Ceramic Transformer Research Articles

Transformation-toughened zirconia: An overview

Zirconia is a “metastable” ceramic, consisting of monoclinic, tetragonal, and cubic phases. Partially stabilized zirconia is preferred choice for dental use since they offer the opportunity to fabricate prosthesis which is not available with other ceramic materials. Phase transformation in zirconia ceramics represents one of the most remarkable innovations in the ceramic field. This phase transformation can have desirable consequences, increase in crack growth resistance which is referred to as “phase transformation toughening”. However, the phase-induced volumetric transformation can also have disastrous consequences, if not properly controlled. This article provides information on crystallography of zirconia and the main characteristics of the tetragonal to monoclinic transformationand also discusses the positive (transformation toughening) and negative aspects (ageing/LTD) of the tetragonal to monoclinic transformation.

Hydrothermal Stability of Hydrogen-Selective Carbon-Ceramic Membranes Derived from Polybenzoxazine-Modified Silica-Zirconia.

This work investigated the long-term hydrothermal performance of composite carbon-SiO2-ZrO2 membranes. A carbon-SiO2-ZrO2 composite was formed from the inert pyrolysis of SiO2-ZrO2-polybenzoxazine resin. The carbon-SiO2-ZrO2 composites prepared at 550 and 750 °C had different surface and microstructural properties. A carbon-SiO2-ZrO2 membrane fabricated at 750 °C exhibited H2 selectivity over CO2, N2, and CH4 of 27, 139, and 1026, respectively, that were higher than those of a membrane fabricated at 550 °C (5, 12, and 11, respectively). In addition to maintaining high H2 permeance and selectivity, the carbon-SiO2-ZrO2 membrane fabricated at 750 °C also showed better stability under hydrothermal conditions at steam partial pressures of 90 (30 mol%) and 150 kPa (50 mol%) compared with the membrane fabricated at 500 °C. This was attributed to the complete pyrolytic and ceramic transformation of the microstructure after pyrolysis at 750 °C. This work thus demonstrates the promise of carbon-SiO2-ZrO2 membranes for H2 separation under severe hydrothermal conditions.

Thermal insulation and antioxidation of vertical graphene oxide‐grafted carbon nanofiber aerogels with ceramic coating

AbstractIn this work, composite aerogels with low thermal conductivity and antioxidation were prepared by introducing graphene oxide (GO) on the carbon nanofibers (CNFs) surface, followed by ceramic coating. CNFs surface‐grafted vertical morphology of GO was used as an enhancer to hinder the heat radiation transmission. The introduced shrinkage‐resistant ceramic coating was used as an antioxidant barrier for carbon materials. The anti‐shrinking ceramic coating was obtained by heat treatment of coating with wrinkle morphology to complete the ceramic transformation. The wrinkle morphology of the coating originated from the gradient crosslinking of the coating before its ceramic transformation. Among them, the gradient crosslinking of the coating could be done by irradiation crosslinking and crosslinker impregnation crosslinking. The thermal insulation and antioxidant of the composite aerogel were jointly investigated. Moreover, the mechanism of CNFs surface grafting GO and the anti‐shrinkage mechanism of the coating were systematically discussed. The experimental results showed that the aerogel exhibited excellent thermal insulation and oxidation resistance in a wide range of temperatures. The structural design of the aerogel not only weakened the thermal radiation transmission to the CNFs aerogel but also significantly enhanced the antioxidant.

Tough and damage-tolerant monolithic zirconia ceramics with transformation-induced plasticity by grain-boundary segregation

Conventional ceria-stabilized tetragonal zirconia (Ce-TZP) with modest flexural strength has rarely been used as compared to yttria-stabilized zirconia, even though it has excellent hydrothermal stability and high toughness. Ce-TZP-based composites were recently developed, being tough and remarkably in combination with transformation-induced plasticity. However, distinct from the widely applied composite approach to improve the strength of Ce-TZP, in this study, a simpler and easily tailorable method was proposed by doping aliovalent oxides that are able to segregate at the zirconia-grain boundaries. 0.2–1 mol% divalent oxides with different cation size (Mg2+, Ca2+, Ba2+ and Sr2+) were selected to dope 10 mol% ceria-stabilized zirconia. CaO and MgO dopants were able to enter the tetragonal Ce-TZP lattice and showed a grain-boundary segregation effect, thereby tailoring the microstructure and transformation behavior. At a higher dopant concentration of 1 mol% MgO or CaO, the ceramics were strong but brittle with a typical elastic linear fracture behavior, whereas at a low dopant concentration of 0.1–0.2 mol% CaO or 0.2–0.4 mol% MgO doping, the ceramics deformed in-elastically to a certain degree without changing the Young’s modulus. At the transition between both fracture behaviors, the best combination of toughness (>10 MPa m1/2), biaxial strength (≥1200 MPa), reliability (Weibull modulus up to 30) and damage-tolerance was obtained. In-situ fracture testing revealed that transformation in such tough and deformable zirconia ceramics took place well before crack initiation with a large transformation zone of ∼100 µm ahead of the crack tip having been formed before failure.

