Conductivity Of Ceramics Research Articles

Electrochemical Flash Sintering: A New Tool to Obtain All Solid-State Batteries in Few Seconds

Nowadays, inorganic All Solid-State Batteries (ASSBs) encounter a strong resurgence of scientific and technological interest stimulated by the discovery of new high conductivity solid electrolytes at room temperature (≥ 1 mS), as well as the development of fast Electrical Current Activated Sintering (ECAS) processes. One of the advantages of ASSBs is that they guarantee a unique safety due to the chemical and thermal stability of the materials. However, manufacturing dense ceramics requires sintering temperatures generally higher than 700 °C to lead to optimal mechanical and conductive properties. At these temperatures, the occurrence of undesired chemical reactions at the interfaces is an issue for electrochemical applications due to the formation of interdiffusion layers that block the charge transfer.For this purpose, Flash Sintering (FS) is very effective to densify conductive ceramics in a few seconds at significantly lower temperatures compared to conventional sintering.1,2 FS consists in making the current directly flows through the sample without neither the use of a conductive die nor the application of a charge. However, this technique requires a reversible electrochemical reaction to allow the charge transfer between the electronic conductor (i.e. the current collectors) and the ionic conductor (i.e. ceramic electrolyte).3 In the case of pure cationic conductors (Li+, Na+, K+, etc.), Pt electrodes which are commonly used for FS, are herein blocking electrodes preventing the current from flowing. A mixed cationic electronic conductor is then required to ensure the charge transfer reaction.Through this work, we demonstrate the feasibility of FS on Li+ ionic conductors such as Li1.3Al0.3Ti1.7(PO4)3 (LATP) or Li1.5Al0.3Ge1.5(PO4)3 (LAGP), using LiCoO2 (LCO) or LiNi1/3Mn1/3Co1/3O2 (NMC) mixed Li+/e- conductors as electrode materials. Using the concept of Electrochemical Flash Sintering, the “flash” event was obtained on two multi-component systems: LATP sandwiched between two pure LCO layers as electrodes and LATP sandwiched between two composite electrodes (LCO + LATP). Microstructural and chemical analyses were employed to characterise the densification at the vicinity of the interfaces. It is shown that a composite electrode both allows the flash to occur and prevents the delamination observed with pure LCO by lowering interfacial strains.4 This multi-material architecture turns out to be the one of an All-Solid-State Li-ion Battery, opening the path of using FS as a promising fast process to build functional multi-materials for energy storage devices. 1. Cologna, M.; Rashkova, B.; Raj, R. Flash sintering of nanograin zirconia in < 5 s at 850°C. J. Am. Ceram. Soc. 2010, 93, 3556–3559.2. Steil, M. C.; Marinha, D.; Aman, Y.; Gomes, J. R. C.; Kleitz, M. From conventional ac flash-sintering of YSZ to hyper-flash and double flash. J. Eur. Ceram. Soc. 2013, 33, 2093–3. Caliman, L.B.; Bouchet, R.; Gouvea, D.; Soudant, P.; Steil, M.C. Flash sintering of ionic conductors: the need of a reversible electrochemical reaction, J. Eur. Ceram. Soc. 2016, 36, 1253–1260.4. Lachal, M.; El. Khal, H.; Bouvard, D.; Chaix, J-M.; Bouchet, R.; Steil, M.C. Electrochemical Flash Sintering of advanced multi-materials for energy storage devices, J. Eur. Ceram. Soc. submitted. Figure 1

Cover Feature: Fluoride‐Based Anion Doping: A New Strategy for Improving the Performance of Protonic Ceramic Conductors of the Form BaZrO3 (ChemElectroChem 10/2020)

The Cover Feature illustrates the enhanced mobility of ionic charge carriers after substitution of F− on the O2− site. Interestingly, weakened chemical bonds were observed between the cations (A or B site) and the oxygen ions by the anion doping strategy resulting in an improved oxygen mobility in the lattice. This finding suggests that targeted anion doping is a promising strategy for the development of a new generation of electrolyte materials. More information can be found in the Aricle by J. Gao et al.

