Spark Plasma Synthesis Research Articles

Overview of spark plasma synthesis and sintering of MgB2 superconductor

This study aims to investigate the sintering mechanisms of magnesium diborides using spark plasma sintering and optimize the sintering process conditions. Three different precursor materials were used: (i) commercial powder MgB2, (ii) mixtures of magnesium and nano boron powder (Mg + 2B), and (iii) mixtures of Mg and MgB4 powder for an ‘in-situ’ reactive synthesis. The density of the obtained bulks exceeds 90% of the theoretical density of the material. The structure and microstructure of the samples were analyzed using x-ray diffraction and scanning electron microscope, which were correlated with their superconducting properties. The critical current density (J c), pinning force (f p), and electrical resistivity (ρ) of the samples were also investigated. The results show that the in-situ reactive synthesis of MgB2 using magnesium and nano boron powder was the most effective method for producing high-quality samples with improved superconducting properties. The findings could lead to the development of more efficient methods for producing high-performance of MgB2 bulks.

Continuous spark plasma synthesis of Au/Co binary nanoparticles with tunable properties

We present here a scalable and environmentally friendly gas phase technique employing atmospheric pressure electrical spark discharge plasmas for the production of Au/Co binaries, an effective catalyst system for the decomposition of hydrogen-rich compounds, such as ammonium borane. We demonstrate that Au/Co alloy nanoparticles can be produced via the spark plasma-based technique. The possibility of varying the morphology and phase structure via real time heat treatment of the generated aerosol to form Au/Co/CoO particles with continuous control over a wide particle compositional range (from 24 to 64 at.% [Co]/([Co] + [Au]) content) is also demonstrated. Since our spark-based approach is proven to be capable of providing reasonable particle yields, these results may contribute to the transition of lab-scale, nanocatalyst-based hydrogen storage systems to real world applications.

(Invited) Garnet-Type Electrolytes for All-Solid-State Lithium Metal Batteries

All solid-state Li batteries are foreseen as the future state of battery technology due to their safety, high energy density, and high potential window as compared to the present organic liquid electrolyte batteries. Li-ion conducting garnet-type electrolytes have received considerable research interests due to their compatibility with Li metal anode, good ionic conductivity (10-3 S/cm) and wide electrochemical window (~ 6V vs. Li).1 Garnet-type Li6.5La3-xAxZr1.5-xTax+0.5O12 (A = Ca, Sr, Ba; x = 0.1, 0.5) solid electrolytes were prepared by conventional solid-state synthesis and spark plasma synthesis (SPS).2-4 The formation of the cubic garnet-type structure was confirmed by powder X-ray diffraction (PXRD). Microstructure of the solid electrolytes were analysed by scanning electron microscopy (SEM) and cross-sectional analyses showed that the SPS processed samples are highly dense compared to the same compositions prepared by conventional solid-state route. The AC electrochemical impedance spectroscopy (EIS) was used to measure the impedance of solid electrolytes and found that all samples exhibit bulk conductivity in the order of 10-4 S/cm at room temperature. SPS processed samples showed an excellent Li-ion charge transfer resistance and the highest critical current density compared to the samples prepared by conventional solid-state synthesis. X-ray photoelectron spectroscopy (XPS) analyses were conducted on SPS-processed samples to quantify the impurity layers on garnet surface. Electrochemical performance of a hybrid cell consisting of liquid Li-ion electrolytes and garnet electrolyte will be discussed. References Wang, K. Fu, S. Palakkathodi Kammampata, D. W. McOwen, A. Junio Samson, L. Zhang, G. T. Hitz, A. M. Nolan, E. D. Wachsman, Y. Mo, V. Thangadurai and L. Hu, Chem. Rev., 2020, 120, 4257–4300.Palakkathodi Kammampata, R. H. Basappa, T. Ito, H. Yamada and V. Thangadurai, ACS Appl. Energy Mater., 2019, 2, 1765–1773.Palakkathodi Kammampata, H. Yamada, T. Ito, R. Paul and V. Thangadurai, J. Mater. Chem. A, 2020, 8, 2581–2590.Yamada, T. Ito, S. P. Kammampata and V. Thangadurai, ACS Appl. Mater. Interfaces, 2020, 12, 36119–36127.

