Needle-shaped Particles Research Articles

Structured reactors on a metal mesh catalyst for various applications

The modified Bayer process allows coating of a metal mesh surface with a continuous aluminum hydroxide layer in the phase of bayerite. Subsequent calcination turns the aluminum hydroxide layer into a η-alumina layer. The method provides the uniform thickness of tens of microns for the alumina layer. Layers cracking, clogging of mesh cells are not observed. The alumina layer is formed by needle-shaped particles which coalesce to each other through common facets during crystallization. The alumina layer with high specific surface area is perfectly suitable as a support for various active components. A series of Fe-containing mesh-catalysts was tested in the NOx reduction with NH3. Addition of Ce and W to Fe increases NOx conversion significantly. The FeCeW catalyst provides almost 100% of the NOx conversion at a space velocity of 40,000h−1 in the range of 350–500°C with a negligible quantity of N2O. A series of Pt-containing catalysts was tested in the reaction of afterburning of hydrocarbons. Addition of tungsten oxide to the Pt/Al2O3 catalyst decreases T50 by 60°C. An increase in the number of wire mesh leads to a drop of T50. The mesh-catalyst provides better light-off performance than the honeycomb catalyst.

Quantifying the effect of fillers on the breakage behaviour of needle-shaped particles

Understanding the relationship between the applied stress and the behaviour of packings of breakable granular particles is required in many chemical engineering applications. A pharmaceutical tablet is an example where a composite packing (a packing containing a mixture of several kinds of particles) is compacted in the process of tablet formation. In this work, the unidirectional compaction and the breakage processes in composite packings formed from a mixture of breakable needle-shaped crystals and elastic spherical filler particles were studied using a Discrete Element Method (DEM) simulation. The evolution of crystal size distribution and contacts topology with the increasing stress was computed for different relative size, volume fraction and elasticity of filler particles inside the packing. We show that crystals breakability in a packing is directly related to the number of contacts among particles and that it can be significantly influenced by an appropriate choice of added filler particles. The results can be used for the development of mathematical models that describe the pharmaceutical tablet production and other processes involving composite packings of fragile particles.

Influence of particle shape on the rheological behavior of three-phase non-brownian suspensions

Abstract Capillary suspensions are three-phase fluids comprising a solid and two immiscible, liquid phases with unique texture and flow properties. So far, research focused on isometric particles, here we discuss how the addition of a second, immiscible fluid affects structure and flow of suspensions including anisotropic particles. Differently shaped calcium carbonate as well as graphite and aluminum particles have been investigated. For needle-shaped and scalenohedral particles no increase in yield stress σy or storage modulus G’ characteristic for a strong capillary force controlled, percolating particle network is observed when a secondary fluid is added. In contrast, a pronounced increase in σy and G’ is found when a secondary fluid is introduced to suspensions of plate-like particles and optical as well as electron microscopy confirm the formation of a sample-spanning network characteristic for capillary suspensions. Suspensions of isometric particles exhibit a distinct maximum in σy or G’ at low fractions of secondary fluid to particle volume fraction ϕsec/ϕsolid ≈ 0.1–0.2, whereas suspensions of plate-like particles exhibit constant σy and G’ values over a wide range of ϕsec/ϕsolid values up to ≈1 until spherical agglomeration occurs. Due to the different shape of the capillary bridges suspensions of plate-like particles can accommodate much larger fractions of secondary fluid until spherical agglomeration sets in than systems including spherical particles thus offering a versatile basic concept for the design of complex multi-component paste-like products.

Microstructural evolution and mechanical properties of an Fe–18Ni–16Cr–4Al base alloy during aging at 950°C

The development of Gen-IV nuclear systems and ultra-supercritical power plants proposes greater demands on structural materials used for key components. An Fe–18Ni–16Cr–4Al (316-base) alumina-forming austenitic steel was developed in our laboratory. Its microstructural evolution and mechanical properties during aging at 950°C were investigated subsequently. Micro-structural changes were characterized by scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy. Needle-shaped NiAl particles begin to precipitate in austenite after ageing for 10 h, whereas round NiAl particles in ferrite are coarsened during aging. Precipitates of NiAl with different shapes in different matrices result from differences in lattice misfits. The tensile plasticity increases by 32.4% after aging because of the improvement in the percentage of coincidence site lattice grain boundaries, whereas the tensile strength remains relatively high at approximately 790 MPa.

