Preparation and properties of InGaZn4O7 ceramic by cold sintering

When the traditional method is used to prepare IGZO ceramic, it needs to be sintered under ultra-high temperatures and for a long time, and the preparation cost is high. To reduce the sintering temperature and energy consumption, a mixed-phase IGZO green compact with ultra-high density was first prepared using cold sintering process. Then, the IGZO ceramic with excellent properties was successfully prepared by the conventional sintering method at low sintering temperature. The effects of sintering temperature on the microstructure, density, and electrical properties of IGZO green compact and ceramic were studied. The densification process of ultrahigh density IGZO green compact was also discussed. The results show that the IGZO green compact with a relative density of over 96% can be obtained under cold sintering at 400 °C/475 MPa and assisted by the acetic acid solution. An IGZO ceramic with a relative density of 98.12% and resistivity of 4.87 × 10⁻³ Ω cm was obtained by sintering at 1100 °C for 5 h. This paper provides a reference for improving green compact density and preparing high-performance transparent oxide ceramics at low temperature.     

Studies of drying and sintering characteristics of gelcast BaTiO3-based ceramic parts

Drying green gelcast parts is an essential step in the gelcasting manufacturing process. In this work, the liquid desiccant method was used for drying of BaTiO₃-based semiconducting ceramic gelcast parts. The results show that the loading level of ceramic powders and the liquid desiccant concentration significantly effect the drying process and the sintering characteristics of the ceramic parts. Lowering the loading level of ceramic powders and increasing the concentration of the liquid desiccant, non-uniform and differential drying in various regions due to great solvent gradient, induces structural and residual stresses which cause defects, such as cracking, bending and other malformations, which make the articles useless during the drying process and sintering procedure. However, when the solid loading of green gelcast parts is increased to more than 45 vol.%, the stresses developed during drying can be greatly reduced, and a higher concentration of the liquid desiccant can be used without inducing defects in the drying process and defect free ceramic with a smooth surface can be obtained. Moreover, the effects of loading level of ceramic powders and thickness of parts on the density of ceramic parts were studied. Higher solid content in the gel, and lower thickness of parts, increase the density of ceramics.     

Direct ink writing of hierarchical porous ultra-high temperature ceramics (ZrB2)

An approach to producing hierarchical multi-scale porous ultra-high temperature ceramics (zirconium diboride, ZrB₂) using 3D printing has been developed. Porous ceramic filaments can be 3D printed via Direct Ink Writing (DIW) (paste extrusion). Millimeter scale porosity is created by the 3D printed scaffold filaments. We introduce 20-micron-scale porosity into the scaffold filaments with the addition of oil to produce capillary suspension paste inks. Micron-scale porosity is also developed by partial sintering of the ceramic. The rheological (flow) properties of the capillary suspension paste inks suitable for printing by extrusion through the needle of the 3D printer have been characterized. The samples are strengthened by partial sintering at high temperatures. Complex-shaped components can be printed and sintered into crack-free components, but distortion during drying and sintering lead to poor shape and tolerance control. X-ray tomography is used to characterize the internal structure of the printed components. Printed test bars measured in 4-point bend testing exhibit high strength to density ratio. Such materials potentially have applications as insulation near very high-temperature surfaces in aerospace applications.     

Effect of synergism of solid loading and sintering temperature on microstructural evolution and mechanical properties of 60 vol% high solid loading ceramic core obtained through stereolithography 3D printing

Solid loading has a significant effect on the curing behavior of slurry and the microstructure and properties of the ceramic core. A high-solid loading slurry can effectively improve the sintering densification of ceramic particles and improve the interlayer bonding strength and mechanical properties at both 25 °C room and higher temperatures. Herein, based on the photopolymerization theory of ceramic slurry, the solid loading was increased from 45 to 60 vol% by adjusting the composition ratio of the resin ceramic powder. Additionally, the optimal sintering temperature of the 60 vol% solid loading ceramic core was 1200 °C. The synergistic effect of the solid loading and sintering temperature controls the sintering shrinkage of the sample within 3.2%; the porosity, high temperature, and room temperature flexural strength were approximately 30%, 24 MPa, and 10 MPa, respectively. The printing preparation of high-solid loading ceramic cores can be used to guide optimizing process parameters on an industrial scale.     

