Modification of Nano-α-Al2O3 and Its Influence on the Surface Properties of Waterborne Polyurethane Resin Composite Passivation Films

Silane coupling agent KH560 was used to modify the surface of nano-α-Al2O3 in ethanol-aqueous solution with different proportions. The particle size of nano-α-Al2O3 was determined by nano-particle size analyzer, and the effects of nano-α-Al2O3 content, ethanol-aqueous solution ratio and KH560 dosage on the dispersion and particle size of nano-α-Al2O3 were investigated. The material structure before and after modification was determined by Fourier transform infrared spectroscopy (FTIR). Aqueous polyurethane resin and inorganic components are combined with modified nano-α-Al2O3 dispersion to form chromium-free passivation solution. The solution is coated on the galvanized sheet, the adhesion and surface hardness are tested, the bonding strength of the coating and the surface hardness of the substrate are discussed. The corrosion resistance and surface morphology of the matrix were investigated by electrochemical test, neutral salt spray test and scanning electron microscope test. The chromium-free passivation film formed after the modification of nano-α-Al2O3 increases the surface hardness of galvanized sheet by about 85%. The corrosion resistance of the film is better than that of a single polyurethane film. The results show that the surface hardness and corrosion resistance of polyurethane resin composite passivation film are significantly improved by the introduction of nano-α-Al2O3.

Performance Research of UPR/Al_2O_3 Composite Particles

UPR/Al2O3 composite particles were synthesized from unsaturated polyester resin(UPR) and nanometer/ultra-fine Al2O3 powders by means of suspension polymerization.The effects of Al2O3 with two different particle diameters on the density and hardness of the composite particles during the synthesis were studied.The results show UPR/Al2O3 composite particles synthesized by suspension polymerization are spherical,smooth,with a yield of 60%～75%(wt),and the particle diameters are 140～250μm;Al2O3 can effectively improves the density and hardness of the composite particles;when the contet is the same,effect of ultra-fine Al2O3 on the density and hardness of the composite particles is better than that of nanometer Al2O3;When the mass fraction of Al2O3 is 55%,the maximum hardness of ultra-fine Al2O3 composite particles and nanometer Al2O3 composite particles are 39.42HV and 25.66HV respectively.

Experimental and Theoretical Studies of CO2 Absorption Enhancement by Nano-Al203 and Carbon Nanotube Particles

The influence of nano-particles on CO2absorption was studied experimentally in a stirred thermostatic reactor.Nano-Al2O3and carbon nanotube(CNT) particles which showed different hydrophobic properties were chosen for the investigation.The experimental results were compared with that of micron-size activated carbon(AC)and Al2O3particles.From the results,no enhancement by micron-size Al2O3was found,and with the increase of Al2O3concentration,the enhancement factor decreased.However,nano-Al2O3showed a weak enhancement for the CO2absorption.AC and CNT particles all intensified the gas-liquid mass transfer effectively,yet the trend of the enhancement factor with stirring speed for the two particles was different.With increasing stirring speed,the enhancement factor of AC particles was decreased,whereas in CNT suspensions it was increased.The experimental phenomena demonstrated a difference in enhancement mechanism for different size particles.For nano-particles,besides the influence of adsorbability and hydrophobicity,the micro-convection caused by Brownian motion should be also taken into account.Considering the micro-convection effect,a theoretical model was developed to shed light on the absorption enhancement by nano-particles.

Aluminum matrix composites reinforced by in situ Al_2O_3 and Al_3Zr particles fabricated via magnetochemistry reaction

Aluminum matrix composites reinforced by in situ Al2O3 and Al3Zr particles are fabricated from A356-Zr(CO3)2 system via magnetochemistry reaction,and the morphologies,sizes and distributions of the in situ particles as well as the microstructures,mechanical mechanisms of the composites are investigated by XRD,SEM,TEM and in situ tensile tests.The results indicate that with the pulsed magnetic field assistance,the morphologies of the in situ particles are mainly with ball-shape,the sizes are in nanometer scale and the distributions in the matrix are uniform.The interfaces between the in situ particles and the aluminum matrix are net and no interfacial outgrowth is observed.These are due to the strong vibration induced by the applied magnetic field in the aluminum melt,which in turn,accelerates the melt reactions.The effects of the magnetic field on the above contributions are discussed in detail.

