Ultrasonic synthesis, characterization and formation mechanism of aggregated nanorings of EuF3

The aggregated nanorings of EuF3 were synthesized via ultrasonic irritation in aqueous solution. The products were characterized by X-ray powder diffraction （XRD）, scanning electron microscopy （SEM）, and transmission electron microscopy （TEM）. XRD pattern proved that the crystalline phase of the EuF3 rings was hexagonal. The SEM and TEM images indicated that the as-prepared EuF3 nanocrystals had ring-like morphology and were aggregated by numerous small crystallites （about 10-15 nm in diameter）; the outer diameter of the rings was in the range of 200--300 nm, while the inner diameter was in the range of 50-80 nm with a thickness of 30-40 nm. Moreover, the time-depend experiments were carried out to disclose the formation mechanism of the as-prepared ring-like nanostructures.     

Optimization of dispersing agents for preparing YAG transparent ceramics

The suspensions of the powder mixture of yttria and alumina were prepared by the aqueous tape casting method. Rodia DP270, Dolapix CE64, citric acid and Dammonium 3008 were used as dispersing agents. The morphologies of the powders and the fracture surface of the green body were observed by scanning electron microscopy (SEM). The zeta potential test was employed to characterize the surface charge states of different suspensions. The dispersion of the suspensions was analyzed by the rheological tests and the sedimentation experiments. The results indicated that the yttria and alumina powder mixtures were well dispersed by the dispersing agents. The rheological curves showed shear thinning behavior. The most efficient dispersing agent was Dammonium 3008. The optimum usage of Dammonium 3008 was 1.0 wt.%. The green body was dense and no interface between the adjacent layers was found. The in-line transmittance of the assintered YAG ceramic was higher than 80% between 400 and 1100 nm.     

Ordering–separation phase transition: The fate of the existing phase diagrams

Co₂V and Co₃V alloys are used as examples to discuss the principles of creating modern phase diagrams to take into account the discovery of an ordering–separation phase transition in alloys. The results of electron-microscopic studies of the Co₂V alloy after heat treatment at various temperatures are presented. A comparison of these results with the conclusions based on the existing Co–V phase diagram demonstrates their disagreement. This disagreement is explained in this work. It is concluded that the ordering–separation phase transition should be taken into account in plotting modern phase diagrams. The Fe–Cr and Ni–Cr phase diagrams are considered with allowance for the ordering–separation phase transition in them. A technique is described to determine the ordering–separation phase transition temperature by transmission electron microscopy. The introduction of the concept of the ordering–separation phase transition is shown to change the principles used by researchers to construct phase diagrams.     

Constructing aligned sequence blocks

Optical and electron microscopy were employed to characterize microstructures formed by thermal mechanical treatment of glycol suspensions of various pure and binary mixtures of the brain-derived galactosphingolipids hydroxy fatty acid cerebroside (HFA-Cer), non-hydroxy fatty acid cerebroside (NFA-Cer) and sulfatide (S-Cer). Negative staining indicated some new features of the neutral cerebroside suspensions in glycol. HFA-Cer formed a small fraction of both unilamellar cylinders (ULCs) (lumina ca. 27 nm) and giant multilamellar cochleates in addition to the typical nonhelical multilamellar cylinders (MLCs) (lumina ca. 10-30 nm). NFA-Cer formed a gel composed of a significant fraction of very long ULCs (lumina ca. 17 nm) without helical substructure, in addition to multilamellar helical structures such as ribbons and cylinders (lumina ca. 70 nm). Anisotropic lamellar micelle-shards of NFA-Cer were also detected by negative staining. S-Cer formed short ULCs (lumina ca. 44 nm) with no obvious helical substructure. Complex mixture data are thought to result from thermodynamic and kinetic factors. HFA-Cer is highly insoluble and promotes a network of rigid intralamellar hydrogen bonding that tends to exclude other lipids. NFA-Cer stabilizes helical defects in the lamellae, and S-Cer enhances disorder or micellization. The processes of microstructure nucleation and lipid phase separation were affected by mixtures such that metastable microstructures were trapped or the length of lamellar cylinders was altered.     

