Conventional Ceramic Processing Research Articles

Dense ceramics by cold reaction sintering using 95 % powdered construction and demolition waste and sodium silicate

This work explores the feasibility of producing ceramic-like materials from recycled construction and demolition waste through cold reaction sintering using sodium silicate as the liquid medium. The recycled material consists of a mixture of ceramics, mortar, and/or plasterboard - common building materials. Samples containing 95 wt% of recycled content were successfully fabricated at 150 ºC, a considerably lower temperature compared to conventional ceramic processes. These samples exhibited dense microstructures with relative densities of ∼ 90 %, as well as promising mechanical properties, including Vickers hardness values comparable to conventional bricks. In particular, samples with 30 % non-ceramic material showed more than twice the hardness when mortar was incorporated. Leaching tests confirmed the chemical stability of the material, with the incorporation of Ca²⁺ ions into non-leachable species, suggesting a reaction during CRS that enhances its durability. Additionally, FTIR analysis showed a blueshift in the signature from 973 cm⁻¹ to 1041 cm⁻¹ under more aggressive conditions, indicating structural changes and improved leachability. The primary advantage of this process would lie in the high recycled content used to create materials. This proposed new method allows obtaining dense pieces at very low temperatures, which also supposes a reduction of energy consumption, and therefore, an improvement of the sustainability of the production process. Given that this construction and demolition waste are often limited to not high added values, this approach not only supports environmental sustainability and resource conservation but also offers a viable pathway to decarbonizing the ceramic industry.

Low-temperature sintering BCZT-Dy ceramics with low strain hysteresis for actuator application

Ba(Cu0.5W0.5)O3 (BCuW)-doped [(Ba0.85Ca0.15)1-xDyx](Zr0.1Ti0.9)O3 (BCZT-xDy, x = 0.001, 0.03) ceramics were prepared by conventional ceramic processing via low-temperature sintering technique. Rather pure perovskite structure and densified morphology with irregular nearly spherical-shape grains are achieved in all ceramics due to liquid-phase sintering. All BCuW-doped BCZT-xDy ceramics present apparent dielectric frequency dispersion and relaxor ferroelectric characteristic due to ion substitution and adding BCuW. The ceramics prepared at optimized sintering temperatures have rather large strain and small strain hysteresis, showing prospect application in piezoelectric high-precision actuators.

Volumetric Additive Manufacturing of SiOC by Xolography.

Additive manufacturing (AM) of ceramics has significantly contributed to advancements in ceramic fabrication, solving some of the difficulties of conventional ceramic processing and providing additional possibilities for the structure and function of components. However, defects induced by the layer-by-layer approach on which traditional AM techniques are based still constitute a challenge to address. This study presents the volumetric AM of a SiOC ceramic from a preceramic polymer using xolography, a linear volumetric AM process that allows to avoid the staircase effect typical of other vat photopolymerization techniques. Besides optimizing the trade-off between preceramic polymer content and transmittance, a pore generator is introduced to create transient channels for gas release before decomposition of the organic constituents and moieties, resulting in crack-free solid ceramic structures even at low ceramic yield. Formulation optimization alleviated sinking of printed parts during printing and prevented shape distortion. Complexsolid and porous ceramic structures with a smooth surface and sharp features are fabricated under the optimized parameters. This work provides a new method for the AM of ceramics at µm/mm scale with high surface quality and large geometry variety in an efficient way, opening the possibility for applications in fields such as micromechanical systems and microelectronic components.

Effect of La3+and Al3+ doping on the crystal structure and magnetic properties of strontium hexaferrites

Modification of crystal structure and magnetic properties of M-type strontium hexaferrites (SrM) doped with foreign ions (Al3+, La3+) was studied, focusing on the distortion of the lattice. Incorporation of Al3+ ions contracted the lattice of SrM and hardened lattice vibration modes with lattice disorders. X-ray diffraction examined the lattice distortion of FeO5 trigonal bipyramidal sites (TBP) revealing that off-center displacement (z0) was reduced to z0 = 0 by heavy Al3+ doping. This reduction of z0 was attributed to stabilization of single-well potential in the positioning of Fe3+ ions in TBP. Furthermore, La3+ doping led to a more significant contraction of the lattice and restored a non-zero off-center displacement of Fe3+ ion in TBP. The polycrystalline ceramics with high coercivity exceeding 21 kOe through the conventional ceramic processing route with concomitant La3+ and Al3+ doping.

