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Ni-containing SiOC bulk ceramics have been prepared by spark plasma sintering at 1300 °C from polysiloxane at Ar atmosphere in the present work. The microstructure and properties of SiOC ceramics with different Ni content were studied. The resultant Ni-containing SiOC ceramics consists of in situ formed turbostractic layer carbon, CNTs (C nanotubes) and SiC crystals which dispersed in the SiOC matrix. With increasing content of Ni, the Ni-containing SiOC ceramics displayed less porosity. And the increasing Ni improved the mechanical, thermal and friction properties of SiOC ceramics. Ni-containing SiOC ceramics developed a carbon friction layer, which enhanced abrasion resistance to provide friction materials with stable friction coefficients and low abrasion values. A decrease in wear mass, from 2.06 to 0.18 mg was observed as the Ni content increasing from 0 to 2 wt%. The primary wear mechanisms of SiOC ceramics were recognized as abrasive wear, fatigue wear, and adhesion wear. [ABSTRACT FROM AUTHOR]

Ni-containing SiOC bulk ceramics have been prepared by spark plasma sintering at 1300 °C from polysiloxane at Ar atmosphere in the present work. The microstructure and properties of SiOC ceramics with different Ni content were studied. The resultant Ni-containing SiOC ceramics consists of in situ formed turbostractic layer carbon, CNTs (C nanotubes) and SiC crystals which dispersed in the SiOC matrix. With increasing content of Ni, the Ni-containing SiOC ceramics displayed less porosity. And the increasing Ni improved the mechanical, thermal and friction properties of SiOC ceramics. Ni-containing SiOC ceramics developed a carbon friction layer, which enhanced abrasion resistance to provide friction materials with stable friction coefficients and low abrasion values. A decrease in wear mass, from 2.06 to 0.18 mg was observed as the Ni content increasing from 0 to 2 wt%. The primary wear mechanisms of SiOC ceramics were recognized as abrasive wear, fatigue wear, and adhesion wear. [ABSTRACT FROM AUTHOR]

SiHfOC ceramics with different Hf contents were prepared by the sol-gel method using polymethylsilsesquioxane and HfOCl 2 ·8H 2 O as the raw materials. The high-temperature structural evolution of the SiHfOC ceramics with different Hf contents was investigated under an inert atmosphere. The results showed that Hf existed in the free state in the SiHfOC precursors with Hf:Si atomic ratios of 0.05 and 0.1. When the Hf:Si ratio was increased to 0.2, Hf was bridged in the SiOC network to form Si–O–Hf bonds, which changed the pyrolysis behavior of the ceramics and improved the ceramic yield. Further, the formation of Si–O–Hf bonds promoted the uniform dispersion of HfO 2 nanocrystals inside the ceramic, which further inhibited carbothermal reduction and increased the thermal stability of the SiHfOC ceramics. [ABSTRACT FROM AUTHOR]

Continuous carbon fiber reinforced SiOC composites (C/SiOC) show promise for high-temperature application. Whereas, the high temperature resistances of SiOC ceramic matrix and carbon fiber are mismatched, which significantly restricts the long-term application of C/SiOC composites at high temperatures above 1250 °C. In this paper, heterogeneous element Y was introduced in C/SiOC composite by taking Y-doped MK resin as raw material to modify the structure of the SiOC ceramic matrix. Characteristics and high temperature evolution behaviors of SiYOC ceramic matrix in the inert environment were investigated. The microstructure, mechanical properties and high-temperature evolution of C/SiYOC composites were analyzed. The density, flexural strength and fracture toughness of the as-fabricated C/SiYOC composites were 1.89 g/cm3, 261.7 MPa and 13.54 MPa•m1/2, respectively. In the process of high-temperature treatment, the mechanical properties of C/SiYOC composites decreased obviously at 1500 °C due to the decomposition of SiYOC ceramics matrix and the carbothermal reductions between matrix and fibers. [ABSTRACT FROM AUTHOR]

Silicon oxycarbide (SiOC) ceramics has been prepared by polymethylsilsesquioxane (MK silicon resin) under inert environment at 1000 °C in the present work. The evolution behavior of compositions and structures of MK silicon resin derived SiOC ceramics at high temperatures in different environments were studied systematically. It was found that in inert environment, the rearrangement of Si–C and Si–O bonds took place at 1200 °C–1500 °C and the carobothermal reductions of SiOC ceramics were activated at 1500 °C. While in reduced pressure environment, lower pressure reduced the activation temperature of carbothermal reductions to 1400 °C. In air environment, partial Si[(O,C) 4 ] network oxidation and free carbon oxidation occurred at high temperatures, which would generate a large amount of SiO 2 and played a protective role in the interior of SiOC ceramics. [ABSTRACT FROM AUTHOR]

