The effect of alkali niobate addition on the phase stability and dielectric properties of Pb (Zn13 Nb23) O3 based ceramic

While Pb (Zn13 Nb23) O3 -PbTi O3 (PZN-PT) single crystals have shown superior ferroelectric properties, less scientific and technical interests have been placed on PZN-PT polycrystalline ceramics due to their poor thermodynamic stability and the difficult processing conditions. Here, we stabilized the PZN-PT based ceramics by adding alkali niobates such as NaNb O3 (NN) and KNb O3 (KN) and investigated their structure and dielectric properties. Two stabilization mechanisms are suggested in alkali niobate added PZN-PT ceramics, increased tolerance factor and enhanced electronegativity difference. KN stabilized the perovskite structure of PZN-PT based ceramics more effectively than NN. Both PZN-PT-KN and PZN-PT-NN ceramics showed the typical behavior of relaxor ferroelectrics. The temperature of maximum dielectric constant of PZN-PT-NN was slightly higher than that of the PZN-PT-KN, which was explained by the difference in ionic size and B -site ordering. © 2007 American Institute of Physics

Structural change in polar nanoregion in alkali niobate added Pb(Zn <inf>1/3</inf>Nb <inf>2/3</inf>) <inf>0.95</inf>Ti <inf>0.05</inf>O <inf>3</inf> single crystal and its effect on ferroelectric properties

Pb(Zn 1/3Nb 2/3) 0.95Ti 0.05O 3 (PZNT) single crystals with 5 mol.% alkali niobate such as LiNbO 3 (LN), NaNbO 3 (NN), and KNbO 3 (KN) were fabricated by using a flux method to investigate the effect of A-site cation radius on the structure and ferroelectric properties of PZNT under electric field (E-field). Their structure and properties showed different electric field dependence. Polarization versus electric field and strain versus electric field curves of PZNT-0.05LN showed E-field induced phase transition from a relaxor state to a normal ferroelectric state. However, only relaxor behavior was observed in PZNT-0.05NN and PZNT-0.05KN. The effect of A-site ion doping is attributed to the change in local lattice distortion and polar nano-region. When smaller cation such as Li ion substitutes Pb ion, the off-center displacement of Nb ion stabilizes rhombohedral lattice distortion. They, in turn, facilitate the development of macro-domains under electric field (E-field) in PZNT-0.05LN. In contrast, the substitution of Pb with larger cations such as Ni and K decreases the rhombohedral distortion of PZNT, which leads to the disappearance of unique E-field induced phase transition from rhombohedral to tetragonal phase in PZNT. Therefore, non-linear electrostrictive behavior of relaxor ferroelectrics is found in PZNT-0.05NN and PZNT-0.05KN. © 2012 American Institute of Physics

A study on fire design accidental loads for aluminum safety helidecks

The helideck structure must satisfy the safety requirements associated with various environmental and accidental loads. Especially, there have been a number of fire accidents offshore due to helicopter collision (take-off and/or landing) in recent decades. To prevent further accidents, a substantial amount of effort has been directed toward the management of fire in the safety design of offshore helidecks. The aims of this study are to introduce and apply a procedure for quantitative risk assessment and management of fires by defining the fire loads with an applied example. The frequency of helicopter accidents are considered, and design accidental levels are applied. The proposed procedures for determining design fire loads can be efficiently applied in offshore helideck development projects

Morphology and Microphase Separation of Star Copolymers

Star copolymers have attracted significant interest due to their different characteristics compared with diblock copolymers, including higher critical micelle concentration, lower viscosity, unique spatial shape, or morphologies. Development of synthetic skills such as anionic polymerization and controlled radical polymerization have made it possible to make diverse architectures of polymers. Depending on the molecular architecture of the copolymer, numerous morphologies are possible, for instance, Archimedean tiling patterns and cylindrical microdomains at symmetric volume fraction for miktoarm star copolymers as well as asymmetric lamellar microdomains for star-shaped copolymers, which have not been reported for linear block copolymers. In this review, we focus on morphologies and microphase separations of miktoarm (A(m)B(n) and ABC miktoarm) star copolymers and star-shaped [(A-b-B)(n)] copolymers with nonlinear architecture. (C) 2014 Wiley Periodicals, Inc.X112123Ysciescopu

Thermoelectric properties of Al-doped mesoporous ZnO thin films

Al-doped mesoporous ZnO thin films were synthesized by a sol-gel process and an evaporation-induced self-assembly process. In this work, the effects of Al doping concentration on the electrical conductivity and characterization of mesoporous ZnO thin films were investigated. By changing the Al doping concentration, ZnO grain growth is inhibited, and the mesoporous structure of ZnO is maintained during a relatively high temperature annealing process. The porosity of Al-doped mesoporous ZnO thin films increased slightly with increasing Al doping concentration. Finally, as electrical conductivity was increased as electrons were freed and pore structure was maintained by inhibiting grain growth, the thermoelectric property was enhanced with increasing Al concentration. © 2013 Min-Hee Hong et al