Thermal decomposition of ammonium molybdates

The thermal behavior of ammonium molybdates, i.e., (NH4)6Mo7O24·4H2O (1) and (NH4)2MoO4 (2), was studied in inert (N2) and oxidizing (air) atmospheres by TG/DTA-MS, XRD, FTIR and SEM. The thermal decomposition sequence of 2 had similarities to 1; however, there were significant differences as well. When both of them were annealed, NH3 and H2O were released parallel, and in air the as-evolved NH3 was burnt partially into NO and N2O. In both atmospheres, while 1 decomposed in four steps, the thermal decomposition of 2 involved 5 steps. In the case of 1, the intermediate products were (NH4)8Mo10O34, (NH4)2Mo4O13 and h-MoO3. In contrast, the decomposition intermediates of 2 were (NH4)2Mo3O10, (NH4)2Mo2O7, (NH4)2Mo4O13 and h-MoO3. By both 1 and 2, the final product was dominated by o-MoO3, accompanied with small amount of Mo4O11 in N2, which was absent in air. Most decomposition steps were endothermic, except for the last step around 400 °C, where crystallization from the residual amorphous phase had an exothermic heat effect. In addition, the combustion of NH3 also changed the DTA curve into exothermic in some cases. The morphology of the final products was characterized by 1–5 μm sheet-like particles, except for annealing 2 in N2, when 0.5- to 1-μm-thick and 5- to 10-μm-long needle-shaped particles were detected.

Effect of the heat treatment time on microstructure and fracture toughness of laser-clad TiB2-TiC pseudoeutectic reinforced TiNi/Ti2Ni intermetallic matrix composite coating

A TiNi/Ti2 Ni intermetallic matrix composite coating reinforced by TiB2 and TiC pseudoeutectic structures was prepared on a Ti6Al4V substrate by laser cladding using Ni based and B4 C powder as the cladding material. The coatings were heat treated for different durations (2, 4, and 6 h) at 600 °C. The microstructures of the heat-treated and untreated coatings were then characterized by X-ray diffraction, scanning electron microscopy, and energy dispersive spectrometry. The microhardness and fracture toughness of the coatings were also evaluated. Results reveal that the coating without heat treatment was mainly composed of TiNi/Ti2 Ni as the matrix and TiB2 /TiC as the reinforcements. TiB2 and TiC belong to the pseudoeutectic microstructures, in which a large number of fine columnar/spherical TiC particles are uniformly distributed within the coarse willow-shaped TiB2 particles. Many fine needle-shaped Ti2 Ni particles were precipitated within the initial TiNi grains in the coatings with heat treatment. With the extension in heat treatment time, more Ti2 Ni particles were precipitated. Furthermore, the average microhardness of the coatings was decreased: 941.3 HV0.2 (0 h) 933.2 HV0.2 (2 h), 903.8 HV0.2 (4 h), 890.4 HV0.2 (6 h), whereas the average fracture toughness presented an opposite trend: 4.18 MPa.m1/2 (0 h), 4.26 MPa.m1/2 (2 h), 4.37 MPa.m1/2 (4 h), 4.90 MPa.m1/2 (6 h).

Effects of Nitrogen Content and Austenitization Temperature on Precipitation in Niobium Micro-alloyed Steels

The influences of nitrogen content and austenitization temperature on Nb(C, N) precipitation in niobium micro-alloyed steels were studied by different methods: optical microscopy, tensile tests, scanning electron microscopy, transmission electron microscopy, physicochemical phase analysis, and small-angle X-ray scattering. The results show that the strength of the steel with high nitrogen content is slightly higher than that of the steel with low nitrogen content. The increase in the nitrogen content does not result in the increase in the amount of Nb(C, N) precipitates, which mainly depends on the niobium content in the steel. The mass fraction of small-sized Nb(C, N) precipitates (1–10 nm) in the steel with high nitrogen content is less than that in the steel with low nitrogen content. After austenitized at 1150 °C, a number of large cuboidal and needle-shaped particles are detected in the steel with high nitrogen content, whereas they dissolve after austenitized at 1200 °C and the Nb(C, N) precipitates become finer in both steels. Furthermore, the results also show that part of the nitrogen in steel involves the formation of alloyed cementite.

