Morphology of Zinc Sulfide Particles Produced from Various Zinc Salts by Homogeneous Precipitation

Colloidal sols of ZnS were prepared by thermal decomposition of thioacetamide in acidic zinc solutions. Precipitation was carried out in the presence of nitrate, acetate, chloride, and sulfate ions. Particle morphology was influenced by the chemical nature of the anions present in the solution as well as the rate of sulfide ion generation. Spherical, monodisperse particles having a specific type of particle size distribution, i.e., monosized, bimodal, or continuous distribution, with mean sizes in the range of 0.15 to 3 μm, were formed depending on the anion type and sulfide ion generation rate. Individual particles always consisted of clusters of sphalerite crystallites except when sulfide ions were generated at low rates and sulfate ions were present. In such cases a mixture of α- and β-ZnS was formed.     

Effects of Chemical Species on the Crystallization Behavior of a Sol-Derived Zirconia Precursor

The thermal and crystallization behaviors of a sol-derived zirconia precursor are affected by the chemical species (such as chloride, acetate, and hydroxyl; i.e., Cl^-, CH₃COO^-, and OH^-) present in the solution in which they are aged. The crystallization temperature of zirconia precipitate increases steadily with decreasing pH when hydrochloric acid is added to the aging mother liquor. A more dramatic increase in crystallization temperature is observed when acetic acid is used to reduce the pH of the aging solution. The precursors aged in the solutions of intermediate pH range demonstrate a typical two-step crystallization behavior, due to the transition from a OH^--dominated surface structure to a CH₃COO^--dominated one. These results show that a higher crystallization temperature results when the OH^- groups attached to the surface of precursor particles are replaced by the CH₃COO^- groups. Only a slight decrease in the crystallization temperature of aged precipitates occurs when free species, such as CH₃COO^- and OH^-, are being removed from the aging solution.     

Bismuth Oxide Nanoparticles by Flame Spray Pyrolysis

Bismuth oxide nanostructured particles were made via the flame spray pyrolysis (FSP) of bismuth nitrate that had been dissolved in a solution of ethanol/nitric acid or in acetic acid. These self-sustaining spray flames produced tetragonal β-Bi₂O₃. The use of ethanol/nitric acid solutions resulted in a mixture of hollow, shell-like, and solid nanograined particles. The particle homogeneity was improved as the content of acetic acid in the precursor solution increased. Solid bismuth oxide nanoparticles were prepared consistent with percolation theory, accounting for the specific volume of the product and the precursor. Using pure acetic acid as the solvent, the effect of FSP variables on spray flame and product powder characteristics was investigated. The specific surface area of the Bi₂O₃ particles could be controlled over a range of 20–80 m²/g by the liquid feed and oxygen gas flow rates for powder production rates of 6–46 g/h.     

Low-Temperature Synthesis of Fully Crystallized Spherical BaTiO3 Particles by the Gel–Sol Method

The synthesis of spherical BaTiO₃ particles was attempted by a new technique, the "gel–sol method," at 45°C. The (Ba–Ti) gel used as a starting material was prepared by aging mixtures of titanyl acylate with a barium acetate aqueous solution ([glacial acetic acid (AcOH)]/[titanium isopropoxide (TIP)] = 4, [barium acetate]/[TIP] = 1) at 45°C for 48 h. Potassium hydroxide (KOH) was used as a catalyst for the formation of BaTiO₃. Powder X-ray diffractometry (XRD) results and Fourier-transform infrared (FT-IR) measurements for the (Ba–Ti) gel showed that the gel was amorphous, but the spatial arrangement of barium and titanium in the (Ba–Ti) gel is similar to that in crystalline BaTiO₃ particles. Fully crystallized spherical BaTiO₃ powder with a particle size of 40–250 nm formed at the very low reaction temperature of 45°C. Scanning electron microscopy images showed that the final particles formed via aggregation of the fine particles that seem to be the primary particles of bulk (Ba–Ti) gel. From the XRD, FT-IR, and Raman spectroscopy analysis, it was found that the crystal structure of the as-prepared particles continuously transformed from cubic to tetragonal as the calcination temperature increased, and high crystalline tetragonal BaTiO₃ phase was obtained at 1000°C after 1 h of heat treatment.     

