Rod-like Ones Research Articles

Laves phase control and tensile properties optimization of DED-arc repaired 718Plus components through the addition of TiC and Cr2C3

Directed energy deposition-arc (DED-arc) additive manufacturing technology was used to repair the damaged 718Plus components. This work shows that TiC/Cr2C3 addition to 718Plus alloy is an effective way to suppress the formation of the unfavorable Laves phase. TiC additions to 718Plus alloy can alleviate the elemental segregation, refine the dendritic structure and promote the formation of blocky TiC-NbC core-shell carbides and NbC carbides, while Cr2C3 additions enable the precipitation of rod-like NbC carbides. During the deposition process, the TiC/Cr2C3 additions were dissolved into the molten pool and decomposed into Ti, Cr, and C. The introduction of additional carbon in the melt drastically consumed the Nb available for Laves phase. The tensile tests show that TiC addition to 718Plus alloy contributed to an increased tensile strength of about 120 MPa due to the reduced amount of Laves phase and the reinforced effect of carbides. The fracture behaviour of carbides was explained in detail. The critical shear stress for blocky carbides to crack is higher than that required for rod-like ones, suggesting that TiC additions were desirable for better ductility compared with Cr2C3 additions.

Salt-Induced Transformations of Hybrid Micelles Formed by Anionic Surfactant and Poly(4-vinylpyridine).

Salt-induced structural transformation of charged hybrid surfactant/polymer micelles formed by potassium oleate and poly(4-vinylpyridine) was investigated by cryo-TEM, SANS with contrast variation, DLS, and 2D NOESY. Cryo-TEM data show, that at small salt concentration beads-on-string aggregates on polymer chains are formed. KCl induces the transformation of those aggregates into rods, which is due to the screening of the electrostatic repulsion between similarly charged beads by added salt. In a certain range of salt concentration, the beads-on-string aggregates coexist with the rodlike ones. In the presence of polymer, the sphere-to-rod transition occurs at higher salt concentration than in pure surfactant system indicating that hydrophobic polymer favors the spherical packing of potassium oleate molecules. The size of micelles was estimated by DLS. The rods that are formed in the hybrid system are much shorter than those in polymer-free surfactant solution suggesting the stabilization of the semi-spherical endcaps of the rods by embedded polymer. 2D NOESY data evidence that in the spherical aggregates the polymer penetrates deep into the core, whereas in tighter packed rodlike aggregates it is located mainly at core/corona interface. According to SANS with contrast variation, inside the rodlike aggregates the polymer adopts more compact coil conformation than in the beads-on-string aggregates. Such adaptive self-assembled polymer-surfactant nanoparticles with water-insoluble polymer are very promising for various applications including drag reduction at transportation of fluids.

Effect of calcium on the thermal denaturation of whey proteins and subsequent fouling in a benchtop fouling device: An experimental and numerical approach

The key role of calcium in whey protein fouling behavior is well known in plate heat exchangers (PHEs), as it affects both the thermal denaturation of proteins and deposition reaction on the surface. However, the complex flow pattern and the closed configuration of PHEs make it hard to investigate this phenomenon in situ. In this paper, a microchannel benchtop fouling device was designed, making it possible to achieve a similar temperature profile to that performed in PHEs but in a laminar regime. A 3D simulation was developed to predict the thermal denaturation of β-lactoglobulin (BLG) as well as its deposition in the microchannel using computational fluid dynamics (CFD). The thermodynamics and heat transfer of the numerical model was validated by experimentally measuring the bulk fluid temperature profile in the microchannel using fluorescence microscopy, where Pyrromethene 556 was used as a temperature indicator. Results revealed a quasi-linear relationship between the pre-exponential factor of deposition reaction and the calcium concentration, implying that the fouling was built in such a pattern that only one calcium ion per one BLG molecule is involved. The imaging of the fouling deposit in situ showed spherical structures of deposits at low calcium levels, while denser and more rod-like ones were found at higher calcium concentrations. The fouling behavior was found to follow a crystallization-like pattern with preference upon the previously fouled layer instead of clean stainless steel surface. These findings confirm the essential role of ionic calcium on the formation of fouling deposits by anchoring the denatured BLG protein upon the surface as well as strengthening the protein-protein interactions for fouling build-up.

