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Open Access Research Article Issue
Xenotime-type high-entropy (Dy1/7Ho1/7Er1/7Tm1/7Yb1/7Lu1/7Y1/7)PO4: A promising thermal/environmental barrier coating material for SiCf/SiC ceramic matrix composites
Journal of Advanced Ceramics 2023, 12 (5): 1033-1045
Published: 10 April 2023
Downloads:402

Rare-earth phosphates (REPO4) are regarded as one of the promising thermal/environmental barrier coating (T/EBC) materials for SiCf/SiC ceramic matrix composites (SiC-CMCs) owing to their excellent resistance to water vapor and CaO–MgO–Al2O3–SiO2 (CMAS). Nevertheless, a relatively high thermal conductivity (κ) of the REPO4 becomes the bottleneck for their practical applications. In this work, novel xenotime-type high-entropy (Dy1/7Ho1/7Er1/7Tm1/7Yb1/7Lu1/7Y1/7)PO4 (HE (7RE1/7)PO4) has been designed and synthesized for the first time to solve this issue. HE (7RE1/7)PO4 with a homogeneous rare-earth element distribution exhibits high thermal stability up to 1750 ℃ and good chemical compatibility with SiO2 up to 1400 ℃. In addition, the thermal expansion coefficient (TEC) of HE (7RE1/7)PO4 (5.96×10−6−1 from room temperature (RT) to 900 ℃) is close to that of the SiC-CMCs. What is more, the thermal conductivities of HE (7RE1/7)PO4 (from 4.38 W·m−1·K−1 at 100 ℃ to 2.25 W·m−1·K−1 at 1300 ℃) are significantly decreased compared to those of single-component REPO4 with the minimum value ranging from 9.90 to 4.76 W·m−1·K−1. These results suggest that HE (7RE1/7)PO4 has the potential to be applied as the T/EBC materials for the SiC-CMCs in the future.

Open Access Research Article Issue
Maximizing the mechanical performance of Ti3AlC2-based MAX phases with aid of machine learning
Journal of Advanced Ceramics 2022, 11 (8): 1307-1318
Published: 29 June 2022
Downloads:175

Mechanical properties consisting of the bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, etc., are key factors in determining the practical applications of MAX phases. These mechanical properties are mainly dependent on the strength of M-X and M-A bonds. In this study, a novel strategy based on the crystal graph convolution neural network (CGCNN) model has been successfully employed to tune these mechanical properties of Ti3AlC2-based MAX phases via the A-site substitution (Ti3(Al1-xAx)C2). The structure-property correlation between the A-site substitution and mechanical properties of Ti3(Al1-xAx)C2 is established. The results show that the thermodynamic stability of Ti3(Al1-xAx)C2 is enhanced with substitutions A = Ga, Si, Sn, Ge, Te, As, or Sb. The stiffness of Ti3AlC2 increases with the substitution concentration of Si or As increasing, and the higher thermal shock resistance is closely associated with the substitution of Sn or Te. In addition, the plasticity of Ti3AlC2 can be greatly improved when As, Sn, or Ge is used as a substitution. The findings and understandings demonstrated herein can provide universal guidance for the individual synthesis of high-performance MAX phases for various applications.

Open Access Research Article Issue
In situ reduced MXene/AuNPs composite toward enhanced charging/discharging and specific capacitance
Journal of Advanced Ceramics 2021, 10 (5): 1061-1071
Published: 16 September 2021
Downloads:111

In this work, gold nanoparticles (AuNPs) decorated Ti3C2Tx nanosheets (MXene/AuNPs composite) are fabricated through a self-reduction reaction of Ti3C2Tx nanosheets with HAuCl4 aqueous solution. The obtained composite is characterized as AuNPs with the diameter of about 23 nm uniformly dispersing on Ti3C2Tx nanosheets without aggregation. The composite (MXene decorated on 4.8 wt% AuNPs) is further employed to construct supercapacitor for the first time with a higher specific capacitance of 278 F·g-1 at 5 mV·s-1 than that of pure Ti3C2Tx and 95% of cyclic stability after 10,000 cycles. Furthermore, MXene/AuNPs composite symmetric supercapacitor with filter paper as separator and H2SO4 as electrolyte, is assembled. The supercapacitor exhibits a high volumetric energy density of 8.82 Wh·L-1 at a power density of 264.6 W·L-1 and ultrafast-charging/ discharging performance. It exhibits as a promising candidate applied in integrated and flexible supercapacitors.

