Interface toughness measurement of environmental barrier coatings for SiC/SiC composites

A simple interface fracture test for ceramics coatings on ceramics matrix composites was developed. A kind of asymmetric double cantilever beam (ADCB) test was proposed so that the interface fracture toughness could be measured by a small and simple-shape specimen without applying inter-laminar shear or tensile loading to CMC substrate. The proposed test was applied to a classic environmental barrier coating (EBC) consisting of mullite layer and Si bond coat on monolithic SiC substrate. A small block specimen of ~3×4×3 mm was cut from the coated substrate, and a notch was machined along the interface. The notch was opened by inserting a wedge to the notch; the notch opening displacement at the notch root was measured. From the critical notch opening displacement and load where the crack starts to propagate, interface fracture toughness was calculated. Several studies have reported that the reaction product is formed at the interface of various multilayer EBC systems with a Si bond coat, and the reaction product may cause the degradation of interface adhesion. To investigate the effect of such reaction products, the test was also applied to the heat-exposed EBC. The interface toughness after the heating was measured as a function of exposure time. The interface toughness varied with exposure time. Formation of a reaction products was observed at the interface during the heating; they grew with exposure time. The variation of the toughness was discussed based on the interface observation and was correlated to the interface reaction products

An evaluation method for interface toughness of environmental barrier coatings (EBCs) on ceramic matrix composites (CMCs)

1. Introduction Application of SiC fiber-reinforced SiC matrix composites (SiC/SiCs) in civil jet engines has been started and is expected to be expand. To use SiC/SiCs in combustion gas at high temperature of 1300-1400 ˚C, an environmental barrier coatings (EBCs) are needed to protect SiC/SiC from corrosion by water vapor. EBC and SiC/SiC substrate is subject to severe heat cycle from service temperature to ambient temperature and thus the thermomechanical durability is required as well as chemical environmental barrier properties. It is necessary to measure interface fracture toughness for the prediction of EBC life time and safe use of SiC/SiC. A variety of test methods evaluating interface adhesion of coating has been proposed. However only a few tests can provide a quantitative interface toughness as a function of the phase angle. Specifically a test for mode I rich loading which is likely to occur at the interface between the EBC and the SiC/SiC substrate with larger coefficient of thermal expansion in the EBC is lacking. In this study, a variation on the asymmetric double cantilever beam (ADCB) test is proposed so that the interface toughness can be measured in a small specimen of simple shape. 2. Experimental procedure A multilayer coating system of mullite topcoat and Si bond coat on monolithic SiC substrate was used. The coating layers of Si and mullite were deposited by atmospheric plasma spray (APS). The thickness of the layer was 100 μm in the Si bond coat and 250 μm in the mullite topcoat The coated SiC plate was cut into the specimen of 4 × 3 mm. A notch was introduced using a diamond wire saw to the depth of 0.5-1 mm along the interface. The notched specimen was mounted on an x-z stage located below a wedge. The insertion of the wedge was done by raising the motorized z stage with a constant speed. The load and notch opening displacement was measured during the test. The test was done until the load decrease almost zero and the coating was removed completely. Please click Additional Files below to see the full abstract

Residual stress measurement of YB silicates by Raman Spectroscopy: First-principles and experimental studies

Components of next-generation gas turbines made from lightweight SiC-based ceramics need environmental barrier coatings (EBCs) to protect from water vapor at high temperature because Si-based ceramics vaporize in such environments. Yb silicates Yb2SiO5 and Yb2Si2O7 are promising EBC materials. In EBCs, residual stresses develop during thermal cycling due to mismatch between the thermal expansion coefficients of the silicate and the underlying ceramics, resulting in critical fatigue of the coating structure [1]. Raman microscopy is one method for measuring stress distributions in coating materials and has the potential to be used for diagnosing EBCs. Its suitability for analyzing stress states of Yb silicates has been unknown. In this study, we examine Raman spectra of Yb2SiO5, and Yb2Si2O7 under hydrostatic pressure based on first-principles calculations based on the density functional theory and we also examine the spectra of Yb2Si2O7 under uniaxial compressive stress in experiments using polycrystalline samples. When no external pressures applied, good agreement between calculated and experimental spectra is obtained as shown in Figure 1. The differences in the spectra between the silicates demonstrate the utility of using Raman microscopy to detect compositional changes in Yb-silicate coatings. From the calculations, lattice vibrations associated with a Raman peak are identified as exemplified by the characteristic mode of Si2O7 units in Yb2Si2O7 shown in figure 1(a). Please click Additional Files below to see the full abstract

