International Journal of Applied Ceramic Technology最新文献

In this work, magnesia-alumina spinel foam ceramics were prepared by foaming-sol method using magnesia alumina spinel as raw material, anionic surfactant potassium oleate (PO) as foaming agent, and alumina sol as curing agent. The curing mechanism and the effect of alumina sol content on the stability of foam slurry and the properties of foam ceramics were investigated. In the foam slurry, the alumina sol can react with PO, so magnesia-alumina spinel can be fixed in the foam structure through the gel network to improve the stability of the foam slurry. The gelation process reduces the viscosity of the foam slurry. The pores of magnesia-alumina spinel foam ceramics sintered at 1500°C are mostly closed pores and the average pore was 29.7–42.1 µm. With the increase of alumina sol content, the bulk density of magnesia-alumina spinel foam ceramics increased from 1.3 to 1.9 g/cm³, the cold compressive strength from 8.8 to 22.7 MPa, and the thermal conductivity from .417 to .806 W·m⁻¹·K⁻¹(350°C).

Binary CaO-MgO-Al₂O₃-SiO₂ (CMAS) ceramics composites of anorthite-cordierite composition were synthesized from natural raw materials (kaolin and dolomite rock). The change of SiO₂/Al₂O₃ ratio in kaolin/dolomite mixtures (12, 24, and 36 wt.%) and synthesized composites along with analysis of their phase composition transformations (X-ray diffraction) during heat treatment (thermogravimetric and differential thermal analysis) give the controlled design of aluminosilicate matrices. The obtained ceramic composites are represented by anorthite, a cordierite-like phase whose ratio varies from 1.3:1 to 2.8:1. Mullite crystals, also included in the composition, reinforce the anorthite-cordierite matrix. The morphostructural features of the samples were studied using optical and scanning electron microscopy. The porosity ranges from 7.8% to 24.2% depending on dolomite content. The impurities of iron and titanium interfering with obtaining a qualitative product are leveled by the presented technique including the heat treatment scheme justified by thermogravimetric analysis. Obtained CMAS-ceramics of anorthite-cordierite composition correspond to industrial international standards by their technical characteristics and exceed the requirements for heat-insulating and chemically resistant materials by compressive strength.

Ytterbium silicate (Yb₂Si₂O₇) and lanthanum zirconate (La₂Zr₂O₇) ceramic powders were synthesized by the sol–gel method. A novel tri-layer La₂Zr₂O₇/Yb₂Si₂O₇/SiC environmental barrier coating was prepared on the surface of C/SiC composites to improve the service temperature of the coating (above the Si melting point, 1683 K). Results show that both Yb₂Si₂O₇ and La₂Zr₂O₇ ceramic powders had extremely high purity and were accompanied by a large number of nanoparticles. The tri-layer La₂Zr₂O₇/Yb₂Si₂O₇/SiC coating can efficiently prevent the oxidation failure of C/SiC composites in 1773 K air environment for more than 100 h with slight weight loss of 5.71 × 10⁻³ g·cm⁻² and the matching weight loss rate of 5.71 × 10⁻⁵ g·cm⁻²·h⁻¹. No significant chemical reaction was observed between Yb₂Si₂O₇ middle and La₂Zr₂O₇ outer coatings during the oxidation process at 1773 K, indicating that the tri-layer La₂Zr₂O₇/Yb₂Si₂O₇/SiC coating had better oxidation stability in 1773 K air environment.

