Microwave hydrothermal synthesis and characterization of rare-earth stannate nanoparticles

Rare-earth stannate (Ln₂Sn₂O₇ (Ln=Y, La-Lu)) nanocrystals with an average diameter of 50 nm were prepared through a facile microwave hydrothermal method at 200℃ within 60 min. The products were well characterized. The effect of reaction parameters such as temperature, reaction time, pH value, and alkali source on the preparation was investigated. The results revealed that the pH value plays an important role in the formation process of gadolinium stannate (Gd₂Sn₂O₇) nanoparticles. By contrast, the alkali source had no effect on the phase composition or morphology of the final product. Uniform and sphere-like nanoparticles with an average size of approximately 50 nm were obtained at the pH value of 11.5. A possible formation mechanism was briefly proposed. Gd₂Sn₂O₇:Eu3+ nanoparticles displayed strong orange-red emission. Magnetic measurements revealed that Gd₂Sn₂O₇ nanoparticles were paramagnetic. The other rare-earth stannate Ln₂Sn₂O₇ (Ln=Y, La-Lu) nanocrystals were prepared by similar approaches.     

Sol-gel preparation and characterization of Co3O4 nanocrystals

A new citrate acid-hydrazine sol-gel route for preparation of Co₃O₄ nanoparticles has been developed. Co₃O₄ nanoparticles with different particle-sizes and morphology were prepared at different heat-treatment temperatures and the pure cubic nanocrystals of Co₃O₄ were obtained at 600℃. The synthesis process was monitored by infrared spectroscopy (IR), thermal gravimetric and differential thermal analysis (TG-DTA). The structure and morphology of Co₃O₄ nanocrystals were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and X-ray-photoelectron spectroscopy (XPS). The infrared absorption bands blue-shifted with particle size decreasing, which could be attributed to increasing surface effect. XPS results showed that predominant species at surface layers of Co₃O₄ nanocrystals are octahedral Co (Ⅲ).     

Influence of chemical liquids on the fatigue crack growth of the AZ31 magnesium alloy

The fatigue crack growth behavior of an AZ31 magnesium alloy was investigated by comparing the effect of zirconate and phosphate chemical liquids. The morphology, components, and phase compositions of the chemical depositions at the fatigue crack tip were analyzed by employing scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD), respectively. For samples with and without the chemical liquids, their stress-intensity factor values at the fatigue crack tip were compared by using a stress-strain gauge. The results demonstrated that a zirconate film (Zr_xO_y·Zn_xO_y) and a phosphate film (Zn₃(PO₄)₂·4H₂O and MgZnP₂O₇) could be formed on the fatigue crack-surface at the fatigue crack tip. The stress distribution was changed because of the chemical depositions and the causticity of the chemical liquids. This could decrease the stress-intensity factor value and thus effectively cause fatigue crack closure, which reduces the fatigue crack growth rate. Moreover, it was found that the fatigue crack closure effect of zirconates was more positive than that of phosphates.     

核壳式磁性微球催化的Knoevenagel反应

Fe₃O₄@SiO₂-NH₂-CMC magnetic nanoparticles(MNPs) could be prepared by covalent modification method via the modification of sodium carboxymethyl cellulose (CMC). IR spectra could be used for the determination of Fe₃O₄@SiO₂-NH₂, Fe₃O₄@SiO₂-NH₂-CMC, Fe₃O₄@SiO₂-NH₂-CMC/MOF5, and Fe₃O₄@SiO₂-NH₂-CMC/IRMOF3 nanoparticles. The results showed that the polysaccharide modification and core-shell modification were successful. Knoevenagel condensation experiments exhibited that, as forFe₃O₄@SiO₂-NH₂-CMC/IRMOF3, the best conversion rate could be obtained.     

Influence of bath composition on the electrodeposition of cobalt-molybdenum amorphous alloy thin films

Cobalt-molybdenum (Co-Mo) amorphous alloy thin films were deposited on copper substrates by the electrochemical method at pH 4.0. Among the experimental electrodeposition parameters,only the concentration ratio of molybdate to cobalt ions ([MoO₄2-]/[Co2+]) was varied to analyze its influence on the mechanism of induced cobalt-molybdenum codeposition. Voltammetry was one of the main techniques,which was used to examine the voltammetric response,revealing that cobalt-molybdenum codeposition depended on the nature of the species in solution. To correlate the type of the film to the electrochemical response,various cobalt-molybdenum alloy thin films obtained from different [MoO₄2-]/[Co2+] solutions were tested. Crack-free homogeneous films could be easily obtained from the low molybdate concentrations ([MoO₄2-]/[Co2+]≈0.05) applying low deposition potentials. Moreover,the content of molybdenum up to 30wt% could be obtained from high molybdate concentration; in this case,the films showed cracks. The formation of these cracked films could be predicted from the observed distortions in the curves of electric current-time (j-t) deposition transients. The films with amorphous structure were obtained. The hysteresis loops suggested that the easily magnetized axis was parallel to the surface of the films. A saturation magnetization of 137 emu·g-1 and a coercivity of 87 Oe of the film were obtained when the deposition potential was -1025mV,and [ MoO₄2-]/[Co2+] was 0.05 in solution,which exhibited a nicer soft-magnetic response.     