Polymer-derived Silicon oxycarbide (SiOC) and yttrium-containing silicon oxycarbide (SiYOC) ceramics were obtained in the present work. To investigate their high temperature behaviors in low pressure atmosphere, these ceramics were further annealed at 1200 °C, 1300 °C, 1400 °C, and 1500 °C. The structure evolutions of SiOC and SiYOC ceramics through heat-treatment were studied. It was found that the carbothermal reductions of SiOC ceramics were activated at 1400 °C and almost finished at 1500 °C. The introduction of Y element played a major role on high temperature stability by influencing the structure evolution of SiOC and hindering the carbothermal reductions. The results show that introducing yttrium to modify the SiOC structure should be an effective way to enhance the thermal stability of SiOC ceramics. [ABSTRACT FROM AUTHOR]

Abstract To protect thermal barrier coatings (TBCs) from calcium-magnesium-alumina-silicate (CMAS) attack, depositing a protective layer has been a promising approach. In this study, a MAX phase compound, Ti 2 AlC, is found to highly resist to CMAS attack, which could be a candidate material for the protective layer. The interaction between Ti 2 AlC pellets and molten CMAS at 1250 °C for 0.5 h, 2 h and 8 h was investigated. Exposed to CMAS melt for 0.5 h, a dense Al 2 O 3 film formed on the surface, accompanied by Al and Ti migrating to the melt. The accumulation of Al and Ti in CMAS triggered its crystallization, forming anorthite and melilite phases. The Al 2 O 3 film and the crystallization of the melt significantly suppressed the CMAS penetration. The film and crystals grew with the heat time. By comparison, some pre-oxidized Ti 2 AlC pellets were also exposed to CMAS attack at 1250 °C. The CMAS on the pre-oxidized pellets only precipitated CaAl 2 Si 2 O 8 anorthite crystals, which exhibited much lower sizes than those in the non-oxidized samples. Also, the pre-oxidized pellets were highly resistant to CMAS penetration. [ABSTRACT FROM AUTHOR]

3.5 mol% Yb 2 O 3 stabilized zirconia (YbSZ) doped with 10 mol% TiO 2 (Ti-YbSZ) was produced, and its hot corrosion behavior exposed to Na 2 SO 4 + V 2 O 5 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, YbVO 4 and m-ZrO 2 formed as corrosion products due to chemical reactions between the ceramics and the salt. Ti 4+ in Ti-YbSZ solid solution keeps stable during the hot corrosion tests, which acts as a stabilizer for ZrO 2 , preventing total decomposition of the t′ phase. After the hot corrosion tests, Ti-YbSZ has an apparently lower m phase content than Y 2 O 3 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. [ABSTRACT FROM AUTHOR]

Hot corrosion behavior of Ba 2 REAlO 5 (RE = Dy, Er, Yb) ceramics exposed to V 2 O 5 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 V 2 O 5 salt at the two temperatures, the corrosion products consisted of REVO 4 , Ba 2 REV 3 O 11 and BaAl 2 O 4 (RE = Dy, Er, Yb). Prolonged heat treatment and elevated temperature promoted the growth of Ba 2 REV 3 O 11 and REVO 4 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. [ABSTRACT FROM AUTHOR]

1 mol% Gd 2 O 3 and 1 mol% Yb 2 O 3 co-doped 3.5 mol% Y 2 O 3 stabilized ZrO 2 (GdYb-YSZ) ceramics in metastable tetragonal (t′) structure were fabricated, and their hot corrosion behaviors were evaluated. The corrosion tests were performed at 700 °C, 800 °C, 900 °C and 1000 °C for 4 h in the presence of Na 2 SO 4 +V 2 O 5 molten salt. After corrosion, t′ phase could still be detected on the corroded surfaces and its content decreased with increasing the corrosion temperature. The corrosion products were composed of doped YVO 4 and m-ZrO 2 , but some amounts of Na 4 V 2 O 7 were found at low corrosion temperatures (700 °C and 800 °C). The corrosion resistance characteristic of GdYb-YSZ was compared with that of YSZ. Under an identical corrosion condition, GdYb-YSZ had less monoclinic phase formed, indicative of a better hot corrosion resistance. The hot corrosion mechanism was discussed in detail. [ABSTRACT FROM AUTHOR]

