Role of Nanocrystalline Spinel Additive on the Properties of Low Cement Castable Refractories

Hydrated magnesium aluminate gel prepared via a cost-competent sol-gel route has been found to retain nanocrystals after optimum thermal treatment. The reactive gel-derived powder incorporated to the matrix of a high alumina based refractory castable upgraded its physical properties as revealed from the laboratory scale results. The performance of sol-gel spinel is better than coprecipitated spinel and almost comparable to presintered spinel powders popularly utilized by the refractory manufacturers. Attempts have been made to evaluate and analyze the better slag corrosion and thermal shock resistance properties of spinel-bonded castable by the nanocrystalline feature of the sol gel spinel. SEM, TEM, SAED, XRD, IR, and the physical properties of selected samples have been studied to understand the characteristics of the respective refractory materials.     

热水解法制备Fe2O3纳米粒子及其在Si表面的分散

用快速热水解的方法,制备直径小于10 nm的单分散Fe(OH)3胶体粒子。X射线衍射(XRD)和透射电镜(TEM)衍射分析表明:Fe(OH)3胶体粒子脱水后转变为Fe2O3纳米粒子。用离心分散的方法,胶体粒子在干燥过程中避免了团聚现象,实现其在Si表面的单层均匀分散覆盖。研究了胶体溶液浓度对胶体粒子尺寸及表面覆盖度的影响:改变胶体溶液的浓度,可以调节胶体粒子在Si表面的覆盖度,但对胶体粒子尺寸的影响不明显。     

Facile Synthesis of Bimetallic Au@Pd Nanoparticles with Core-shell Structures on Graphene Nanosheets

In this paper, we report a simple one-step thermal reducing method for synthesis of bimetallic Au@Pd nanoparticles with core-shell structures on the graphene surface. This new type of Au@Pd-G composites is characterized by transmission electron microscopy, high resolution transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction. It is found that Au@Pd nanoparticles with an average diameter of 11 nm are well dispersed on the graphene surface, and the Au core quantity as well as the Pd shell thickness can be quantitatively controlled by loading different amounts of metallic precursors, and the involved core-shell structure formation mechanism is also discussed. The ternary Pt/Au@Pd-G composites can also be synthetized by the subsequent Pt doping. The catalytic performance of Au@Pd-G composites toward methanol electro-oxidation in acidic media is investigated. The results show that Au@Pd-G composites exhibit higher catalytic activity, better stability and stronger tolerance to CO poisoning than Pd-G and Au-G counterparts.     

Effect of Yttrium Addition on Microstructural Characteristics and Superplastic Behavior of Friction Stir Processed ZK60 Alloy

As-extruded ZK60 and ZK60-Y magnesium alloy plates were successfully processed via friction stir processing （FSP） at a tool rotation rate of 1600 r/rain and a traverse speed of 200 mm/min. FSP resulted in the formation of equiaxed recrystallized microstructures with the average grain sizes of ,-8.5 and -4.7 μm in the ZK60 and ZK60-Y alloys, respectively. Moreover, FSP broke and dispersed the MgZn2 and W-phase （Mg3Zn3Y2） particles and dissolved MgZn2 phase in the FSP ZK60 alloy. With the addition of rare earth element yttrium （Y） into the ZK60 alloy, the ratio of the high angle grain boundaries （HAGBs） in the FSP alloys increased from 64% to 90%, and a certain amount of twins appeared in the FSP ZK60-Y alloy. The maximum elongation of 1200% and optimum strain rate of 3 X 10-3 s-1 achieved at 450 °C in the FSP ZK60-Y alloy were substantially higher than those of the FSP ZK60 alloy. This is attributed to the fine grains with high ratio of HAGBs and the distribution of a large number of dispersed second phase particles with high thermal stability in the FSP ZK60-Y alloy. Grain boundary sliding was identified as the primary deformation mechanism in the FSP ZK60 and ZK60-Y alloys from the superplastic data analyses and surficial morphology observations.     