Cost-effective integrated strategy for the fabrication of hard-magnet barium hexaferrite powders from low-grade barite ore

Ultrafine barium hexaferrite (BaFe₁₂O₁₉) powders were synthesized from the metallurgical extracts of low-grade Egyptian barite ore via a co-precipitation route. Hydrometallurgical treatment of barite ore was systematically studied to achieve the maximum dissolution efficiency of Fe (~99.7%) under the optimum conditions. The hexaferrite precursors were obtained by the co-precipitation of BaS produced by the reduction of barite ore with carbon at 1273 K and then dissolved in diluted HCl and FeCl₃ solution at pH 10 using NaOH as a base; the product was then annealed at 1273 K in an open atmosphere. The effect of Fe3+/Ba2+ molar ratio and the addition of hydrogen peroxide (H₂O₂) on the phase structure, crystallite size, morphology, and magnetic properties were investigated by X-ray diffraction, scanning electron microscopy, and vibrating sample magnetometry. Single-phase BaFe₁₂O₁₉ powder was obtained at an Fe3+/Ba2+ molar ratio of 8.00. The formed powders exhibited a hexagonal platelet-like structure. Good maximum magnetization (48.3 A·m2·kg–1) was achieved in the material prepared at an Fe3+/Ba2+ molar ratio of 8.0 in the presence of 5% H₂O₂ as an oxidizer and at 1273 K because of the formation of a uniform, hexagonal-shaped structure.     

Effect of Some Additives on the Microstructure and Properties of Andalusite-cordierite Refractory

The effect of some additives on the microstructure and properties of andalusite-cordierite refractory is concerned with. A study has been made on Al₂O₃, Cr₂O₃ and SiC powders, which are selected as additives and added respectively to the standard formulation in varying amounts as extra content (2%, 4%, or 6%). As the results indicate, Al₂O₃ (best at 4%) and SiC (best at 2%) can improve the microstructure and the properties of the material.But Cr₂O₃ shows the effect to the contrary.     

Synthesis and characterization of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> prepared from atmospheric pressure acid leach liquors of nickel laterite ores

A chemical precipitation-thermal decomposition method was developed to synthesize Co₃O₄ nanoparticles using cobalt liquor obtained from the atmospheric pressure acid leaching process of nickel laterite ores. The effects of the precursor reaction temperature, the concentration of Co2+, and the calcination temperature on the specific surface area, morphology, and the electrochemical behavior of the obtained Co₃O₄ particles were investigated. The precursor basic cobaltous carbonate and cobaltosic oxide products were characterized and analyzed by Fourier transform infrared spectroscopy, thermogravimetric differential thermal analysis, X-ray diffraction, field-emission scanning electron microscopy, specific surface area analysis, and electrochemical analysis. The results indicate that the specific surface area of the Co₃O₄ particles with a diameter of 30 nm, which were obtained under the optimum conditions of a precursor reaction temperature of 30℃, 0.25 mol/L Co2+, and a calcination temperature of 350℃, was 48.89 m2/g. Electrodes fabricated using Co₃O₄ nanoparticles exhibited good electrochemical properties, with a specific capacitance of 216.3 F/g at a scan rate of 100 mV/s.     

Effect of main inclusions on crack initiation in bearing steel in the very high cycle fatigue regime

This work aims to investigate the effect of main inclusions on crack initiation in bearing steel in the very high cycle fatigue (VHCF) regime. The size and type of inclusions in the steel were quantitatively analyzed, and VHCF tests were performed. Some fatigue cracks were found to be initiated in the gaps between inclusions (Al₂O₃, MgO-Al₂O₃) and the matrix, while other cracks originated from the interior of inclusions (TiN, MnS). To explain the related mechanism, the tessellated stresses between inclusions and the matrix were calculated and compared with the yield stress of the matrix. Results revealed that the inclusions could be classified into two types under VHCF; of these two, only one type could be regarded as holes. Findings in this research provide a better understanding of how inclusions affect the high cycle fatigue properties of bearing steel.     

