Electrospray Deposition of Cellulose Nanofibers on Paper: Overcoming the Limitations of Conventional Coating

While the potential of cellulose nanofibers to enhance the mechanical and barrier properties of paper is well-known, there are many uncertainties with respect to how to apply them. In this study, we use not only bulk addition of micro-/nanofibers and bar coating with oxidized nanofibers, but also a combination of these and, as a novel element, electrospray deposition of nanofiber dispersions. Characterization involved testing the strength of uncoated and coated paper sheets, their resistance to air flow, their Bendtsen roughness, and their apparent density, plus visualization of their surface and cross-sections by scanning electron microscopy. As expected, bulk addition to the unrefined pulp was sufficient to attain substantial strengthening, but this enhancement was limited to approximately 124%. Following this, surface addition by bar coating improved air resistance, but not strength, since, as applying nanocellulose at high consistency was technically unfeasible, this was performed several times with detrimental drying stages in between. However, replacing bar coating with electrospraying helped us overcome these apparent limitations, producing enhancements in both barrier and tensile properties. It is concluded that electrosprayed nanofibers, owing to their uniform deposition and favorable interactions, operate as an effective binder between fibers (and/or fines).

Long-Life Coatings for Offshore Structures

Coatings are used on offshore steel structures to prevent corrosion and to preserve their appearance. Conventional coating systems require repainting after only 10-15 years. Fluoropolymer coatings have been used on offshore structures since the mid-1980’s. These coatings offer excellent corrosion protection as well as good gloss and color retention for more than 30 years in some cases. Using fluorinated coating systems can substantially lower life cycle coating costs and require fewer maintenance cycles than conventional coatings.

Perspectives for conventional coating processes using High-Speed Laser Cladding

The most commonly used surface protection technologies against wear and corrosion are electro-chemical hard chromium plating or thermal spraying. But these coating technologies have limits. Additionally, due to health concerns, hard Chrome plating is under increasingly restrictive use in Germany, the European Union and in the Asian market. One technology which is currently under investigation for replacing conventional coating processes plating in these instances is the High-Speed Laser Cladding. Using High-Speed Laser Cladding (High-Speed Laser Metal Deposition, HS-LMD), which is a DED (Directed Energy Deposition) process, a laser beam is melting powder particles, which are fed coaxially into the laser beam, before these particles hit the substrate. Using a laser as the heat source, heat input into workpiece can be minimized and fast thermal cycles can be achieved. This allows for a very low dilution of additive material into workpiece – typically < 10μm – and high feed rates between 100-500 m/min can be achieved. Layers generated by this process can be locally adjusted in thickness between 50-300 μm per layer. Since each layer is metallurgically bonded to the substrate or the layer before, multi layers or multi-material approaches are feasible. By use of the afore mentioned unique process features, new and in properties tailored coating systems become possible.

Control of the Pore Structure of Plasma-Sprayed Thermal Barrier Coatings through the Addition of Unmelted Porous YSZ Particles

In this study, a new pore structure control method for plasma-sprayed thermal barrier coatings (TBCs) through the addition of unmelted, porous yttria-stabilized zirconia (YSZ) particles was investigated. Through a unique way of feeding powder, two powder feeders were used simultaneously at different positions of the plasma flame to deposit a composite structure coating in which a conventional plasma-sprayed coating was used as a matrix and unmelted micro-agglomerated YSZ particles were dispersed in the dense conventional coating matrix as second-phase particles. The effects of the distribution and content of second-phase particles on the microstructure, mechanical properties, and lifetime were explored in a furnace cyclic test (24 h) of the composite coating. The mechanical properties and lifetime of the composite coating depend on the content and morphology of the particles embedded in the coating. The lifetime of the composite structure coatings is significantly higher than that of the conventional coatings. By adjusting the spraying parameters, the lifetime of the composite coating prepared under the optimum process is up to 145 days, which is about three times that of the conventional coating. The results of this study provide guidance for the preparation of high-performance composite structure TBCs.

