V2O5 Molten Salt Research Articles

Plasma-sprayed GNP/CNT reinforced lanthanum-cerate coatings: Hot corrosion assessment in Na2SO4-V2O5 environment

This study investigates the hot-corrosion behavior of Carbon nanotube/Graphene-nanoplatelets (CNT/GNP)-reinforced lanthanum cerate (LC) coatings in a Na2SO4–V2O5 molten salt environment at 1350 °C for varying durations. Coatings were prepared using APS and characterized using XRD, FESEM, Raman, XPS, etc., techniques. The CNT/GNP-reinforced LCGC hybrid composite coating exhibited superior hot-corrosion resistance compared to LC and LCG coatings. The uniform dispersion of GNPs/CNTs within the coating matrix and the creation of protective LC oxides enhanced corrosion resistance. These findings highlight the potential of GNP/CNT-reinforced coatings in protecting high-temperature components like combustion chambers and gas turbine engines from hot corrosion.

Degradation of atmospheric plasma sprayed Gd4Al2O9 coating attacked by molten Na2SO4+V2O5 salt mixture at 700–950 °C

In this work, investigation on degradation of the APS Gd4Al2O9 as a new coating against the 50 wt% Na2SO4+50 wt% V2O5 molten salt mixture at 700oC–950 °C for 2 h and 10 h has been conducted. Results indicate that the as-sprayed Gd4Al2O9 coating exhibited outstanding corrosion resistances. Factors related to higher Gd3+ cation ratio, Gd2O3 as a stronger basic oxide than Al2O3, Gd–O with larger chemical bond length and lower bond energy were responsible for a rapid formation of a continuous GdVO4 corrosion layer at any temperature level and corrosion duration. Amorphous phase with much reduced chemical bond strengths in the as-sprayed Gd4Al2O9 coating leading to a significantly reduced apparent porosity level but rather increased corrosion reaction speed played an important role in consuming and solidifying the molten salt mixture as fast as possible.

Hot corrosion mechanism and thermal cycling performance of air-plasma-sprayed LaYbZr2O7 thermal barrier coatings in the vanadate-containing molten salts

LaYbZr2O7 has been regarded as a promising thermal barrier coatings (TBC) material due to its excellent mechanical and thermal properties. In this study, the LaYbZr2O7 coating was prepared by atmospheric plasma spraying (APS), and its hot corrosion mechanism and thermal cycling performance in vanadate-containing molten salts (V2O5 and Na2SO4 + V2O5) were investigated. Results indicated the hot corrosion reaction of LaYbZr2O7 coatings in molten V2O5 was temperature dependent, attributed to the thermal decomposition of ZrV2O7 above 800 °C. A continuous dense corrosion layer could form on the top surface of LaYbZr2O7 coatings after hot corrosion in molten V2O5 salt, effectively preventing the further penetration of molten salt. However, the dense corrosion layer could not form when exposed to Na2SO4 + V2O5 molten salts at 1000 °C, since the formation of NaVO3 could improve the mobility of molten salts and slow the precipitation reaction rate of corrosion products. Furthermore, thermal cycling tests indicated that the Na2SO4 + V2O5 mixture could be more detrimental to LaYbZr2O7 coatings than single V2O5 salt, and the dense corrosion layer could act as a sacrifice layer to protect the inner coating from corrosion degradation. The hot corrosion mechanism of LaYbZr2O7 was discussed in detail based on the Lewis acid-base and dissolution-precipitation rule.

