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Ytterbium aluminum garnet (Yb3Al5O12) is considered as a promising thermal barrier material. However, the main limitations of Yb3Al5O12 for thermal barrier applications are relative low thermal expansion coefficient and high thermal conductivity. In order to overcome these obstacles, herein, a new high entropy (Y0.2Yb0.2Lu0.2Eu0.2Er0.2)3Al5O12 ceramic was designed, and then powders and bulk were prepared through solid-state reaction method and spark plasma sintering (SPS), respectively. The thermal expansion coefficient of HE (Y0.2Yb0.2Lu0.2Eu0.2Er0.2)3Al5O12 is (8.54 ± 0.29) × 10−6 K-1 at 673 K–1273 K, which is about 9% higher than that of Yb3Al5O12. The thermal conductivity of HE (Y0.2Yb0.2Lu0.2Eu0.2Er0.2)3Al5O12 ceramic is 3.81 W·m-1 K-1 at 300 K, which is about 18 % lower than that of Yb3Al5O12. Moreover, there is no reaction between HE (Y0.2Yb0.2Lu0.2Eu0.2Er0.2)3Al5O12 and thermally grown (TG) Al2O3 even at 1600 °C. After annealing at 1590 °C for 18 h, the average grain size of HE (Y0.2Yb0.2Lu0.2Eu0.2Er0.2)3Al5O12 increases only from 1.56 μm to 2.27 μm. Close thermal expansion coefficient to TG Al2O3, low thermal conductivity, good phase stability, excellent chemical compatibility with TG Al2O3 and slow grain growth rate make HE (Y0.2Yb0.2Lu0.2Eu0.2Er0.2)3Al5O12 promising for thermal barrier applications.

Developing electromagnetic (EM) wave absorbing materials with low reflection coefficient and optimal operating frequency band is urgently needed on account of the increasingly serious EM pollution. However, the applications of common EM absorbing materials are encumbered by poor high-temperature stability, poor oxidation resistance, narrow absorption bandwidth or high density. Herein, the strong EM absorption capability and wide efficient absorption bandwidth of high entropy ceramics are reported for the first time, which are designed by a combination of the novel high entropy (HE) rare earth silicide carbides/rare earth oxides (RE3Si2C2/RE2O3). Three HE powders, i.e., HERSC-1 (HE (Tm0.2Y0.2Dy0.2Gd0.2Tb0.2)3Si2C2), HERSC-2 HE (Tm0.2Y0.2Pr0.2Gd0.2Dy0.2)3Si2C2/HE (Tm0.2Y0.2Pr0.2Gd0.2Dy0.2)2O3) and HERSC-3 (HE (Tm0.2Y0.2Pr0.2Gd0.2Tb0.2)3Si2C2/HE (Tm0.2Y0.2Pr0.2Gd0.2Tb0.2)2O3), are synthesized. Although HERSC-1 exhibits a limited absorption effect (the minimum reflection loss (RLmin) is -11.6 dB at 3.4 mm) and a relatively narrow effective absorption bandwidth (EAB) of 1.7 GHz, the optimal absorption RLmin value and EAB of HERSC-2 and HERSC-3 are -40.7 dB (at 2.9 mm), 3.4 GHz and-50.9 dB (at 2.0 mm), 4.5 GHz, respectively, demonstrating strong microwave absorption capability and wide absorption bandwidth. Considering the better stability, low density and strong EM absorption effect, HE ceramics are promising as a new type of EM absorbing materials.

Rare-earth tantalates and niobates (RE3TaO7 and RE3NbO7) have been considered as promising candidate thermal barrier coating (TBC) materials in next generation gas-turbine engines due to their ultra-low thermal conductivity and better thermal stability than yttria-stabilized zirconia (YSZ). However, the low Vickers hardness and toughness are the main shortcomings of RE3TaO7 and RE3NbO7 that limit their applications as TBC materials. To increase the hardness, high entropy (Y1/3Yb1/3Er1/3)3TaO7, (Y1/3Yb1/3Er1/3)3NbO7, and (Sm1/6Eu1/6Y1/6Yb1/6Lu1/6Er1/6)3(Nb1/2Ta1/2)O7 are designed and synthesized in this study. These high entropy ceramics exhibit high Vickers hardness (10.9–12.0 GPa), close thermal expansion coefficients to that of single-principal-component RE3TaO7 and RE3NbO7 (7.9×10−6-10.8×10−6C−1 at room temperature), good phase stability, and good chemical compatibility with thermally grown Al2O3, which make them promising for applications as candidate TBC materials.

