Predicting the Degradability of Bioceramics through a DFT-based Descriptor

Bioceramics have attracted extensive attention for bone defect repair due to their excellent bioactivity and degradability.However,challenges remain in matching the rate between bioceramic degradation and new bone formation,necessitating a deeper understanding of their degradation properties.In this study,density functional theory(DFT)calculations was employed to explore the structural and electronic characteristics of silicate bioceramics.These findings reveal a linear correlation between the maximum isosurface value of the valence band maximum(VBM_(Fmax))and the degradability of silicate bioceramics.This correlation was subsequently validated through degradation experiments.Furthermore,the investigation on phosphate bioceramics demonstrates the potential of this descriptor in predicting the degradability of a broader range of bioceramics.This discovery offers valuable insights into the degradation mechanism of bioceramics and holds promise for accelerating the design and development of bioceramics with controllable degradation.

Preparation and Photostriction Properties of BiFeO_(3)-BaTiO_(3)Ceramics

Under illumination by 405,520 and 655 nm monochromatic visible light(light intensity of 30 kW/m^(2)),large photostriction(ΔL/L)of 0.19%,0.13%and 0.26%for 67BiFeO_(3)-33BaTiO_(3)(67BF-33BT)lead-free ferroelectric ceramics are obtained,respectively.By studying the ferroelectric and photoelectric properties in conjunction with in situ Raman spectroscopy,it is found that the photostrictive effect of 67BF-33BT is not caused by the electrical strain induced by abnormal photovoltaic voltage,but related to the optical induced oxygen octahedral distortion.The 67BF-33BT lead-free ferroelectric material with excellent photostrictive response in the visible light region is expected to play an important role in the field of optical drive electromechanical devices.

Oxidation behavior of amorphous and nanocrystalline SiBCN ceramics–Kinetic consideration and microstructure

In this study,the structural evolution of SiBCN ceramics during crystallization and its effects on oxidation behavior involving different atomic units or formed phases in amorphous or crystalline SiBCN ceramics were analyzed.The amorphous structure has exceptionally high oxidation activity but presents much better oxidation resistance due to its synchronous oxidation of atomic units and homogeneous composition in the generated oxide layer.However,the oxidation resistance of SiBCN ceramic will degrade during the continual crystallization process,especially for the formation of the nanocapsule-like structure,due to heterogeneous oxidation caused by the phase separation.Besides,the activation energy and rate-controlling mechanism of the atomic units and phases in SiBCN ceramics were obtained.The BNCx(Ea=145 kJ/mol)and SiC(2-x)(Ea=364 kJ/mol)atomic units in amorphous SiBCN structure can be oxidized at relatively lower temperatures with much lower activation energy than the corresponding BN(C)(Ea=209 kJ/mol)and SiC(Ea=533 kJ/mol)phases in crystalline structure,and the synchronous oxidation of the SiC(2-x)and BNCx units above 750C changes the oxidation activation energy of BNCx(Ea=332 kJ/mol)to that similar to SiC(2-x).The heterogeneous oxide layer formed from the nanocapsule-like structure will decrease the activation energy SiC(Ea=445 kJ/mol)and t-BN(Ea=198 kJ/mol).

Moderate Fields, Maximum Potential: Achieving High Records with Temperature‑Stable Energy Storage in Lead‑Free BNT‑Based Ceramics