Precipitation of Non-spherical Particles in Aluminum Alloys Part II: Numerical Simulation and Experimental Characterization During Aging Treatment of an Al-Mg-Si Alloy

This is the second part of the investigation on the precipitation of needle-shaped particles. In part I, two particle aspect ratio-dependent correction factors are introduced to describe the effects of non-spherical precipitate shape on precipitate growth kinetics. In this part II, the two factors are integrated into a CALPHAD-coupled multi-component Kampmann–Wagner numerical model to predict precipitation kinetics of needle-shaped metastable particles during aging treatment of an Al-Mg-Si alloy. The predictions are compared with transmission electron microscopy observations on precipitate number density, volume fraction, and size distribution. Improved agreement is reported, and in particular, the shape of the predicted particle size distribution density function becomes more realistic.

Preparation of calcium silicates with long-fiber (needle) particles

The results of our experimental studies of processes for the synthesis of calcium silicate and hydrosilicate powders with needle-shaped particles from phosphogypsum (technogenic calcium-containing raw material) and sodium silicate block (silicon-containing product of chemical industry) under hydrothermal and microwave-hydrothermal conditions are presented.

A hybrid aluminium alloy and its zoo of interacting nano-precipitates

An alloy with aluminium as its base element is heat treated to form a multitude of precipitate phases known from different classes of industrial alloys: Al–Cu(–Mg), Al–Mg–Si–Cu, and Al–Zn–Mg. Nanometer-sized needle-shaped particles define the starting point of the phase nucleation, after which there is a split in the precipitation sequence into six phases of highly diverse compositions and morphologies. There are several unique effects of phases from different alloy systems being present in the same host lattice, of which we concentrate on two: the replacement of Ag by Zn on the Ω interface and the formation of combined plates of the θ′ and C phases. Using atomically resolved scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy, we investigate the formation mechanisms, crystal structures and compositions of the precipitates.

Effect of two-pass friction stir processing on the microstructure and mechanical properties of as-cast binary Al–12Si alloy

The effect of two-pass friction stir processing (FSP) on the microstructural evolution, mechanical properties and impact toughness of as-cast Al–12Si alloy was investigated systematically. Severe plastic deformation imposed by FSP resulted in a considerable fragmentation of the needle-shaped eutectic silicon particles into the smaller ones. The length of eutectic Si particles decreased from 27±23μm to about 2.6±2.4μm. The average aspect ratio of 6.1±5.1 for eutectic Si particles in the as-cast state decreased to about 2.6±1.0 after FSP with a corresponding increase in their roundness. The hardness, strength, ductility and impact toughness of the alloy increased simultaneously after two-pass FSP. The increase in the yield and tensile strength values after FSP was about 20% and 29%, respectively. The FSPed alloy exhibited 25% elongation to failure and 15% uniform elongation which were almost seven times and five times higher, respectively, than those of the as-cast alloy. The hardness of the alloy increased from 58 Hv0.5 for the as-cast state to about 67 Hv0.5 after FSP. The absorbed energy during impact test increased to about 8.3J/cm2 after FSP, which is about seven times higher than that of the as-cast alloy. Improvements in all mechanical properties were mainly attributed to the radical changes of the shape, size and distribution of the eutectic silicon particles along with the breakage and refined of the large α-Al grains during two-pass FSP.

Phase formation and luminescence of Sr2SiO4:Eu2+ nanopowders prepared by a hybrid process

Sr2SiO4:0.01Eu2+ (S2S:Eu2+) nanopowders were prepared by a hybrid process, and the effects of different silicon sources (tetraethyl orthosilicate and colloidal SiO2) and flux on the structure and luminescence were investigated. The phase ratio of β- to α′-S2S (Rβ/α′), the phase purity, and the particle morphology were strongly affected by the silicon sources and the flux. The synthesized powders mainly consisted of needle-shaped particles whose size depended on the preparation conditions. The photoluminescence (PL) spectra exhibited two emission bands at around 485 and 535nm, which dominantly originated from the Eu(I) and Eu(II) sites, respectively. The addition of flux dramatically enhanced the PL intensities of the S2S:Eu2+ powders by about 340–400% with the exception of the powder synthesized using colloidal SiO2 with a concentration of 1.1M. The PL intensity was closely correlated with Rβ/α′, which significantly increased when flux was used.

