Nickel-based super alloys are gaining more significance, now-a-days, with extensive applications in aerospace, marine, nuclear reactor and chemical industries. Several characteristics including ...superior mechanical and chemical properties at elevated temperature, high toughness and ductility, high melting point, excellent resistance to corrosion, thermal shocks, thermal fatigue and erosion are primarily responsible for wide domain of application. Nevertheless, machined surface integrity of nickel-based super alloys is a critical aspect which influences functional performance including fatigue life of the component. This review paper presents state-of-the-art on various surface integrity characteristics during machining of nickel-based super alloys. Influence of various cutting parameters, cutting environment, coating, wear and edge geometry of cutting tools on different features of surface integrity has been critically explained. These characteristics encompass surface roughness, defects (surface cavities, metal debris, plucking, smeared material, redeposited material, cracked carbide particles, feed marks, grooves and laps), metallurgical aspects in the form of surface and sub-surface microstructure phase transformation, dynamic recrystallisation and grain refinement and mechanical characteristics such as work hardening and residual stress. Microstructural modification of deformed layer, profile of residual stresses and their influence on fatigue durability have been given significant emphasis. Future research endeavour might focus on development of new grades, advanced processing techniques of the same to ensure their superior stability of microstructure and thermo-mechanical properties along with advanced manufacturing processes like additive manufacturing to achieve highest level of fatigue durability of safety critical components while maintaining acceptable surface integrity and productivity.
•State-of-the-art review of machined surface integrity of nickel-based super alloys.•Effects of various cutting condition on surface integrity critically explained.•Surface topography, microstructure, work hardening and residual stress emphasized.•Surface integrity correlated with fatigue life of safety critical components.
The uncertain future of protected lands and waters Golden Kroner, Rachel E; Qin, Siyu; Cook, Carly N ...
Science (American Association for the Advancement of Science),
05/2019, Letnik:
364, Številka:
6443
Journal Article
Recenzirano
Odprti dostop
Protected areas are intended to safeguard biodiversity in perpetuity, yet evidence suggests that widespread legal changes undermine protected area durability and efficacy. We documented these legal ...changes-protected area downgrading, downsizing, and degazettement (PADDD) events-in the United States and Amazonian countries and compiled available data globally. Governments of the United States and Amazonian countries enacted 269 and 440 PADDD events, respectively. Between 1892 and 2018, 73 countries enacted 3749 PADDD events, removing 519,857 square kilometers from protection and tempering regulations in an additional 1,659,972 square kilometers; 78% of events were enacted since 2000. Most PADDD events (62%) are associated with industrial-scale resource extraction and development, suggesting that PADDD may compromise biodiversity conservation objectives. Strategic policy responses are needed to address PADDD and sustain effective protected areas.
This paper compares the performance over time of seven different operation modes with the scope of investigating realistic degradation responses of a polymer electrolyte membrane water electrolysis ...(PEM WE) to different operation modes for grid-balancing services. Among these modes are constant current and constant voltage operations at different temperatures and current cycling operations, including a solar profile. It was found that faster current cycling improved the overall cell performance over the test period of 500 h, mainly due to a decrease in total ohmic resistance, which is also observed during the break-in phase preceding the experiments. Dynamic operation led to more severe fluoride emission from the catalyst binder, which improved the performance in terms of cell potential but could be a concern for long term degradation as membrane thinning promotes higher gas crossover. All other operation modes on the other hand suffered from an increase in total ohmic resistance, leading to an overall performance decrease, which is suspected to be due to the passivation of the Ti components. Higher operating temperatures were found to enhance cell performance, but are detrimental from a durability point of view since they exacerbate both membrane thinning and passivation processes.
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•Dynamic operation does not enhance degradation.•Effect of membrane thinning was separated from other degradation mechanisms.•Temperatures above 80 °C require mitigation strategies for all components.
