Fabrication Of Powders Research Articles

Correlation with the composition of the different parts of p-type Bi0.5Sb1.5Te3 sintered bulks and their thermoelectric characteristics

Evaporation of tellurium (Te) occurs during most of the fabrication methods which leads to a strong deviation on thermoelectric properties. Due to the existence of volatile tellurium has been a great challenge to determine the accurate chemical compositions in the Bi0.5Sb1.5Te3 compound for optimizing the carrier concentration. Herein, we systematically verify the reliability and understand the correlations between chemical composition and thermoelectric properties at different portions of large (25 mm), thick (30 mm) samples. The results reveal that spark plasma sintered samples didn’t show any significant evaporation of Te. However, the chemical composition slightly changed, resulting in the final thermoelectric figure of merit at different portions of thick samples varied typically within a 10% error. Moreover, this work supports that the selection of the powder fabrication and compaction method plays a crucial role on the final thermoelectric properties of the material, as the combining of gas atomization and spark plasma sintering can prohibit the evaporation of tellurium and any possible inhomogeneous stress field or temperature distribution in large-sized graphite die to SPS.

Fabrication of ZrB2-SiC powder with a eutectic phase for sintering or plasma spraying

Spherical ZrB2-SiC powder with a eutectic phase was synthesised via induction plasma spheroidisation (IPS) in this study. The influence of H2 flow and reaction chamber pressure on the powder microstructure was investigated during the induction plasma spheroidisation process. The powders have an evidently better fluidity (< 44 s/50 g) and a larger apparent density (>1.65 g/cm3) after IPS treatment. With an increase in H2 flow or pressure, the shape of surface grains successively shows an irregular, hexagonal, and rectangular shape because the grain growth mechanism changes from surface energy to diffusion activation energy. There is serious mass loss of SiC on the surface because of pure active oxidation and sublimation during the IPS treatment. The cross section of the ZrB2-SiC powder indicates a dense microstructure comprising coarse ZrB2 and intergranular eutectic phases. Furthermore, the corresponding ZrB2-SiC bulk ceramics and coating fabricated using the IPS-treated powder both contain eutectic phase.

Laser sintering of graphene nanoplatelets encapsulated polyamide powders

This paper presents a comprehensive study in the fabrication and safety of new nanocomposite powders for laser sintering. The nanocomposite powder is based on a core-shell structure where nanoparticles (graphene nanoplatelets, GNP) are encapsulated on the surface of the polymeric particles (polyamides PA12) in a thin layer of poly(vinyl alcohol) (PVA). Powder rheology data as well as SEM and TEM showed that GNP were dispersed well in the PVA coating and improved flow. Half time crystallisation kinetics was used to determine differences induced in the polymer and the laser sintering process by the presence of GNP. Nanosafety aspects, critical in a manufacturing environment, are also considered here and exposure monitoring tests were carried out. Results confirmed a low nanoparticle air exposure and therefore confirmed the successful surface encapsulation of the GNP in nanocomposite powders. The laser-sintered 0.1GNP/PVA-PA12 parts showed enhanced mechanical properties in tensile, compression and 3-point bending test.

Carbon nanotubes, orange dye, and graphene powder based multifunctional temperature, pressure, and displacement sensors

This work presents design, fabrication, and investigation of carbon nanotube (CNT), orange dye (OD), and graphene powder based multifunctional sensors. The output of the multifunctional sensors is observed as change in resistance and impedance values for an input change in temperature, pressure, and compressive displacement between the sensors electrodes. Using these sensors, temperature variation ranging from 30 to $$65^{\circ }\hbox {C}$$ , pressure 0 to 0.1 $$\hbox {kgf\,cm}^{-2}$$ and longitudinal compressive displacements of 0 to 110 $$\upmu \hbox {m}$$ are measured as change in resistance and impedance at two fixed frequencies, i.e., 100 Hz and 100 KHz. An increase in both resistance and impedance of the sensors is observed with increase in temperature. The temperature coefficients of the sensors having resistances $$\sim 470$$ $$\Upomega$$ and $$\sim 890$$ $$\Upomega$$ were $$1.0\%\,{}^{\circ }\hbox {C}^{-1}$$ and $$1.9\%\,{}^{\circ }\hbox {C}^{-1}$$ , respectively, when evaluated for temperatures ranging from 30 to $$65^{\circ }\hbox {C}$$ . For applied pressure 0 $$\hbox {kgf\,cm}^{-2}$$ to 0.1 $$\hbox {kgf\,cm}^{-2}$$ and displacement 0 to 110 $$\upmu \hbox {m}$$ the resistance of the multifunctional sensor decreases 1.3 to + 12.7 times (from 6730 $$\Upomega$$ to 5210 $$\Upomega$$ and 3410 $$\Upomega$$ to 269 $$\Upomega$$ ) and 3.18 to 7.53 times (2235 $$\Upomega$$ to 702 $$\Upomega$$ and 6787 $$\Upomega$$ to 901 $$\Upomega$$ ), respectively. With increased thickness of OD layer from 300 $$\upmu \hbox {m}$$ to 570 $$\upmu \hbox {m}$$ , the output resistance and impedance of the sensors as a function of temperature also increased, exhibiting the improved sensitivity, however, at the expense of decreased pressure and displacement response of the sensors. Therefore, the thickness of OD film can be used as a design parameter for a desired sensitivity value to cater a particular application. The proposed multifunctional sensor can be a good candidate to measure temperature, pressure, and displacement of an industrial unit, such as flex bonding head because it offers light weight, simpler design, low maintenance, and eventually low cost.

