Communication - an approach to measuring local electrochemical impedance for monitoring cathodic disbondment of coatings

An electrochemically integrated multi-electrode array has been used for monitoring and visualizing the cathodic disbondment of
defective coatings by measuring local electrochemical impedance. Compared with the conventional electrochemical impedance and
local current measurement approaches, this new approach significantly enhances the sensitivity of detecting the propagation of
coating disbondment by eliminating the effects of the dominating low impedance regions, such as those that arise at coating defects,
and thus increases the visibility of higher impedance regions deep in the disbonded coating. Furthermore, it facilitates the probing
of electrode processes and mechanisms in selected local electrode regions.

Microstructure and hardness characterisation of laser coatings produced with a mixture of AISI 420 stainless steel and Fe-C-Cr-Nb-B-Mo steel alloy powders

Fe-C-Cr-Nb-B-Mo alloy powder and AISI 420 SS powder are deposited using laser cladding to increase the hardness for wear resistant applications. Mixtures from 0 to 100 wt.% were evaluated to understand the effect on the elemental composition, microstructure, phases, and microhardness. The mixture of carbon, boron and niobium in the Fe-C-Cr-Nb-B-Mo alloy powder introduces complex carbides into a Fe-based matrix of AISI 420 SS which increases its hardness. Hardness increased linearly with increasing Fe-C-Cr-Nb-B-Mo alloy, but substantial micro-cracking was observed in the clad layer at additions of 60 wt.% and above; related to a transition from a hypoeutectic alloy containing α-Fe/α' dendrites with an (Fe,Cr)2B and γ-Fe eutectic to primary and continuous carbo-borides M2B (where M represents Fe and Cr) and M23(B,C)6 carbides (where M represents Fe, Cr, Mo) with MC particles (where M represents Nb and Mo). The highest average hardness, for an alloy without micro-cracking, of 952 HV was observed in a 40 wt.% alloy. High stress abrasive scratch testing was conducted on all alloys at various loads (500, 1500, 2500 N). Alloy content was found to have a strong effect on the wear mode and the abrasive wear rate, and the presence of micro-cracks was detrimental to abrasive wear resistance.

Fluorine-free superhydrophobic coatings with pH-induced wettability transition for controllable oil-water separation

We present a simple, environmentally friendly approach to fabricating superhydrophobic coatings with pH-induced wettability transition. The coatings are prepared from a mixture of silica nanoparticles and decanoic acid-modified TiO2. When the coating is applied on cotton fabric, the fabric turns superhydrophobic in air but superoleophilic in neutral aqueous environment. It is permeable to oil fluids but impermeable to water. However, when the coated fabric is placed in basic aqueous solution or ammonia vapor, it turns hydrophilic but underwater superoleophobic, thus allowing water to penetrate through but blocking oil. Therefore, such a unique, selective water/oil permeation feature makes the treated fabric have capability to separate either oil or water from a water-oil mixture. It may be useful for development of smart oil-water separators, microfluidic valves, and lab-on-a-chip devices.

Conductive polymer coatings

Conducting polymer-coated textiles possess a wide range of electrical properties. The surface resistivity is influenced by concentrations of the reactants, the thickness of the coating, the nature of the substrate surface, the extent of penetration of the polymer into the textile structure, and the strength of the binding of the coating to the textile surface. Low resistivity in fabric results from highly doped thicker coatings that penetrate well into the textile structure, thus enabling good electrical contact between fibers. Microwave studies showed that conductive textiles are not highly effective as electromagnetic shielding materials owing to their medium-level conductivity and therefore large skin depth. Combined with the fact that coatings are around 1. ?m thick, they cannot act as effective reflective barriers to electromagnetic radiation. However, because they are highly absorptive in the microwave region, absorbing materials can be designed in conjunction with conductive textiles. Study of Fourier transform-infrared spectra of aged polypyrrole films has shown an increase in intensity of an ?,?-unsaturated conjugated carbonyl peak that may be linked to the increase in resistance but cannot be the only factor, because the rate of electrical decay was influenced by several factors such as temperature, the type and concentration of the dopant, and the aging time, all of which signify a complex mechanism of degradation of conductivity. Degradation is a major concern for conductive textile systems that needs to be characterized before considering these materials for potential applications.