3.5 mol% Er 2 O 3 stabilized ZrO 2 (ErSZ) and Gd 2 Zr 2 O 7 powders were produced by a chemical co-precipitation and calcination method, and ErSZ was used to toughen Gd 2 Zr 2 O 7 . The phase structure, toughness and thermal conductivities of ErSZ toughened Gd 2 Zr 2 O 7 ceramics were investigated. When the ErSZ content was below 15 mol%, the compound consisted of pyrochlore phase, the ordering degree of which decreased with the increase of the ErSZ content. High ErSZ doping led to the formation of metastable tetragonal (t′) phase in the compound. The addition of ErSZ in Gd 2 Zr 2 O 7 benefited its toughness, mainly attributable to the presence of t′ phase in the compound. With the increase of the ErSZ content in the compound, the thermal conductivity first decreased and then showed an upward tendency, and 10 mol% ErSZ toughened Gd 2 Zr 2 O 7 exhibited the lowest thermal conductivity. [ABSTRACT FROM AUTHOR]

Sm 2 Zr 2 O 7 and (Sm 0.5 Sc 0.5 ) 2 Zr 2 O 7 ceramics were fabricated by a chemical co-precipitation and calcination method, and their hot corrosion behaviors in Na 2 SO 4 +V 2 O 5 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 Sm 2 Zr 2 O 7 ceramics were composed of SmVO 4 and monoclinic-ZrO 2 , while those of (Sm 0.5 Sc 0.5 ) 2 Zr 2 O 7 ceramic consisted of SmVO 4 and Zr 5 Sc 2 O 13 . Considering the fact that Zr 5 Sc 2 O 13 is more desirable than monoclinic-ZrO 2 for thermal barrier coating applications, (Sm 0.5 Sc 0.5 ) 2 Zr 2 O 7 showed better corrosion resistance to Na 2 SO 4 +V 2 O 5 salt than Sm 2 Zr 2 O 7 . The hot corrosion mechanisms of Sm 2 Zr 2 O 7 and (Sm 0.5 Sc 0.5 ) 2 Zr 2 O 7 in Na 2 SO 4 + V 2 O 5 salt were discussed in detail. [ABSTRACT FROM AUTHOR]

Y 2 O 3 stabilized ZrO 2 (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% RE 2 O 3 (RE=La, Nd, Gd, Yb) and 1 mol% Yb 2 O 3 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 RE 3+ 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 RE 3+ 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. [ABSTRACT FROM AUTHOR]

(RE 0.9 Sc 0.1 ) 2 Zr 2 O 7 and pure RE 2 Zr 2 O 7 (RE=La, Sm, Dy, Er) compounds were synthesized by a chemical-coprecipitation and calcination method, and their phase structure, thermal expansion behavior and fracture toughness were investigated. Compared with pure RE 2 Zr 2 O 7 , (La 0.9 Sc 0.1 ) 2 Zr 2 O 7 and (Sm 0.9 Sc 0.1 ) 2 Zr 2 O 7 exhibited larger lattice parameters mainly due to the presence of Sc 3+ interstitial ions, while (Dy 0.9 Sc 0.1 ) 2 Zr 2 O 7 and (Er 0.9 Sc 0.1 ) 2 Zr 2 O 7 had smaller lattice parameters, might attributable to the substitution of Sc 3+ for RE 3+ . With the addition of 10 mol% Sc 2 O 3 , the thermal expansion coefficients of La 2 Zr 2 O 7 and Sm 2 Zr 2 O 7 were obviously enhanced, while those of Dy 2 Zr 2 O 7 and Er 2 Zr 2 O 7 decreased, which was considered to have close relationship with the solid-solution mechanisms of Sc 2 O 3 in (RE 0.9 Sc 0.1 ) 2 Zr 2 O 7 . 10 mol% Sc 2 O 3 doping benefited the fracture toughness of (RE 0.9 Sc 0.1 ) 2 Zr 2 O 7 (RE=La, Sm, Dy, Er), which could be attributed to the increased cohesive energy due to the lattice distortion. [ABSTRACT FROM AUTHOR]