Preparation, crystallization, and wetting of ZnO-Al2O3-B2O3-SiO2 glass-ceramics for sealing to Kovar

A novel type of ZnO-Al₂O₃-B₂O₃-SiO₂ glass-ceramics sealing to Kovar in electronic packaging was developed, whose thermal expansion coefficient and electrical resistance are 5.2×10-6/℃ and over 1×1013 Ω·cm, respectively. The major crystalline phases in the glass-ceramic seals were ZnAl₂O₄, ZnB₂O₄, and NaSiAl₂O₄. The dielectric resistance of the glass-ceramic could be remarkably enhanced through the control of alkali metal ions into crystal lattices. It was found that crystallization happened first on the surface of the sample, leaving the amorphous phase in the inner, which made the glass suitable for sealing. The glass-ceramic showed better wetting on the Kovar surface, and sealing atmosphere and temperature had great effect on the wetting angle. Strong interracial bonding was obtained, which was mainly attributed to the interracial reaction between SiO₂ and FeO or Fe₃O₄.     

Cleanliness of Ti-bearing Al-killed ultra-low-carbon steel during different heating processes

During the production of Ti-bearing Al-killed ultra-low-carbon (ULC) steel, two different heating processes were used when the converter tapping temperature or the molten steel temperature in the Ruhrstahl-Heraeus (RH) process was low:heating by Al addition during the RH decarburization process and final deoxidation at the end of the RH decarburization process (process-I), and increasing the oxygen content at the end of RH decarburization, heating and final deoxidation by one-time Al addition (process-Ⅱ). Temperature increases of 10℃ by different processes were studied; the results showed that the two heating processes could achieve the same heating effect. The T.[O] content in the slab and the refining process was better controlled by process-I than by process-Ⅱ. Statistical analysis of inclusions showed that the numbers of inclusions in the slab obtained by process-I were substantially less than those in the slab obtained by process-Ⅱ. For process-I, the Al₂O₃ inclusions produced by Al added to induce heating were substantially removed at the end of decarburization. The amounts of inclusions were substantially greater for process-Ⅱ than for process-I at different refining stages because of the higher dissolved oxygen concentration in process-Ⅱ. Industrial test results showed that process-I was more beneficial for improving the cleanliness of molten steel.     

Processes of depositing platinum on carbon nanotubes and their effect on performance of proton exchange membrane fuel cell

The ultrafine platinum nanoparticles deposited on the surfaces of carbon nanotubes (Pt/CNTs) were prepared by a chemical precipitation method and used as the catalyst of proton exchange membrane fuel cell. The depositing process parameters such as the solution pH value, Pt content and treatment temperature were analyzed. The experimental results show that the optimum process parameters to prepare Pt/CNTs are the solution pH value of 7.0, the theoretical Pt content of 25% (mass fraction) and the heating temperature of 500℃, under the conditions the best performance of the proton exchange membrane fuel cell can be obtained and its voltage can reach 580 mV at a current density of 500 mA/cm2.     

Preparation of CuInSe2 thin films by four-step process

A simple process for the deposition of CulnSe₂ thin films was described. The CulnSe₂ compound was prepared by selenization of Cu-In alloy precursors, which were electrodeposited at a constant current. The selenized precursors were compacted and then annealed. The films were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results indicate that single-phase CulnSe₂ is formed at 250℃ and its crystallinity of this phase is improved as the annealing temperature rises. The losses of In occur in selenization process. The dense CulnSe₂ film with comparatively smooth surface can be obtained by compaction under the pressure of 200 MPa.     

Synthesis and characterization of ceria nanoparticles by complex-precipitation route

Ceria(CeO₂)nanoparticles were successfully synthesized via a simple complex-precipitation route that employs cerium chloride as cerium source and citric acid as precipitant.The elemental analysis results of carbon,hydrogen,oxygen,and cerium in the precursors were calculated,and the results revealed that the precursors were composed of Ce(OH)₃,Ce(H₂Cit)₃,or CeCit.X-ray diffraction analysis showed that all ceria nanoparticles had a face-centered cubic structure.With the molar ratio of citric acid to Ce³+(n)of 0.25 and pH of 5.5,the specific surface area of the sample reached the maximum value of 83.17 m²/g.Ceria nanoparticles were observed by scanning electron microscopy.Selected area electron diffraction patterns of several samples were obtained by transmission electron microscopy,and the crystal plane spacing of each low-exponent crystal plane was calculated.The ultraviolet(UV)–visible transmittance curve showed that ceria can absorb UV light and pass through visible light.Among all samples,the minimum average transmittance of ultraviolet radiation a(UVA)was 4.42%,and that of ultraviolet radiation b(UVB)was 1.56%.     