Fluoride‐Based Anion Doping: A New Strategy for Improving the Performance of Protonic Ceramic Conductors of the Form BaZrO3

AbstractA new strategy is reported to improve the performance of BaZrO3‐based protonic ceramic conductors by substitution on the anion sublattice, specifically replacing F− in the O2− site. The F−‐doped material exhibited higher conductivity under both reducing and oxidizing atmospheres compared to the undoped oxide. Ab initio calculations and X‐ray photoelectron spectroscopy results showed that the improved performance can be attributed to weakened chemical bonding between the cations (A or B site) and the oxygen ions as a result of F− doping, resulting in improved oxygen mobility. Finally, improved performance was demonstrated by using BaZr0.8Y0.2O3‐δ‐σFσ (σ=0.1) as the electrolyte in protonic ceramic fuel cells measurements. The anions doping strategy shows great promise for the development of a new generation of high‐performance electrolyte materials.

Vacuum-tight ceramic composite materials based on alumina modified with multi-walled carbon nanotubes

We develop the method of production of conductive vacuum-tight ceramics based on Al2O3 modified by multiwall carbon nanotubes (MWCNTs) at extremely low their content. The method is based on the use of nanopowders of α-Al2O3 combined with application of highly efficient distribution of MWCNTs on the surface of the initial oxide particles, provided by using ultrasonicated MWCNT suspensions stabilized with surfactant. The usage of surfactant destructing of MWCNT agglomerates of structure results in the elimination of cavities in ceramic matrix and improvement vacuum-tight properties of composites. The results can provide the optimization of production technology of strong vacuum-tight ceramics which are perspective for the production of conducting ceramics for accelerating tubes in pulse linear accelerators. Such materials would make it possible to avoid using high-voltage resistive voltage splitters and simultaneously suppress transverse resonance modes usually leading to transverse instability of intense beams in long accelerating structures.

Беспотенциальный корпус силового модуля

In this paper we present an optimal design of a ceramic-metal sealed power module package. In our design the leads of the package are mounted on alumina ceramic substrates with through vias, which have been soldered by the high-temperature silver solder at the slots in the package base plate. Base plate is made of pseudoalloy, thermal expansion of which is in a good agreement with alumina ceramics. Substrate made of highly conductive aluminium-nitride ceramics, which is designed for mounting the functional elements of the module, is soldered to the flange with 450-500°С melting point solder. Suggested design provides resistance to cyclic temperature changes of -196+100°C, eliminates thermomechanical effects leading to damage to ceramic substrates during sealing by roll-seam welding, and ensures minimal bending of the bearing surface of the flange.

Carbon nanotubes reinforced alumina matrix nanocomposites for conductive ceramics by additive manufacturing

Alumina has been extensively used due to its high toughness and hardness, low bulk density, and thermal stability without interaction with the matrix at high temperature. However, the non-conductivity at room temperature narrows its broader applications. Carbon nanotube (CNT) is a suitable candidate to adjust the electrical property of alumina matrix composites due to its high electrical conductivity. By using material extrusion 3D printing (ME3DP), we fabricated 3D CNT/alumina green bodies using inks with controlled rheological properties for high printability. The printed green bodies with CNT loading from 3 wt% to 10 wt% were thermally treated to remove binders and sinter the 3D parts at temperatures from 900 to 1400 °C. The sintered samples showed a good dispersion of CNT in the alumina matrix and improved electrical conductivity. The electrical conductivity of the composites measured up to 10-1 S/m at 7 wt.% CNT loading, compared to the electrical conductivity of 10-13 S/m of pure alumina.