Study on Interface between Sub-micron Particles and Matrix in Al_2O_3p/Al Composites

The microstructural characteristic of 1070AI matrix composites reinforced by 0.15 祄 AI2O3 particles whose volume fraction was 40% was investigated by TEM and HREM. The results showed that the interface between the matrix and reinforcements was clean and bonded well, without any interfacial reaction products. There were some preferential crystallographic orientation relationships between Al matrix and AI2O3 particle because of the lattice imperfection on the surface of Al2O3 particles.

Synergistically Toughening Effect of SiC Whiskers and Nanoparticles in Al_2O_3-based Composite Ceramic Cutting Tool Material

In recent decades, many additives with different characteristics have been applied to strengthen and toughen Al2O3-based ceramic cutting tool materials. Among them, SiC whiskers and SiC nanoparticles showed excellent performance in improving the material properties. While no attempts have been made to add SiC whiskers and SiC nanoparticles together into the ceramic matrix and the synergistically toughening effects of them have not been studied. An Al2O3-SiCw-SiC np advanced ceramic cutting tool material is fabricated by adding both one-dimensional SiC whiskers and zero-dimensional SiC nanoparticles into the Al2O3 matrix with an effective dispersing and mixing process. The composites with 25 vol% SiC whiskers and 25 vol% SiC nanoparticles alone are also investegated for comparison purposes. Results show that the Al2O3-SiCw-SiCnp composite with both 20 vo1% SiC whiskers and 5 vol% SiC nanoparticles additives have much improved mechanical properties. The flexural strength of Al2O3-SiCw-SiCnp is 730＋ 95 MPa and fracture toughness is 5.6 ± 0.6 MPa.m1/2. The toughening and strengthening mechanisms of SiC whiskers and nanoparticles are studied when they are added either individually or in combination. It is indicated that when SiC whiskers and nanoparticles are added together, the grains are further refined and homogenized, so that the microstructure and fracture mode ratio is modified. The SiC nanoparticles are found helpful to enhance the toughening effects of the SiC whiskers. The proposed research helps to enrich the types of ceramic cutting tool and is benefit to expand the application range of ceramic cutting tool.

Fabrication and Studying the Mechanical Properties of A356 Alloy Reinforced with Al₂O₃-10% Vol. ZrO₂Nano-particles through Stir Casting

Al2O3-ZrO2 with a high level of hardness and toughness is known as ceramic steel. Due to its unique properties it can be used as a reinforcement in fabrication of metal matrix composites. In this study, nanoparticles of Al2O3-10% ZrO2 with an average size of 80 nm were used to fabricate Al matrix composites containing 0.5, 1, 1.5 and 2 wt.% of the reinforcement. The fabrication route was stir casting at 850?C. There is no report about usage of this reinforcement in fabrication of composites in the literature. The microstructures of the as-cast composites were studied by scanning electron microscope (SEM). Density measurement, hardness and tensile properties were carried out to identify the mechanical properties of the composites. The results revealed that with increasing the reinforcement content, density decreased while yield, ultimate tensile strength and compressive strength increased. Also, hardness increased by increasing the reinforcement content up to 1 wt.% Al2O3-10% ZrO2 but it decreased in the samples containing higher amounts of reinforcement.

Influence of the Ratio of Ethanol to Water on the Agglomeration of Al_2O_3/Y_2O_3-ZrO_2 Nanoparticles

A method of heating ethanol-aqueous salt solution combined with co-precipitation was used to synthesize Al2O3/ZrO2 nanoparticles. The analysis of DSC and XRD revealed that the transformation temperature from amorphous to crystal phase was about 850 ℃. The grain size was increased with the raising of calcine temperature. The alcohol-water ratio did not affect the formation of main crystal phases, but affected the agglomeration of nanoparticles based on the results of TEM. When alcohol-water ratio was 5∶1, the dispersion of nanoparticles was good. When there was not alcohol, the dispersion of nanoparticles was poor because there was only pure co-precipitation reaction and the speed of co-precipitation reaction was too high to have enough time of PEG. dispersing particles.

