Acicular Particles Research Articles

Titanium foam through powder metallurgy route using acicular urea particles as space holder

In the present work, Ti foam has been synthesized employing powder metallurgy route. Irregular titanium powder particles were used as the matrix and acicular urea particles as the space holder. The distribution of the urea particles in the matrix of the compacted mass was observed to be fairly uniform. Pore morphology and compressive behavior of the resulting foam have been studied. The processed foam consisted of acicular porous regions of size up to 500 μm. The porous regions contained a large number of micro-pores along with the occasional presence of coarse pores, the latter thought to be unhealed portions of the original acicular pores. The foam delineated a distinct plateau region with plateau stress of 275 MPa and energy absorption capacity of 55 MJ/m 3.

Electrical Properties of 1–3 Piezocomposites Prepared from Textured KSr2Nb5O15 (KSN) Ceramic Fibers

Highly [001] textured KSr2Nb5O15 (KSN) ceramic fibers were fabricated by a combination of novel alginate gelation method and templated grain growth using acicular KSr2Nb5O15 template particles. Fibers were drawn from alginate based slurries without or with 10 wt% KSN template particles. A maximum texture fraction of 0.96 was obtained. Piezocomposites with 1–3 connectivity were prered from the KSN fibers and their electrical and electromechanical properties were investigated. Dielectric constant of 90, piezoelectric charge coefficient of 60 pC/N, remnant polarization of 10 μC/cm2 and electric field induced strain of up to 0.036% were obtained from piezocomposites with textured fibers.

Effects of Sr-modification, iron-based intermetallics and aging treatment on the impact toughness of 356 Al–Si–Mg alloy

Impact toughness as a property has been acquiring increased importance in recent years, since data regarding this property can provide a means for assessing alloy ductility under high rates of deformation. The main objective of this study is to investigate the effects of Sr-modification, Fe-based intermetallic phases and aging conditions on the impact toughness of widely used 356 alloys. The total absorbed energy was measured using a computer-aided instrumented Instron Charpy impact testing machine. Increasing the level of iron additions decreases the impact energy values of 356 alloys to a noticeable degree (~35–57%). The addition of 0.1 wt% Mn to non-modified 356 alloys seems to have no observable effect on the impact energy, while increasing the Mn addition to 0.4 wt% produces a slight improvement in the impact energy values for non-modified and Sr-modified 356 alloys compared to that of those containing only iron under the same conditions. The application of solution heat treatment in combination with Sr-modification was found to significantly improve the impact energy of as-cast 356 alloys, particularly at low iron additions. Artificial aging of non-modified and Sr-modified 356 alloys at 180 °C diminishes the impact energy values with an increase in the aging time up to 8 h compared to those obtained under the solution heat-treated conditions. On the other hand, aging at 220 °C for 12 h increases the impact energy values of Sr-modified 356 alloy containing 0.12 wt% Fe and combined 0.2 wt% Fe–0.1 wt% Mn to about 20 and 18 J, respectively. The fracture behavior of non-modified 356 alloys containing 0.12 wt% Fe is mainly controlled by the acicular eutectic Si particles whereas β-iron platelets act as crack initiation sites and provide further path for final crack propagation in non-modified 356 alloys containing 0.9 wt% Fe. The β-iron platelets and π-iron phase particles contribute largely to crack initiation and propagation in the Sr-modified 356 alloys containing 0.9 wt% Fe.

Research on forge-quenching process of nodular cast iron

A new quenching process for nodular cast iron named forge-quenching heat treatment is developed. Nodular cast iron underwent hot forging immediately followed by quenching at 790°C in water. Compared with conventional quenched nodular cast iron, microstructure analysis shows the existence of finer acicular martensitic structure and prolate ellipsoids graphite particles in forge-quenched nodular cast iron. The hardness and impact test results show that the forge-quenched nodular cast iron presents superior mechanical properties to conventional quenched nodular cast iron. The wear rate and the friction coefficient are 2 times lower than quenched white cast iron which is used as grinding balls.

