International Journal of Applied Ceramic Technology最新文献

The corrosion of slag on refractories usually starts from the matrix, so improving the slag resistance of the matrix is of great significance for the slag resistance of the refractories. To clarify the influence of matrix on the slag resistance of magnesia–carbon refractories, the slag corrosion experiments were conducted at 1873 K on MgO–C refractories, low-carbon MgO–C refractories, and MgO–SiC–C refractories. The results showed that the slag resistance of MgO–C refractories was higher than that of low-carbon MgO–C refractories, and the slag resistance of MgO–SiC–C refractories was superior to that of low-carbon MgO–C refractories. The interaction between MgO–SiC–C refractories and slag generated high melting point phases such as forsterite and spinel, reducing the routes for the slag to infiltrate the inside of the refractories. MgO–SiC–C refractories reacted with slag to increase the viscosity of the slag, the viscosity being 86.3% and 51.9% higher than in the case of low-carbon MgO–C and MgO–C refractories, respectively. Compared with MgO–SiC–C refractories, MgO–C refractories did not exhibit overwhelming advantages in slag resistance. Due to the low-carbon content and good slag resistance, MgO–SiC–C refractories were promising low-carbon magnesia-based refractories for high-temperature industries.

Mullite ceramics with high purity and toughness were prepared by hot-press sintering of pyrophyllite at 1300°C using AlOOH nanomaterials with different sizes and morphologies (nanoparticles, nanorods, nanoflakes, and micro-sized sea urchin–like) as additives. Among the four types of AOOH additives, the incorporation of nanoflakes and sea urchins resulted in the formation of a relatively uniformly distributed and tightly packed microstructure within the ceramics, which significantly improved the density and mechanical properties of the ceramic materials. Compared to nano-sized AlOOH, the addition of micron-sized sea urchin–like AlOOH could produce mullite ceramics with best purity and flexural strength. The flexural strength and fracture toughness of ceramics prepared from micro-sized sea urchin–like AlOOH and pyrophyllite reach 427.34 ± 1.99 MPa and 4.68 ± .31 MPa m^1/2, respectively. During the ball milling process, the originally micron-sized sea urchin–like AlOOH particles were broken down into micro- and nano-sized AlOOH particles. The resulted micron and nanoscale AlOOH particles exhibited synergistic and multi-scale effects with pyrophyllite, which contributed to the formation of uniformly sized and densely arranged mullite crystals within the ceramics. Additionally, the bridging between the mullite crystals further improved the mechanical properties of the mullite ceramic material.

Sc₂O₃–CeO₂–Y₂O₃– stabilized zirconia (ScCeYSZ) nanoparticles with different percentages of stabilizer agents [sample1: 1.8 wt.% (Sc₂O₃) 8.3 wt.% (CeO₂) 1.9 wt.% (Y₂O₃), sample 2: 1.1 wt.% (Sc₂O₃) 9.0 wt.% (CeO₂) 1.9 wt.% (Y₂O₃), sample 3: .5 wt.% (Sc₂O₃) 9.6 wt.% (CeO₂) 1.9 wt.% (Y₂O₃) stabilized zirconia] were synthesized with Pechini method and consolidated by spark plasma sintered method. The results showed that despite the [(sample)₁: 1.8 wt.% (Sc₂O₃) 8.3 wt.% (CeO₂) 1.9 wt.% (Y₂O₃)] had lower density and higher porosity percentage compared to other samples, it had better calcium–magnesium–alumina–silicate (CMAS) corrosion resistance compared to other samples and the yttria-stabilized zirconia nanopowders (nano-YSZ) sample. It was due to the higher acidic nature and tetragonality of the (sample)₁ sintered body compared to other samples and YSZ ceramic in the CMAS corrosive medium. Moreover, the results of phase and microstructural analysis following CMAS corrosion revealed the formation of the monoclinic phase and rod-shaped CaAl₂Si₂O₈ particles on the surface of the sampled sintered sample. However, the nano-YSZ sample corroded homogenously and delamination occurred after the CMAS corrosion test.

Sand-casting molds suffer from surface defects and low strength. An organic–inorganic binder conversion process, wherein an organic binder is converted to an inorganic binder, has been proposed to increase the application temperature of the sand-casting mold and simplify the manufacturing process for precision casting. However, the usable temperature of the typical SiO₂–Na₂O binder system is limited to approximately 1000°C owing to the low liquefaction temperature of the compound. The resulting glass phase (Na₂SiO₃) exhibits low viscosity, and the casting of large objects results in low strength. Therefore, in this study, we propose a SiO₂–Na₂O–ZrO₂ ternary inorganic binder system; the addition of zirconia (ZrO₂) into sodium silicate (Na₂SiO₃) as an inorganic binder was expected to increase the operating temperature of the mold and improve its mechanical properties. The results confirmed that the addition of ZrO₂ improved the mechanical properties by preventing the formation of Na₂SiO₃. In addition, a higher sintering temperature corresponded to smaller and larger amounts of Na₂SiO₃ and Na₂ZrSiO₅, respectively, and thus a higher strength. Therefore, we expect our developed ternary inorganic binder system to be highly advantageous for producing molds for high-temperature and precision casting.

Porous calcium silicate ceramic has been prepared by ultrafast high-temperature process in several minutes. The effect of sintering current and starch content on the phase composition, pore structure, compressive strength, and air permeability have been investigated. Homogeneous pores can be formed during the fast decomposition of calcium silicate hydrate, calcium carbonate, and starch. The optimized composition shows the high compressive strength (over 7 MPa), porosity (60.8%), and air permeability (379.4 L/m² s). Results showed that the ultrafast high-temperature sintering method can achieve homogenous porous structure in much shorter time than conventional furnace sintering.

