Induction Thermal Plasma Research Articles

Preparation of spherical Gd2Zr2O7 powders by RF induction thermal plasma process

Spherical Gd2Zr2O7 (GZO) powders with a uniform particle size distribution are successfully prepared using a novel industrial approach, which combines spray-drying process and thermal plasma sintering technology together. In this, GZO powders with pyrochlore structure as the main phase are first synthesized via a solid-state reactive route using a mixture of the milled Gd2O3 powders and ZrO2 powders as starting materials. The influence of sintering temperature on the microstructure of prepared powders is researched. Then, GZO granules are prepared after wet-grinding and spray-drying process, which exhibit a spherical shape with the average particle size of 46.5 μm. RF induction thermal plasma is finally used to sinter the granulated particles, and the influence of feeding rate on the properties of spherical powders is investigated. The apparent density of plasma sintered GZO spherical powders is increased from 1.53 g/cm3 to 2.29 g/cm3 when the feeding rate of granulated powders is 80 g/min, and further increased up to 3.90 g/cm3 when the feeding rate is 15 g/min. Such powders are in potential demand for plasma sprayed coatings and additive manufacturing techniques, and the successful synthesis of spherical GZO powders may guide the way toward the preparation of many other spherical rare earth zirconates powders.

Boron nitride nanotube-based creatinine biosensors for athlete physical condition monitoring

Monitoring creatinine levels is critical for evaluating renal function and muscular health in athletes. Creatinine is a waste product of creatine metabolism in skeletal muscle, and is filtered by the kidneys at a relatively constant rate. Elevated serum creatinine can indicate impaired kidney function, rhabdomyolysis, or skeletal muscle trauma. In athletes, creatinine levels increase after intense exertion due to muscle breakdown and myoglobin release. Abnormal creatinine signifies poor training adaptation, overtraining, or trauma. Therefore, close monitoring of creatinine in athletes provides insight into their physical condition. Current laboratory methods for measuring creatinine like Jaffe reaction and high-performance liquid chromatography are accurate but time-consuming, requiring blood sampling. Biosensors offer rapid, painless creatinine detection from small volumes, but current versions suffer from instability, use of mediators, and lack portability. Boron nitride nanotubes (BNNTs) are promising materials for electrochemical biosensing due to their structure, surface chemistry, and biocompatibility. Here, we report BNNT-based electrochemical biosensors for detecting creatinine in blood samples from athletes. BNNTs synthesized by induction thermal plasma technique were used to immobilize creatinine metabolizing enzymes. Creatinine levels were measured by chronoamperometry and compared to isotope dilution mass spectrometry. We demonstrate high sensitivity and selectivity of the BNNT biosensor with facile fabrication method and portable platform, promising for rapid creatinine monitoring in athletes. This can provide insight into muscular damage and renal function during training and competition.

D03-ordered Fe3Al magnetic nanopowders synthesized by low oxygen induction thermal plasma

D03-ordered Fe3Al alloy with a large anomalous Nernst coefficient is considered as a promising candidate for a low-cost, flexible, and durable magneto-thermoelectric generator (MTG). To improve the thermoelectric performance of the more and more complex and smaller MTG modules, the incorporation of high-quality magnetic nanopowders (MNPs) is one solution. However, synthesizing fully chemically ordered MNPs without coalescence and/or oxidation with a conventional approach is challenging. In this study, we demonstrated, for the first time, D03-ordered (degree of ordering = 0.48) Fe3Al MNPs synthesized via a low oxygen thermal plasma process combined with appropriate post-annealing treatment. The resulting single crystalline MNPs are spherical in shape with a mean particle diameter of 116 ± 96 nm and exhibit a soft magnetic characteristic (saturation magnetization ≈ 112 emu/g; and coercivity ≈ 5 Oe at room temperature). The fundamental alloying mechanism during the thermal plasma process was investigated via numerical calculations, confirming that the alloying followed the route through the Fe-Al droplet. Our results will potentially aid the mass synthesis of chemical ordered MNPs for wearable energy harvesting and self-powered Internet of things applications.