Structure modification and electrical properties by Mn2O3 dopant addition to SnO2 varistor system

This work aims to study the effect of Mn2O3 additions on the electrical properties and microstructure characteristics of a SnO2-based ceramic varistor system doped additionally with Sb2O5, Cr2O3, and CoO. The specimens were prepared using conventional ceramic processing and homogenized by a high-energy ball milling system using the following composition: (98.99-X) % SnO2 – 0.05% Cr2O3 – 0.05% Sb2O5 – 1.00% CoO – X% Mn2O3 where X = 0.00, 0.05, 0.10, 0.20, 0.50 and 1% mol. Characterization by TG-DSC/DTA, XRD, XPS, and SEM/EDS, and the proposed chemical and defect-formation reactions allowed the conclusion that Mn2O3 additions produce alterations of the microstructure consisting of the in situ formation of the spinel Co2MnO4 secondary phase and modification of the potential barriers in the intergranular regions, where, in addition, oxygen vacancies are formed. With the 0.05 mol % Mn2O3, the grain size (average in the range of 2–3 μm) drops by 20 %, thus augmenting the grain boundaries. Altogether, this leads to a decrease in the nonlinearity coefficient (α) and an advantageous displacement of the breakdown electric field (EB). The 0.05 mol % Mn2O3 specimen compares favorably with the reference material by surpassing the EB value by a factor of 8. Elucidation of Mn2+ and Co2+ in 1 mol % Mn2O3 specimens by XPS suggests the role of MnO and CoO as intermediate phases, essential for Co2MnO4 formation. The pathway for in situ formation of Co2MnO4 is set forth based on the above characterization techniques in conjunction with proposed chemical and defect-formation reactions.

Sintering temperature optimization for enhanced magnetic performance in La–Ca–Co doped strontium ferrite

The effectiveness of employing La-Ca-Co co-doping has been demonstrated as the optimal approach for enhancing the magnetic performance of strontium ferrite. However, limited studies have explored the evolution of the magnetoplumbite phase and its correlation with the sintering temperature. In our research, La-Ca-Co doped strontium ferrite permanent magnets were fabricated using a conventional ceramic process and a two-step sintering technique. After sintering at different temperatures, all the samples possess proper c-axis orientation. When the sintering temperature was raised from 1175 °C to 1205 °C, there was an upward trend observed in the remanence Br, increasing from 430 mT to 439 mT. The coercivity Hcj exhibited an increase from 380 kA/m and reached its peak at 397 kA/m at 1185 °C. Although the Br value remained favorable, the coercivity experienced substantial deterioration, reaching its lowest point at 303 kA/m at 1205 °C. Under a sintering temperature of 1195 oC, magnetic performance with optimal energy product was achieved, with Br of 439 mT, Hcj of 379 kA/m, Hcb of 318 kA/m, and (BH)max of 35.5 kJm-3.

A comprehensive study on MnZn ferrite materials with high saturation magnetic induction intensity and high permeability for magnetic field energy harvesting

Manganese-zinc (MnZn) ferrites have important applications in energy conversion, transmission, and harvesting. MnZn ferrite for magnetic field energy harvesting is expected to enhance the saturation magnetic induction (Bs), initial permeability (μi), and Curie temperature (Tc) aspects simultaneously, which is beneficial to the energy harvesting efficiency and safety of the device. In this paper, various formulations of MnZn ferrite samples were prepared by the conventional oxide ceramic process. The cation distribution was determined through Rietveld refinement of XRD patterns Based on this, the M–T curves were fitted by combining Néel molecular field theory with Brillouin functions. The greatest influence on the Curie temperature was found to be the molecular field coefficient between the A and B sites. The magnetization mechanism of MnZn ferrite was comprehensively analyzed by fitting the complex permeability spectrum, magnetocrystalline anisotropy constant, and magnetostriction coefficient. The ratio of domain wall displacement magnetization to domain rotation magnetization shows an increasing and then decreasing trend with Fe content, while |K1| shows an opposite trend. Finally, MnZn ferrite materials with excellent overall performance (Bs = 505mT, μi = 9016, Tc = 447 K) were prepared by investigating the magnetization mechanism.

