Doping of alkali metals in precursor solutions demonstrates an effective strategy to achieve high efficiency Cu2ZnSn(S,Se)4 solar cells. The properties of doped films are related to alkali metal ...radius. Smaller alkali atoms are beneficial for increasing carrier concentration, whereas larger atoms are conducive to grain growth. Over 8% efficiency of K‐doped Cu2ZnSn(S,Se)4 solar cell with optimized CdS thickness is realized.
Single-phase (Ni, Pt)Al coatings with and without Hf addition were prepared via electroplating a Pt/Pt-Hf layer and subsequent gaseous phase aluminisation. The initial microstructure and oxidation ...behaviour of two coatings were investigated comparatively. The results show that finer grains were obtained in Hf-doped Pt-plating layer and as-received (Ni, Pt)Al coating, which contributes to better high temperature performance and oxide scale peeling resistance. Additionally, Hf can effectively retard the θ-Al2O3 transformed to α-Al2O3 during the early oxidation and enhanced oxidation resistance during the stable oxidation. The effect of Hf on inhibiting detrimental sulfur in acid-(Ni, Pt)Al during high-temperature exposure were intensively discussed.
•Hf-doped (Ni, Pt)Al exhibits finer grain size due to the genetic role of prophase.•Hf retards the transformation from θ-Al2O3 to α-Al2O3 in the early oxidation stage.•The Hf addition significantly enhance the oxidation resistance of Acid-(Ni, Pt)Al.•Hf eliminates the harmful effects of impurity sulfur in (Ni, Pt)Al was revealed by the first principles.
•Steam changed the scale morphologies in low atmosphere, but slowed the scale thickening rate in high atmosphere.•Volatilisation of chromia occurred in the presence of both water vapour and oxygen at ...650 °C.•No NiCr2O4 spinel was formed at a detectable level in any gas mixture due to slow growth at 650 °C.•The critical Cr content required for chromia maintenance varied with gas composition.
Binary Ni-Cr alloys containing 5−30 wt% Cr were exposed to Ar-20O2, Ar-20O2-20H2O, Ar-20CO2, Ar-20CO2-20H2O and Ar-20H2O (vol.%) at 650 °C. In dry/wet O2, and dry CO2, 5−25 Cr alloys formed a three-layered structure: an external NiO layer, an inner oxide layer and an internal oxidation zone. The Ni-30Cr alloy formed a continuous chromia layer, with local outer NiO islands in dry/wet O2, but a continuous Ni-rich outer layer in dry CO2. In wet CO2/water vapour alone, all alloys underwent internal oxidation, nickel metal expulsion and NiO formation. Gas composition effects on the Cr concentration required for chromia formation are discussed.
A Pt-modified NiCoCrAlY coating was prepared on N5 via arc ion plating (AIP), Pt-electroplating, and subsequent vacuum annealing treatments. To perform a comparison between the properties of the ...modified and normal NiCoCrAlY coatings, the isothermal oxidation performances of the Pt-free and Pt-modified NiCoCrAlY coatings were evaluated at 1100 °C in static air. The results indicate that the Pt-rich overlayer on the Pt-modified NiCoCrAlY coatings exhibited superior oxidation resistance, and the adherent, thinner scale of α-Al2O3 inhibited the formation of detrimental (Ni, Co)(Cr, Al)2O4 spinel oxide. Furthermore, the addition of Pt effectively delayed the Al2O3 oxide phase transformation from θ to α in the early stage and markedly decreased the level of residual stress. The mechanism of forming the Pt-rich overlayer and its effect on thermally grown oxide (TGO) failure during high-temperature oxidation are discussed in detail, and the effect of Pt on improving the TGO growth, stress evolution, and spallation resistance are highlighted.
•Pt-rich overlayer serves as Al-pumper, which inhibiting the formation of (Ni,Co)(Cr,Al)2O4 spinel.•The Pt-rich overlayer consisted of NiAl and Ni3Al without any PtAl2 phase were clearly characterized by TEM.•Pt delays θ-to-α Al2O3 transformation in initial oxidation stage.•Lesser growth stress and better adhesion of TGO are achieved on Pt-modified NiCoCrAlY coating.
A thermal barrier coating system comprising Pt-modified NiCoCrAlY bond coating and nanostructured 4 mol.% yttria stabilized zirconia (4YSZ, hereafter) top coat was fabricated on a second generation ...Ni-base superalloy. Thermal cycling behavior of NiCoCrAlY-4YSZ thermal barrier coatings (TBCs) with and without Pt modification was evaluated in ambient air at 1100 °C up to 1000 cycles, aiming to investigate the effect of Pt on formation of thermally grown oxide (TGO) and oxidation resistance. Results indicated that a dual layered TGO, which consisted of top (Ni,Co)(Cr,Al)2O4 spinel and underlying α-Al2O3, was formed at the NiCoCrAlY/4YSZ interface with thickness of 8.4 μm, accompanying with visible cracks at the interface. In contrast, a single-layer and adherent α-Al2O3 scale with thickness of 5.6 μm was formed at the interface of Pt-modified NiCoCrAlY and 4YSZ top coating. The modification of Pt on NiCoCrAlY favored the exclusive formation of α-Al2O3 and the reduction of TGO growth rate, and thus could effectively improve overall oxidation performance and extend service life of TBCs. Oxidation and degradation mechanisms of the TBCs with/without Pt-modification were discussed.
