The effect of single and combined coagulation/flocculation methods on the sedimentation behavior and conductivity of bentonite suspensions with different swelling potentials

ABSTRACT

In this study, the sedimentation behavior of bentonite (Na and Ca bentonite) suspensions with different swelling potentials was investigated with single and combined coagulation and flocculation methods. The samples exhibited a negative surface charge over a broad pH range and had a relatively high suspension stability. Al₂(SO₄)₃, FeCl₃, MgCl₂, CaCl₂, and NaCl were used as coagulants. All coagulants have provided sedimentation efficiencies higher than 85% with Ca bentonite suspension, but only 22% efficiency was seen with Na bentonite suspensions. The effectiveness of coagulants increased with higher ionic values of the metal salts. Versus monovalent cations, multivalent cations had a greater influence on the zeta potential of the samples. Higher coagulant concentrations enhance the conductivities of the suspensions. In flocculation, anionic (A-150), cationic (C-521) and nonionic (N-100) flocculants were used. For a Ca bentonite suspension, all flocculants have 98% efficiency. The anionic flocculant was more efficient than cationic and nonionic ones for Na bentonite suspension. The dual-flocculation of cationic and anionic flocculant combinations and pre-destabilization via coagulants of Na bentonite suspension were also studied. Better flocculation performance was achieved with these combined methods.     

A structural and corrosion study of triethoxysilyl and perfluorooctyl functionalized polyhedral silsesquioxane nanocomposite films on AA 2024 alloy

A tri-functional polyhedral oligomeric silsesquioxane (POSS) based silane precursor R_xR_yR_z(SiO_3/2)_n (x + y + z = n = 6, 8, 10, ….) bearing 3-(N-(3-triethoxysilylpropyl)ureido)propyl, isooctyl and perfluoropropyl groups was synthesized and investigated as corrosion protective coating for AA 2024 alloy. Infrared reflection-absorption (IR RA) combined with X-ray photoelectron spectroscopy and atomic force microscopy provided information about partial self-assembling of coatings having a fluorine enriched upper layer with a low surface energy (γ^tot = 12.37 mN/m). The structural changes that accompanied corrosion produced under chronocoulometrical conditions were assessed from ex-situ IR RA spectra. A new band at 1690-1700 cm^− 1 appeared above the corrosion potential, and was assigned to the formation of amidonium ions and consequent relaxation of urea-urea associations.     

In-situ magnetic deposition field effect on sheet resistance of Permalloy films

We have measured the real-time in-situ sheet resistance (R_□) of a Permalloy (Py) film during the film-growth period in a vacuum under various magnetic deposition-field (H) conditions: a longitudinal direct-current (dc) field (H = H_x), a transverse dc field (H = H_y), and a rotating field (H = H_r) with the frequency (f) at 0.6, 1.4, 2.5, 10, and 100 Hz, respectively. The results show that R_□(H_y) > R_□(H_x) ? R_□(H = 0) ? R_□(H = H_r), when Py film is just before or near the coalescence stage of the film-growth process. The reason for these phenomena is that a dc field (H = 0, H_x, or H_y) tends to make the structure of the film more anisotropic, while a rotating field (H = H_r) tends to make the film more isotropic. Moreover, based on the quantum tunneling mechanism, the fact that there will be many more tunneling events through which an electron can be transported down a piece-by-piece connected film with an anisotropic than with an isotropic structure should naturally lead to the observed results above. Finally, we also explain why in the R_□ versus f plot (under the condition of film thickness t_f = 1 nm), there exists a minimum R_□ at f = f_min = 2.5 Hz.     

The generation of particles to observe quantized vortex dynamics in superfluid helium

We describe a method to prepare a sample of superfluid helium-4 with hydrogen particles suspended within it. The method is to dilute hydrogen gas with helium at room temperature, and bubble the mixture through liquid helium at a temperature above the superfluid phase transition temperature, T_λ ≈ 2.17 K. The procedure yields a suspension of micron-sized particles whose total volume is about 10⁵ times smaller than the fluid volume. The fluid and suspension are then cooled to a temperature below T_λ. We show that the particles, so prepared in superfluid helium, are useful for studying superfluid flows and, in particular, the dynamics of quantized vortices. In addition, the particle-superfluid helium system is rich in not yet fully explained interactions. We review preliminary investigations that include observing the vortex lattice in rotating helium, vortex reconnection in quantized vortex turbulence, and vortex ring decay. These data illustrate the basic mechanisms of dissipation in superfluid turbulence.     