Laves Phase in 22Cr-27Ni-2Ti-Al Austenitic Valve Steel

The Thermo-Calc software was employed to calculate the equilibrium phase of 22Cr-27Ni-2Ti-Al austenitic valve steel,and the Laves phase in this steel was investigated after solid solution and aging by means of scanning electron microscopy( SEM),transmission electron microscopy( TEM) and X-ray diffraction( XRD).Results show that the microstructure of the experimental steel consists of γ,γ',Laves and Nb C.Laves phases mainly precipitate on grain boundaries,with granular and fibrous morphologies.The size of the granular Laves phase is about 50-600 nm,and the fibrous Laves phase is composed of short strip Laves phases which are 300-600 nm in length and 50-150 nm in width.These two morphologies of Laves phase coarsen with increasing aging temperature,and this steel possesses the highest strength and hardness at aging temperature of 760 ℃.     

The chitin crystallite in arthropod cuticle

Electron microscopy has revealed that chitin from a representative selection of insect orders (plus one crustacean and one arachnid) is localized in crystallites about 2.8 nm across. Furthermore, these crystallites are arranged on an hexagonal or pseudo-hexagonal lattice, the lateral order of which varies considerably. The lattice becomes secondarily reoriented during cuticle expansion following an ecdysis. The size of the 'unit cell' has been measured both by optical diffraction and direct measurements of the micrographs, permitting an estimate of the chitin and resilin content for locust rubberlike cuticle. The number of poly-N-acetyl-glucosamine chains per sheet and sheets per crystallite can be estimated from the physical dimensions of the crystallite. Each crystallite is unlikely to comprise more than 3 sheets and 6 chains per sheet. The calculated and measured density of alpha-chitin can be shown to be in close agreement.     

Structural disordering in WC thin films induced by SiC additions

An investigation has been conducted into the structural disordering in WC thin films induced by SiC additions. The effect of this disordering on film hardness is also reported. In this investigation, WC-SiC films with a SiC content varying from 11.6 to 38.2 pct were deposited using dual rf magnetron sputtering. The relative Si and W content in the films was determined using electron microprobe analysis. Analysis by X-ray diffraction (XRD) confirmed that, within this compositional range, the film structure transformed from crystalline to amorphous. The XRD patterns showed that the crystalline films consisted primarily of WC_1−x , along with a small amount of W₂C; no clear evidence for a separate crystalline SiC phase was found. High-resolution transmission electron microscopy (HRTEM) studies showed that with a lower Si content, the films consisted of crystallites 3 to 5 nm in diameter embedded in an amorphous phase. As the Si content increased, the amorphous phase content increased, both as interlayers between crystallites and as particles within the crystallites. Further Si increases led to a structure consisting of a high density of interconnected amorphous particles within well-defined semicrystalline domains separated by a thin amorphous interlayer. At the highest Si content, a clear two-phase morphology evolved, consisting of two nearly amorphous but distinct phases, which suggests a fine-scale partial-phase separation between the WC and the SiC. At the atomic level, it was found that Si decreased the coherence length within the crystalline phase, resulting in a structure of mixed crystalline/highly disordered phases scaled in the range of 2 to 4 nm. Despite the significant alterations in the film structures due to SiC additions, the hardness and modulus of the films were essentially constant within the compositional range of the transition, although films with SiC contents of less than ∼11 pct had significantly lower hardness levels. It is proposed that the effects of Si on hardness can be explained in terms of competition between the percolation threshold and the amorphization-inducing effect of Si.     

Drying kinetics of single drops by ferrite suspensions

Conclusions The process of drying of ferrite suspensions with solid-phase concentrations ranging from 30 to 65% occurs in three stages. In the second, limiting stage evaporation takes place. The length of this period depends on external heat-transfer and mass-transport conditions (drop diameter and temperature of the ambient atmosphere). In ferrite suspensions composed of charge material and an aqueous solution of polyvinyl alcohol the physicomechanical bond between the moisture and material predominates. Plant for the production of ferrite powder by the suspension spray-drying method can be calculated and designed using heat-transfer and moisture-transport equations for capillary porous solids.Translated from Poroshkovaya Metallurgiya, No. 3(207), pp. 76–78, March, 1980.     