A multigraph is modeled as a bag of graphs. Exact multigraph matching search aims to find all multigraphs that are the same as the query multigraphs from the data multigraph datasets. To the best of ...our knowledge, works regarding exact multigraph matching search have not been reported although they have a very wide range of application scenarios. In this article, we propose an efficient algorithm to solve the problem of exact multigraph matching search. We first propose a definition of exact multigraph matching and its Basic Method (BM), called BM, which has a considerable amount of graph isomorphism detection calculations and, thus, has very high computational complexity. Obviously, it is impractical to compare the query multigraph to each data multigraph in the multigraph datasets. To reduce the search space, multiple filtering conditions are proposed to obtain a candidate result set containing all the final results, including the cardinality filter, the vertex filter, the edge filter, the size filter, and the star filter. Then, each multigraph in the candidate result set is verified with the Improved BM (IBM) algorithm. Moreover, an offline and Multilayer Inverted Index (MII), named MII, is proposed to further accelerate the search process. Finally, we propose an Exact Multigraph Matching Search (EMMS) algorithm, based on the abovementioned technologies. We also analyze its time complexity. Extensive experiments on real datasets demonstrate the effectiveness and efficiency of the proposed algorithms.
A NiCoCrAlYSiHf+NiAl composite coating was deposited onto a second-generation single-crystal superalloy René N5 by methods of arc ion plating and magnetron sputtering. After vacuum annealing, the ...composite coating exhibited a gradient distribution of elements, in which Al was enriched in outer layer and Cr was enriched in inner layer. Compared with conventional NiCoCrAlYSiHf and β-NiAl coatings, the composite coating was evaluated in isothermal and cyclic oxidation tests at 1100 °C in ambient air. The results showed that the oxidation rate of the composite coating was lower than that of NiCoCrAlYSiHf coating. Meanwhile, the extent of interdiffusion between coating and substrate in the composite coating was slighter compared with that in the β-NiAl coating. Microstructure evolutions of the composite coating after annealing and further oxidation test are investigated.
Using Cu2ZnSn(S,Se)4 (CZTSSe) as a model system, we demonstrate the kinetic control of solid–gas reactions at nanoscale by manipulating the surface chemistry of both sol–gel nanoparticles (NPs) and ...colloidal nanocrystals (NCs). Specifically, we first identify that thiourea (commonly used as sulfur source in sol–gel processes for metal sulfides) can transform into melamine upon film formation, which serves as surface ligands for as-formed Cu2ZnSnS4 (CZTS) NPs. We further reveal that the presence of these surface ligands can significantly affect the outcome of the solid–gas reactions, which enables us to effectively control the selenization process during the fabrication of CZTSSe solar cells and achieve optimal film morphologies (continuous large grains) by fine-tuning the amount of surface ligands used. Such enhancement leads to better light absorption and allows us to achieve 6.5% efficiency from CZTSSe solar cells processed via a sol–gel process using nontoxic, low boiling point mixed solvents. We believe our discovery that the ligand of particulate precursors can significantly affect solid–gas reactions is universal to solid-state chemistry and will boost further research in both understanding the fundamentals of solid-state reactions at nanoscale and taking advantage of these reactions to fabricate crystalline thin film semiconductors with better morphologies and performances.
A novel metal-enamel interlocking coating was designed and prepared
in situ
by co-deposition of Ni-enamel composite layer and subsequent air spray of enamel with 10 wt% nanoscale Ni. During the ...firing process, the external enamel layer was melted and jointed with the enamel particles at the upper part of the Ni-plating layer to form the enamel pegs. Thermal shock tests of pure enamel, enamel with 10 wt% Ni composite and metal-enamel interlocking coatings were conducted at 600 °C in water and static air. The results indicated that the metal-enamel interlocking showed superior thermal shock resistance to both pure enamel and enamel with 10 wt% Ni composite coatings. The enhanced performance was mainly attributed to the advantageous effects of mechanical interlocking of the enamel pegs formed at the enamel/Ni-plating interface. Meanwhile, during thermal shock test, big clusters formed by nanoscale Ni agglomerations were oxidised to be a Ni/NiO core–shell structure while small single nanoscale Ni grains were oxidised completely, which both improved the thermal shock resistance of enamel coating significantly.
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