Research Article Issue
All-inorganic dual-phase halide perovskite nanorings
Nano Research 2020, 13 (11): 2994-3000
Published: 20 July 2020
Downloads:27

In the present work, we report the growth of all-inorganic perovskite nanorings with dual compositional phases of CsPbBr3 and CsPb2Br5 via a facile hot injection process. The self-coiling of CsPbBr3-CsPb2Br5 nanorings is driven by the axial stress generated on the outside surface of the as-synthesized nanobelts, which results from the lattice mismatch during the transformation of CsPbBr3 to CsPb2Br5. The tailored growth of nanorings could be achieved by adjusting the key experimental parameters such as reaction temperature, reaction time and stirring speed during the cooling process. The photoluminescence intensity and quantum yield of nanorings are higher than those of CsPbBr3 nanobelts, accompanied by a narrower full width at half maximum (FWHM), suggesting their high potential for constructing self-assembled optoelectronic nanodevices.

Open Access Research Article Issue
Physical and mechanical properties of hot-press sintering ternary CM2A8 (CaMg2Al16O27) and C2M2A14 (Ca2Mg2Al28O46) ceramics
Journal of Advanced Ceramics 2018, 7 (3): 229-236
Published: 10 October 2018
Downloads:30

The new ternary CM2A8 (CaMg2Al16O27) and C2M2A14 (Ca2Mg2Al28O46) pure and dense ceramics were first prepared by a hot-press sintering technique, and their physical and mechanical properties were investigated. The purity of obtained CM2A8 and C2M2A14 ceramics reaches 98.1 wt% and 97.5 wt%, respectively. Their microstructure is dense with few observable pores, and their grain size is about a few dozen microns. For their physical properties, the average apparent porosity of CM2A8 and C2M2A14 ceramics is 0.18% and 0.13%, and their average bulk density is 3.66 g/cm3 and 3.71 g/cm3, respectively. The relative density of CM2A8 ceramic is 98.12% and that of C2M2A14 ceramic is 98.67%. The thermal expansivity (50–1400 ℃) of CM2A8 and C2M2A14 ceramics is 9.24×10–6 K–1 and 8.92×10–6 K–1, respectively. The thermal conductivity of CM2A8 and C2M2A14 ceramic is 21.32 W/(m·K) and 23.25 W/(m·K) at 25 ℃ and 18.76 W/(m·K) and 19.42 W/(m·K) as temperature rises to 350 ℃, respectively. In addition, the mechanical properties are also achieved. For CM2A8 ceramic, the flexural strength is 248 MPa, the fracture toughness is 2.17 MPa·m1/2, and the Vickers hardness is 12.26 GPa. For C2M2A14 ceramic, the flexural strength is 262 MPa, the fracture toughness is 2.23 MPa·m1/2, and the Vickers hardness is 12.95 GPa.

Open Access Research Article Issue
Synthesis of Al4SiC4 powders via carbothermic reduction: Reaction and grain growth mechanisms
Journal of Advanced Ceramics 2017, 6 (4): 351-359
Published: 19 December 2017
Downloads:17

Highly pure Al4SiC4 powders were prepared by carbothermic reduction at 2173 K using Al2O3, SiO2, and graphite as raw materials. The obtained Al4SiC4 powders owned hexagonal plate-like grains with a diameter of about 200-300 μm and a thickness of about 2-6 μm. Based on the experimental results, the reaction of Al4SiC4 formation and grain evolution mechanisms were determined from thermodynamic and first-principles calculations. The results indicated that the synthesis of Al4SiC4 by the carbothermic reduction consisted of two parts, i.e., solid-solid reactions initially followed by complex gas-solid and gas-gas reactions. The grain growth mechanism of Al4SiC4 featured a two-dimensional nucleation and growth mechanism. The gas phases formed during the sintering process favored the preferential grain growth of (0010) and (11¯0) planes resulting in formation of hexagonal plate-like Al4SiC4 grains.

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