Transition-layer of core–rim structures and β→α transformation in SiC ceramics

Similar to Si3N4 ceramics, β→α phase transformation in SiC ceramics plays a key role in tailoring the microstructures thus optimizing related properties. SiC microstructures are dominated with the core–rim structures by AlN-solution, and by EBSD analysis, α-lamellae were revealed as stacking-faults (SF) and twin-boundaries (TB) in β-grains, co-existing with the core–rim structures as α/β→α’/β’ transformation by sintering. The structural transformation can proceed much further by gas-pressure-sintering than hot-pressing with only RE2O3 agents, while the latter retain a high-density of SF/TB in the metastable β-SiC grains. By high-angle secondary-electron imaging, nanoscale transition-layer (TL) was observed as an inter-phase to fully separate the core and rim, which is created by a transitory equilibrium in the solution–reprecipitation process. The enrichment of AlN or RE in TL demonstrates their segregation to core surface until reaching the super-saturation and before the growth of rims. With higher AlN or RE solution and after sintering, a shear stress can develop from TL contour to drive the expansion of SF/TB in Martensitic transition, especially under an external isotropic pressure. The combinations of β→α transformation, core–rim structures and viscous liquid-phase enable the comprehensive assessment of sintering–microstructure–property–performance relationship of SiC ceramics, as demonstrated for their creep behaviors and fracture toughness.

Design and implementation of LTCC coreless transformers for intelligent solid-state switch

This paper designs, manufactures, and evaluates a multilayer coreless low temperature coiffed ceramic (LTCC) transformer for solid state power controller (SSPC) applications. A series of circular spiral transformers with different layers and turns are fabricated in 2 ∼ 6 layers LTCC. The transformers are simulated and analyzed by using simulation software HFSS, in which the analysis results can be used for the design basis of transformers. The comparison results of these different transformers in terms of resistance, self-loss, Q-factor, mutual inductance, coupling coefficient, and energy efficiency are presented. The working area of the best performance of these transformers for SSPC application is determined, and the IDU used in SSPC implementation based on LTCC coreless transformer is completed.

A phase-field model for interactive evolution of phase transformation and cracking in superelastic shape memory ceramics

This work presents a modified phase-field model for accurate coupling of phase transformation and cracking in shape memory ceramics. The existing phase-field models underestimate the elastic response at the beginning of the mechanical response. We modified the chemical free energy to control the rate of phase transformation and consequently obtain a physical elastic response before initiation of phase transformation. First, the forward and reverse martensitic phase transformation in a superelastic single crystal 3 mol% yttria-stabilized tetragonal zirconia is studied. Then, the interaction between phase transformation and fracture under displacement-controlled loading condition is investigated. The model predicts a realistic mechanical response and the experimentally observed microstructure and crack deflection due to the phase transformation. In addition, the model captures the reverse phase transformation and the stress drop due to the crack propagation.

Comparison of BSPT and PZT Piezoelectric Ceramic Transformers for High‐Temperature Power Supplies

High‐temperature power electronics is an advancing area of research, especially given the widespread availability of wide bandgap semiconductors. Herein, a suitability analysis of (1−x)BiScO3−xPbTiO3 (BSPT) as a material for high‐temperature piezoelectric transformers (PTs) is presented and compared to state‐of‐the‐art Pb(Zr1−xTix)O3 (PZT). Initially, both materials are compared using a variety of metrics to prove the suitability of BSPT as a material for constructing PTs specifically for high‐temperature applications. PTs based on the two materials are designed and fabricated, and then subsequently characterized using impedance measurements. Finally, half‐bridge resonant inverters are constructed using both PTs and the performance of each inverter measured over a range of ambient temperatures. The result of these experiments confirms the suitability of BSPT for PT applications and shows the excellent performance of BSPT PTs at temperatures in excess of that possible with PZT‐based PTs.

