Search results for "medium"
showing 10 items of 3746 documents
Preparation of mixed oxides MNdO3, with M=Cr, Fe. Comparison of several methods
1993
Abstract Different methods for the formation of NdCrO3 and NdFeO3, having the perovskite-like structure, were studied including the ceramic method, simultaneous precipitation of hydroxides and simultaneous crystallization from aqueous solutions of nitrates. Preparation of mixed oxides from hydroxides simultaneously precipitated lowered the temperature and time required for their formation. In the case of NdCrO3 the formation process from hydroxides and nitrates occurred through the chromate, NdCrO4, without intermediate decomposition of the precursor to metal oxides, which lead to the mixed oxide by 600°C.
Electrochemical Determination of the Fe(III)/Fe(II) Ratio in Archaeological Ceramic Materials Using Carbon Paste and Composite Electrodes
2002
A method for determining the iron(III)/iron(II) ratio in ceramic materials based on microsample attachment to graphite/polyester composite electrodes is presented. This quotient is of considerable interest for determining the nature and firing conditions of the original materials in archaeological ceramics. The electrochemistry of iron in ceramic materials in acetic/acetate and Na2EDTA aqueous solutions is described in terms of reductive dissolution processes of iron(III) materials and oxidative dissolution processes of iron(II) ones. The iron(III)/iron(II) ratio is determined from peak area measurements in linear scan voltammograms performed in 0.10 M acetic/acetate buffer (pH 4.70) and 0.…
Traversing Phase Fields towards Nanosized Beta Tricalcium Phosphate
2013
The difficulty of beta tricalcium phosphate (β-TCP) crystallization in aqueous media opens the question whether β-TCP can be produced using an alternative pathway. Amorphous calcium phosphate (ACP) is metastable in an aqueous environment and prefers a more stable apatite phase. Others have transformed a crystallized calcium deficient hydroxyapatite (Ca-def HAp) into β-TCP, but automatic transformation from ACP to Ca-def HAp followed by transformation to β-TCP has not been addressed. This work shows the formation of Ca-def HAp after different aging times of ACP and the subsequent transition to β-TCP. An amorphous phase with a Ca/P ratio of 1.5 was synthesized, rinsed, filtered and excess flu…
UV-tunable upper critical solution temperature behavior of azobenzene containing poly(methyl methacrylate) in aqueous ethanol
2015
A series of azobenzene containing copolymers were synthesized by post-modification of poly(methyl methacrylate-co-pentafluorophenyl methacrylate) with an amine-functionalized azobenzene. Light- and thermo-responsive behavior of these copolymers was investigated in ethanol–water solvent mixtures with various amounts of ethanol. The upper critical solution temperature (UCST) of the polymer solutions, resulting from the poly(methyl methacrylate), was found to be highly tunable by the substitution degree of the copolymers as well as the ethanol content of the solvent mixture. In addition, the copolymers are light responsive based on the cis–trans isomerization of the azobenzene group under UV i…
Model colloids to study surface – ligand interactions in nanosized Fe3O4
2019
Using electrodispersion of metallic iron in an aqueous environment without additional reagents we create a chemically clean model system based on nanosized synthetic magnetite where the details of magnetic metal oxide – surfactant chemisorption can be studied by high fidelity magnetometry with nanometric precision. A comparative analysis of model colloidal solutions based on oleic acid and iron Fe2+ oleate indicates a significant influence of the mode of surfactant adsorption on the magnetic diameter of the particles.
Continuous dynamic recrystallization phenomena modelling in friction stir welding of aluminium alloys: A neural-network-based approach
2007
The current paper focuses on the continuous dynamic recrystallization phenomena (CDRX) occurring in friction stir welding processes of AA6082 T6 aluminium alloys. In particular, in order to predict the average grain size, a properly trained neural network is linked to the finite element method (FEM) model of the process. The utilized net, which takes as inputs the local values of strain, strain rate, and temperature, was trained starting from experimental data and numerical results. The obtained results show the capability of the artificial intelligence (AI) technique in conjunction with the FE tool to predict the final microstructure in the joint section.
The Effect of Grain Size of the Stock on Electrical Characteristics of the Li0.03Na0.97Ta0.05Nb0.95O3Perovskite Ceramics
2012
The microstructure and electrical properties of two samples of the ferroelectric Li0.03Na0.97Ta0.05Nb0.95O3 ceramic solid solution prepared from initial charge stocks of different dispersity by conventional ceramics technology are compared. The average size of grains and concentration of pores in the samples are found to be of little difference while the electrical properties of the ceramics are strongly affected by the grain size of the initial mixture. The difference in properties is due to conditions at the diffusion stage of the solid-phase synthesis caused by differences in composition of larger grains rather than the grain size itself.
Influence of Axial Pressure on the Electrical Properties of Li0.06Na0.94NbO3 Ceramic
2011
Lead-free ceramic Li0.06Na0.94NbO3 was synthesized using a conventional solid-state processing. The single-phase perovskite structure was identified by X-ray powder diffraction technique. The values of lattice parameters of Li0.06Na0.94NbO3 are lower than those for pure NaNbO3. The EDS analysis shows the fairly homogeneous distribution of all elements throughout the grains. An axial pressure significantly influences electric properties. With increasing pressure the peak intensity in the ϵ(T) curve decreases, the peak becomes diffused and shifts to a lower temperature. The value of tanδ increases with increasing axial pressure and its local maximum shifts towards lower temperatures.
Origin of pressure-induced insulator-to-metal transition in the van der Waals compound FePS3 from first-principles calculations
2020
The authors acknowledge the assistance of the University Computer Center of Saint‐Petersburg State University in the accomplishment of high‐performance computations. A.K. is grateful to the Latvian Council of Science project no. lzp‐2018/2‐0353 for financial support.
Preparation and properties of radio-frequency-sputtered half-Heusler films for use in solar cells
2011
Abstract The class of half-Heusler compounds opens possibilities to find alternatives for II–VI or III–V compound semiconductors. We aim to find suitable substitutes for the cadmium sulphide buffer layer in chalcopyrite-based thin film solar cells, where the buffer layer is located between the p-type chalcopyrite absorber and an n-type transparent window layer. We report here the preparation of radio-frequency-sputtered lithium copper sulphide “LiCuS” and lithium zinc phosphide “LiZnP” films. The optical analysis of these films revealed band gaps between 1.8 and 2.5 eV, respectively. Chemical properties of the film surface and both interfaces between the film and a Cu ( In , Ga ) Se 2 layer…