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.

Low-firing and temperature stability regulation of tri-rutile MgTa_(2)O_(6)microwave dielectric ceramics

A glass frit containing Li_(2)O-MgO-ZnO-B_(2)O_(3)-SiO_(2)component was used to explore the low-temperature sintering behaviors and microwave dielectric characteristics of tri-rutile MgTa_(2)O_(6)ceramics in this study.The good low-firing effects are presented due to the high matching relevance between Li_(2)O-MgO-ZnO-B_(2)O_(3)-SiO_(2)glass and MgTa_(2)O_(6)ceramics.The pure tri-rutile MgTa_(2)O_(6)structure remains unchanged,and high sintering compactness can also be achieved at 1150℃.We found that the Li_(2)O-MgO-ZnO-B_(2)O_(3)-SiO_(2)glass not only greatly improves the low-temperature sintering characteristics of MgTa_(2)O_(6)ceramics but also maintains a high(quality factor(Q)×resonance frequency(f))value while still improving the temperature stability.Typically,great microwave dielectric characteristics when added with 2wt%Li_(2)O-MgO-ZnO-B_(2)O_(3)-SiO_(2)glass can be achieved at 1150℃:dielectric constant,ε_(r)=26.1;Q×f=34267 GHz;temperature coefficient of resonance frequency,τ_(f)=-8.7×10^(-6)/℃.

纳米MnO_(2)炭基复合材料的制备及吸附去除水中La(Ⅲ)离子性能研究

稀土是一种珍贵的战略资源,但其开发冶炼过程会产生大量废水并造成严重的环境污染,因此如何高效吸附去除废水中稀土离子被大量研究。通过共沉淀法将纳米MnO_(2)负载至生物炭(Biochar, BC)表面,得到纳米MnO_(2)炭基复合材料(Nano-MnO_(2)Carbon Matrix Composites, MBC),并用于吸附去除废水中的La(Ⅲ)离子。研究通过表征分析材料的物理和化学结构变化,考察了应用环境条件对MBC吸附La(Ⅲ)离子性能的影响,在308 K、pH=6.0条件下,0.55 g/L MBC对20 mg/L La(Ⅲ)离子模拟废水进行吸附处理,24 h后吸附效率达到95.65%。吸附动力学、等温线和热力学研究显示,MBC对La(Ⅲ)离子的吸附过程符合拟一级动力学模型和Langmuir模型,为单分子层吸附,最大吸附质量比可达43.49 mg/g;通过D-R模型计算的Es为23.12 kJ/mol,表明吸附过程偏向于化学吸附,且是自发的吸热过程。MBC经5次循环后,吸附性能仍达到初始吸附质量比的79.18%,MBC作为炭基吸附剂用于吸附水中的La(Ⅲ)离子,展现出一定的应用前景。

喷涂法负载TiO_(2)/MnO_(2)陶瓷膜催化臭氧氧化降解染料废水

染料废水存在排放量大、色度高、COD大、可生化性差、难降解等特点,其处理存在低效高耗的问题.本研究首先通过水热法制备了TiO_(2)/MnO_(2)催化剂,对催化剂进行了XRD、XPS、SEM/EDS表征,以罗丹明B(RhB)溶液为模拟染料废水,进行了催化臭氧氧化降解RhB的性能对比研究.再通过喷涂成膜技术将TiO_(2)/MnO_(2)催化剂负载于平板式陶瓷膜表面,研制成反应性陶瓷膜(TiO_(2)/MnO_(2)-CM),自制了配套膜反应器,研究了TiO_(2)/MnO_(2)-CM水处理系统对RhB降解去除效果和水通量变化规律.结果表明,本工作成功合成了棒状和不规整球状结合的TiO_(2)/MnO_(2)催化剂,XPS结果表明存在Mn^(4+)活性中心,促进了催化臭氧活化能力.喷涂TiO_(2)/MnO_(2)催化剂后,陶瓷膜的纯水通量略有下降,12层为适宜的喷涂层数,采用TiO_(2)/MnO_(2)-CM对2 L初始浓度为20 mg·L^(−1)的RhB在臭氧浓度为2.5 g·m^(−3)条件下,反应40 min去除率可达100%,去除效率远高于空白膜,陶瓷膜负载TiO_(2)/MnO_(2)有助于提高O_(3)溶解性、加速生成·OH.本工作可为染料废水等难降解有机废水的高效低耗处理,提供新技术思路.