Doping Fe and Co Induced Modification in the Structural, Optical and Colossal Permittivity of Nb-doped TiO2 Ceramics

Fe/Nb and Co/Nb co-doped TiO2 ceramics were synthesized by conventional ceramic solid-state reaction process in order to create a high dielectric permittivity substance. Comprehensive structural, optical and dielectric studies were carried out on the samples of formula Nb:TiO2, Fe:(TiO2:Nb) and Co:(TiO2:Nb). The structural and optical characterizations were performed with X-ray diffraction and diffuse reflection spectroscopy, respectively. The dielectric properties including colossal permittivity (CP) were investigated at room temperature in the frequency range of 0.1-100 kHz. The novelty of the present work was to create a CP (ϵ′∼104-105) in host TiO2 by codoping with (Co/Nb) and study the change in the CP by using Fe ions instead of Co ions. The results were explained in the framework of the core/shell model and doping mechanisms.

Electrical Conductivity and Electrochemical Performance of Pr Doped Ceria

PCO (Praseodymium Cerium Oxide) solid solution (0-50% PrOx) has been prepared by the conventional solid-state ceramic processing of mixed CeO2 and PrOx powders in the desired stoichiometry at 1500°C in air. Synthesized powder has been characterized for phase chemistry and lattice structure. Electrochemical characteristics of the synthesized powder has been examined using electrochemical impedance spectroscopy. The observed increase in the electrical conductivity of PCO are associated with increased concentration of oxygen vacancies created by replacement of Ce4+ ions with Pr+3 ions. The addition of PrOx also lowered the polarization and ohmic losses.

Fine-grained high-performance Ba0.85Ca0.15 Zr0.1Ti0.9O3 piezoceramics obtained by current-controlled flash sintering of nanopowders

Due to environmental concerns, extensive research has been carried out to develop high-performance lead-free piezoceramics capable of replacing commercial lead-based materials. The lead-free (Ba0.7Ca0.3)TiO3 −Ba(Zr0.2Ti0.8)O3 system has emerged as a candidate for room temperature transducer applications because a high piezoelectric charge coefficient is achieved in this system for compositions at the morphotropic phase boundary. However, conventional ceramic processing of these eco-friendly piezoceramics demands high energy consumption because long-lasting, high-temperature heat treatments are needed, which often lead to microstructural degradation that compromises the material reliability. Field-assisted flash sintering has started to be explored since the application of an adequate electric field was shown to significantly reduce the sintering time and temperature, thereby controlling grain growth. In this work, Ba0.85Ca0.15Zr0.1Ti0.9O3 ceramics are obtained by current-controlled flash sintering of mechanosynthesized nanopowders. Exhaustive control of the sintering parameters allows tailoring of the microstructure, which allows dense fine-grained flash-sintered ceramics exhibiting a high electric field-induced strain response to be obtained.

Dielectric and gyromagnetic structure modulations of Zn–Sn codoped yttrium–iron–garnet based on the density‐generalized functional theory and P–V–L bond theory

AbstractHerein, the crystal structure, dielectric properties, and gyromagnetic characteristics of Zn–Sn codoped Y3ZnxSnxFe5−2xO12 (x = 0.0–0.5) prepared using a conventional ceramic process were investigated. According to the first‐principles’ calculations and complex crystal bonding theory, Zn2+–Sn4+ codoping can increase the relative dielectric constant (εr) by enhancing the average ionicity. The x‐ray photoelectron spectroscopy (XPS) and Raman analysis results indicate that an appropriate amount of Zn2+–Sn4+ codoping can help improve the microscopic morphology, maintain the appropriate ratio of divalent iron ions, and reduce the microwave magnetic and electrical losses of YIG ferrites. The optimized microwave properties are as follows. Y3Zn0.3Sn0.3Fe4.4O12 after sintering at 1400°C; εr = 15.6; dielectric loss, that is, tanδε = 4.3 × 10−4; saturation magnetization, that is, 4πMS = 2244 G; ferromagnetic resonance linewidth, that is, ΔH = 37 Oe. These properties can help improve the performance of high‐frequency microwave components by enhancing the properties of ferrite.

Electrical Conductivity and Electrochemical Performance of Pr Doped Ceria

PCO (Praseodymium Cerium Oxide) solid solution (0-50% PrOx) has been prepared by the conventional solid-state ceramic processing route using CeO2 and PrOx powders in the desired stoichiometry and sintering at 1500°C in air. Synthesized powder has been characterized for phase chemistry and lattice structure. Electrochemical characteristics of the synthesized powder has been examined using electrochemical impedance spectroscopy. The observed increase in the electrical conductivity of PCO are associated with increased concentration of oxygen vacancies created by the replacement of Ce4+ ions with Pr+3 ions. The addition of PrOx also lowered the polarization and ohmic losses.