Surface Integrity Analysis of Ceramics Machined by Wire EDM Using Different Trim Cut Technologies

Electrically conductive ceramics are increasingly used in tooling and chemical industry, because of their high thermal and chemical resistance. The high hardness of the material is a major challenge for conventional manufacturing processes. Wire electrical discharge machining (WEDM) offers a good alternative, because the machining process is independent of the hardness. Nevertheless, the thermal material removal principle of WEDM leads to a microstructure change in the near-surface layer, which affects the load-bearing capacity of the material. In order to minimize these damages and to increase the load-bearing capacity, trim cuts must be used. Up to now, there are no processing technologies available on WEDM-machines for machining electrically conductive ceramics. Therefore, this study deals with the surface integrity improvement of zirconia/tungsten carbide (TZP-WC) as an electrically conductive ceramic by developing a material-specific technology with main and trim cuts. The surface improvement is verified by means of surface roughness measurements, cross-section analysis and bending strength tests. The dominant material removal mechanisms were identified to be melting, evaporation and spalling. This leads to smooth but glassy surfaces. The variation of the EDM characteristics caused a variation in the structure of the resulting surface. However, the discharge energy has a strong impact on both surface condition and removal mechanism. Bending strengths of over 900 MPa could be achived by creating a smooth and nearly crack-free rim zone. Trim cuts with higher electrical discharge energies cause fatal damage in the surface and lead to a breakdown of the bending strength.

A BiVO4 photoanode grown on porous and conductive SnO2 ceramics for water splitting driven by solar energy

The transformation of solar energy into chemical energy stored as hydrogen fuel underlies the water splitting process into O2 and H2 in photo-electrochemical (PEC) cells. This a potentially promising technology to generate renewable and clean energy. To make this technology commercially viable, the engineering of appropriate low-cost and robust photo-electrode materials and substrates is needed. In this study, we introduce BiVO4-photoelectrodes grown on conductive bulk SnO2–Sb2O5 ceramics acting as porous substrate. For these photoelectrodes, the value of photocurrent density of 1.1 mA/cm2 was achieved in 0.1 M NaOH electrolyte at 1.23 V vs. RHE (reversible hydrogen electrode) under LED light (λ = 455 nm). This PEC performance of these BiVO4 photoelectrodes is reached in spite of using a simple and low-cost deposition technique, where the BiVO4-precursor is delivered to the bulk porous ceramic substrate as a nebulized aerosol in air-flow at room temperature. The high porosity of the ceramic substrate permits some permeation of the aerogel into the pores to a depth of several micrometers to provide a 3D-growth of the BiVO4-coating on conductive SnO2 grains. The film thickness of the BiVO4 on individual grains is approximately 100 nm. This construction of the photoelectrode leads to an effective interface with good absorption of solar radiation and good electron harvesting. The bulk ceramics assure favorable conditions for electron collection and charge transport, which results in a good PEC performance with this type of photoanode.

Electrical discharge machinable (Y, Nd) co-stabilized zirconia – Niobium carbide ceramics

Electrical discharge machining (EDM) of electrically conductive ceramics offers the possibility to manufacture customized ceramic components from sintered blanks. In this study two different yttria neodymia co-stabilized TZP materials containing 28 vol% niobium carbide were manufactured by hot pressing at 1275 °C–1400 °C and axial pressure of 60 MPa and compared to a 3Y-TZP based reference. The co-stabilized ceramics offer a strength up to 1250 MPa and a hardness of 14 GPa. The fracture resistance can be tailored between 7.4–9.7 MPa√m by variation of the yttria/neodymia ratio and the sintering temperature. These composites, however, require an exact setup of machining parameters. Die sinking EDM experiments revealed that the dominant material removal mechanism is melting. Machined surfaces can achieve low roughness Ra =0.3 μm combined with material removal rates of 1.5 mm³/min. The choice of excessively high energy parameters in EDM may lead to crack formation, spallation and phase accumulation during re-solidification.

