Synthesis of the Precursor of Aluminum–Calcium Oxide Systems by Anodic Oxidation of Aluminum in Aqueous Solutions

An aluminum oxide system is obtained by electrolysis with a soluble anode and by the subsequent thermal treatment of the precipitate. It is shown that this system can be modified with calcium oxide in the process of synthesis. The influence of the synthesis conditions (the anodic current density and the electrolyte composition) on the formation of finely dispersed particles of the aluminum–calcium systems is studied. The structure and properties of the powder particles obtained by the electrochemical method are studied using the methods of laser diffraction, X-ray diffraction analysis, and electron microscopy.     

GeS2-In2S3-CdS体系玻璃的形成与性能

通过实验确定了ＧｅＳ２－Ｉｎ２Ｓ３－ＣｄＳ体系的玻璃形成区,其玻璃形成区较小,主要是在富含ＧｅＳ２区域。研究了它的热性能和透红外性能,结果表明：ＧｅＳ２－Ｉｎ２Ｓ３－ＣｄＳ体系玻璃转变温度在５７３－６９３Ｋ之间,红外截止波长为１１μｍ,具有较大的红外载波和较低的声子能量。ＧｅＳ２－Ｉｎ２Ｓ３－ＣｄＳ体系玻璃的密度约为３．０ｇ／ｃｍ＾３,玻璃在空气中能稳定存在而无风化现象产生。     

Assembly of β-SiC Nanowires film and humidity sensing performance

β-SiC materials have been seen as the third-generation semiconductor widely used in kinds of photoelectric device, high temperature electronics, and other fields. Compared with ordinary semiconductors, β-SiC materials have huge potential application in replacing monocrystalline silicon in extreme environments because of their numerals extraordinary chemical and physical properties. Based on this, β-SiC nanowires obviously are more desirable in any way. Here, we present a modified chemical vapor deposition (CVD) method to synthesis β-SiC nanowires, which needs no protect gas, and transfer it to Si/SiO₂ substrates equipped with Au electrodes. The microstructure of the as-prepared samples is tested by field emission scanning electron microscopy (FESEM). The humidity sensing performance of electronic device is measured by electrochemical workstation test equipment. It shows that the resistance of β-SiC nanowires increases with increasing environment humidity within very short response/recovery time-0.5 seconds/0.5 seconds and also performs excellent cycling stability. Such advantage superiorities make it highly possible to apply β-SiC nanowires into various environments.     

Armor Options: A Comparison of the Dynamic Response of Materials in the Aluminum Oxide–Aluminum Nitride Family

For armor applications, ceramic materials are often useful due to their high dynamic strength. In some instances, in addition to high strength, the armor must also be transparent, which significantly limits the choices of materials. Materials in the aluminum oxide–aluminum nitride family (including Al₂O₃ and AlON) are both strong and transparent. Only the end compound AlN is opaque. In this paper, the dynamic response to shock loading is examined for these materials to better understand the material response. Despite the chemical similarities, significant differences exist in the shock response and will be discussed.     

Explosive Synthesis of Ultradisperse Aluminum Oxide in an Oxygen‐Containing Medium

Explosive synthesis of ultradisperse aluminum oxide in an oxygencontaining medium is studied. Synthesis conditions that are most optimal for production of the material in the ultradisperse state are determined. A physical model of the process is proposed. It is shown that attenuation of the shock wave causes separation of the shockcompressed material into liquid and solid layers. Possible mechanisms of aluminum combustion with subsequent dispersion of aluminum into the oxygencontaining medium of the explosive chamber are considered. It is shown that ultradisperse aluminum oxide powder is produced mainly from the second layer of the shockcompressed material. Experimental dependences of the yield of the disperse fraction on synthesis conditions are explained using the model proposed.     

Hot Photoluminescence in γ-In2Se3 Nanorods

The energy relaxation of electrons in γ-In₂Se₃ nanorods was investigated by the excitation-dependent photoluminescence (PL). From the high-energy tail of PL, we determine the electron temperature (T _e) of the hot electrons. The T _e variation can be explained by a model in which the longitudinal optical (LO)-phonon emission is the dominant energy relaxation process. The high-quality γ-In₂Se₃ nanorods may be a promising material for the photovoltaic devices.     

Thionation of β-lactams to β-thiolactams by silica-supported P2S5

In this paper, an improved method for the thionation of β-lactams is described. Using a solid-supported P₂S₅ reagent and heating under reflux conditions, β-thiolactams were obtained in good to excellent yields. Also the reaction time reduced significantly compared with that achieved under the more conventional method using P₂S₅ alone. Furthermore, inexpensive and easily available starting materials simple reaction conditions and a simple purification process are some other advantages of this method.     