High Pressure (HP) in Spark Plasma Sintering (SPS) Processes: Application to the Polycrystalline Diamond.

High-Pressure (HP) technology allows new possibilities of processing by Spark Plasma Synthesis (SPS). This process is mainly involved in the sintering process and for bonding, growing and reaction. High-Pressure tools combined with SPS is applied for processing polycrystalline diamond without binder (binderless PCD) in this current work. Our described innovative Ultra High Pressure Spark Plasma Sintering (UHP-SPS) equipment shows the combination of our high-pressure apparatus (Belt-type) with conventional pulse electric current generator (Fuji). Our UHP-SPS equipment allows the processing up to 6 GPa, higher pressure than HP-SPS equipment, based on a conventional SPS equipment in which a non-graphite mold (metals, ceramics, composite and hybrid) with better mechanical properties (capable of 1 GPa) than graphite. The equipment of UHP-SPS and HP-SPS elements (pistons + die) conductivity of the non-graphite mold define a Hot-Pressing process. This study presents the results showing the ability of sintering diamond powder without additives at 4–5 GPa and 1300–1400 °C for duration between 5 and 30 min. Our described UHP-SPS innovative cell design allows the consolidation of diamond particles validated by the formation of grain boundaries on two different grain size powders, i.e., 0.75–1.25 μm and 8–12 μm. The phenomena explanation is proposed by comparison with the High Pressure High Temperature (HP-HT) (Belt, toroidal-Bridgman, multi-anvils (cubic)) process conventionally used for processing binderless polycrystalline diamond (binderless PCD). It is shown that using UHP-SPS, binderless diamond can be sintered at very unexpected P-T conditions, typically ~10 GPa and 500–1000 °C lower in typical HP-HT setups. This makes UHP-SPS a promising tool for the sintering of other high-pressure materials at non-equilibrium conditions and a potential industrial transfer with low environmental fingerprints could be considered.

Mg3Pt2: Anionic Chains in a Eu3Ga2-Type Structure.

The binary phase Mg3Pt2 was prepared by direct reaction between the elements or by spark-plasma synthesis starting with MgH2 and PtCl2. The compound crystallizes in the monoclinic space group C2/c with a = 7.2096(3) Å, b = 7.1912(4) Å, c = 6.8977(3) Å, and β = 106.072(3)° and is isotypic to Eu3Ga2. Analysis of the electron density within the quantum theory of atoms in molecules shows a significant charge transfer from Mg to Pt in agreement with the electronegativity difference. Further study of the chemical bonding with the electron localizability approach reveals the formation of Pt chains stabilized by a complex system of multicenter interactions involving Mg and Pt species. The metallic character of Mg3Pt2 is confirmed by electronic structure calculations and physical measurements.

Spark Plasma Synthesis and Tribological Behaviour of Ti-Ni-TiCN Nanocomposite

The conventional method of producing titanium components introduces defects into the matrix of the materials, thus resulting in poor microstructure, tribological properties and performance of the materials in service. To overcome these challenges, a Ti-Ni-TiCN nanocomposite was developed using the novel spark plasma sintering (SPS) technique. The morphology and the phases present in the initial powders and the sintered specimen were investigated using the scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) techniques. The dry sliding wear behaviour of the sintered samples was studied at ambient temperature by ball-on-disc tests, under an applied normal load of 25 N. The presence of unreacted TiCN, in-situ formed TiN and Ti2Ni intermetallic phases were revealed by the SEM/EDS analysis and confirmed by the XRD results. The developed titanium matrix nanocomposite displayed a much lower coefficient of friction and wear resistance than the CP-Ti. The strong interface between the matrix and the reinforcements prevents the reinforcements from pulling out of the matrix. Ti-Ni-TiCN nanocomposite showed the predominance of abrasive wear while mixed wear mode was observed, in the CP-Ti. The developed material has the capacity to replace CP-Ti and perform admirably in a tribo-system.

Molybdenum Oxides MoOx: Spark-Plasma Synthesis and Thermoelectric Properties at Elevated Temperature

Molybdenum oxides MoOx in the composition range 2 ≤ x ≤ 3 were synthesized and compacted by the solid-state reaction of powdered α-MoO3 with Mo in the spark-plasma synthesis (SPS) process at temper...