Improvement of Ductility of Powder Metallurgy Titanium Alloys by Addition of Rare Earth Element

Ti-4.5Al-6.0Mo-1.5Fe, Ti-6Al-1Mo-1Fe and Ti-6Al-4V alloys were prepared by blended elemental powder metallurgy （PM） process, and the effects of Nd on the microstructures and mechanical properties were investigated by scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and X-ray diffraction （XRD）. It was found out that the addition of Nd increased the density of sintered titanium alloys slightly by a maximum increment of 1% because small amount of liquid phase occurred during sintering. The addition of Nd shows little effect on the improvement of tensile strength, while the elongation is significantly improved. For example, the elongation of Ti-4.SAl-6.0Mo-1.5Fe can be increased from 1% without addition of Nd to 13% at a Nd content of 1.2 wt pct.     

Thermal Diffusivity Determination of Protoporphyrin IX Solution Mixed with Gold Metallic Nanoparticles

Nanoparticles appear to be ideally suited for applications in targeted thermal effects in medical therapies and photothermally activated drug delivery; all depend critically on the thermal transport between the nanoparticles and the surrounding liquid. In this work thermal lens spectroscopy (TLS) was used to determine the thermal diffusivity of protoporphyrin IX (PpIX) solutions mixed with gold metallic nanoparticles. PpIX disodium salt (DS) was used in a HCl solution at 25%. Fluids containing gold (Au) nanoparticles at different concentrations were prepared and added to the PpIX solutions. For each solution, UV–Vis spectroscopy was used to obtain the optical absorption spectrum, and transmission electron microscopy (TEM) was used to obtain the gold nanoparticle size. From the TLS signal intensity, it was possible to determine the characteristic time constant of the transient thermal by fitting the theoretical expression to the experimental data. From this characteristic time, the thermal diffusivity was obtained for each solution. The results show that the thermal diffusivity of PpIX mixed with gold nanoparticles increases with an increase of the nanoparticle metallic concentration.     

Microstructure Control of Nanoporous Silica Thin Film Prepared by Sol-gel Process

Nanoporous silica films were prepared by sol-gel process with base, acid and base/acid two-step catalysis.Transmission electron microscope （TEM） and particle size analyzer were used to characterize the microstructure and the particle size distribution of the sols. Scanning electron microscopy （SEM）, atomic force microscopy （AFM） and spectroscopic ellipsometer were used to characterize the surface microstructure and the optical properties of the silica films. Stability of the sols during long-term storage was investigated. Moreover,the dispersion relation of the optical constants of the silica films, and the control of the microstructure and properties of the films by changing the catalysis conditions during sol-gel process were also discussed.     

Influence of Burner Scale‐up on Characteristics of Flame‐Synthesized Titania and Silica Nanoparticles

The influence of geometrically‐similar upscaling of a laboratory diffusion flame burner on the morphology, specific surface area and phase composition of titania and silica nanoparticles has been investigated. For these two materials systems, two flame configurations were studied using both a laboratory‐size and an upscaled burner. Independent of the burner size, smaller and more aggregated particles form in the double diffusion flame, while spherical particles result from the single diffusion flame. The titania and silica powders produced in the upscaled burner have a lower specific surface area and are less homogeneous, despite being synthesized at the same overall flame stoichiometry and gas outlet velocities as used with the laboratory burner. These results can be explained by the increase in flame height, which causes the residence time of the growing particles in the high‐temperature flame to increase. The larger single diffusion flame stems from the longer radial diffusion paths between the reactant gases in the upscaled burner.     

Novel approach to the synthesis of core-shell particles by sacrificial polymer shell method

In this work a new approach has been developed for the synthesis of SiO₂@Y₂O₃ particles with core-shell structure. The method is based on the synthesis of a covalently bonded sacrificial polymer shell grown onto silica particles. It is suitable to promote and stabilize the adsorption of different ions, namely Yttrium from its nitrate solution. After calcination and consequent elimination of the sacrificial polymer shell, the SiO₂@Y₂O₃ core-shell particles are obtained. Results reveal that the shell thickness of these core-shell particles is higher and more uniform than that of particles prepared without sacrificial polymer shell.     

