Mass-Spectrometric Study of the Kinetics of Ionic and Molecular Sublimation of Sodium Chloride Single Crystals

A mass-spectrometric method is used to study the kinetics of ionic and molecular sublimation of sodium chloride single crystals. The positive ions Na⁺, Na₂ ⁺, and Na₂Cl⁺ were identified in the mass spectrum in the temperature range 820–970 K. Up to 970 K no emission of negative ions was observed. The temperature dependence of thermal ion currents, lnI _i – (1/T), exhibits a maximum and a minimum successively with increasing temperature. These features are identified with a change in the electrical properties of the surface. It is inferred that in the intrinsic temperature range the sign of the surface charge in NaCl is negative and thus the Gibbs free energy of formation of cation vacancies is greater than that of anion vacancies. In the electron impact ionization mass spectrum of molecular fluxes vaporized from an open crystal surface, Na⁺, NaCl⁺, and Na₂Cl⁺ ions originating from NaCl and Na₂Cl₂ precursors are detected in the temperature range 779–982 K. The dimer-to-monomer ratio is found to be of the same order of magnitude in the cases of equilibrium and free-surface vaporization. However, the dependence on temperature of this ratio is different in these two cases. Mechanisms which account for this observation are discussed in light of the terrace–ledge–kink and surface charge models.     

Effect of different aqueous synthesis parameters on the size of CdSe nanocrystals

The variation of CdSe nanoparticle size as a function of synthesis conditions is presented. Cadmium sulphate (CdSO₄), cadmium chloride (CdCl₂) and sodium selenosulphate (Na₂SeSO₃) solutions were used as precursors. Nanoparticles were synthesized by aqueous chemical methods. The synthesis parameters studied were pH, Cd:Se ratio and the type of stabilizing agent. Three different stabilizing agents were used, thioglycolic acid, mercaptoethanol and poly(vinyl pyrrolidone). Fourier transform infrared spectroscopy results confirmed the presence of the stabilizing agent on the surface of the nanoparticles. Ultraviolet visible and X-ray powder diffraction measurements were used to estimate the trend of size variations of the particles with different synthesis parameters, which agreed fairly by both techniques and the crystal structure. Additionally, the size of the nanoparticles was obtained by transmission electron microscopy measurements. Whilst the effect of pH was different for each of the different stabilizing agents due to the different chemical groups in the thiol compounds and the size of the nanoparticles varied with the used stabilizing agents, the effect of Cd:Se ratio in the size of nanoparticles showed the same tendency for the several stabilizing agents.     

Investigations of the properties of the manganese dioxide suspensions in the presence of guar gum and carboxymethylcellulose

Properties of manganese dioxide suspensions in the presence of two polysaccharides: non-ionic guar gum (GG) and anionic carboxymethylcellulose (CMC) were investigated using NaCl as a background electrolyte. The colloidal stability of MnO₂ suspensions in the presence and absence of these two polymers was measured. It was found that both polymers improve stability of measured suspensions. This fact results from steric stabilization (low polymer concentrations) and depletion stabilization (high polymer concentrations) for MnO₂ particles covered with macromolecules. Next the kinetics of the adsorption of these two polymers on MnO₂ as well as the heats of GG and CMC adsorption processes were measured. The obtained data proved that CMC is adsorbed more effectively on the manganese dioxide surface than guar gum. To obtain more information about the changes of adsorption of these polymers on MnO₂ some factors influencing this process (pH, ionic strength of the background electrolyte) were investigated. The data obtained from the surface charge density and the zeta potential measurements allowed the analysis of the structure of the electric double layer created by polymers on the solid surface.     