Ti-MO低碳超高强钢中相间析出强化

在不同温度下对Ti-Mo低碳钢进行等温转变,对热轧板进行力学性能检测,利用扫描电镜、透射电镜、选区电子衍射等方法进行组织观察,同时分析了相间析出粒子的形貌、尺寸和分布规律.结果显示,随着等温温度降低,钢的强度提高,延展性降低,屈强比增大.在透射试样中观察到两种不同形态分布的相间析出碳化物:平面型相间析出和曲面型相间析出.相间析出碳化物的平均直径为4.30nm,平均纵横比为1.375.在650℃等温保温1 h时,相间析出强化对铁素体相强度的增量在400MPa以上.      

Surface modification of superparamagnetic nanoparticles (Ferrofluid) studied with particle electrophoresis: application to the specific targeting of cells

Colloidal aqueous suspension of superparamagnetic nanoparticles (9 nm in diameter) composed of maghemite (gamma Fe2O3) and forming an ionic ferrofluid in aqueous solution are covalently coupled with lectins, enzymes or antibodies, using specific thiol chemistry. The surface charge modifications of nanoparticles, caused by ligand coupling, were monitored by measuring their electrophoretic mobilities using laser-Doppler velocimetry. Particle electrophoretic mobility (PEM) changes are shown to correlate well with the amount of ligand fixed on the particles, as probed by its biological activity. The PEM method provides a useful tool to optimize ligand immobilization at the surface of nanoparticles, and may be advantageous when biological activity measurements are not convenient.     

应用选择性磁罩盖法磁选分离镍黄铁矿与蛇纹石

针对镍黄铁矿和蛇纹石浮选难分离,提出采用磁罩盖法进行磁分离.结果表明,控制一定的矿浆物化条件,随着磁种磁铁矿的添加,镍黄铁矿的磁选回收率随之升高,而蛇纹石的回收率基本保持很低,可实现两者的良好分离.人工混合矿分离结果表明,磁种质量分数为5%时,获得的精矿Ni品位为19.89%,回收率为92.46%,MgO质量分数为4.72%;X射线衍射和扫描电镜分析结果显示磁铁矿在镍黄铁矿表面产生了罩盖,在蛇纹石表面未产生明显的罩盖;Zeta电位测试和DLVO理论计算结果表明,添加六偏磷酸钠后,蛇纹石表面电性由正变负,而对镍黄铁矿和磁铁矿表面电性未产生显著影响,从而使磁铁矿与蛇纹石间的相互作用变为排斥,而与镍黄铁矿之间仍为吸引,因而磁铁矿选择性罩盖在镍黄铁矿表面,增强其磁性,实现与蛇纹石的磁分离.      

轧制工艺对Ti微合金化马氏体钢力学性能的影响

 通过采用扫描电镜、透射电镜、X射线衍射以及相分析等手段来观察组织的微观结构和对析出相的验证,研究轧制温度对轧态Ti微合金化马氏体钢强度的影响。研究结果表明,通过降低轧制温度可以明显提高含Ti马氏体钢的屈服强度,这主要是因为当轧制温度从1100℃降低到950℃过程中,形变诱导析出大量的TiC析出相,随着轧制温度的降低,析出相数量明显增加,并且平均尺寸也逐渐变小。马氏体中大量存在的1～20nm范围的析出相可以起到明显的析出强化作用。     

Liquid-liquid extraction of a recombinant protein with a reverse micelle phase

Recombinant cytochrome b5 was extracted to a reversed micelle phase of a cationic surfactant (hexadecyltrimethylammonium bromide, CTAB) in cyclohexane/decanol and back-extracted to a fresh aqueous phase. Depending on the experimental conditions, i.e., temperature, pH, and ionic strength, the extraction is controlled by either hydrophobic (pH close to the pI and high ionic strength) or electrostatic (pH far from the pI and low ionic strength) interactions. The protein interacts strongly with the surfactant aggregate once it is extracted to the organic phase, and it is very difficult to back-extract it to a new aqueous phase.     