(Gd 1− x Yb x ) 2 Zr 2 O 7 ( x =0, 0.02, 0.04, 0.06, 0.08, 0.1) compounds were synthesized by solid state reaction, and their phase structure and thermal conductivities were investigated. (Gd 1− x Yb x ) 2 Zr 2 O 7 ( x =0, 0.02, 0.04, 0.06) exhibited pyrochlore structure, while (Gd 1− x Yb x ) 2 Zr 2 O 7 ( x =0.08, 0.1) fluorite phase. The ordering degree of (Gd 1− x Yb x ) 2 Zr 2 O 7 ( x =0, 0.02, 0.04, 0.06) pyrochlores decreased with increasing the Yb 2 O 3 content. Among the (Gd 1− x Yb x ) 2 Zr 2 O 7 ceramics investigated, (Gd 0.94 Yb 0.06 ) 2 Zr 2 O 7 yielded the lowest thermal conductivity of ~1.14 W/mk at 800 °C, which was nearly 25% lower than that of Gd 2 Zr 2 O 7 . The structural disorder could cause the initial decrease in the thermal conductivity, and the reduced complexity of crystal structure resulting from the pyrochlore-fluorite phase transformation might contribute to the increased thermal conductivity. [ABSTRACT FROM AUTHOR]

Thermal barrier coatings (TBCs) are susceptible to degradation caused by environmental deposits mainly composed of calcium–magnesium–aluminum–silicon (CMAS). In this work, the degradation of electron beam physical vapour deposition (EB-PVD) yttria stabilized zirconia (YSZ) TBC due to CMAS attack was investigated. To protect the YSZ coating, a Pt film and a Gd 2 Zr 2 O 7 (GZO) layer were deposited onto the YSZ coating surface by electroplating and EB-PVD, respectively. The coatings were heat treated at 1250 °C for 4 h with CMAS deposits, and their microstructure and chemical composition after CMAS attack were investigated. Electroplating a dense and defect-free Pt film on YSZ coating could provide effective protection from CMAS attack, but EB-PVD GZO coating was unable to prevent molten CMAS infiltration, mainly due to the large inter-columnar gaps. The associated mechanisms were discussed in detail. [ABSTRACT FROM AUTHOR]

(Gd 1− x Sc x ) 2 Zr 2 O 7 ( x =0, 0.025, 0.05, 0.075, 0.1, 0.2) ceramics were synthesized by chemical co-precipitation and calcination and their phase structure, thermal expansion behavior and mechanical properties were investigated. (Gd 1− x Sc x ) 2 Zr 2 O 7 ( x =0, 0.025, 0.05, 0.075) exhibited pyrochlore structure. The ordering degree decreased and the lattice parameter increased with increasing the Sc 2 O 3 content, but high Sc 2 O 3 doping led to a pyrochlore-fluorite phase transformation and to a decrease in the lattice parameter. Among the (Gd 1− x Sc x ) 2 Zr 2 O 7 ceramics investigated, (Gd 0.925 Sc 0.075 ) 2 Zr 2 O 7 yielded the largest thermal expansion coefficient (TEC). The structural disorder and lattice expansion could cause the initial increase in the TEC, and the decrease in the lattice parameter might contribute to the reduced TEC. Increasing Sc 2 O 3 content benefited the fracture toughness of (Gd 1− x Sc x ) 2 Zr 2 O 7 , which could be attributed to the increased cohesive energy due to the lattice distortion and structural disorder. [ABSTRACT FROM AUTHOR]

La 2 Ce 2 O 7 (LC) has been considered as one of the promising thermal barrier coating (TBC) candidates for operating above 1250 °C. In this work, a LC/yttria stabilized zirconia (YSZ) double ceramic layer TBC was produced by electron beam physical vapor deposition (EB-PVD). Hot-corrosion behavior of the LC/YSZ TBC exposed to Na 2 SO 4 +V 2 O 5 or V 2 O 5 salt at 900 °C was investigated. After hot corrosion in Na 2 SO 4 +V 2 O 5 salt for 4 h, a porous layer mainly composed of (La 0.75 Ce 0.25 )VO 4 and CeO 2 was formed on the LC layer. In V 2 O 5 salt, the molten salt directly reacted with La 2 Ce 2 O 7 solid solution, leading to the formation of (Ce 0.5 La 0.5 )VO 4 . The hot corrosion mechanisms of the LC/YSZ TBC in the two molten salts were discussed. [ABSTRACT FROM AUTHOR]

La 2 Ce 2 O 7 (LC) has been considered as one of the promising thermal barrier coating (TBC) candidates for operating above 1250 °C. In this work, a LC/yttria stabilized zirconia (YSZ) double ceramic layer TBC was produced by electron beam physical vapor deposition (EB-PVD). Hot-corrosion behavior of the LC/YSZ TBC exposed to Na 2 SO 4 +V 2 O 5 or V 2 O 5 salt at 900 °C was investigated. After hot corrosion in Na 2 SO 4 +V 2 O 5 salt for 4 h, a porous layer mainly composed of (La 0.75 Ce 0.25 )VO 4 and CeO 2 was formed on the LC layer. In V 2 O 5 salt, the molten salt directly reacted with La 2 Ce 2 O 7 solid solution, leading to the formation of (Ce 0.5 La 0.5 )VO 4 . The hot corrosion mechanisms of the LC/YSZ TBC in the two molten salts were discussed. [ABSTRACT FROM AUTHOR]