Effects of quenching on the microstructure and magnetic properties of MnBi nanopowders synthesized by low-oxygen induction thermal plasma

Fine and magnetically hard MnBi powders with limited surface oxidation were unprecedentedly synthesized with a high-throughput low-oxygen induction thermal plasma (LO-ITP) system for rare-earth-free permanent magnets (REF-PMs) application. Furthermore, by inducing quenching during the LO-ITP process, one can effectively reduce the as-processed Mn-Bi particle size from 63.9 to 49.8 nm and promote the formation of magnetic hard low-temperature phase of MnBi (LTP-MnBi, 72 to 84 wt%) with enhanced surface diffusion during post-annealing. The dominant LTP-MnB in the quenched and post-annealed MnBi powders was confirmed with detailed microstructure analysis. With higher weight fraction of LTP-MnBi, the quenched and post-annealed MnBi powders showed improved magnetic properties with a higher saturation magnetization (56.7 vs. 60.1 Am2/kg) and stronger coercivity (188.4 vs. 371.0 kA/m) than the powders without quenching. This work paved a new path for the mass production of high-purity and fine LTP-MnBi powders for synthesizing REF-PMs and/or related sustainable energy and automotive applications.

Boron nitride nanotubes synthesis from ammonia borane by an inductively coupled plasma

Boron nitride nanotubes (BNNTs) have been studied extensively due to their unique properties. Hydrogen-assisted induction thermal plasma with hBN powder has been reported in the past to produce high-yield small-diameter BNNTs. However, removal of unprocessed hBN and other BN-based impurities has been a challenge. This study presents a new approach for BNNT synthesis using ammonia borane (AB) as the raw material while maintaining the high yield and similar nanotube diameter and number of walls. Our findings demonstrate that the use of AB results in enhanced synthesis of BNNTs with reduced B and BN impurities formation. The presence of H in the proximity of B following AB decomposition facilitated more efficient formation of BH-based precursors that also lowered the partial pressure of B and restricted its condensation and coagulation into large B particles, ultimately leading to an increased density of B seeds required for BNNTs nucleation. Both the increased formation of BNNT precursors and B seeds contributed to more efficient BNNTs formation. XRD analysis revealed that AB-BNNTs contained no hBN, less tBN, and more BNNTs compared to hBN-BNNTs. Additionally, TGA and OES measurements confirmed formation of less B and production of more BH species, respectively. Our results suggest that AB as a feedstock for BNNT synthesis in induction thermal plasma offers a promising alternative to hBN powder.

Synthesis of single‐phase high‐entropy diboride powders and their spheroidization process

AbstractSpherical (Zr.2Ti.2Ta.2Nb.2Mo.2)B2 powders with a uniform particle size distribution are successfully prepared using a novel industrial approach, which combines spray‐drying process and thermal plasma sintering technology together. In this, single‐phase (Zr.2Ti.2Ta.2Nb.2Mo.2)B2 powders are first synthesized via a borothermal reduction process using a mixture of individual metallic oxides and boron powders as starting materials. The influence of boron powder content on the structure of prepared powders is researched. Then, (Zr.2Ti.2Ta.2Nb.2Mo.2)B2 granules are prepared after wet‐grinding and spray‐drying process, which exhibit a spherical shape and homogeneous element distribution. RF induction thermal plasma is finally used to sinter the granulated particle, and the apparent density of sintered spherical powders is increased to 2.57 g/cm3 from 1.43 g/cm3. Such powders are in potential demand for additive manufacturing techniques, and the successful synthesis of spherical (Zr.2Ti.2Ta.2Nb.2Mo.2)B2 powders may guide the way toward the preparation of many other spherical high‐entropy diboride powders.

