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1.
Lei Guo Chenglong Zhang Qing He Jianxing Yu Zheng Yan Fuxing Ye Chengyi Dan Vincent Ji 《Journal of the European Ceramic Society》2018,38(10):3555-3563
Ba2REAlO5 (RE?=?Dy, Er, Yb) powders were synthesized by a solid state reaction method, followed by cold pressing and sintering to produce pellets for hot corrosion tests. When exposed to V2O5?+?Na2SO4 molten salt at 900?°C and 1000?°C for 4?h and 20?h, REVO4, Ba3(VO4) 2 and BaAl2O4 formed as corrosion products due to chemical interactions between the ceramics and the molten salt, which were temperature and time independent. After the hot corrosion tests at 1000?°C, continuous, dense reaction layers with a thickness of ~80?μm formed on the sample surfaces, which had an effective function on suppressing further penetration of the molten salt. The hot corrosion mechanisms of Ba2REAlO5 are proposed based on Lewis acid-base rule, phase diagrams and thermodynamics. From a thermodynamics perspective, the molten salt directly reacting with Ba2REAlO5 is difficult compared with Yb2O3, Al2O3 and BaO. 相似文献
2.
《Ceramics International》2020,46(7):8543-8552
In order to evaluate the application prospects of NdYbZr2O7 as a novel TBC material, NdYbZr2O7 ceramic was synthesized via a solid-state reaction sintering method, and its hot corrosion behavior exposed to V2O5 and Na2SO4 + V2O5 molten salts at 900 °C, 1000 °C, and 1100 °C was comparatively investigated. For the V2O5 salt, the primary corrosion products were granular (Nd,Yb)VO4 as well as cube-like m-ZrO2. The corrosion layer consisted of two distinct layers, one of which was Zr-rich layer and another was V-rich layer. In the case of Na2SO4 + V2O5, NaVO3, as an intermediate product, played an important role in dissolving the NdYbZr2O7 ceramic. Herein, the (Nd,Yb)VO4 exhibited a rod/plate-like morphology, which could be attributed to the synergistic effect of low driving force and low nucleation rate. Since the molten salt infiltration rate was superior to the pore filling rate throughout the hot corrosion, the thickness of corrosion layer increased with the rise of temperature. The hot corrosion mechanisms of NdYbZr2O7 ceramic in various molten salts were discussed based on the phase diagram, Lewis acid-base rule and chemical thermodynamics. On this basis, the NdYbZr2O7 coating was prepared by atmospheric plasma spray (APS) and it exhibits a higher corrosion resistance compared to YSZ coating. 相似文献
3.
《Journal of the European Ceramic Society》2017,37(1):289-296
Calcium-magnesium-alumina-silicate (CMAS) attack has been considered as a significant failure mechanism for thermal barrier coatings (TBCs). As a promising series of TBC candidates, rare-earth phosphates have attracted increasing attention. This work evaluated the resistance characteristics of LnPO4 (Ln = Nd, Sm, Gd) compounds to CMAS attack at 1250 °C. Due to the chemical reaction between molten CMAS and LnPO4, a dense, crack-free reaction layer, mainly composed of Ca3Ln7(PO4)(SiO4)5O2 apatite, CaAl2Si2O8 and MgAl2O4, was formed on the surface of compounds, which had positive effect on suppressing CMAS infiltration. The depth of CMAS penetration in LnPO4 (Ln = Nd, Sm, Gd) decreased in the sequence of NdPO4, SmPO4 and GdPO4. GdPO4 had the best resistance characteristics to CMAS attack among the three compounds. The related mechanism was discussed based on the formation ability of apatite phase caused by the reaction between molten CMAS and LnPO4. 相似文献
4.
《Journal of the European Ceramic Society》2020,40(12):4101-4110
In this work we reported a new class of rare earth oxy-apatite, RE9.33(SiO4)6O2, with superior molten silicate resistant capability which shows promising application for thermal barrier coatings (TBCs). Three RE elements with different ion radius, i.e., Gd, Nd and La, were selected to prepare RE9.33(SiO4)6O2 bulk using co-precipitation and pressless-sintering. After 8-h CMAS attack at 1300 °C, the specimens exhibited a dense, continuous reprecipitated layer at RE-apatite/CMAS interface, which is predominantly controlled by a dissolution-reprecipitation mechanism distinguishing from the sacrificial material which is usually with reaction layer being formed. With an increase of ion radius, apatite is easier to crystallize in the melt. 相似文献
5.