Structural and electronic properties of cubic CeO2: Unpaired electrons in CeO2

AbstractThe high performance of cerium dioxide (CeO2) as support for Au in catalysis relies on its ability to anchor Au clusters and transfer charge to the gold nanoparticles. These two processes are governed by oxygen vacancy formation. To study the localization and the mobility of the electrons left behind by the vacancy from the relaxed oxygen, an experimental and theoretical study is hereby reported. CeO2 powder was synthesized by the polyacrylamide gel method and its microstructure was characterized by X‐ray diffraction and high resolution scanning electron microscopy. We have determined the presence of only the fluorite cubic phase in our samples and the formation of acicular particles of ∼1 μm in length. In the electron spin resonance study, we observed that the unpaired electrons are quasi free. A single‐line paramagnetic signal is observed that exhibits spin characteristics with a g‐value of 2.0039 at room temperature. This compares well to the value of 2.0023 determined for free electrons. In addition, we have conducted a theoretical study using a density functional theory cluster approach and calculate the electron spin density of CeO2 clusters. We find that spin density clouds are localized around the cerium ions. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010

The anisotropic morphology of silver particles in Y-123/Y-24Nb1/Ag nanocomposite bulk high-temperature superconductors

Y2Ba4CuNbO12 (Y-24Nb1) and silver (Ag) are recognized as potential candidates for improving both flux pinning and the mechanical properties of bulk rare earth (RE)–Ba–Cu–O [(RE)BCO] high-temperature superconductors (HTS). Recent attempts to add Ag2O to superconducting Y-123/Y2Ba4CuNbO12 composites, however, have produced a highly anisotropic morphology of Ag particles in samples grown by top-seeded melt growth (TSMG). This morphology has been attributed to strong particle pushing effects due to the presence of Y-24Nb1 nanoparticles in the composite microstructure. An investigation of the formation of anisotropic Ag particles in the YBCO bulk microstructure indicates that these pushing effects generate different morphological microstructural zones in the composite. These include a zone free of inclusions other than acicular Ag particles, a zone of segregated additives (i.e., Y-24Nb1, Y-211, and Ag), and a zone containing fine Ag and other particles distributed uniformly throughout the local microstructure. The particle pushing/trapping theory has been used to explain these extraordinary features of the distribution of Ag inclusions. The superconducting and mechanical properties of samples containing very fine silver inclusions are also discussed briefly.

Intracellular and extracellular mineralization of a microbial community in the Edmond deep-sea vent field environment

Microbial biomineralization in submarine hydrothermal environments provides an insight into the formation of vent microfossils and the interactions between microbes, elements and minerals throughout the geological record. Here, we investigate microbial biomineralization of a deep-sea vent community in the Edmond vent field and provide ultrastructural evidence for the formation of microfossils and biogenic iron-rich minerals related to Archaea and Bacteria. Environmental scanning electron microscopy (ESEM) analysis shows that filamentous and spiral microbes are encrusted by a non-crystalline silica matrix and minor amounts of iron oxides. Examination by transmission electron microscopy (TEM) reveals acicular iron-rich particles and aggregates that occur either intracellularly or extracellularly. A culture-independent molecular phylogenetic analysis demonstrates a diverse range of Bacteria and Archaea, the majority of which are related to sulfur metabolism in the microbial mats. Both Archaea and Bacteria have undergone silicification, in a similar manner to microorganisms in some terrestrial hot springs and indicating that silicification may be driven by silica supersaturation and polymerization. Formation mechanisms of intracellular and extracellular iron oxides associated with microbes are discussed. These results enhance our understanding of microbial mineralization in extreme environments, which may be widespread in the Earth's modern and ancient hydrothermal vent fields.

Growth of uniform lath-like α-(Fe,Al)OOH and disc-like α-(Fe,Al) 2O 3 nanoparticles in a highly alkaline medium

The effects of aluminium (Al 3+)-dopant on the precipitation of uniform lath-like α-FeOOH particles, the obtention and growth of α-(Fe,Al)OOH and α-(Fe,Al) 2O 3 solid solutions, particle size and shape were investigated using X-ray powder diffraction, Mössbauer and Fourier transform infrared spectroscopies, field emission scanning electron microscopy and energy dispersive X-ray spectroscopy. Acicular α-FeOOH particles, precipitated in a highly alkaline medium with the addition of tetramethylammonium hydroxide (TMAH), were used as reference material. The influence of Al-dopant was investigated by adding varying amounts of Al 3+ ions to the initial FeCl 3 solution. In the presence of lower concentrations of aluminium ions (up to 11.11 mol%) α-(Fe,Al)OOH as a single phase was formed, whereas higher concentrations led to an additional obtention and growth of α-(Fe,Al) 2O 3. Al-for-Fe substitution in the α-FeOOH and α-Fe 2O 3 structures was confirmed by a decrease in the unit-cell dimensions, a decrease in the hyperfine magnetic field and an increase in the wave number of the infrared absorption bands. The presence of lower concentrations of aluminium ions (up to 11.11 mol%) in the precipitation system did not affect the size and shape of the α-(Fe,Al)OOH particles, whereas higher concentrations influenced a decrease in the length and aspect ratio. In the presence of 42.86 mol% Al 3+ ions fairly uniform disc-shaped α-(Fe,Al) 2O 3 were formed.