Phase evolution and hot corrosion behavior of Yb2O3 and CeO2 co-doping YSZ ceramics under high temperature

The phase instability of 6–8 wt% Y2O3 partially stabilized ZrO2 (YSZ) in high temperature and molten salt corrosion environment seriously limits its application above 1200 °C. In this study, the chemical co-precipitation method prepared Yb2O3 and CeO2 co-doping YSZ (YbCeYSZ) ceramic materials to improve the above issues. It was proposed to improve the defect of high-temperature phase instability of CeO2-doped YSZ materials by adding Yb2O3. The phase stability, thermal insulation properties, and Na2SO4 + V2O5 molten salt corrosion behavior of YbCeYSZ ceramic materials were studied. The results showed that 2.5 mol% Yb2O3-4 mol% CeO2-YSZ material (2.5Yb4CeYSZ) had no monoclinic phase (m-ZrO2) after holding at 1500 °C for 120 h due to forming more defect clusters in the system. Meanwhile, the 2.5Yb4CeYSZ had excellent thermal insulation performance and molten salt corrosion resistance, which was attributed to the strong phonon scattering in the 2.5Yb4CeYSZ material system and the low reactivity between the stabilizer and the corrosive salt.

Evaluation of Hot Corrosion Behavior of WC-Co-Cr Coatings Coated by the HVOF Method

Thermal spray coating techniques have wide-ranging applications in various fields, including marine, automotive, biomedical, and aerospace industries. These methods are popularly used because materials coated with thermal spray coatings exhibit excellent resistance to oxidation, erosion, corrosion, and abrasive environments, particularly at high temperatures. The present study utilized the high-speed oxy-fuel (HVOF) technique, a state-of-the-art thermal spray coating method, to apply a hard cermet ceramic coating material consisting of WC-Co-Cr onto a 316L stainless steel substrate. Isothermal hot corrosion tests were also conducted at 750°C in the presence of 45% Na2SO4 and 55% V2O5 hot corrosion salts for 1, 3, and 5 hours. Advanced characterization techniques such as X-Ray Diffractometry (XRD), Energy Dispersive Spectrum (EDS), scanning electron microscopy (SEM), and elemental mapping analysis devices were used to characterize the samples coated with the HVOF technique before and after hot corrosion tests. The findings indicate that WC-Co-Cr hard coatings, which are known for their high resistance to abrasion, sustain severe damage at high temperatures. The coating was damaged after 5 hours in the hot corrosion tests performed in the presence of V2O5 and Na2SO4 molten salt at 750°C.

Hot oxidation and corrosion behaviour of boiler steel fabricated by wire arc additive manufacturing

Boiler Steels undergo severe degradation in corrosion resistance due to oxide scale formation at elevated temperatures. In this study, the comparative hot oxidation and hot corrosion resistance of wire arc additive manufactured SS 308L (WAAM 308L) was examined in hot air and Na2SO4–60% V2O5 molten salt environments at 700 °C. The corrosion resistance at elevated temperature was analysed using thermo-kinetic curves, corrosion products, and morphology of the oxides. The hot oxidation kinetics revealed that WAAM processed SS 308L specimens has excellent resistance and the weight gain reached 3.10 mg/cm2 with thinner oxide scale formation. Hot corrosion kinetics of WAAM processed SS 308L specimens highlighted the higher weight gain (37.0 mg/cm2) in molten salt environment and is attributed to the acceleration of oxide scale formation by the salts at elevated temperatures. Also, the development of Ni3V2O8 and Fe2O3 along with the depletion of Cr2O3 significantly influenced the corrosion resistance at elevated temperatures. The findings of this study reveal the potential of WAAM to produce customized parts for high-temperature applications.

Hot Corrosion Behavior of Inconel 625 in Na2SO4 and V2O5 Molten Salt System

This study aimed to examine the corrosion behavior of Inconel 625 in a molten salt system of sodium sulfate and vanadium pentoxide at varying temperatures and durations. The corrosion products, microstructure, and element distribution of hot extruded Inconel in Na2SO4 and V2O5 molten salt systems were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS) analyses. This study demonstrates that corrosion of the alloy increases with time at a constant temperature. During the initial stage of corrosion, the surface of the alloy is primarily composed of a dense oxide layer consisting of Cr2O3 and NiO. However, after exposure to the salt bath for 24 h, a chemical reaction occurs between the alloy and vanadium (V), resulting in the formation of CrVO4 and Ni3V2O8. Furthermore, the intrusion of sulfur (S) element into the matrix leads to the formation of internal sulfides, including Ni-, Cr-, and Mo-based sulfides, which accelerate intergranular and intracrystalline corrosion. As the corrosion temperature rises, the surface microstructure of the corrosion layer transforms from powder to salt particles and then to massive particles. The corrosion products exhibit a clear stratification, while the alloy undergoes simultaneous oxidation and vulcanization processes.