Reactive Spark Plasma Synthesis of Porous Bioceramic Wollastonite

A method was proposed for reactive spark plasma synthesis (R-SPS) of a porous (Ssp = 12.7–8.56 m2/g) and structurally strong (σcomp = 201.1–393.2 MPa) bioceramic composite material based on wollastonite (CaSiO3) containing 20 wt % hydroxyapatite (HAP). In this method, the precursor is an amorphous composite that is based on a mixture of xonotlite (Ca6Si6O17 · 2OH) with HAP and a pore-forming agent and is prepared by the sol–gel (template) synthesis. The originality of the method consists in the formation of crystalline ceramic wollastonite by the transformation of its hydrated form, xonotlite, under spark plasma heating conditions. The densification dynamics, phase formation, and microstructural changes of the formed CaSiO3/HAP ceramic at various (500–900°C) R-SPS temperatures were studied by XRD, TGA/DTA, SEM, BET method, and porosimetry. Microbiological evaluation of the efficiency of the formation of Pseudomonas aeruginosa bacterial films on the surface of samples of the produced CaSiO3/HAP ceramic was performed, in particular, in comparison with a noncomposite material in the absence of HAP. The proposed R-SPS method ensures the creation of a porous, structurally strong composite ceramic containing a biocompatible component (HAP). This ceramic can be promising for producing ceramic bone implants for bone defect restoration.

Development of Mn/Mn and Mn/Mg High Temperature TE Devices

Skeleton-type 20-pair MnSi1.74/Al3Mn3Si4 and MnSi1.74/Mg2Si devices, usable below 600°C, are fabricated successfully. Ni top-electrodes are brazed to the p- and n-thermoelectric (TE) blocks. 50 x 40 x 2mm3 metallic bases are used. The TE-blocks, 10x3x7 mm3 in size, are cutout from the 30mm ϕ x 7mm pellets synthesized by the spark plasma synthesis (SPS) technique. The thermoelectric performance of the Mn/Mn and Mn/Mg devices are 1.44W and 2.79W between 600 °C (hot side) to100 °C (cold side), respectively. While the internal resistance of the devices is 0.43 and 0.55 Ω slowly increasing from 100 °C to 600 °C.

Obtaining Material Based on Copper Selenide by the Methods of Powder Metallurgy

Copper selenide is a promising material for power generation in a medium-temperature range 600–1000 K. A number of features of the Cu–Se system, namely, the existence of phase transition in a Cu2Se compound, the high speed of the diffusion of Cu ions, and the high vapor pressure of Se at elevated temperatures, make it necessary to carry out a series of experimental investigations to develop and optimize the methodology for obtaining the bulk material based on copper selenide. The influence of mechanochemical synthesis regimes and subsequent compaction method on the thermoelectric properties and structure of copper selenide is studied. The source material is obtained by mechanochemical synthesis. The methods of hot pressing (HP) and spark plasma synthesis (SPS) are used to obtain the bulk samples. The investigation of the structure and phase composition is performed by the X-ray diffraction and scanning electron microscopy. It is shown that increasing the duration of the mechanochemical synthesis up to 5 h leads to the depletion of copper in powders and to the formation of nonstoichiometric β-phase Cu1.83Se, which persists after SPS. A comparison of the structure and properties of the material obtained by SPS and HP showed that the material obtained by HP has a greater degree of grain defects. The highest thermoelectric efficiency ZT = 1.8 at a temperature of 600°C is achieved for the material obtained by SPS. It is shown that low thermal conductivity is the main factor affecting the value of the thermoelectric efficiency ZT of the studied materials. The difference in the values of thermal conductivity of the materials obtained by different methods is related to the electronic component of thermal conductivity.

