Calcia-doped yttria-stabilized zirconia for thermal barrier coatings: synthesis and characterization

Doping with other oxides has been a stabilization method of ZrO2 for thermal barrier coating applications. Such a stabilized system is 7-8mol% YO1.5-doped zirconia (7YSZ), which has been in use for around 20years. In this study, calcia (CaO) and yttria (Y2O3) have been used for doping ZrO2 to produce a stable single-phase cubic calcia-doped yttria-stabilized zirconia (CaYSZ). This has been synthesized using wet chemical synthesis as well as by solid-state synthesis. Unlike partially stabilized zirconia where 5mol% CaO is doped into ZrO2, CaYSZ has been found to be stable up to 1600°C. Detailed CaYSZ synthesis steps and phase characterization are presented. Wet chemical synthesis resulted in a stable single-phase CaYSZ just after 4h treatment at 1400°C, whereas a 36h annealing at 1600°C is required for CaYSZ synthesis during solid-state processing. The CaYSZ has been found stable even for 600h at 1250°C. Coefficient of thermal expansion and sintering temperature of CaYSZ was found to be 11×10−6K−1 and 1220°C, respectively, which are comparable to 7YSZ. An increase in sintering rate with increasing dopant concentration has also been observe

Rank one and mixing differentiable flows

We construct, over some minimal translations of the two torus, special flows under a differentiable ceiling function that combine the properties of mixing and rank one

Correlation Function Approach for Estimating Thermal Conductivity in Highly Porous Fibrous Materials

Heat transport in highly porous fiber networks is analyzed via two-point correlation functions. Fibers are assumed to be long and thin to allow a large number of crossing points per fiber. The network is characterized by three parameters: the fiber aspect ratio, the porosity and the anisotropy of the structure. We show that the effective thermal conductivity of the system can be estimated from knowledge of the porosity and the correlation lengths of the correlation functions obtained from a fiber structure image. As an application, the effects of the fiber aspect ratio and the network anisotropy on the thermal conductivity is studied

Fast Numerical Methods for the Design of Layered Photonic Structures with Rough Interfaces

Modified boundary conditions (MBC) and a multilayer approach (MA) are proposed as fast and efficient numerical methods for the design of 1D photonic structures with rough interfaces. These methods are applicable for the structures, composed of materials with arbitrary permittivity tensor. MBC and MA are numerically validated on different types of interface roughness and permittivities of the constituent materials. The proposed methods can be combined with the 4x4 scattering matrix method as a field solver and an evolutionary strategy as an optimizer. The resulted optimization procedure is fast, accurate, numerically stable and can be used to design structures for various applications

Microbial synthesis of silver nanoparticles by streptomyces glaucus and spirulina platensis

Microbial synthesis of nanoparticles has a potential to develop simple, costeffective and eco-friendly methods for production of technologically important materials. In this study, for the first time a novelactinomycete strain Streptomyces glaucus71 MD isolated from a soy rhizosphere in Georgiais for the first time extensively characterized and utilized for the synthesis of silver nanoparticles. Scanning Electron Microscope (SEM) allowed observing extracellular synthesis of nanoparticles, which has many advantages from the point of view of applications. Production of silver nanoparticles proceeded extracellularlywith the participation of another microorganism, bluegreen microalgae Spirulinaplatensis (S. platensis). In this study it is shown that the production rate of the nanoparticles depends not only on the initial concentration of AgNO3 but also varies with time in a nonmonotonic way. SEM study of silver nanoparticles remaining on the surface of microalgae revealed that after 1 day of exposure to 1 mM AgNO3 nanoparticles were arranged as long aggregates along S. platensiscells strongly damaged by silver ions. However, after 5 days of exposure to silver S. platensiscells looked completely recovered and the nanoparticles were distributed more uniformly on the surface of the cells. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2067

Correlation Function Analysis of Fiber Networks: Implications for Thermal Conductivity

The heat transport in highly porous fiber structures is investigated. The fibers are supposed to be thin, but long, so that the number of the inter-fiber connections along each fiber is large. We show that the effective conductivity of such structures can be found from the correlation length of the two-point correlation function of the local conductivities. Estimation of the parameters, determining the conductivity, from the 2D images of the structures is analyzed

Potential of Glassy Carbon and Silicon Carbide Photonic Structures as Electromagnetic Radiation Shields for Atmospheric Re-entry

During high-velocity atmospheric entries, space vehicles can be exposed to strong electromagnetic radiation from ionized gas in the shock layer. Glassy carbon (GC) and silicon carbide (SiC) are candidate thermal protection materials due to their high melting point and also their good thermal and mechanical properties. Based on data from shock tube experiments, a significant fraction of radiation at hypersonic entry conditions is in the frequency range from 215 to 415 THz. We propose and analyze SiC and GC photonic structures to increase the reflection of radiation in that range. For this purpose, we performed numerical optimizations of various structures using an evolutionary strategy. Among the considered structures are layered, porous, woodpile, inverse opal and guided-mode resonance structures. In order to estimate the impact of fabrication inaccuracies, the sensitivity of the reflectivity to structural imperfections is analyzed. We estimate that the reflectivity of GC photonic structures is limited to 38% in the aforementioned range, due to material absorption. However, GC material can be effective for photonic reflection of individual, strong spectral line. SiC on the other hand can be used to design a good reflector for the entire frequency range

4-Ethynyl-2,2,6,6-tetra­methyl-1,2,5,6-tetra­hydro­pyridine N-oxide

The six-membered ring of the title compound, C11H16NO, has a distorted envelope conformation. The piperidine N atom deviates by 0.128 (1) Å from the plane through its three neighbouring atoms. In the crystal structure, mol­ecules are connected by inter­molecular Cethyn­yl—H⋯O contacts to form chains extending in the [10] direction

Design of Reflective, Photonic Shields for Atmospheric Reentry

We present the design of one-dimensional photonic crystal structures, which can be used as omnidirectional reflecting shields against radiative heating of space vehicles entering the Earth's atmosphere. This radiation is approximated by two broad bands centered at visible and near-infrared energies. We applied two approaches to find structures with the best omnidirectional reflecting performance. The first approach is based on a band gap analysis and leads to structures composed of stacked Bragg mirrors. In the second approach, we optimize the structure using an evolutionary strategy. The suggested structures are compared with a simple design of two stacked Bragg mirrors. Choice of the constituent materials for the layers as well as the influence of interlayer diffusion at high temperatures are discussed