Synthesis and Fluorescence of Europium-Doped Barium Fluoride Cubic Nanocolumns

Europium-doped barium fluoride cubic nanocolumns were synthesized from the quaternary water in oil reverse microemulsions. In this process, the aqueous cores of water/cetyl trimethyl ammonium bromide (CTAB)/n-butanol/n-oe-tane reverse mieroemulsions were used as mieroreaetors for the precipitation of europium doped barium fluoride. XRD analysis shows that under the dopant concentration of 0.06% (molar fraction), the products are single phase. The result products are cubic column-like with about 30 - 50 nm edge length of cross section, and about 200 nm of length obtained from the transmission electron microscopy (TEM), and atomic force microscopy (AFM). Under the 0.06% (molar fraction) of dopant concentration, the fluorescence of Eu^2 and Eu^3 under the 589 of excitation wavelength is observed.     

Spray deposited Nb2O5 thin film electrodes for fabrication of dye sensitized solar cells

Nb₂O₅ thin film electrodes have been deposited on indium tin oxide substrates by spray pyrolysis technique. XRD analysis reveals tetragonal phase of the film. Reticulated micro-fibrous surface morphology has been observed by scanning electron microscopy and atomic force microscopy indicates closely packed crystallites. Film thickness found using a stylus profilometer is around 26 nm. Transmittance spectra show the film to be 70–80% transparent in the visible region. Direct, indirect band gap and phonon energy are also estimated. Cyclic voltammetry measurement indicate distinct anodic peak during negative potential of the scan due to Li extraction. A reversible colour change from transparent to grey has been observed. The photo-electrochemical characteristic of the dye sensitized solar cell is studied by recording the I-V characteristics of the unsealed type cell under illumination of 40 mW/cm² using a solar simulator.     

Influence of Sediment Structure on Erosional Strength and Density of Kaolinite Sediment Beds

The role of sediment pore-water chemistry and the resulting particle structure in determining the erosional stability of settled cohesive sediment beds in rivers, lakes, and estuaries is examined. Kaolinite sediment is used as the surrogate sediment in this experimental investigation with the beds settled from concentrated suspensions. The bed stability with respect to erosion or resuspension is measured in a laboratory flume as a function of sediment pore-water chemistry. The chemical properties varied are sediment pH, ionic strength, and natural organic matter. The remolded bed sample is prepared from a sediment suspension having controlled chemical properties that is allowed to settle into the flume bed where its erosional strength and density are determined with depth in the sample. Different structures of settled beds are observed with changes in chemical parameters. Under low pH and low organic content conditions, the initial suspension before settling is flocculated. The resulting settled beds show strong stratification with respect to erosional strength but weak stratification of bulk density with depth. On the other hand, under high pH or high organic content conditions at low ionic strength, the initial suspension is dispersed. The resulting settled beds have lower erosional strength and weak stratification of erosional strength with depth but strong stratification of bulk density with depth. This research shows that the relationship between erosional strength and bulk density of a settled bed depends strongly on the structure of the sediment particle associations as determined by pore-water chemistry.     