PREPARATION OF SPHERICAL， MONODISPERSED NANOMETER Eu_2O_3 PARTICLES

Spherical, monodispersed europium hydroxycarbonate particles wereobtained by homogeneous precipitation with urea in aqueous solution of Eu.(NO3)3at elevated temperature.The particles were readily converted to the uniformEu2O3 with average particle size of 50nm after calcined at 750℃.

Fluorescence spectra of colloidal self-assembled CdSe nano-wire on substrate of porous Al2O3/Au nanoparticles

We present a self-assembly method to prepare array nano-wires of colloidal CdSe quantum dots on a substrate of porous Al2 O3 film modified by gold nanoparticles. The photoluminescence(PL) spectra of nanowires are in situ measured by using a scanning near-field optical microscopy(SNOM) probe tip with 100-nm aperture on the scanning near-field optical microscope. The results show that the binding sites from the edge of porous Al2 O3 nanopores are combined with the carboxyl of CdSe quantum dots’ surface to form an array of CdSe nanowires in the process of losing background solvent because of the gold nanoparticles filling the nano-holes of porous Al2 O3 film. Compared with the area of nonself-assembled nano-wire, the fluorescence on the Al2 O3/Au/CdSe interface is significantly enhanced in the self-assembly nano-wire regions due to the electron transfer conductor effect of the gold nanoparticles’ surface. In addition, its full width at half maximum(FWHM) is also obviously widened. The method of enhancing fluorescence and energy transfer can widely be applied to photodetector, photocatalysis, optical display, optical sensing, and biomedical imaging, and so on.

Properties of Dispersion Casting of Y2O3 Particles in Hypo,Hyper and Eutectic Binary Al-Cu Alloys

In the present work,the dispersion casting of Y-2O-3 particles in aluminum-copper alloy was investigated in terms of microstructural changes with respect to Cu contents of 20 （hypo）,33 （eutectic） and 40 （hyper） wt pct by scanning electron microscopy （SEM） and energy dispersive spectroscopy （EDS）.For the fabrication of Al-Cu alloy dispersed Y-2O-3 ceramic particles,stir casting method was employed.In case of Al-20 wt pct Cu alloy （hypoeutectic）,SEM images revealed that primary Al was grown up in the beginning.After that,eutectic phase with well dispersed ceramic particles was formed.In case of eutectic composition,Y-2O-3 particles were uniformly dispersed in the matrix.When the Cu is added into Al up to 40 wt pct （hypereutectic）,primary phase was grown up without any Y-2O-3 ceramic particles in the early stage of solidification.Thereafter, eutectic phase was formed with well dispersed ceramic particles.It can be concluded that Y-2O-3 ceramic particles is mostly dispersed in case of eutectic composition in Al-Cu alloy.

Comments on“Adsorption behavior of heavy metal ions by carbon nanotubes grown on microsized Al_2O_3 particles”

Recently, Hsieh and Horng [1] published the paper entitled as above. In section 3 results and discussion, the authors mentioned the first and the second order kinetic models without any quotations. In fact these two kinetic models have been published [2-5]. In order to distinguish a kinetics model based on the ad- sorption capacity of a solid from the one based on the concentration of a solution, Lagergren＇s first-order rate equation has been called pseudo-first-order [6-7]. The Lagergren＇s equation has been widely cited, but there are far more mistakes made in the quotation and in the reference section of papers, including the title, the author＇s name, journal title, year of publishing, volume, and page number [3]. In addition, the second order kinetic expression for the adsorption systems of divalent metal ions using sphagnum moss peat has been reported by Ho [8].

The Effect of Fabrication Conditions on the Morphology and Photocatalytic Activity of Bismutite Bi₂O₂CO₃Particles

In this study, three-dimensional bismutite Bi2O2CO3 nanoparticels (BSC NPs) have been synthesized through a facile hydrothermal treatment under mild conditions. The reaction temperatures and NaOH concentration have a vital influence on the physical and photocatalytic properties of the obtained BSC NPs. The crystal structure, morphology, chemical composition, specific surface area and photoresponse of as-obtained catalysts were characterized by X-ray diffraction, Scanning electron microsprctrosopy, Energy-dispersive spectroscopy, N2 adsorption/desorption isotherms and UV-Vis spectra, respectively. Furthermore, Rhodamine 6G was used as model reaction to evaluate the photocatalytic activity of BSC NPs. As a result, there was no obvious effect of hydrothermal reaction temperature and NaOH concentration on phase structure and UV-visible light response;while the morphology, BET surface area and photoactivity were affected by hydrothermal reaction temperature and NaOH concentration.