CaO–MgO–Al 2 O 3 –SiO 2 (CMAS) deposition significantly degrades the performance of thermal barrier coatings (TBCs). In this study, the microstructure evolution of CMAS glass at temperatures below its melting point was investigated in order to study the potential influence of temperature on the applicability of CMAS glass in TBCs. The CMAS glass fabricated in this study had a melting point of 1240 °C, became opaque, and underwent self-crystallization when the temperature reached 1000 °C. After heat treatment at 1050 °C, diopside and anorthite phases precipitated from the glass; at a higher temperature (1150 °C), diopside, anorthite, and wollastonite were formed as the self-crystallization products. An increase in the dwelling time resulted in the transformation of diopside to wollastonite and anorthite. At 1250 °C, all products formed a eutectic microstructure and melted. The results indicate that even at low temperatures, CMAS glass underwent microstructure evolution, which could influence the coating surface and stress distribution when deposited on TBCs. [ABSTRACT FROM AUTHOR]

Gd2O3 and Yb2O3 co-doped 3.5mol% Y2O3–ZrO2 and conventional 3.5mol% Y2O3–ZrO2 (YSZ) powders were synthesized by solid state reaction. The objective of this study was to improve the phase stability, mechanical properties and thermal insulation of YSZ. After heat treatment at 1500°C for 10h, 1mol% Gd2O3–1mol% Yb2O3 co-doped YSZ (1Gd1Yb-YSZ) had higher resistance to destabilization of metastable tetragonal phase than YSZ. The hardness of 5mol% Gd2O3–1mol% Yb2O3 co-doped YSZ (5Gd1Yb-YSZ) was higher than that of YSZ. Compared with YSZ, 1Gd1Yb-YSZ and 5Gd1Yb-YSZ exhibited lower thermal conductivity and shorter phonon mean free path. At 1300°C, the thermal conductivity of 5Gd1Yb-YSZ was 1.23W/mK, nearly 25% lower than that of YSZ (1.62W/mK). Gd2O3 and Yb2O3 co-doped YSZ can be explored as a candidate material for thermal barrier coating applications. [ABSTRACT FROM AUTHOR]

Abstract: The phase stability, microstructural evaluation and thermo-physical properties of BaLn2Ti3O10 (BLnT, Ln=Nd and Sm) ceramics for thermal barrier coating (TBCs) application have been investigated. BLnT (Ln=Nd and Sm) powders is found thermally stable at 1500°C after exposure for 110h, and the bulk materials exhibit lamellar structure. BLnT (Ln=Nd and Sm) bulk materials show anisotropy in thermo-physical properties due to the insertion of Ba atoms between [Ln2Ti3O10] (Ln=Nd and Sm) sheets. The thermal conductivities of BLnT (Ln=Nd and Sm) are apparently lower than those of ZrO2–8Y2O3 (8YSZ). Also, BaSm2Ti3O10 exhibits relatively lower thermal conductivity as compared to BaNd2Ti3O10. The thermal expansion coefficient (TEC) of BLnT (Ln=Nd and Sm) is found comparable to that of 8YSZ. BaNd2Ti3O10 exhibits relatively larger TEC than BaSm2Ti3O10. The above results suggest that BLnT (Ln=Nd and Sm) ceramics could be a good potential material for TBC applications. [Copyright &y& Elsevier]

A material-modified Fresnel reflection enhancing high-sensitive fiber-tip temperature sensing method is theoretically proposed and experimentally demonstrated. High refractive index semiconductive nano-ZnO and nano-TiO 2 as doping materials enhance the Fresnel reflection in fiber tip probes, and the interference spectrum of these reflected light shows better sensing performance than when undoped. On this basis, the sensitivity is further improved by utilizing ultraviolet (UV) irradiation due to the UV sensibility of the modified materials. By comparing the sensing performance of different material-doping sensing probes, the ZnO-doped fiber tip sensor witnesses the highest temperature sensitivity, which is 94.1 pm/°C. Thanks to the positive role of UV irradiation, this number increases to 141 pm/°C. The proposed fiber tip sensor has a sturdy structure, simple and economical preparative process, competitive sensitivity, high linearity, satisfactory repeatability, and stability. The micron-scale reflective probe enables better detection of extreme environments and can be expected to conduct high-sensitivity temperature sensing in industrial, biomedical, chemical, environmental, and military regions. [ABSTRACT FROM AUTHOR]