The increasing awareness of environmental concerns has prompted a surge in the exploration of leadfree,high-power ceramic capacitors.Ongoing efforts to develop leadfree dielectric ceramics with exceptional energystorage performance(ESP)have predominantly relied on multicomponent composite strategies,often accomplished under ultrahigh electric fields.However,this approach poses challenges in insulation and system downsizing due to the necessary working voltage under such conditions.Despite extensive study,bulk ceramics of(Bi_(0.5)Na_(0.5))TiO_(3)(BNT),a prominent lead-free dielectric ceramic family,have seldom achieved a recoverable energy-storage(ES)density(Wrec)exceeding 7 J cm^(−3).This study introduces a novel approach to attain ceramic capacitors with high ESP under moderate electric fields by regulating permittivity based on a linear dielectric model,enhancing insulation quality,and engineering domain structures through chemical formula optimization.The incorporation of SrTiO_(3)(ST)into the BNT matrix is revealed to reduce the dielectric constant,while the addition of Bi(Mg_(2/3)Nb_(1/3))O_(3)(BMN)aids in maintaining polarization.Additionally,the study elucidates the methodology to achieve high ESP at moderate electric fields ranging from 300 to 500 kV cm^(−1).In our optimized composition,0.5(Bi_(0.5)Na_(0.4)K_(0.1))TiO_(3)–0.5(2/3ST-1/3BMN)(B-0.5SB)ceramics,we achieved a Wrec of 7.19 J cm^(−3) with an efficiency of 93.8%at 460 kV cm^(−1).Impressively,the B-0.5SB ceramics exhibit remarkable thermal stability between 30 and 140℃ under 365 kV cm^(−1),maintaining a Wrec exceeding 5 J cm^(−3).This study not only establishes the B-0.5SB ceramics as promising candidates for ES materials but also demonstrates the feasibility of optimizing ESP by modifying the dielectric constant under specific electric field conditions.Simultaneously,it provides valuable insights for the future design of ceramic capacitors with high ESP under constraints of limited electric field.

Microstructure and Oxidation Behavior of ZrB_(2)-SiC Ceramics Fabricated by Tape Casting and Reactive Melt Infiltration

ZrB_(2)-based ceramics typically necessitate high temperature and pressure for sintering,whereas ZrB_(2)-SiC ceramics can be fabricated at 1500℃using the process of reactive melt infiltration with Si.In comparison to the conventional preparation method,reactive synthesis allows for the more facile production of ultra-high temperature ceramics with fine particle size and homogeneous composition.In this work,ZrSi_(2),B4C,and C were used as raw materials to prepare ZrB_(2)-SiC via combination of tape casting and reactive melt infiltration herein referred to as ZBC ceramics.Control sample of ZrB_(2)-SiC was also prepared using ZrB_(2) and SiC as raw materials through an identical process designated as ZS ceramics.Microscopic analysis of both ceramic groups revealed smaller and more uniformly distributed particles of the ZrB_(2) phase in ZBC ceramics compared to the larger particles in ZS ceramics.Both sets of ceramics underwent cyclic oxidation testing in the air at 1600℃for a cumulative duration of 5 cycles,each cycle lasting 2 h.Analysis of the oxidation behavior showed that both ZBC ceramics and ZS ceramics developed a glassy SiO_(2)-ZrO_(2) oxide layer on their surfaces during the oxidation.This layer severed as a barrier against oxygen.In ZBC ceramics,ZrO_(2) is finely distributed in SiO_(2),whereas in ZS ceramics,larger ZrO_(2) particles coexist with glassy SiO_(2).The surface oxide layer of ZBC ceramics maintains a dense structure because the well-dispersed ZrO_(2) increases the viscosity of glassy SiO_(2),preventing its crystallization during the cooling.Conversely,some SiO_(2) in the oxide layer of ZS ceramics may crystallize and form a eutectic with ZrO_(2),leading to the formation of ZrSiO_(4).This leads to cracking of the oxide layer due to differences in thermal expansion coefficients,weakening its barrier effect.An analysis of the oxidation resistance shows that ZBC ceramics exhibit less increase in oxide layer thickness and mass compared to ZS ceramics,suggesting superior oxidation resistance of ZBC ceramics.

Pore Control and Mechanical Properties of Alumina Ceramics Using Direct Ink Writing

Ceramics with proper pore sizes and geometry are critical to many applications,so that lots of efforts have been made to achieve the goal.Direct ink writing(DIW),an additive manufacturing technique,is cost-effective and accessible.It is interesting to study the ability to control the pore size and geometry by the DIW technique.In this study,alumina ceramics were prepared with special focus on the pore configuration and the performance of printed samples was tested.The porous structures with different pore sizes(minimum pore size of 200μm)and different shapes(honeycomb,lattice and triangle)were printed.The printed structures shrunk uniformly and maintained the original geometry after firing,they did not show any visible defects or deformations,and the microstructure was uniform and dense.It was found the honeycomb structures exhibited superior mechanical strength at the same porosity compared to lattice and triangle structures,which reached 55 MPa with a porosity of 70%.The high strength with the high porosity was attributed to the highly controlled microstructure,i.e.,uniform pore sizes,pore shapes and interconnectivity.