Stability,electrochemical behaviors and electronic structures of iron hydroxyl-phosphate

Iron hydroxyl-phosphate with a uniform spherical particle size of around 1 μm, a compound of the type Fe_2−y□_y(PO₄)(OH)_3−3y(H₂O)_3y−2 (where □ represents a vacancy), has been synthesized by hydrothermal methods. The particles are composed of spheres of diameter <100 nm. The compound exhibits good electrochemical performance, with reversible capacities of around 150 mAh g⁻¹ and 120 mAh g⁻¹ at current densities of 170 mA g⁻¹ and 680 mA g⁻¹, respectively. The stability of crystal structure of this material was studied by TGA and XRD which show that the material remains stable at least up to the temperature 200 °C. Investigation of the electronic structure of the iron hydroxyl-phosphate by GGA + U calculation has indicated that it has a better electronic conductivity than LiFePO₄.     

Pore characteristics of Ca(OH)2 foams: Impact of surfactant–mineral interaction

Slake lime (Ca(OH)₂) foams were prepared via a mechanical foaming and gelcasting method. The Ca(OH)₂ foams were systematically characterized in terms of pore size and porosity according to expansion ratio (E_R). The results showed that the physical properties of the Ca(OH)₂ foams increased with E_R. Additionally, the Ca(OH)₂ foams with E_R = 4 showed considerably larger pore size (727.5 μm) as compared to those with smaller E_R (8.8 and 20.1 μm for E_R = 2 and 3, respectively). In order to further elucidate the mechanism, SiO₂ and Al₂O₃ foams with same E_R were prepared and compared. Additional experiments were also conducted, such as rheological behavior of slurry, electrical property of starting materials, and surfactant (sodium lauryl sulfate, SLS)–mineral adsorption capacity. The results showed that the pore size of the SiO₂ and Al₂O₃ foams was much smaller than that of the Ca(OH)₂ foams. The discrepancy in the pore size between three foams was due to the difference in the adsorption capacity of SLS onto mineral surfaces. Specifically, the loss of SLS from aqueous phase by the SLS–Ca(OH)₂ interaction resulted in the decrease in the surface tension of the Ca(OH)₂ slurry, and consequently led to the increase in bubble size (i.e., final pore size).     

Synthesis and electrical properties of ordered perovskite oxide Cd3−x−yCuxAyTeO6 (A = Li, Na; 0.00 ≤ x, y ≤ 0.15)

Polycrystalline Cd_3−x−yCu_xA_yTeO₆ (A = Li, Na) samples were prepared by solid-state reaction, and their crystal structure and electrical properties were investigated. In Cd_3−xCu_xTeO₆ and Cd_3−yA_yTeO₆ (A = Li, Na), the maxim solubility of x and y was 0.15 and 0.15 for A = Li, 0.05 for A = Na, respectively. For co-substituted samples Cd_2.9−yCu_0.1Li_yTeO₆ and Cd_2.9−yCu_0.1Na_yTeO₆, the maxim solubility of x was the same as single substitution above-mentioned. The alkali-metal substituted samples Cd_3−yA_yTeO₆ (A = Li, Na) showed a negative Seebeck coefficient, which indicates that the major conduction carriers are electron. On the other hand, the co-substituted samples Cd_2.9−yCu_0.1A_yTeO₆ (A = Li, Na) represented a positive Seebeck coefficient, and major conduction carriers were hole through substitution by copper ions.     

Thermal stability against reduction of LaMn1−yCoyO3 perovskites

Thermal and reduction-oxidation stability of substituted LaMn_1−yCo_yO₃ perovskite-type oxides (0.0 ≤ y_Co ≤ 1.0) prepared by the citrate route have been studied by means of surface area, X-ray diffraction, FTIR spectroscopy and magnetic properties. The perovskite orthorhombic structure is found for y_Co ≤ 0.5, with the exception of y_Co = 0.1, which corresponds better to rhombohedral LaMnO_3.15. For y_Co > 0.5 the diffraction profiles are quite similar to the cobaltite’s rhombohedral structure. Magnetic iso-field studies (ZFC-FC) reveal that, for y_Co ≤ 0.50, the system presents an antiferromagnetic canted-like ordering of the Mn/Co sublattice, in which the presence of divalent Co ion creates Mn³⁺-Mn⁴⁺ pairs that interact ferromagnetically through the oxygen orbital. This interpretation is confirmed by the magnetization loops, in which the magnetic moment increases when substituting Mn for Co. Therefore, the general trend is: for y_Co ≤ 0.5, the Co ions are inserted in the manganite structure and for y_Co > 0.5, the Mn ions are inserted in cobaltite structure. The enhancement of the ferromagnetic properties and the thermal stability against reduction for y_Co = 0.5 is attributed to optimized Co²⁺-Mn⁴⁺ interactions.     