MnO_(2)纳米片与带正电荷的AIE分子荧光检测GSH以及IMP门的构建

谷胱甘肽(glutathione,GSH)是由谷氨酸、半胱氨酸和甘氨酸结合而成的含有巯基的三肽,广泛存在于各种生物当中,对生物体内有着重要的作用。因此,能方便、快速、准确的检测GSH在体内的水平十分有必要。MnO_(2)纳米片是一种带负电的、具有氧化性的过渡金属氧化物。将带有负电荷的MnO_(2)纳米片与带有正电荷的两个季铵盐基团的二苯乙烯基蒽衍生物DSAI结合,制备成DSAI/MnO_(2)复合探针。将DSAI/MnO_(2)复合探针加入GSH后,MnO_(2)纳米片被解,DSAI的荧光得到恢复。基于以上现象可定量GSH,并且构建出以MnO_(2)纳米片和GSH为输入的分子逻辑门。

锰浸出液制备棒状β-MnO_(2)纳米材料

湿法浸出锰矿或锰渣中的锰得到的硫酸锰浸出液中含有钙、镁杂质离子,对后续锰产品的纯度造成很大影响。为深度除硫酸锰浸出液中的Ca^(2+)、Mg^(2+),并最大化利用锰浸出液,可以将净化后的锰浸出液制备成高附加值的MnO_(2)纳米材料。以含钙、镁的硫酸锰浸出液为研究对象,将锰浸出液除钙、镁后,以(NH_(4))_(2)S_(2)O_(8)为氧化剂,采用水热法将净化后的锰浸出液制备成高附加值的MnO_(2)纳米材料,探究溶液的pH、反应温度、反应时间对制备MnO_(2)纳米棒物相和形貌的影响。结果表明:当反应温度为150℃、反应时间为10 h、加入氧化剂用量为理论量、反应pH为1~7的条件下制备出的β-MnO_(2)结晶度最好。

Improved microwave dielectric properties of MgAl_(2)O_(4)spinel ceramics through(Li_(1/3)Ti_(2/3))^(3+)doping

A series of nominal compositions MgAl_(2-x)(Li_(1/3)Ti_(2/3))_(x)O_(4)(x=0,0.04,0.08,0.12,0.16,and 0.20)ceramics were successfully prepared via the conventional solid-state reaction route.The phase compositions,microstructures,and microwave dielectric properties were investigated.The results of x-ray diffraction(XRD)and scanning electron microscopy(SEM)showed that a single phase of MgAl_(2-x)(Li_(1/3)Ti_(2/3))_(x)O_(4)ceramics with a spinel structure was obtained at x≤0.12,whereas the second phase of MgTi_(2)O_(5)appeared when x>0.12.The cell parameters were obtained by XRD refinement.As the x values increased,the unit cell volume kept expanding.This phenomenon could be attributed to the partial substitution of(Li_(1/3)Ti_(2/3))^(3+)for Al^(3+).Results showed that(Li_(1/3)Ti_(2/3))^(3+)doping into MgAl_(2)O_(4)spinel ceramics effectively reduced the sintering temperature and improved the quality factor(Q_f)values.Good microwave dielectric properties were achieved for a sample at x=0.20 sintering at 1500℃in air for 4 h:dielectric constantε_(r)=8.78,temperature coefficient of resonant frequencyτ_(f)=-85 ppm/℃,and Q_(f)=62300 GHz.The Q_(f)value of the x=0.20 sample was about 2 times higher than that of pure MgAl_(2)O_(4)ceramics(31600 GHz).Thus,MgAl_(2-x)(Li_(1/3)Ti_(2/3))_(x)O_(4)ceramics with excellent microwave dielectric properties can be applied to 5G communications.

Physics-embedded machine learning search for Sm-doped PMN-PT piezoelectric ceramics with high performance

Pb(Mg_(1/3)Nb_(2/3))O_(3)–PbTiO_(3)(PMN-PT)piezoelectric ceramics have excellent piezoelectric properties and are used in a wide range of applications.Adjusting the solid solution ratios of PMN/PT and different concentrations of elemental doping are the main methods to modulate their piezoelectric coefficients.The combination of these controllable conditions leads to an exponential increase of possible compositions in ceramics,which makes it not easy to extend the sample data by additional experimental or theoretical calculations.In this paper,a physics-embedded machine learning method is proposed to overcome the difficulties in obtaining piezoelectric coefficients and Curie temperatures of Sm-doped PMN-PT ceramics with different components.In contrast to all-data-driven model,physics-embedded machine learning is able to learn nonlinear variation rules based on small datasets through potential correlation between ferroelectric properties.Based on the model outputs,the positions of morphotropic phase boundary(MPB)with different Sm doping amounts are explored.We also find the components with the best piezoelectric property and comprehensive performance.Moreover,we set up a database according to the obtained results,through which we can quickly find the optimal components of Sm-doped PMN-PT ceramics according to our specific needs.