シジョウ トワ ツクリダス モノ ヤサイ スイーツ デ アラタナ シジョウ オ ソウゾウシタ パティスリー ポタジエ

ビジネス・フォーラム特別講

Scalable bacterial production of moldable and recyclable biomineralized cellulose with tunable mechanical properties

Sustainable structural materials with excellent impact-resistance properties are urgently needed but challenging to produce, especially in a scalable fashion and with control over 3D shape. Here, we show that bacterial cellulose (BC) and bacterially precipitated calcium carbonate self-assemble into a layered structure reminiscent of tough biomineralized materials in nature (nacre, bone, dentin). The fabrication method consists of biomineralizing BC to form an organic/inorganic mixed slurry, in which calcium carbonate crystal size is controlled with bacterial poly(γ-glutamic acid) and magnesium ions. This slurry self-assembles into a layered material that combines high toughness and high impact and fire resistance. The rapid fabrication is readily scalable, without involving toxic chemicals. Notably, the biomineralized BC can be repeatedly recycled and molded into any desired 3D shape and size using a simple kitchen blender and sieve. This fully biodegradable composite is well suited for use as a component in daily life, including furniture, helmets, and protective garments.The authors thank Ward Groutars and Elvin Karana for useful discussions. K.Y. is supported financially by the China Scholarship Council (CSC no.201706630001). S.B. is funded by the Air Force Office of Scientific Research, Asian Office of Aerospace Research and Development (grant no. FA2386-18-1-4059)

Evaluation of the anti-inflammatory effects of synthesised tanshinone I and isotanshinone I analogues in zebrafish

During inflammation, dysregulated neutrophil behaviour can play a major role in a range of chronic inflammatory diseases, for many of which current treatments are generally ineffective. Recently, specific naturally occurring tanshinones have shown promising anti-inflammatory effects by targeting neutrophils in vivo, yet such tanshinones, and moreover, their isomeric isotanshinone counterparts, are still a largely underexplored class of compounds, both in terms of synthesis and biological effects. To explore the anti-inflammatory effects of isotanshinones, and the tanshinones more generally, a series of substituted tanshinone and isotanshinone analogues was synthesised, alongside other structurally similar molecules. Evaluation of these using a transgenic zebrafish model of neutrophilic inflammation revealed differential anti-inflammatory profiles in vivo, with a number of compounds exhibiting promising effects. Several compounds reduce initial neutrophil recruitment and/or promote resolution of neutrophilic inflammation, of which two also result in increased apoptosis of human neutrophils. In particular, the methoxy-substituted tanshinone 39 specifically accelerates resolution of inflammation without affecting the recruitment of neutrophils to inflammatory sites, making this a particularly attractive candidate for potential pro-resolution therapeutics, as well as a possible lead for future development of functionalised tanshinones as molecular tools and/or chemical probes. The structurally related β-lapachones promote neutrophil recruitment but do not affect resolution. We also observed notable differences in toxicity profiles between compound classes. Overall, we provide new insights into the in vivo anti-inflammatory activities of several novel tanshinones, isotanshinones, and structurally related compounds

Allelopathic effects of Ulva pertusa, Corallina pilulifera and Sargassum thunbergii on the growth of the dinoflagellates Heterosigma akashiwo and Alexandrium tamarense