Additive Technologies as Breakthrough Solutions for Creating Advanced Functional Materials

The main directions of the development of additive technologies at the Peter the Great St. Petersburg Polytechnic University are considered. Fabrication and research of spherical powders of complexly alloyed alloys for additive production from metal waste and of functionally graded materials with variable structure, chemical composition and porosity, synthesis of intermetallic titanium alloys by selective laser melting are considered among other examples.

In situ synthesis of ultrafine TiO2 nanoparticles modified g-C3N4 heterojunction photocatalyst with enhanced photocatalytic activity

To improve the redox performance and light absorption property, the 2D/0D g-C3N4/TiO2 heterojunction photocatalyst were successfully fabricated by co-annealing process based on melamine powder and ultrafine TiO2 nanoparticles (about 9.87 nm) obtained from electrochemical etching technology. The surface micromorphology, crystal structure, basic element composition, chemical structure, specific surface and optical performance were analyzed by SEM-EDS, TEM, HR-TEM, XRD, XPS, FTIR and Ultraviolet–visible diffuse reflection spectra (UV–vis DRS). The photocatalytic performance of g-C3N4/TiO2 photocatalyst was assessed by the degradation of tetracycline hydrochloride (TC) under simulated sunlight irradiation. The results showed that the obtained TiO2 powder had extremely smaller particle size and higher photocatalytic activity than commercial P25. The coupling of 0D TiO2 nanoparticles and 2D g-C3N4 nanosheet further promoted the visible light absorption performance of TiO2. The unique g-C3N4/TiO2 heterojunction photocatalyst exhibited remarkable photocatalytic performance for the degradation of TC, whose degradation rate could reach to 99.40% under 120 min irradiation. The kinetic constant of the g-C3N4/TiO2 photocatalyst was 1.48 times of that of TiO2. The ESR results confirmed ·OH and ·O2– radicals produced in the photocatalytic process. This work could provide an effective reference for the fabrication of ultrafine TiO2 powder and binary heterojunction photocatalyst with excellent photocatalytic activity for organic pollutants degradation in water purification.

Fabrication Of TiO₂ Nanoflowers Powder with Various Concentration Of CTAB

Nanostructures titanium dioxide (TiO₂) such as nanoflowers and nanorods have contribute in many application. Among TiO₂ nanostructures, TiO₂ nanoflowers gives high surface area that contribute in good binding properties and reducing internal stress and increasing strength of the ceramics.This paper presents fabrication of TiO₂ nanoflowers powder to overcome the cracking problem in ceramic industry. In this study, fabricated rutile- phased TiO₂ nanoflower powder has been successfully synthesized by using hydrothermal method and the surface morphology, structural properties, and the composition of TiO₂ nanoflower powder also identified. The fabricated TiO₂ are characterized using Field Emission Scanning Electron Microscopy (FESEM) to observe the surface morphology of TiO₂, X-ray Dispersion (XRD) was used to determine the crystallite phase and EDX for element composition in fabricated TiO₂ powder. The synthesized TiO₂ powder was obtained from the reaction between deionized water (DI), hydrochloric acid (HCl), Titanium Butoxide (TBOT) and Cetyltrimethylammonium Bromide (CTAB). The hydrothermal temperature is 150 C̊with fixed hydrothermal time of 10 hours. The parameters varied is the mass of surfactant used, CTAB. The hydrothermal method is proven suitable to fabricate semiconductor materials due to its advantages that parameters are easily modified and can be performed under closed system with low operational temperature. Increased amount of CTAB used make the gap between the nanorod become closer and stronger. The diffraction peaks of all sample hardly changed, but the intensity for each sample was enhanced as the mass of CTAB used increased. The structure also become well crystallined in rutile phase structure.