Ni silicide formation on epitaxial Si1 − yCy/(001) layers

The formation of Ni silicides on Si_1 − yC_y (y = 0.01 and 0.018) epilayers grown on Si(001) has been investigated. The presence of C atoms was found to significantly retard the growth kinetics of NiSi and enhances the thermal stability of thin NiSi films. For Ni(11 nm)/Si_0.982C_0.018 samples, the process window of NiSi was shifted and extended to 450-700 °C. Moreover, there was an additional strain introduced into the Si_1 − yC_y epilayers during Ni silicidation. This work shows the potential of Ni silicidation on Si_1yC_y for device applications.     

Synthesis and electrorheological performance of nanosized composite with polar inorganic compounds

To obtain an economical and applicable electrorheological (ER) material, a novel nanocomposite composed of polar inorganic compounds, NH₄Al(OH)₂CO₃, AlO(OH) and (NH₄)₂SO₄, has been synthesized using low-toxic and economical and facile starting materials by a simple chemical reaction process. The experimental result shows that this material has better ER performance. The static yield stress (τ_y) of the suspension (50 wt%) of the material in silicone oil reached 22.8 kPa at a DC electric field of 4 kV/mm, and the relative yield stress (τ_r) (the ratio of the yield stresses with to without an electric field) is also higher (12.7-33.3 for different concentration suspensions). The composition, grain size, dielectric and surface properties of the material have been studied by the elemental analyses, X-ray diffraction (XRD), infrared spectroscopy (IR), transmission electron microscopy (TEM), dielectric spectroscopy and determinations of the surface area and surface energy of the material. The influences of the grain size, dielectric and surface properties on ER performance of the material have been discussed.     

Eu-Mössbauer spectroscopic and X-ray diffraction study on EuyM1−yO2−x (0 ≤ y ≤ 1.0) (M = Th, U)

¹⁵¹Eu-Mössbauer spectroscopic and powder X-ray diffraction (XRD) study has been performed for the Eu_yM_1−yO_2−x (M = Th and U) systems over the entire composition range of 0 ≤ y ≤ 1.0. The XRD results of the Eu-Th system showed that a very wide defect-fluorite (DF) type phase in which oxygen vacancies (V_O) are disordered (x = y/2) is formed for 0 ≤ y < 0.5 and that two-phase regions sandwitching a narrow C-type (C) single phase around y ≈ 0.8 appear for 0.5 < y < 0.8 (DF + C) and 0.82 < y < 1.0 (C + B-type (monoclinic) Eu₂O₃). The Mössbauer results show that the isomer shifts (ISs) of Eu³⁺ in this system smoothly increase with Eu composition, y. The decrease of average coordination number (CN) of O²⁻ around Eu³⁺ with increasing y (CN = 8 − 2y) (x = y/2) results in the decrease of the average EuO bond length, which is due to the decrease of repulsion force between O²⁻ anions. This result confirms that the IS of Eu³⁺ correlates well with the average EuO bond length in oxide systems. For the Eu-U system, the lattice parameter, a₀, of the system decreases almost linearly with y, in accordance with the calculated a₀ versus y curve for the oxygen-stoichiometric (i.e. x = 0) fluorite-type dioxide (CN = 8). The ISs of Eu³⁺ in this composition range remain almost constant around 0.5 mm/s, which is comparable to those of pyrochlore oxides (Eu₂Zr₂O₇ and Eu₂Hf₂O₇ (y = 0.5)) with O²⁻-eight-fold coordinated Eu³⁺(CN = 8).     