Preparation and characterization of porous ceramics prepared by kaolinite gangue and Al(OH)_3 with double addition of MgCO_3 and CaCO_3

Porous ceramics were prepared from kaolinite gangue and Al（OH）3 with double addition of MgCO3 and CaCO3 by the pore-forming in-situ technique.The characterizations of porous ceramics were investigated by X-ray diffractometry,scanning electron microscopy,and mercury porosimetry measurements,etc.It is found that although the decomposition of MgCO3 and CaCO3 has little contribution to the porosity,the double addition of MgCO3 and CaCO3 strongly affects the formation of liquid phase,and then changes the phase compositions,pore characterization,and strength.The appropriate mode is the sample containing 1.17wt% MgCO3 and 1.17wt% CaCO3,which has high apparent porosity（41.0%）,high crushing strength（53.5 MPa）,high mullite content（76wt%）,and small average pore size（3.24 μm）.

Fabrication of Transparent Polycrystalline Yttria Ceramics by Combination of SPS and HIP

Transparent polyerystalline yttria is a promising optical ceramics with excellent physical and chemical properties. A commercial yttria powder with a mean particle size of 1.0μm and narrow size distribution was selected as the starting material. Transparent polyerystalline yttria ceramics without any additives were successfully prepared by hot isostatic pressing (HIP) at 1700℃for 2 h under the pressure of 200 MPa in Ar following spark plasma sintering (SPS). The as-prepared specimens consist of uniform grains of ~ 40μm. Scanning electron microscopy (SEM) images show their pore-free structure. The influences of the yttria powder and sintering process on the properties of the yttria ceramics, including the microstructure and optical properties, were further investigated in our study.

Mechanical properties and plasma erosion resistance of BN_p/Al_2O_3-SiO_2 composite ceramics

BNp/Al2O3-SiO2 system ceramic matrix composites with different volume fractions （10%-60%） of hexagonal BN particulates （BNp） were prepared by hot-press sintering technique. Phase components, microstructure, mechanical properties and plasma erosion resistance were also investigated. With the increase of h-BNp content, relative density and Vickers＇ hardness of the composite ceramics decrease, while the flexural strength, elastic modulus and fracture toughness increase and then decrease. The plasma erosion resistance linearly deteriorated with the increase of BNp content which is mainly determined by the density, crystal structure and atomic number of the elements.

Automatic Damage Detection of Engineering Ceramics Ground Surface Based on Texture Analysis

Ground textures seriously interfere with the exact identification of grinding damage. The common nondestructive testing techniques for engineering ceramics are limited by their difficulty and cost. Therefore, this paper proposes a global image reconstruction scheme in ground texture surface using Fourier transform (FT). The lines associated with high-energy frequency components in the spectrum that represent ground texture information can be detected by Hough transform (HT), and the corresponding high-energy frequency components are set to zero. Then the spectrum image is back-transformed into the spatial domain image with inverse Fourier transform (IFT). In the reconstructed image, the main ground texture information has been removed, whereas the surface defects information is preserved. Finally, Canny edge detection is used to extract damage image in the reconstructed image. The experimental results of damage detection for the ground texture surfaces of engineering ceramics have shown that the proposed method is effective.

DIELECTRIC PROPERTIES OF ZNTIO_3 MICROWAVE CERAMICS CONSOLIDATED WITH MGTIO_3

Stabilized ZnTiO4 was prepared by doping magnesium oxide through traditional solid state reaction. The experimental results indicate that zinc titanate crystals doped with magnesium oxide grow well and the decomposition into Zn2TiO4 and TiO2 is restrained through traditional solid state reaction, By adjusting molar ratio of MgO, better properties can be obtained The dielectric properties of the ceramics doped with 30% MgO（ molar percentage） sintered at 1060℃ are as follows：the value of quality factor is greater than 20000（6.5 GHz ）, the temperature coefficient of resonance frequency is about 2 ± 10^-6 /℃,the dielectric constant ranges from 180 to 22.Besides,it is proved that heat treatment can optimize microstructure and the value of quality factor, which increases from 23833.93 to 47584.00 after 2h of heat treatment at 1040℃.