Abstract: LaTi2Al9O19 (LTA) is one of the most promising materials for new thermal barrier coatings (TBCs) to fulfill the demand of advanced gas turbines owing to its high temperature stability and low thermal conductivity. In the present study, a finite element (FE) based numerical study has been carried out to investigate the stress distribution in LTA single layered coating system in comparison with traditional yttria stabilized zirconia (YSZ) TBC. Stresses in YSZ/LTA double ceramic layer TBC system are also determined and presented for comparative analysis. The thermal cycling effect is simulated by sequent increment in TGO thickness in a series of FE simulations. In-plane stresses (σ xx ), out-of-plane stresses (σ yy) and shear stresses (σ xy ) are determined for all systems, and peak stress values are presented for quantitative comparison. Elastic strain energy stored in TGO of all systems is calculated from FE results for TBC structural integrity assessment. It has been found that maximum in-plane and shear stresses are lower in the double ceramic layer coating system than in the single layer ceramic coating system. However, peak axial tensile and compressive stresses in the double ceramic layer coating are very close or higher than those in the single layer topcoat. Calculation of elastic store energy shows that double ceramic layer TBC system may exhibit better stability as compared to single layer systems. Results are presented to explain the failure mechanism in LTA coatings. [Copyright &y& Elsevier]

Abstract: BaLa2Ti3O10 (BLT) with Ruddlesden–Popper structure is investigated as a material for thermal barrier coatings (TBCs). BLT shows excellent sintering resistance and remains phase stability at 1500°C for 110h. After annealing at 1500°C for 1h, BLT bulk material exhibits c-axis textured structure with c-axis parallel to the hot pressing direction. Thermal expansion coefficients of BLT in a–b plane are in the range of 9.5×10−6–11.3×10−6 K−1, whereas those along c-axis range from 10.4×10−6 to 12.1×10−6 K−1, which are comparable to those of 8YSZ. The thermal conductivities of BLT in a–b plane and along c-axis are 1.41–1.71 and 1.31–1.60W/mK, respectively, nearly 20% lower than those of 8YSZ. The anisotropy in thermo-physical properties is attributed to the insertion of weakly bonded Ban the BLT crystal. [Copyright &y& Elsevier]

A composite fiber Fabry-Perot interferometer (FPI) -based optical fiber temperature sensor is theoretically proposed and practically demonstrated in this work, in which the composite FPI is formed by covering the end face of single-mode fiber with ultraviolet (UV) adhesive and nano-TiO 2 coating using the dip-coating method. With the superior thermo-optic characteristic of UV adhesive and the UV absorption of nano-TiO 2 , the sensitivity of the composite FPI temperature sensor can be effectively enhanced by UV irradiation. After five times of TiO 2 dip-coating processes, the composite FPI has a higher temperature sensitivity of 75.3 pm/°C (R2 = 0.9754) under 365 nm UV light, in which the measurement range is from 25 °C to 130 °C and the detection accuracy is 0.66 °C. The proposed sensor has a simple structure and preparation process, competitive sensitivity, high linearity, and satisfactory repeatability and stability, which can be an appropriate candidate to realize high-precision temperature sensing in industrial, chemical, biological, and environmental applications. [ABSTRACT FROM AUTHOR]

In marine environment, thermal barrier coatings (TBCs) face coupling corrosion of calcium magnesium aluminum silicate (CMAS) and molten salt leading to premature failure. In this study, microstructure evolution of TBCs resulting from CMAS + NaVO 3 (CN) coupling corrosion is investigated, and a corrosion protection method based on laser glazing is proposed. TBC degradation by the CN coupling corrosion is mainly due to the high penetration ability of the melt. Laser glazed TBCs have improved resistance to the coupling corrosion, however, the vertical cracks in the glazed layer provide paths for melt penetration. TBCs with double laser-glazed layer are designed, with vertical cracks in the glazed layer being bifurcated and staggered, which could largely suppress CN melt infiltration, and also exhibits excellent phase and microstructure stability in the coupling corrosion condition. This type of laser modified TBC is confirmed to be attractive against the coupling corrosion. [ABSTRACT FROM AUTHOR]