Hot-Corrosion Behavior of Gd2O3–Yb2O3 Co-Doped YSZ Thermal Barrier Coatings in the Presence of V2O5 Molten Salt

In this study, thermal barrier coatings (TBC) consisting of 3.5 mol% Yb2O3-stabilized ZrO2 co-doped with 1 mol% Gd2O3 and 1 mol% Yb2O3 (referred to as GdYb-YSZ) were fabricated by means of air plasma spraying. The as-fabricated coatings exhibited a metastable tetragonal (t′) structure. The hot-corrosion behavior of the GdYb–YSZ TBCs was investigated at 700, 800, 900, and 1000 °C for 10 h in the presence of V2O5 molten salt. During the corrosion tests, the t′ phase transformed into a monoclinic (m) phase; nevertheless, it was still detected on the corroded surfaces. The amount of t′ phase decreased with increasing corrosion temperature. The corrosion products formed on the GdYb-YSZ TBCs in V2O5 comprised Yb, Gd-doped YVO4, and m-ZrO2, irrespective of the temperature of corrosion. However, higher temperatures changed the morphologies of the Yb- and Gd-doped YVO4 corrosion products. The GdYb–YSZ TBCs exhibited improved corrosion resistance to V2O5 molten salt when compared to YSZ TBCs, and the related mechanism is discussed in detail in this paper.

Hot corrosion behaviour of the γ‐Y2Si2O7 ceramic exposed to NaVO3 or V2O5 molten salt

AbstractThe hot corrosion behaviour of the γ‐Y2Si2O7 ceramic exposed to NaVO3 or V2O5 molten salt was studied at 1000–1300°C. YVO4 was identified as the corrosion product due to the chemical interaction of the two corrosive agents with the γ‐Y2Si2O7 ceramic. Although YVO4 produced in the two corrosion reactions had the same crystallographic structure, they had different morphologies. YVO4 produced by the corrosion of NaVO3 with the γ‐Y2Si2O7 ceramic showed a rod‐like shape, whereas it was particle‐shaped in the corrosion reaction of V2O5 with the γ‐Y2Si2O7 ceramic. Additionally, the degradation of γ‐Y2Si2O7 ceramic by V2O5 was more severe than that by NaVO3, and the thickness of the corrosion layer significantly increased with temperature. In this study, a model describing the formation of the corrosion product was established, and the formation of YVO4 with different morphologies in the two corrosion reactions was explained based on the growth characteristics of the YVO4 crystals.

Comparative investigation on the hot corrosion failure of YSZ and GdYb-YSZ double-ceramic-layer thermal barrier coatings under Na2SO4+V2O5 molten salts

The 5.2Gd2O3-5.6Yb2O3-9.5Y2O3 co-doped ZrO2 (GdYb-YSZ) double-ceramic-layer (DCL) thermal barrier coatings (TBCs) were prepared by atmospheric plasma spraying (APS) in this work. Hot corrosion behavior and failure mechanism of the APS GdYb-YSZ DCL and single-layer yttria partially stabilized zirconia (YSZ) TBCs under the Na2SO4+V2O5 molten salts were comparably investigated. The YSZ coating suffered from severe breakage after the hot corrosion test due to its poor corrosion resistance and easy infiltration by molten salts. In contrast, GdYb-YSZ DCL coating exhibited a better resistance to crack propagation and a significantly longer corrosion lifetime than the YSZ coating, which was attributed to the protective effect of the upper GdYb-YSZ layer. On the one hand, the superior phase stability of the GdYb-YSZ DCL coating could slow down the generation speed of phase transformation stress. On the other hand, the higher corrosion reaction rate of the upper GdYb-YSZ layer could suppress the further infiltration of molten salts into the inner TBCs, which improved the structural integrity of TBCs in corrosive environments.