Preparation and Upconversion Luminescence of Y_3Al_5O_(12):Yb^(3+),Er^(3+)Transparent Ceramics

YAG： 1% （atom fraction） Yb^3＋ , 0.5% （atom fraction） Er3＋ transparent ceramics were fabricated by the solid state reaction method using high-purity Y2O3, Al2O3, Yb2O3, and Er2O3 powders as starting materials. The mixed powder compact was sintered at 1760 ℃ for 6 h in vacuum and annealed at 1500 ℃ for 10 h in an air atmosphere. The ceramics consisted of about 10μm grains and exhibited a pore-free structure. The optical transmittance of the ceramics at 1064 nm was nearly 80%. Upconversion emissions were investigated on the ceramics pumped by a 980 nm continuous wave diode laser, and strong green emission centered at 523 and 559 nm and red emission centered at 669 nm were observed, which originated from the radiative transitions of ^2H11/2→^4I15/2, ^4S3/2→^4I15/2, and ^4F9/2→^4I15/2 of Er^3＋ ions, respectively.

Effect of small changes in sintering temperature on varistor properties and degradation behavior of V-Mn-Nb-Gd co-doped zinc oxide ceramics

The effect of small changes in sintering temperature on microstructure, electrical properties, dielectric characteristics, and degradation behavior of V-Mn-Nb-Gd co-doped zinc oxide ceramics was investigated. With the increase of sintering temperature, the densities of the sintered pellets decreased from 5.54 to 5.42 g/cm3 and the average grain size increased from 4.1 to 11.7 μm. The breakdown field(E1 m A) decreased noticeably from 7138 to 920 V/cm with the increase of sintering temperature. The varistor ceramics sintered at 900 ℃ exhibited excellent nonohmic properties, which were 66 for the nonohmic coefficient and 77 μA/cm2 for the leakage current density. Concerning stability, the varistors sintered at 900 ℃ exhibited the strongest accelerated degradation characteristics, with ΔE1 mA =-9.2% for DC accelerated degradation stress of 0.85 E1 m A at 85 °C for 24 h.

Preparation of Porous Silica Ceramics with Low Dielectric Constant

Porous silica ceramics has been prepared with the starch consolidation casting method. Slurries with various fractions of starch added in were prepared by ball-milling. The evaluation of the microstructures was done through two techniques： Hg porosimetry and SEM investigation. The bending strength of the sintered samples varied within the range of 10 MPa-20 MPa and the low dielectric constant within the range of 2.0-2.4 correspondent with the porosity of 42%-56%. The ceramics holds a brilliant promise of being a kind of core material used in sandwich-like electromagnetic windows.

Effect of Y_2O_3, CeO_2 on Sintering Properties of Si_3N_4 Ceramics

The effect of rare earth oxides Y 2O 3 or CeO 2 on sintering properties of Si 3N 4 ceramics was studied and the mechanism of assisting action during sintering was analyzed. The results indicate that the best sintering properties appear in Si 3N 4 ceramics with 5% Y 2O 3 or 8% CeO 2. Secondary crystallites are formed at grain boundaries after heat treatment, which decreases the amount of glass phase and contributes to the improvement of high temperature mechanical properties of silicon nitride.

Sintering Behavior and Microwave Dielectric Properties of BBSZL Glass-doped ZnTiO_3 Ceramics for LTCC Applications

A novel low temperature co-fired ceramic(LTCC) material was fabricated by zinc titanate(ZnTiO_3) ceramics doped with B_2O_3-BaO-SiO_2-ZnO-Li_2O(BBSZL) glass. The influences of BBSZL glass on wetting behavior, sintering activation energy, phase composition, microstructure and microwave dielectric properties were investigated. The experimental results show that the sintering temperature of ZnTiO3 ceramics can be reduced from 1 100 to 925 ℃, meanwhile the sintering activation energy is decreased from 465.32 to 390.54 kJ·mol^(-1) by BBSZL glass aid, respectively. Moreover, BBSZL glass can inhibit the high Q×f ZnTiO_3 phase decompose into the low Q×f value Zn_2TiO_4 phase, which is propitious to obtain high Q×f value LTCC material. The ZnTiO_3-BBSZL composite sintered at 925℃ displays the excellent microwave dielectric properties with ε_r of 21.8, Q×f value of 42000 GHz, and τ_f of-75 ppm·℃^(-1).