A review of two-step sintering for ceramics

The development of high-density ceramic materials with fine-grained microstructures has been studied to considerably improve their properties for high-performance applications. Many alternatives have been searched to refine their microstructure by changing their composition and/or processing. Among such alternatives, the densification of ceramic materials by sintering curve control is an effective, simple and economical microstructure refinement method. Thus, different thermal treatment techniques such as spark plasma sintering and microstructural forms of control such as the control of sintering conditions have been used to obtain nanostructured materials. One of the techniques widely used in recent years is two-step sintering. Two-step sintering (TSS) is a promising method used to obtain high-density bodies and smaller grain sizes. Two TSS methodologies are known: sintering with thermal pretreatment at a low sintering temperature, followed by a second stage at elevated temperature, and the more recent approach presented by Chen and Wang, which has been the most widely used. In addition to the sintering conditions (temperature, heating rate and sintering holding times) that must be suitable for each composition type, the starting materials, particle size and processing method may influence the obtained microstructure, especially the reduced grain size and increased densification. The current review of two-step sintering presents the effect of this technique on the grain density and sizes of different ceramic materials. The influence of the addition of doping agents and its effect on the mechanical properties in different systems is also presented in the current study.     

Production of ceramic foam filters for molten metal filtration using expanded polystyrene

Filtration of molten metals with ceramic foam filters is a proven method in order to remove the inclusions. This paper develops a new approach for the production of ceramic foam filters. In the conventional method of ceramic foam filter production, polyurethane sponges are used.In this work, ceramic foam filter was produced by using expanded polystyrene. Polystyrene is expanded in a specially designed mold by steam to form polystyrene patterns. Various ceramic slurries are then poured into the polystyrene cell and allowed to air dry. After the shaping operation, filters are subjected to sintering process under various conditions. By this new method, filter channel sizes can be controlled and traps with desired configurations can be formed. Some tests were applied to the produced filters. Thermal shock tests ensured that the filters could withstand temperatures of 1450 °C. Water absorption test showed that bauxide based material absorbed water more than the others.     

Reuse of mineral wool waste and recycled glass in ceramic foams

Novel ceramic foams have been prepared by high temperature sintering of waste mineral wool and waste glass using SiC as a foaming agent. The aim of the research was to understand the effects of composition and sintering conditions on the properties and microstructure and produce commercially exploitable ceramic foams. Optimum ceramic foams were formed from 40 wt% mineral wool waste and 2 wt% SiC, sintered at 1170 °C using a heating rate of 20 °C/min with a 20 min hold at peak temperature. The ceramic foams produced had a bulk density of 0.71 g/cm³ and a uniform pore size distribution. The research shows that ceramic foams can be formed from waste mineral wool and these can be used for thermal insulation with associated economic and environmental benefits.     

Microwave Dielectric Properties of Scheelite Structured PbMoO4 Ceramic with Ultralow Sintering Temperature

In this work, a low‐firing microwave dielectric ceramic PbMoO₄ with tetragonal structure was prepared via a solid‐state reaction method. The sintering temperature ranges from 570°C to 670°C. Ceramic samples with relative densities above 97% were obtained when sintering temperature was around 600°C. The best microwave dielectric properties were obtained in the ceramic sintered at 650°C for 2 h with a permittivity ~26.7, a Q × f value about 42 830 GHz (at 6.2 GHz) and a temperature coefficient value of 6.2 ppm/°C. From the X‐ray diffraction, backscattered electron imaging results of the cofired sample with 30 wt% silver and aluminum additive, the PbMoO₄ ceramic was found not to react with Ag and Al at 630°C. The microwave dielectric properties and low sintering temperature of PbMoO₄ ceramic make it a candidate for low‐temperature cofired ceramic applications.     

Low-temperature sintering of (Pb1−xCdx)(Zr0.965Ti0.035)O3 ferroelectric ceramics for multilayer device application

Low-temperature sintering behaviour and ferroelectric properties of lead zirconate titanate (PZT95/5) ferroelectric (FE) ceramics doped with CdO were investigated. The addition of CdO significantly promoted the densification and decreased the sintering temperature of PZT95/5 ceramic. When the addition of CdO content is 1?mol-%, PCZT95/5 ceramics with a relative high density of approximately 97.5% can be obtained by sintering at 1100°C and exhibits excellent electric properties with d₃₃ values of 65 pC/N, this d₃₃ value is close to that of PZT95/5 ceramic sintered at 1350°C. With an increase in the CdO content, the FE phase content decreases and the antiferroelectric (AFE) phase content increases gradually. When the CdO content is 2?mol-%, the most of FE phase of PCZT 95/5 ceramics changes to AFE phase, the polarisation value is quite small and the d₃₃ value drops to zero.     

Screening Sintering Aids for (K0.5Na0.5)NbO3 Ceramics

Searching for suitable sintering aids for ceramic materials is important and tedious work. In this study, we introduce a simple and effective method, named liquid phase screening method (LPSM), for rapidly screening sintering aids for KNN ceramics. By measuring the structure and properties, we demonstrated that the suitable sintering aids for KNN can be quickly determined by LPSM. The new sintering aids found by this method, GeO₂ and borax which have not been reported before, lead to improved properties.     