Full-scale collapse testing of a steel stiffened plate structure under axial-compressive loading at a temperature of −80°C

The aim of the paper was to develop a test database of the ultimate strength characteristics of full-scale steel stiffened plate structures under axial compressive loading at a temperature of −80°C. This paper is a sequel to the authors’ articles (Paik et al. 2020a, https://doi.org/10.1016/j.istruc.2020.05.026 and Paik et al. 2020b, https://doi.org/10.1080/17445302.2020.1787930). In contrast to the earlier articles associated with room temperature or cryogenic condition, this paper investigated the effect of a low temperature at −80°C which is within the boundary range of temperature of the ductile-to-brittle fracture transition for carbon steels. A material model representing the test conditions was also proposed to capture the characteristics of carbon steels at low temperatures both in tension and in compression, and it was used in finite element method simulations of the full-scale experiment. A comparison between numerical analyses and experiments showed that the proposed model could successfully predict the failure modes and ultimate strength characteristics at low temperatures for stiffened plate structures under axial compressive loading conditions

Fresh and sea water immersion corrosion testing on marine structural steel at low temperature

The aim of the present study is to experimentally examine the corrosion progress characteristics of steel associated with fresh and sea water immersion at low temperature. Three types of steel, namely mild steel (Grade A) and high tensile steel (Grades A and D) are tested under various corrosive conditions in the fresh water, in the sea water and in the air at a temperature of 18°C, 0°C and −10°C. Mass loss of test specimen due to corrosion is measured at a monthly interval and it is converted to a loss of steel plate thickness. Based on the test database, the effects of parameters affecting the corrosion progress are discussed. Test database obtained in the present study is documented

Safety-zone layout design for a floating LNG-Fueled power plant in bunkering process

The use of natural gas (NG) as an energy source is increasing. This paper studies the safety-zone layout design of a floating power plant fueled by NG. Hazards from the unwanted release of liquefied NG (LNG) in bunkering or NG in operation always exist, and it is thus important to reduce the associated risk to an acceptable level. One engineering technique used to reduce this risk involves the design of a safety zone to prevent and minimize exposure to unwated release of LNG or NG that may occur during the bunkering process. Industry practices are available for the design of the layout of such safety-zones, but their applicability to floating power plants is uncertain, and a more intuitive approach is required. The objective of this study is to discuss the challenges of establishing safety zones on floating power plants by reviewing and comparing existing industrial practices and to propose a hybrid approach for the design of a safety-zone layout. The applicability of the proposed hybrid approach is discussed with an applied example

A Preliminary Risk Assessment on the Development of a Small-Scaled Floating Power Plant

This paper introduces a preliminary risk assessment method carried out on a newly developed floating power plant. The small-scale floating power plant has been developed to provide electric power for areas on demand, and this is a kind of a new concept system which is not clearly classified in the maritime industry. To grant the feasibility for this novel system design, a set of risk assessment activities is essentially required, and in this context, a hazard identification (HAZID) study is conducted at the very early stage of the plant design. The aims of this HAZID study are to verify the inherent safety of the initial plant design and to provide any recommendations on the next design stages. For this purpose, the potential hazards are identified in view of personnel, structural, and asset effects in association with the operation of the power plant and all the identified hazards and relevant risks are assessed with the defined criteria using a simple risk matrix. As a result, the risk or safety level of the conceptual plant design is estimated, and some design changes are suggested to give a better balance between the safety and the cost of the plant system. Overall, this paper shows how the primitive risk assessment techniques are utilized as a practical engineering tool in the development of the marine system

Methods for determining the optimal arrangement of water deluge systems on offshore installations

Offshore installations are prone to fire and/or explosion accidents. Fires have particularly serious consequences due to their high temperatures and heat flux, which affect humans, structures and environments alike. Due to the hydrocarbon explosions caused by delayed ignition following gas dispersion, fires can be the result of immediate ignition after gas release. Accordingly, it can be difficult to decrease their frequency, which is an element of risk (risk=frequency×consequence), using an active protection system (APS) such as gas detectors capable of shutting down the operation. Thus, it is more efficient to reduce the consequence using a passive protection system (PSS) such as water spray. It is important to decide the number and location of water deluge systems, thus the aim of this study is to introduce a new procedure for optimising the locations of water deluge systems using the water deluge location index (WLI) proposed herein. The locations of water deluge systems are thus optimised based on the results of credible fire scenarios using a three-dimensional computational fluid dynamics (CFD) tool. The effects of water spray and the effectiveness of the WLI are investigated in comparison with uniformly distributed sprays