The thermal conductivities of as-sprayed yttria-stabilized zirconia thermal barrier coating prepared by atmospheric plasma spraying at different temperatures are investigated based on quantitative microstructural analysis. Multiple linear regression is used to develop quantitative models which describe the relationship between multiple elements such as porosity, grain boundary density, monoclinic phase content, temperature and thermal conductivity. Results reveal that the thermal conductivity of the coating is mainly determined by the porosity and grain boundary density below 300 °C and by the monoclinic phase content above 800 °C. Furthermore, based on the significance testing analysis, the confidence interval under a confidence level of 95% at different temperatures enables researchers to predict the thermal conductivity based on microstructural information.

Optimized doped TiO2 is necessary for efficient visible light harvesting and widening the applications spectrum of TiO2-based materials. Titanium dioxide doped with silver and/or vanadium has been synthesized by one-pot hydrothermal method without post-calcination. Codoping induced visible light absorption while maintaining the photoactive anatase phase along with good crystallinity. Synthesized products are in nanometer range and possess high specific surface area. Having nearly spherical morphology, the particles are distributed and the particle size estimated from TEM observation is in accordance with the XRD results. Spectroscopic investigations reveal that the doped atoms successfully entered the TiO2 lattice modifying the band structure. The narrowed band gap allows visible light photons for absorption, and the codoped samples displayed enhanced visible light absorption among the synthesized samples. Photodegradation performance evaluated under visible light irradiations showed that silver- , vanadium-codoped TiO2 have the best visible light photocatalytic activity attributed to stable configuration, high visible light absorption, coupling between silver and vanadium and their optimal doping concentration.

Co3O4/NiO/C microspheres with a multilayered ball-in-ball hollow nanoarchitecture were synthesized via carbonization and oxidation treatments of Morella-rubra-like CoNi-based metal–organic frameworks (CoNi-MOFs). The shell walls of each ball were entirely composed of uniform nanorods. This unique multilayered hollow structure can strongly mitigate the change in the volume of the electrodes, which maintains the structural integrity of the Co3O4/NiO/C hybrids during the lithiation–delithiation process. In addition, the C scaffolds improve the conductivity of the electrode and function as a buffer material to mitigate the pulverization of Co3O4 and NiO nanoparticles. Therefore, in Li-ion cells, the multilayered Co3O4/NiO/C hybrids exhibit a high reversible capacity (864 mA h g−1 at 1 A g−1), an excellent rate capacity (421 mA h g−1 at 4 A g−1), and a long-lifetime cycling performance (776 mA h g−1, even after 1000 cycles at 1 A g−1) for Li storage.

•Ga and/or N doped TiO2 is synthesized by one pot hydrothermal method.•Spin polarized DFT based calculations for pure and doped models are performed.•The optical and catalytic properties of synthesized samples were evaluated.•The experimental and calculations results are compared and discussed.•Ga doped TiO2 provided suitable band structure with enhanced photocatalytic property.Ga and/or N doped TiO2 nanoparticles synthesized by one pot hydrothermal method possess pure anatase phase with spherical morphology. Calculations based on density functional theory (DFT) explained the band gap narrowing, origin of optical absorption and the possible changes in the photocatalytic activity of synthesized nano-photocatalysts. Analysis of band structure and density of states revealed that N and Ga, N codoping introduced some partially occupied states above the valance band maximum which might influence the electron hole pair recombination. Calculations as well as experiments confirmed the shifting of absorption edge towards visible regime due to doping. Spectroscopic investigations confirmed the existence of dopant atoms in the doped samples. Ga doped TiO2 samples provided the best photocatalytic activity compared to the synthesized samples attributed to the suitable band structure, enhanced optical absorption and effective separation between photoexcited carriers.

•An automated procedure was proposed to evaluate the porosity of TBCs•This procedure could estimate the cumulative porosity and uniformity, size and shape of pores.•The porosity obtained by the automated procedure was repeatable and comparable.•The influence of plasma spraying parameters in porosity was evaluated.An automated procedure, termed as panoramic statistics, was proposed to characterize the microstructure of thermal barrier coatings. An experimental assessment of this approach was conducted by a comparison to mercury intrusion porosimetry (MIP) and Archimedean methods, and the deviations and uncertainties among them were analyzed. Based on the quantification of image contrast and threshold, the overall porosity measured in a panoramic area of 2 mm × 2 mm was much more reproducible than that of MIP, and was in agreement with the result of Archimedean. Large variations of local porosity along the thickness of coatings revealed the non-uniformity of porosity and the importance of applying panoramic statistics. The pore size distribution was consistent with the estimation of MIP. The shape distribution of pores can only be comprehensively analyzed using the present method. This technique will provide a more accurate and reliable estimation of microstructure for coatings and other ceramics.