Ever increasing attention is being paid to deterioration prediction and service life modelling of reinforced concrete structures. Research has progressed to a stage where service life models and ...design philosophies are, to varying degrees, included in some codes and standards, such as the fib Model Codes and ISO 13823. This has helped to base practical durability design on sound engineering approaches. This paper reviews service life modelling and prediction, and service life design, covering limit state design philosophies and deterioration models. An overview on recent developments, and a critical review on common assumptions in service life modelling and on the application and limitations of the various approaches, are presented. It is emphasised that design approaches and models need to be validated with field observations. It is argued that a performance-based approach is the most suitable engineering tool for durability design.
Knowledge about the resistance of wood-polymer composites (WPCs) to biological attack is of high importance for purpose-oriented use in outdoor applications. To gain this knowledge, uniform test ...methods are essential. EN 15534-1 (2018) provides a general framework, including the recommendation of applying a pre-weathering procedure before the biological laboratory tests. However, the procedure's manner is not specified, and its necessity assumes that a durability test without such pre-weathering will not produce the structural changes that occur during outdoor use. To verify this assumption, this study examined the influence of natural, ground-level pre-weathering on the material properties of different WPC variants, which were tested at intervals of six months in four durability tests under laboratory conditions in accordance with EN 15534-1 (2018). Weathering factors were calculated from determined characteristic values such as mass loss, and loss in moduli of elasticity (MOE) and rupture (MOR). The weathering factors based on mechanical properties tended to decrease with increasing weathering duration. The expected negative influence of pre-weathering on these material properties was thus not confirmed. The weathering factors based on mass loss were subject to high variation. No significant effect of pre-weathering on mass loss due to fungal attack became evident. Overall, the necessity of a pre-weathering step in biological durability tests shall be questioned based on the presented results.
•The paper reviews the utilization of natural volcanic pozzolan (NPs) in the production of AAM.•The available raw materials are a vital aspect for the technological transition of the AAM.•This review ...analyzed the role of characteristics of NPs in the alkaline activation.•This paper can encourage and promote the research on the alkaline activation of NPs.•This review presents the future challenges and opportunities in this topic.
Alkali-activated materials (AAM) represent a line of research of great interest around the world as a real alternative to replace Portland cement (OPC). Despite this global interest, it is believed that current and future research should focus on overcoming the challenges that this technology faces with regard to its application at an industrial level. One of the main barriers to scale at the industrial level is the scarcity of studies on truly available and sustainable raw materials (precursors and activators). This review emphasizes natural volcanic pozzolans (NPs), also named volcanic ashes, as a globally available and sustainable raw material for industrial production of AAM in the foreseeable future. To this end, the most important findings about mechanical performance and durability reported by researchers at a global level are presented and described, and a constructive analysis is carried out in order to establish the future challenges and opportunities to carry out a technological transition of these advances (industrial application) in countries rich in materials derived from volcanic activity.
•Core-shell structured lightweight aggregate (CSA) was produced by cold bonding method.•Effects of curing method and surface treatment on properties of CSA were investigated.•CSA and expanded clay ...aggregate (ECA) were used for production of lightweight concrete.•Mechanical and durable Properties of concrete made of either CSA or ECA were compared.
In this study, core-shell structured lightweight aggregates (CSA) were produced through the cold bonding method, by encapsulating an expanded perlite particle (as a core structure) within a shell matrix composed of cement, fly ash and expanded perlite powder. The effect of different curing regimes on the mechanical and microstructural properties of the CSA were studied. To enhance the characteristics of the aggregates produced, they were surface treated by a mixture of cement and silica fume, using two different treatment methods. Afterwards, the properties of lightweight concrete made of either CSA or expanded clay aggregate (ECA) were compared closely in terms of their potential economic and environmental benefits, in response to the high energy consumption associated with the production of ECA. The results revealed that curing at a relative humidity of 99% is the most appropriate curing method for CSA. In addition, treating the CSA surface contributes significantly to enhancing its bulk crushing strength, by about 14–18%. The findings also demonstrate the feasibility of using CSA to produce lightweight aggregate concrete, with a dry density and compressive strength ranging from 1115 to 1540 kg/m3 and from 17.9 to 25.8 MPa, respectively, with a corresponding thermal conductivity range of 0.3169–0.6660 W/m·K.