Effects of copper cation and acetate anion on the growth of PbO2 on a SnO2/Ti substrate

The effects were examined of copper(II) cations and acetate anions on the nucleation, growth and electrochemically active surface area of lead dioxide on a SnO₂/Ti electrode. The nucleation rate of electrodeposited lead dioxide was greater in the presence of Cu(II), but smaller in the presence of acetate anions when compared with that of pure PbO₂. The growth rate of the nuclei of PbO₂ was greater for acetate-doped PbO₂ but it was smaller for Cu(II)-modified PbO₂ in comparison with pure PbO₂. The acetate-doped PbO₂ was grown in the form of hemispheres, whereas the Cu(II)-modified PbO₂ was in the form of multi-sided pyramids whose growth axes are directed towards the center of the sphere. The average size of crystal aggregates for electrodeposited lead dioxide became enlarged in the presence of Cu(II). The morphology of the PbO₂ film was smooth in appearance in the presence of acetate anions. The growth of PbO₂ on the SnO₂/Ti substrate was demonstrated not to be an instantaneous process, but is preceded by progressive nucleation with preferential island growth. PbO₂ doped with the acetate anion resulted in a significant increase of the electrochemically active surface area (Q^*); by contrast, values of Q^* for lead dioxide modified with Cu(II) decreased.     

Sol—Gel Fabrication of Pb(Zr0.52 Ti0.48)O3 Thin Films Using Lead Acetylacetonate as the Lead Source

Lead zirconium titanate (PZT) thin films of the morphotropic phase boundary composition [Pb(Zr_0.52Ti_0.43)O₃] were deposited on platinum-coated silicon by a modified sol-gel process using lead acetylacetonate as the lead source. The precursor solution for spin coating was prepared from lead acetylacetonate, zirconium n -butoxide, and titanium isopropoxide. The use of lead acetylacetonate instead of the widely used lead acetate trihydrate provided more stability to the PZT precursor solution. Films annealed at 700°C for 12 min formed well-crystallized perovskite phase of Pb(Zr_0.52Ti_0.48)O₃. Microstructures of these films indicated the presence of submicrometer grains (0.1 to 0.2 μm). The dielectric constant and loss values of these films measured at 10 kHz were approximately 1200 and 0.04, respectively, while the remanent polarization and coercive field were ∼ 13 μC/cm² and ∼ 35 kV/cm. Aging of the solution had almost no effect on the dielectric and ferroelectric properties of these films.     

Relations Between Normal Boiling Point and Melting Point for Simple Halides and Oxides

For most halides the normal boiling point ( T_b in kelvin units) is given by the relation: T_b= 440 n_c ( ip·ea·d ²) ⁻¹ , where n_c is the coordination number of the cation, ip the first ionization potential of the metal (in electron volts), ea the electron affinity of the anion former (in electron volts), and d the bond length in the crystal (in nanometers). Similar relations are found for oxides. For both classes the following relation applies: T_b/T_f= 1 + 0.67 /V _a , where TI is the melting point of the crystal and V_a is the valence of the anion. Exceptions occur when inert ( s² ) electron pairs form the outer shield of the cation or anion core, when electron spin pairing occurs between halogen or oxygen atoms, when there are direct interactions between metal atoms, or when n_c is not the same in the molten and crystalline states. Further, it is shown that covalency related to the asymmetric polarization of anions by cations with partially filled valence shells can markedly increase cohesion in the melt. This relates to plasticity in the solid as well.     

Composite polymeric particles with ZnS shells

We report on a preparation of hybrid particles with polymeric cores and ZnS shells. Two types of monodisperse sterically stabilized polystyrene particles with hydroxyl-terminated PEG chains (PS/PEGMA) or β-diketone groups (PS/AAEM) on the surface have been prepared and characterized. Formation of ZnS layer on the surface of submicron particles has been studied by SEM and EDX. Deposition of ZnS on the surface of PS/PEGMA particles is not uniform and leads to formation of ‘raspberry’ morphology with rough surface. It has been found that presence of β-diketone groups on the particle surface leads to formation of well-defined ZnS layers. It has been assumed that such effect is due to the complexation of Zn cations by β-diketone groups leading to nucleation and growth of ZnS crystals on the polymer particle surface. Polymeric particles were completely covered with ZnS if the loaded amount of inorganic material was higher then 40 wt%. The thickness of ZnS layer on the particle surface can be easily varied by changing the ZnS load (in present study maximal thickness of the ZnS shell was 70 nm). It has been found that increase of the ultrasound power leads to considerable increase of the ZnS deposition on the particle surface without strong changes of the particle morphology. Hybrid particles have been investigated with XRD technique and their optical properties were studied by UV-spectroscopy. The colloidal stability of obtained particles was studied by separation analyser. Sedimentation experiments indicate that colloidal stability of obtained composite particles depends strongly on loaded ZnS amount and pH value of the aqueous medium. It has been found that highest sedimentation velocities (or maximum of instability) were determined by ZnS loads, which provide complete coverage of the particle surface. Increase of the ZnS layer thickness led to better stability of hybrid particles in aqueous medium.     