To improve the photoelectrochemical properties of TiO2, an approach of codoping is introduced to simultaneously tailor the band gap and control the life time of photoexcited electron–hole pairs. Molybdenum doping is used to extend the optical absorption of TiO2 while silver inclusion in the molybdenum-doped TiO2 network improves the separation between the photogenerated carriers leading to improved photodegradation response. X-ray photoelectron spectroscopy (XPS) confirmed the existence of dopant atoms in the bulk lattice and the codoped sample exhibits enhanced photodegradation performance compared to monodoped samples. With less structure modifications and stable structure, the silver molybdenum codoped TiO2 highly improve the wide functionalities of TiO2 in photoelectrochemical applications.

•A simpler method to prepare bulk amorphous materials is introduced.•Bulk amorphous Al2O3-YSZ materials are prepared by APS using crystalline powders.•Nanocrystalline Al2O3-YSZ materials are achieved by heat treatment.•Effect of annealing temperature on nanocrystalline materials is investigated.This study reports a simple method for the preparation of bulk amorphous materials by rapid solidification of their crystalline powders. Bulk amorphous Al2O3-YSZ materials have been successfully prepared by atmospheric plasma spraying (APS) using Al2O3-YSZ mixed crystalline powders near eutectic composition. Nano-crystalline Al2O3-YSZ materials with homogeneous nanostructure were achieved by heat treating bulk amorphous Al2O3-YSZ materials at 1050 °C. When annealing temperature was above 1250 °C, the lotus leaf structure was formed because of connection between large numbers of Al2O3 nano-grains due to sintering. Therefore, it can be concluded that annealing temperature of amorphous Al2O3-YSZ materials need to be controlled between Tc (onset crystallization temperature) and 1250 °C avoiding large area of sintering to achieve homogeneous nanocrystalline ceramics.

•YSZ coatings were fabricated by plasma spraying.•The behavior of crack generation and extension was characterized by 3D technology.•Relationship between cracks and other microstructures in YSZ coatings was found.Yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) were prepared by plasma spraying. Thermally grown oxide (TGO) was formed between the YSZ layer and the bond coat during heat treatment of the YSZ TBCs. The generation and extension behavior of cracks before and after heat treatment were characterized by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) combined with 3D reconstruction technology. The characterization results give a direct evidence that the generation and extension of cracks is closely related to other microstructures such as columnar grains, TGO morphology, TGO composition, and TGO orientation. For example, large interlaminar cracks in as-sprayed YSZ coatings often appeared along with columnar grains, which can be explained by their similar formation conditions. The formation of new cracks such as vertical cracks, plane cracks and other cracks along the TGO grain boundary after heat treatment often resulted from TGO growth stresses. Therefore, the generation and extension of cracks can be controlled by regulating the formation of columnar grains and TGO.

Aluminum (Al) is a trace element found in hard tissues, and the induction of bone diseases by Al accumulation has generated interest in the role and mechanism of Al in bone metabolism. Because hydroxyapatite (HA) constitutes the main inorganic content of human hard tissues, the biological effect of Al in human hard tissues is closely related to the intrinsic state of Al-doped HA (Al-HA). However, few investigations to date have focused on the crystallography of Al-HA. Herein, we determined the crystallographic characteristics and energy states of Al-HA by conducting theoretical and experimental studies. Al-HA [Ca10−1.5xAlx(PO4)6(OH)2] with a defect structure was synthesized. XRD patterns and morphology images revealed that doping of Al decreased the crystallinity and the HA nanocrystal size. The optimized crystal structure indicated that Al was preferentially substituted for Ca(2) and Ca vacancies appeared at the Ca(2)1 site. Al doping locally distorted the regularity and integrity of the HA crystal structure, leading to the occurrence of Ca2+ vacancies and the displacement and rotation of OH− and [PO4]3− chains. The total energy of Al-HA increased and the stability decreased. Consequently, Al-HA might be readily degraded by osteoclasts and bone resorption could be accelerated. The destruction and over-resorption of bones caused by excessive Al could result in abnormal bone metabolism. The present findings not only provide the first crystallographic information on the disruptive effects of Al doping in HA but also complement the present understanding of the mechanisms underlying Al-induced bone diseases.