Features of the production and study of electrophysical characteristics (BeO + TiO2)-ceramics by impedance spectroscopy

The resulting electrically conductive two-component BeO ceramics with the addition of micro and nanocrystalline TiO 2 powder, which can be used as a material absorber of scattered microwave radiation in high-power electronic devices. The nature of the appearance of electrical conductivity and absorption of the microwave field in (BeO + TiO 2 )-ceramics has not been completely established. The impedance spectroscopy method was the first to investigate the electrical and dielectric characteristics of this ceramics in the frequency range from 100 Hz to 100 MHz, depending on the presence of a micro- and nanosized TiO 2 phase in the composition of BeO ceramics. It has been established that the static resistance of ceramics with the addition of a TiO 2 nanopowder is significantly reduced compared with the resistance of the original ceramics with TiO 2 micropowder. It is shown that the real and imaginary components of the dielectric constant of the studied ceramics increase to abnormally large values as the frequency of the effective electric field decreases, and in the high frequency range f ≥ 10 8 Hz, the process of dielectric relaxation begins, leading to an increase in the dielectric loss angle. The dielectric characteristics of ceramic samples are determined under blocking conditions for through conduction. The effect of TiO 2 micropowder additives on dielectric polarization processes with increasing frequency up to 12·10 9 Hz is considered. Ill. 8. Ref. 26.

Electrical discharge machining of ceramic nanocomposites: sublimation phenomena and adaptive control

The productivity of electrical discharge machining (EDM) is relatively low owing to the natural laws of electrical erosion. Precise EDM demands uninterrupted control of the discharge gap and adjustment of process parameters. It is particularly critical for processing large workpieces with complex linear surfaces and for materials with threshold conductivities such as the new advanced ceramic nanocomposites Al2O3+TiC and Al2O3+SiCw+TiC(30–40%). In these cases, adequate flushing of erosion products is hampered by the geometry of the working space or by the small value of the required discharge gap, which does not exceed 2.2–2.5 μm. The methods of adaptive control in modern computer numerical control systems of EDM equipment based on measuring the electrical parameters in the working zone have been shown to be ineffective in the cases described above. This study aims to investigate the natural phenomena of material sublimation under discharge pulses for conductive ceramics and nanocomposites. The measured conductivities of the samples are higher than the percolation threshold. However, the question of machinability remains open owing to detected processing interruptions and poor quality of machined surfaces. New knowledge on EDM of conductive ceramics and nanocomposites can improve the final quality of the machined surfaces and productivity of the method by the introduction of advanced monitoring and control methods based on acoustic emissions. The manuscript presents an up-to-date overview and current state of the research on the subject area. The obtained morphology of the samples and discussion of the findings complete the experimental part of the study. The scientific basis for a new type of adaptive control system is provided. This can improve the effectiveness of parameter control for machining conductive ceramics and nanocomposites and contribute to an increase in the EDM performance for the most critical cases.

(Invited) Recent Progress in Low-Temperature Proton Conducting Ceramics for Hydrogen Isotope Processing

Proton conducting ceramics (PCCs) are of considerable interest for use in energy conversion and storage applications, electrochemical sensors, and separation membranes. PCCs that combine performance, efficiency, stability, and the ability to operate at low temperatures are particularly attractive for these applications. This presentation summarizes the progress made towards developing low temperature proton conducting ceramics (LT-PCCs), which are defined as operating in the temperature range of 25-400°C. The structure of these ceramic materials, the characteristics of proton conducting mechanisms, and the potential applications for LT-PCCs will be summarized with particular emphasis paid to interfacial protonic conduction. Three temperature zones are defined in the LT-PCC operating regime based on the predominant proton transfer mechanism occurring in each zone. The variation of material properties such crystal structure, conductivity, microstructure, fabrication methods required to achieve the requisite grain size distribution, along with typical strategies pursued to enhance the proton conduction are addressed. Finally, a perspective regarding applications of these materials to low temperature (LT) solid oxide fuel cells, hydrogen separation membranes and emerging areas in the nuclear industry including off gas capture and isotopic separations are presented. Figure 1

Peculiarities of charge carrier relaxation in grain boundary of gadolinium-doped ceria ceramics