The magnetic property of CoFe2O4 assembly by the gradient magnetic field

The CoFe2O4 assembly was synthesized through the thermal decomposition under the gradient magnetic field. The applied magnetic field (AMF) changes the spherical-like aggregates in the case of the field-free synthesis to the rod-like ones synthesized in the AMF. All the assemblies consist of nanoparticles (NPs). The AMF reduces and adjusts the size of NPs and hence the magnetic properties, enabling us to obtain the single-domain and super-paramagnetic NPs. The AMF can change the coercivity in a broad range of 213 Oe ~ 11,500 Oe and increase the remanence ratio at 10 K from 0.64 to 0.75. This work reports a new route to synthesize the magnetic materials with the clean surface, different particle size and magnetic properties, suitable for the demands in different applications, simply by changing the strength of AMF in the absence of any additives and templates.

Revisiting stress-strain behavior and mechanical reinforcement of polymer nanocomposites from molecular dynamics simulations.

Through coarse-grained molecular dynamics simulations, the effects of nanoparticle properties, polymer-nanoparticle interactions, chain crosslinks and temperature on the stress-strain behavior and mechanical reinforcement of polymer nanocomposites (PNCs) are comprehensively investigated. By regulating the filler-polymer interaction (miscibility) in a wide range, an optimal dispersion state of nanoparticles is found at moderate interaction strength, while the mechanical properties of PNCs are improved monotonically with the increase of the particle-polymer interaction due to the tele-bridge structures of nanoparticles via polymer chains. Although smaller-sized fillers more easily build interconnected structures, the elastic moduli of PNCs at the percolation threshold concentration where a three-dimensional filler network forms are almost independent of nanoparticle size. Compared with spherical nanoparticles, anisotropic rod-like ones, especially with larger aspect ratio and rod stiffness, contribute exceptional reinforcement towards polymer materials. In addition, the elastic modulus with the strain, derived from the stress-strain curve, shows an analogous nonlinear behavior to the amplitude-dependence of the storage modulus (Payne effect). Such a behavior originates essentially from the failure/breakup of the microstructures contributing to the mechanical reinforcement, such as bound polymer layers around nanoparticles or nanoparticle networking structures. The Young's modulus as a function of the nanoparticle volume fraction greatly exceeds that predicted by the Einstein-Smallwood model and Guth-Gold model, which arises primarily from the contribution of the local/global filler network. The temperature dependence of the Young's modulus is further examined by mode coupling theory (MCT) and the Vogel-Fulcher-Tammann (VFT) equation, and the results indicate that the time-temperature superposition principle holds modestly above the critical temperature on the short-time (small-length) scale of elastic response. This work is expected to provide some guidance on controlling and improving the mechanical properties and nonlinear behavior of PNCs.

Rod-like and mushroom-like Co3O4–CeO2 catalysts derived from Ce-1,3,5-benzene tricarboxylic acid for CO preferential oxidation: effects of compositions and morphology

Rod-like and mushroom-like Co3O4–CeO2 catalysts were synthesized using CeBTC MOFs as self-sacrifice templates. The two kinds of Co3O4–CeO2 catalysts with different shapes were characterized by SEM, TEM, N2 physical-sorption, XRD, TPR, Raman, XPS. The effects of compositions and morphology on the catalytic activity were investigated. The catalytic activities of Co3O4–CeO2 are correlated with the results of SEM, TEM, N2 physical-sorption, XRD, TPR, Raman, XPS to give insights into the catalytic sites. The results indicate the obtained Co3O4–CeO2 catalysts exhibit rod-like and mushroom-like, replicating the morphology of CeBTC templates. The catalytic activities of Co3O4–CeO2 were arranged in this sequence: Co1Ce > Co6Ce > Co2Ce > Co4Ce > Co8Ce, regardless their different catalyst morphology. The mushroom-like catalysts are superior to the rod-like ones due to their high surface areas and small Co3O4 crystal sizes. The sequence of catalytic activity versus Co/Ce ratio are coincidence with the order of Co–Ce synergistic interaction and Co3+/Co deduced from results of XRD, TPR, Raman, XPS. This evidence revealed that the Co–Ce synergistic interaction and Co3+ ions are responsible for the high activity of Co3O4–CeO2 catalysts. The highest CO conversion of 99% catalyst was achieved over M-Co1Ce catalyst with 12.5% CO2 and 15% H2O at 215 °C, 20,000 mL g−1 h−1. In addition, CO conversion of M-Co1Ce catalyst maintained more than 99% for 54 h in the atmosphere of simulated reformate at 20,000 mL g−1 h−1, suggesting the M-Co1Ce catalyst demonstrates potential in practice application.