Irradiation-Induced Amorphous-to-Crystalline Phase Transformations in Ceramic Materials

Amorphous ceramics are a unique class of materials with unusual properties and functionalities. While these materials are known to crystallize when subjected to thermal annealing, they have sometimes been observed to crystallize athermally when exposed to extreme irradiation environments. Because irradiation is almost universally understood to introduce disorder into materials, these observations of irradiation-induced ordering or crystallization are unusual and may partially explain the limited research into this phenomenon. However, the archival literature presents a growing body of evidence of these irradiation-induced amorphous-to-crystalline (a-to-c) phase transformations in ceramics. In this perspective, the summary and review of examples from the literature of irradiation-induced a-to-c transformations for various classifications of ceramics are provided. This work will highlight irradiation conditions and material parameters that appear most influential for activating a-to-c transformations, identify trends, examine possible mechanisms, and discuss the impact of a-to-c transformations on material properties. Finally, future research directions that will enable researchers to harness a-to-c transformations to tailor materials behaviors will be provided.

Superior Energy-Storage Properties in Bi0.5Na0.5TiO3-Based Lead-Free Ceramics via Simultaneously Manipulating Multiscale Structure and Field-Induced Structure Transition.

Pratical applications have put forward great challenges to the comprehensive energy-storage performance of ceramic material. Here, a novel route of simultaneously manipulating multiscale structure and the field-induced structural transformation in (Bi0.5Na0.5)TiO3-based ceramics is proposed to address the above concern. The multiscale structure of 0.88(Bi0.5Na0.5)TiO3-0.12BaTiO3 solid solutions such as grain and domain size, band gap, and phase structure can be adjusted by adding antiferroelectric NaNbO3. Simultaneously, a field-induced P4bm relaxor antiferroelectric to P4mm ferroelectric phase transformation can be obtained by constructing a P4mm-P4bm phase boundary, which is expected to require a lower energy barrier compared with the field-induced P4bm relaxor antiferroelectric to R3c ferroelectric transformation in other (Bi0.5Na0.5)TiO3-based ceramics. The optimized field-induced structural transformation behavior and the formation of nanodomains enables a minimized polarization hysteresis but an enhanced maximum polarization. Moreover, the decreased grain size together with increased band gap leads to a significantly improved breakdown strength. Accordingly, a giant energy density Wrec ∼ 8.0 J/cm3, a high efficiency η ∼ 86%, a short discharging time t0.9 ∼ 41 ns, and a good temperature stability (Wrec = 1.32 ± 0.12 J/cm3, η = 88.5% ± 2.5% @ 25-200 °C) are simultaneously obtained in 0.63(Bi0.5Na0.5)TiO3-0.12BaTiO3-0.25NaNbO3 relaxor antiferroelectric ceramics, demonstrating large potentials for the ceramic capacitor applications.

Enhanced bioactivity and low temperature degradation resistance of yttria stabilized zirconia/clay composites for dental applications

Yttria stabilized zirconia (YSZ)/clay composites were produced to improve osseointegration and undesired tetragonal-to-monoclinic phase transformation (low temperature degradation, LTD) of YSZ ceramics so that long-term clinical success of YSZ implants is achieved. Various amounts (0.5,1,2, and 4 wt%) of clay was incorporated to YSZ. Predetermined amounts of clay and YSZ were mixed and pressed uniaxially at 15 MPa into compacts that were subsequently pressureless sintered at 1450 °C. Density, compressive strength, hardness and indentation crack resistance of 4 wt% clay incorporated YSZ/clay composite were 5.77 ± 0.01 g/cm3, 1188 ± 121 MPa, 1223 ± 9 HV, and 4.4 ± 0.1 MPa√m, respectively. Additionally, biological properties of YSZ/clay composites were assessed in vitro using bone cells. Incorporation of 4 wt% clay significantly enhanced bone cell proliferation, spreading, and functions. Moreover, a significant increase in the LTD resistance of YSZ was achieved upon 4 wt% clay incorporation. The findings collectively suggest that YSZ/clay composites have a potential to be used as an alternative material for dental applications.

Engineering of silicone-based blends for the masked stereolithography of biosilicate/carbon composite scaffolds

Silicone resins, filled with phosphates and other oxide fillers, have been recently proposed as feedstock for the manufacturing of scaffolds with a composition resembling that of commercial Biosilicate® glass-ceramics. Silicones and engineered fillers enable the preparation of novel carbon-containing Biosilicate-based composites and, fundamentally, the easy application of additive manufacturing technologies. After successful demonstration of the applicability of direct ink writing of silicone-based pastes, the present paper is dedicated to preparation of highly porous scaffolds obtained by masked stereolithography, starting from a simple blend of silicone resin with commercial photocurable acrylates. Deviations in the desired phase assemblage were corrected by calibration of the silicone/fillers ratio. The more advanced printing technology, combined with ceramic transformation, allowed fabrication of scaffolds with a complex geometry and a distinctive control of overall porosity.