Recently multielements solid solution has shown significant improvement to the mechanical properties of parent MAX phases. Therefore, in this work, five elements with different radii were incorporated to check the effect on properties of MAX phases. (Nb_0.8Ti_0.05Zr_0.05Mo_0.05Hf_0.05)₄AlC₃ (MAX_Hf) and (Nb_0.8Ti_0.05Zr_0.05Mo_0.05Ta_0.05)₄AlC₃ (MAX_Ta) ceramics were successfully synthesized using the spark plasma sintering technique. The microstructure and elemental map analysis results further confirmed that the five transition metals were successfully solid soluted at the M-sites of the hexagonal M₄AlC₃ unit cell. The mean elemental compositions for M-site elements were achieved as Nb_0.85Ti_0.052Zr_0.035Mo_0.027Hf_0.036 and Nb_0.847Ti_0.051Zr_0.043Mo_0.025Ta_0.033 for MAX_Hf and MAX_Ta ceramics, respectively. The electrical and thermal conductivities of multielement solid solution MAX phases were decreased compared to pure Nb₄AlC₃. However, Mechanical properties were significantly increased with the solid solution of five transition metals. The fracture toughness, flexural strength, compressive strength and Vickers hardness (10 N) of MAX_Hf and MAX_Ta ceramics were achieved as 8.87 MPa m^1/2, 448 MPa, 867 MPa, 6.5 GPa and 10.36 MPa m^1/2, 557 MPa, 1039 MPa, 8.2 GPa, respectively. The enhanced mechanical properties suggest the effectiveness of the solid solution strengthening effect and provide new opportunities to further tailor the mechanical properties of the MAX phase ceramics.

The effect of LaB₆ on the densification and microstructure of pressure-less sintered 0.4B₄C–0.4SiC–0.2ZrB₂ ternary ceramic with eutectic composition was investigated. The Vickers hardness, bending strength, and fracture toughness of the quaternary ceramic were discussed based on the microstructural characteristics. The densification of the 0.4B₄C–0.4SiC–0.2ZrB₂ ceramic was enhanced with increasing LaB₆ content from 0 to 70 mol% (the proportion to B₄C–SiC–ZrB₂). When the LaB₆ content was 50 mol%, the densification rate of the composite ceramic reached a peak. The 0.27B₄C–0.27SiC–0.13ZrB₂–0.33LaB₆ quaternary composite ceramic has reached a density of over 95% after being sintered at 2 100°C for 1 h. The B₄C and SiC phases had refined grains of 1–3 µm with intragranular structures in the as-sintered ceramics. The hardness and strength reached 17.9 ± .8 GPa and 307 ± 38 MPa, respectively. Crack deflection and branching were ascribed to the improved fracture toughness of 3.78 ± .26 MPa·m^1/2. This study provides new ideas for fabricating dense non-oxide ceramic composites with enhanced properties.

The potential of electrochemical water splitting to tackle energy and environmental issues has garnered substantial interest. In the present work, an effective ZnS/In₂Te₃ has been constructed by hydrothermal support on a stainless-steel strip and explored for oxygen evolution. The addition of ZnS modifies the band structure of In₂Te₃ and enhances its specific conductivity and capacitance on an intrinsic level, making rapid ion transportation. The optimized ZnS/In₂Te₃ displayed efficient oxygen evolution reaction (OER) performance with an overpotential of 228 mV and a Tafel slope of 111 mV dec⁻¹ with cyclic activity up to 1000 cycles in 1 M KOH solution. ZnS/In₂Te₃ has a large surface area (28 m³g⁻¹) and a charge capacitance of (.037 mF), according to studies using Brunauer–Emmett–Teller and double-layer capacitance. Combining several strategies improves overall electrochemical performance of ZnS/In₂Te₃, making it a promising option for use in state-of-the-art OER.