Microstructure and hot corrosion performance of stainless steel 347 produced by wire arc additive manufacturing

The present work reports the feasibility of wire arc additive manufacturing (WAAM) process to manufacture SS 347 components for high temperature applications. The microstructure of WAAM processed SS 347 (WAAM 347) comprised of austenite and residual delta-ferrite while the ferrite fraction varied between 1.40 and 4.20% along the building direction. Cyclic hot corrosion behaviour of WAAM 347 specimens were investigated under the Na2SO4–60%V2O5 molten salt at 700 °C by measuring the weight change. Higher weight gain was noticed in the samples exposed to hot corrosion because of the deposition of molten salt mixture. X-ray diffraction results revealed the formation of oxides like Fe2O3, FeV2O4, and Ni3V2O8 while the presence of NiCr2O4 and Cr2O3 lowers the corrosion rate at elevated temperatures. The absence of spallation due to the good adherence of oxide-scales highlights that WAAM 347 structures are suitable for elevated temperature applications.

Comparison of Hot Corrosion Behavior of YSZ, YSZ/Mullite and YSZ/Mullite Gradient Coatings on Nickel Base Superalloy Prepared by Plasma Spray Method

Three types of thermal barrier coatings, namely NiCrAlY/YSZ double-layer, NiCrAlY/YSZ/mullite three-layer and NiCrAlY/YSZ/gradient of YSZ and mullite coatings, were deposited on a nickel-base superalloy using a plasma spray method. Hot corrosion studies of the plasma-sprayed thermal barrier coatings were conducted in 45wt% Na2SO4 + 55 wt% V2O5 molten salt at 1050 °C. Microstructure and morphology of the coatings were examined and compared by scanning electron microscopy and X-ray diffraction. The addition of mullite in thermal barrier coating results in the mullite phase reacting with corrosive salt and oxygen to form NaAlSiO4 phase. In addition to this phase, alumina (Al2O3) and Na2O phases are also formed. The presence of alumina phase (Al2O3) along with Na2O leads to formation of NaAlO2. A dense layer of NaAlO2 can increase the resistance to hot corrosion of the coating compared to YSZ coating.

Blocking effect in Nb-engineered high-entropy oxides with strengthened grain boundary corrosion resistance

Lanthanum-cerium oxide derived high-entropy ceramics have been verified to be promising thermal barrier coatings (TBCs) materials for the protection of hot-end components in high-performance aero-engines/gas turbines. However, the dissatisfactory hot corrosion resistance of TBCs to Na2SO4 + V2O5 molten salt from fuel exhaust is identified as a crucial bottleneck. Herein, a stabilization element Nb is introduced into typical high-entropy cerates to strengthen the corrosion resistance. When corroded, it favors an intermittent generation of spindle-shaped corrosion products at grain boundary and effectively blocks the further penetration of corrosion medium. Compared with other constituent elements, Nb in the as-designed material presents a weak adsorption energy (-0.43 eV) with the final reaction intermediate of corrosion medium (VO43-). It yields an anchoring effect to stabilize the pristine crystal structure. What’s more, the differential charge density of Ce is highly influenced by Nb, leading to a strong interaction with VO43-. With Ce tightly adsorbed around the corrosion products, it cooperatively hinders the further infiltration of molten salts. These findings provide an interesting insight into the rational design of superior corrosion-resistant high-entropy TBCs.