Thermoelectric Hexagonal A-Mg-Si with A = Sr and Ba Zintl Phases

Hexagonal A-Mg-Si with A = Sr and Ba Zintl phases are promising candidates for p-type magnesium silicides usable with n-Mg2Si under 900 K. We synthesized p-type A-Mg-Si Zintl phases by the spark plasma synthesis procedure. Mg2Si and Mg2A powders were mixed at the ratio of 1−x/x with x = 0.3–0.4. Two-step synthesis was performed at 850 K for 20 min and 1100 K for 20 min under uniaxial pressure at 30 MPa. Sintered pellets exhibited a stable p-type thermoelectric property. These pellets consisted of several unknown phases. We found two semiconductor phases, namely A2Mg4Si3 and A2Mg12Si7. The crystal structures of the 2/4/3- and 2/12/7-phases were \( P\bar{6}2m\) (No. 189)- and \( P6_{3} /m\) (No. 176)-types, respectively. Sr0.70Mg2Si, Ba3Mg10Si7 and Sr3Mg10Si7 phases are newly found and characterized by a single crystal diffraction study. Previously found Sr2Mg4Si3 single phase polycrystalline 30φ × 10 mm pellets were successfully synthesized. The thermoelectric performance of the Sr2Mg4Si3 single phase sample was tested. The pellets exhibit p-type behavior from room temperature to 700 K. The thermal conductivity, κ, was almost constant at 1.1 W/mK from 350 K to 700 K.

Thermoelectric Properties of SnO2 Ceramics Codoped with Sb and Zn Prepared by Reactive Spark Plasma Synthesis Followed by Thermal Treatment

Thermoelectric Properties of SnO2 Ceramics Codoped with Sb and Zn Prepared by Reactive Spark Plasma Synthesis Followed by Thermal Treatment

Diffusion-Controlled Formation of Ti2O3 during Spark-Plasma Synthesis

The spark-plasma-sintering (SPS) technique has successfully been applied for the single-step direct synthesis of Ti2O3 from a mixture of powders of rutile/anatase with titanium. The components react by diffusion through the grain boundaries, forming several intermediate phases locally. A single-phase material of titanium(III) oxide is obtained in compact bulk form after 180 min of SPS treatment at 1473 K. The electrical and thermal transport properties of such a SPS-prepared material measured in the temperature range between 300 and 800 K reflect the known semiconductor-to-metal transition above 400 K. The observed metallic-like electrical and thermal conductivity above this temperature is in good agreement with previously reported results. A maximum of the thermoelectric figure-of-merit ZT = 0.04 is achieved at 350 K.

Structural and thermoelectric properties of BaRCo4O7 (R = Dy, Ho, Er, Tm, Yb, and Lu)

The structure and thermoelectric properties of a series of barium lanthanide cobaltites, BaRCo4O7 (R = Dy, Ho, Er, Tm, Yb, and Lu), which were prepared using the spark plasma synthesis technique, have been investigated. The space group of these compounds was re-determined and confirmed to be P31c instead of the reported P63mc. The lattice parameters a and c range from 6.26279(2) Å to 6.31181(6) Å, and from 10.22468(6) Å to 10.24446(15) Å for R = Lu to Dy, respectively. The crystal structure of BaRCo4O7 is built up from Kagome sheets of CoO4 tetrahedra, linked by triangular layers of CoO4 tetrahedra. The values of figure of merit (ZT) of the BaRCo4O7 samples were determined to be around 0.02 at 800 K. X-ray diffraction patterns of these samples have been determined and submitted to the Powder Diffraction File.

Spark plasma synthesis and densification of TaB 2 by pulsed electric current sintering

The synthesis and consolidation in one processing step of single phase tantalum diboride by Spark Plasma Sintering (SPS) is proposed. TaB 2 formation from Ta and B elemental powders takes place at about 800 °C through a solid-state combustion reaction while product densification requires higher temperatures. Consolidation is significantly improved (~ 96% density) when increasing the applied pressure from 20 to 60 MPa immediately after the synthesis reaction occurs. Simplicity, short duration, milder temperatures and pressure conditions, in comparison with other routes utilized so far for obtaining bulk TaB 2 are, along with the good mechanical properties of the obtained product, the main benefits of the adopted approach.

Preparation of Dense Ultrafine TiAl Alloys by Spark Plasma Synthesis from Mechanically Activated Powders

Powder of Ti-46at%Al alloy was synthesized through mechanical activation (MA) and then sintered and concurrently consolidated in a short sintering time of 900 s by using spark plasma sintering (SPS) process. The XRD and SEM profiles show that the microstructures of TiAl alloys contained γ TiAl and small amount α-2 Ti3Al phase, whose amount can be controlled by the sintering temperature. The compacts retained the original fine-grained fully densified bodies by avoiding an excessively high sintering temperature. The alloys sintered at higher temperature with this process showed a coarser microstructure. So it is possible to produce dense nanostructured TiAl alloys by mechanically activated spark plasma sintering (MASPS) within a very short period of time.