FLUENCE OF PHASE FORMATION PROCESSES IN LITHIUM ZIRCONATECERAMICS ON STRENGTHAND THERMAL PROPERTIES

The article is devoted to the study of the properties of lithium zirconate ceramics obtained by solid-phase synthesis. The choice of lithium zirconateceramics as objects of study is due to the great prospects for their use as materials for tritium propagation. Results of a study of the influence of the LiO/ZrO2/Li2ZrO3→ LiO/Li2ZrO3 → Li2ZrO3type phase transformations in ceramics, depending on the annealing temperature, on the strength and thermophysical parameters of ceramics are obtained. During the studies, it was found that the change in hardness and crack resistance are directly dependent on the phase composition and concentration of impurity phases in the composition of ceramics. It has been determined that the displacement of lithium oxideand zirconium dioxide impurity phases leads to an increase in hardness and an increase in resistance to cracking under single compression. It has been established that at annealing temperatures above 900°C, the change in strength and thermophysical parameters is minimal. At the same time, a change in the phase composition of the LiO/ZrO2/Li2ZrO3→ Li2ZrO3type ceramics leads to an increase in the thermal conductivity coefficient by (15-20)%

Understanding spatial networking and industrial district evolution from firms’ strategies

ABSTRACT Positioned in the study of firm heterogeneity in industrial districts (IDs), this study analyses how mergers and acquisitions (M&A) differ between local and non-local acquirers, impacting district evolution. Focusing on the Castellon ceramic tile district transformation, from acquisitions over 2012–2022, M&A and their implication for the local district are discussed, cross-fertilizing strategy and IDs literatures. Findings, from using mixed-methods, reveal that in IDs, the M&A process remarkably differs between local and non-local firms. While local firms tend to specialize in the related focal business, targeting local acquisitions to achieve internal synergies from a better valuation and integration of acquisitions, foreign firms seek access to tacit knowledge through relational and network synergies through diversification. Effects on the territory from M&A are also discussed.

Grains refinement mechanism of (Ti,Ta)3SiC2/Al2O3 composite ceramics

(Ti,Ta)3SiC2/Al2O3 composite ceramics were prepared by hot-pressing sintering using TaC as Ta source. X-ray diffraction analysis showed that the maximum of solid solubility of Ta in Ti3SiC2 were determined to be from 7.5 to 10 at%. With the increase of TaC contents, the grain size of Ti3SiC2 reduced obviously. Combined Wulff theorem and first-principle calculations, the probable mechanism of this refinement phenomenon was revealed. When Ta atoms substitute Ti in surface atomic layers, the surface energy of (001) plane increased significantly compared to those of (100) plane, which restricted the growth of (001) facets. As it is the largest exposed surface, the lower growth rate of (001) facets lead to the grains refinement. The results will provide theoretical guidance for surface modification and morphological transformation of Ti3SiC2-based ceramics.

Effects of Y 2 O 3 /MgO ratio on mechanical properties and thermal conductivity of silicon nitride ceramics

In this work, the effects of Y2O3/MgO ratio on the densification behavior, phase transformation, microstructure evolution, mechanical properties, and thermal conductivity of Si3N4 ceramics were investigated. Densified samples with bimodal microstructure could be obtained by adjusting the ratio of Y2O3/MgO. It was found that a low Y2O3/MgO ratio facilitated the densification of Si3N4 ceramics while a high Y2O3/MgO ratio benefited the phase transformation of Si3N4 ceramics. Best mechanical properties (flexural strength of 875 MPa, and fracture toughness of 8.25 MPa·m1/2, respectively) and optimal thermal conductivity of 98.04W/(m·K) were achieved in the sample fabricated with Y2O3/MgO ratio of 3:4 by sintering at 1900°C for 4 h.

Effects of holding time on structure and the properties of spodumene/mullite composite ceramics

AbstractIn this paper, spodumene/mullite ceramics with good thermal shock resistance were prepared from spodumene, quartz, talc, and clay when the sintering temperature was 1270℃. In the sintering process, the effect of holding time on densification, mechanical properties, phase transformation, microstructure, and thermal shock resistance of the composite ceramics were investigated. The phase transition and microstructures of the ceramics were identified via X‐ray diffraction (XRD) and scanning electron microscopy (SEM). The interaction between holding time and bulk density was studied by response surface methodology. The result show that an appropriate holding time can improve the mechanical properties of spodumene/mullite ceramics. When the holding time was kept 90 min, the spodumene/mullite ceramics with the apparent porosity was .47%, the bulk density was 2.28 g/cm3, and bending strength was 63.46 MPa. Furthermore, since no cracks formed after 20 thermal shock cycles for the composite ceramics with a bending strength decreasing rate of 12.66%, it is revealed that spodumene/mullite ceramics exhibit good thermal shock resistance. Therefore, this study can provide beneficial guidance for both industrial production and energy conservation.