Sintering,crystallization and dielectric properties of CaO-B_2O_3-SiO_2 system glass ceramics

CaO-B203-SiO2 （CBS） glass powders are prepared by conventional glass melting method at different melting temperatures whose properties and microstructures are characterized by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. It is found that there are SiO2 and some unknown phases in CBS glass melting liquid from 1 300 ℃ to 1 500 ℃ and the amount of these phases decreases with the increase of the melting temperature. The CBS glass melted at 1 450 ℃ could be sintered from 830 ℃ to 930 ℃ and the bulk densities of the samples are all higher than 2.4 g/cm^3. From the points of the properties and energy conservation, the melting temperature of 1 450 ℃ is the optimal melting temperature. The glass ceramic sintered at 850 ℃ exhibits better dielectric properties： er=6.33, tan6=2.2×10^-3 at 10 GHz, and the major phases of the samples are CaSiO3, CaB2O4 and SiO2.

Sea Urchin Spines as a Model-System for Permeable,Light-Weight Ceramics with Graceful Failure Behavior.Part Ⅱ.Mechanical Behavior of Sea Urchin Spine Inspired Porous Aluminum Oxide Ceramics under Compression

Sea urchin spines were chosen as a model system for biomimetic ceramics obtained using starch-blended slip casting. Porous alumina ceramics with cap-shaped layers with different alternating porosities were found to have superior fracture behavior under bulk compression compared to ceramics with uniform porosity.They fail in a cascading manner,absorbing high amounts of energy during extended compression paths.The porosity variation in an otherwise single phase material mimicks the architectural microstructure design of sea urchin spines of Heterocentrotus mammillatus,which are promising model materials for impact protection.

Ferroelectric behaviour of 30nm BaTiO3 ceramics prepared by high pressure assisted sintering

Dense nanocrystalline BaTiO3 ceramics with a homogeneous grain size of 30 nm was obtained by pressure assisted sintering. The ferroelectric behaviour of the ceramics was characterized by the dielectric peak at around 120 ℃, the P-E hysteresis loop and some ferroelectric domains. These experimental results indicate that the critical grain size for the disappearance of ferroelectricity in nanocrystalline BaTiO3 ceramics fabricated by pressure assisted sintering is below 30 nm. The ferroelectric property decreasing with decreasing grain size can be explained by the lowered tetragonality and the ＇dilution＇ effect of grain boundaries.

Synthesis of glass ceramics from kaolin and dolomite mixture

Cordierite- and anorthite-based binary glass ceramics of the CaO-MgO-Al2O3-SiO2 （CMAS） system were synthesized by mixing local and abundant raw minerals （kaolin and doloma by mass ratio of 82/18）. A kinetics study reveals that the activation energy of crystalli- zation （Ea） calculated by the methods of Kissinger and Marotta are 438 kJ·mol^-1 and 459 kJ·mol^-1, respectively. The Avrami parameter （n） is estimated to be approximately equal to 1, corresponding to the surface crystallization mechanism. X-ray diffraction （XRD） analysis shows that the anorthite and cordierite crystals are precipitated from the parent glass as major phases. Anorthite crystals first form at 850℃, whereas the μ-cordierite phase appears after heat treatment at 950℃. Thereafter, the cordierite allotropically transforms to α-cordierite at 1000℃. Complete densification is achieved at 950℃; however, the density slightly decreases at higher temperatures, reaching a stable value of 2.63 kg·m^-3 between 1000℃ and 1100℃, The highest Vickers hardness of 6 GPa is also obtained at 950℃. However, a substantial decrease in hardness is recorded at 1000℃; at higher sintering temperatures, it slightly increases with increasing temperature as the ct-cordierite crystallizes.