Calcium-magnesium-alumina-silicate (CMAS) attack has been regarded as one of the significant failure mechanisms for thermal barrier coatings (TBCs). In this study, CMAS corrosion behavior of BaLa 2 Ti 3 O 10 , a novel TBC material, is investigated at 1300 °C and 1350 °C for 0.5 h, 4 h, 12 h and 24 h. Results reveal that BaLa 2 Ti 3 O 10 has high resistance to molten CMAS infiltration, attributable to the formation of a dense reaction layer. X-ray diffraction, scanning electron microscope, energy dispersive spectroscope, transmission electron microscope confirm that the layer consists of apatite, celsian and perovskite phases. With increased corrosion duration, the layer retains good phase stability and the thickness increases. The formation of corrosion products and the reaction layer are discussed according to a dissolution-reprecipitation mechanism and the optical basicity theory. [ABSTRACT FROM AUTHOR]

LaPO 4 powders were produced by a chemical co-precipitation and calcination method. The ceramic exhibited a monazite structure, kept phase stability at 1400 °C for 100 h, and had low thermal conductivity (~ 1.41 W/m K, 1000 °C). LaPO 4 /Y 2 O 3 partially stabilized ZrO 2 (LaPO 4 /YSZ) double-ceramic-layer (DCL) thermal barrier coatings (TBCs) were fabricated by air plasma spray. The LaPO 4 coating contained many nanozones. Thermal cycling tests indicated that the spallation of LaPO 4 /YSZ DCL TBCs initially occurred in the LaPO 4 coating. The failure mode was similar to those of many newly developed TBCs, probably due to the low toughness of the ceramics. LaPO 4 /YSZ DCL TBCs were highly resistant to V 2 O 5 corrosion. Exposed to V 2 O 5 at 700–900 °C for 4 h, La(P,V)O 4 formed as the corrosion product, which had little detrimental effect on the coating microstructure. At 1000 °C for 4 h, a minor amount of LaVO 4 was generated. [ABSTRACT FROM AUTHOR]

TiO 2 films were grown onto unheated 5083 aluminum alloy substrates by reactive magnetron sputtering from a pure Ti target in Ar-O 2 gas mixture in different power, bias voltage, Ar/O 2 ratio and deposition time at room temperature. The effects of different deposition parameters on the structure and properties of TiO 2 films were investigated systematically by field emission scanning electron microscope (FESEM), atomic force microscope (AFM), X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), nanoindentation tests, electrochemical tests and antibacterial tests. The results show that power and bias voltage are two main factors to affect the structure and properties of TiO 2 films during the sputtering process. XRD results show that anatase phase is the main phase of the film, and the enhanced content of anatase phase with the increase of sputtering power and bias voltage. Nanoindentation tests exhibit that higher H/E (Hardness/Modulus) ratio can be achieved by depositing TiO 2 film. And the corrosion resistance and antifouling property are all improved after depositing TiO 2 film. 2# sample shows the optimal corrosion resistance, E corr and I corr are −0.27388 V and 3.7232 μA/cm 2 , respectively. 1# sample exhibits excellent antibacterial property, the d ensity of bacteria is only 217 cell / mm 2 , which is 484% higher than that of uncoated matrix. [ABSTRACT FROM AUTHOR]

Nanostructured GdPO 4 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 V 2 O 5 and Na 2 SO 4 +V 2 O 5 salts at 900 °C for 4 h. Results indicate that dense reaction layers, consisting of GdVO 4 and Gd 4 (P 2 O 7 ) 3 , form on the coating surfaces, which could suppress further penetration of the molten salts. In the V 2 O 5 molten salt, the reaction layer is thicker and less molten salt trace could be found beneath the layer. [ABSTRACT FROM AUTHOR]

Coupling corrosion resulting from calcium-magnesium-alumina-silicate (CMAS) and molten salt causes severe attack to YSZ thermal barrier coatings (TBCs). In this study, a Sc-doped Gd 2 Zr 2 O 7 (GZO-Sc) coating is prepared on the YSZ coating to alleviate CMAS + NaVO 3 (CN) corrosion. Results revealed that the GZO-Sc coating largely prevented CN (with a melting point of 1188 °C) attack to YSZ coatings at 1200 °C and 1250 °C. At the test temperatures, CN melted and penetrated the GZO-Sc coating, during which the melt and the coating reacted to form a dense reaction layer, consisting of Gd 8 Ca 2 Si 6 O 26 -based apatite and c-ZrO 2 based fluorite phase independent on the temperature and time. With the increase of the dwell time, V was separated from CN melt during infiltration, causing many CaAl 2 Si 2 O 8 crystals at the bottom of the reaction layer and a V-rich layer beneath the reaction layer, which were beneficial to the CN corrosion resistance of the coatings. [ABSTRACT FROM AUTHOR]