Two different gadolinium-doped ceria ceramics are prepared from two different powders, one commercially available synthesised by solid state reaction and another produced by tartaric acid assisted sol–gel synthesis. The specimens have a different microstructure, while the XRD patterns of powders showed a pure cubic fluorite structure without any impurity phase. The electrical properties are studied at frequencies up to 10 GHz by combining broadband 2-electrode and 4-electrode impedance spectroscopy methods. Primary electrical measurements showed that the values of grain conductivity and its activation energies for both ceramics were nearly the same. However, due to different contributions of the grain boundary mediums, total conductivities and their activation energies are found to be considerably different. The advantage of the 4-electrode method allowed us to measure the pure electrical response of grain boundaries, bypassing any interferences caused by interfacial impedance. By using these data, the temperature behaviour of distribution of relaxation times in the grain boundary is studied. A broadening of this distribution with increasing temperature is found for both specimens, contrary to a previously observed phenomenon in the grain of oxygen ion conductive ceramics and single crystals. It is shown that, supposing individual relaxation times behave according to the Arrhenius law, both activation energy and pre-exponential factor must be distributed.

Studies of structural and morphological properties of cuprate conductive ceramics after electrochemical treatment in alkaline electrolyte

This study is focused on detail research of the structural and morphological changes in cuprate ceramics Bi1.7Pb0.3Sr2CaCu2Ox (B(Pb)SCCO 2212) and Bi1.7Pb0.3Sr2CuOx (B(Pb)SCCO 2201) during the electrochemical treatment. Their electrochemical reduction behavior is investigated by Cyclic Voltammetry (CV) and Chronopotentiometry (CP) in 7 M KOH. The used ceramic powders are physicochemically characterized before and after the electrochemical test. It has been found that ceramics are reduced during the charging process. The reduction products are different oxides and hydroxides as well as Cu and Bi metals. Their presence probably improve the overall conductivity of the electrode and the contact between the particles of the negative active mass. On the other hand, the Ca- and Sr-products in the case of B(Pb)SCCO 2212 modification decrease the solubility of ZnO in the electrolyte and suppress the shape change of the electrode.

Flash joining of conductive ceramics in a few seconds by flash spark plasma sintering

The feasibility of flash joining conductive ceramics using spark plasma sintering is demonstrated. It is shown that graphite disks can be joined in a few seconds (6–10 s electric discharge time) using a SiOC precursor (methyl silicone resin) as an interlayer. Differently from usual flash experiments, the process does not require any pre-heating, allowing a dramatic reduction of the processing time. XPS analysis of the joint revealed a clear evolution of the chemical environment of silicon with a progressive transition from SiOC to SiO2/SiC. Mechanical tests were performed to determine the fracture toughness (1.0 ± 0.2 MPa m0.5) and fracture energy (40.6 ± 9.8 J/m2) of the interfaceFlash joining can be applied beyond graphite joining, and opens a novel and flexible processing route for many conductive ceramics, as demonstrate by preliminary work on Kanthal® Super MoSi2 and Cf-reinforced SiC.

Development of Metal Supported Cells Using BaZrO3-Based Proton Conducting Ceramics

Proton Conducting Ceramics (PCCs) enable a variety of potential applications, such as hydration or dehydration of chemicals in addition to fuel cells and electrolysers. Here we demonstrate the development of PCCs in the third-generation architecture, i.e. porous Metal Supported (MS) cells, performed in the project DAICHI based on the expertize of MS-solid oxide cells in the European project EVOLVE. Engineering the electrode and electrolyte coating process on a porous ITM metal substrate, (La,Sr)MnO3 electrode and intermediate electrolyte layers were successfully fabricated to reduce the pore size from a few tens of µm (MS) to below hundred nm. A few µm-thick BaZrO3-based electrolyte layer was coated on the top of nano-porous intermediate layer by Pulsed Laser Deposition (PLD). The results demonstrated dense and crack-free MS-PCC cells obtained under optimal PLD conditions and with the entire processing below 1000°C.