Enhanced thermal and anti‐ablation properties of high‐temperature resistant reactive POSS modified boron phenolic resin

AbstractTo further improve the anti‐ablation property of boron phenolic resin (BPR), high‐temperature resistant reactive trisilanolheptaphenyl POSS (3OH‐POSS) was synthesized to modify BPR. The thermal stability of BPR was significantly improved. The initial decomposition temperature of the prepared 3OH‐POSS modified BPR (POSSBPR) was increased from 226.0 to 390.2°C and the chars at 800 and 1000°C was increased from 71.1 and 66.7% to 75.1 and 73.7%, respectively with 20% 3OH‐POSS addition. The prepared POSSBPR castings obtained linear ablation rate (LAR) and mass ablation rate (MAR) were as low as −0.122 mm/s and 0.0465 g/s. And the LAR and MAR of high silica fiber reinforced composites (HSC/POSSBPR) were 0.123 mm/s and 0.0602 g/s, respectively. Moreover, the mechanism of high‐temperature carbon microcrystalline and ceramic structure transformation, and ablation performance enhancement of POSSBPR were determined by X‐ray diffraction, X‐ray photoelectron spectroscopy, and Raman spectroscopy. Results indicated that the introduction of 3OH‐POSS promotes the formation of ordered graphite structure of BPR and forms high‐temperature species, such as SiC ceramic, on the ablated surface, which subsequently improves the ablation resistance of the material.

Study of the mechanisms of the t-ZrO2 → c-ZrO2 type polymorphic transformations in ceramics as a result of irradiation with heavy Xe22+ ions

In this work, we present the results of a study of the t-ZrO2 → c-ZrO2 type polymorphic transformations in ZrO2 ceramics resulting from irradiation with heavy ions with different energies and fluences. The relevance of this work lies in obtaining new data on the radiation resistance of oxide ceramics to irradiation, as well as the effect of defect formation processes on the change in structural and strength properties. During the studies carried out, it was found that an increase in the energy of incident ions leads to an acceleration of the polymorphic transformation processes, and in the case of an ion energy of 230 MeV, the complete polymorphic transformation occurs at an irradiation dose of 5 × 1013 ion/cm2. It was found that polymorphic transformations caused by irradiation lead to crystal lattice swelling and deformation. At the same time, depending on the degree of polymorphic transformations, the crystal structure deformation rate changes. An analysis of the strength properties showed that the formation of a more stable cubic phase at high radiation doses slows down the processes of hardness and swelling reduction. The dependences obtained indicate that in the case of incident ion energies of more than 200 MeV, the formed cubic c-ZrO2 phase leads to an increase in resistance to radiation damage and a slowdown in degradation processes.

Phase transformation and grain-boundary segregation in Al-Doped Li7La3Zr2O12 ceramics

Cubic phase garnet-type Li7La3Zr2O12 (LLZO) is a promising solid electrolyte for highly safe Li-ion batteries. Al-doped LLZO (Al-LLZO) has been widely studied due to the low cost of Al2O3. The reported ionic conductivities were variable due to the complicated Al3+-Li+ substitution and LixAlOy segregation in Al-LLZO ceramics. This work prepared Li7−3xAlxLa3Zr2O12 (x = 0.00~0.40) ceramics via a conventional solid-state reaction method. The AC impedance and corresponding distribution of relaxation times (DRT) were analyzed combined with phase transformation, cross-sectional microstructure evolution, and grain boundary element mapping results for these Al-LLZO ceramics to understand the various ionic transportation levels in LLZO with different Al-doping amounts. The low conductivity in low Al-doped (0.12~0.28) LLZO originates from the slow Li+ ion migration (1.4~0.25 μs) in the cubic-tetragonal mixed phase. On the other hand, LiAlO2 and LaAlO3 segregation occur at the grain boundaries of high Al-doped (0.40) LLZO, resulting in a gradual Li+ ion jump (6.5 μs) over grain boundaries and low ionic conductivity. The Li6.04Al0.32La3Zr2O12 ceramic delivers the optimum Li+ ion conductivity of 1.7 × 10−4 S cm−1 at 25 °C.