Effect of Heat Treatment on the Microstructure and Hardness of 17Cr-0.17N-0.43C-1.7 Mo Martensitic Stainless Steel

The microstructure and hardness of a nitrogen-containing martensitic stainless steel were investigated as a function of heat treatment using optical microscopy, electron microscopy, amount of retained austenite, and hardness measurement. The steel was subjected to three heat treatments: hardening, cryo treatment, and tempering. The hardness of the steel in different heat-treated conditions ranged within 446-620 HV. The constituents of microstructure in hardened condition were lath martensite, retained austenite, M23C6, M7C3, MC carbides, and M(C,N) carbonitrides. Upon tempering at 500 °C, two new phases have precipitated: fine spherical Mo2C carbides and needle-shaped Cr2N particles.

Microwave-assisted Synthesis of Zinc Oxide Nanoparticles

Synthesis of nanoparticles and ultrafine particles of zinc oxide with controlled morphology using microwave irradiation is carried out by various methods. The effect of type of precursor as well as the time and the microwave irradiation power on the structure and size of ZnO nanoparticles have been studied. Particles Studied by SEM, TEM images and XRD analyze. By increasing the time of synthesis from 10 to 15minutes needle-shaped particles with a diameter of 50-150nm can be achieved. While increasing the microwave power from 540 to 680 watts, flower-shaped particles are obtained. By replacing zinc nitrate with zinc acetate, at different power and time of irradiation, needle-shaped particles are obtained and diameter of needles is decreased.

Mechanical behavior of porous commercially pure Ti and Ti–TiB composite materials manufactured by selective laser melting

Commercially pure titanium (CP-Ti) and Ti–TiB composite parts with three different porosity levels (i.e. 10%, 17% and 37%) were produced by selective laser melting (SLM). Scanning electron microscopy (SEM) investigations show that martensitic (α′) microstructure exists in SLM-processed CP-Ti parts, whilst SLM-processed Ti–TiB composites present needle-shape TiB particles distributed in α-Ti matrix. Mechanical properties of these porous samples decrease with porosity level increasing. The yield strength and elastic modulus of porous CP-Ti parts range 113–350MPa and 13–68GPa respectively, which are much lower than those for porous Ti–TiB counterparts (234–767MPa and 25–84GPa respectively) mainly due to the strengthening effect induced by TiB particles in Ti–TiB samples. Compression stress–strain curves of 37% porous CP-Ti parts show a typical three-stage behavior of ductile porous metals. Also, the elastic moduli of both 37% porous CP-Ti and Ti–TiB samples are similar to that of human bone. SEM investigations of the porous CP-Ti samples after compression testing show that no crack presents until 50% compressive strain and most of deformation is absorbed by porous areas. In contrast, μ-CT investigations indicate that all porous Ti–TiB samples fail at early stages of compression testing due to cracks resulting from insufficient ductility of struts of porous areas, because they are not able to accommodate high strains of the deformation at high strengths.

The correlation between the structural and luminescent properties of Ca2SiO4:Eu2+ nanopowders prepared by the sol-gel process.