《Ceramics International》2017,43(15):11944-11952
Hot corrosion behavior of Ba2REAlO5 (RE = Dy, Er, Yb) ceramics exposed to V2O5 molten salt at 900 °C and 1000 °C was investigated, providing a better understanding of their corrosion resistance as promising thermal barrier coatings. Obvious surface reactions occurred forming continuous, dense reaction layers on the top surfaces of the samples, the types of corrosion products being temperature and time independent. After heat treatment for 4 h and 20 h in V2O5 salt at the two temperatures, the corrosion products consisted of REVO4, Ba2REV3O11 and BaAl2O4 (RE = Dy, Er, Yb). Prolonged heat treatment and elevated temperature promoted the growth of Ba2REV3O11 and REVO4 grains. The reaction layer had a positive function on suppressing further penetration of the molten salt. The mechanism by which the corrosion reaction occurs is proposed based on Lewis acid-base rule, phase diagrams and thermodynamics. 相似文献
6.
Jinshuang Wang Luyao Chen Mengdi Chen Yuyang Wu Yinghui Wang Yongsheng Yu Junbin Sun Bing Liu Qiangshan Jing 《Ceramics International》2021,47(16):22965-22975
In this study, the destabilization resistance of Sc2O3 and CeO2 co-stabilized ZrO2 (SCZ) ceramics was tested in Na2SO4 + V2O5 molten salts at 750°C–1100 °C. The phase structure and microstructure evolution of the samples during the hot corrosion testing were analyzed with X-ray diffraction (XRD), Raman spectra, scanning electron microscopy (SEM), energy dispersive X-ray spectrum (EDS), and X-ray photoelectron spectroscopy (XPS). Results showed that the destabilization of SCZ ceramics at 750 °C was the result of the chemical reaction with V2O5 to produce m-ZrO2 and CeVO4, and little ScVO4 was detected in the Sc2O3-rich SCZ ceramics. The primary corrosion products at 900 °C and 1100 °C were CeO2 and m-ZrO2 due to the mineralization effect. The Sc2O3-rich SCZ ceramics exhibited excellent degradation resistance and phase stability owing to the enhanced bond strength and the decreased size misfit between Zr4+ and Sc3+. The destabilization mechanism of SCZ ceramic under hot corrosion was also discussed. 相似文献
7.
Kurusaroor Mana Manu Chinnathambi Karthik Lii‐Cherng Leu Kokken Anlin Lazar Rick Ubic Mailadil Thomas Sebastian 《Journal of the American Ceramic Society》2013,96(5):1504-1511
The crystal structure and microwave dielectric properties of apatite‐type LiRE9(SiO4)6O2 ceramics (RE = La, Pr, Nd, Sm, Eu, Gd, and Er) have been investigated. The densification of lithium apatites has been greatly improved with the addition of 1 wt% LiF. Selected area electron diffraction and X‐ray diffraction (XRD) Rietveld analysis confirm that these compounds belong to the P63/m (No. 176) space group with hexagonal crystal symmetry. The porosity‐corrected relative permittivity was found to decrease with decreasing ionic polarizability of RE3+ ions. Relationships between the structural parameters and microwave dielectric properties have been examined. The observed variation in the quality factor of LiRE9(SiO4)6O2 + 1 wt% LiF ceramics (RE = La, Pr, and Nd) was correlated with average cation covalency (%). The temperature coefficient of resonant frequency was found to depend on the bond valence sum of cations. LiEr9(SiO4)6O2 + 1 wt% LiF ceramics showed good microwave dielectric properties with εr = 12.8, Qu × f = 13000 GHz and τf = +17 ppm/°C. All the compositions showed low coefficient of thermal expansion with thermal conductivity in the range 1.3–2.8 W (m K)?1. 相似文献
8.