Morphology Control and Optical Absorption Properties of Ag Nanoparticles by Ion Implantation

Ion implantation is a powerful method for fabricating nanoparticles in dielectric.For the actual application of nanoparticle composites,a careful control of nanoparticles has to be achieved.In this letter,the size,distribution and morphology of Ag nanoparticles are controlled by controlling the ion current density,ion implantation sequence and ion irradiation dose.Single layer Ag nanoparticles are formed by Ag+ion implantation at current density of 2.5μA/cm2.By Ag and Cu ions sequential implantation,the siz...     

分形理论在耐火纤维材料的导热特性研究中的应用

运用分形理论对多孔介质的几何结构进行描述，建立了耐火纤维材料的导热分形模型，并据此模型推导出其有效导热系数计算式；公式表明，耐火纤维材料的导热过程除了与气、固两相的物性和温度有关外，还与其体积分率以及孔隙分形维数有关。通过应用此计算式进行计算，得出了耐火纤维材料的有效导热系数计算值，而且计算结果与实验数据吻合得比较好，表明该导执模型计算式具有较高的表达精度。     

Effects of Na2O on the Thermal Shock Resistance of Aluminosilicate Refractory Ceramics

This report presents the results of an experimental study of the effects of Na₂O on the thermal shock resistance (number of cold shock cycles to failure) of aluminosilicate refractory ceramics. The addition of 4-6% mole is shown to improve the thermal shock resistance, which is characterized by the number of shock cycles to failure. The Na₂O changes the viscosity-temperature characteristics, and the glass transition temperatures in ways that enhance the crack-tip shielding due to viscoelastic/grain bridging mechanisms. The improved thermal shock resistance is attributed to the shielding effects of viscoelastic crack bridging by glassy phases between mullite platelets     

Fabrication of spiral-shaped microfluidic channels in glass by femtosecond laser

Long spiral-shaped microfluidic channels in glass have been fabricated by femtosecond laser direct writing. After hydrofluoric acid etching and post baking, the laser modified regions in glass formed hollow microstructures. The diameter size and the screw-pitch of the channels can be set freely. The experimental results showed that the etched internal surface of the microchannel by hydrofluoric acid will become smoother after the subsequent baking. The incident laser power and scanning speed can also influence the channel quality.     

纳米颗粒对氨水鼓泡吸收性能的强化实验

结合Danckwerts的界面更新模型,初步分析了纳米颗粒强化氨水鼓泡吸收过程的机理。改变不同的氨气流量和基液氨水浓度,进行了Al2O3纳米颗粒对氨水鼓泡吸收性能的强化实验。实验表明:Al2O3纳米颗粒对氨水鼓泡吸收性能具有强化效果;在实验条件下,加纳米颗粒的吸收效果最大可以达到没有加纳米颗粒的1.22倍;在保持其它条件一定时,随着氨气流量增加,溶液吸收率增加,但有效吸收率出现有增大也有减小的不规律特征,而随着基液氨水浓度的增加,有效吸收率增加比较明显。为研制小型氨水吸收式制冷机的鼓泡式吸收器提供参考。     

Synthesis and Magnetic Properties of Nanoparticles of Fe-Co Alloys and Their Oxides Prepared by Chemical Vapor Condensation

Nanoparticles of Fe-Co alloys and their oxides with the particle size below 20 nm were prepared by chemical vapor condensation process. The pure Ar, Ar+1%O2, Ar+3%O2 and Ar+6%O2 were used as carrier gases, with iron carbonyl and cobalt carbonyl as the precursors. XRD patterns showed that Fe-Co metallic nanoparticles were synthesized by using pure Ar as carrier gas, and only metal oxides were obtained using Ar+(>3)%O2 as carrier gas. The HRTEM images and TG-DTA curves were used to study the core-shell structure of the different nanoparticles. The nanoparticles obtained in pure Ar consist of black core and light shell with thickness of 2~4 nm. However, in the particles obtained in Ar+6%02, the oxides core with visible lattice fringes are surrounded by thin shell.