Ca2SiO4:Eu2+ powders were prepared by the sol-gel process using calcium nitrate hydrate, europium nitrate hydrate, and tetraethyl orthosilicate (TEOS). The effects of the amount of TEOS, firing temperatures, and the Eu2+ concentration on the structural and luminescence properties were investigated. The CaO impurity phase was produced and it strongly contributed to emission properties. The prepared powders were composed of irregular-shaped particles, square plates (CaO), and/or needle-shaped particles, depending on the amount of TEOS, while with excess TEOS content (1.2 M), Ca2SiO4:Eu2+ crystals were contained in the glass matrix. The photoluminescence excitation (PLE) spectra of the synthesized powders widely covered from 250 to 450 nm. The related PL emission spectra showed green emissions (- 510 nm), which resulted from two overlapped Gaussian emission bands centered at 502 and 550 nm assigned to the 4f(7)-4f(6)5d1 transitions of the Eu(II) and Eu(I) sites, respectively. Eu2+ ions were incorporated into CaO as well as Ca2SiO4, and thus the Eu2+ concentration in Ca2SiO4 was adjusted by the amount of the CaO phase in samples. As a result, the strongest green emission of Ca2SiO4:Eu2+ was obtained with 0.9 M TEOS.

Synthesis of Barium Hexaferrite with Addition of Tapioca as Rodlike Template

Barium hexaferrite is categorized as hexagonal ferrite material with ferrimagnet properties. Barium hexaferrite has high coercivity, curie temperature, anisotropy magnetic field, and chemical stability that is often used as permanent magnet. It can be synthesized by using bottom up or top down method. The bottom up method of sol-gel has potential advantages in industry application compared to the top down method because of low energy requirement, more homogeneous product, and low time consuming to achieve nanometer size. The development of sol-gel method by using tapioca and chitosan as surfactant increases the quality of the product. Tapioca is used to increase anisotropy properties of particles by changing the particles shape into rodlike shape whereas chitosan is used to stabilize them at small size. Molar ratio of Fe3+/Ba2+ is set on 12 and the ratio of tapioca/chitosan is set on 1/3, 1/2, and 1. Iron (III) nitrate is used as Fe3+ source whereas barium nitrate is used as Ba2+ source. Condensation is done by heating up the sol system in the oven at 100OC. The product then is calcined at 1000OC with holding time of 3 hours. The calcined product is then characterized by X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), and Vibrating Sample Magnetometer (VSM). XRD result shows that the hematite phase has still been formed. The occurrence of the phase indicates that the reaction between iron and barium is uncompleted. SEM images show the existence of needle and rod-shaped particles with diameter of 200nm–550nm. It explains that tapioca can be used as rodlike template. The increase of tapioca tends to enlarge the rod-shaped particle and remove the needle-shaped particle. VSM result shows that the highest value of Br is found in the sample of tapioca/chitosan with the ratio of 1/3 and the value of 24 emu/g. The fact indicates that the optimal ratio of tapioca/chitosan is 1/3.

Influence of cerium oxide (CeO2) nanoparticles on the microstructure and hardness of tin–silver–copper (Sn–Ag–Cu) solders on silver (Ag) surface-finished copper (Cu) substrates

Nano-sized, non-reacting, non-coarsening CeO2 particles with a density close to that of solder alloy were incorporated into Sn–3.0 wt%Ag–0.5 wt%Cu solder paste. The interfacial microstructure and hardness of Ag surface-finished Cu substrates were investigated, as a function of reaction time, at various temperatures. After the initial reaction, an island-shaped Cu6Sn5 intermetallic compound (IMC) layer was clearly observed at the interfaces of the Sn–Ag–Cu based solders/immersion Ag plated Cu substrates. However, after a prolonged reaction, a very thin, firmly adhering Cu3Sn IMC layer was observed between the Cu6Sn5 IMC layer and the substrates. Rod-like Ag3Sn IMC particles were also clearly observed at the interfaces. At the interfaces of the Sn–Ag–Cu based solder-Ag/Ni metallized Cu substrates, a (Cu, Ni)–Sn IMC layer was found. Rod-like Ag3Sn and needle-shaped Cu6Sn5 IMC particles were also observed on the top surface of the (Cu, Ni)–Sn IMC layer. As the temperature and reaction time increased, so did the thickness of the IMC layers. In the solder ball region of both systems, a fine microstructure of Ag3Sn, Cu6Sn5 IMC particles appeared in the β-Sn matrix. However, the growth behavior of the IMC layers of composite solder doped with CeO2 nanoparticles was inhibited, due to an accumulation of surface-active CeO2 nanoparticles at the grain boundary or in the IMC layers. In addition, the composite solder joint doped with CeO2 nanoparticles had a higher hardness value than the plain Sn–Ag–Cu solder joints, due to a well-controlled fine microstructure and uniformly distributed CeO2 nanoparticles. After 5 min of reaction on immersion Ag-plated Cu substrates at 250 °C, the micro-hardness values of the plain Sn–Ag–Cu solder joint and the composite solder joints containing 1 wt% of CeO2 nanoparticles were approximately 16.6 and 18.6 Hv, respectively. However after 30 min of reaction, the hardness values were approximately 14.4 and 16.6 Hv, while the micro-hardness values of the plain Sn–Ag–Cu solder joints and the composite solder joints on Ag/Ni metallized Cu substrates after 5 min of reaction at 250 °C were approximately 15.9 and 17.4 Hv, respectively. After 30 min of reaction, values of approximately 14.4 and 15.5 Hv were recorded.