Lei Guo Zheng Yan Jianxing Yu Chenglong Zhang Mingzhu Li Fuxing Ye Vincent Ji 《Ceramics International》2018,44(1):261-268
3.5 mol% Yb2O3 stabilized zirconia (YbSZ) doped with 10 mol% TiO2 (Ti-YbSZ) was produced, and its hot corrosion behavior exposed to Na2SO4 + V2O5 molten salt was investigated. The as-fabricated ceramic mainly consists of metastable tetragonal (t′) phase. When exposed to the molten salt at 700 °C, 800 °C, 900 °C and 1000 °C for 2 h and 10 h, YbVO4 and m-ZrO2 formed as corrosion products due to chemical reactions between the ceramics and the salt. Ti4+ in Ti-YbSZ solid solution keeps stable during the hot corrosion tests, which acts as a stabilizer for ZrO2, preventing total decomposition of the t′ phase. After the hot corrosion tests, Ti-YbSZ has an apparently lower m phase content than Y2O3 doped Zirconia and YbSZ, indicative of better corrosion resistance. The hot corrosion mechanism of Ti-YbSZ is proposed based on Lewis acid-base rule, phase diagrams and thermodynamics. 相似文献
9.
《Ceramics International》2016,42(12):13849-13854
Sm2Zr2O7 and (Sm0.5Sc0.5)2Zr2O7 ceramics were fabricated by a chemical co-precipitation and calcination method, and their hot corrosion behaviors in Na2SO4+V2O5 molten salt were investigated. Hot corrosion tests were carried at 700 °C, 800 °C and 900 °C for 4 h, and corroded surfaces were investigated using X-ray diffractometer and scanning electron microscopy. The corrosion products of Sm2Zr2O7 ceramics were composed of SmVO4 and monoclinic-ZrO2, while those of (Sm0.5Sc0.5)2Zr2O7 ceramic consisted of SmVO4 and Zr5Sc2O13. Considering the fact that Zr5Sc2O13 is more desirable than monoclinic-ZrO2 for thermal barrier coating applications, (Sm0.5Sc0.5)2Zr2O7 showed better corrosion resistance to Na2SO4+V2O5 salt than Sm2Zr2O7. The hot corrosion mechanisms of Sm2Zr2O7 and (Sm0.5Sc0.5)2Zr2O7 in Na2SO4+ V2O5 salt were discussed in detail. 相似文献
10.
《Ceramics International》2020,46(3):2618-2623
Hot corrosion behavior of Yb2Si2O7 bulk exposed to NaVO3 molten salt was investigated at 1000–1500 °C for 2 h. Results showed that YbVO4 was produced on the bulk surface at 1000–1200 °C because of the acidity of the corrosion medium. The corrosion product of Yb2SiO5 was yielded at 1300–1500 °C due to the transformation of the corrosion medium from acidity to alkalinity. The content of YbVO4 in the products decreased as the temperature increased, while that of Yb2SiO5 increased with an increase in temperature. In this paper, various hot corrosion mechanisms of Yb2Si2O7 bulk exposed to NaVO3 molten salt are discussed based on the formation of YbVO4 and Yb2SiO5. 相似文献
11.
《Journal of the European Ceramic Society》2019,39(13):3778-3787
Corrosive attack of the molten 50 wt. % V2O5 + 50 wt.% Na2SO4 salt mixture has been comparably studied for the APS YSZ and LnMgAl11O19 (LnMA, Ln = Nd, Sm, Gd) thermal barrier coatings upon a 10 h anneal at 1100 °C in air. The YSZ coating suffered from a deepest infiltration of the molten salt along its thickness direction through the open and connected pores as well as inter-lamellae microcracks. A large number of newly formed voids were widely distributed in the YSZ coating due to the corrosion degradation followed by the t, t’ to m-ZrO2 phase transformation. While, a relative thin corrosion layer mainly consisting of α-Al2O3 and LnVO4 were present for the corroded LnMA coatings. The much reduced number of open pores and connected microcracks together with the rapid chemical reaction between the molten salt and LnMA coatings, especially for the NdMA coating, preventing further infiltration of the molten salt, was beneficial to mitigate further attacks to the inner coating at the expense of sacrificing a thinner top layer. The presences of amorphous phases were thought to further accelerate the corrosion reaction and strengthen such a corrosion protection mode for all the APS LnMA coatings. 相似文献
12.