MOCVD growth of HfSixOy films from hafnium β-diketonato silylamides and siloxides

New hafnium β-diketonato-silylamide and siloxides namely Hf(thd)₂[N(SiMe₃)₂]₂ (1), Hf(thd)₂(OSiMe₃)₂ (2) and Hf(thd)₂(OSi^tBuMe₂)₂ (3) (thd=2,2,6,6-tetramethyl-3,5-heptanedionate) were investigated as single-source precursors for low-pressure pulsed liquid injection MOCVD of HfSi_xO_y thin films on Si(1 0 0) and R-plane sapphire. Films were characterized by XRD, XPS and AFM. The growth rate increased in order 1>2>3 in agreement with the decreasing precursor thermal stability. The activation energy was ∼80-100 kJ/mol. The as-deposited at 550-800 °C films were essentially amorphous; hafnia reflections appeared after 1 h annealing at 900 °C probably due to phase separation into amorphous Si-rich silicate and crystallized HfO₂. The surface of the films showed similar amounts of Hf and Si (∼1:1) and was overstoichiometric in oxygen (ratio O/(Hf+Si) >2). The bulk of the films was Hf-rich (70-85% of Hf/ Hf+Si) and slightly oxygen-deficient. The new complexes are attractive single-source precursors for the deposition of pure and very smooth (R_a∼0.7 nm, <1% relative to thickness) HfSi_xO_y films. Dielectric constant 11.3 and leakage current density 8×10⁻⁴ A/cm² (at −1 V) were measured for a 22 nm thick film.     

Approaches for evaluating Young's and shear moduli in terms of a single SAW velocity via the SAM technique

In ultrasonic material investigations Young's modulus, E, and shear modulus, G, conventionally expressed in terms of the velocities of longitudinal (V_L,) and transverse (V_T) modes, are usually difficult to determine from a single measurement, in particular for scanning acoustic microscopy. Therefore, using Viktorov formula and physically acceptable approximations, we derive simple expressions for E and G in terms of the velocity, V_i, of just one propagating mode (including Rayleigh mode V_R). It was found that (E, G) = (α_i, β_i)ρV_i². The validity of these expressions is successfully tested, analytically and graphically, for a great number of materials representing a large spectrum of densities, 1000 kg/m³ < ρ < 22 000 kg/m³, and characterized by a wide interval of velocities, 1400 m/s < V_L < 12 000 m/s.     

Sub-Gap Modulated Photo Current Spectroscopy performed on Cu(Inx,Ga1 − x)(Sey,S1 − y)2 based solar cells

Sub-Gap Modulated Photo Current Spectroscopy (SGMPCS) is an excellent tool in order to investigate the band gap defect density of the absorber layer, directly on Cu(In_x,Ga_1 − x)(Se_y,S_1 − y)₂ (CIGSS) based solar cells. This technique is essentially sensitive to defect states located in the absorber layer, which has the lowest band gap of the heterojunction solar cell. It allows the determination of the σ · N(E) product, where σ is the defect Optical Cross Section (OCS) and N(E) is its Density Of States (DOS).We have developed an analytical model, allowing to derive the above product from the imaginary part of the ac photocurrent of the solar cell, under reverse applied dc bias. We have then applied this model to study the defect density of the co-evaporated CIGS (i.e. y = 1) absorber layer of a heterojunction solar cell. Two different defect distributions have been exhibited by SGMPCS, the properties of which vary with thermal annealing.Correlation with Admittance Spectroscopy allows us to derive an estimation of the defect OCS.     

High-frequency magneto-electrical properties of Zn1 − x − yAlxCoyO thin films

The Al doping effects on high-frequency magneto-electric properties of Zn_{1 − x − y}Al_xCo_yO (x = 0-10.65 at.%) thin films were systematically studied. In the current work, the Zn_{1 − x − y}Al_xCo_yO thin films were deposited by magnetron co-sputtering onto quartz substrates. The magneto-impedance spectra of the thin films were measured by an impedance analyzer. Among all the doped films studied, the thin film with 6.03 at.% Al-doping showed the highest ac conductivity and relaxation frequency. To characterize the relaxation mechanism underlying the magneto-electric properties, a Cole-Cole impedance model was applied to analyze the impedance spectra. The analyzed result showed that the magneto-impedance of the Zn_{1 − x − y}Al_xCo_yO is contributed by multiple processes of magnetization dynamics and dielectric relaxation. The results imply that Zn_{1 − x − y}Al_xCo_yO may be applicable for high-frequency magneto-electric devices.     