Interfacial microstructure and hardness of nickel (Ni) nanoparticle-doped tin–silver–copper (Sn–Ag–Cu) solders on immersion silver (Ag)-plated copper (Cu) substrates

Sn–Ag–Cu composite solder has been prepared by adding Ni nanoparticles. Interfacial reactions, the morphology of the intermetallic compounds (IMC) that were formed, the hardness between the solder joints and the plain Cu/immersion Ag-plated Cu pads depending on the number of the reflow cycles and the aging time have all been investigated. A scallop-shaped Cu6Sn5 IMC layer that adhered to the substrate surface was formed at the interfaces of the plain Sn–Ag–Cu solder joints during the early reflow cycles. A very thin Cu3Sn IMC layer was found between the Cu6Sn5 IMC layer and the substrates after a lengthy reflow cycle and solid-state aging process. However, after adding Ni nanoparticles, a scallop-shaped (Cu, Ni)–Sn IMC layer was clearly observed at both of the substrate surfaces, without any Cu3Sn IMC layer formation. Needle-shaped Ag3Sn and sphere-shaped Cu6Sn5 IMC particles were clearly observed in the β-Sn matrix in the solder-ball region of the plain Sn–Ag–Cu solder joints. Additional fine (Cu, Ni)-Sn IMC particles were found to be homogeneously distributed in the β-Sn matrix of the solder joints containing the Ni nanoparticles. The Sn–Ag–Cu–0.5Ni composite solder joints consistently displayed higher hardness values than the plain Sn–Ag–Cu solder joints for any specific number of reflow cycles–on both substrates–due to their well-controlled, fine network-type microstructures and the homogeneous distribution of fine (Cu, Ni)–Sn IMC particles, which acted as second-phase strengthening mechanisms. The hardness values of Sn–Ag–Cu and Sn–Ag–Cu–0.5Ni on the Cu substrates after one reflow cycle were about 15.1 and 16.6 Hv, respectively–and about 12.2 and 14.4 Hv after sixteen reflow cycles, respectively. However, the hardness values of the plain Sn–Ag–Cu solder joint and solder joint containing 0.5 wt% Ni nanoparticles after one reflow cycle on the immersion Ag plated Cu substrates were about 17.7 and 18.7 Hv, respectively, and about 13.2 and 15.3 Hv after sixteen reflow cycles, respectively.

The preparation of dendrite- and needle-shaped alloy particles coated on copper powders by polyvinylpyrrolidone in displacement reaction and thermal conductivity on composites’ characterization

This study focused on the preparation of dendrite- and needle-shaped alloy particles coated on the surface of copper powders by different molecular weights of polyvinylpyrrolidone (PVP)—namely, 3500, 8000, 10,000, 55,000 and 360,000—in displacement reaction and the thermal conductivity on composites’ characterization. The structure, size, and morphology of the particles were investigated using scanning electron microscopy (SEM). The EDX demonstrated that the alloy particles simultaneously have different ratios of copper (Cu) and silver (Ag) elements for dendrite-shaped and needle-shaped alloy particles. The 15% of PVP with a molecular weight of 8000g/mol formed the largest dendritic-shaped Ag–Cu alloy particle, with an average width of 3±1μm, in which 60% of Ag–Cu alloy particles included resin to enhance composites with the largest thermal conductivity at 0.5956W/(mK).