Mixing narrow coarse and fine coal fractions – The maximum volume fraction of suspensions

A main objective of coal-water slurry fuel (CWSF) preparation is to achieve maximum loading of coal. In the absence of a strong colloidal attractive force, the maximum loading is determined by the packing density of the particles which in turn is a function of the particle size distribution. In this study, coal fractions of different mean sizes with a narrow distribution were separated by sieving. Mixtures of different mean coarse to fine size ratios were then prepared. For each size ratio, different amounts of coarse particle contents were prepared. With these different mixtures, water was added to produce the CWSF. The maximum volume packing density, φ_max, for each mixture was determined using a rheological vane yield stress technique. The determination of φ_max involving the direct yield stress measurements of extremely high concentration suspensions is an entirely new and accurate approach. It was found that the highest φ_max was obtained when the coarse to fine ratio was ～10 located at a coarse coal content of 70 wt%. This result is consistent with that obtained by theoretical modelling of bimodal mixing of monodisperse size spheres with a size ratio of 10. At lower size ratio, φ_max obtained at the optimum coarse coal content was lower.     

Pitting susceptibility of UNS NO. 8904 stainless steel in bromide-sulphide solution

The effect of sulphide ion on the pitting corrosion behaviour of UNS* no. 8904 (904L) stainless steel (SS) in 0.6 M NaBr at 25 °C has been investigated by using potentiodynamic anodic polarization and electrochemical impedance spectroscopy techniques. The pitting potential, E _pit, in 0.6 M NaBr + 10^–2 M Na₂S was more negative than that obtained in 0.6 M NaBr, and decreased with increasing temperature in the range 25–60 °C. Scanning electron microscopy observation showed that elemental sulphur formed on the steel surface before E _pit was reached in 0.6 M NaBr + 10^–2 M Na₂S at 60°C. E _pit of 904L SS pH independent in the pH range from 3–10 of 0.6 M NaBr + 10^–2 M Na₂S at 25 °C, while at high pH values the pitting was suppressed. The impedance measurements showed that the charge transfer resistance, R _t, decreased with time, when the controlled potential became higher than E _pit.     

Preparation of amino-functionalized magnetite nanoclusters by ring-opening polymerization and application for targeted magnetic resonance imaging

Here we developed a ring-opening polymerization strategy for preparation of biocompatible and amino-functionalized superparamagnetic iron oxide nanoclusters (SPIONCs). The functionalized SPIONCs could be further applied for folate-receptor (FR)-targeted magnetic resonance imaging (MRI). The citrate-stabilized SPIONCs were synthesized by solvothermal reaction using biocompatible trisodium citrate (Na₃Cit) as the coordinating and stabilizing ligand and then the amino groups were covalently bonded to them through a ring-opening polymerization of epichlorohydrin and further treatment with ammonium hydroxide. The products were confirmed by XPS, FTIR, Zeta potential, and amino quantitative analysis. The amino-functionalized SPIONCs have good stability in aqueous solution and low cytotoxicity to cell lines. By in vitro MRI and quantitative element analysis, we demonstrated the FR-mediated delivery of the folic acid-conjugated SPIONCs (Fe₃O₄–FA) targeting FR-positive cell line such as human ovarian carcinoma cell. In conclusion, high magnetization, good stability, and effective FR-mediated uptake of the functionalized SPIONCs made them promising candidates for use as MRI contrast agents.     

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.     

Effect of citrate on poly(vinyl pyrrolidone)-stabilized gold nanoparticles formed by PVP reduction in microwave (MW) synthesis

Colloidal PVP (poly(vinyl pyrrolidone))–stabilized gold nanoparticles (PVP–AuNPs) are synthesized in aqueous solution with PVP as a reducing and stabilizing agent using a short microwave (MW) heating duration of 1 min. The size and uniformity of the synthesized PVP–AuNPs can be varied by modifying the concentration of sodium citrate (Na₃Ct), which acts predominantly as mediator of the stability of PVP–AuNP formation during the rapid synthesis. Due to the increase in the Na₃Ct concentration, the number of citrate ions adsorbed on the growing surface of AuNPs increase, and less reactive gold solute complexes are formed, leading to slow stable reactions that produce small, uniform colloidal PVP–AuNPs. We therefore demonstrate that by adjusting the Na₃Ct concentration used in the PVP reduction, the diameter of PVP–AuNPs was varied from 19.47 ± 3.97 nm to 7.94 ± 0.14 nm when using constant concentrations of chloroauric acid (HAuCl₄) and PVP.     

