Chemistry and Structure of Beta Silicon Carbide Implanted with High-Dose Aluminum

Single-crystal β-SiC was implanted with aluminum to 3.90 × 10¹⁷ ions/cm² at 168 keV at 773 K. The resultant compositional and structural characteristics were studied by Rutherford backscattering spectrometry, Auger electron spectroscopy, X-ray photoelectron spectroscopy, and cross-sectional transmission electron microscopy. No aluminum redistribution was observed during implantation. The Si-to-C ratio exhibited a negative deviation from unity in the implanted region. The shift in the photoelectron binding energies indicated the formation of aluminum carbide. The studies by electron microscopy showed that the implanted region consists of slightly misoriented β-SiC crystals and textured crystalline aluminum carbide precipitates     

Effect of oxygen donor alcohol on nonaqueous precipitation synthesis of alumina powders

Monodispersed alumina powders were prepared via nonaqueous precipitation process using aluminum powders as aluminum source, acetic acid as precipitant. Effect of oxygen donor and solvent alcohol such as methanol, ethanol, isopropanol on the preparation of ultrafine alumina powders and the precursor reaction mechanism have been investigated by XRD, FT-IR, TEM, FE-SEM and performance tests of sintered bodies. The intermolecular condensation of methanol with the catalysis of Lewis acid aluminum methoxide leads to hydrolysis of aluminum methoxide, forming amorphous precipitates, dehydration polycondensation of aluminum hydroxide and resulting in serious agglomeration of precipitates and alumina powders, the worst morphology and properties of sintered body. The pulling electron effect and steric hindrance of isopropyl group make the structure of aluminum isopropoxide overwhelmingly stable and relatively arduous to be replaced by precipitant acetic acid, which results in underdeveloped crystallinity and agglomeration of both precipitates and alumina powders, poor morphology and properties of sintered body. The optimized oxygen donor and solvent alcohol is ethanol. Monodispersed, high crystallinity C₄H₇AlO₇ precipitates and alumina powders can be obtained when ethanol is used as oxygen donor and solvent, and the highest relative density, mechanical properties and the most homogeneous microstructure was obtained. The density, flexural strength, volume resistivity, breakdown voltage and thermal expansion coefficient are 99.1% of TD, 128.0?±?2.2?MPa, 9.8?×?10¹⁶ Ω?cm, 45.2?kV/mm and 7.6?×?10^?6 °C^?1, respectively. Precursor reaction mechanism is deduced that aluminum powders react with oxygen donor alcohol to form aluminum alkoxide with the catalyst iodine, and then react with acetic acid to form crystal C₄H₇AlO₇ precipitates. Nonaqueous precipitation method is expected to become a promising candidate for mass production of alumina powders.     

Kristallstrukturuntersuchungen an Fettalkoholen und Fettsäuren mit Elektronen- und Röntgenbeugung I

Studies on Crystal Structures of Fatty Alcohols and Fatty Acids Using Electron and X-Ray Diffraction I For the homologous series of even numbered saturated fatty alcohols from dodecanol (C₁₂H₂₅OH) up to hexacosanol (C₂₆H₅₃OH) the almost orthorhombic unit cells of the β₀₁-modifications could be shown by using electron and X-ray diffraction. Fouriersynthesis based on hkO-reflexes showed the presence of a β₀₂-form which has half the edge length c compared to the β₀₁-modification. Moreover, the eight γ₃- to γ₁₀-modifications of the various alcohols were detected. Unit cell parameters and the chain tilt were determined for all crystal structures. By X-ray diffraction, stearic acid was shown to exhibit five β_n-(n = 2, 4, 5, 8) and seven γ₂- to γ₈-forms. The β_n-forms consist of molecules tilted over the short subcell a_s-axis, whereas in γ_n-forms the molecular chains are tilted over the b_s-axis. All the modifications of alcohols and fatty acids studied have an orthorhombic subcell, while the neighbouring molecules in monomolecular layers are turned to each other at an angle of about 90°.     