Low-Temperature Sintering of Bi(Ni0.5Ti0.5)O3-BiFeO3-Pb(Zr0.5Ti0.5)O3 Ceramics and Their Performance.

A low-temperature sintering strategy was realized for preparing 0.21Bi(Ni0.5Ti0.5)O3-0.05BiFeO3-0.74Pb(Zr0.5Ti0.5)O3 (0.21BNT-0.05BF-0.74PZT) ceramics by conventional ceramic processing by adding low melting point BiFeO3 and additional sintering aid LiBO2. Pure perovskite 0.21BNT-0.05BF-0.74PZT ceramics are prepared at relatively low sintering temperatures, and their structure presents tetragonal distortion that is affected slightly by the sintering temperature. The 1030 °C sintered samples have high densification accompanied by relatively large grains. All ceramics have excellent dielectric performance with a relatively high temperature of dielectric constant maximum, and present an apparent relaxation characteristic. A narrow sintering temperature range exists in the 0.21BNT-0.05BF-0.74PZT system, and the 1030 °C sintered 0.21BNT-0.05BF-0.74PZT ceramics exhibit overall excellent electrical performance. The high-temperature conductivity can be attributed to the oxygen vacancies' conduction produced by the evaporation of Pb and Bi during sintering revealed by energy dispersive X-ray measurement.

C-axis Oriented Polycrystalline BaFe12-xCoxO19 (x = 0, 0.3, 0.6, 0.9) for Millimeter Wave Self-biased Circulator at Ka Band

The anisotropic hexagonal magnetic material is prepared using conventional ceramic process. The high magnetic anisotropy field of hexagonal is essential to extend the device bandwidth for circulator operating at millimeter wave band. The modified hexagonal BaFe12-xCoxO19 with about 9 kOe anisotropy field and its Electromagnetic property are presented. And a simulation certificating the circulator at Ka-band is given at the end of the paper.

Microstructure-dependent magnetic permeability in ferrites from nanoparticles

Ferrite samples of composition Cu0.12Ni0.23Zn0.65(Fe2O4) have been prepared by a conventional ceramic process using different sintering temperatures and dwell times. The average particle size is around 25–30 nm and, after sintering, the average grain size increases to 0.2–5 μm and the relative density is between 88 and 95 % of the theoretical density.This paper shows that the mathematical model previously tested on ferrite microparticles with the same composition, is also capable to fit the measured complex magnetic permeability-imaginary part (μ″) and to explain why this magnetic property decreases when the particle size of the starting powder changes from micro to nano size. The model confirms the dependence of the magnetizing mechanisms (spin rotation and domain-wall motion) on the two microstructural parameters: average grain size (G) and relative density (ϕ) of the sintered body.

Frequency dependence studies of dielectric, impedance and permeability properties of Y3+ substituted Li0.5Zn0.1Ti0.1Fe2.3O4 ferrites

Polycrystalline ferrites having compositional formula Li0.5Zn0.1Ti0.1YxFe2.3-xO4 (x = 0.00, 0.02, 0.04, 0.06, 0.08, 0.10) were synthesized by the conventional ceramic process. The sample’s XRD analysis indicated the formation of a single phase with a spinel structure. With the doping of Y3+ ions the lattice constant and the crystallite size were altered, the lattice constant increased with Y3+ doping which is due to the larger ionic radius of Y3+ as compared to Fe3+ and the crystallite decreases with the doping of Y3 ions which may be attributed to the size mismatch between Y3+ and Fe3+ ions. The room temperature dielectric and impedance properties were investigated with the change of frequency in the range of 500 Hz-5 MHz using an Impedance Analyzer (E4990A). The impedance studies showed the contribution of grain effect to the overall electrical response. The initial permeability measured for all the samples from 1 MHz to 20 MHz remained nearly constant except in the frequency range 11–16 MHz where initial permeability exhibited resonance. The results were analyzed and discussed in the paper.