Control of Dispersolds in 7475 Aluminum Alloy

7475 aluminium alloy is widely used in aerospace industry and military field. There are many dispersoid former elements in 7475 aluminium alloy, such as Mn, Cr, Ti, Zr and Sc. And the dispersoid configuration has important effect on the performance of alloy wrought. The characteristic of dispersoids in the semi-continuous casting ingot of 7475 aluminum alloy and the evolution of their distribution during rolling have been investigated. The size, shape and distribution of dispersoids are controlled by pre-treatment before homogenization. The results show that there are many coarse triangular, irregular block and spindly rod-like dispersoids which contain some of Cr and Mg and a little of Cu and Zn in the 7475 aluminum alloy which subject to conventional one-step homogenization treatment. The size and the distribution of the Cr-containing dispersoids is not uniform. The width of the coarse dispersoids is close to 1 micron and the length of the spindly rod-like dispersoids is more than 4 microns. There is no dispersoids in the center of the dendritic grains, but the nonuniform distribution of dispersoids is eliminated when the hot rolling reduction exceed 80%. The dispersoids can be significantly refined and homogenously distributed by pre-treated before the conventional one-step homogenized. The pre-treatment can stimulate the nucleation of Cr-containing dispersoids, narrow down the dispersoids free zone. The size of the dispersoids is dramatically reduced by pre-treated before the conventional homogenization, and the width of the coarse dispersoids and length of the spindly rod-like ones are less than 300 nm and 1 micron.

Strong difference between optical properties and morphologies for J-Aggregates of similar cyanine dyes

Optical properties and morphologies of molecular aggregates of two similar cyanine dyes (BIC and TDBC) have been studied. The dyes have the same 5,5′,6,6′-tetrachlorobenzimidacarbocyanine chromophore part and differ just in one methyl group in alkyl chains. Due to such a similarity of the dye molecular structures, their aggregates are often supposed to have similar structure. However the difference in optical properties was reported in some publications assuming different structures of the J-aggregates. Indeed, we have found distinct morphologies for BIC and TDBC J-aggregates: spherical species for BIC J-aggregates and rod-like ones for TDBC J-aggregates. The difference in morphologies and, hence, structures is the reason of unlike optical properties of these J-aggregates.

From optimized monovalent ligands to size-controlled dendrimers: an efficient strategy towards high-activity DC-SIGN antagonists

This short review describes our work on the development of dendrimeric antagonists of DC-SIGN, a dendritic cells (DCs) receptor recognizing highly mannosylated structures and primarily involved in the recognition of viruses such as HIV. The structure of pseudo-di-mannoside and pseudo-tri-mannoside compounds was first finely modified to obtain DC-SIGN ligands that were more stable and selective than mannose. Their DC-SIGN affinity differences were amplified once presented on multivalent dendrimer-like scaffolds, including poly-alkyne terminated and phenylene-ethynylene rod-like ones. Libraries of mannosylated dendrimers were synthesized, improving their stability and maximizing their monodispersity. The effect of the dendrimers valency, structure, and size on DC-SIGN affinity and antiviral potency was investigated. Both the valency and the topology of the architectures were revealed as key parameters for activity optimization, together with the intrinsic affinity of the monovalent ligand. The stability, rigidity, and length of the scaffolds were also tuned. The design of geometrically adapted scaffolds afforded one of the most potent inhibitors of DC-SIGN mediated HIV infections to date. This monodispersed, not cytotoxic, and highly active compound was also tested with DCs; its internalization into endolysosomal compartments and its ability to induce the overexpression of signaling molecules makes it a good precursor to produce pathogen-entry inhibitors with immunomodulant properties.

