid oxide fuel cells

Nanocrystalline SOFC cathode materials of perovskite family, La_1?xSr_xM_1?yCo_yO₃, where 0 < x ≤ 0.5, 0 < y ≤ 0.8 (M is transitional metal = Mn or Fe), have been synthesized at a relatively low temperature by combustion synthesis using alanine as a novel fuel. Detailed X-ray powder diffraction analyses show 47–96% phase purity in the as-synthesized powder and upon calcination at ～825 °C single-phase material is obtained wherein the nanocrystallinity (crystallite size ～19–24 nm) is retained. Densification studies of the materials are carried out within 900–1100 °C. The coefficient of thermal expansion (CTE) of these cathodes is measured. Electrical conductivity of the cathodes sintered at different temperatures are measured in the temperature range 700–900 °C and correlated with the density of the sintered materials. The electrochemical performances of Ni-YSZ anode-supported SOFC having YSZ electrolyte (～10 μm) with CGO interlayer (～15 μm) are studied with the developed cathodes in the temperature range 700–800 °C using H₂ as fuel and oxygen as oxidant. Highest current density of ～1.7 A/cm² is achieved during testing at 800 °C measured at 0.7 V with a cathode composition of La_0.5Sr_0.5Co_0.8Fe_0.2O₃. Precipitation of nanocrystalline grains over the core grains in porous microstructure of this cathode might be one of the reasons for such high cell performance.     

Influence of pressure on filtration of aqueous alumina suspensions

The dispersibility of colloidal alumina particles (median size 310 nm) was related to the surface potential, the solid concentration in a suspension and the pressure applied to the particles. The consolidation behavior of colloidal alumina particles with an isoelectric point pH 8.7 was examined using a developed pressure filtration apparatus at 1–10 MPa of applied pressure. The height of 7 or 20 vol% alumina suspensions at pH 3.0, 7.8 and 9.0 as a function of filtration time was fitted by a filtration model developed for a flocculated suspension rather than a traditional filtration model for a dispersed suspension. An increased pressure, a decrease of particle concentration and a porous microstructure of colloidal cake reduced the consolidation time of alumina suspension. The wet alumina compacts were significantly compressed during filtration but relaxed after the release of the applied pressure. However, the packing density of alumina compact after calcination at 700 °C was almost independent of the filtration pressure and controlled by the structure of network of alumina particles in a solution.     

Testing media influences on the dielectric properties of lead sodium niobate glass-ceramics

The influences of testing media on the breakdown strength (BDS) and dielectric properties of glass-ceramics in the Na₂O–PbO–Nb₂O₅–SiO₂ system were investigated. This work was brought out by consideration of the electric conductance, dielectric constant and breakdown strength of different testing media, which are the main reasons for the different dielectric properties and BDS values of the identical dielectric sample. Leakage current (LC), P–E hysteresis loops, C–V curves and breakdown tests show that the BDS and the dielectric properties of the glass-ceramics could be optimized through using appropriate testing medium. It turns out that three favorable characteristics of the dielectric composites could be optimized in silicon/castor oil mixture: the lowest LC (LC = 6.72 × 10^?6 A, at E = 25 kV/mm), thin P–E hysteresis loops and low hysteresis. Furthermore, the highest BDS of the glass-ceramic was obtained in glycerin (BDS = 105.6 kV/mm with sample thickness of 0.108 mm) compared to other media.     

High temperature properties of multiferroic BiFeO3–DyFeO3–BaTiO3 solid solutions

Dielectric and magnetic properties of the xBiFeO₃–yDyFeO₃–zBaTiO₃ solid solution ceramics at high temperature range of RT ∼600 °C have been characterized. For the more detailed understandings of the multiferroic property, the relation between the crystal structure transition, magnetic transition, dielectric transition with increasing temperature have been analyzed. Residual magnetization M_r under the low and high applied magnetic fields (H = 20 Oe, 8 kOe) and the dielectric properties, ɛ_r and tan δ, with varying measuring frequency and temperature have been characterized using the vibrating sample magnetometer and LCR meter, respectively. The neutron diffraction data has been collected at the temperature range of RT ∼800 °C. The low DyFeO₃ concentration samples (y = 0, 0.025) show the magnetic transitions at temperature range of 410–430 °C, while the high DyFeO₃ samples (y ≥ 0.05) show the additional transition at 250–290 °C. The magnetic transition at 410–430 °C corresponds to the crystal structural transition to the tetragonal P4mm from the rhombohedral R-3c, at which the BiFeO₃ and the DyFeO₃ samples lose their antiferromagnetic ordering.     

Capillary rise properties of porous mullite ceramics prepared by an extrusion method using organic fibers as the pore former

Porous mullite ceramics with unidirectionally oriented pores were prepared by an extrusion method to investigate their capillary rise properties. Rayon fibers 16.5 μm in diameter and 800 μm long were used as the pore formers by kneading with alumina powder, kaolin clay, China earthen clay and binder with varying Fe₂O₃ contents of 0, 5 and 7 mass%. The resulting pastes were extruded into cylindrical tubes (outer diameter (OD) 30–50 mm and inner diameter (ID) 20–30 mm), dried at room temperature and fired at 1500 °C for 4 h. The bulk densities of the resulting porous ceramics ranged from 1.31 to 1.67 g/cm³, with apparent porosities of 43.2–59.3%. The pore size distributions measured by Hg porosimetry showed a sharp peak at 10.0 μm in the sample without Fe₂O₃ and at 15.6 μm in the samples containing Fe₂O₃; these pores, which arose from the burnt-out rayon fibers, corresponded to total pore volumes ranging from 0.24 to 0.34 ml/g. SEM showed a microstructure consisting of unidirectionally oriented pores in a porous mullite matrix. Prismatic mullite crystals were well developed on the surfaces of the pore walls owing to the liquid phase formed by the Fe₂O₃ component added to color the samples. The bending strengths of the tubular samples ranged from 15.6 to 26.3 MPa. The height of capillary rise, measured under controlled relative humidities (RH) of 50, 65 and 85%, was greater in the ceramics containing Fe₂O₃ than in those without Fe₂O₃, especially in the thinner samples. The maximum capillary rise reached about 1300 mm, much higher than previously reported. This excellent capillary rise ability is thought to be due to the controlled pore size, pore distribution and pore orientation in these porous mullite ceramics.