直流辉光放电质谱法测定高纯α-Al 2 O 3颗粒中16种杂质元素

采用高纯Ga作为辅助电极,通过考察取样量、放电参数对基体信号强度、信号稳定性、基体和Ga的信号比值的影响,建立了直流辉光放电质谱法(dc-GDMS)测定高纯α-Al_(2)O_(3)颗粒中的Li、Be、Na、Mg等16种杂质元素含量的分析方法。当选取3颗2 mm左右大小的α-Al_(2)O_(3)颗粒用Ga包裹,在1.6 mA/950 V的放电参数下,基体27 Al信号稳定,强度为3.2×10^(8) cps,Al、Ga的信号比约为1∶270。采用实验方法对α-Al_(2)O_(3)颗粒独立测定5次,相对标准偏差均在30%以内。为了验证Ga对α-Al_(2)O_(3)颗粒测定结果的影响,分别采用电感耦合等离子体发射光谱法(ICP-OES)和dc-GDMS法对易于消解的γ-Al_(2)O_(3)粉进行测定。对于dc-GDMS法,选择压在Ga上的γ-Al_(2)O_(3)粉直径约为4~5 mm,在同样的放电参数下,27 Al的信号强度为3.0×10^(9) cps,Al、Ga的信号比约为1∶29。γ-Al_(2)O_(3)粉的GDMS测定结果和ICP-OES基本一致。采用Ga作辅助电极测定α-Al_(2)O_(3)颗粒和γ-Al_(2)O_(3)粉的检出限均可达ng/g。

氮掺杂碳改性Ni/Al2O3催化剂的甲烷干重整反应性能研究

在甲烷干重整反应(DRM)中,常规浸渍法制备的Ni/Al2O3催化剂常因过多积炭导致催化剂失活,因此研究如何提高Ni/Al2O3催化剂的抗积炭能力具有重要意义。通过浸渍法和高温碳化法制备的氮掺杂碳表面修饰的Ni/Al2O3催化剂Ni/Al2O3@NC-3和Ni/Al2O3@NC-5(3和5分别代表多巴胺聚合时间为3 h和5 h)在DRM中表现出了较强的抗积炭性能。使用X射线衍射(XRD)、拉曼(Raman)光谱、X射线光电子能谱(XPS)、热重(TG)和扫描电镜(SEM)等表征手段对催化剂的结构和电性质进行了分析,并探讨了氮掺杂碳的引入对催化剂稳定性和抗积炭性能的影响。XPS结果表明,Ni/Al2O3@NC-3和Ni/Al2O3@NC-5催化剂中金属Ni与氮掺杂碳发生了电子相互作用,形成了催化惰性的Ni+物种,由此减缓了CH_(4)的裂解速率,进而有效地减少了积炭的产生。在经8 h活性测试后,Ni/Al2O3@NC-3催化剂的CH_(4)转化率和CO_(2)转化率分别维持在52.2%和62.3%,且反应后Ni/Al2O3@NC-3催化剂的积炭量仅为7%(质量分数,下同),远远低于Ni/Al2O3催化剂的积炭量(25%)。

ALD-coated ultrathin Al_2O_3 film on BiVO_4 nanoparticles for efficient PEC water splitting

Bismuth vanadate(BiVO_4) is a promising semiconductor material for solar energy conversion via photoelectrochemical(PEC) water splitting,whereas its performance is limited by surface recombination due to trapping states.Herein,we developed a new method to passivate the trapping states on BiVO_4 surface using ultrathin aluminum oxide(Al_2O_3) overlayer by atomic layer deposition.The coated ultrathin Al_2O_3 film on BiVO_4 significantly enhanced photocurrent densities of the BiVO_4 anodes under standard illumination of AM1.5 G(100 mW/cm2).The electrochemical impedances and photoluminescence spectra were studied to confirm that the improved PEC water splitting performance of BiVO_4 was due to the decreased surface recombination state on BiVO_4,which effectively enhanced the charge separation.