Synthesis and formation mechanism of high-purity Ti3AlC2 powders by microwave sintering

High-purity titanium aluminum carbide (Ti₃AlC₂) powders were synthesized by a microwave sintering method using different titanium sources as raw materials. The prepared products were characterized by differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results indicated that the synthesized Ti₃AlC₂ powders have high purity (97.5%) and even distribution of the grain size when using a 3TiH₂/1.2Al/2C mixture as raw materials when the microwave sintering temperature and time were 1300°C and 30 minutes, respectively. The formation mechanism of the Ti₃AlC₂ is described as proceeding via four stages. The solid-phase reaction between titanium and aluminum occurs below the melting point of aluminum and the main product is a Ti₃Al phase, which is an observed intermediate compound for the formation of Ti₂AlC and Ti₃AlC₂. Thus, this study provides a beneficial approach to low-temperature synthesis of high-purity Ti₃AlC₂ materials.     

A novel way to production yttrium glass microspheres for medical applications

In this paper a novel method of producing yttrium aluminum silicate microspheres is reported. Yttrium aluminum silicate microspheres around 20–50 μm in size were obtained when an aqueous solution of Y(NO₃)₃ and Al(NO₃)₃ was added to tetraethyl orthosilicate (TEOS) and pumped into stirred silicone oil. The particles produced by this method are regularly shaped and very close to spherical. The amorphous structure, Y-O-Si bonds, spherical shapes, composition, and element distribution were investigated by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray fluorescence spectroscopy (XRF), carbon/sulfur analysis, and SEM/EDS mapping analysis. The results obtained demonstrate that the silicone oil spheroidization method is suitable for the production of yttrium aluminum silicate microspheres. This study also reveals that a high temperature is not required for the production of yttrium aluminum silicate microspheres.     

Physical properties of V-doped TiO2 nanoparticles synthesized by sonochemical-assisted process

V-doped TiO₂ nanoparticles were synthesized by sonochemical process using titanium isopropoxide as a titanium source, vanadyl acetylacetonate as a dopant source. Sonication was conducted using sonic horn operated at 20 kHz for 20 min until the completely precipitated product was reached. The as-synthesized precipitates with various vanadium dopant (1–5 mol %) were calcined at 500–1000 °C for 4 h. The relevant physical properties of the nanoparticles were characterized by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and transmission electron microscope (TEM). The anatase phase TiO₂ nanoparticles can be synthesized by sonochemical process. Post calcinations process results in the anatase-to-rutile phase transformation and the enhancement in crystallinity with increasing temperature. The results also indicate good incorporation of V ions in TiO₂ lattices and significant effect of V dopant on alternation of interplanar spacing of TiO₂.     

Preparation of Ag@AgI-intercalated K4Nb6O17 composite and enhanced photocatalytic degradation of Rhodamine B under visible light

In this study, a novel plasmonic photocatalyst, Ag@AgI intercalated layered niobate, was synthesized via a microwave-assisted ion-exchange method. The composite materials prepared were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray fluorescence spectrometry (XRF), Brunauer–Emmett–Teller (BET) and ultraviolet–visible diffuse reflection spectra (UV–vis). The as-prepared plasmonic photocatalyst exhibited an enhanced and stable photocatalytic performance for the degradation of Rhodamine B (RhB) and up to 83% of RhB was degraded in 40 min under visible light irradiation. The mechanism of separation of the photo-generated electrons and holes at the K₄Nb₆O₁₇/Ag@AgI composite was discussed.     

Cd speciation in biomass fly ash particles after size separation by centrifugal SPLITT

The finest particle size fractions (≤25 μm) in four fly ash samples from fluidised bed combustion of three biomass based fuels and a municipal solid waste fuel were size separated using a centrifugal SPLITT fractionation cell. The ashes were separated into different size fractions and the cadmium concentration, partition and speciation in each separated fraction were then investigated in relation to their possible leaching.The fractionation was evaluated by environmental scanning electron microscopy, which also provided indications of the associations between Cd and other main elements on the particles through the use of X-ray fluorescence mapping. The total concentration of Cd in each fraction was determined by AAS analysis which showed different dependences on the ash particle size in the case of biomass or waste fuels. In addition, the speciation of Cd in each fraction, investigated by sequential chemical extractions and X-ray powder diffraction analysis, showed Cd to be present mainly as non-easy leachable forms, i.e. oxide and silicates. A readily leachable fraction was found only in the municipal solid waste fly ashes.     