Yttrium aluminum perovskite (YAlO3) is a promising candidate material for environmental barrier coatings (EBCs) to protect Al2O3f/Al2O3 ceramic matrix composites (CMCs) from the corrosion of high-temperature water vapor in combustion environments. Nevertheless, the relatively high thermal conductivity is a notable drawback of YAlO3 for environmental barrier coating application. Herein, in order to make REAlO3 more thermal insulating, a novel high-entropy rare-earth aluminate ceramic (Y0.2Nd0.2Sm0.2Eu0.2Er0.2)AlO3 was designed and synthesized. The as-prepared (Y0.2Nd0.2Sm0.2Eu0.2Er0.2)AlO3 ceramic possesses close thermal expansion coefficient (9.02 × 10―6 /oC measured from room temperature to 1200 °C) to that of Al2O3. The thermal conductivity of (Y0.2Nd0.2Sm0.2Eu0.2Er0.2) AlO3 at room temperature is 4.1 W·m−1 K−1, which is almost one third of the value of YAlO3. Furthermore, to effectively prevent the penetration of water vapor from possible pores/cracks of coating layer, which are often observed in T/EBCs, a tri-layer EBC system REAlO3/RE3Al5O12/(Al2O3f/Al2O3 CMCs) is designed. Close thermal expansion coefficient to Al2O3 and low thermal conductivity of (Y0.2Nd0.2Sm0.2Eu0.2Er0.2)AlO3, as well as the formation of dense garnet layer at (Y0.2Nd0.2Sm0.2Eu0.2Er0.2)AlO3/Al2O3 interface, indicate that this new type of high-entropy ceramic is suitable as a candidate environmental barrier coating material for Al2O3f/Al2O3 CMCs.

Sintering at high temperature is a serious problem for porous thermal insulating ceramics. To search for sintering-resistant ceramics, ZrP2O7 is selected as the backbone material and porous ZrP2O7 ceramics with 40−60 vol% porosities and strength of 3−14 MPa are fabricated. The volume shrinkage of the 60 vol% porosity ZrP2O7 is only 1.4 % when heated at 1773 K for 6 h and the thermal conductivity, which is as low as 0.18 W m-1 K-1, keeps almost unchanged. The dielectric constants are stable in the frequency range of 7−19 GHz when the temperature increases from 298 K to 1273 K. As the porosity increases from 44 % to 60 %, the dielectric constant at 19 GHz and 1273 K decreases from 3.4 to 2.5. Good sintering-resistance, ultra-low thermal conductivity and low dielectric constant at high temperatures make porous ZrP2O7 suitable for applications as thermal insulating and wave-transmitting materials at high temperatures.

Transpiration cooling technique is a reusable and high-efficiency thermal protection system (TPS), which is potential to improve the reusability and security of re-entry space vehicle. Relatively low density, high permeability and high porosity are general requirements for porous media of transpiration cooling systems. In this work, a new porous high entropy metal hexaboride (Y0.2Yb0.2Sm0.2Nd0.2Eu0.2)B-6 is designed and prepared by the in-situ reaction/partial sintering method. Two reaction routes are designed to synthesize (Y0.2Yb0.2Sm0.2Nd0.2Eu0.2)B-6, including boron thermal reduction and borocarbon thermal reduction. The as-prepared porous HE (Y0.2Yb0.2Sm0.2Nd0.2Eu0.2)B-6 ceramics possess homogeneous microstructure and exhibit low density, high porosity, high compressive strength and high permeability. The combination of these properties makes porous HE (Y0.2Yb0.2Sm0.2Nd0.2Eu0.2)B-6 promising as a candidate porous media for various transpiration cooling applications. (C) 2019 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Damage tolerant and easily machinable ceramics play important roles in the field of thermal sealing and insulation. Herein, a soft and machinable β-Zr2O(PO4)2 ceramic with excellent thermal shock resistance is reported through detailed investigation on its mechanical properties. β-Zr2O(PO4)2 exhibits low hardness (5.9 GPa), low Pugh’s ratio (G/B = 0.36) and good thermal shock resistance. It also can be machined by WC tools and tolerant to damage. The damage tolerance is demonstrated by the residual strength versus indentation load curve as well as the load-displacement curve during compression strength test. From the crystal structure point of view, the mechanism that underpins the damage tolerance of β-Zr2O(PO4)2 is the anisotropic chemical bonding within the crystal structure, which results in low and anisotropic shear deformation resistance. The possible slip systems of β-Zr2O(PO4)2 are (010)[100] and (100)[010].