Strengthening Effect of Extruded Mg-8Sn-2Zn-2Al Alloy: Influence of Micro and Nano-Size Mg₂Sn Precipitates.

In this study, Mg-8Sn-2Zn-2Al (TZA822) alloys with varying Mg2Sn contents prior to extrusion were obtained by different pre-treatments (without and with T4), and the strengthening response related to micro and nano-size Mg2Sn precipitates in the extruded TZA822 alloys was reported. The results showed that the morphology of nano-size Mg2Sn precipitates exhibits a significant change in basal plane from rod-like to spherical, owing to the decrement in the fraction of micro-size particles before extrusion. Meanwhile, the spherical Mg2Sn precipitates provided a much stronger strengthening effect than did the rod-like ones, which was ascribed to uniform dispersion and refinement of spherical precipitates to effectively hinder basal dislocation slip. As a consequence, the extruded TZA822 alloy with T4 showed a higher tensile yield strength (TYS) of 245 MPa, ultimate tensile strength (UTS) of 320 MPa and elongation (EL) of 26.5%, as well as a lower degree of yield asymmetry than their counterpart without T4. Detailed reasons for the strengthening effect were given and analyzed.

Improvement of the creep resistance of FeCo–2V alloy arising from a small addition of Cr

This work presents our recent findings that a small addition (0.5 at. %) of Cr to FeCo–2V alloy leads to a great improvement in creep resistance. High resolution electron microscopy was applied to study microstructural evolution of the Cr added alloy during the creep process performed at 600 °C under 200 MPa. At an initial step of the creep, there appear plate-like precipitates with bcc/fcc structure as well as some rod-like ones with hcp structure. A coherent relationship is identified between the precipitates and bcc FeCo matrix. With prolonging the creep, the rod-like hcp precipitates are revealed to remain in the bcc matrix, showing a good stability under the creep condition and in turn resulting in piling-up of dislocations to a great extent around the precipitates. In addition, the Cr added alloy is shown to have a large stress exponent of 8.4, indicating a strong interaction between dislocations and the hcp precipitates.

Multiple morphologies of YF3: Eu3+ microcrystals: Microwave hydrothemal synthesis, growth mechanism and luminescence properties

Uniform and well-crystallized orthorhombic YF3:Eu3+ phosphors with different morphologies (rod-like, spindle-like and gearwheel-like) were prepared by a facile microwave-assisted hydrothermal method. The as-synthesized products were systematically characterized by X-ray powder diffractometer (XRD), thermal field emission scanning electron microscope (FE-SEM), high resolution transmission electron microscope (HRTEM), and photoluminescence (PL) spectrometer. The results indicate that reaction temperature and time have great impact on the morphology and size of the products. A possible formation mechanism of the micro-gearwheel like particle was proposed based on the time-dependent experiments and HRTEM results. The emission spectrum recorded for an excitation wavelength of 392nm exhibited a strongest emission peak centered at 592nm, corresponding to the magnetic dipole of the 5D0→7F1 transition of Eu3+ ions. The quenching concentration was found at 20mol% doping of Eu3+. The investigation on morphology-dependent luminescence properties reveals that the gearwheel-like YF3:Eu3+ powders exhibit the strongest orange–red emission, while the intensity of rod-like ones is the lowest.

Morphological Effect of Non-targeted Biomolecule-Modified MNPs on Reticuloendothelial System.

Magnetic nanoparticles (MNPs) with special morphology were commonly used as biomaterials, while morphological effects of non-targeted biomolecule-modified MNPs on biological behaviors were still unclear. In this research, spherical and rod-like Fe3O4 in a comparable size were synthesized and then surface-modified by bovine serum albumin (BSA) as a model of non-targeted biomolecule-modified MNPs. Morphological effects were featured by TEM and quantification of in vitro phagocytic uptake, as well as the in vivo quantification of particles in reticuloendothelial system (RES)-related organs of normal Kunming mice. For these non-targeted BSA-modified MNPs, intracellular distributions were the same, but the rod-like MNPs were more likely to be uptake by macrophages; furthermore, the BSA-modified MNPs gathered in RES-related organs soon after intravenous injection, but the rod-like ones were expelled from the lung more quickly and expelled from the spleen more slowly. These preliminary results may be referable if MNPs or other similar biomolecule-modified nanoparticles were used.