Kinetics of discharge of zinc at the dropping mercury electrode

The rate of the discharge reaction of zinc ions at the dropping mercury electrode is diminished if the concentration of the indifferent surface inactive electrolyte is increased, because of the decrease of the potential difference in the diffuse double layer. It diminishes also with increase of radius of the alkali-metal cations present in the electrolyte and with increase of charge of the cation of the electrolyte. A strong retarding effect is exhibited by tetraalkylammonium cations, which increases with the size of the alkyl group. The electrode reaction rate increases in presence of iodide anions, as manifested by formation of a new, more positive wave. In presence of iodide and tetraalkylammonium cations together the process is accelerated at more positive potentials and is retarded at more negative potentials.

All these phenomena are analogous to those observed with the hydrogen-evolution reaction at the mercury electrode, and are the opposite of those observed with anions of the persulphate type.

Abstract

La vitesse de décharge de Znl²⁺ sur électrode à mercure gouttante diminue quand s'accroît la concentration superficielle d'un électrolyte inactif, par suite de l'abaissement de la tension électrique dans la couche diffuse. Elle diminue aussi quand s'accroîssent le rayon on la charge des cations de l'électrolyte. Les cations tétraalkylammonium exercent un effet fortement retardateur, qui augmente avec l'encombrement du groupe alkyl. La vitesse s'élève par centre en présence d'anions I⁻. Si cet anion est accompagné d'un des cations précédents, le processus s'accélère aux tensions plus positives et se ralentit aux tensions plus négatives. Tons ces phénomènes, contrastant avec ceux manifestés avec les anions du type persulfate, sont comparables à ceux observés dans l'évolution d'hydrogène sur électrode de mercure.

Abstract

The influence shown by the composition of the electrode double layer on the electrode reaction rate of the zinc ion is quite similar to analogous effects observed with the hydrogen-evolution reaction at mercury electrodes. The decrease of the rate of the latter process with increase of the radius of alkali-metal cations, of the charge of the cation of the electrolyte and of the concentration of the electrolyte was described by Herasymenko and lendyk.²¹ The strong retardation of this process by quaternary cations and the acceleration by iodide was found by Yofa, Kabanov and co-workers.²² Tsa Chuan Sin and Yofa²³ observed the combined effect of iodide and tetraalkylammonium cations which at positive potentials accelerate the hydrogen evolution reaction slightly over the value in presence of iodide only, but retard it at more negative potentials.

From the similar features of both reactions it may be concluded that in spite of a different total reaction path, the rate-determining step is identical, i.e. the transfer of the charged particle from its hydration sheath to the electrode. It is expected that analogous phenomena will be observed with other cations which are not adsorbed too strongly at the electrode (cf. the influence of surface-active cations on the discharge of T1⁺ and Cd^{2+ 24,25}).

All the effects of the double-layer structure connected with the electrode reaction of the zinc ion are just the opposite of those observed with the reduction of anions of persulphate type.²⁰     

Effect of anions and cations on the aqueous phase catalytic hydrogenation of C=C bonds

The influence of solution composition (nature of anions and cations, pH) in the aqueous phase catalytic hydrogenation of C=C bonds (maleic acid) has been investigated.

In weakly acidic solutions (of pH 3 and 6) the influence of the commonly used anions (ClO₄⁻, HSO₄⁻/SO₄²⁻, Cl⁻) is less important than that obtained in solutions of pH 0.3, found in previous works [Electrochim. Acta 45 (2000) 4299]. This difference can be ascribed to a weaker adsorption of the anion on platinum, as well as, to the different nature of the competitively adsorbed maleic acid species (molecular form or anionic adsorption) depending on the solution pH. In the presence of (hydrogeno)phosphates the lowest activities are obtained implying that these anions are the most strongly adsorbed on platinum.

An important promotion of platinum activity in the presence of cations has also been found. This effect depends on the size of the cation and can be attributed to the modification of the work function and, consequently, of the adsorption properties of platinum.     