The influence of sintering condition on microstructure, phase composition, and electrochemical performance of the scandia-ceria-Co-doped zirconia for SOFCs

Samples of 6 mol% Sc2O3 - 1 mol% CeO2 co-doped ZrO2 were fabricated by conventional ceramic processing methods and sintered at various temperatures from 1000 to 1650?C in air. The sintering conditions on microstructure and phase content are investigated using various characterization methods, including pycnometry, diffraction, and spectroscopy. The electrical conductivity of samples was investigated using electrochemical impedance spectroscopy (EIS). The effect of inductive load (measured from room temperature to 800?C) is discussed in low to high temperature regimes. At T<400?C since the arc is not a complete semicircle, the high-frequency arc could be fit using a constant phase element (CPE), while by subtraction of inductive load, a good fit is achieved using a capacitor element instead of CPE. The Arrhenius conductivity plot of samples reveals that the specimen sintered at 1600?C for 6 hours exhibits the highest conductivity. The activation energy (Ea) and conductivity preexponential (?0) factor are calculated from a linear fit to data that decreases by the increase in sintering temperature.

Development Status of Control Rod Neutron Absorber Materials for Light Water Reactors with Extended Control Rod Lifetime and Enhanced Safety

The control rod neutron absorbers for light water reactors with extended control rod lifetime and enhanced safety are being developed. It is an innovative material concept that can extend the lifetime by reducing irradiation-induced swelling compared to the existing control rod neutron absorber materials by utilizing the oxide-based materials. Furthermore, it can enhance the safety by improving various characteristics such as oxidation, eutectic reaction, volatilization behaviors of neutron absorber material. First, the oxide-based composition composed of a combination of neutron absorbers and structure stabilizers has been designed as material candidates for neutron absorber materials for control rods. The preliminary manufacturability test of the designed neutron absorber material candidates, and it has been confirmed a possibility that the designed material candidates can be fabricated using the conventional ceramic manufacturing process. In addition, the neutronic calculation/analysis and various out-of-pile tests (neutron absorber phase stability, oxidation and corrosion resistance, interaction and eutectic reaction between neutron absorber material and control rod tube material, melting behavior, etc.) are in progress. It has been also preparing the in-reactor swelling test of the selected material candidates at the HANARO research reactor in KAERI.

Development of Multi-Cation-Doped M-Type Hexaferrite Permanent Magnets

We report enhanced permanent magnet performance for multi-cation–substituted M-type Sr-hexaferrites (SrM) prepared using conventional ceramic processes. The final cation composition, Sr0.4Ca0.3La0.3Fe10.2Co0.1Mn0.1Si0.05Mg0.05O19, could be derived through stepwise and systematic cation composition designs, processing, and characterization. The hexaferrites sample sintered in the temperature range of 1200–1220 °C showed an enhanced coercivity (HC) of approximately 4.0 kOe and a residual magnetic flux density (Br) of 2.5–2.6 kG. When samples of the same composition were fabricated into anisotropic magnets through a magnetic-field molding process, performance parameters of Br = 4.42 kG, HC = 3.57 kOe, and BHmax = 4.70 M·G·Oe were achieved, a significant improvement over Br = 4.21 kG, HC = 3.18 kOe, and BHmax = 4.24 M·G·Oe for the non-substituted SrFe12O19 magnet processed under optimized conditions.

Enhancement of the Magnetic Properties in Si4+-Li+-Substituted M-Type Hexaferrites for Permanent Magnets

A series of charge-balanced Si4+-M1+,2+ (M = Mg2+, K+, Li+) substitution compositions with the chemical formulae of SrFe12−2xSixMgxO19 (x = 0, 0.05, 0.1, 0.2), Sr1−yFe12−ySiyKyO19 (y = 0.05, 0.1, 0.2), and SrFe12−z(Si0.6Li0.6)zO19 (z = 0.05, 0.1, 0.2, 0.4, 0.6) were prepared using conventional ceramic processes. While the sole doping of Si with x = 0.1 (SrFe12−xSixO19 (x = 0.1)) causes a noticeable Fe2O3 phase formation, the co-doping of Si-Mg and Si-Li allow a single M-type phase formation with x up to x = 0.1 and z = 0.4, respectively. Notably, a 2.6% increase in the saturation magnetization was obtained for Si-Li-substituted SrM with z = 0.05—that is, SrFe11.95Si0.03Li0.03O19. Enhancement of the magnet performance can also be achieved when anisotropic permanent magnets are fabricated based on the substitution composition SrFe11.95Si0.03Li0.03O19. The remnant magnetic flux density was improved by 2.5% compared to that of the unsubstituted SrM (from 4207 to 4314 G). The maximum energy product (BHmax) value also increased from 4.24 to 4.46 M·G·Oe. The enhancement in permanent magnet performance is attributed to the increase in the MS of SrM by the optimal Si-Li substitution. This is a promising result because enhanced permanent magnet performance is achieved with intrinsic magnetic property improvement.