MnO2@NC纳米带的制备及储锂性能研究

采用水热法成功合成了一种新型氮掺杂碳修饰MnO2纳米带(MnO2@NC)。将该材料作为锂离子电池负极时,在2 A g-1的大电流密度下循环1000次后,其可逆比容量可达310.4 mAh g-1,并展现出卓越的倍率并能。与未改性MnO2相比,MnO2@NC表现出更好的倍率性能、更高的比容量和容量保持率。电化学测试分析表明,MnO2@NC电化学性能提高的原因在于电荷转移电阻的降低、缩短的Li+扩散距离以及更为优异的电极动力学。?

The Coupled Thermo-Chemo-Mechanical Peridynamics for ZrB_(2) Ceramics Ablation Behavior

The ablation of ultra-high-temperature ceramics(UTHCs)is a complex physicochemical process including mechanical behavior,temperature effect,and chemical reactions.In order to realize the structural optimization and functional design of ultra-high temperature ceramics,a coupled thermo-chemo-mechanical bond-based peridynamics(PD)model is proposed based on the ZrB_(2) ceramics oxidation kinetics model and coupled thermomechanical bond-based peridynamics.Compared with the traditional coupled thermo-mechanical model,the proposedmodel considers the influenceof chemical reactionprocessonthe ablation resistanceof ceramicmaterials.In order to verify the reliability of the proposed model,the thermo-mechanical coupling model,damage model and oxidation kinetic model are established respectively to investigate the applicability of the proposedmodel proposed in dealing with thermo-mechanical coupling,crack propagation,and chemical reaction,and the results show that the model is reliable.Finally,the coupled thermo-mechanical model and coupled thermo-chemo-mechanical model are used to simulate the crack propagation process of the plate under the thermal shock load,and the results show that the oxide layer plays a good role in preventing heat transfer and protecting the internal materials.Based on the PD fully coupled thermo-mechanical model,this paper innovatively introduces the oxidation kinetic model to analyze the influence of parameter changes caused by oxide layer growth and chemical growth strain on the thermal protection ability of ceramics.The proposed model provides an effective simulation technology for the structural design of UTHCs.

Effects of Co_(2)O_(3)Addition on Microstructure and Properties of SiC Composite Ceramics for Solar Absorber and Storage

SiC composite ceramics for solar absorber and storage integration are new concentrating solar power materials.SiC composite ceramics for solar absorber and storage integration were fabricated using SiC,black corundum and kaolin as the raw materials,Co_(2)O_(3)as the additive via pressureless graphite-buried sintering method in this study.Influences of Co_(2)O_(3)on the microstructure and properties of SiC composite ceramics for solar absorber and storage integration were studied.The results indicate that sample D2(5wt%Co_(2)O_(3))sintered at 1480℃exhibits optimal performances for 119.91 MPa bending strength,93%solar absorption,981.5 kJ/kg(25-800℃)thermal storage density.The weight gain ratio is 12.58 mg/cm2after 100 h oxidation at 1000℃.The Co_(2)O_(3)can decrease the liquid phase formation temperature and reduce the viscosity of liquid phase during sintering.The liquid with low viscosity not only promotes the elimination of pores to achieve densification,but also increases bending strength,solar absorption,thermal storage density and oxidation resistance.A dense SiO_(2) layer was formed on the surface of SiC after 100 h oxidation at 1000℃,which protects the sample from further oxidation.However,excessive Co_(2)O_(3)will make the microstructure loose,which is disadvantageous to the performances of samples.

A robust fluorine-containing ceramic cathode for direct CO_(2) electrolysis in solid oxide electrolysis cells

Stro ntium-doped lanthanum ferrite(LSF)is a potential ceramic cathode for direct CO_(2) electrolysis in solid oxide electrolysis cells(SOECs),but its application is limited by insufficient catalytic activity and stability in CO_(2)-containing atmospheres.Herein,a novel strategy is proposed to enhance the electrolytic performance as well as chemical stability,achieved by doping F into the O-site of the perovskite LSF.Doping F does not change the phase structure but reduces the cell volume and improves the chemical stability in a CO_(2)-rich atmosphere.Importantly,F doping favors oxygen vacancy formation,increases oxygen vacancy concentration,and enhances the CO_(2) adsorption capability.Meanwhile,doping with F greatly improves the kinetics of the CO_(2) reduction reaction.For example,kchem increases by 78%from3.49×10^(-4) cm s^(-1) to 6.24×10^(-4) cm s^(-1),and Dchem doubles from 4.68×10^(-5) cm^(2) s^(-1) to 9.45×10^(-5)cm^(2) s^(-1).Consequently,doping F significantly increases the electrochemical performance,such as reducing R_(p) by 52.2%from 0.226Ωcm^(2) to 0.108Ωcm^(2) at 800℃.As a result,the single cell with the Fcontaining cathode exhibits an extremely high current density of 2.58 A cm^(-2) at 800℃and 1.5 V,as well as excellent durability over 200 h for direct CO_(2) electrolysis in SOECs.