High coercivity cobalt carbide nanoparticles processed via polyol reaction: a new permanent magnet material

Cobalt carbide nanoparticles were processed using polyol reduction chemistry that offers high product yields in a cost effective single-step process. Particles are shown to be acicular in morphology and typically assembled as clusters with room temperature coercivities greater than 3.4 kOe and maximum energy products greater than 20 kJ m−3. Consisting of Co3C and Co2C phases, the ratio of phase volume, particle size and particle morphology all play important roles in determining permanent magnet properties. Further, the acicular particle shape provides an enhancement to the coercivity via dipolar anisotropy energy as well as offering potential for particle alignment in nanocomposite cores. While Curie temperatures are near 510 K at temperatures approaching 700 K the carbide powders experience an irreversible dissociation to metallic cobalt and carbon thus limiting operational temperatures to near room temperature. These findings warrant more extensive investigation of this and other magnetic carbide systems in which particle size, chemistry and morphology are optimized.

Supercritical antisolvent processing of γ-Indomethacin: Effects of solvent, concentration, pressure and temperature on SAS processed Indomethacin

γ -Indomethacin (IMC) is successfully processed with the supercritical antisolvent (SAS) technique. Pure, acicular (needle-like) particles of the α-polymorph are consistently obtained with SAS as the solvent, concentration, temperature and pressures are varied. Controlled changes in process parameters yield significant changes in particle size. Enhanced dissolution profiles are observed with IMC processed with SAS as opposed to the unprocessed IMC. The reduced particle size, as well as the α-polymorphic form of IMC, contributes to the enhanced dissolution rate.

Mössbauer study of oxygen adducts in solid Fe(II) phthalocyanines

Beta iron phthalocyanines (β-FePc) oxygenated at low temperatures were investigated with the help of 57Fe Mössbauer spectroscopy and X-ray diffractometry (XRD). The oxygenation of FePc complex is the key step in the pyrolysis of the flat layered molecules that yields acicular iron carbide particles encaged in uniform carbon shells. Mössbauer spectroscopy revealed that upon oxygenation of β-FePc new species were formed which could be associated with FeIIIPc oxygen adducts in high spin and low spin states. The temperature dependent Mössbauer measurements showed the interconversion of the low spin species into high spin species upon raising the temperature.

Spectroscopic and electron microscopic investigation of iron oxides formed in a highly alkaline medium in the presence of rhodium ions

The effect of the presence of rhodium ions on the formation of iron oxides in a highly alkaline precipitation system was investigated using X-ray powder diffraction (XRD), 57Fe Mössbauer and FT-IR spectroscopies, field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDS). Acicular α-FeOOH particles precipitated in a highly alkaline medium with the addition of tetramethylammonium hydroxide (TMAH) were used as reference material. Characterization of α-FeOOH samples formed in the presence of rhodium ions showed a somewhat smaller mean crystallite size, increased unit-cell dimensions, a reduced average hyperfine magnetic field and a slight shift in the position of IR absorption bands in comparison with the reference α-FeOOH sample. By additional heating of the precipitation system, α-FeOOH precipitated in the presence of rhodium ions transformed to α-Fe 2O 3 crystals in the form of hexagonal bipyramids via a dissolution–recrystallization process. Metallic rhodium nanoparticles were formed simultaneously by the reduction of Rh 3+ ions in the presence of the products of TMAH thermal decomposition (trimethylamine and methanol). These rhodium nanoparticles acted as a catalyst for the reductive dissolution of α-Fe 2O 3 particles and the formation of Fe 3O 4 crystals in the form of octahedrons.