Effect of sintering temperature on the characteristics of ceramic hollow spheres produced by sacrificial template technique

Ceramic hollow spheres were produced by a sacrificial template technique with subsequent sintering under temperatures ranging from 1100 °C to 1250 °C. The effect of the sintering temperature on the structure of the ceramic hollow spheres was investigated by optical and scanning electron microscopy, and a gas adsorption method. The results show that the structure of the ceramic hollow spheres can be controlled, with the retention of the hollow spherical shape, by variation of the sintering temperature. Increase of the sintering temperature from 1100 °C to 1250 °C decreased the outer diameter of the ceramic hollow spheres by 14 percent, the shell thickness by 18 percent, and the void area ratio of the shell surface by 9.2 times; both of the specific surface area and the total pore volume of ceramic hollow spheres decreased by 60 percent.     

Pressureless sintering of transparent AlON ceramic with assimilable γ-Al2O3 as sintering promoting additives

Transparent aluminum oxynitride (AlON) ceramic was successfully fabricated without doping sintering additive by the pressureless sintering method. Γ-Al₂O₃ nano-powder that can be assimilated by the AlON matrix was used for promoting the densification of AlON during the sintering. The sintering behavior of AlON and the effects of γ-Al₂O₃ nano-powder on the phase, hardness, and transmittance of AlON have been investigated in detail. The mechanisms of γ-Al₂O₃ nano-powder on the AlON green body modifying and the sintering promoting are revealed. The transmittance of the AlON ceramic is dramatically enhanced by doping γ-Al₂O₃ nano-powder and the 2 mm thick sample doped with 2.5 wt% γ-Al₂O₃ nano-powder shows an inline transmittance above 81% at 1500 nm.     

Preparation of Ceramic Well Plates for Combinatorial Methods Using the Morphogenic Effects of Droplet Drying

When droplets of a ceramic suspension dry on a non-wetting substrate, powder migrates to the periphery and builds there a wall of powder. This intriguing phenomenon, which is a nuisance in some processes, can be used to make arrays of ceramic wells on a ceramic substrate. These wells can, after sintering, be used to hold ceramic samples made from powder by controlled mixing of ceramic inks or could be made from ceramics that act as heterogeneous catalysts and used to hold reactants. The well plates can even be made from electrically conducting ceramics so that electrical property measurements can be made with a ground electrode.     

Cold-sintered Na2WO4-Ni0.2Cu0.2Zn0.6Fe2O4 ceramics with matched permittivity and permeability for miniaturized antenna

(1-x)Na₂WO₄–xNi_0.2Cu_0.2Zn_0.6Fe₂O₄ (NWO-NCZO) ceramic composites (x = 0–0.6) were successfully prepared by the cold sintering method under a uniaxial pressure of 200 MPa at 150°C for 30 min. The microstructures and electromagnetic properties of (1-x)NWO-xNCZO ceramic composites with different NCZO contents have been systematically investigated. The obtained biphasic NWO-NCZO ceramic composites possess dense microstructures. The 0.4NWO–0.6NCZO ceramic composite exhibits a matched relative permittivity and relative permeability of around 8 in the frequency range from 10 to 200 MHz, which is beneficial for impedance matching between antenna and free space. A prototype of microstrip antenna based on the developed NWO-NCZO ceramic composite is designed and to demonstrate its application in miniaturized antennas. The simulation results revealed that the size of the radiation patch of the antenna can be reduced by 60% yet with bandwidth being enhanced 26.5 times when the 0.4NWO–0.6NCZO ceramic composite is selected as the substrate instead of pure NWO ceramic.     

原材料和制备工艺对硅酸锌陶瓷微波介电性能的影响

为了提高硅酸锌介质陶瓷的性能,研究了添加物、原材料和制备工艺对其微波介电性能的影响。采用固相法、并以去离子水代替乙醇作分散剂制备陶瓷粉料,闭腔法测量其无载Q值和频率温度系数。研究结果表明原材料的粒度、球磨工艺和烧结温度对Q.f值影响大,添加物TiO2不仅调节频率温度系数(τf),而且促进陶瓷烧结。当TiO2(wt%)12%,1240℃烧结时,获得优良的微波介电性能:介电常数(εr)为10.2,Q.f=91640GHz,τf=-5.78ppm/℃。并用该组成的材料制作了中心频率f0=5.4GHz,带宽Δf=96MHz,插损小于1.3dB的两级片式介质带通滤波器,可以用于通信系统。     

Plastic deformation and effects of water in room‐temperature cold sintering of NaCl microwave dielectric ceramics

NaCl ceramics were prepared by room‐temperature cold sintering using moistened NaCl powder with 4 wt% water and dry pressing using dehydrated powder. When the applied uniaxial pressure is low, the relative density of dry‐pressed NaCl ceramic is significantly lower than that of cold‐sintered ceramic, while the former is 98.5%‐99.3% and much higher than the latter (94.3%‐94.6%) for high applied pressure of 200‐300 MPa. The uniaxial pressure‐induced plastic deformation dominates the densification of dry‐pressed NaCl ceramic, and also plays a role during cold sintering as well as the dissolution‐precipitation process. The lower density of cold‐sintered NaCl ceramic under high applied pressure is attributed to the trapped water in ceramic body during cold sintering. Besides, the presence of water always promotes the microstructural homogeneity, which is responsible for the much higher Qf value of cold‐sintered NaCl ceramic. The optimal microwave dielectric properties with ε_r = 5.55, Qf = 49 600 GHz, and τ_f = ?173 ppm/°C are obtained in cold‐sintered NaCl ceramic under the applied pressure of 300 MPa, indicating that it is a promising candidate as a microwave dielectric material.     