Calcium-magnesium-alumina-silicate (CMAS) and molten salt corrosion pose great threats to thermal barrier coatings (TBCs), and recently, a coupling effect of CMAS and molten salt has been found to cause even severer corrosion to TBCs. In this study, the crystallization behavior of CMAS and CMAS+NaVO 3 is investigated for potentially clarifying their corrosion mechanisms to TBCs. Results indicated that at 1000 °C and 1100 °C, CMAS was crystallized to form CaMgSi 2 O 6 , while at 1200 °C, the crystallization products were CaMgSi 2 O 6 , CaSiO 3 and CaAl 2 Si 2 O 8. The introduction of NaVO 3 in CMAS reduced the crystallization ability, and as the NaVO 3 content increased, glass crystallization occurred at a lower temperature, with crystallization products mainly consisting of CaAl 2 Si 2 O 8 and CaMgSi 2 O 6. At 1200 °C, CMAS+10 wt% NaVO 3 was in a molten state without any crystallization, which suggested that NaVO 3 addition in CMAS could reduce its melting point, indicating enhanced penetration ability in TBCs and thus increased corrosiveness. [ABSTRACT FROM AUTHOR]

The corrosion of YSZ TBCs attacked by calcium–magnesium–aluminosilicate (CMAS) is a serious problem. Yttrium tantalite (YTaO 4), a new kind of potential thermal barrier ceramic material, was expected to replace the YSZ to manufacture the TBCs because of its great thermophysical characteristics. In this study, porous YTaO 4 ceramic pellets, instead of actual TBCs, were used to investigate the CMAS corrosion resistance at 1250 °C. Results indicated that CMAS couldn't cover the whole surface of YTaO 4 pellets homogeneously because of low wettability between liquid CMAS and YTaO 4 , in addition, there was almost no reaction layer after 4 h reaction. The XRD results showed that M-YTaO 4 , M′-YTaO 4 , Ca 2 Ta 2 O 7 and Y 2 Si 2 O 7 were the main four phases after reaction and there was no phase containing the elements of Mg and Al. Compared with YSZ TBCs, this new kind of potential thermal barrier ceramic material showed well resistance to CMAS corrosion. [ABSTRACT FROM AUTHOR]

Calcium-magnesium-alumina-silicate (CMAS) has posed enormous threat to thermal barrier coatings (TBCs). In this study, a series of newly developed TBC ceramics, BaLn 2 Ti 3 O 10 (Ln=La, Nd), are found to have high resistance to the penetration of molten CMAS at 1250 °C. The formation of a continuous, dense crystalline layer, mainly composed of apatite and CaTiO 3 phases, on the sample surfaces contributed to this desirable attribute. The accumulation of Ba in the molten CMAS triggered the crystallization of the melt, leading to the formation of many BaAl 2 Si 2 O 8 celsian crystals above the crystalline layer, which could reduce the mobility of the molten CMAS. The mechanisms by which the CMAS attacks BaLn 2 Ti 3 O 10 samples are discussed. The results indicate that Ba is an effective element for altering CMAS composition, and doping Ba in TBCs might be an attractive way of mitigating CMAS attack. [ABSTRACT FROM AUTHOR]

Hot corrosion behavior of (Gd 0.9 Sc 0.1 ) 2 Zr 2 O 7 ceramic exposed to V 2 O 5 molten salt at 700–1000 °C was investigated, providing better understanding of its corrosion resistance as a promising thermal barrier coating. Obvious corrosion reaction occurred between (Gd 0.9 Sc 0.1 ) 2 Zr 2 O 7 and V 2 O 5 molten salt after 4 h heat treatment, corrosion products being temperature dependent. At 700 °C, large amount of Sc 2 O 3 doped ZrV 2 O 7 and GdVO 4 , together with a minor amount of Sc 2 O 3 -stabilized tetragonal ZrO 2 ( t -ZrO 2 ), formed on the sample surfaces. With the increase of the test temperature, Sc 2 O 3 doped ZrV 2 O 7 turned to decompose, leading to the formation of more t -ZrO 2 . At 900 °C and 1000 °C, the corrosion products were composed of GdVO 4 and t -ZrO 2 . The mechanism by which the corrosion reaction occurs is proposed based on phase diagrams and Lewis acid-base rule. [ABSTRACT FROM AUTHOR]