Two-phase equilibrium in individual nanoparticles of Bi-Sn

When evaluating the path of phase transformations in systems with nanoscopic dimensions, one often relies on bulk phase diagrams for guidance because of the lack of phase diagrams that show the effect of size. In order to provide insight into how phase diagrams can very when a high surface curvature exists, binary alloys of Bi and Sn were investigated as a collection of individual crystalline particles vapor deposited onto amorphous carbon substrates in ultra-high vacuum. These crystallites were annealed after deposition to equilibrate the phases and structures. After annealing, they were transferred to the transmission electron microscope for analysis of the phase state as a function of composition and surface curvature, i.e., particle radius. Individual crystallites were analyzed with respect to crystallinity, two-phase or one-phase coexistence, and composition. The data show that there is a critical size below which there is no limit to the solubility, in strong contrast to that found in the bulk system, which is a simple eutectic alloy with less than 0.3 pct solubility on the bismuth-rich solid solution side of the phase diagram and about 15 pct on the tin-rich side. The change in solubility limit with size was found to be equally strong in both the tin-rich terminal solid solution and the bismuth-rich terminal solid solution. A thermodynamic approach to using free-energy expressions modified to account for surface curvature can be successful in showing the shift in solubility with size. It is shown that the appropriate thermodynamic potential to minimize is a modified Helmholtz free energy. This article is based on a presentation made in the symposium “Phase Transformations Within Small-Size Systems: Thermodynamics, Phase Equilibria and Kinetics,” which occurred February 14–16, 2005, during the TMS Spring Meeting in San Francisco, CA, under the auspices of the ASMI/MPMD-Phase Transformations, EMPMD/SMD-Chemistry & Physics of Materials, and EMPMD-Nanomaterials Committees.     

淬火工艺对铜沉淀强化UHS钢组织性能的影响

 超高强度钢不仅可以降低海洋装备本身质量，而且节约能源，但这类钢应用过程中要求具有良好的强韧性匹配，而淬火工艺显著影响其后续的相变和性能。采用Thermo Calc软件、光学显微镜、扫描电镜以及透射电镜等研究了淬火工艺对低碳(w(C)<0.05%)铜沉淀硬化超高强海工钢组织性能的影响。结果表明，910 ℃淬火、450 ℃时效处理后峰值硬度达到386HV，700 ℃时效后空冷可得到部分二次马氏体组织，峰值硬度为357HV。525 ℃以下时效，富铜相析出的平均半径约为5 nm，产生较高的强化增量。820~910 ℃淬火，随着淬火温度降低，细小的(Nb，Ti)C粒子能够有效抑制奥氏体晶粒的长大，细化晶粒和马氏体板条块，同时基体中小角度界面密度增加，强韧性提高。其中820 ℃淬火强度最高达到1 109 MPa，-80 ℃ V型冲击功为91 J。     

Interface structures of γ-iron crystallites embedded in magnesium oxide crystalline films

Nanometer-size γ-iron (f.c.c-iron) crystallites were prepared in FeMgO composite films made by a vacuum-codeposition of Fe and MgO onto NaCl surfaces at 350°C. The crystallites were stable at room temperatures. High-resolution electron microscopy revealed that the crystallites were epitaxially embedded inside MgO single crystal films and the interfacial lattice was deformed for accomodation of lattice misfit of 14% between γ-Fe and MgO. The magnetic property of the crystallites was measured to be ferromagnetic similar to usual α-Fe. The appearance of the ferromagnetism may originate partly from an expansion of the lattice constant of interface regions from 0.36 nm, which was calculated recently to be a saddle point of the magnetic phase-transition from anti-ferromagnetism to ferromagnetism. The interface structures were thus studied by high-resolution electron microscopy, nanometer-area electron diffraction and dark-field method.     

X120管线钢回火过程中断口分离问题研究

针对一种高强度X120管线钢高温回火条件下出现的夏比冲击试样断口分离现象。利用扫描电镜、透射电镜及冲击试验机等,从磷、硼、锰等元素的偏析,晶界处第二相如碳化物、合金析出物等的析出及长大角度进行讨论分析。研究结果表明：随回火温度升高,断口分离加剧,分离平均长度及数量增加。夏比冲击功降幅达60％;断口分离先于主断口形成,导致试验钢表面能增加,刚度、主断口裂纹形成功及裂纹扩展功下降;磷、硼、锰等元素在晶界偏聚引起的回火脆性导致分离裂纹产生,夹杂物对分离起促进作用,尺寸较大的第二相弱化了晶界强度。