Research and application prospect of short carbon fiber reinforced ceramic composites

With the advantage of high temperature resistance, low expansion, low density and excellent thermal stability, carbon fiber reinforced ceramic composites have a very wide range of applications in aerospace, military, energy, chemical industries and transportation. Short carbon fiber reinforced ceramic composites are characterized by simple processes, low manufacturing costs, short preparation times and automated production, can be used in fields such as friction materials and thermal protection system. This paper reviews the current status and recent advances in research on homogenization techniques, mechanical properties, thermal properties and frictional properties of short carbon fiber reinforce ceramic composites. Different processing routes for short carbon fiber reinforced ceramic composites, including reactive melt infiltration (RMI), hot pressing (HP), spark plasma sintering (SPS) and pressureless sintering, the advantages and drawbacks of each method are briefly discussed. The future development direction of low-cost manufacturing short carbon fiber reinforced ceramic composites is prospected.     

Immobilization of uranium in cristobalite ceramic through adsorption on mesoporous SBA-15 and further sintering process

The development of an adsorbent which can be easily transformed into stable ceramic waste forms through a simple route is necessary for the treatment of the radioactive wastewater. Herein, we report on the immobilization of uranium in cristobalite ceramic through adsorption on mesoporous SBA-15 and further sintering process. The mesoporous SBA-15 with short pore length was synthesized and employed to remove uranium from aqueous solution. Subsequently, the SBA-15 with adsorbed U (U/SBA-15) was solidified by sintering. The effects of sintering temperature and U content on the structure, densification and aqueous durability of the obtained cristobalite ceramic waste forms were investigated. The results indicate that the U/SBA-15 can be transformed into stable cristobalite ceramic after sintering at 1100–1400 °C for 6 h. Furthermore, all the obtained cristobalite ceramic waste forms exhibit good aqueous durability (∼10⁻⁴ g m^-2 d^-1). This work demonstrates a potential route and adsorbent to dispose the radioactive wastewater.     

Multi-material ceramic material extrusion 3D printing with granulated injection molding feedstocks

Material Extrusion (MEX) is an advanced technology for polymer 3D printing and countless printers are commercially available. MEX has also been demonstrated for ceramics. For that purpose, thermoplastic binders are filled with high loads (>40 vol%) of a ceramic powder. The printed parts are subsequently debound and sintered. In contrast to most MEX printers, the ceramic printer presented herein works with granulated feedstock instead of filaments. Therefore, the development of novel feedstocks is faster and more straightforward since the challenges associated with filament production are omitted. Furthermore, commercial ceramic injection molding (CIM) feedstocks can be used which allows fast prototyping with the same material that is later used in high-quantity industrial production by CIM.In this study, a method to fabricate multi-material ceramic parts using a granulate-fed printer is presented. Examples of multi-material printing include colored ZrO₂ parts as well as ceramic high-temperature heating elements in various shapes consisting of an electrically conductive and a non-conductive component. Light- and electron microscopy confirms that the layer adhesion before and after sintering is flawless, even between different materials if the material combination is chosen carefully. All feedstocks are based on a commercially available CIM binder filled with the desired ceramic powder. Consequently, the feedstock preparation as well as optimizing of debinding and sintering conditions are simple and reproducible.     

A further report on finite element analysis of sintering deformation using densification data—Error estimation and constrained sintering

In a previous paper, Kiani et al. [Kiani, S., Pan, J., Yeomans, J. A., Barriere, M. B. and Blanchart, P., Finite element analysis of sintering deformation using densification data instead of a constitutive law. J. Eur. Ceram. Soc., 2007, 27, 2377–2383] proposed an empirical numerical method to calculate the sintering deformation of ceramic powder compacts without knowing the viscosities and sintering potential. The method was validated by free sintering experiments using specimens with non-uniform initial densities. Two new developments are reported in this paper: (a) a method of error estimation is developed which can be used to check if the empirical analysis is valid after the analysis; (b) a range of case studies are presented showing that the empirical solutions provide very good approximations to the solutions obtained using full constitutive laws not only for free sintering but also for highly constrained sintering of single- or multi-layered films.