Mechanical properties of Mg-8Gd-3Y-0.5Zr alloy with bimodal grain size distributions

The Mg-Gd-Y-Zn-Zr alloys are representational and potential age-hardening systems as reported in the past ten years,but their mechanical properties are still dependent on the grain size and its distribution.The effect of bimodal structure on mechanical properties of Mg-8Gd-3Y-0.5Zr alloy with bimodal grain size distributions was investigated.The results suggested that the volume fraction of fine grain(FG)and coarse grain(CG)could be controlled by combined processes of hot forging,extrusion and annealing.And for the present alloys with bimodal grain size distribution,the improvement of strength is still attributed to the grain refinement.The morphology of bimodal grain size distribution has a marked impact on the ductility of the alloy,i.e.with the increase of coarse grain volume fraction,the elongation to failure increases at the beginning and then decreases.The mechanism of the toughening effect of bimodal grain size distribution on the Mg-Gd-Y-Zn-Zr alloys with bimodal grain size structure has been discussed.

Corrosion behavior of electrodeposited Ni with normal and bimodal grain size distribution

The corrosion behavior of electrodeposited Ni with normal and bimodal grain size distribution was investigated.The microstructure of samples was researched by SEM,EBSD,TEM and XRD.The corrosion behavior was studied by potentiodynamic tests and electrochemical impedance.Nanocrystalline Ni with(100)and(111)textures was prepared by an electrodeposition method.The Ni samples with different grain size distributions and twins were then obtained by heat treatment of nanocrystalline Ni at different temperatures.The effect of grain size on corrosion behavior of the sample depends on the ability of the environment to passivate.In the case where passive film forms on the sample surface,the corrosion resistance of the sample increases with decreasing grain size.Conversely,the corrosion resistance decreases with decreasing grain size when there is no passivation.The corrosion behavior of samples with bimodal grain size distribution obeys the rule of mixture.

Influence of Particle Size Distribution of Bimodal Reactive Alumina on Properties of LCC Refractory Castables

The effect of particle size distribution of alumina has been investigated for silica-free tabular alumina low cement castables（ LCC）. Three different combinations of alumina have been included in the matrix formulation of the castables. All the three combinations are composed of a bimodal reactive alumina and a fine ground monomodal reactive alumina. The first A1 and second A2 combinations are respectively composed of bimodal and monomodal aluminas from Alteo,with a different fine /coarse particles ratio for the bimodal alumina. The two Alteo combinations have been compared with a third combination C composed of a bimodal commercially available grade and a monomodal commercially available grade. Optimization of particle size packing has been performed for the three different formulations using the Dinger and Funk model. With this optimization,the two formulations based on Alteo material（ PFR,PBR and PFR40） achieve the same level of performance in applicative tests（ flowability,cold physical properties,mechanical resistance,crystalline phases,thermal shocks and corrosion） as reference solutions on the market.

Dependence of bimodal size distribution on temperature and optical properties of InAs quantum dots grown on vicinal GaAs （100） substrates by using MOCVD

Self-assembled lnAs quantum dots （QDs） are grown on vicinal GaAs （100） substrates by using metal-organic chemical vapour deposition （MOCVD）. An abnormal temperature dependence of bimodal size distribution of InAs quantum dots is found. As the temperature increases, the density of the small dots grows larger while the density of the large dots turns smaller, which is contrary to the evolution of QDs on exact GaAs （100） substrates. This trend is explained by taking into account the presence of multiatoinic steps on the substrates. The optical properties of InAs QDs on vicinal GaAs（100） substrates are also studied by photoluminescence （PL） . It is found that dots on a vicinal substrate have a longer emission wavelength, a narrower PL line width and a much larger PL intensity.

Synthesis and Characterization of Bimodal Mesoporous Silica

Mesoporous silica with controllable bimodal pore size distribution was synthesized with cetyltrimethylammonium bromide （CTAB） as chemical template for small mesopores and silica gel as physical template for large mesopores. The structure of synthesized samples were characterized by Fourier transform infrared （FT-IR） spectroscopy, X-ray diffraction （XRD）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and N2 adsorption-desorption measurements. The experimental results show that bimodal mesoporous silica consists of small mesopores of about 3 nm and large mesopores of about 45 nm. The small mesopores which were formed on the external surface and pore walls of the silica gel had similar characters with those of MCM-41, while large mesopores were inherited from parent silica gel material. The pore size distribution of the synthesized silica can be adjusted by changing the relative content of TEOS and silica gel or the feeding sequence of silica gel and NH4OH.