The microstructures of three atmospheric plasma-sprayed (APS) Al2O3-ZrO2 coatings were investigated using x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The differences in the microstructures of the three Al2O3-ZrO2 coatings, including their phase compositions, cracks, pores, grain sizes, and solid solutions, were analyzed in detail. A close relationship was observed between the thermal conductivities of the coatings and the microstructures, and the Al2O3-YSZ coatings with more spherical pores, fewer vertical cracks, and finer grains exhibited the lowest thermal conductivity of 0.91 W/m·K. Compared with YSZ coatings, Al2O3-YSZ coatings can exhibit lower thermal conductivity, which may be attributed to the formation of an amorphous phase, smaller grains, and Al2O3-YSZ solid solution.

•YSZ TBCs were fabricated by plasma spraying.•Diffusion mechanism controlling the growth of TGO is analyzed.•Ionic species that dominated the growth of TGO layer is confirmed.•Direct evidence on the diffusion path of Al and Ni is found.Yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) were prepared by plasma spraying. The as prepared YSZ TBCs were characterized by scanning electron microscopy (SEM), Electron backscatter diffraction (EBSD) and focused ion beam (FIB) systems before and after heat treatment. A thermally grown oxide (TGO) layer was formed between YSZ topcoat and bond coat after heat treatment. EBSD results revealed that the TGO layer was composed of α-Al2O3 and cubic Al2NiO4 layers. Mechanism controlling the growth of the TGO layer were analyzed in detail. It was found that the AlNi phase gradually disappeared from bond coat during heat treatment, which provided Al and Ni sources for the formation of TGO. Meanwhile, EBSD results confirmed that the growth of the TGO layer was dominated by the diffusion of Al and Ni rather than O penetration. Furthermore, direct evidence on the diffusion pathways of Al and Ni was also found, indicating that Al and Ni proceeded along the pores, cracks and YSZ grain boundaries to promote the further growth of TGO layer with increased heat treatment time.

The oriented hierarchical architecture of hydroxyapatite (HA) shows excellent performance in multiple functions in human hard tissues such as bone and teeth. It is a challenge to mimic the architecture of biomineralization products. This study introduces a simple method for the hierarchical architecture of pure stoichiometric HA by a one-pot hydrothermal process without adding any organic molecules. The reaction process is researched by XRD, FT-IR, SEM, and TEM, and the HA crystal growth mechanism is discussed. The short rod-like HA nanocrystals are orderly assembled into micrometer-sized platy particles with the DCPD (CaHPO4·2H2O, brushite) shape retained. The ordered HA hierarchical architectures are achieved through topotactic transformation due to the crystal structural similarity from DCPD through DCPA (CaHPO4, monetite) to HA. It is found for the first time that the growth of HA crystals on DCPA is accompanied by orientation relationship of HA [1̅10] // DCPA [110] and HA (112) // DCPA (1̅12). The resemblance between the crystal structures promotes the direct phase transition. The results provide new insights into the formation mechanism of ordered HA hierarchical architectures and give hints for designing hierarchically assembled nanoarchitecture in synthetic work.

Almost fully amorphous coatings of near-eutectic alumina-yttria-stabilized zirconia (Al2O3-YSZ) were prepared by air plasma spraying using Al2O3 and 8 mol.% YSZ crystalline-mixed powders. The coatings consist of mostly an amorphous phase with a small amount of nanocrystals. Various characterization techniques were used to understand coating formation and the origins of the different phases within the coatings. The formation of the mostly amorphous structure is attributed to the high glass-forming ability of Al2O3-YSZ and the appropriate plasma spraying conditions. A small number of nanocrystals are produced during crystallization of the incoming molten droplets or by recrystallization of the solidified splats by accumulated heat. Scanning electron microscopy shows that the coatings have a dense, layered structure with low porosity, and bright-field transmission electron microscopy images indicate sharp interface rather than grit-blasted wavy surface between splats and substrates in the coatings. The as-sprayed amorphous coatings crystallized at around 920 °C and micro-hardness of the as-sprayed amorphous coatings was 8.12 GPa.