Molten salt synthesis and tunable photoluminescent properties of Eu3+–Tb3+ doped NaY(MoO4)2 microcrystals

Octahedron-like and rod-like NaY(MoO4)2 microcrystals with tetragonal scheelite-type structure were successfully synthesized by a low cost molten salt method using NaCl as the reaction medium. The as-obtained products were characterized by powder X-ray diffractometer, thermal field emission scanning electron microscope, and photoluminescence spectrometer. The results show that NaY(MoO4)2 with different morphologies have been controllably obtained via adjusting calcining temperature and reaction time. Under the UV light excitation, the emission intensity of the octahedron-like NaY(MoO4)2:Eu3+/Tb3+ microcrystals is stronger than the rod-like ones. Moreover, the luminescence colors of the Eu3+–Tb3+ co-doped NaY(MoO4)2 octahedron-like microcrystals can be tuned from red, orange, yellow and green-yellow to green by simply adjusting the relative doping concentrations of the activator ions, which might have potential application in the areas such as optoelectronic devices in the future.

Hydrothermal growth of upright-standing ZnO sheet microcrystals

Abstract Large-scale upright-standing ZnO sheet microcrystals were fabricated on Zn substrate using sodium oxalate as structure-directing agent by a hydrothermal method at low temperature (70 °C) without any surfactant. The sheets are about 3–5 μm in dimension and 100–300 nm in thickness. The strong and narrow diffraction peaks of ZnO indicate that the sample has a good crystallinity and size. The morphology of sheet-like ZnO varied with the concentrations of sodium oxalate and reaction time. The sheet-like ZnO would transform into rod-like ones when sodium oxalate was substituted by equivalent sodium acetate. The formation of sheet-like ZnO is attributed to the preferable adsorption of oxalate anions on (0 0 0 1) face of ZnO, which inhibits the intrinsic growth of ZnO. Additionally, the continuous growth in six (0 1 −1 0) directions that have the lowest surface energy leads to the formation of hexagonal sheets.

Synthesis of ZnO microstructures in glycerol/water solution

Abstract Zinc oxide (ZnO) microrods with high aspect ratio and microstructures with flowerlike morphologies have been synthesized successfully in a glycerol/water reaction system by a simple solvothermal method without adding any surfactants or templates at 180 °C. Experimental results indicated that the flowerlike ZnO microstructures were transformed into rodlike ones with increasing amounts of zinc acetate dihydrate (Zn(Ac) 2 ·2H 2 O) and sodium hydroxide (NaOH) because of the rapid nucleation and growth, indicating that the concentration of reactants is the key to control the morphologies of ZnO samples. In contrast, double-columned and double-hemisphered ZnO microstructures were fabricated using similar solvothermal conditions without adding NaOH by adjusting the proportion of glycerol and water, for these crystallites were generated mainly by esterification between Zn(Ac) 2 ·2H 2 O and glycerol. Time-dependent experiments have also been conducted to explore the evolution of ZnO morphologies. The growth mechanism of as-prepared ZnO structures synthesized in different conditions was discussed.

Preparation of Barium Sulfate Nanoparticles in an Interdigital Channel Configuration Micromixer SIMM-V2

BaSO4 nanoparticles were synthesized by precipitation of Na2SO4 and BaCl2 at their concentrations close to their saturation concentrations in a commercially available micromixer, SIMM-V2. The particle size of BaSO4 was dependent on the flow rate at the saturation concentrations, exhibiting a Z-type change with increasing the flow rate. The average particle size of BaSO4 particles could be adjusted by decreasing the Na2SO4 concentration. Decreasing the molar ratio R to less than 1 resulted in agglomerated round BaSO4 particles, while dispersible rod-like ones were produced when R = 1.2–1.8. The wastewater separated from each synthesis solution could be reused to prepare the BaCl2 solution, resulting in a slight increase in the mean particle size and broadened particle size distribution after eight cycles. The optimized preparation process could produce 2 kg/h of BaSO4 nanoparticles with a mean particle size of 28 nm with a narrow particle size distribution.