A hematite photoelectrode grown on porous and conductive SnO2 ceramics for solar-driven water splitting

Photoelectrochemical water splitting using solar energy is a highly promising technology to produce hydrogen as an environmentally friendly and renewable fuel with high-energy density. This approach requires the development of appropriate photoelectrode materials and substrates, which are low-cost and applicable for the fabrication of large area electrodes. In this work, hematite photoelectrodes are grown by aerosol assisted chemical vapour deposition (AA-CVD) onto highly-conductive and bulk porous SnO2 (Sb-doped) ceramic substrates. For such photoelectrodes, the photocurrent density of 2.8 mA cm-2 is achieved in aqueous 0.1 M NaOH under blue LED illumination (λ = 455 nm; 198 mW cm-2) at 1.23 V vs. RHE (reversible hydrogen electrode). This relatively good photoelectrochemical performance of the photoelectrode is achieved despite the simple fabrication process. Good performance is suggested to be related to the three-dimensional morphology of the porous ceramic substrate resulting in excellent light-driven charge carrier harvesting. The porosity of the ceramic substrate allows growth of the photoactive layer (SnO2-grains covered by hematite) to a depth of some micrometers, whereas the thickness of Fe2O3-coating on individual grains is only about 100–150 nm. This architecture of the photoactive layer assures a good light absorption and it creates favourable conditions for charge separation and transport.

Impedance Spectroscopy (BeO+TiO2)-Ceramics with Additive of TiO2 Nanoparticles

The present study is aimed at obtaining electrically conductive two-component ceramics based on BeO with the addition of micro and nanocrystalline TiO2 powder. The ceramics of the composition (BeO+TiO2) is used in radio-electronic equipment as effective absorbers of microwave radiation and in other areas of modern electronics. The nature of the appearance of electrical conductivity and absorption of the microwave field in (BeO+TiO2) ceramics has not been completely established. The impedance spectroscopy method for the first time investigated the electrical and dielectric characteristics of this ceramics in the frequency range from 100 Hz to 100 MHz, depending on the presence of micro and nano-sized TiO2 phases in the composition of the BeO ceramics. It was established that the static resistance of ceramics with the addition of titanium oxide nanopowder is significantly reduced compared with the resistance of the original ceramics with TiO2 micropowder. It is shown that the real and imaginary components of the dielectric constant of the studied ceramics increase to abnormally large values when the frequency of the effective electric field decreases, and in the high frequency range f ≥ 108 Hz, the process of dielectric relaxation begins, leading to an increase in the dielectric loss tangent. The dielectric characteristics of these ceramic samples under conditions of blocking through conduction are determined

Electrical arc machining: Process capabilities and current research trends

Electrical arc machining is the thermal energy-based unconventional machining process, which utilizes energy of arc to melt and vaporize workpiece material. Electrical arc machining has the capability to machine advanced materials such as metal matrix composites, superalloys, and conductive ceramics effectively. The process is considered to be efficient than most of the other unconventional machining processes in terms of the material removal rate. But it has got limitations because it results in a very poor surface finish. Tool wear rate, recast layer formation, surface and subsurface cracks, and geometrical inaccuracy are other limitations up to a certain extent. In this paper, the comprehensive review of research carried out so for in the area of electrical arc machining has been presented. The paper discusses the detailed experimental and theoretical studies done on electrical arc machining to elucidate the effects of various input control factors on different quality characteristics. The paper also contains modeling and optimization studies done so far in electrical arc machining and finally discusses the future research possibilities in the area.

Electrochemical Ceramic Membrane Reactors in Future Energy and Chemical Process Engineering

AbstractElectrochemical ceramic membrane reactors (ECMRs) with their unique ability to efficiently couple electrical, chemical, and thermal energy sectors can be a large part of the transition toward renewable energies and defossilized economies. ECMRs utilize ceramic conductors to extract or distribute oxide ions or protons – directly controlled by an external electric current. This article gives an overview of ECMR properties along with the functionalities and advantages. For many reactions, e.g., the direct synthesis of ammonia, ECMRs are not available at the preferred temperature range of 300 – 550 °C. To evidence the possibility of such reactors, functional materials are reviewed. A simple thermodynamic methodology is proposed to determine the suitability of reactions for particular combinations of coupled energy sectors.