In Situ Reaction Strengthening and Toughening of B_(4)C/TiSi_(2)Ceramics

B_(4)C-SiC-TiB_(2)ceramics were prepared by in situ reactive hot-pressing sintering with TiSi_(2)as an additive.The reaction pathways of TiSi_(2)and B_(4)C were investigated.The sintering was found to be a multistep process.The reaction started at approximately 1000℃,and TiB_(2)was formed first.Part of Si and C started to react at 1300℃,and the unreacted Si melted at 1400℃to form a liquid phase.TiSi_(2)predominantly affected the intermediate sintering process of B_(4)C and increased the sintering rate.Due to the unique reaction process of TiSi_(2)and B_(4)C,a large number of aggregates composed of SiC and TiB_(2)were generated.The results showed that composite ceramics with the optimal flexural strength of 807 MPa,fracture toughness of 3.2 MPa·m1/2,and hardness of 32 GPa,were obtained when the TiSi_(2)content was 10 wt%.

Effect of CaO/SiO_(2) Slag Mass Ratio on Dissolution Rate of Alumina-based Refractory Ceramics

The dissolution of alumina-based refractory ceramics in CaO-Al2O3-SiO_(2)slag melts was performed based on the in-situ observation system of an ultra-high-temperature laser confocal microscope,and the effect of the CaO/SiO_(2)slag mass ratio(C/S ratio)on the dissolution rate of alumina-based refractory ceramics was investigated.The results indicate that the dissolution rate increases with an increase of the C/S ratio and is mainly controlled by diffusion.During the early stage of dissolution,for all C/S ratios,the dissolution process conforms to the classical invariant interface approximation model.During the later stage of dissolution,when the C/S ratio is≥6,the dissolution process is significantly different from the model above because of the formation of a thick interfacial layer,which can be explained by dissolution kinetics.

Tribological properties of nanostructured Al_2O_3-40%TiO_2 multiphase ceramic particles reinforced Ni-based alloy composite coatings

The Ni-based alloy composite coatings reinforced by nanostructured Al2O3-40%TiO2 multiphase ceramic particles were prepared on the surface of 7005 aluminum alloy by plasma spray technology. The microstructure and tribological properties of the composite coatings were researched. The results show that the composite coatings mainly consist of γ-Ni, α-Al2O3, γ-Al2O3 and rutile-TiO2 etc, and exhibit lower friction coefficients and wear losses than the Ni-based alloy coatings at different loads and speeds. The composite coating bears low contact stress at 3 N and its wear mechanism is micro-cutting wear. As loads increase to 6-12 N, the contact stress is higher than the elastic limit stress of worn surface, and the wear mechanisms change into multi-plastic deformation wear, micro-brittle fracture wear and abrasive wear. With the increase of speeds, the contact temperature of worn surface increases. The composite coating experiences multi-plastic deformation wear, fatigue wear and adhesive wear.

Interface characteristics of Al_2O_3－13%TiO_2 ceramic coatings prepared by laser cladding

Al2O3-13%TiO2 （mass fraction） coatings, prepared by laser cladding on nickel-based alloy, were heated using high frequency induction sources. The coating microstructure and the interface between bond coating and ceramic coating were characterized by SEM, XRD and EDS. The results show that two-layer substructure exists in the ceramic coating： one layer evolving from fully melted region where the sintered grains grow fully; another layer resembling the liquid-phase-sintered structure consisting of three-dimensional net where the melted Al2O3 particles are embedded in the TiO2-rich matrix. The mechanism of the two-layer substructure formation is also explained in terms of the melting and flattening behavior of the powders during laser cladding processing. The spinel compounds NiAl2O4 and acicular compounds Cr2O3 are discovered in the interface between bond coating and ceramic coating. It proves that the chemical reactions in the laser cladding process will significantly enhance the coating adhesion.