Evolution of the Morphology of Zinc Oxide/Silica Particles Made by Spray Combustion

Pure and mixed ZnO–SiO₂ particles were made by flame-spray pyrolysis of zinc acetate and hexamethyldisiloxane or SiO₂ sol dispersed in methanol or water-in-oil emulsion, respectively. The product particles were characterized by nitrogen adsorption, infrared absorption, and X-ray diffraction. The evolution of solid or hollow particle formation along the flame axis was unraveled by transmission electron microscopy after collection by thermophoretic sampling. The effects of silicon precursor and solvent on product particle characteristics were evaluated. The characteristics of the product particles were controlled by the Si precursor and solvent.     

Synthesis of Rare-Earth Gallium Garnets by the Glycothermal Method

Single-phase rare-earth gallium garnets were obtained by the reaction of stoichiometric mixtures of gallium acetylacetonate and rare-earth (Nd-Lu) acetates in 1,4-butanediol at 300°C (glycothermal reaction). Particles of gadolinium gallium garnet (GGG) and other gallium garnets with rare-earth elements larger than Gd were spherical with diameters of 0.5-2 μm, while particles of garnets with smaller rare-earth ions (Tb-Lu and Y) were much smaller (100-300 nm) with particle size distributed in a quite narrow range. TEM observation revealed that each particle was essentially a single crystal grown from one nucleus, but that defects frequently occurred during the crystal growth. Cerium and praseodymium gallium garnets were also formed when the reaction was carried out in the presence of GGG seed crystals. Hydrothermal reactions of the same starting materials under identical conditions yielded mixtures of gamma-Ga₂O₃ and the garnet phase.     

Spectroscopic Studies on the Localization of Vanadium(IV) in Vanadium-Doped Zircon Pigments

The origin of the blue color observed for vanadium-doped zircon powders that have been prepared either in the presence or the absence of fluxes (NaF) has been investigated by analyzing the localization and distribution of the vanadium species in the zircon matrix. In both cases, the unit-cell parameters determined from the X-ray diffraction patterns of the samples and the results obtained from X-ray absorption (X-ray absorption near-edge structure and extended X-ray absorption fine structure), infrared, and electron spin resonance spectroscopies indicated that V⁴⁺ cations form a solid solution with the zircon lattice, substituting for both Si⁴⁺ and Zr⁴⁺ cations, although to a greater extent for the former. These vanadium cations are heterogeneously distributed in the zircon matrix, being mainly located in the outer layers of the particles in two different situations: "aggregated" in nearby lattice positions with V⁴⁺-V⁴⁺ distances ( d _V-V) of <8 Å (0.8 nm), and isolated with respect to other V⁴⁺ cations ( d _V-V > 8 Å). The strongest blue color that is observed for samples prepared in the presence of NaF seems to be due to the higher amount of V⁴⁺ cations incorporated to the zircon lattice, because this flux agent does not have any structural role.     

Attack of Glass by Chelating Agents

The chemical attack of a soda-lime glass by the combined action of ethylene diamine tetraacetic acid and ortho-dihydroxy benzene (catechol) in dilute aqueous solution is reported u a function of pH. A pronounced maximum occurs in the rate of attack at a pH value determined by the anionic species present. The effects are ascribed to the chelation of the protective cations A1³⁺, Ca²⁺, and Mg²⁺ by ethylene diamine tetraacetic acid and to the chelation of Si⁴⁺ by catechol.     

In Situ Surface Modification of Silicon Carbide Particles Using Al3+ Complexes and Polyelectrolytes in Aqueous Suspensions

Silicon carbide (SiC) particles were modified in situ , using Al³⁺ complexes in aqueous media, via control of Al(NO₃)₃concentration and pH. The Al³⁺ formed hydrolyzed complexes that adsorbed onto the charged sites on the SiC particle surfaces. As a result, the surface-modified SiC particles behaved in an alumina-like manner in the approximate pH range 5–8. The modified SiC particles were further treated with two types of polyelectrolytes that were sequentially adsorbed onto the particle surface, to give a maximum surface charge. As a result of this surface-modification process, the SiC could be dispersed with Al₂O₃in aqueous media without heteroaggregation.     

Structural Characterization and Protein Adsorption Property of Hydroxyapatite Particles Modified With Zinc Ions

Zinc-containing hydroxyapatite particles (Zn/HAp) were prepared by an ion exchange reaction process involving hydroxyapatite (HAp) particles with aqueous solutions containing various amounts of zinc nitrate. The Zn²⁺ ion was partially substituted for the Ca²⁺ ion position in the HAp lattice, and hence, the obtained samples had changed little in crystallinity, particle size, and specific surface area. Adsorption of bovine serum albumin (BSA) and β₂-microglobulin (β₂-MG) in solutions containing both BSA and β₂-MG was examined. As the Zn²⁺ ion content in the apatites increased, the adsorbed amount of BSA was almost constant, whereas that of β₂-MG increased.     