Structure and durability evaluation of blast furnace slag coatings and thermal barrier coatings (TBCs) under high temperature conditions

A high temperature aggressive environment is a great challenge for the long lifetime of thermal barrier coatings (TBCs). In this study, the hot corrosion and isothermal oxidation behavior of blast furnace slag (BFS) and yttria stabilized zirconia (YSZ) coated TBC systems were systematically investigated under high temperature conditions. This study aims to analyze the evaluation of microstructural properties of thermally sprayed CoNiCrAlY/BFS and CoNiCrAlY/YSZ coatings before and after high temperature oxidation and hot corrosion tests. For this purpose, the coatings were isothermally oxidized at 900 °C for 8, 24, 50, and 75 h. Hot corrosion behavior of CoNiCrAlY/BFS and CoNiCrAlY/YSZ coatings deposited on Inconel 718 superalloy substrates were studied at 900 °C in a Na2SO4 and V2O5 molten salt environment. CoNiCrAlY/BFS and CoNiCrAlY/YSZ TBC systems exposed to Na2SO4+ V2O5 molten salt at 900 °C investigate the hot corrosion behavior. The microstructure of coatings, formation of thermally grown oxide (TGO) layer, and degradation of coatings during isothermal oxidation and hot corrosion conditions were investigated. The oxidation and hot corrosion mechanisms were discussed. BFS, could be a potential alternative for the YSZ ceramic top coating in TBCs. The TBC system with BFS can be preferred for oxidation damage due to its low cost. YSZ and BFS TBCs are highly resistant to Na2SO4 and V2O5 molten salt environment.

A comparative study on the hot corrosion behavior of plasma sprayed Sm/Gd doped La2Zr2O7/YSZ and Sm and Gd co-doped La2Zr2O7/YSZ coatings

Gd2O3 and Sm2O3 co-doped LZ ceramic ((La0.5Gd0.25Sm0.25)2Zr2O7/YSZ) are designed and prepared by atmospheric plasma spraying (APS). It is the aim of this study to investigate the similarities and differences between co-doped sample and mono-doped samples, (La0.5Gd0.5)2Zr2O7/YSZ and (La0.5Sm0.5)2Zr2O7/YSZ on hot corrosion behaviors exposed to Na2SO4 + V2O5 molten salts. Thermodynamic calculations are used to predict the hot corrosion mechanism before experiments. Characterization and hot corrosion behavior are analyzed using X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM). Results indicate that the main hot corrosion products are composed of rare-earth vanadates ((La, Gd)VO4, (La, Sm)VO4 and (La, Gd, Sm)VO4, respectively) and ZrO2. After 10 h of corrosion, the reaction layer evolves into trilayered structure containing Zr-rich layer, V-rich layer and mixed-layer. The formation mechanism is discussed in detail. The co-doped sample exhibits excellent degradation resistance, which can be attributed to the higher entropy value. The formation of the particular trilayered structure occurs earlier in the co-doped sample, which also provides a role in reducing the degradation rate of ceramics.

Hot corrosion behavior of APS YSZ coatings treated by laser micro glazing (LMG) under molten salts (V2O5 +Na2SO4)

In this study, yttria-stabilized zirconia (YSZ) coatings prepared by atmospheric plasma spraying (APS) were glazed by a nanosecond pulsed laser (laser micro glazing, LMG). The hot corrosion mechanism of as-sprayed, ground, and LMGed YSZ coatings was investigated at a temperature of 1100 ºC in V2O5 and Na2SO4 molten salts for 20 h. The results show that a dense LMGed layer with narrow network of segmented microcracks (sub-micron level) was formed after the LMG process. Compared to the single-time LMG, pores can be effectively eliminated after six-times laser irradiation. The hot corrosion behavior of YSZ coatings exposed to molten V2O5 +Na2SO4 demonstrates that pores in the single-time LMGed layer seriously affect its hot corrosion resistance. After multiple LMG, the volume fraction of the m-ZrO2 decreases from 53% to 27% with the disappearance of pores. The quantity of the corrosion products YVO4 was greatly reduced and the depth of the damaged area diminished from 37.073 µm to 20.918 µm, which shows a significant improvement in molten salts corrosion resistance.