Fabrication of Cr2AlC powder by molten salt electrolysis at 850 °C with good oxidation resistance

The Cr2AlC is a typical ternary intermetallic who possesses unique properties such as good high temperature oxygen resistance, excellent mechanical strength, and so on, making it a potential ceramic candidate to be utilized under a relatively strict circumstance. In this paper, a straightforward and cheaper process was proposed to synthesize high quality and uniform micron-size Cr2AlC, via electrochemical reduction of Cr2O3/Al2O3/C mixed powder at only 850 °C. It is demonstrated that Cr2AlC was formed by the following three steps. Firstly, Cr2O3 was reduced to metallic Cr and react with carbon to form CrnCm. Then formed CrnCm will react with reduced alumina to form Cr2AlC. The SEM-EDS images confirmed the homogeneous distribution of Cr, Al and C in micron-size Cr2AlC powder. And the TEM and TG results further demonstrate the excellent layered structure and good oxidation resistance of Cr2AlC powder. This work realizes and provides a low-cost and scalable low temperature technique to prepare homogeneous MAX phase powders for commercial applications.

Size-dependent effects of Ti powders in the pure aluminum matrix composites reinforced by carbon nanotubes

Carbon nanotube reinforced aluminum matrix (CNT/Al) composites with various microstructures were fabricated by powder metallurgy via introducing nano-sized and micron-sized Ti powders into the CNT-Al system. The size-dependent effects of Ti powders on the microstructure evolution and mechanical properties were further investigated. The results reveal that the best enhancement (∼51% of UTS) was obtained by adding 80 nm sized Ti powders into the CNT/Al composite compared with the composite without Ti addition, which mainly derives from the synergistic strengthening of the homogenously dispersed CNTs, a large quantity of in-situ formed nano-sized TiAl3 particles and fine grains. Meanwhile, it is also noted that the addition of micron-sized Ti powders can help the CNT dispersion in powder fabrication stage, and subsequently in-situ formed core-shell structured particles with different interface reaction degree in the Al matrix. Among them, 1 μm was determined to be the optimal size of Ti for the maximum formation of core-shell structured particles, which best exploits the load transfer ability of TiAl3 shell layers at their interfaces, and finally attributes to significant strength enhancement (∼35% of UTS). This research provides a valuable reference concerning the size effects of addition metal in future fabrication of CNTs reinforced metal matrix composites with alternative microstructure.

Fabrication of nanoscale graphene-zirconia powder by hydrothermal method

Fabrication of nanoscale graphene-zirconia powder by hydrothermal method

Recycling of waste flat glass in the fabrication of Si3N4 powder by the carbo‐thermal reduction and nitridation

AbstractThe recycle rate of waste flat glass is quite low in spite of higher SiO2 content and its pre‐melted characteristic. This study searched a novel approach for the fabrication of Si3N4 powder by carbo‐thermal reduction and nitridation from waste glass. For comparison, starting powder mixtures were prepared from silica and waste SLS (soda‐lime‐silica) glass. Carbo‐thermal reduction and nitridation process was conducted using two temperatures and different atmospheres. The results showed that equiaxed, micron size β‐Si3N4 particle could be synthesized from waste glass. The use of waste glass reduced the amount of fiber‐like Si3N4 particles and SiC phase by increasing the amount of the liquid phase formed. This study proved the utilization of waste flat glass as a low cost and environment friendly SiO2 source.