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.

Simulation of the pore size distribution function for a deformable soil

In order to obtain an indirect estimation method of the pore size distribution function(PSDF)for a deformable soil,both the soil-water characteristic curve in the form of gravimetric water content(w-SWCC)and the shrinkage curve(SC)are used as the input parameters.The w-SWCC defines the relationship between the gravimetric water content and soil suction.The SC illustrates the variation of the void ratio with respect to different water contents.10 points in the w-SWCC were selected as initial conditions.By adopting different void ratios,a group of soil-water characteristic curve in the form of the degree of saturation(S-SWCC)can be obtained.Based on Kelvin's capillary law,the S-SWCCs can be converted into a group of PSDFs.In the group of PSDFs,each PSDF represents the geometric pore space in soil corresponding to a given void ratio.From the proposed methodology,it is observed that a bimodal PSDF can be gradually changed into a unimodal PSDF when the soil is compressed.The Chataignier clay is selected as the verification and it shows that the simulation results agree well with the measured results from the mercury intrusion porosimetry(MIP)test.In addition,the discrepancies between both direct measurement data using the MIP test and the indirect estimated results from the proposed method are also discussed.

基于起动概率的清水冲刷双峰型泥沙粗化层级配计算

基于双峰型级配泥沙的非均匀性,引入由双峰系数、相对粒径组成的双峰型泥沙隐暴系数修正均匀沙上举力系数与拖曳力系数,采用均匀沙相对暴露度分布得到力臂期望值,结合近底水流的随机性,建立双峰型泥沙起滚概率计算公式。基于床面泥沙起悬与起滚两种起动方式,建立清水冲刷双峰型泥沙粗化层级配预报多步计算模式,并进行参数敏感性分析。经试验资料验证,公式预报精度良好。

Controllable preparation of γ-alumina nanoparticles with bimodal pore size distribution in membrane dispersion microreactor

In this paper,we present a new method for preparing γ-alumina nanoparticles with a bimodal pore size distribution by using an efficiently mixing membrane dispersion microreactor.NH4HCO3and AI2(SO4)3.18H2Owere reacted under vigorous mixing to give an ammonium aluminum carbonate hydroxide (AACH)precursor.γ-Alumina was obtained by calcination of AACH at 550℃ for 6h.The effects of NH4HCO3concentration,pH during aging,and reaction temperature were investigated.The mechanism of bimodal pore formation was clarified.The results showed that large pores (10-100nm) were mainly formed in the reactor and during aging,and small pores (0-10nm)were mainly formed during calcination.When the concentration of NH4HCO3was 1.5mol/L,the aging pH was 9.2,and the reaction temperature was 80℃,γ-alumina with a specific surface area of 504.7m^2/g and pore volume of 1.76mL/g was obtained.The average size of the large pores was about 30nm,and the average size of the small pores was about 4nm.

Fabrication and Dealloying Behavior of Monolithic Nanoporous Copper Ribbons with Bimodal Channel Size Distributions

Monolithic nanoporous copper （NPC） ribbons with bimodal channel size distributions can be fabricated through chemical dealloying of Mg-32 Cu alloy in an acidic solution at room temperature. The microstructure of the as- dealloyed samples was characterized by X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray analysis. These NPC ribbons are composed of interconnected large-sized channels （hundreds of nm） with highly porous channel walls （tens of nm）. Both large- and small-sized channels are open, bicontinuous, and interpenetrating. Additionally, it is the first time to find that the evolution process of porous structure along the thickness direction of samples during the dealloying is from the interior to exterior, which is just contrary to the coarsening process along the thickness direction during the post-dealloying. Meanwhile, the corresponding mechanism is discussed in detail.