Thermal barrier coatings (TBCs) are key materials of turbines for propulsion and power generation. The failure mechanism of TBCs is a crucial problem in scientific community and need to be resolved. Failure of TBCs is a complicated process affected by its own performance, microstructure and service environment. In this study, thermal barrier coatings of ZrO2 were prepared by plasma spraying method. A SEM with heating system is used to study in situ microstructure change of TBCs at service temperature. Changes in microstructure and interfaces as well as healing and development of cracks are revealed. It is expected that the investigation of the failure mechanism of the TBCs from a microscopic point help to improve service life of the TBCs by providing a reliable basis to solve the failure problem.

The melting index of particle was measured to quantitatively characterize the spraying parameters of as-sprayed YSZ coatings. Moreover, new and reliable representation of melting index was achieved, using in-flight particle temperature and velocity. The prediction of microstructure features, such as total porosity and spheroidal porosity of as-sprayed coatings, could be available by the quantitative relationship between melting index and porosity. Based on the real microstructure characteristics, finite element models were generated to simulate heat transfer and calculate thermal conductivity of coatings. The large deviation between the experimental thermal conductivity and simulation results was attributed to the influence of microcracks, which was not shown in as-analyzed images due to resolution limit. Taking all the effects of microcracks and porosity into account comprehensively, the calculation model of thermal conductivity was established with the calculated error lower than 10%.

Plasma-sprayed yttria-stabilized zirconia coatings have a complex microstructure consisting of a variety of pores and cracks. These microstructure features which are determined by the spray process are known to influence the thermal conductivity of coatings. In this article, the microstructure features such as total porosity, large pores, and small pores were quantified by means of scanning electron microscopy (SEM) and image analysis, and for each spray process, the particle velocity and particle temperature were measured prior to impact onto the substrate using the online monitoring system (Spray Watch 2i). Multiple linear regression was used to find the relationship between the particle state and the spray gun parameters. The linear regression models were also investigated between the particle state and the microstructure features, in addition, between the microstructure features and the thermal conductivity. The comprehensive correlation of spray process-microstructure-thermal conductivity was established for plasma-sprayed ZrO2 coatings.

TiO2 coatings of different thickness were prepared by a thermal spray process. It was found that the external bias applied to the as-sprayed TiO2 coating could significantly improve its photocatalytic performance, which was characterized by decomposition of methylene blue (MB) solution. The decomposition efficiency increased with increasing external bias voltage. However, for voltage greater than 15 V, the decomposition efficiency remained constant. The TiO2 coating with a thickness of 6 μm showed the best photocatalytic performance under an external bias voltage of 15 V.

RuO2–IrO2–TiO2/Ti anodes are widely used in chlor-alkali and chlorate industry. The working life is of particular importance for anodes. The relationship between the content of IrO2 and working life was investigated. The microstructure of the anode with 0.5 mg/cm2 IrO2 is much more homogeneous than those with lower IrO2 contents. Both the size of particles containing RuO2 and IrO2 and the content of rutile TiO2 phase in anodes decrease with increased IrO2 content. The working life of anode with 0.5 mg/cm2 IrO2 is almost double that of the anode with 0.3 mg/cm2 IrO2.

Aluminum (Al) is a trace element found in hard tissues, and the induction of bone diseases by Al accumulation has generated interest in the role and mechanism of Al in bone metabolism. Because hydroxyapatite (HA) constitutes the main inorganic content of human hard tissues, the biological effect of Al in human hard tissues is closely related to the intrinsic state of Al-doped HA (Al-HA). However, few investigations to date have focused on the crystallography of Al-HA. Herein, we determined the crystallographic characteristics and energy states of Al-HA by conducting theoretical and experimental studies. Al-HA [Ca10−1.5xAlx(PO4)6(OH)2] with a defect structure was synthesized. XRD patterns and morphology images revealed that doping of Al decreased the crystallinity and the HA nanocrystal size. The optimized crystal structure indicated that Al was preferentially substituted for Ca(2) and Ca vacancies appeared at the Ca(2)1 site. Al doping locally distorted the regularity and integrity of the HA crystal structure, leading to the occurrence of Ca2+ vacancies and the displacement and rotation of OH− and [PO4]3− chains. The total energy of Al-HA increased and the stability decreased. Consequently, Al-HA might be readily degraded by osteoclasts and bone resorption could be accelerated. The destruction and over-resorption of bones caused by excessive Al could result in abnormal bone metabolism. The present findings not only provide the first crystallographic information on the disruptive effects of Al doping in HA but also complement the present understanding of the mechanisms underlying Al-induced bone diseases.