Prospects of Low-Pressure Cold Spray for Superhydrophobic Coatings

A major challenge in materials engineering is the development of new materials and methods and/or novel combination of existing ones, all fostering innovation. For that reason, this study aims at the synergy between low-pressure cold spray (LPCS) as a tool for coating deposition and sol-gel technique for fabrication of the feedstock powder. The complementarity of both methods is important for the examined topic. On one side, the LPCS being automized and quick mean provides the solid-state of feedstock material in nondestructive conditions and hence the hydrophobicity imparted on the sol-gel route is preserved. On the other side, the sol-gel synthesis enables the production of oxide materials with enhanced deformability due to amorphous form which supports the anchoring while LPCS spraying. In the paper, several aspects including optimal fluoroalkylsilane (FOTS) concentration or substrate roughness are examined initially for altering the superhydrophobicity of produced coatings. Further, it is shown that the appropriate optimization of feedstock powder, being submicron silica matrices covered with two-layer FOTS sheath, may facilitate the anchoring process, support roughening the substrate or cause enhancement the coating hydrophobicity. All the discussion is supported by the characteristics including surface morphology, wettability and thermal behaviour examined by electron microscopy, water contact angle measurements and thermal analysis (TGA/DSC), respectively. The coatings presented in the paper are characterized by an uneven thickness of up to a few silica particles, but final hydrophobicity is provided uniformly on the surface by the formation of multi-level roughness by a detachment of outer layer from the SiO2 particles. Thus, the presented approach constitutes a simple and fast solution for the fabrication of functionalized coatings using LPCS including industrial potential and fundamental research character.

Nanoparticle Size-Fractionation through Self-Standing Porous Covalent Organic Framework Films.

Covalent organic frameworks (COFs) have attracted attention due to their ordered pores leading to important industrial applications like storage and separation. Combined with their modular synthesis and pore engineering, COFs could become ideal candidates for nanoseparations. However, the fabrication of these microcrystalline powders as continuous, crack-free, robust films remains a challenge. Herein, we report a simple, slow annealing strategy to construct centimeter-scale COF films (Tp-Azo and Tp-TTA) with micrometer thickness. The as-synthesized films are porous (SABET =2033 m2 g-1 for Tp-Azo) and chemically stable. These COFs have distinct size cut-offs (ca. 2.7 and ca. 1.6 nm for Tp-Azo and Tp-TTA, respectively), which allow the size-selective separation of gold nanoparticles. Unlike, other conventional membranes, the durable structure of the COF films allow for excellent recyclability (up to 4 consecutive cycles) and easy recovery of the gold nanoparticles from the solution.

Nanoparticle Size‐Fractionation through Self‐Standing Porous Covalent Organic Framework Films

AbstractCovalent organic frameworks (COFs) have attracted attention due to their ordered pores leading to important industrial applications like storage and separation. Combined with their modular synthesis and pore engineering, COFs could become ideal candidates for nanoseparations. However, the fabrication of these microcrystalline powders as continuous, crack‐free, robust films remains a challenge. Herein, we report a simple, slow annealing strategy to construct centimeter‐scale COF films (Tp‐Azo and Tp‐TTA) with micrometer thickness. The as‐synthesized films are porous (SABET=2033 m2 g−1 for Tp‐Azo) and chemically stable. These COFs have distinct size cut‐offs (ca. 2.7 and ca. 1.6 nm for Tp‐Azo and Tp‐TTA, respectively), which allow the size‐selective separation of gold nanoparticles. Unlike, other conventional membranes, the durable structure of the COF films allow for excellent recyclability (up to 4 consecutive cycles) and easy recovery of the gold nanoparticles from the solution.

The influence of process parameters on the chemical and structural properties of solution combustion prepared vanadium pentoxide

The present study shows the effects of the process parameters on the combustion synthesised’ powder properties using a systematic design of experiments. It describes the fabrication of high purity V2O5 powders with the manipulation of fuel types and fuel-to-oxidizer ratios. Additionally, for the first time the mixture of fuels was used to demonstrate clearly the role of the fuel on the powder properties. Flame temperature of the reaction was calculated for each parameter to understand how the reaction kinetics affect the powder properties especially primary particle size and morphology. Correlation between the physical and chemical properties of the powders and the precursor’s condition was successfully built.

Mechanically milled powder from cotton gin trash for diverse applications

There are very few reports, if any, on the physicochemical changes during the powder fabrication of cotton gin trash (CGT), an abundant source of lignocellulose. This particular study can be very informative for the production of new CGT composite materials. In our current study, we investigated the changes in particle size, morphology, surface area, chemical structure, crystallinity, thermal and moisture properties of CGT at different stages of the milling operation. An attritor milling of CGT up to 4 h reduced the particle size (from 144.2 μm to 6.2 μm) and enhanced the surface area up to 2.5 times without damaging its original properties, including crystallinity and chemical structure. Milling operation beyond 4 h did not further reduce the particle size effectively, though affected the thermal stability of CGT. Overall, it is suggested that the milled CGT can be a sustainable source of lignocellulose powder for use in a wide area of applications.

