Enhanced UV- and visible-light driven photocatalytic performances and recycling properties of graphene oxide/ZnO hybrid layers

Light induced catalytic processes have attracted significant attention during the last years for wastewater treatment due to their efficiency in decomposition of organic contaminants. In this study we report the synthesis of graphene oxide (GO)/ZnO hybrid layers with high photocatalytic efficiency using laser radiation. The results show that the hybrid layers exhibit much improved photodecomposition efficiency as compared to pure GO or ZnO both under UV and visible-light irradiation. The enhanced photocatalytic efficiency of the hybrid as compared to the reference pure ZnO and GO layers was attributed to the contribution of GO to the separation and transport of the photogenerated charge carriers. Additionally, under visible light irradiation the organic molecules can act as first sensitizers in the degradation process. The recyclability of the layers was also investigated through repetitive photodegradation cycles under UV- or visible-light irradiation. After consecutive degradation runs, the hybrid photocatalyst layers were still stable and retained high degradation efficiency, ensuring reusability. The photocatalytic activity of the layers was correlated with the gradual change of their chemical structure during consecutive degradation cycles. Owing to the high photodegradation efficiency, reusability, and ease of recovery the synthesised hybrid layers consisting of easily available materials are suitable for environmental purification applications.     

Properties of starch–cellulose fiber films produced by tape casting coupled with infrared radiation

Tape casting is a suitable process for large-scale production of biodegradable films. This study presents a comparison of three drying procedures of starch–cellulose films: i) conduction drying, ii) infrared drying (42.3?W?m^?2, higher infrared heating power damaged the films), and iii) conduction-infrared drying. All the drying procedures were performed at approximately 60°C. Drying times from the second and third methods were close to 1?h, half the time observed for conduction drying. Films from the second and third methods showed similar hygroscopicity (0.15?g.?g^?1, RH 43%), tensile strength (31.3?MPa, RH 58%), and glass transition temperature (?12.13°C, RH 43%).     

Improved properties of scandia and yttria co-doped zirconia as a potential thermal barrier material for high temperature applications

Due to the limited temperature capability of current YSZ thermal barrier coating (TBC) material, considerable effort has been expended world-wide to research new candidates for TBC applications above 1200?°C. Our study suggested that Sc₂O₃ and Y₂O₃ co-doped ZrO₂ (ScYSZ) had excellent t’ phase stability even after annealed at 1500?°C for 336?h. The thermal expansion coefficient of ScYSZ was comparable to the value of YSZ. The thermal conductivity of fully dense ScYSZ was in the range of 2.13–1.91?W?m^?1?K^?1 (25–1300?°C), approximately 25% lower than that of YSZ. Although the fracture toughness of dense ScYSZ was slightly lower than YSZ, an evident decline in elastic modulus was found. Additionally, thermal cycling lifetime of plasma sprayed ScYSZ coating (914 cycles) at 1300?°C was about 2.6 times longer than its YSZ counterpart. The superior comprehensive properties confirm that ScYSZ is a prospective candidate material for high-temperature TBC application.     

Prolong the durability of La2Zr2O7/YSZ TBCs by decreasing the cracking driving force in ceramic coatings

Service lifetime and thermal insulation performance are both crucial for the application of thermal barrier coatings (TBCs). In this study, layered structure design under equivalent thermal insulation conception is introduced to lower the cracking driving force in TBCs, and with the goal of prolonging TBCs lifetime. Three groups of layered LZO/YSZ TBCs were designed with same thermal insulation of 500?μm YSZ, the LZO layers were deliberately designed with different initial elastic modulus. Virtual crack closure technique (VCCT) calculation result showed that the energy release rates at the crack tips are 28.2, 22, and 18.8?N/m corresponding to the initial elastic modulus of 70, 60, and 50?GPa. After gradient thermal cyclic tests with surface temperature of 1300?°C, TBCs with lowest initial elastic modulus showed the longest lifetime, and more than double of pure YSZ TBCs. This study provides a new option for the improvement of TBCs lifetime.     

Phase equilibria in the zirconia–yttria/gadolinia–silica systems

Phase equilibria in ZrO₂-YO_1.5-SiO₂ (ZYS) and ZrO₂-GdO_1.5-SiO₂ (ZGS) were experimentally assessed at 1400?°C and 1600?°C as they can offer insight on reactions between thermal barrier coatings (TBCs) based on ZrO₂-YO_1.5/GdO_1.5 and molten silicate deposits in gas turbine engines. Features shared in both systems include the absence of ternary compounds and no ternary solubility in the binary phases. In ZYS however, a quaternary invariant reaction was observed that eliminates the zircon-disilicate equilibrium at higher temperatures. The results suggest no appreciable difference in the reactions between silica and thermal barrier oxides based on ZrO₂-YO_1.5 or ZrO₂-GdO_1.5, or environmental barrier coatings based on the corresponding Y/Gd silicates. The phase diagrams derived from these experiments are part of a broader effort to develop thermodynamic databases that can help guide the design of next-generation TBCs.     