《Ceramics International》2016,42(6):7360-7365
Y2O3 stabilized ZrO2 (YSZ) has been considered as the material of choice for thermal barrier coatings (TBCs), but it becomes unstable at high temperatures and its thermal conductivity needs to be further reduced. In this study, 1 mol% RE2O3 (RE=La, Nd, Gd, Yb) and 1 mol% Yb2O3 co-doped YSZ (1RE1Yb–YSZ) were fabricated to obtain improved phase stability and reduced thermal conductivity. For 1RE1Yb–YSZ ceramics, the phase stability of metastable tetragonal (t′) phase increased with decreasing RE3+ size, mainly attributable to the reduced driving force for t′ phase partitioning. The thermal conductivity of 1RE1Yb–YSZ was lower than that of YSZ, with the value decreasing with the increase of the RE3+ size mainly due to the increased elastic field in the lattice, but 1La1Yb–YSZ exhibited undesirably high thermal conductivity. By considering the comprehensive properties, 1Gd1Yb–YSZ ceramic could be a good potential material for TBC applications. 相似文献
13.
《Ceramics International》2017,43(10):7797-7803
Nanostructured GdPO4 coatings, designed as the outer layer of double-ceramic-layer thermal barrier coatings (DCL-TBCs), were produced by air plasma spraying (APS). The coatings have close chemical composition to that of the agglomerated particles used for thermal spray. Nanozones with porous structure are embedded in the coating microstructure, having a percentage of ~30%. Hot corrosion tests of the coatings were carried out in V2O5 and Na2SO4+V2O5 salts at 900 °C for 4 h. Results indicate that dense reaction layers, consisting of GdVO4 and Gd4(P2O7)3, form on the coating surfaces, which could suppress further penetration of the molten salts. In the V2O5 molten salt, the reaction layer is thicker and less molten salt trace could be found beneath the layer. 相似文献
14.
CaO–MgO–Al2O3–SiO2 (CMAS) corrosion behaviour of LaMgAl11O19/GdPO4 thermal barrier coating materials
《Ceramics International》2023,49(16):26578-26588
CaO–MgO–Al2O3–SiO2 (CMAS) corrosion poses serious hidden dangers for the application of thermal barrier coatings (TBCs). In this study, LaMgAl11O19 (LMA) and GdPO4 were mixed at molar ratios of 2:1, 1:1 and 1:2 to prepare LMA/GdPO4 materials, and the CMAS corrosion behaviours of these materials were investigated at 1300°C–1500 °C for 20 h and 40 h. It was demonstrated that temperature was the main factor influencing the corrosion behaviours and products. The materials were damaged at 1300 °C by the crystallization of CMAS melts to form CaAl2Si2O8. In contrast, the materials were corroded by CMAS melts via the reaction between CMAS and GdPO4 at 1500 °C. These results indicate that the addition of GdPO4 to LMA can improve the resistance of the LMA material to CMAS corrosion. 相似文献
15.
Zhanhui Peng Pengfei Liang Bi Chen Yichen Xiang Hui Peng Di Wu Xiaolian Chao Zupei Yang 《Ceramics International》2019,45(9):11899-11904
The molten salt method was adopted in this work to synthesize CdCu3Ti4O12 precursor powders and was found capable of notably reducing the sintering temperature. It was also found that the grain size gradually increases and the grain shape changes from spherical to cubic with increasing proportions of molten salt. The optimal sintering conditions were found to be at approximately 730?°C with the addition of 20% molten salt. After further sintering at 975?°C, the obtained perovskite ceramics exhibited a high dielectric constant at low frequencies. 相似文献
16.
《Ceramics International》2020,46(15):23629-23635
Cr3C2-NiCr/NiCrAlY coating was prepared by high velocity oxygen fuel (HVOF) spraying. The microstructure and the Na2SO4 hot corrosion behavior at different temperatures of the coating were investigated. The Na2SO4 hot corrosion mechanism of Cr3C2-NiCr coating was also discussed. The results showed that HVOF Cr3C2-NiCr coating was relatively dense and mainly composed of Cr3C2, NiCr and a small amount of Cr7C3 three phases. The dense Cr2O3 layer was formed on the surface of Cr3C2-NiCr coating after Na2SO4 corrosion at 750 °C to further prevent corrosion. The coating had produced the obvious longitudinal crack with the increase of hot corrosion temperature up to 900 °C. The corrosion mechanism of Cr3C2-NiCr coating against the Na2SO4 salt at high-temperature was as follows: firstly, the protective oxidizing film was formed at 750 °C, then the protective oxide film dissolved at the interface between the coating and Na2SO4 salt with the hot corrosion temperature increasing up to 900 °C, and subsequently the dissolved anions and cations could migrate to the interface between molten salt and air and the loose and unprotected oxides were regenerated, thereby exacerbating the failure of the coating. 相似文献
17.