Degradation of CeO2 and TiO2 co-stabilized ZrO2 by the V2O5 molten salts and Na2SO4 + V2O5 molten salts

In this study, (Ce0.15Ti0.05)Zr0.80O2 (CTZ) with the tetragonal (t) phase was fabricated by solid-state reaction, and the destabilization resistance of CTZ ceramic was investigated in V2O5, and Na2SO4 + V2O5 molten salts, respectively. After CTZ was corroded in V2O5 molten salt at 700 °C for 2 h, ZrV2O7 and CeVO4 were formed, and the t phase was the main crystalline phase on the CTZ surface. After CTZ was corroded in V2O5 molten salt at 800 °C or 900 °C for 2 h, the amount of CeVO4 increased significantly, and CTZ surface underwent a more corrosion degradation than at 700 °C. After CTZ was corroded in Na2SO4 + V2O5 molten salts at 700 °C or 800 °C for 2 h, the hot corroded products were m-ZrO2 and CeVO4. However, after CTZ was corroded in Na2SO4 + V2O5 molten salts at 800 °C for 10 h or 900 °C for 2 h or 10 h, a new phase of CeO2 was formed due to the mineralization effect. The destabilization of CTZ ceramic under hot corrosion was mainly caused by the chemical interaction and phase transformation.

Hot corrosion behavior of dense CYSZ/YSZ bilayer coatings deposited by atmospheric plasma spray in Na2SO4 + V2O5 molten salts

In this work, the hot corrosion (HC) resistance of bilayer thermal barrier coatings (TBC) architectures composed of dense Ceria-Yttria Stabilized Zirconia (CYSZ) and Yttria-Stabilized Zirconia (YSZ) deposited using the Atmospheric Plasma Spray (APS) technique was evaluated. Two kinds of HC tests were performed using different salt concentrations and thermal cycling (adding fresh salt between cycles) with a constant salt mixture (Na 2 SO 4 -V 2 O 5 ) and constant testing temperature (900 °C). The results showed that the HC mechanism changes with the testing procedure, and the outer dense CYSZ layer acts as a barrier to protect the inner layers against HC degradation. However, the formation of vertical cracks during the coating deposition process affected the corrosion resistance of the TBC systems. • Dense CYSZ layer overlay increases the hot corrosion resistance of TBC system. • Mechanisms of coating's degradation were identified. • Vertical cracks reduce the hot corrosion resistance of the TBC system.

Hot corrosion product and corrosion layer evolution of La2(Zr0.75Ce0.25)2O7 coating exposed to vanadate-sulfate salts at 1050 °C

In this work, plasma-sprayed La2(Zr0.75Ce0.25)2O7 (LCZ) coatings were submitted to hot corrosion tests at 1050 °C in different molten salts: single V2O5 and V2O5 + Na2SO4 mixtures. Several analyses, including XRD, SEM and EDS were employed to characterize the corrosion product and corrosion layer. The hot corrosion behavior of LCZ coating depended on the molten salt. In single V2O5 molten salt, LCZ coatings were corroded for different durations. It was found that (La, Ce)VO4 and m-ZrO2 were formed on the coating surface, independent on duration. The thickness of the corrosion layer increased with increasing duration and then remained unchanged in single V2O5 molten salt. In the mixed V2O5 + Na2SO4 molten salts, the LCZ coating surface was partially corroded and only (La, Ce)VO4 was formed. The morphologies of (La, Ce)VO4 particles have an important relationship with Na2SO4 content. Moreover, the corroded zone can be divided into three layers based on the microstructure and chemical composition. A model which well described the formation mechanism was proposed. These results demonstrated that single V2O5 was more corrosive to LCZ coating than mixed V2O5 + Na2SO4 molten salts.

Degradation of Ceo2 and Tio2 Co-Stabilized Zro2 by the V2o5 Molten Salts and Na2so4 + V2o5 Molten Salts

Degradation of Ceo2 and Tio2 Co-Stabilized Zro2 by the V2o5 Molten Salts and Na2so4 + V2o5 Molten Salts