Dysprosium (Dy)-doped (Y_1−xDy_x)₃Si₂C₂ (x = 0, 0.1, 0.3, 0.5) solid solution ceramics were successfully fabricated using an in situ reaction spark plasma sintering technology, for the first time. The effect of various Dy doping contents (x) on the microstructure, mechanical, and thermal properties of (Y_1−xDy_x)₃Si₂C₂ ceramics was investigated. The (0 2 0) crystal plane spacing of (Y_0.5Dy_0.5)₃Si₂C₂ was 7.813 Å, which was smaller than that of Y₃Si₂C₂, due to the fact that the atomic radius of Dy is smaller than that of Y. The Dy doping facilitated the consolidation of (Y_1−xDy_x)₃Si₂C₂, thus a highly dense (Y_0.5Dy_0.5)₃Si₂C₂ ceramic material with a low open porosity of 0.14% was successfully obtained at a relatively low temperature of 1 200°C. As the content of Dy doping (x) increased from 0 to 0.5, the purity of (Y_1−xDy_x)₃Si₂C₂ ceramics increased from 88.3 to 90.7 wt.%, while the grain size of (Y_1−xDy_x)₃Si₂C₂ ceramics decreased from 0.59 to 0.46 µm. As a result, the Vickers hardness and thermal conductivity of the (Y_0.5Dy_0.5)₃Si₂C₂ material was 7.1 GPa and 9.8 W·m⁻¹·K⁻¹, respectively.

Chromium–corundum, as a common refractory material, is broadly applied in high-temperature kilns due to its superior thermal stability and high melting point. Unfortunately, this refractory is susceptible to corrosion and destruction under extreme furnace conditions by chemical erosion, mechanical wear, and thermal shock, which significantly shortens its useful life. Accordingly, in recent years, the issue of how to improve the slag corrosion resistance, mechanical, and sintering properties of chromium–corundum refractories has aroused widespread attention. In this work, the corrosion behavior and application status of chromium–corundum refractories in Ausmelt furnace, waste incinerator, coal water slurry gasifier, and HImelt melting reduction furnace are analyzed and discussed. To improve the service life of chromium–corundum refractories, the enhancement method and mechanism of sintering performance, mechanical properties, slag corrosion resistance, and thermal shock resistance are also summarized. Finally, some suggestions and prospects are made for the enhancement and longevity of chromium–corundum refractories.

Although the residual stress in one-side coating (type-I coating) on a beam specimen can be determined by comparing the bending deformation before and after coating, the stress of a coated component without bending deformation (type-II coating) is difficult to obtain via conventional methods, especially at high temperature. An image relative method is presented to determine variations in the curvature radius with temperatures for stress analysis at high temperature. A relationship between the residual stresses in type-I and type-II coatings was established so that the residual stress of type-II coating was determined from the measured stress in type-I coating. Thus, the core issue is to measure the temperature dependence of the bending deformation of the sample with one-side coating. The temperature dependence of the residual stress in thermal barrier coatings on metal substrate was obtained by continuously photographing deflections of the beam specimen at temperatures ranging from 20°C to 1000°C, and the residual stress in components with symmetrical coatings in the temperature range was then determined.

Pyroplastic deformation is still an important defect caused during firing in the manufacture of porcelain tiles when there is no control over the raw materials used in the formulation of ceramic tiles. The present study used mixing design as a tool in the development of pastes formulations for Brazilian porcelain tile manufacturing in order to reduce their pyroplastic deformation. Ceramic industry in Brazil has typical and complex way to set up porcelain tile formulations, using regularly more than a dozen raw materials. Therefore, the originality in this work was understanding the formulation by means of a pseudocomponent-based approach (multiminerals triaxial diagram) and defining parameters that minimize that problem. Eleven different raw materials, supplied by Brazilian ceramic manufacturer, were used and characterized according to their physical–chemical properties. Later, raw materials were divided into three chemical categories and through a simplex-centroid mixture design, defining the maximum limit of feldspar in 70%, 10 formulations in the experimental region were defined. All formulations were analyzed for particle size distribution, bulk density (postpressing and postburning), mechanical strength (postpressing and postfiring), thermal shrinkage, water absorption, and pyroplastic deformation. Thus, formulations that presented the most admissible behavior in the manufacture of porcelain tiles were selected, and tests were carried out for chemical, mineralogical, thermal (differential scanning calorimeter [DSC]/thermogravimetric [TG]), thermal expansion, porosity analysis, and optical fleximeter (pyroplasticity). All results were analyzed using response surfaces with data obtained by analysis of variance (ANOVA). Mixture design method proved to be a valuable tool to observe the behavior of raw materials and to optimization of Brazilian porcelain tile formulations.