Fabrication of Metal Powders for Energy-Intensive Combustible Compositions Using Mechanochemical Treatment: 2. Structure and Reactivity of Mechanically Activated Al–Modifier–SiO2 Mixtures

The results of studying the particles of the aluminum–modifier–quartz composites after mechanochemical treatment (MCT) in a planetary centrifugal mill by various physicochemical methods are presented. Graphite (C), polyvinyl alcohol (PVA), and stearic acid (SA) are used as modifiers. To increase the dispersive ability of plastic metallic powders (metal–modifier), MCT was performed in the presence of quartz, the weight fraction of which in the composite varies from 5 to 20%. The largest grinding of aluminum particles is observed with an increase in the graphite content from 5 to 20% and SiO2 content from 5 to 10% in the composition of aluminum–modifier–quartz composites. The particle decreases, while that of crystallites increases with the MCT of the Al–SA–SiO2 system with an increased quartz content in the composite. The maximal imperfection of aluminum after MCT is characteristic of the Al–SA–5%SiO2 samples. An increase in the particle size and, correspondingly, a decrease in the specific surface with rather small crystallite sizes are observed after MCT for the Al–PVA–SiO2 composition. It is shown that the imperfection of the crystalline structure of aluminum particles increases with an increase in the quartz content in the system. The synthesized powder material is a composite formation of aluminum and quartz particles bound by polymer formed based on polyvinyl alcohol in this case. The MCT of the Al–modifier–SiO2 mixtures results in an increase in the powder activity both due to the accumulation and redistribution of defects in aluminum particles and due to the change of the surface structure due to the incorporation of modifying additives into the destructed oxide layer. The conceptual model of transformation of the surface layer and subgrain structure of aluminum particles during MCT is presented.

Design and Fabrication of High Activity Retention Al-Based Composite Powders for Mild Hydrogen Generation.

Al–Bi–Sn–Cu composite powders for hydrogen generation were designed from the calculated phase diagram and prepared by the gas atomization process. The morphologies and structures of the composite powders were investigated using X-ray diffraction (XRD) and a scanning electron microscope (SEM) equipped with energy-dispersive X-ray (EDX) spectroscopy, and the results indicate that the Cu additive enhanced the phase separation between the Al-rich phase and the (Bi, Sn)-rich phase. The hydrogen generation performances were investigated by reacting the materials with distilled water. The Al–Bi–Sn–Cu powders reveal a stable hydrogen generation rate, and the Al–10Bi–7Sn–3Cu (wt%) powder exhibits the best hydrogen generation performance in 50 °C distilled water which reaches 856 mL/g in 800 min. In addition, the antioxidation properties of the powders were also studied. The Al–10Bi–7Sn–3Cu (wt%) powder has a good resistance to oxidation and moisture, which shows great potential for being the hydrogen source for fuel cell applications.

Fabrication of mesoporous TiVN powders and their electrochemical performance

Fabrication of mesoporous TiVN powders and their electrochemical performance

Oxygen Effects on Solidification Behavior of Gas Tungsten Arc–Welded Laser Powder Bed Fusion–Fabricated 304L Stainless Steel

Abstract The laser powder bed fusion (L-PBF) process inherently accumulates interstitial gas elements during powder fabrication and laser deposition processes. Such elements can lead to localized variations in the weld pool and affect the solidification behavior (when compared with its wrought equivalent), in addition to chemical microsegregation within the fabricated material. This study was conducted to characterize the solidification behavior of gas tungsten arc (GTA) welds made on L-PBF 304L stainless steel. The effect of surface active elements on the local solidification rates was studied. An emphasis was placed on the role local solidification rates and temperature gradients throughout the weld play on the resultant weld solidification structure and microsegregation. It was determined that gas tungsten arc welds on L-PBF 304L stainless steel exhibited a vermicular ferrite solidification structure compared with a mix of vermicular and lathy ferrite structure in wrought 304L. The varying convective thermal gradients in the weld pool affected the solidification modes and partitioning of elements, leading to fluctuations of microsegregation in the L-PBF 304L. Macroscopically, such partitioning affected the surface tension within the weld pool, producing asymmetric weld pool geometries. The compositional differences between wrought and L-PBF fabricated 304L stainless steels resulted in irregular solidification behaviors during welding affecting the final weld microstructure.