Nanotwin-assisted nitridation of quenched FeNi alloy nanopowders for rare-earth-free magnets

L10-ordered FeNi alloy with a high uniaxial magnetic anisotropy and large magnetic moment is a promising candidate for rare-earth-free permanent magnets applications. However, the synthesis of this chemically ordered phase remains a longstanding challenge because of its low chemical order–disorder transition temperature (200–320 °C). Although a non-equilibrium synthetic route based on a nitrogen topotactic reaction has been proposed as a valid approach, the volume fraction and degree of chemical ordering of the product phase are limited. Herein, we propose a promising approach that promotes the efficient formation of L10-ordered nitride phase in FeNi nanopowders by introducing a quenching treatment during a low-oxygen induction thermal plasma process. The quenched FeNi nanopowders possessed much smaller powder sizes (40.4 vs 74.0 nm), exhibited higher number densities of nanotwins (39.8% vs 24.1%) and formed much larger volume fraction (33.6 wt.% vs 0.6 wt.%) of ordered phase than the unquenched nanopowders. Notably, quenching-induced high-density nanotwins led to the dominant coverage of serrated {001} crystal facets over the surfaces of the FeNi nanopowders. Such unique features substantially accelerated the formation of the L10-ordered nitride phase in the FeNi nanopowders because the 〈001〉 crystallographic orientation had the highest nitrogen diffusivity. This work provides not only a valid synthetic approach for mass production of the L10-ordered nitride phase in FeNi nanopowders but also novel insights into the crystal-defect-assisted nitridation of nanomaterials.

Formation Mechanism of Amorphous Li4GeO4 Nanoparticles Synthesized by Induction Thermal Plasma for All-Solid-State Batteries

Induction thermal plasma as an advanced synthesis method for amorphous nanoparticles attracts a lot of attention. Amorphous Li4GeO4 nanoparticles were synthesized by induction thermal plasma with different Li/Ge molar ratios and quenching gas flow rates. Transmission electron microscopy, X-ray diffraction, and Raman spectroscopy were conducted to understand the product morphology and chemical composition. The formation mechanism was investigated according to experimental results and thermodynamic analysis. The topological order of prepared nanoparticles was discussed in the short range and intermediate range based on O–Ge–O and Ge–O–Ge angle distributions, respectively. An enhanced amorphous degree of Li4GeO4 and a fraction of high-temperature-phase γ-Li4GeO4 were obtained in high Ge content and quenching rate conditions. The amorphous Li4GeO4 degree achieved around 65% with 10 L/min quenching gas injection. However, excessive Ge content and quenching rate also result in byproduct Li2GeO3 formation. The above results indicate that amorphous Li4GeO4 nanoparticles can be efficiently synthesized by induction thermal plasma with an appropriate Li/Ge molar ratio and quenching rate.

Feedstock feeding duration influence on silicon nanoparticle synthesis using tandem modulated induction thermal plasmas with intermittent feedstock feeding

Influences of feedstock feeding duration on the size and composition of synthesized nanoparticles produced using tandem-type modulated induction thermal plasma (tandem-MITP) with time-controlled feeding of feedstock (TCFF) were investigated both experimentally and numerically. This tandem-MITP+TCFF method has been confirmed to give highly efficient evaporation of the feedstock during on-time and also highly efficient nucleation during off-time. Furthermore, the time duration of feedstock feeding in a modulation cycle is an important factor for ascertaining the production rate. The experimentally obtained results indicate that a higher rate of smaller nanoparticle production was obtained at the duty factor of feedstock feeding D F valve of 40% in range of D F valve from 27% to 100%. This result suggests control of the formation and coagulation growth of nanoparticles by controlling the feedstock feeding time. The developed simulation model can also predict that reducing the ratio of feedstock feeding time produces high-density Si vapor, which is converted efficiently into nanoparticles because the evaporated vapor is cooled by the strong entrained gas flow at the downstream region. Numerically and experimentally obtained results were compared in terms of the particle size distribution, indicating reasonably good mutual agreement. These experimentally obtained and numerical results indicate control of the feedstock feeding time as desirable for nanoparticle synthesis. • Si nanoparticles were synthesized using tandem-type modulated induction thermal plasma (tandem-MITP). • Influences of feedstock feeding duration on Si nanoparticles produced were investigated. • A smaller nanoparticles were obtained when the duty factor of the feedstock feeding was set as 40%. • Numerical and experimental particle size distribution results indicate reasonably good agreement.