Effectiveness of sodium silicate as gangue depressants in iron ore slimes flotation

The recovery of iron from the screw classifier overflow slimes by direct flotation was studied. The relative effectiveness of sodium silicates with different silica-to-soda mole ratios as depressants for silica and silicate bearing minerals was investigated. Silica-to-soda mole ratio and silicate dosage were found to have significant effect on the separation efficiency. The results show that an increase of Fe content in the concentrate is observed with concomitant reduction in SiO₂ and Al₂O₃ levels when a particular type of sodium silicate at a proper dosage is used. The concentrate of 58.89wt% Fe, 4.68wt% SiO₂, and 5.28wt% Al₂O₃ with the weight recovery of 38.74% and the metal recovery of 41.13% can be obtained from the iron ore slimes with 54.44wt% Fe, 6.72wt% SiO₂, and 6.80wt% Al₂O₃, when Na₂SiO₃ with a silica-to-soda mole ratio of 2.19 is used as a depressant at a feed rate of 0.2 kg/t.     

Structure characteristics and electrochemical properties of LiMn2O4 modified by LiCoO2

In order to improve the cycle performance of LiMn₂O₄, the modified LiMn₂O₄ was prepared by solid-state reactions using LiMn₂O₄ and LiCoO₂ as precursors. XRD and EDS were used to study the structure properties of the modified LiMn₂O₄. The electrochemical properties of the modified LiMn₂O₄ were also investigated. The results show that Li and Co atoms could insert into the LiMn₂O₄ crystal lattice and a newly formed spinel phase, modified LiMn₂O₄ was obtained. The modified LiMn₂O₄ exhibits excellent cycle ability at room and elevated temperatures compared to pure LiMn₂O₄. The improved electrochemical stability of the modified LiMn₂O₄ attributes to the entrance of Li and Co ions inserted into the spinel crystal structure.     

Effect of different additives on the properties of lithium alanate

LiAIH₄ doped with Ni and Ce(SO₄)₂ additives and the effect of doping on temperature and hydrogen release were studied by pressure-content-temperature (PCT) experiment and X-ray diffraction (XRD) analysis. It is indicated that doping with Ni induces a significant decrease in temperature in the first step and LiAlH₄ doped with 1mol% Ni presents the most absorption of hydrogen. Doping with Ce(SO₄)₂ also causes a marked decrease, while the amount of hydrogen release changes only slightly. The results from X-ray diffraction analysis show that doping does not cause any structural change; Ni and Ce-containing phases are not observed at room temoerature or even at 250℃.     

Influence of calcium content on solid ratio of inclusions in Ca-treated liquid steel

It has been found that Ca-treated liquid steel can be cast at a lower superheat. To ascertain the reason for the improved castability of Ca-treated liquid steel and to find the optimal range of calcium content, the behavior of calcium in liquid steel was studied in terms of the relationship between the calcium content and solid ratio of inclusions. The relationship between the calcium content and solid ratio of inclusions was obtained by means of the classification of nonmetallic inclusions in solid and liquid steels at casting temperature according to the Al₂O₃-CaO-SiO₂ phase diagram. The optimum calcium content should be 17-23 ppm.     

钙热还原碳化硼制备硼化钙粉末

The method of calciothermic reduction of B₄C was proposed for preparing CaB₆. The phase transition and morphology evolution during the reaction were investigated in detail. The experimental results reveal that Ca first reacts with B₄C to generate CaB₂C₂ and CaB₆ at a low temperature and that the CaB₂C₂ subsequently reacts with Ca to produce CaB₆ and CaC₂ at a high temperature. After the products were leached to remove the byproduct CaC₂, pure CaB₆ was obtained. The grain size of the prepared CaB₆ was 2–3 μm, whereas its particle size was 4–13 μm; it inherited the particle size of B4C. The residual C content of the product was decreased to 1.03wt% after the first reaction at 1173 K for 4 h and the second reaction at 1623 K for 4 h.     

Effect of cooling rate on the crystallization behavior of perovskite in high titanium-bearing blast furnace slag

The effect of cooling rate on the crystallization of perovskite in high Ti-bearing blast furnace (BF) slag was studied using confocal scanning laser microscopy (CSLM). Results showed that perovskite was the primary phase formed during the cooling of slag. On the slag surface, the growth of perovskite proceeded via the successive production of quasi-particles along straight lines, which further extended in certain directions. The morphology and structure of perovskite was found to vary as a function of cooling rate. At cooling rates of 10 and 30 K/min, the dendritic arms of perovskite crossed obliquely, while they were orthogonal at a cooling rate of 20 K/min and hexagonal at cooling rates of 40 and 50 K/min. These three crystal morphologies thus obtained at different cooling rates respectively corresponded to the orthorhombic, cubic and hexagonal crystal structures of perovskite. The observed change in the structure of perovskite could probably be attributed to the deficiency of O2?, when Ti₂O₃ was involved in the formation of perovskite.