Growth of TiO2-based nanotubes on Ti–6Al–4V alloy

The possibility of tailoring titania nanotube films on Ti–6Al–4V alloy is investigated using electrolytes based on NH₄H₂PO₄ with the addition of different concentrations of NH₄F. Several morphologies from high aspect ratio nanotubes to barrier layers are achieved by the control of the electrolyte composition, regarding its pH and fluoride concentrations. The morphology and composition of the anodic layers were evaluated by scanning and transmission electron microscopy, Rutherford backscattering spectroscopy (RBS) and Wavelength dispersive X-ray fluorescence spectroscopy.The formation efficiency and the fluoride ions content in the nanotubes depend on the F concentration in the electrolyte. The higher concentration of fluoride ions in the electrolyte promotes an increase of the F incorporated in the nanotubes, about 12 at.% but, reduces the nanotube formation efficiency. However, no significant presence of phosphorus was detected into the films by means of the above-mentioned analytical techniques.     

Phase Constitution and Dynamic Properties of Spark Plasma‐Sintered Alumina–Titanium Composites

Al₂O₃/Ti composites of various metal to ceramic ratios were fabricated by the spark plasma sintering (SPS) technique. The effects of titanium concentration in the initial mixture on phase composition, and on the static and dynamic (planar impact testing) mechanical properties of the SPS‐processed composites were investigated. It was observed that the significant alumina dissolution in titanium takes place during SPS treatment. The composites fabricated from starting alumina/titanium powder mixtures with a mass fraction of titanium less than 0.8 consisted of two phases, alumina and a solid solution of oxygen and aluminum in titanium. For starting mixtures with higher titanium content, the presence of a Ti₃Al intermetallic phase with a relatively low fraction of dissolved oxygen was detected. Changes in phase composition could explain the effect of titanium content in the starting mixture on physical and mechanical properties of the composites. Mechanisms governing the dynamic response of the composites under loading of different intensities are discussed.     

Degradation of alumina refractory bricks by sintering Mn low-alloy steels

The economic importance of the corrosion and wear of refractory materials is indisputable because these processes determine the viability of any high-temperature liner used in metallurgical processes. The degradation mechanism of lining materials (refractory bricks) in contact with corrosive gases can be studied by examining the penetration rate or the chemical corrosion that results from the circulation of the atmosphere over the refractory material (by diffusional and convective transport). During the sintering of steel containing Mn, the high vapour pressure of Mn enables its sublimation during thermal cycling; therefore, Mn is incorporated into the sintering atmosphere. Although the diffusion of Mn in steel samples is beneficial, the presence of Mn in a sintering atmosphere can modify the composition of refractory components. As a result of atmosphere-refractory interactions, a new phase is formed. In this study, the changes in refractory materials as a function of exposure time to atmospheres containing Mn_(g) at the most common sintering temperature, 1120 °C, were investigated. The microstructural changes in the refractory materials and the consequences of the presence of Mn_(g) were analysed using optical microscopy, electron microscopy with X-ray (EDS) microanalysis, X-ray diffraction, and X-ray fluorescence (XRF).     

Reinforcing effect of multi-walled carbon nanotubes on microstructure and mechanical behavior of AA5052 composites assisted by in-situ TiC particles

In this research, the synergistic effects of multi-walled carbon nanotubes and in-situ synthesized titanium carbide (TiC) on the mechanical performance of aluminum hybrid composites were studied. The microstructural characterization involving the influence of both titanium carbide and carbon nanotubes was investigated. The reinforcing effects of both titanium carbide and multi-walled carbon nanotubes on the micro-hardness, tensile strength, and impact strength of the composites were also investigated. The microstructures of the fractured tensile and impact test surfaces were examined through FESEM (Field Emission Scanning Electron Microscope). Clear peaks of titanium carbide (TiC) and aluminum carbide (Al₄C₃) were observed in the X-Ray Diffraction (XRD) analysis. The micro-hardness of the aluminum composites was significantly improved after the reinforcement with CNT and TiC. The highest ultimate tensile strength and yield strength were found with Al–9%TiC-1%MWCNT and are equal to 206.44 MPa and 136.15 MPa, respectively, whereas a 16% decrease in the impact strength of Al–9%TiC-1%MWCNT was witnessed when compared to base alloy. The effects, such as CNT pull-out, CNT bridging was seen from tensile fractography of the composites. Further, the crack initiation from the pull-out cavity was also assumed to affect the fracture mechanism. Cleavage facets were associated both with the impact and tensile fracture surfaces of the composites. With the superior mechanical properties obtained, the aluminum hybrid composite can be replaced for different structural applications.     

Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@SiO<Subscript>2</Subscript>@TiO<Subscript>2</Subscript>-OSO<Subscript>3</Subscript>H: an efficient hierarchical nanocatalyst for the organic quinazolines syntheses

A sulfonic acid functionalized titanium dioxide quasi-superparamagnetic nanocatalyst Fe₃O₄@SiO₂@TiO₂-OSO₃H with average size of 61 nm and semispherical shape with surface area about 97 m² g^?1 with saturation magnetization 17.7 emu g^?1 and the coercivity 9.84 Oe was successfully synthesized. The structure and morphology of the nanocatalyst was characterized by Fourier transform infrared spectroscopy (FT-IR), energy-dispersive X-ray spectroscopy, X-ray diffraction pattern, transmission electron microscopy, field-emission scanning electron microscopy, vibrating sample magnetometer and Brunauer–Emmett–Teller surface area analysis. The catalytic usage of the nanocatalyst was exemplified in synthesis of 2,3-dihydroquinazolin-4(1H)-one and spiroquinazolin-4(3H)-one derivatives in deep eutectic solvents (DESs) based on choline chloride and urea. We suggest that the synergistic effects in catalytic activities of titanium dioxide, organic acid and the CO₂ capture property of DES are the main reasons for the improvement of catalytic activity. The synthesized spiroquinazolinones and dihydroquinazolinones derivatives were characterized by FT-IR, ¹H and ¹³C nuclear magnetic resonance spectroscopy. The magnetic nanocatalyst exhibit high catalytic activity and can be simply separated from reaction media by an external magnet in a few seconds and could be reused for six cycles without significant loos in activity, which indicates the good immobilization of sulfonic acid on the magnetic titanium dioxide support. Furthermore, the solvent which has been used in this work can be readily isolated and reused for several times.     

Nascent morphology of syndiotactic polystyrene synthesized over silica-supported metallocene catalyst

The nascent morphology of semi-crystalline syndiotactic polystyrene (sPS) polymerized over silica-supported pentamethyl cyclopentadienyl titanium trimethoxide (Cp^∗Ti(OCH₃)₃) catalyst in a liquid slurry polymerization has been investigated under various reaction conditions. The scanning electron microscopic analysis of nascent polymers reveals that sPS molecules grow as long nanofibrils of 30-50 nm diameter and X-ray diffraction analysis shows the co-crystalline phases including both sPS and low molecular weight guest molecules of monomer and diluent. The energy dispersive X-ray spectroscopy also shows that the disintegration of silica primary particles occurs during the polymerization as evidenced by the uniform dispersion of silicon and aluminum in a polymer particle. The fibrous growth of the polymer inside a polymer particle leads to the shape replication of the original silica particles.     

Post-mortem analysis of alumina-magnesia-carbon refractory bricks used in steelmaking ladles

Post-mortem studies in secondary steelmaking ladles are an important way to determine the factors related to Alumina-Magnesia-Carbon (AMC) refractory corrosion. AMC refractory bricks installed in the impact zone of a steelmaking ladle bottom were analyzed after 100 castings. X-ray diffraction, X-ray fluorescence chemical analysis, reflected optical light microscopy, scanning electron microscopy, energy dispersive X-ray spectrometry, density and porosity measurements, and mercury porosimetry were used to analyze the chemical and physical characteristics of the slag, the unused refractory and the slag+steel attacked bricks. The corrosion process produced a specific microstructure characterized by: i) a thick discontinuous slag layer composed by secondary spinel+steel+liquid; ii) a thick dense, cracked, and continuous layer consisting of calcium aluminates+steel+liquid at the slag/refractory interface; iii) next to this layer, a wide densified layer with a uniform microstructure in which corundum aggregates and spinel crystals were linked together by elongated CaAl₁₂O₁₉ crystals.The formation of these reaction layers constituted a barrier that effectively suppressed the massive slag penetration and surely reduced the wear rate. Thermodynamic calculations based on simplified and complex condensed phase equilibrium diagrams, were used to further understanding of the corrosion mechanism.     