Synthesis of amorphous Li3BO3 nanoparticles as solid electrolyte for all-solid-state battery by induction thermal plasma

Synthesis of amorphous Li3BO3 by induction thermal plasma was conducted systematically with the investigation of formation mechanism. The TEM, XRD, Raman and XPS were conducted to understand the morphology and chemical composition of products. The formation mechanism was investigated based on experiment results and thermodynamic analysis. Crystalline Li3BO3 was injected into plasma as raw material. Different mole ratios of Ar and O2 were selected as plasma sheath gas to understand O2 effect on the composition and amorphous degree of products. Ar was selected as quenching gas injected into the plasma to understand quenching rate effect on amorphous Li3BO3 generation. Amorphous Li3BO3 was synthesized successfully with agglomerated state. The products contained Li6B4O9 and Li4B2O5 besides Li3BO3. Higher amorphous Li3BO3 degree was obtained at higher O2 and quenching gas flow rates. The experiment results indicate that the high quenching rate promotes amorphous Li3BO3 generation but increases the possibility of by-product generation.

Influence of Impurities from Manufacturing Process on the Toxicity Profile of Boron Nitride Nanotubes.

The toxicity of boron nitride nanotubes (BNNTs) has been the subject of conflicting reports, likely due to differences in the residuals and impurities that can make up to 30-60% of the material produced based on the manufacturing processes and purification employed. Four BNNTs manufactured by induction thermal plasma process with a gradient of BNNT purity levels achieved through sequential gas purification, water and solvent washing, allowed assessing the influence of these residuals/impurities on the toxicity profile of BNNTs. Extensive characterization including infrared and X-ray spectroscopy, thermogravimetric analysis, size, charge, surface area, and density captured the alteration in physicochemical properties as the material went through sequential purification. The material from each step isscreened using acellular and in vitro assays for evaluating general toxicity, mechanisms of toxicity, and macrophage function. As the material increased in purity, there are more high-aspect-ratio particulates and a corresponding distinct increase in cytotoxicity, nuclear factor-κB transcription, and inflammasome activation. There isno alteration in macrophage function after BNNT exposure with all purity grades. The cytotoxicity and mechanism of screening clustered with the purity grade of BNNTs, illustrating that greater purity of BNNT corresponds to greater toxicity.

Study of Ablation Phenomena of Polymer Bulk Irradiated by Thermal Plasmas Using Induction Thermal Plasma Technique

Study of Ablation Phenomena of Polymer Bulk Irradiated by Thermal Plasmas Using Induction Thermal Plasma Technique

Surface Cleaning Effect of Bare Aluminum Micro-Sized Powder by Low Oxygen Induction Thermal Plasma.

The development of bare metal powder is desirable for obtaining conductive interfaces by low-temperature sintering to be applied in various industries of 3D printing, conductive ink or paste. In our previous study, bulk Al made from Al nanopowder that was prepared with low-oxygen thermal plasma (LO-ITP), which is the original metal powder production technique, showed high electrical conductivity comparable to Al casting material. This study discusses the surface cleaning effect of Al particles expected to be obtained by peeling the surface of Al particles using the LO-ITP method. Bare metal micro-sized powders were prepared using LO-ITP by controlling the power supply rate and preferentially vaporizing the oxidized surface of the Al powder. Electrical conductivity was evaluated to confirm if there was an oxide layer at the Al/Al interface. The Al compact at room temperature produced from LO-ITP-processed Al powder showed an electrical conductivity of 2.9 · 107 S/m, which is comparable to that of cast Al bulk. According to the microstructure observation, especially for the interfaces between bare Al powder, direct contact was achieved at 450 °C sintering. This process temperature is lower than the conventional sintering temperature (550 °C) of commercial Al powder without any surface cleaning. Therefore, surface cleaning using LO-ITP is the key to opening a new gate to the powder metallurgy process.