The effect of humic acid on the stability and aggregation kinetics of WO3 nanoparticles

The physicochemical properties including size, hydrodynamic diameter, agglomeration rate, surface area, crystal structure, and surface charge were determined for WO₃ using x-ray diffraction spectroscopy (XRD), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET), UV-Vis spectrometer (DRS), and Zetasizer Nano ZS. The stability and aggregation behavior of WO₃ were investigated using dynamic light scattering (DLS) to monitor the hydrodynamic size and zeta potential. The effect of ionic strength was further studied using NaCl, MgCl_2. and CaCl₂ electrolytes at pH 5 as well as the effect of humic acid. WO₃ nanoparticles behaved similarly in deionized water suspensions and in the presence of NaCl electrolytes. The stability of nanoparticles was notable at low concentration (1?ppm) of humic acid particularly with NaCl electrolytes. Divalent cations enhanced agglomeration of nanoparticles even at the highest concentration of humic acid due to the formation of cation-humic acid bridges. The Derjaguin–Landau–Verwey–Overbeek theory was used to investigate the interaction energies, and it was found that van der Waals attraction forces are dominant in the presence of divalent cations.     

3D Interconnected Carbon Fiber Network‐Enabled Ultralong Life Na3V2(PO4)3@Carbon Paper Cathode for Sodium‐Ion Batteries

Sodium‐ion batteries (NIBs) are an emerging technology, which can meet increasing demands for large‐scale energy storage. One of the most promising cathode material candidates for sodium‐ion batteries is Na₃V₂(PO₄)₃ due to its high capacity, thermal stability, and sodium (Na) Superionic Conductor 3D (NASICON)‐type framework. In this work, the authors have significantly improved electrochemical performance and cycling stability of Na₃V₂(PO₄)₃ by introducing a 3D interconnected conductive network in the form of carbon fiber derived from ordinary paper towel. The free‐standing Na₃V₂(PO₄)₃‐carbon paper (Na₃V₂(PO₄)₃@CP) hybrid electrodes do not require a metallic current collector, polymeric binder, or conducting additives to function as a cathode material in an NIB system. The Na₃V₂(PO₄)₃@CP cathode demonstrates extraordinary long term cycling stability for 30 000 deep charge–discharge cycles at a current density of 2.5 mA cm^?2. Such outstanding cycling stability can meet the stringent requirements for renewable energy storage.     

The surface characteristics of polyacrylamide-coated silicon carbide powder used in the preparation of highly concentrated ceramics suspensions

Polyacrylamide (PAAM) coating layer was formed by chemical methods on the SiC powder surface. The surface characteristics of polyacrylamide (PAAM)-coated silicon carbide (SiC) powder were analyzed. The carbonyl band of amide and NH₂ deformation absorbing band existed at 1638 cm^–1, 1619 cm^–1 in the Fourier Transform Infrared Spectra (IR). Transmission electron microscopy (TEM) showed clearly the powder was coated by an organic compound layer which was PAAM judged by the reaction. The result of Differential Scanning Thermal Analyses (DSC) and Thermogravimetic (TG) showed the oxidizing decomposion temperature of PAAM was 411.9°C. The coating layer changed the surface characteristics of the SiC powder. At pH = 5, the suspensions of homogeneity and stability with 55 vol% solid content was prepared.     

The effect of polyelectrolyte on fabrication of macroporous ZrO<Subscript>2</Subscript> ceramics

The effect of polyethylenimine (PEI) on preparing macroporous ZrO₂ materials via heterocoagulation coating process was investigated, using ZrO₂ nanoparticles as the building materials and polystyrene spheres as the organic templates. When PEI was applied to modify the surface charge of ZrO₂ nanoparticles, it was found that 40–50% of initial PEI amount remained excess in the suspensions. Adsorption of excess PEI on the surface of polystyrene spheres resulted in partial coating of the polystyrene spheres by ZrO₂ nanoparticles at 1 wt% PEI and even no coating at 3 wt% PEI. Microstructure studies revealed that ZrO₂ ceramics prepared without using PEI had quite ordered macropores, while the ZrO₂ framework was partially collapsed at 1 wt% PEI and disordered macropores were observed at 3 wt% PEI.     