Dielectric properties and phase transitions of La_2O_3- and Sb_2O_3-doped barium strontium titanate ceramics

The dielectric properties and phase transition characteristics of La2O3- and Sb2O3-doped barium strontium titanate ceramics prepared by solid state route were investigated. The microstructure was identified by X-ray diffraction method and scanning electron microscope was also employed to observe the surface morphologies. It is found that （La,Sb）-codoped barium strontium titanate ceramics exhibit typical perovskite structure and the average grain size decreases dramatically with increasing the content of Sb2O3. Both La3＋ ions and Sb3＋ ions occupy the A-sites in perovskite lattice. The dielectric constant and dielectric loss of barium strontium titanate based ceramics are obviously influenced by La2O3 as well as Sb2O3 addition content. The tetragonal-cubic phase transition of La2O3 modified barium strontium titanate ceramics is of second order and the Curie temperature shifts to lower value with increasing the La2O3 doping content. The phase transition of （La,Sb）-codoped barium strontium titanate ceramics diffuses and the deviation from Curie-Weiss law becomes more obvious with the increase in Sb2O3 concentration. The temperature corresponding to the dielectric constant maximum of （La,Sb）-codoped barium strontium titanate ceramics decreases with increasing the Sb2O3 content, which is attributed to the replacement of host ions by the Sb3＋ ions.

Ti_(3)SiC_(2)陶瓷材料制备方法研究进展

作为MAX相家族重要成员,钛硅化碳Ti_(3)SiC_(2)除了具有耐高温、抗氧化性能外,还具有与金属类似的优异导电性、导热性和可加工性,在电接触材料、热交换器构件材料、润滑材料等领域展现出较大的应用潜力,成为当前一种备受关注的新型陶瓷材料。现有的Ti_(3)SiC_(2)制备方法主要有无压烧结、热压烧结、热等静压、放电等离子烧结、前驱体转换陶瓷、反应熔体浸渗法、熔盐法、化学气相沉积、物理气相沉积等。本文首先阐述了Ti_(3)SiC_(2)材料的结构与性能,然后重点综述了国内外Ti_(3)SiC_(2)陶瓷材料的制备方法,最后展望了Ti_(3)SiC_(2)陶瓷材料的应用前景。

铜增韧Mo_(2)BC陶瓷的力学性能和摩擦学性能

采用快速热压反应烧结法制备高强韧Mo_(2)BC/Cu陶瓷基复合材料。研究铜含量对Mo_(2)BC/Cu复合材料的微观组织、力学性能和摩擦学性能的影响,并对其增韧机制和磨损机理进行分析。研究结果表明:Cu均匀地分散在Mo_(2)BC基体中,具有细化晶粒的作用。Mo_(2)BC/Cu复合材料中铜可以添加的最大质量分数为7.5%。随着铜含量的增加,Mo_(2)BC/Cu复合材料的弯曲强度和断裂韧性增加。当Cu质量分数为7.5%时,复合材料的弯曲强度和断裂韧性最高,分别为625.1 MPa和7.4 MPa·m^(1/2),与Mo_(2)BC陶瓷相比,分别提高了24%和62%,其主要的增韧机制为铜的塑性变形、晶粒拔出、桥接效应和裂纹的偏转。此外,铜的添加还可以明显提高Mo_(2)BC/Cu复合材料的摩擦磨损性能。当Cu质量分数为2.5%时,复合材料的摩擦因数可低至0.36,磨损量最小,耐磨性最优,其主要的磨损机制为轻微的二体磨粒磨损和氧化磨损。

Na_(2)O对锂铝硅微晶玻璃析晶及性能的影响

采用熔融法制备了不同Na_(2)O含量的透明锂铝硅微晶玻璃,通过DSC、XRD、FESEM等测试方法研究了不同Na_(2)O含量对玻璃析晶及性能的影响。结果表明:Na_(2)O的引入能显著降低玻璃的转变温度和析晶温度,抑制LiAlSi_(4)O_(10)晶相的析出。但Na_(2)O的引入促使微晶玻璃中析出Li_(2)Si_(2)O_(5)新相,并且随着Na_(2)O引入量的增加,Li_(2)Si_(2)O_(5)转变为主晶相。由于晶体尺寸均为纳米级,主晶相的转变对透过率影响较小,微晶玻璃的可见光透过率均高于85%。主晶相的转变有效增强了微晶玻璃的机械性能,其弯曲强度由300 MPa提升至331 MPa。Na_(2)O的引入有效增强了Na-K交换,Na_(2)O含量为4%(质量分数)的Li 2O-Al_(2)O_(3)-SiO_(2)微晶玻璃在410℃的KNO_(3)熔盐中交换6 h后,维氏硬度由7.108 GPa提升至7.403 GPa,弯曲强度由331 MPa提升至470 MPa。