Anodic Oxidation of Nitric Oxide on Au/Nafion®: Kinetics and Mass Transfer

The rate determining step for the anodic oxidation of nitric oxide on Au/Nafion^® was experimentally and theoretically found to beNO + Au Au–NO_ads The anodic oxidation of nitric oxide was first order with respect to nitric oxide. The reaction rate constant increased from 3.3×10^–5 to 9.6×10^–5cm s^–1 as the applied potential increased from 0.74 to 0.77V. The anodic oxidation of nitric oxide was controlled by the electrochemical kinetics when the anodic potential was less than 0.8 V. When the potential was greater than 1.0 V, it was located in the mass transfer region. The limiting current increased from 1184 to 1589A with increase in gas flow rate from 250 to 750ml min^–1 when the potential was set at 1.05 V and the concentration of nitric oxide was 100 ppm. The diffusion resistance in the gas diffusion layer can be neglected for gas flow rates greater than 750 ml min^–1. The diffusivity of nitric oxide and the equivalent diffusion layer thickness within the porous electrode were evaluated to be 3.43×10^–4cm²s^–1 and 0.051 cm, respectively.     

Research of positron annihilation and hydration of doped β-C2S

The lifetime spectrum of positron in β-C₂S of added Na₂O or P₂O₅ is studied with positron annihilation technique. According to the theory of the capture of positron, we discuss the relationship between lifetime spectrum parameters obtained through experiment and the microstructure of β-C₂S. The results show that the long living component τ₂ (about 470 ps) represents the capture of positron in the defects of Ca²⁺ vacancies and that the intensity of I₂ of τ₂ decreases with the increasing of Na⁺ and increases with the increasing of P⁵⁺. The results also verify that Na⁺ replaces Ca²⁺ and creates anion vacancies; while P⁵⁺ replaces Si⁴⁺ and creates cation vacancies. Vacancy concetration increases Na⁺ and P⁵⁺. Our work shows that the positron annihilation technique is a useful tool for studying the change of microstructure defects in doped β-C₂S. The relationship between heat treatment and hydration activity of doped β-C₂S and its impurities are also studied and discussed.     

Fabrication and thermoelectric properties of SrTiO3–TiO2 composite ceramics

The paper presents the results of preparing biphase SrTiO₃–TiO₂ ceramics as a promising system for n-type thermoelectrics using the features of a two-dimensional electron gas. Ceramics was obtained by reactive spark plasma sintering of SrCO₃ and TiO₂. The dynamics of phase transformations are shown; it is clarified that phase transformations are not the driving force of sintering. The mutual stabilization of the SrTiO₃ and TiO₂ phases is shown. Unique data on the assessment of the temperature gradient in the system have been obtained. A comparison of the thermoelectric characteristics of biphasic ceramics and its constituent phases allows concluding that the role of the two-dimensional electron gas is reduced to modulating the properties of bulk phases. Clear signs of size quantization were detected by the X-ray luminescence method, which is expressed in the blueshift of the luminescence spectrum by 22.3 ± 0.8 meV.     

Methods and Approaches of the Sol–Gel Technology for the Surface Modification of Aluminum Oxide Powders

The results of studies, sol–gel synthesis, and the sedimentation stability of complex multicomponent sol–gel systems of the “silica sol modified with Co(NO₃)₂ · 6H₂O, Al(NO₃)₃ · 9H₂O with α-Al₂O₃ or γ-Al₂O₃ as highly dispersed filler” type are generalized. The physical–chemical processes accompanying the formation of modifying layers on the powder oxide particles are examined. The promising prospects of applying α-Al₂O₃ powders modified with a silicate layer of the composition (wt %) 1.2K₂O · 3Al₂O₃ · 3.2CaO · 12.5Na₂O · 28.1B₂O₃ · 52SiO₂ in the fabrication of ceramic materials with improved strength characteristics are demonstrated.     

Fabrication of Al2O3–ZrO2 ceramics with high porosity and strength

This study describes the synthesis of ceramics, in which a micrometre-sized Al₂O₃–ZrO₂ nanopowder was used as an oxide base for the hardening of the materials. To a suspension of this mixed metal oxide, the pore-forming crystallisation additives camphor and carbamide were added to produce ceramics with thin permeable pores. Camphor crystallised in the oxide suspension in the form of single pentagonal stars and сarbamide crystallised in the form of thin elongated needles. The use of the different crystallisation additives allowed the formation of ceramics after sintering that have both permeable and complex pore morphologies, where anisotropic properties were observed using carbamide as an additive but not when camphor was used. The total porosity of the resulting ceramics was 51.3%, with a compressive strength in the range of 17.3–92.3 MPa.     