Manganese Local Environment Modulation via SiO4 Substitution to Boost Sodium Storage Performance of Na4MnCr(PO4)3

Manganese-based Na superionic conductors (NASICONs) Na₄MnCr(PO₄)₃ with three-electron reaction are attractive cathode materials for sodium-ion batteries. However, the irreversible distortion of Mn local structure leads to sluggish electrode kinetics, voltage hysteresis, and poor cycling stability. Here, SiO₄ is introduced to substitute PO₄ to modulate the local environment of Mn to activate the redox activity and stabilize the reversibility of Na₄MnCr(PO₄)_2.9(SiO₄)_0.1 (NMCP-Si). A combined experimental and theoretical investigation have been undertaken to reveal the evolution of electronic structures and Na storage properties associated with SiO₄ substitution. The NMCP-Si exhibits much-enhanced rate capability and cycling stability, being attributed to the unique Jahn-Teller distortion (Mn³⁺) that facilitates sodium de/insertion kinetics by optimizing the Na ion diffusion channels. This work addresses the challenge of stabilizing the structure of Mn-based NASICONs and represents a breakthrough in understanding how to improve the Na⁺ conductivity by regulating local structure.     

Relationship of Surface Area of pH-Dependent Suspensions and Water Retention

Abstract

The equilibrium water retention, M_W/M_S, of suspensions having a pH-dependent surface charge (carbonate-containing aluminum hydroxide and fumed silica) appears to be due to water adsorbed by the surface as well as water retained in pores. The water retained in pores has a lower limit determined by the closest packing porosity. Maximal water retention occurred when the pH was equal to the point of zero charge and attractive particle interactions predominated. The contribution of pore water to M_W/M_S can be minimized by selecting a pH significantly different from the point of zero charge. The water retention properties of the suspension under these conditions are believed to be due to adsorption and the closest packing porosity. Preliminary results indicate that this M_W/M_S can be related to the surface area of the suspended solid.     

Synthesis by a soft chemistry route and characterization of LixNi1 ? xO (0 < x < 0.5) compounds: Behavior in molten carbonates

Li_xNi_{1 – x}O powders and Li_xNi_{1 – x}O/Au with 0 < x < 0.5 are synthesized by a soft chemistry route. Analysis of Li_xNi_{1 – x}O by XRD shows an evolution from NiO (0 < x < 0.3) to LiNiO₂ (0.3 < x < 0.5) structures. The stability of Li_xNi_{1 – x}O/Au (0 < x 0.5) compounds synthesized by soft chemistry is studied in molten (Li_0.52Na_0.48)₂CO₃ eutectic at 650°C, under the cathode atmosphere used in molten carbonate fuel cells (air/CO₂: 70/30). After a 48 h immersion, analysis by XRD of the lithiated nickel oxide shows that lithium ions diffuse from the oxide to the bulk of the melt. The major oxide detected at the surface of the sample has a composition very close to that of NiO formed in situ at the surface of a nickel foil. Hence, highly lithiated nickel oxides are not stable in the melt. Li_xNi_{1 – x}O is rapidly transformed confirming the very high stability of Ni(II) in the working conditions.     

Structural analysis of Si-substituted hydroxyapatite: zeta potential and X-ray photoelectron spectroscopy

The aim of this study was to determine the effect of the incorporation of silicon on the surface charge of hydroxyapatite (HA) and to assess surface structural changes of HA and Si–HA induced by dissolution in both static and dynamic systems. X-ray photoelectron spectroscopy (XPS) analysis showed that SiO₄ ^4– groups were substituted for PO₄ ^3– groups in the silicon-hydroxyapatite (Si–HA) lattice according to a previously proposed substitution mechanism without the formation of other crystalline phases, such as tricalcium phosphate or calcium oxide. The substituted silicon induced a decrease in the net surface charge and the isoelectric point of HA as determined by zeta potential (ZP) measurements. At physiological pH=7.4 the surface charge of Si–HA was significantly lowered compared to unmodified HA, i.e. –50±5 to –71±5 eV, caused by the presence of silicate groups in the HA lattice, which may account for a faster in vitro apatite formation using SBF testing. XPS results indicated that silicon seems to be preferentially leached out from Si–HA surface compared to other ionic species after dissolution studies in tris-buffer using a dynamic system.     