Structural Evolution During Mechanical Milling of Bimodal-Sized Al_2O_3 Particles Reinforced Aluminum Matrix Composite

Hybrid aluminum matrix composite powders reinforced with bimodal-sized Al2O3 particles were synthesized by mechanical milling.Two different approaches were investigated for the addition of submicron-and nano-sized Al2O3 particles to the aluminum powders,It was observed that the simultaneous addition of bimodal-sized Al2O3 particles to the aluminum powders resulted in an equiaxed morphology of the composite powders and the average particle size stabilized after 5 h of milling,indicating that the presence of bimodal-sized particles has greater effect on accelerating milling process as compared to nano-sized particles;the grain size of the aluminum matrix in composite powders was reduced to under 40 nm,approximate to the value obtained in the separate addition case,while a lower rate of refining was observed due to hindrance of submicron-sized particles on the interactions between nano-sized particles and the aluminum matrix.

Dependence of tensile properties on microstructural features of bimodal-sized ferrite/cementite steels

A medium-carbon steel was processed through different warm rolling techniques,and the microstructural features with bimodal grain size distribution were found to be different.The combination of strength and ductility was ameliorated in the steel processed through warm rolling characterized by biaxial reduction.The enhanced strength is attributed to the densely distributed fine intragranular cementite particles and the small grain size in the coarse grain regions.The enhanced uniform elongation is due to the improved work hardening behavior at the large-strain stage.This work hardening behavior is predominantly ascribed to the finely dispersed intragranular particles.The relatively small grain size with nearly equiaxed shape in the coarse grain regions helps stabilize the uniform deformation to a large strain.

火灾烟雾颗粒粒谱动态分布

采用扫描电子迁移粒径谱仪，对木材明火、棉绳阴燃、聚氨酯明火、正庚烷明火和工业酒精明火中产生的烟雾气溶胶进行在线测量，记录并分析随时间变化的烟颗粒浓度变化和粒径谱分布信息．结果表明，在火灾探测器做出响应之前，正庚烷明火的烟颗粒粒径主要分布在100～500nm，木材和聚氨酯明火及棉绳阴燃的是50～400nm．五种试验火在材料基本耗尽前的烟颗粒数目浓度随时间不断增大，小于50nm的烟颗粒相对浓度随时间增长．烟雾颗粒粒径分布呈双峰偏态特征，除酒精燃烧试验火的粒径分布出现自保持特征外，其他燃烧试验火在不断生成、凝并及迁移动态变化中，粒径分布形状发生改变．归一化颗粒数浓度，粒径分布的几何平均中径向右移动，粒径分布随时间展宽，因此验证了试验火烟雾颗粒的快速凝并效应．

双孔结构非饱和压实土微观结构演化模型

在最优含水率干侧压实的黏土一般具有明显的双孔结构,其集聚体间孔隙(又称宏观孔隙)和集聚体内孔隙(又称微观孔隙)对土体宏观水力和力学特性影响差异显著,同时,水-力耦合作用下两种孔隙的演化规律也存在明显不同。双孔结构非饱和土对应的孔径分布函数为双峰孔径分布形式,该分布函数可通过叠加宏观孔隙和微观孔隙的单峰孔径分布曲线得到,并通过平移量、缩放量和分散度3个演化参数对双孔结构土的孔隙演化规律进行描述。通过构建在力学及水力加、卸载过程中演化参数与孔隙比之间的关系,提出了适用于描述变吸力下非饱和压实土的微观结构演化模型。分别基于所开展的桂林红黏土压汞试验数据和文献中的米尼亚卢博瓦膨胀土试验数据,对所建立的微观结构演化模型进行参数标定,并通过模型预测结果与试验结果的对比,验证了所建立模型的适用性。

双粒径组分YSZ纳米粉体的成型、烧结与电学性能研究

介绍了单粒径组分和双粒径组分YSZ纳米粉体的成型与烧结行为以及烧结体电学性能的研究。其中采用双粒径组分配料,在传统的单轴施压情况下成型,即能明显降低YSZ陶瓷膜的致密烧结温度,在1400℃烧结样品的相对密度可以达到93%,1550℃烧结样品的相对密度能达到99%;所制备YSZ致密陶瓷膜在800℃的离子电导率为0.4S/cm。