Fabrication and microstructure of Al2O3–ZrO2(3Y)–SiC nanocomposites

Al₂O₃–ZrO₂(3Y)–SiC composite powder was prepared by the heterogeneous precipitation method. Calcinating temperature of the powder was important to obtain dense sintered body. The nanocomposites were got by hot-pressing, and addition of ZrO₂ did not raise the sintering temperature. Some Al₂O₃ grain shape was elongated, and Al₂O₃ grain size was about μm. Nano SiC particles were observed uniformly distributing throughout the composites, and most of them were located within the matrix grains. Because SiC particles located within ZrO₂ grains influenced the phase transformation of ZrO₂, the sintering of nanocomposites, which controlled grain size and transformable ZrO₂ amount, become important to get high performance. The strength of 80 wt% Al₂O₃–15 wt% ZrO₂–5 wt% SiC nanocomposites was 555 MPa, and toughness was 3·8 MPa m^1/2, which were higher than those of monolithic Al₂O₃ ceramics. ©     

Fabrication and characterization of porous β-tricalcium phosphate scaffolds coated with alginate

All porous materials have a common limitation which is lack of strength due to the porosity. In this study, two different methods have been used to produce porous β-tricalcium phosphate (β-TCP) scaffolds: liquid-nitrogen freeze casting and a combination of the direct-foaming and sacrificial-template methods. Among these two methods, porous β-TCP scaffolds with acceptable pore size and compressive strength and defined pore-channel interconnectivity were successfully fabricated by the combined direct-foaming and sacrificial-template method. The average pore size of the scaffolds was in the range of 100–150 µm and the porosity was around 70%. Coating with 4 wt% alginate on porous β-TCP scaffolds led to higher compressive strength and low porosity. In order to make a chemical link between the β-TCP scaffolds and the alginate coating, silane coupling agent was used. Treated β-TCP scaffold showed improvements in compressive strength of up to 38% compared to the pure β-TCP scaffold and 11% compared to coated β-TCP scaffold.     

Evaluation of β-diketone-containing Polymeric Coupling Agents for Enhancing the Adhesion of Epoxy to Aluminum

β-diketone-containing polymeric coupling agents (PCA) were evaluated as potential adhesion enhancers for an epoxy/aluminum bond system. Torsional shear joint measurements revealed that the β-diketone-containing PCA did not influence the joint strength and durability, positively or negatively, as compared with untreated controls. Grazing angle infrared spectroscopy revealed that despite reactivity of the β-diketone-containing monomer with aluminum substrates, no reactivity of the β-diketone was observed once the monomer was incorporated into the polymer. Deposition studies showed that the resulting PCA coating thickness following treatment and solvent rinsing was not a function of solvent solubility parameter, solution concentration, or immersion time. It was hypothesized that preferential physisorption of the phenyl and/or epoxy functionalities in the PCA inhibited reactivity of the β-diketone functionality.     

Enhanced Activity of Spinel-type Ga2O3–Al2O3 Mixed Oxide for the Dehydrogenation of Propane in the Presence of CO2

Catalytic performance of a series of Ga₂O₃–Al₂O₃ mixed oxides prepared by alcoholic-coprecipitation method for the dehydrogenation of propane in the presence of CO₂ was investigated. It is shown that the combination of Ga and Al oxides greatly improved the performance of the Ga₂O₃-based materials for catalytic dehydrogenation of propane, with the highest performance attainable at a Ga₂O₃–Al₂O₃ catalyst with a 20 mol% aluminum content. While the same tendency was observed for the specific activity normalized by BET surface area, significantly enhanced stability was achieved for Ga₂O₃–Al₂O₃ with higher aluminum content. X-ray diffraction (XRD) revealed that a homogeneous spinel-type Ga₂O₃–Al₂O₃ solid solution is uniformly formed by substitution of Ga³⁺ for Al³⁺ in the Al₂O₃ lattice. The enhanced activity of Ga₂O₃–Al₂O₃ mixed oxides was accounted for by the abundance of surface weak acid sites due to the synergetic interaction between Ga₂O₃ and Al₂O₃ in the solid solution systems.     

Synthesis, Electrical Measurement, and Field Emission Properties of α-Fe2O3 Nanowires

α-Fe₂O₃ nanowires (NWs) were formed by the thermal oxidation of an iron film in air at 350 °C for 10 h. The rhombohedral structure of the α-Fe₂O₃ NWs was grown vertically on the substrate with diameters of 8–25 nm and lengths of several hundred nm. It was found that the population density of the NWs per unit area (D _NWs) can be varied by the film thickness. The thicker the iron film, the more NWs were grown. The growth mechanism of the NWs is suggested to be a combination effect of the thermal oxidation rate, defects on the film, and selective directional growth. The electrical resistivity of a single NW with a length of 800 nm and a diameter of 15 nm was measured to be 4.42 × 10³ Ωcm using conductive atomic force microscopy. The field emission characteristics of the NWs were studied using a two-parallel-plate system. A low turn–on field of 3.3 V/μm and a large current density of 10⁻³ A/cm² (under an applied field of about 7 V/μm) can be obtained using optimal factors of D _NWs in the cathode.     

Fabrication of aerogels from cellulose nanofibril grafted with β-cyclodextrin for capture of water pollutants

Journal of Porous Materials - Interactions at the molecular and surface chemistry are some of the key factors that determine the adsorption capacity of pollutants and emerging contaminants in...