Laser ablation protection of polymer matrix composites by adhesive inorganic coatings

Further utilization of polymer matrix composites (PMCs) in the aerospace industry is threatened by the development of laser weapons, resulting from weak oxidation resistance, low operation temperature and poor anti-laser ablation performance of the PMCs. Preparing an adhesive inorganic coating on the surface of components is an effective method to improve the laser irradiation resistance. Anti-laser ablation coatings composed of ZrO₂ as pigment and sodium silicate as binder with different curing agents (including SiO₂ and Na₂SiF₆) are fabricated on the PMCs substrate with brush painting. Influence of the different curing agents on anti-laser ablation of the coatings at the laser wavelength of 1064 nm is investigated. The rear surface temperature of substrate with coatings, containing SiO₂ and Na₂SiF₆, decreases from 240 to 60 and 70 °C, respectively, when testing at 1000 W for 5 s. After irradiation test at 1000 W for 10 s, the coating with SiO₂ as curing agent shows slight molten state on the surface, while the coating with Na₂SiF₆ is broke down, because coating containing SiO₂ possesses more compact microstructure and fewer cracks than that with Na₂SiF₆.     

A New Type of Capping Agent in Nanoscience: Metal Cations

Capping agents are the essential factor in nanoscience and nanotechnology. However, the types of capping agents are greatly limited. Defying conventional beliefs, here is shown that metal cations can also be considered as capping agents for oxide nanoparticles, particularly in maintaining their colloidal stability and controlling their facets. Here the general stabilizing effects of multivalent cations for oxide nanoparticles, and the facet controlling role of Al³⁺ ions in the growth and ripening of Cu₂O octahedra, are demonstrated. This discovery broadens the view of capping agent and opens doors for nanosynthesis, surface treatment, and beyond.     

Chemistry and Kinetics of ZnO Growth from Alkaline Hydrothermal Solutions

Special features (polar growth and nonstoichiometry) of ZnO single crystals grown on seed plates of various crystallographic orientations in the ZnO–KOH–H₂O and ZnO–KOH–LiOH–H₂O hydrothermal systems are analyzed. The growth proceeds via the interaction of ZnO^2- ₂ anions with crystal surfaces, and its rate depends on the atomic structure and electric charge of the surface. The mechanism underlying the influence of Li⁺ ions on polar ZnO growth is considered. Partial replacement of Zn²⁺ by Li⁺ decreases the positive charge on the (0001) face and hinders the attachment of ZnO^2- ₂ anions. The incorporation of Li ions into the (0001¯) face decreases its negative charge and accelerates growth in the [0001¯] direction.     

Facile and green synthesis of cobalt oxide nanoparticles using ethanolic extract of Trigonella foenumgraceum (Fenugreek) leaves

Cobalt oxide nanoparticles (Co₃O₄ NPs) were successfully synthesized using ethanolic extract of Trigonella foenumgraceum L. (fenugreek) leaves as a green, potentially low cost, and easily biosynthesized method. The organic bioactive compounds present in fenugreek leaves extract acted as both reducing agents and stabilizing agents for synthesizing metal NPs from cobalt chloride hexahydrate as a precursor. As evidence from UV/Visible spectroscopy, energy dispersive spectroscopy (EDS), and X-ray diffraction analysis (XRD) studies, high alkaline pH was found favorable for the preparation of pure and crystallized single-phase Co₃O₄ NPs. The interaction of biomolecules from fenugreek leaves extract with Co₃O₄ NPs was defined by Fourier transform infrared spectroscopy (FTIR) analysis and X-ray photoelectron spectroscopy (XPS). The hydrodynamic size and surface charge of the biosynthesized NPs were measured using light-scattering (DLS) and zeta potential analyses; revealed the formation of negative charged Co₃O₄ NPs with uniform hydrodynamic size distribution. According to transmission electron microscopy (TEM) analysis, quasi-spherical Co₃O₄ NPs were synthesized with an average size of 13.2 nm under the modified condition of pH 12 and reaction time of 2 h through inexpensive, environmental friendly benign synthesis process without the use of any additional toxic chemical.