《Journal of the European Ceramic Society》2005,25(6):793-799
Rare-earth silicon-oxynitride J-phases, Ln4Si2O7N2 (Ln=Y, La, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu), were prepared by the N2 gas-pressured sintering method at 1 MPa of N2 and 1500–1700 °C. The Rietveld analysis was carried out for X-ray powder diffraction data measured at room temperature. The crystal structures of Ln4Si2O7N2 were refined with the structure model of La4Si2O7N2 for Ln=La, Pr, Nd, and Sm, and with that of Lu4Si2O7N2 for Ln=Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. The refined monoclinic unit-cell parameters (lengths a, b, c, angles β, and volume V) increased linearly in their two series of Ln with increasing ionic radii of rare-earth atoms. Discontinuities of the unit-cell parameters were found between the two Ln series. 相似文献
18.
Mikito Kitayama Kiyoshi Hirao Koji Watari Motohiro Toriyama Shuzo Kanzaki 《Journal of the American Ceramic Society》2001,84(2):353-58
β-Si3 N4 ceramics sintered with a series of rare-earth (RE = La, Nd, Gd, Y, Yb and Sc) oxide additives were fabricated by hot pressing and subsequent annealing. Their microstructures, lattice oxygen contents, and thermal conductivities were evaluated. Mean grain size increased, while lattice oxygen content decreased, and hence, thermal conductivity increased with decreasing ionic radius of the rare-earth element. In all cases, a marked change was observed in the order of ionic radius from La to Nd to Gd, and a little change was observed below them. Rare-earth oxide additives significantly influenced the thermal conductivity of β-Si3 N4 , unlike in the case of AlN. 相似文献
19.
《Ceramics International》2020,46(13):21367-21377
In this work, Gd2Hf2O7 ceramics were synthesized and investigated as a potential thermal barrier coating (TBC) material. The phase composition, microstructure and associated thermal properties of Gd2Hf2O7 ceramics were characterized systematically. Results show that the thermal conductivity of Gd2Hf2O7 ceramics is 1.40 Wm−1K−1 at 1200 °C, ~25% lower than that of 8 wt% yttria partially stabilized zirconia (8YSZ). Gd2Hf2O7 ceramics also present large thermal expansion coefficients, which decrease from 12.0 × 10−6 K−1 to 11.3 × 10−6 K−1 (300–1200 °C). Besides, the hot corrosion behaviors of Gd2Hf2O7 ceramics exposed to V2O5 and Na2SO4 + V2O5 salts at temperatures of 900–1200 °C were discussed in great detail. We pay much attention on the corrosion process, corrosion mechanism and corrosion damage of Gd2Hf2O7 ceramics subjected to molten V2O5 and Na2SO4 + V2O5 salts at different temperatures. 相似文献
20.
Zicheng Wei Qingqing Yang Bin Meng Chen Li Xinyu Ping Congcong Fang Han Zhang 《International Journal of Applied Ceramic Technology》2023,20(4):2392-2400
Six rare-earth tantalate high-entropy ceramics of (5RE.2)Ta3O9 (RE represents any five elements selected from La, Ce, Nd, Sm, Eu, Gd) were designed and prepared by spark plasma sintering process at 1400°C in this study. The (5RE.2)Ta3O9 ceramics only consist of a single-phase solid solution with perovskite structure. Their relative densities are all above 90%, and the average grain size is in the range of 1.47–2.92 μm. The thermal conductivity of (5RE.2)Ta3O9 ceramics is in 2.24–1.90 W m−1 K−1 (25°C–500°C), which is much lower than that of yttria-stabilized zirconia. In six samples, (La.2Nd.2Sm.2Gd.2Eu.2)Ta3O9 possesses a thermal conductivity of 1.90 W m−1 K−1, a thermal expansion coefficient of 3.47 × 10−6 K−1 (500°C), a Vickers hardness of about 7.33 GPa, and a fracture toughness of about 5.20 MPa m1/2, which are suitable for its application as thermal barrier coatings. 相似文献