Spark Plasma synthesis and diffusion of Cu and Ag in vanadium mixed valence oxides

Spark Plasma sintering (SPS) technique allows powders to be compacted at low temperature with a very short holding time. The powder loaded into a carbon die is heated via direct current pulses and simultaneously submitted to an uni-axial pressure of several MPa. Full density of the sample is achieved within minutes. This process is used to study Cu and Ag metals interactions with V2O5 oxide. Syntheses of MxV2O5 phases (M = Cu, Ag) have been achieved within minutes. Thus Cu and Ag atoms penetrate microcrystals of V2O5 oxide at a high speed, shearing its crystal network and simultaneously rebuilding the crystal structures of the prototype networks β, β′, e or δ MxV2O5. To account for the formation of these phases identified by X-ray diffraction, structural mechanisms are proposed. Cu and Ag atomic diffusion parameters have been determined from energy dispersive X-ray spectroscopy (EDX) and electron micropobe analysis (EPMA) line scans. High values of diffusion coefficients have been determined. Cu atoms diffuse faster than Ag, DCu ≈ 4 × 10−8 m2/s and DAg ≈ 0.5–1 × 10−9 m2/s in e and δ MxV2O5 phases, respectively. Their formation may also be used as a model for further investigations into the diffusion mechanisms of atoms in solids and for a better understanding of the SPS process.

A new way to make solid state chemistry: Spark plasma synthesis of copper or silver vanadium oxide bronzes

The spark plasma sintering technique for various materials, oxides, nitrides, carbides, metals, composites, etc. is undergoing a rapid development following pioneering work in Japan. Here, the technique is used to create a new route to make solid state chemistry. The M–V–O system (M = Cu, Ag, Zn) was selected and direct interaction of M with vanadium pentoxide was performed. Remarkable syntheses have been achieved within minutes, paving the way for new materials. The M x V 2O 5 phases formed with Cu and Ag belong to the mixed valence metal–vanadium oxide bronzes whose structures and electric properties are of interest for applications as electrode materials in lithium batteries. Their formation may also be used as a model for further investigations in order to follow the diffusion mechanisms of atoms in solids and to get a better understanding of the SPS process. In this experiment M atoms penetrate micro-crystals of V 2O 5 oxide at a high speed, shearing their crystal network and rebuilding simultaneously in the mean time the crystal structure of the prototype structures β, β′, ɛ or δ M x V 2O 5.

Fabrication of dense ultrafine TiAl alloys by spark plasma synthesis from mechanically activiated powders

Powder of Ti-46at%Al alloy was synthesized through mechanical activation(MA) and then sintered and concurrently consolidated in a short sintering time of 900 s by using a spark plasma sintering(SPS) process. The XRD and SEM profiles show that the microstructures of TiAl alloys contained γ TiAl and small amount α-2 Ti3Al phase, whose amount can be controlled by the sintering temperature. The compacts retained the original fine-grained fully densified bodies by avoiding an excessively high sintering temperature. The alloys sintered at higher temperature with this process showed a coarser microstructure. So it is possible to produce dense nanostructured TiAl alloys by mechanically activated spark plasma sintering (MASPS) within a very short period of time.

Effect of ball milling on simultaneous spark plasma synthesis and densification of TiC–TiB 2 composites

The effect of ball milling pre-treatment of the starting Ti, B 4C and C powders mixture on the synthesis of dense TiC/TiB 2 composite was investigated through the combined use of a SPEX mill and the spark plasma sintering (SPS) apparatus. When unmilled reactants were used, amorphous carbon was converted to TiC through a combustion reaction with elemental titanium, while the complete conversion is achieved through a relatively slow reaction between the residual Ti and B 4C. In contrast, powders ball milled for 24 h reacted completely under combustion regime. SPS product density was observed to increase from about 97% to 100% of the theoretical value, when the original powders were milled for 6 h, while further increase of the milling time led to a slight decrease in product density. Crystallite size of both boride and carbide phases decreased with milling down to about 50 nm after 24 h of mechanical treatment. The latter one also allowed for the formation of a material with relatively finer microstructure and more homogeneous phase distribution.