高固含量阳离子水性聚氨酯的合成与性能

通过向软段中引入不同阳离子亲水链段十二胺聚氧乙烯醚(PAE),设计合成了一系列高固含量、高稳定性的阳离子水性聚氨酯。通过红外光谱、粒径、拉伸力学、热重分析、吸水率及接触角等测试对乳液及胶膜进行分析。研究发现,在PAE环氧乙烷(EO)数目为10,n(PAE)∶n(POL7112)=1∶9,n(NCO)/n(OH)=1.2时,可合成固含量为51.28%的阳离子水性聚氨酯,体系显良好双峰粒径分布趋势;随着PAE加入量的增加,胶膜的断裂伸长率显著增大,拉伸强度略有小幅下降趋势;热稳定性明显提高;随着PAE分子中EO数目的增加,乳液粒径变小,稳定性增强,胶膜的亲水性显著增强。

单峰和双峰土水特征曲线基本参数的确定

土水特征曲线基本参数(如进气值、残余吸力值和过渡区脱湿曲线的斜率等)的确定是预测非饱和土强度、渗透性以及本构关系的基础。基于修正Fredlund和Xing拟合方程,提出单峰和双峰土水特征曲线基本参数的确定方法。首先,对试验数据点进行最优化拟合,获取拟合方程的参数,对于双峰土水特征曲线,根据试样的孔径分布特征将其分段进行拟合;其次,根据拟合方程的几何关系求出过渡区和残余区土水特征曲线的斜率及其切线方程;再根据切线方程可以准确地确定单峰和双峰土水特征曲线的进气值、残余吸力值等。最后,利用单峰和双峰土水特征曲线的试验数据,验证了此方法的可行性。

双峰分布超细聚酰亚胺粉末的制备

为使聚酰亚胺(PI)材料可以使用选择性激光烧结(SLS)技术进行快速成型,根据SLS成型技术的耗材要求,以二苯醚四甲酸二酐(ODPA)、4,4′-二氨基二苯醚(ODA)为单体,设计并制备了醚酐型聚酰胺酸(PAA),使用溶液沉淀法制备出PI模塑粉,并通过两种亚胺化机理相配合的工艺调节模塑粉的粒径。对制得的产物进行了红外光谱分析、微观形貌分析、粒度分析以及热学性能分析。结果表明:PI模塑粉亚胺化完全,表面形貌近似球形或半球形,粒径分布集中于2μm以下或在2μm以下及30~40μm区间双峰分布,同时在350~360℃可熔融,完全可应用于SLS成型技术。

退火对CdSe量子点荧光影响的色度学研究

制备出两种尺寸的Cd Se量子点。结合色度学分析,比较了固化在PMMA基质中两种尺寸Cd Se量子点在退火中发生的不同变化以及相应光谱颜色的改变。小尺寸Cd Se量子点在退火中有团聚的趋势,退火后荧光明显红移,如果退火温度超过一定范围,会产生显著的双尺寸分布效应,对应的色度坐标有从白光区域向上移动到绿色区域的趋势。较大尺寸的Cd Se量子点,其热稳定性相对更好,退火造成荧光红移,对应绿色区域中的色度坐标有向右移动的趋势,但颜色改变不明显,因此更适合于发光显示方面的应用。

双峰孔分布Al_2O_3载体的研究

采用两种不同孔径分布的拟薄水铝石干胶粉，制备呈明显双峰孔分布的Al2O3载体。考察原料粉体、孔结构调节剂种类和用量以及焙烧温度等对Al2O3载体的孔分布的影响，并采用N2物理吸附法和高压压汞法分析载体孔结构。结果表明，两种干胶粉按质量1：1混合时，能改变单一粉体的堆积状态，制得载体兼具单一原料制备载体时的孔分布，孔容达到最大，为1．58cm^3·g^-1，且孔径分布集中在（10～100）nm和300nm以上；加入不同孔结构调节剂后，对载体孔径分布调节作用相似，孔径分布更为集中；添加质量分数5％尿素后，（10～100）nm孔径分布达到62．1％；载体的比表面积随尿素含量增加依次降低，适量添加调节剂可制得所需最佳孔径分布；载体在约920℃焙烧时，晶型为1相和8相的混合相。