High Rate Anodic Dissolution of 100Cr6 Steel in Aqueous NaNO 3 Solution

The high rate anodic dissolution of 100Cr6 steel in NaNO₃ electrolytes of various concentrations and at different temperatures was investigated. Galvanostatic flow channel experiments were used to examine the current efficiency of the steel substrate. Below 6 A cm^–2(zone A), oxygen evolution dominates, while at higher current densities iron dissolution prevails (zone C). Potentiodynamic polarization studies indicated a complete substrate surface passivation up to +1.8V (vs NHE), and periodic fluctuations of the current density at higher anode potentials (> +1.8 V) due to severe oxygen evolution. Rotating cylinder measurements served for polarization studies at lower current densities in the region of dominating oxygen evolution. Scanning electron micrographs revealed a correlation between the current efficiency and the coverage of the substrate surface with an electronically conductive film at current densities of 2, 9 and 20 A cm^–2. The microstructure of the black, solid surface film developing during the high rate anodic dissolution of the steel was found to be heterogeneous and very porous. The main film components, as determined by X-ray diffraction and Auger electron spectroscopical measurements, were amorphous iron oxides, Fe _x O _y , and inert carbides, M₃C, originating from the steel matrix. An activation–repassivation process is proposed, which is responsible for the development of the complex multilayer (multiphase) structure observed at the steel substrate surface.     

Reactive Processing of a ZrB2 / ZrC / Zr–Si Ceramic Composite with a Controlled Oxygen Potential

A Zr–Si liquid reacted with B₄C in a graphite enclosure was configured to control the oxygen potential (10^?45 kPa) to form a ZrB₂ / ZrC / Zr – Si ceramic composite. The graphite enclosure was placed in a temperature gradient with the hot zone at >2133 K to react Zr – Si with B₄C and with the opposite end approximating 933–1000 K at the position of an aluminum melt. A ZrB₂ / ZrC / Zr – Si composite forms with the scanning‐electron microscope (SEM), microstructures showing rectangular ZrB₂ precipitates and hexagonally shaped ZrC precipitates embedded in a Zr – Si matrix.     

PLGA–TiO2 as a Carrier System for Drug Release

This paper reports the results of the PLGA–TiO₂ nanocomposite regarding the green synthesis of titanium dioxide nanoparticles using a natural extract, its characterization, and encapsulation with poly(lactic-co-glycolic acid) (PLGA). UV–visible spectrometry was used for the identification of terpenes present in the extracts. The morphology of the nanoparticles was determined by scanning electron microscopy. Infrared spectroscopy was used for the determination of functional groups, while X-ray diffraction was used to determine the crystal structure. The analysis of the extended release of the encapsulated extract in the matrix of the nanomaterial resulted in a maximum visible UV absorbance at approximately 260 nm and confirmed the synthesis of titanium dioxide nanoparticles. Moreover, terpenes enhance synthesis and stabilize titanium dioxide nanoparticles. The synthesized structures are spherical and amorphous, 44 nm in size, and encapsulated at 65 nm.     

掺铁二氧化钛纳米晶的制备及其光催化性能

通过溶胶-凝胶法室温制备了掺杂铁二氧化钛纳米晶光催化剂。采用透射电子显微镜、X射线衍射仪、能谱元素分析仪、紫外-可见分光光度计等对所得产物进行表征。以甲基橙为目标降解物,对未掺杂的二氧化钛纳米晶及掺杂铁的二氧化钛纳米晶进行了光催化降解性能研究,并对其降解机理进行了分析。结果表明:适量的铁掺杂有利于提高二氧化钛纳米晶的光催化性能和对甲基橙的降解率。铁的最佳掺杂量为25%[Fe占(Ti+Fe)的摩尔分数]。掺杂铁的二氧化钛纳米晶光催化性能优于纯二氧化钛纳米晶,在光照150min后,甲基橙的降解率达75%以上。     

Densification and grain growth of CuO-doped Pr6O11 varistors

The effect of CuO doping on the microstructure and electrical properties of Pr₆O₁₁ varistors was investigated. Samples were prepared by conventional ceramic techniques, and were sintered at 1150 °C in air for 2 h. The microstructure was investigated by scanning electron microscopy (SEM). The phases and chemical composition were analyzed by X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). The results indicated that CuO can promote the densification of the Pr₆O₁₁-based varistors to 95.8% of the theoretical density. CuO forms a solid solution with Pr₆O₁₁ up to 0.5 mol%, above which Pr₂CuO₄ precipitates in the grain boundary. From the I–V measurements, minor CuO doping can improve the nonlinear electrical properties. A further increase in CuO content induces a reduction in the nonlinear electrical properties due to the consumption of absorbed oxygen on the grain surfaces.