Designing stainless steel surfaces with anti-pitting properties applying laser ablation and organofluorine coatings

Long-lasting and superhydrophobic stainless steel with anti-pitting properties is achieved by modifying conventional AISI 304L through a two-step strategy: 1) application of a femtosecond surface laser ablation treatment to generate micro-nano structures on the surface; and 2) deposition of organofluorine nanometric coating. Samples with two different patterns, namely paraboloid- and cauliflower-like, are approached and investigated by means of contact angle hysteresis, X-ray photoelectron spectroscopy, and electrochemical techniques. Results indicate that the stainless steel surface acquires efficient anticorrosive properties due to the homogenization and refinement of the patterned microstructure into a magnetite rich phase, in combination with the formation of a carbonaceous and sol–gel layer. The adherent semiconducting oxide layer is stable over time in presence of an aggressive chloride environment. The prepared superhydrophobic surfaces prevent the steel substrates from getting wet with water, protecting them from the pitting corrosion caused by the electrolyte intrusion. The corrosion resistance is explained by a mechanism in which, in addition of the silane coating, the air trapped into the micro-nano patterned surfaces plays an important role.Peer ReviewedPostprint (author's final draft

Rheological Properties Related to Extrusion of Polyolefins

Rheological properties related to the extrusion of polyolefins are the shear viscosity, the elongational viscosity, the slip velocity and their temperature- and pressure-dependencies. These properties are measured in the rheology lab mainly via a parallel-plate rheometer and a capillary rheometer. Then appropriate rheological models have to be used to account for all these properties. Such models are either viscous (e.g., the Cross model) or viscoelastic (e.g., the K-BKZ model). The latter gives the best fitting of the experimental data and offers excellent results in numerical simulations, especially in extrusion flows. Wall slip effects are also found and measured by rheometric flows. Modeling of extrusion flows should make use of appropriate slip models that take into effect the various slip parameters, including the effects of shear stress, molecular characteristics, temperature and pressure on the slip velocity. In this paper the importance of these properties in extrusion are discussed

Solution and melt viscoelastic properties of controlled microstructure poly(lactide)

A series of controlled microstructure poly(lactide) (PLA) samples were synthesized using a novel chiral dinuclear indium catalyst capable of living polymerization of lactide. PLAs with different ratios of L- to D- monomer ratios of 100:0, 90:10, 75:25, 50:50, and 0:100 were investigated. The relationship between intrinsic viscosity and the absolute molar mass distribution of the samples obtained by light scattering gel permeation chromatography in tetrahydrofuran gives [η] = 0.014 + 0.75 Mw, a scaling law of typical coil dimensions of linear macromolecules in good solvent. The melt rheological study includes determination of zero-shear viscosity and its relationship with the molecular weight, the relaxation spectrum, and its relation with molecular weight characteristics, as well as plateau modulus and other important rheological parameters that are helpful in predicting the linear viscoelasticity of PLA. Emphasis is placed on the uniaxial melt behavior of these polymers. At low temperatures, significant strain hardening is observed, which gradually disappears with an increase in temperature and decrease of Hencky strain rate. The K-BKZ constitutive equation is used to model the experimental data. It is concluded that in spite of their linear structure, PLAs exhibit strain hardening which is not due to strain-induced crystallization, and it is solely due to the dynamics of molecular relaxation

FUNDAMENTAL PHENOMENA IN WOOD RFV DRYING WITH 50-Ohm AMPLIFIER TECHNOLOGY

Radio frequency/vacuum drying (RFV) experiments were conducted on thick (200-250 mm) softwoods by using a 50-Ohm amplifier as the radio frequency (RF) source. The power densities selected were low to ensure highest quality of the final product and that no internal checking will occur. The effect of dryer pressures and power densities on the drying kinetics and product quality was examined for two different wood species. A number of experimental observations and drying characteristics are analyzed and discussed in detail. The concept of the identity drying card is applied and useful information concerning the drying mechanisms and the relevant phase transitions is obtaine

Mechanical Characterization of Arteries: Comparison of Square and Cruciform Biaxial Tests Using Inverse Modeling Technique

Peer reviewed: NoNRC publication: Ye

Entry flows of polylactides with slip

The entry capillary flow of four different polylactides (previously characterized by Othman et al. (2012)) has been modeled with both a viscous (Cross) and a viscoelastic (K-BKZ) model. The modeling takes into account slip-at-the-wall, which was found to increase with decrease of molecular weight. The flow through different capillary dies and apparent shear rates show the excess pressure losses (ends correction), which are smaller than those for other similar linear polymer melts. The viscous simulations capture well the ends correction, while the viscoelastic simulations improve these predictions, as they also account for the viscoelastic nature of the polymer melts. It is concluded that solely viscous modeling can capture their flow behavior satisfactorily