Comparative Study of Influence of Simultaneous Modulation of Upper-Coil and Lower-Coil Currents on Silicon Nanoparticles Synthesized Using Tandem-Type Modulated Induction Thermal Plasmas

Comparative Study of Influence of Simultaneous Modulation of Upper-Coil and Lower-Coil Currents on Silicon Nanoparticles Synthesized Using Tandem-Type Modulated Induction Thermal Plasmas

Effect of Methane Injection Methods on the Preparation of Silicon Nanoparticles with Carbon Coating in Induction Thermal Plasma

Effect of Methane Injection Methods on the Preparation of Silicon Nanoparticles with Carbon Coating in Induction Thermal Plasma

Improvement of barium tungsten cathode and investigation of thermionic emission performance

<sec>The Ba-W cathode consists of the porous W matrix and the aluminate. During cathode operation, the Ba atoms are generated in the pores through the thermal reaction between the W and aluminate, and then diffuse along the pore channels to the W surface, lowering the work function. Therefore, the Ba yield and the Ba diffusion are significantly influenced by the micro pore structure of the matrix and the phase composition of the aluminate.</sec><sec>Firstly, the matrix is fabricated with the narrow particle size distribution powder by the spark plasma sintering (SPS) technique, which shows the narrow pore size distribution (FWHM = 0.43 μm). Then the spherical powder with good fluidity and high tap density is prepared using the RF induction thermal plasma. The matrix prepared with spherical powder exhibits narrower pore size distribution (FWHM = 0.4 μm), smooth pore channels and good inter-pore connectivity. The two matrixes prepared with narrow particle powder and spherical powder are named N-matrix and S-matrix, respectively.</sec><sec>The aluminates are prepared using the solid phase method and the liquid phase method, separately. The particles of solid phase aluminate precursor present all shapes and all sizes, while the particles of the liquid phase aluminate precursor are uniform in size and identical in shape. The phase of solid phase aluminate and the phase of liquid phase aluminate are analyzed by XRD, the results show that the former consists of the effective Ba<sub>3</sub>CaAl<sub>2</sub>O<sub>7</sub> phase and other impurity phases, while the latter is composed of two effective phases of Ba<sub>3</sub>CaAl<sub>2</sub>O<sub>7</sub> and Ba<sub>5</sub>CaAl<sub>4</sub>O<sub>12</sub>.</sec><sec>The N+S and S+S cathodes are obtained by using the solid phase aluminate to impregnate the N-matrix and the S-matrix, and the <i>U</i>-<i>j</i> characteristics of the two cathodes are investigated. The double logarithmic curves of <i>U</i> and <i>j</i> show that the slope of 1.37 in the space charges limited (SCL) region for the S + S cathode is higher than that of 1.25 for the N+S cathode, so the S+S cathode exhibits better emission uniformity. The current density at the deviation point (<i>j</i><sub>DEV</sub>) of the N+S cathode and that of the S+S cathode are 6.6 A·cm<sup>–2</sup> and 6.96 A·cm<sup>–2</sup>, respectively. So the improvement on the matrix obviously raises the emission uniformity of cathode, but the current density is increased less.</sec><sec>Based on the excellent matrix of the S+S cathode, the S+L cathode is obtained by improving the aluminate of the S+S cathode with liquid phase aluminate. The <i>U</i>-<i>j</i> characteristics show the slope of the S+L cathode reaches to 1.44, and the <i>j</i><sub>DEV</sub> is 21.2 A·cm<sup>–2</sup>. So the improvement on the aluminate not only increases the uniformity, but also raises the current density.</sec><sec>The present study shows that the <i>U-j</i> curve calculated from the classical thermionic emission (TE) theory accords well with that of the S + L cathode at 1000 ℃, which indicates that the Ba-W cathode follows the classical TE theory rather than other emission theories, and the Ba-O dipole layer just changes the work function of the cathode.</sec>