A simple solvothermal route to synthesize carbon microspheres

Carbon micro-spheres were prepared by a simple solvothermal route in a stainless steel autoclave. Absolute ethanol was used as carbon source and solvent, and nickel as catalyst, obtained by reducing Ni(Ac) 2 in absolute ethanol. Carbon microspheres were obtained at 500 °C for 48h. The samples were characterized by X-ray powder diffractometer, scanning and transmission electron microscopy, and Raman spectroscopy. Results showed that there were acicular and spherical carbon particles in the as-prepared samples. The carbon microspheres had diameters ranging from 1 to 2 μm. and the acicular particles had diameters ranging from 1 to 2 μm and lengths ranging from 3 to 6 μm. The yield of carbon micro-spheres was over 95% with a narrow size distribution and perfect shape.

PH and temperature dependent facile precipitation of nano-goethite particles in Fe(NO 3) 3–NaOH–NH 3NH 2HSO 4–H 2O medium

A new synthesis route for producing nanosized crystallites of acicular goethite particles using ferric nitrate, hydrazine sulphate and sodium hydroxide is reported. The process steps essentially consist of a four-step procedure: (i) partial reduction of Fe(III) to Fe(II) due to the addition of hydrazine sulphate to ferric nitrate solution, (ii) formation of ferrihydrite primary particles, (iii) their transformation to goethite, and (iv) the growth of the goethite nuclei. X-ray diffraction, transmission electron microscopy and infrared spectroscopy data have been used to determine the phase formation under different pH and temperature conditions. Depending on the pH of precipitation ferrihydrite (pH 2–5), goethite (pH 7) or a mixture of goethite and magnetite (pH 9–12) was obtained when precipitation was carried out in the presence of hydrazine sulphate whereas in its absence under similar conditions only ferrihydrite was formed up to a pH of 9 and at pH 12 a mixture of ferrihydrite and goethite was observed. Addition of hydrazine sulphate reduced the pH formation of goethite. Precipitation was also carried out by maintaining temperature in the range of 300–353 K at a pH of 3. The results show that uniform goethite particles of 200–400 nm length with a high axial ratio of 10, can be obtained at a pH of 7 at room temperature and pure goethite can also be obtained at 353 K at a pH of 3.

Dynamic magnetic hysteresis in a liquid suspension of acicular maghemite particles

This paper presents theoretical and experimental studies on the magnetodynamics and energy absorption in a dilute suspension of small ferromagnetic particles with magnetic hysteresis and mechanical mobility in an AC magnetic field. Experiments with 0.1% suspensions of acicular particles of gamma ferric oxide in solid and liquid matrices, subjected to a 430 Hz magnetic field with an intensity of up to 1200 Oe, revealed important role of particle mobility. The main qualitative and quantitative features of the phenomenon are in agreement with a model of joint magneto-mechanical dynamics of particles with a chain-of-spheres mode of incoherent magnetic reversal.

Cyclic deformation behavior of a cast aluminum alloy

Due to effective weight reduction and subsequent improvement in fuel economy of vehicles, as well as flexibility in fabrication and high strength-to-weight ratio, cast A356 Al–Si–Mg alloy is being used to replace some relatively heavy components in the automotive industry. However, very limited data on low cycle fatigue (LCF) resistance have been reported on this alloy especially in T5 condition. This study was aimed to evaluate cyclic deformation characteristics, LCF resistance, and fracture mechanisms of A356 alloy in the T5, T6 and modified T6 conditions in relation to their microstructural features. It was observed that the microstructure of this alloy consisted of primary α-Al matrix and eutectic regions containing Si particles, which were acicular in the T5 condition and spherical in the T6 and ModT6 conditions. The ModT6 material had higher yield strength (YS) and ultimate tensile strength (UTS) but lower strain hardening exponent than the T6 material, while the T5 material had lower YS and UTS but higher initial strain hardening exponent than the T6 material. Cyclic stress amplitudes remained basically stable at lower strain amplitudes, and cyclic hardening occurred at higher strain amplitudes. In comparison to the T5 and ModT6 materials, the T6 material exhibited a higher cyclic hardening capacity, giving rise to a longer fatigue life. Crack initiation in both tensile and fatigue tests was observed to occur at the sub-surface pores in all the three material conditions. The T5 material had quasi-cleavage fracture characteristics due to the presence of acicular Si particles, while the T6 and ModT6 exhibited dimple-like fracture features. Fatigue striations, coupled with some secondary cracks and microvoids, were observed to occur in the fatigue crack propagation regime.