硝基苯加氢一锅法合成对乙酰氨基苯酚

针对目前工业上现有对乙酰氨基苯酚(APAP)合成工艺存在的问题,探索了乙酸和锌盐混合溶液中以硝基苯为原料一锅法直接合成APAP新工艺,对对氨基苯酚(PAP)的酰化反应以及酰化与加氢反应的耦合过程进行了研究和分析。结果表明:乙酸和锌盐在促进苯基羟胺重排生成PAP上具有明显的协同促进作用,可明显提高加氢反应中生成PAP的选择性,选择性最高达到了76.8%。加氢反应过程中,硫酸锌对乙酸和PAP的酰化反应具有明显的抑制作用,而乙酸锌的影响则明显要小。乙酸锌浓度为170 mmol/L时,乙酸对PAP酰化反应转化率可以达到50%以上。采用加氢反应结束后降温再利用乙酸酐酰化的方法可使生成的PAP完全转化为APAP,APAP最高收率超过70%。     

Control of Grain-Boundary Pinning in Al2O3/ZrO2 Composites with Ce3+/Ce4+ Doping

The control of the microstructure of Ce-doped Al₂O₃/ZrO₂ componsites by the valence change of cerium ion has been demonstrated. Two distinctively different types of microstructure, large Al₂O₃ grains with intragranular ZrO₂ particles and small Al₂O₃ grains with intergranular ZrO₂ particles, can be obtained under identical presintering processing conditions. At doping levels greater than ∼ 3 mol% with respect to ZrO₂, Ce³⁺ raises the alumina grain-boundary to zirconia particle mobility ratio. This causes the breakaway of grain boundary from particles and the first type of microstructure. On the other hand, Ce⁴⁺ causes no breakaway and produces a normal intergranular ZrO₂ distribution. The dramatic effect of Ce³⁺ on the relative mobility ratio is found to be associated with fluxing of the glassy boundary phase and is likewise observed for other large trivalent cation dopants. The ZrO₂ second phase acts as a scavenger for these trivalent cations, provided their solubility limit in ZrO₂ is not exceeded.     

Single-Source Sol-Gel Synthesis of Nanocrystalline ZnAl2O4: Structural and Optical Properties

Nanometer-sized zinc aluminate (ZnAl₂O₄) particles were synthesized from heterometal alkoxides, [ZnAl₂(OR)₈], possessing an ideal cation stoichiometry for the ZnAl₂O₄ spinel. ZnAl₂O₄ is formed at 400°C, which is the lowest temperature reported for the formation of monophasic ZnAl₂O₄. ²⁷Al magic-angle spinning nuclear magnetic resonance spectroscopy revealed that ZnAl₂O₄ possesses an inverse structure at <900°C, while the normal spinel phase is observed at higher temperatures. The homogeneity of the in-depth composition and Zn:Al stoichiometry (1:2) was confirmed by electron spectroscopy for chemical analysis. Evaluation of the valence-band spectra of ZnAl₂O₄ and ZnS suggested that the hybridization of O 2 p and Zn 3 d orbitals is responsible for lowering the bandgap in the latter. The average crystallite size showed an exponential relationship to the calcination temperature (X-ray diffractometry and transmission electron microscopy data). The optical spectra of different spinel powders (average particle sizes, 20–250 nm) showed that the absorption edge exhibits a blue shift as particle size decreases.     

Nanoscale ZnO and Al-Doped ZnO Coatings on ZnS:Ag Phosphors and their Cathodoluminescent Properties

Blue-emitting ZnS:Ag phosphors were coated with nanoscale zinc oxide (ZnO) and Al-doped ZnO (AZO) and the cathodoluminescence (CL) performance of the coated phosphors was investigated. The nanoscale coating was obtained by controlling the hydrolysis reaction of ZnCl₂ alcoholic solution using diethylamine as a gradual OH⁻ former, and Al doping was performed to increase the electrical conductivity of ZnO. The coatings were composed of either nanosized particles or a continuous nano layer, and the AZO-coated phosphor had a more uniformly covered surface. The coated phosphors exhibited improved aging behavior under CL excitation and the AZO coating was more effective at suppressing the degradation, possibly due to its uniformity and high conductivity.