Condensation of cometary silicate dust using an induction thermal plasma system

Glass with embedded metal and sulfides (GEMS) is a major component of chondritic porous interplanetary dust particles. Although GEMS is one of the most primitive components in the Solar System, its formation process and conditions have not been constrained. We performed condensation experiments of gases in the system of Mg–Si–O (MgSiO3 composition) and of the S-free CI chondritic composition (Si–Mg–Fe–Na–Al–Ca–Ni–O system) in induction thermal plasma equipment. Amorphous Mg-silicate particles condensed in the experiments of the Mg–Si–O system, and their grain size distribution depended on the experimental conditions (mainly partial pressure of SiO). In the CI chondritic composition experiments, irregularly shaped amorphous silicate particles of less than a few hundred nanometers embedded with multiple Fe–Ni nanoparticles of ≤20 nm were successfully synthesized. These characteristics are very similar to those of GEMS, except for the presence of FeSi instead of sulfide grains. We propose that the condensation of amorphous silicate grains smaller than a few tens of nanometers and with metallic cores, followed by coagulation, could be the precursor material that forms GEMS prior to sulfidation.

Numerical study of nanoparticle formation in two-coil tandem-type modulated induction thermal plasmas with simultaneous modulation of upper- and lower-coil currents

A numerical study was conducted of nanoparticle (NP) formation and growth in two-coil tandem-type modulated induction thermal plasma (tandem MITP) with method of moment. Two-coil tandem MITP, which has two induction coils in one plasma torch, has been developed for the synthesis of large amounts of NPs. The two-coil tandem MITP is operated by modulated or non-modulated two coil currents for induction thermal plasma under a transient state. Furthermore, time-controlled feedstock feeding (TCFF) is involved with tandem MITP. For this tandem MITP + TCFF method, we developed a numerical model with three components: calculation of time-varying tandem-MITP fields, calculation of intermittent feeding of feedstock particles including dynamic motion, heating and evaporation of feedstock particles, and the calculation of NP formation and growth from feedstock vapour in time-varying tandem MITP fields. Two-way interactions among these three parts were also considered. Calculation was made Si NP formation in Ar tandem MITP with intermittent feeding of feedstock Si microparticles. Calculation results demonstrated that two-coil tandem-type MITP with simultaneous modulation of upper-coil and lower-coil currents can produce more rapid decay in the temperature field in the reaction chamber during the off-time, and that this rapid temperature decay promotes nucleation of NPs and suppresses particle growth. This finding indicates that tandem MITP can offer a temperature field with greater variation, which is preferred for NP synthesis.

Synthesis of boron nitride nanosheets powders using a plasma based bottom-up approach

Boron nitride nanosheets (BNNS) are graphene-like materials with large bandgap and excellent thermal/chemical stability. Current BNNS synthesis methods show low yield and/or purity preventing effective implementation in real-life applications. This work reports two catalyst-free bottom-up approaches for BNNS synthesis using induction thermal plasma. High enthalpy and cooling rates of this plasma allow BNNS to form homogeneously when using solid ammonia borane (AB) as a precursor. In this case, clusters of B x N y H z nucleate to form particles of critical sizes on which BNNS propagate while releasing H2. Using boron powders instead of AB produces BNNS through a heterogeneous route. In this case, boron undergoes spheroidization while active nitrogen species diffuse on the liquid surface to form boron nitride nanowalls which propagate into BNNS. The operating pressure and nitrogen loading are shown to control BNNS nucleation and growth and minimize by-products. An optimum operating pressure of 62 kPa provides axial velocities necessary for decomposing AB and melting boron. The synthesis process is well controlled yielding homogeneously grown BNNS of 30 × 30 nm sheet lateral sizes and ∼8 atomic layers, while the heterogeneously grown BNNS are of 100 × 100 nm and ∼20 layers. Both homogeneous and heterogeneous routes lead to BNNS structures showing exceptional crystallinity with defect-free stacking of the BN planes.

Preparation of Carbon-Coated Silicon Nanoparticles with Different Hydrocarbon Gases in Induction Thermal Plasma

Preparation of Carbon-Coated Silicon Nanoparticles with Different Hydrocarbon Gases in Induction Thermal Plasma