1,256 research outputs found
Chromate conversion coatings and their current application
This paper describes formation, composition and possible production technologies of application chromate coatings. Summation of common examples of applications of these coatings in corrosion protection of metals and alloys is provided. Individual chromate coatings are divided by their dominant anions either with CrVI or CrIII. Restrictions of chromate coatings with dominantly CrVI and related toxicity of hexavalent chromium is discussed in detail. In conclusion, examples of both chromium and other, alternative coatings are summed up. Application of these coatings as a protection for concrete hot-dip galvanized reinforcement is also reviewed
Phonons in MgB2 by Polarized Raman Scattering on Single Crystals
The paper presents detailed Raman scattering study of the unusually broad E2g
phonon mode in MgB2 crystal. For the first time, it is shown by the polarized
Raman scattering on few-micron-size crystallites with natural faces that the
observed broad Raman feature really does obey the selection rules of an E2g
mode. Raman spectra on high quality polycrystalline superconducting MgB2 wires
reveal a very symmetric E2g phonon line near 615 1/cm with the room temperature
linewidth of 260 1/cm only. Additional scattering of different polarization
dependence, observed in certain crystallites is interpreted as weighted phonon
density of states induced by lattice imperfections.Comment: 4 pages + 7 figure
Reaction kinetics of the formation of intermetallic Fe – Zn during hot - dip galvanizing of steel
This review article mainly describes the composition of intermetallic Fe - Zn, i.e. zeta (ζ), delta (δ1k + δ1p), gamma1 (Γ1) and gamma (Γ) on galvanized steel during low temperature galvanization (t ~ 450 °C). It gives detailed the formation, growth of individual phases during galvanization and their interaction. In terms of the kinetics, the formation of the coating is defined by a parabolic kinetic equation of the growth of different intermetallic phases under ideal conditions. From the available literature the rate constants of the formation of individual intermetallic phases and also for the total coating are cited. The composition of the intermetallic phases, iron content, crystal structure, and group symmetry in which the surface of galvanized steel forms
Continuation of Periodic Solutions of Dissipative and Conservative Systems: Application to Elastic Pendulum
Continuation is an efficient algorithm for finding solutions
of systems of nonlinear algebraic equations where the solutions form a one-dimensional continuum.
Such systems arise naturally when investigating equilibrium points
and periodic solutions of ordinary differential equations with one parameter. Continuation of isolated periodic solutions of dissipative systems is a well-established technique. Less attention has been devoted
to continuation of periodic solutions of conservative systems,
where periodic solutions typically form a one-parameter family.
To specify a single periodic solution, additional condition
must be considered. However, this gives an over-determined system,
which has no solution when working with approximate numerical
values. We propose a simple algorithm which solves this difficulty by using singular value decomposition of the Jacobian matrix.
This algorithm is applied to the conservative model of elastic pendulum. A branch of
periodic solutions with constant energy is found which is born by the period doubling bifurcation
of vertical oscillations
Study of polycaprolactone wet electrospinning process
Wet electrospinning is a useful method for 3-dimensional structure control of nanofibrous materials. This innovative technology uses a liquid collector instead of the metal one commonly used for standard electrospinning. The article compares the internal structural features of polycaprolactone (PCL) nanofibrous materials prepared by both technologies. We analyze the influence of different water/ethanol compositions used as a liquid collector on the morphology of the resultant polycaprolactone nanofibrous materials. Scanning electron micro-photographs have revealed a bimodal structure in the wet electrospun materials composed of micro and nanofibers uniformly distributed across the sample bulk. We have shown that the full-faced, twofold fiber distribution is due to the solvent composition and is induced and enhanced by increasing the ethanol weight ratio. Moreover, the comparison of fibrous layers morphology obtained by wet and dry spinning have revealed that beads that frequently appeared in dry spun materials are created by Plateau-Rayleigh instability of the fraction of thicker fibers. Theoretical conditions for spontaneous and complete immersion of cylindrical fibers into a liquid collector are also derived here
Custos de operações florestais: noções e conceitos.
A base conceitual; Os fatores de produção; Objetivos das empresas florestais; Os diferentes nĂveis financeiros; Os custos; Tipos de custos; Custos fixos e custos variáveis; O comportamento dos custos; Os momentos de custos empresariais; As categorias de análise financeira; Análise econĂ´mica versus análise financeira Análise financeira dos diferentes nĂveis; Limitações da análise financeira; Análise de investimentos; Cálculo de investimento; Avaliação de risco; Consideração de outros aspectos; Proposta de controle de custos; O sistema de registros; Inventário patrimonial; Os custos comuns; Os mecanismos de análise.bitstream/item/51985/1/DOC-373.pdfVersĂŁo eletrĂ´nica
Corrosion properties of chromia based eco - friendly coatings on mild steel
Ceramic nanocrystalline coatings of chromium oxide (III) on steel S235JRH-1.0038 (EN 10025-1) were prepared using the liquid precursor plasma spraying (LPPS) method from ammonia dichromate (VI). Their structure and anti – corrosion properties were compared to the standard chromium oxide (III) coating prepared by thermal spraying. The newly prepared coatings had very high adhesion and minimal porosity. Anticorrosion properties were characterized by the means of the electrochemical impedance spectroscopy (EIS), measuring the charge transfer resistance Rct and capacitance of electrical double layer CPEdl in the 0,5 mol/l NaCl. Coatings of Cr2 O3 prepared by the LPPS method showed unambiguously improved anti - corrosion properties
Modelling of Radiative Transfer in Air Arc Plasma
The objective of this work is to compare the accuracy of several approximate models of radiative properties for the prediction of radiative transfer in air arc plasma at the temperatures in the range of 300 - 25 000 K and the pressure of 0.1 MPa. Calculated absorption coefficients are used to generate the parameters of different models. The radiative transfer inside the cylindrically symmetrical air plasma with prescribed temperature profile was studied. The equation of radiative transfer was solved using the P1 and SP3 approximations, calculated radiative source term in the energy equation (net emission) was compared with results obtained by spectral integration
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