Electrodeposition, composition and structure of Zn—Cr alloys

The effect of polyethylene glycol (PEG 1500) as additive and of deposition conditions on Zn—Cr alloy electrodeposition from an acidic sulfate electrolyte at room temperature, without agitation was investigated. PEG polarizes the overall cathodic reaction and inhibits Zn deposition. Cr codeposition with Zn starts at a cathodic potential of about –1,95 V vs Hg/Hg₂SO₄, which is reached at current density of about 20 A dm^–2 in galvanostatic conditions. Zn—Cr alloy coatings containing up to 28 at % Cr were obtained depending on the plating conditions. SEM observations showed an island-like structure, formed by the local growth of crystals, which covered the surface during further deposition. In the first stages of electrodeposition the powder diffraction spectra contain lines of b.c.c. -(Zn,Cr) phase (a 3.02 Å). After 30 s deposition time weak lines of Zn-based phase (a 2.67 Å, c 4.90 Å) appear, and become clearly visible in coatings deposited for 90 s. The average Cr content in the alloy coatings decreases with advancing deposition. The as-plated surface contains C in organic compounds and Zn(OH)₂. After 50 min sputtering, Zn and a mixture of Cr, Cr₂O₃ and Cr₇C₃ were found. The presence of organic C and O, probably from inclusions of PEG, were also detected.     

Synthesis,spectral properties,and application of 1,8‐naphthalimide fluorophores for modified polymers

The presence of the epoxy group in the structure of 1,8‐naphthalimide fluorophores opens up possibilities to prepare compounds with new valued properties through covalent bonding to both polyamide and epoxy oligomers. Two new 4‐(1‐amino‐2,3‐epoxypropyl)‐9‐substituted‐1,8‐naphthalimides were synthesized, and their absorption and fluorescence characteristics were determined. The introduction of the substituent contributes to both the yellow color and strong fluorescence of the compounds, the quantum yield being about 0.9. The possibility for structural coloration of polyamide textile materials and epoxy oligomers has been investigated. The modified polymers are with intense green fluorescence, possessing a strong resistance to various physico‐chemical treatments and light. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1863–1869, 2001     

Multigrid methods with space–time concurrency

Computing and Visualization in Science - We consider the comparison of multigrid methods for parabolic partial differential equations that allow space–time concurrency. With current trends in...     

Phosphorous content and distribution in the NPP Kozloduy RPV Unit 1 Weld 4 metal

Phosphorous content and in depth distribution in the NPP Kozloduy Unit 1 Weld 4 metal were investigated. Wet chemical analysis was carried out on chips cut layer by layer at five levels reaching 7.1 mm distance from the inner RPV wall. The measured average concentration of P was 0.046% which is considerably lower than expected. No typical intercrystal fracture was found in 1 mm² specimen impact broken at −120°C under vacuum. Auger electron spectroscopy was applied in order to investigate the distribution of phosphorous on grain boundaries in the weld metal. Single regions of increased P content were found mainly on the periphery of secondary cracks or in zones of small size facets. In depth distribution of P in these regions was obtained by argon sputtering. The character of the in depth profile was more typical for the case of P-containing precipitations than of P segregation. The measured low P concentration and the character of P distribution could be regarded as less harmful to the mechanical properties, especially for the toughness of the weld metal, compared to the case of grain boundary segregation.     

Composition of electrodeposited Zn–Cr alloy coatings and phase transformations induced by thermal treatment

Zn–Cr alloy coatings were obtained in a flow cell, for modeling the process of high speed electrodeposition on steel strips. Alloy coatings, containing between 6 and 18 at.% Cr were annealed at 260 °C in an inert atmosphere. The phase composition and the crystallographic characteristics of “as prepared” and “annealed” coatings, were studied by XRD. It is shown that non-equilibrium δ- and Γ-(Zn,Cr) phases are major constituents of the “as prepared” coatings. On annealing, equilibrium ζ-CrZn₁₃ phase precipitates from δ- and Γ-supersaturated solid solutions. The lattice parameters and the similarities in phase composition of the annealed coatings, deposited onto two types of substrates – low carbon steel and Cr plated (protected) low carbon steel – show that if Fe from the substrate “contaminates” the precipitated ζ-CrZn₁₃ phases, its relative amount do not exceed few tenths of a percent.The influence of the elemental composition, conditions of electrochemical deposition, and post-deposition thermal treatment on phase composition of the coatings is discussed.     

A locally optimized reordering algorithm and its application to a parallel sparse linear system solver

A coarse-grain parallel solver for systems of linear algebraic equations with general sparse matrices by Gaussian elimination is discussed. Before the factorization two other steps are performed. A reordering algorithm is used during the first step in order to obtain a permuted matrix with as many zero elements under the main diagonal as possible. During the second step the reordered matrix is partitioned into blocks for asynchronous parallel processing (normally the number of blocks is equal to the number of processors). It is possible to obtain blocks with nearly the same number of rows, because there is no requirement to produce square diagonal blocks. The first step is much more important than the second one and has a significant influence on the performance of the solver. A straightforward implementation of the reordering algorithm will result inO(n ²) operations. By using binary trees this cost can be reduced toO(NZ logn), whereNZ is the number of non-zero elements in the matrix andn is its order (normallyNZ is much smaller thann ²). Some experiments on parallel computers with shared memory have been performed. The results show that a solver based on the proposed reordering performs better than another solver based on a cheaper (but at the same time rather crude) reordering whose cost is onlyO(NZ) operations.