Conductivity of reduced La2Mo2O9 based oxides: The effect of tungsten substitution

The electrical properties of reduced LAMOX-type oxides (La_1.9Y_0.1Mo_2−yW_yO_9−δ with y = 0, y = 0.5, y = 1.0) were investigated by complex impedance spectroscopy.When reduced at 605 °C in hydrogen, La_1.9Y_0.1Mo₂O_9−δ is 10 times and 3 × 10⁵ times more conductive at 605 and 180 °C, respectively, than in air at the same temperatures. The conductivity curve presents a low slope (0.37 eV versus 1.2 eV in air).Besides, the stabilising effect of tungsten against reduction is evidenced, in good agreement with previous reports.In low oxygen partial pressures however (PO₂ < 10⁻¹⁸ Pa), the decomposition of the materials is detected, whatever the tungsten content (0 ≤ y ≤ 1 in La_1.9Y_0.1Mo_2−yW_yO_9−δ). This observation points out the efficiency limit of Mo⁶⁺/W⁶⁺ substitution to stabilise the structure against reduction, and the limit for an application as IT-SOFC electrolyte.However, given the high electronic conductivity upon reduction, the application of these materials in IT-SOFC electrodes could be considered.     

On the effective viscosity of suspensions

This work discusses the classical problem of effective viscosity of a Newtonian fluid with rigid spherical particles. It argues that the simple non-interaction approximation when formulated correctly yields an effective viscosity ratio for the suspension in the form μ/μ₀ = (1 − 2.5?)⁻¹ that remains accurate at much higher volume fractions of particles ? than the usual first-order approximation μ/μ₀ = 1 + 2.5?.     

New superconducting lead cuprate with 1201 structure, (Pb0.5B0.5) (SrLa)CuOz

New Pb-based superconducting cuprate with the 1201 structure has been synthesized in the (Pb_1 − yB_y)(Sr_2 − xLa_x)CuO_z system. From X-ray powder diffraction study, the almost-single 1201 phase sample is found to be obtained at x = 1.0 and y = 0.5 for the nominal composition of (Pb_1 − yB_y)(Sr_2 − xLa_x)CuO_z. The crystal structure has a tetragonal symmetry with the lattice parameters of a = 0.3779 nm and c = 0.8654 nm. The sample shows an onset of superconductivity at about 32 K as measured by the temperature dependence of the DC magnetic susceptibility.     

Ferroelectric and ferromagnetic properties of Gd-doped BiFeO3–BaTiO3 solid solution

The solid solutions of Bi_1−x−yGd_xBa_yFe_1−yTi_yO₃ have been prepared via solid-state reaction method with the aim to obtain magnetoelectric coupling (i.e., linear relation between magnetization and electric field) at room temperature. Optimum calcination and sintering strategies for obtaining pure perovskite phase, high density ceramics and homogeneous microstructures have been determined. All the samples of the composition Bi_1−x−yGd_xBa_yFe_1−yTi_yO₃ (x = 0.1 and y = 0.1, 0.2, and 0.3) reported in the present work are tetragonal at room temperature. The maximum ferroelectric transition temperature (T_c) of this system was 150–170 °C with the dielectric constant peak of 2300 at 100 kHz for y = 0.1. Above T_c the dielectric constant is decreasing up to a certain temperature and then increasing with temperature similar to that observed in other perovskites due to chemical inhomogeneities in both A and B sites of the ABO₃ cell. The variation of ferroelectric and magnetic properties was followed by piezoresponse force microscopy and vibrating sample magnetometer, respectively. Well-saturated piezoelectric loops were observed for all composition indicating room temperature ferroelectricity.     

Reducibility study of oxide-ion conductors La2−xBaxMo2−yAyO9−δ (A = W, Al, Ga) assessed by impedance spectroscopy

The reducibility of oxide-ion conductors La_2−xBa_xMo_2−yW_yO_9−δ (x = 0, 0.06; y = 0, 0.1, 0.5, 1.0) and La₂Mo_1.9A_0.1O_9−δ (A = Al, Ga) were studied in the reducing atmosphere of 5%H₂ + Ar by means of impedance spectroscopy measurement. The introduction of Ba at La site in La₂Mo_2−yW_yO₉ can lower the sintering temperature by about 100 K in comparison with the La₂Mo_2−yW_yO₉ samples. All substitutions can enhance the conductivity and improve the reducibility in the temperature range from 548 to 923 K. The double substitution of Ba and W as well as substitution of Al or Ga at Mo sites has a better stabilizing effect than the single tungsten substitution. Among these substitutions the introduction of Al has the best stabilizing effect.