Effect of pores and acicular eutectic silicon particles on the performance of Al–Si–Mg (AS7G03) casting

Excellent castability, corrosion resistance and high specific strength has made cast Al–Si–Mg alloys a suitable candidate material for various aerospace application. Aluminium alloy casting AS7G03, belonging to Al–Si–Mg series of cast alloy in Y23 condition, is being used as outlet adaptor of liquid propellant tank for Indian space programme. During developmental stage, one of the castings namely oxidizer tank outlet adaptor failed and parted in to two pieces during the proof pressure test (PPT) at 22 bar. This paper brings out the details of investigation and correlates the effect of pores and acicular unmodified silicon particle on the performance of the material.

Gold in the weathering crust at the Suzdal' deposit ( Kazakhstan)

A comparative analysis of morphology and geochemistry was made for gold from the primary ores and weathering crust of the Suzdal' gold deposit, Eastern Kazakhstan. The deposit is localized in Carboniferous carbonaceous-terrigenous strata and is of gold-sulfide type. Study of gold from primary ores showed that it occurs mainly in two species: free and so-called invisible. Free gold is crystallomorphic segregations and irregular-shaped grains up to tens of microns in size; it occurs in intergrowths with sulfides, quartz, carbonate, and mica-chlorite aggregate. Most of gold particles have a fineness of 930–980‰, with some grains showing wide variations in composition. Invisible gold (probably chemically combined) is present in fine-acicular arsenopyrite and, less frequently, pyrite. Being transported to the weathering crust, all this gold served as a source for “neogenic” gold of diverse morphologic forms. We recognized crystalline (isometric, prismatic, acicular, and tabular) particles and drusoid gold aggregates in the form of exotic intergrowths of crystallomorphic and sinter-shelly grains. The grains tend to coarsen from bottom to top of the weathering crust. Several generations of gold of different granulometric classes are observed. We have revealed seed and layer growth and dissolution structures in crystals of early generations overgrown with fine grains. All these gold varieties are associated with hypergene minerals. Most of this gold is of high fineness (on the average, 995‰). The hypergene gold particles are chemically homogeneous high-grade, without rims. The results of studies suggest that the high-grade hypergene gold formed in the weathering crust as a result of the dissolution of invisible gold of sulfides and its local redistribution and deposition in oxidizing media. This is also evidenced from the tendency of gold to coarsen from bottom to top of the weathering crust. A distinctive feature of secondary gold is well-expressed crystals and their great diversity.

Synthesis of rutile TiO2 with high specific surface area by self-hydrolysis of TiOCl2 in the presence of SDS

Rutile TiO2 with high specific surface area was synthesized by self-hydrolysis of TiOCl2 in the presence of sodium dodecyl sulfate (SDS). The aggregates of rutile acicular particles formed from 0.5 M TiOCl2 at 50°C. In order to synthesize rutile with high specific surface area, the effect of surfactant was investigated. Three kinds of surfactants were used in this study, such as stearyltrimethylammmonium chloride (C18TAC) as cationic surfactant, polyoxyethylene lauryl ether (Brij35) as nonionic surfactant, and SDS as anionic surfactant. Neither C18TAC nor Brij35 was influenced on the morphology of rutile particles. On the other hand, the addition of SDS was effective for the formation of mesopore, which led to specific surface area of 210 m2/g in product.

Formation of iron oxides in a highly alkaline medium in the presence of palladium ions

The effect of the presence of palladium ions in a highly alkaline precipitation system on the formation of iron oxides was investigated using X-ray powder diffraction (XRPD), Mössbauer and FT-IR spectroscopies, field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDS). Acicular α-FeOOH particles precipitated in a highly alkaline medium with the addition of tetramethylammonium hydroxide (TMAH) were used as reference material. The initial addition of palladium ions to that precipitation system had a significant effect on the formation of iron oxide phases and their properties. In the presence of palladium ions, the initially formed α-FeOOH has been transformed to α-Fe 2O 3 crystals in the form of hexagonal bipyramids via a dissolution–reprecipitation mechanism with a simultaneous formation of metallic palladium nanoparticles. These palladium nanoparticles acted as a catalyst for the reductive dissolution of α-Fe 2O 3 particles and the formation of Fe 3O 4 crystals in the form of octahedrons. Increase in the initial concentration of palladium ions in the precipitation system accelerated the transformation process α-FeOOH → α-Fe 2O 3 → Fe 3O 4 and influenced changes in the shape of α-Fe 2O 3 and Fe 3O 4 particles.