Low thermal conductivity, matched thermal expansion coefficient and good compatibility are general requirements for the environmental/thermal barrier coatings (EBCs/TBCs) and interphases for Al2O3f/Al2O3 composites. In this work, a novel high-entropy (HE) rare-earth phosphate monazite ceramic (La0.2Ce0.2Nd0.2Sm0.2Eu0.2)PO4 is designed and successfully synthesized. This new type of HE rare-earth phosphate monazite exhibits good chemical compatibility with Al2O3, without reaction with Al2O3 as high as 1600 °C in air. Moreover, the thermal expansion coefficient (TEC) of HE (La0.2Ce0.2Nd0.2Sm0.2Eu0.2)PO4 (8.9 × 10-6/°C at 300–1000 °C) is close to that of Al2O3. The thermal conductivity of HE (La0.2Ce0.2Nd0.2Sm0.2Eu0.2)PO4 at room temperature is as low as 2.08 W·m-1·K-1, which is about 42% lower than that of LaPO4. Good chemical compatibility, close TEC to that of Al2O3, and low thermal conductivity indicate that HE (La0.2Ce0.2Nd0.2Sm0.2Eu0.2)PO4 is suitable as a candidate EBC/TBC material and an interphase for Al2O3f/Al2O3 composites.

ZrP2O7 is a promising material for high temperature insulating applications. However, decomposition above 1400 °C is the bottleneck that limiting its application at high temperatures. To improve the thermal stability, a novel multicomponent equimolar solid solution (TiZrHf)P2O7 was designed and successfully synthesized in this work inspired by high-entropy ceramic (HEC) concept. The as-synthesized (TiZrHf)P2O7 exhibits good thermal stability, which is not decomposed after heating at 1550 °C for 3 h. It also shows lower thermal conductivity (0.78 W m−1 K−1) compared to the constituting metal pyrophosphates TiP2O7, ZrP2O7 and HfP2O7. The combination of high thermal stability and low thermal conductivity renders (TiZrHf)P2O7 promising for high temperature thermal insulating applications.

Immune response to implantation materials plays a critical role during early local inflammation and biomaterial-induced regeneration or restoration. A novel platelet concentrate termed i-PRF (injectable platelet-rich fibrin) has recently been developed without any additives by low centrifugation speeds. To date, scientists have investigated the capability of releasing growth factors to improve regeneration but have ignored whether i-PRF can inhibit the inflammatory effect around the wound. The present study investigated the anti-inflammation effects of i-PRF on immune response-related cells, especially macrophages and dendric cells. We found that i-PRF reduced pro-inflammatory M1 phenotype of macrophages and activated dendritic cells around muscle defect that was injected with bacterial suspension. Moreover, in vitro experiments showed similar results. i-PRF deleted inflammatory response caused by lipopolysaccharide to some extent. We determined that TLR4, an activator of inflammatory stimulation and p-p65, a key factor belongs to classical inflammatory related NF-κB signal pathway, can be inhibited by use of i-PRF. Results indicate the potential anti-inflammatory role of i-PRF during regeneration and restoration.

The critical requirements for the environmental barrier coating (EBC) materials of silicon-based ceramic matrix composites (CMCs) include good tolerance to harsh environments, thermal expansion matches with the interlayer mullite, good high-temperature phase stability, and low thermal conductivity. Cuspidine-structured rare-earth aluminates RE4Al2O9 have been considered as candidates of EBCs for their superior mechanical and thermal properties, but the phase transition at high temperatures is a notable drawback of these materials. To suppress the phase transition and improve the phase stability, a novel cuspidine-structured rare-earth aluminate solid solution (Nd0.2Sm0.2Eu0.2Y0.2Yb0.2)4Al2O9 was designed and successfully synthesized inspired by entropy stabilization effect of high-entropy ceramics (HECs). The as-synthesized HE (Nd0.2Sm0.2Eu0.2Y0.2Yb0.2)4Al2O9 exhibits a close thermal expansion coefficient (6.96×10-6 K-1 at 300–1473 K) to that of mullite, good phase stability from 300 to 1473 K, and low thermal conductivity (1.50 W·m–1·K–1 at room temperature). In addition, strong anisotropic thermal expansion has been observed compared to Y4Al2O9 and Yb4Al2O9. The mechanism for low thermal conductivity is attributed to the lattice distortion and mass difference of the constituent atoms, and the anisotropic thermal expansion is due to the anisotropic chemical bonding enhanced by the large size rare-earth cations.