The allelopathic effects of fresh tissue, dry powder and aqueous extracts of three macroalgae, Ulva pertusa, Corallina pilulifera and Sargassum thunbergii, on the growth of the dinoflagellates Heterosigma akashiwo and Alexandrium tamarense were evaluated using coexistence culture systems in which concentrations of the three macroalga were varied. The results of the coexistence assay showed that the growth of the two microalgae was strongly inhibited by using fresh tissue, dry powder and aqueous extracts of the three macroalga; the allelochemicals were lethal to H. akashiwo at relatively higher concentrations of the three macroalga. The macroalgae showing the most allelopathic effect on H. akashiwo and A. tamarense using fresh tissue were U. pertusa and S. thunbergii, using dry powder were S. thunbergii and U. pertusa, and using aqueous extracts were U. pertusa and C. pilulifera. We also examined the potential allelopathic effect on the two microalgae of culture filtrate of the three macroalga; culture medium filtrate initially exhibited no inhibitory effects when first added but inhibitory effects became apparent under semi-continuous addition, which suggested that continuous release of small quantities of rapidly degradable allelochemicals from the fresh macroalgal tissue were essential to effectively inhibit the growth of the two microalgae

Bioinspired approaches for toughening of fibre reinforced polymer composites

In Nature, there are a large range of tough, strong, lightweight and multifunctional structures that can be an inspiration to better performingmaterials. Thiswork presents a review of structures found in Nature, frombiological ceramics and ceramics composites, biological polymers and polymers composites, biological cellular materials, biological elastomers to functional biological materials, and their main tougheningmechanisms, envisaging potential mimicking approaches that can be applied in advanced continuous fibre reinforced polymer (FRP) composite structures. For this, themost common engineering compositemanufacturing processes and current composite damage mitigation approaches are analysed. This aims at establishing the constraints of biomimetic approaches development as these bioinspired structures are to be manufactured by composite technologies. Combining both Nature approaches and engineering composites developments is a route for the design and manufacturing of high mechanical performance and multifunctional composite structures, therefore new bioinspired solutions are proposed.This research was funded by the project “IAMAT—Introduction of advanced materials technologies into new product development for the mobility industries”, with reference MITP-TB/PFM/0005/2013, under the MIT-Portugal program and in the scope of projects with references UIDB/05256/2020 and UIDP/05256/2020, exclusively financed by FCT - Fundação para a Ciência e Tecnologia

Algicidal activity of polyunsaturated fatty acids derived from Ulva fasciata and U. pertusa (Ulvaceae, Chlorophyta) on phytoplankton

Isolation of algicidal compounds from Ulva fasciata revealed that the algicidal substances were the polyunsaturated fatty acids (PUFAs) as hexadeca-4,7,10,13-tetraenoic acid (HDTA) C16:4 n-3, octadeca-6,9,12,15- tetraenoic acid (ODTA) C18:4 n-3, α-linolenic acid (ALA) C18:3 n-3 and linoleic acid (LA) C18:2 n-6. The fatty acid composition of four species of Ulvaceae (U. fasciata, U. pertusa, U. arasakii and U. conglobota) was analyzed by capillary gas chromatography to investigate the relationship with the algicidal activity. The results indicate that highly algicidal species, U. fasciata and U. pertusa, showed higher contents of C16:4 n-3, C18:3 n-3, and C18:4 n-3. Concentrations of these PUFAs released from the seaweed in the culture medium were also analyzed. These PUFAs were found to be significantly active against Chattonella antiqua, C. marina, Fibrocapsa japonica, Heterosigma akashiwo, Karenia mikimotoi, moderately effective against Heterocapsa circularisquama, Prorocentrum minimum, P. sigmoides, Scrippsiella trochoidea, whereas low effective against Alexandrium catenella and Cochlodinium polykrikoides. It is suggested that the PUFAs are useful mitigation agents to remove several harmful effects without causing detrimental effects on surrounding marine living organisms