TY - JOUR
T1 - Improved thermal stability and infrared emissivity of high-entropy REMgAl11O19 and LaMAl11O19 (RE=La, Nd, Gd, Sm, Pr, Dy; M=Mg, Fe, Co, Ni, Zn)
AU - Zhu, Haolin
AU - Liu, Ling
AU - Xiang, Huimin
AU - Dai, Fu Zhi
AU - Wang, Xiaohui
AU - Ma, Zhuang
AU - Liu, Yanbo
AU - Zhou, Yanchun
N1 - Publisher Copyright:
© 2021
PY - 2022/3/30
Y1 - 2022/3/30
N2 - LaMgAl11O19 (LMA), characterized by high melting point, low density and thermal conductivity as well as good infrared emissivity, is regarded as a potential candidate for the thermal protection of hypersonic vehicles. Nevertheless, the unsatisfied phase stability at high temperature results in declining of the emissivity below 6 μm, which limits the extensive applications of LaMgAl11O19. In order to overcome this obstacle, three dense bulk high-entropy ceramics, (La0.2Nd0.2Gd0.2Sm0.2Pr0.2)MgAl11O19 (HE LMA-1), (La0.2Nd0.2Gd0.2Sm0.2Dy0.2)Mg Al11O19 (HE LMA-2) and La(Mg0.2Fe0.2Co0.2Ni0.2Zn0.2)Al11O19 (HE LMA-3), were designed and successfully prepared through solid state reaction at 1700 °C for 4 h in one step. XRD analyses show that the phase compositions of HE LMA-1, HE LMA-2 and HE LMA-3 are single-phase solid solutions with the relative density of 95.61%, 95.49% and 94.31%, respectively. Heat treatment experiments demonstrate that the phase composition of HE LMA-1 remains a single phase after high-temperature heating, while second phase appears in other two samples. The stability of HE LMA-1 is attributed to small average size difference δ (∼4%) of constitute elements. Intriguingly, the average emissivity of HE LMA-1 in the range of 3–6 μm reaches 0.9, which is significantly higher than that of LMA and other two HE LMA samples. The emissivity of all samples remains above 0.95 from 6 to 10 μm. In the far infrared region (10–14 μm), although the emissivity of these specimens decreases slightly, it still exceeds 0.85. The UV–Vis absorption spectra indicate that the formation of many discrete impurity energy levels with small intervals in HE LMA-1 promotes the f electrons to transit between adjacent impurity energy levels and conduction band, which enhances the infrared emission of HE LMA-1 below 6 μm. In a word, with improved phase stability and thermal emissivity in infrared range, high-entropy REMgAl11O19, especially (La0.2Nd0.2Gd0.2Sm0.2Pr0.2)MgAl11O19 (HE LMA-1), is a promising candidate in thermal protection coatings of hypersonic vehicles.
AB - LaMgAl11O19 (LMA), characterized by high melting point, low density and thermal conductivity as well as good infrared emissivity, is regarded as a potential candidate for the thermal protection of hypersonic vehicles. Nevertheless, the unsatisfied phase stability at high temperature results in declining of the emissivity below 6 μm, which limits the extensive applications of LaMgAl11O19. In order to overcome this obstacle, three dense bulk high-entropy ceramics, (La0.2Nd0.2Gd0.2Sm0.2Pr0.2)MgAl11O19 (HE LMA-1), (La0.2Nd0.2Gd0.2Sm0.2Dy0.2)Mg Al11O19 (HE LMA-2) and La(Mg0.2Fe0.2Co0.2Ni0.2Zn0.2)Al11O19 (HE LMA-3), were designed and successfully prepared through solid state reaction at 1700 °C for 4 h in one step. XRD analyses show that the phase compositions of HE LMA-1, HE LMA-2 and HE LMA-3 are single-phase solid solutions with the relative density of 95.61%, 95.49% and 94.31%, respectively. Heat treatment experiments demonstrate that the phase composition of HE LMA-1 remains a single phase after high-temperature heating, while second phase appears in other two samples. The stability of HE LMA-1 is attributed to small average size difference δ (∼4%) of constitute elements. Intriguingly, the average emissivity of HE LMA-1 in the range of 3–6 μm reaches 0.9, which is significantly higher than that of LMA and other two HE LMA samples. The emissivity of all samples remains above 0.95 from 6 to 10 μm. In the far infrared region (10–14 μm), although the emissivity of these specimens decreases slightly, it still exceeds 0.85. The UV–Vis absorption spectra indicate that the formation of many discrete impurity energy levels with small intervals in HE LMA-1 promotes the f electrons to transit between adjacent impurity energy levels and conduction band, which enhances the infrared emission of HE LMA-1 below 6 μm. In a word, with improved phase stability and thermal emissivity in infrared range, high-entropy REMgAl11O19, especially (La0.2Nd0.2Gd0.2Sm0.2Pr0.2)MgAl11O19 (HE LMA-1), is a promising candidate in thermal protection coatings of hypersonic vehicles.
KW - High-entropy ceramics
KW - Infrared emissivity
KW - LaMgAlO
KW - Thermal stability
KW - UV-Vis absorption
UR - http://www.scopus.com/inward/record.url?scp=85115014481&partnerID=8YFLogxK
U2 - 10.1016/j.jmst.2021.06.068
DO - 10.1016/j.jmst.2021.06.068
M3 - Article
AN - SCOPUS:85115014481
SN - 1005-0302
VL - 104
SP - 131
EP - 144
JO - Journal of Materials Science and Technology
JF - Journal of Materials Science and Technology
ER -