The self‐healing of zinc‐ion batteries (ZIBs) will not only significantly improve the durability and extend the lifetime of devices, but also decrease electronic waste and economic cost. A poly(vinyl ...alcohol)/zinc trifluoromethanesulfonate (PVA/Zn(CF3SO3)2) hydrogel electrolyte was fabricated by a facile freeze/thaw strategy. PVA/Zn(CF3SO3)2 hydrogels possess excellent ionic conductivity and stable electrochemical performance. Such hydrogel electrolytes can autonomously self‐heal by hydrogen bonding without any external stimulus. All‐in‐one integrated ZIBs can be assembled by incorporating the cathode, separator, and anode into hydrogel matrix since the fabrication of PVA/Zn(CF3SO3)2 hydrogel is a process of converting the liquid to quasi‐solid state. The ZIBs show an outstanding self‐healing and can recover electrochemical performance completely even after several cutting/healing cycles.
A self‐healing PVA/Zn(CF3SO3)2 hydrogel electrolyte was developed by a facile freeze/thaw strategy. It can self‐heal by hydrogen bonding without external stimuli. All‐in‐one integrated Zn ion batteries (ZIBs) can be assembled by incorporating the cathode, separator, and anode into a hydrogel matrix. The ZIBs show an outstanding self‐healing ability and can recover electrochemical performance completely even after several cutting/healing cycles.
•Research papers on fly ash and fly ash-slag geopolymer mortar are reviewed.•Research papers from the period 2005 to 2020 are discussed.•Fresh and hardened properties are elaborated.•Mechanical ...properties, durability and thermal resistance are also addressed.•Comparison between fly ash and fly ash-slag mortar are presented.•Influence of various additives on the properties are also discussed.
Geopolymer is a sub-class of alkali activated materials composed of base materials containing aluminosilicates which can be used for construction with reduced environmental impact by utilisation of waste material leading to economical construction. This study reviews the properties of fly ash and fly ash-slag geopolymer mortar including microstructural properties, fresh properties such as setting time and workability, hardened properties such as compressive strength and tensile strength and durability properties (thermal resistance, shrinkage, acid resistance, chloride resistance, sulphate resistance). The effect of types of alkaline solutions, its concentration, and combination of different types of alkaline activators, fine aggregate to binder ratio, alkaline solution to binder ratio, curing temperature and curing duration, and presence of different types of superplasticizers are discussed. The study also reviews the effect of different additives such as silica fume, alccofine, quartz powder, alumina, epoxy, bio-additives, different types of fibres, nano-materials in fly ash and fly ash-slag geopolymer mortar. The present study carried out elaborate discussion of the effect of mix proportioning on fresh, hardened and durability properties of fly ash geopolymer and fly ash-slag geopolymer mortar. The study summarises the common findings from the reviewed research papers.
We propose the pseudobrookite Fe2TiO5 nanofiber with abundant oxygen vacancies as a new electrocatalyst to ambiently reduce nitrate to ammonia. Such catalyst achieves a large NH3 yield of 0.73 mmol ...h−1 mg−1cat. and a high Faradaic Efficiency (FE) of 87.6 % in phosphate buffer saline solution with 0.1 M NaNO3, which is lifted to 1.36 mmol h−1 mg−1cat. and 96.06 % at −0.9 V vs. RHE for nitrite conversion to ammonia in 0.1 M NaNO2. It also shows excellent electrochemical durability and structural stability. Theoretical calculation reveals the enhanced conductivity of this catalyst and an extremely low free energy of −0.28 eV for nitrate adsorption at the presence of vacant oxygen.
Pseudobrookite Fe2TiO5 nanofiber with oxygen vacancies is proposed as an efficient electrocatalyst for reducing nitrate to ammonia, which achieves a large NH3 yield of 0.73 mmol h−1 mg−1cat. and a high Faradaic efficiency of 87.6 %. It also shows excellent electrochemical durability and structural stability. Theoretical calculations reveal its high electrical conductivity and extremely low free energy for nitrate adsorption.