EB-PVD alumina (Al2O3) as a top coat on 7YSZ TBCs against CMAS/VA infiltration: Deposition and reaction mechanisms

Al₂O₃ was deposited as a top coat on a standard 7YSZ layer (or layers) by means of EB-PVD technique and the corresponding morphology of the Al₂O₃/7YSZ coatings was studied in detail. This multi-layer TBC system was tested against calcium-magnesium-aluminium-silicate (CMAS) recession by performing infiltration experiments for different time intervals from 5?min to 50?h at 1250?°C using two types of synthetic CMAS compositions and Eyjafjallajökull volcanic ash (VA) from Iceland. The results show that the studied EB-PVD Al₂O₃/7YSZ coatings react quickly with CMAS or VA melt and form crystalline spinel (MgAl_2-xFe_xO₄) and anorthite (CaAl₂Si₂O₄) phases. The presence of Fe-oxide in the CMAS has been found to be key element in influencing the spinel formation which was proved to be more efficient against CMAS sealing in comparison to the Fe-free CMAS compositions. Even though a rapid crystallization was assured, shrinkage cracks in the EB-PVD alumina layer produced during the crystallization heat treatment have proven to be detrimental for the CMAS/VA infiltration resistance. To overcome these microstructural drawbacks, an additional alumina deposition method, namely reaction-bonded alumina oxide (RBAO), was applied on top of EB-PVD Al₂O_3. RBAO acts as a sacrificial layer forming stable reaction products inhibiting further infiltration.     

Wetting,infiltration and interaction behavior of CMAS towards columnar YSZ coatings deposited by plasma spray physical vapor

Thermal barrier coatings (TBCs) produced by electron beam physical vapor deposition (EB-PVD) or plasma spray (PS) usually suffer from molten calcium-magnesium-alumino-silicate (CMAS) attack. In this study, columnar structured YSZ coatings were fabricated by plasma spray physical vapor deposition (PS-PVD). The coatings were CMAS-infiltrated at 1250?°C for short terms (1, 5, 30?min). The wetting and spreading dynamics of CMAS melt on the coating surface was in-situ investigated using a heating microscope. The results indicate that the spreading evolution of CMAS melt can be described in terms of two stages with varied time intervals and spreading velocities. Besides, the PS-PVD columnar coating (～100?μm thick) was fully penetrated by CMAS melt within 1?min. After the CMAS attack for 30?min, the original feathered-YSZ grains (tetragonal phase) in both PS-PVD and EB-PVD coatings were replaced by globular shaped monoclinic ZrO₂ grains in the interaction regions.     

Robocast zirconia-toughened alumina scaffolds: Processing,structural characterisation and interaction with human primary osteoblasts

Zirconia-toughened alumina (ZTA) is the gold-standard ceramic in hip arthroplasty, but still lacks direct osseointegration and a metal shell, often coated with a bioactive layer, is currently required. The latter could potentially be replaced by a thinner, architectured ZTA layer, thereby allowing for larger acetabular components, with larger range of motion and lower dislocation risk. Robocasting may be an adequate technique to fabricate the architectured layer. Therefore, as a first step, this study aimed to produce ZTA scaffolds (3D-ZTA) by robocasting and assess their in vitro response. Shape retention was achieved by using a stable, well-dispersed, high solid loading ink injected in acid pH waterbath. 3D-ZTA exhibit regularly spaced microporous, rough struts and fully interconnected macroporosity. Human primary osteoblasts were homogenously distributed inside 3D-ZTA and showed increased osteogenic marker expression compared to 2D-ZTA control. Further work will focus on optimizing scaffold design to improve cell retention and extracellular matrix maturation.     

Fabrication of ZnO-functionalized polypyrrole microcomposite as a protective coating to enhance anticorrosion performance of low carbon mild steel

In the present work, PPy, ZnO, and polypyrrole/zinc oxide (PPy/ZnO) microcomposites (1, 2, and 5 wt%) were prepared and their properties have been tuned for anticorrosion applications on low carbon mild steel. The synthesized products: ZnO, PPy, and composites were characterized by various sophisticated analytical techniques such as XRD, FTIR, Raman, FESEM, EDX, UV–VIS, TGA, and BET. The band frequencies observed at 480 and 588 cm⁻¹ in FTIR spectrum correspond to stretching vibrations of Zn-O and N-H bonds, respectively, broadening of the bands in the composites indicate strong interactions between ZnO and PPy matrix. The potentiodynamic polarization study of PPy and PPy/ZnO composite was carried out in 3.5% NaCl solution to investigate the corrosion resistance efficiency. PPy/1 wt% ZnO (I_corr = 190 nA) composite coating on low carbon mild steel was observed to exhibit best corrosion protection property compared to PPy (121 μA), 2 and 5 wt% ZnO (242, 295 nA) composites. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48319.     

Innovative conductive polymer composite coating for aircrafts lightning strike protection

A new kind of high electrical conductive epoxy coating with low filler rate was investigated for lightning strike protection (LSP) of carbon fiber reinforced polymer (CFRP). The coating without CFRP substrate was firstly studied. The influence of silver submicronic wires (AgSWs) with a high aspect ratio on the electrical behavior is observed; that is, the electrical resistivity evolution, the current density value, and the electrical conduction mechanisms as function of temperature. The preponderant electrical conduction mechanism is an Ohmic behavior. The higher level of conductivity obtained is 5.5 × 10⁵ S m⁻¹ for 9% vol of AgSWs. Lightning strike tests were carried out on an epoxy/AgSWs coating filled with 8% in volume (74 gsm) and deposited on a CFRP. The ultrasonic testing after lightning strike on coated CFRP shows no structural delamination and demonstrates the interest of this new route for an efficient LSP. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48700.