Microstructure and Tribological Behavior of Al2O3 Particle Reinforced Al Matrix Composites Fabricated by Spark Plasma Sintering

Nanoparticles and microparticles reinforced Al matrix composites were fabricated by spark plasma sintering, and the microstructure and tribological properties were investigated systemically. The nano-Al2O3 particle and micro-Al2O3 particle uniformly dispersed in Al matrix composites. The introduction of nanoparticles is beneficial to the decrease of friction coefficient and wear rate, while microparticles are responsible to the high friction coefficient, resulting in the abrasive wear. With the introduction of both nanoparticles and microparticles, their synergic effect will lead to the variation of tribological behavior.

Fabrication of Fine-Grained Si_3N_4-Si_2N_2O Composites by Sintering Amorphous Nano-sized Silicon Nitride Powders

Si3N4-Si2N2O composites were fabricated with amorphous nano-sized silicon nitride powders by the liquid phase sintering （ LPS ）. The Si2 N2O phase was generated by an in-situ reaction 2 Si3 N4 （ s ） ＋ 1.5 02 （ g ） = 3 Si2 N2O （ s ） ＋ N2 （ g ） . The content of Si2 N2 O phase up to 60% in the volume was obtained at a sintering temperature of 1 650℃ and reduced when the sintering temperature increased or decreased, indicating the reaction is reversible. The mass loss, relative density and average grain size increased with increasing the sintering temperature. The average grain size was less than 500 nm when the sintering temperature was below 1 700 ℃. The sintering procedure contains a complex crystallization and a phase transition ： amorphous silicon nitride→equiaxial α- Si3 N4→ equiaxial β- Si3 N4→ rod- like Si2 N2O→ needle- like β- Si3N4 . Small round-shaped β→ Si3 N4 particles were entrapped in the Si2 N2O grains and a high density of staking faults was situated in the middle of Si2 N2O grains at a sintering temperature of 1 650 ℃. The toughness inereased from 3.5 MPa·m^1/2 at 1 600 ℃ to 7.2 MPa· m^1/2 at 1 800 ℃ . The hardness was as high as 21.5 GPa （Vickers） at 1 600 ℃ .

Influence of Molten Salt on Luminescent Intensity and Particle Size of Y_2O_3:Eu^(3+) Phosphor

The Y-Eu oxalate precursor was prepared with a homogeneous precipitation method. And the additives, Na2CO3, S, NaCl or their combination, were introduced into the precursor to prepare Y2O3 ：Eu^3＋ red phosphors at 1000 1300 ℃ for 2 h. The effect of molten salts on particle size and luminescent intensity was studied. The experimental results showed that the complex molten salt （Na：CO3 ＋ S ＋ NaCl） was conductive to enhance the luminescent intensity of Y2O3 ：Eu^3＋. The emission intensity of the phosphor prepared with these additives at 1300 ℃ was about 45% higher than that of the one prepared without molten salt, and about 11% higher than that of the corresponding commercial phosphor. Meanwhile, the particle size of Y2O3 ：Eu^3＋ phosphor was controlled effectively with the molten salt.

Synthesis and Characterization of Superparamagnetic Fe₃O₄@SiO₂Core-Shell Composite Nanoparticles

The Fe3O4@SiO2 composite nanoparticles were obtained from as-synthesized magnetite (Fe3O4) nanoparticles through the modified St?ber method. Then, the Fe3O4 nanoparticles and Fe3O4@SiO2 composite nanoparticles were characterized by means of X-ray diffraction (XRD), Raman spectra, scanning electron microscope (SEM) and vibrating sample magnetometer (VSM). Recently, the studies focus on how to improve the dispersion of composite particle and achieve good magnetic performance. Hence effects of the volume ratio of tetraethyl orthosilicate (TEOS) and magnetite colloid on the structural, morphological and magnetic properties of the composite nanoparticles were systematically investi-gated. The results revealed that the Fe3O4@SiO2 had better thermal stability and dispersion than the magnetite nanoparticles. Furthermore, the particle size and magnetic property of the Fe3O4@SiO2 composite nanoparticles can be adjusted by changing the volume ratio of TEOS and magnetite colloid.