Silicon carbide nanofiber/silicon carbide (SiC_nf/SiC) composites with a laminar stacking structure were prepared by the slurry impregnation hot-press sintering using aluminum (Al) powder, boron (B) powder, and carbon black as sintering aids. SiC_nf paper was fabricated using nanofibers and impregnated with the slurry of SiC_np and sintering aids, and the SiC_nf/SiC preforms were fabricated by the alternating stack of the SiC_nf paper and SiC_np. The pyrolysis carbon and boron nitride interface layers were deposited on the surface of SiC_nf by chemical vapor deposition and vacuum impregnation-pyrolysis methods. The effects of different sintering temperatures on the relative density, porosity, sectional microscopic morphology, and mechanical properties of the composites were investigated. The results show that the fracture toughness of SiC_nf/SiC composites is significantly improved. The mechanical properties of the composites were optimized at a sintering temperature of 1950°C and a sintering pressure of 30 MPa, with flexural strength and fracture toughness of 548 MPa and 15.86 MPa·m^1/2, respectively. The liquid phase Al₈B₄C₇ compound generated at the high temperature promoted the densification of the composites.

A powder compact with anion-uptake ability was prepared prior to the proceeding of the solid-state reaction involving layered double hydroxide (LDH) and kaolinite during calcination. LDH features anion-exchangeable capability, and kaolinite is used as a raw potty material because of the sintering property. In the present study, the solid-state reaction of LDH with kaolinite did not proceed at 750°C, resulting in the formation of a mixture of layered double oxide (LDO) and metakaolinite. Unlike LDO, which typically undergoes anion-uptake accompanied by LDH reconstruction, metakaolinite does not revert to kaolinite without the use of hydrothermal conditions. In addition, the powder compact composed of LDO crumbled, whereas the one containing a mixture of LDO and metakaolinite remained intact. When the powder compact of LDO and metakaolinite mixture was immersed in a methyl orange (MO) aqueous solution, an LDH–MO intercalation compound was generated within the compact. By contrast, no such compound was generated when LDO powder was immersed in an MO aqueous solution. These results indicated that the successful preparation of a powder compact with distinct anion-uptake ability was different from powder, owing to that the solid-state reaction of LDO with metakaolinite did not proceed at 750°C.

In the present work, five compositions in the BaO–MgO–SiO₂ ternary system were chosen, and ceramics were prepared using the solid-state reaction method. Single phases were formed easily for the first four compositions, and BaMgSi₃O₈ ceramics were found to be a mixture of both BaSi₂O₅ and MgSiO₃, according to X-ray diffraction results. Among all the compositions, Ba₂MgSi₂O₇ ceramic sintered at 1225°C possesses the highest Qf (Q = 1/dielectric loss = 1/tanδ, f = resonant frequency) value ∼55 010 GHz along with relative permittivity ∼8.0 and temperature coefficient of resonant frequency (TCF) ∼−57.5 ppm/°C. With 3 wt.% BCB (BaO–B₂O₃–CuO) additions, Ba₂MgSi₂O₇ ceramic was well densified at 950°C with a relative permittivity ∼8.1, Qf value ∼28 920 GHz (at 12.37 GHz) and TCF value ∼‒56.6 ppm/°C. These series ceramics with low relative permittivity values might be good candidates for low-temperature co-fire ceramic technology substrate applications.

The influence of tetraethyl orthosilicate (TEOS) on the plasma etching behavior of yttrium aluminum garnet (Y₃Al₅O₁₂, yttrium aluminum garnet [YAG]) was systematically studied. Dense YAG bulk specimens were hot-press sintered at a relatively low temperature of 1450°C for 2 h under 20 MPa, using TEOS as a sintering additive. The etching properties of YAG ceramics, doped with different TEOS contents, were evaluated using an inductively coupled plasma etcher with an incident plasma power of 1500 W for up to 2 h. It was observed that the addition of .3 wt.% TEOS optimally reduced the surface roughness of YAG ceramics post-plasma etching. Transmission electron microscopy and X-ray fluorescence tests clarified that a densification-promoting TEOS-induced residual Si-rich phase at the triple junction for the over-doped TEOS (≥.5 wt.%) specimen acts as a pit-initiation site during plasma etching, which eventually results in increased surface roughness.

In this paper, tabular corundum aggregates were prepared using the rolling ball method and semi-dry pressing combined with the cold isostatic pressing method, using industrial alumina raw powder as the raw material and water as the binder, respectively. Then, the influence of various molding methods on phase composition, microstructure, pore characteristics, densification, and physical properties was investigated by X-ray diffraction, scanning electron microscopy, and Archimedes’ principle. The results revealed that tabular corundum aggregates prepared using the rolling ball method had higher bulk density and lower apparent porosity. It also rendered a relatively homogeneous grain size distribution and a high cylinder compressive strength retention rate of 68.0%. The grain size distribution and pore size distribution of tabular corundum aggregates prepared using semi-dry pressing combined with the cold isostatic pressing method were wide, and there were a few large pores, which decreased the strength and densification. Green density was a key factor influencing the sintering; the two molding methods minimized porosity and improved the green density through collision extrusion and external force, respectively. Meanwhile, the molding process also increased the contact points between particles and the material migration channels, which had an impact on the densification mechanism of tabular corundum aggregates.