Amphiphilic ferrocenylated alkylpyridinium: the formation of micelles and hydrogels and their disaggregation induced by an external stimulus

Ferrocene-containing amphiphiles [py-N-(CH2)nOCH2Fc]Cl (n = 6 (1a), 8 (1b), 10 (1c); py = C5H5N, Fc = Fe(C5H4)(C5H5)) were synthesized. The absorption spectra of 1a-1c in the presence of a small amount of dye (Nile red and pyrene) in aqueous media suggested the formation of micelles which encapsulated the dye molecules. Two critical micelle concentrations were observed at 1.1 mM and 2.3 mM at 20 °C. Compounds 1a and 1c showed a single CMC for each, while the formation of two kinds of micelles, the spherical and rod-like ones, depended on the concentrations. The addition of an oxidant, NaOCl, to the aqueous solution of the micelles of 1b turned ferrocene to ferrocenium and caused the disaggregation of the micelles. The addition of α-cyclodextrin (α-CD) to 2b caused the disaggregation of the micelle and the formation of water-soluble [2]- and [3]pseudorotaxane [{py-N-(CH2)8OCH2Fc}(α-CD)m]Cl (1b(α-CD)m) (m = 1, 2), while mixing 1c and α-CD in water formed the rotaxane gel. The addition of NaOCl to the hydrogel of 1c and α-CD changed the gel to sol.

Effect of Co on Si and Fe-containing intermetallic compounds (IMCs) in Al–20Si–5Fe alloys

The effects of cobalt addition on microstructure and mechanical properties of Al–20Si–5Fe–XCo (X=0, 1, 3, and 5) alloys were reported in this study. The alloys were produced by both conventional sand casting and melt-spinning at 20m/s disk velocity. Microstructures of the samples were investigated using X-ray diffractometry (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Vickers micro-hardness tester was used for hardness measurements. Results showed that Co addition can alter morphology of Fe-bearing intermetallic compounds (IMCs) from long rod/needle-like structures to short rod-like ones, and lead to a more homogenous distribution in the microstructure. Addition of 5wt% Co leads to a decrease in average size of the primary silicon phases in as-cast Al–Si alloys. In melt-spun alloys, with the addition of Co, the microstructure became finer and more homogenously distributed, while thickness of the featureless zone has seen great increase. The optimum Fe to Co ratio was found to be 1 for suppressing the undesirable effect of Fe-bearing acicular/needle-like intermetallic compounds.

Plasmonic Titania Photocatalysts Active under UV and Visible-Light Irradiation: Influence of Gold Amount, Size, and Shape

Plasmonic titania photocatalysts were prepared by titania modification with gold by photodeposition. It was found that for smaller amount of deposited gold (≤0.1 wt%), anatase presence and large surface area were beneficial for efficient hydrogen evolution during methanol dehydrogenation. After testing twelve amounts of deposited gold on large rutile titania, the existence of three optima for 0.5, 2 and >6 wt% of gold was found during acetic acid degradation. Under visible light irradiation, in the case of small gold NPs deposited on fine anatase titania, the dependence of photoactivity on gold amount was parabolic, and large gold amount (2 wt%), observable as an intensively coloured powder, caused photoactivity decrease. While for large gold NPs deposited on large rutile titania, the dependence represented cascade increase, due to change of size and shape of deposited gold with its amount increase. It has been thought that spherical/hemispherical shape of gold NPs, in comparison with rod-like ones, is beneficial for higher level of photoactivity under visible light irradiation. For all tested systems and regardless of deposited amount of gold, each rutile Au/TiO2 photocatalyst of large gold and titania NPs exhibited much higher photoactivity than anatase Au/TiO2 of small gold and titania NPs.