Nanocoatings in modern construction

The review analyzes the state of the nanocoating market, shows main types of nanocoatings, as well as drivers and barriers to their development and application. Modern progress in the field of nanotechnology allows us to attribute nanocoating to high performance materials, the structure and properties of which can be “designed” according to specific functional criteria and the level of environmental impact. They present unique remarkable characteristics compared to conventional coating materials in construction industry. The government’s grandiose plans to commission new housing and road infrastructure, as well as ambitious projects to develop the Arctic and ensure national security, should lead to the growth of the industry as a whole, as well as to an increase in demand for more efficient, innovative building materials, including nanocoatings and nanopaints

Effective Harmful Organism Management I: Fabrication of Facile and Robust Superhydrophobic Coating on Fabric

Advances in harmful organism management are highly demanding due to the toxicity of conventional coating approaches. Exploiting biomimetic superhydrophobicity could be a promising alternative on account of its cost-effectiveness and eco-friendliness. Here, we introduce a facile method to fabricate a robust superhydrophobic coating on a fabric substrate. This is achieved by sequentially spraying TiO2-epoxy resin nanocomposite material and fluorocarbon-silane modified SiO2 nanoparticles (FC-silane SiO2 NPs). The superhydrophobicity is attributed to the nanoparticles constituting a micro/nano hierarchical structure and the fluorocarbon of the modified SiO2 NPs lowering the surface energy. The epoxy resin embedded in the coating layer plays an important role in improving the robustness. The robustness of the superhydrophobic surface is demonstrated by measuring the water slide angle of surfaces that are subject to salty water at 500 rpm stirring condition for up to 13 days. This study focuses on ensuring the superhydrophobicity and robustness of the coating surface, which is preliminary work for the practical management of macrofoulers. Based on this work, we will perform practical harmful organism management in seawater as a second research subject.

Conductive Electrospun Polyaniline/Polyvinylpyrrolidone Nanofibers: Electrical and Morphological Characterization of New Yarns for Electronic Textiles

Advanced functionalities textiles embedding electronic fibers, yarns and fabrics are a demand for innovative smart cloths. Conductive electrospun membranes and yarns based on polyaniline/polyvinylpyrrolidone (PANI/PVP) were investigated using the chemical modification of PANI instead of using conventional coating processes as in-situ polymerization. PANI was synthesized from the aniline monomer and the influence of the oxidant-to-monomer ratio on electrical conductivity was studied. The optimized conductivity of pellets made with pressed PANI powders was 21 S·cm−1. Yarns were then prepared from the t-Boc-PANI/PVP electrospun membranes followed by PANI protonation to enhance their electrical properties. Using this methodology, electrospun membranes and yarns were produced with electrical conductivities of 1.7 × 10−2 and 4.1 × 10−4 S·cm−1.

Effects of Feedstocks and Laser Remelting on Microstructural Characteristics of ZrO2-7wt.%Y2O3 Thermal Barrier Coatings Prepared by Plasma Spraying

Conventional and nanometer aggregate ZrO2-7wt.%Y2O3 ceramic powders taken as raw materials, plasma spraying and plasma spraying-laser remelting compound technology was used to prepare conventional and nanostructured thermal barrier coatings on the TiAl alloy surface. Effects of powder structure (feedstock) and laser remelting on organizational structure and phase of the coatings were analyzed using scanning electron microscope (SEM) and X-ray diffractometer (XRD). Results indicate that: conventional plasma sprayed ceramic coating presents typical lamellar stacking features; plasma sprayed nanostructured coating consists of fully melted region and partially melted region, presenting a two-phase structure. Under the comprehensive impacts of laser power, energy density, temperature field distribution in the laser action region, ceramic heat conductivity coefficient and coating thickness and other factors, the coating presents obvious lamellar structural features after laser remelting; the upper part is compact columnar crystal remelting region and the lower part is residual plasma spraying region. Due to toughening effect of residual nanoparticles in the remelting region of laser remelted nanostructured coating, grain-boundary strength is high and there are a considerable number of transgranular fractures, but the fractures in the remelting region of laser remelted conventional coating are basically intergranular fractures. Conventional plasma sprayed ceramic coating is mainly of tetragonal phase together with a small quantity of monoclinic phases, but nanometer plasma sprayed ceramic coating only has non-equilibrium tetragonal phases. After laser remelting, both conventional coating and nanometer coating mainly have non-equilibrium tetragonal phases with a small quantity of cubic phases.

Mechanical properties and residual stress of HVOF sprayed nanostructured WC-17Co coatings

Nanostructured WC-17Co, 2C-12Co coatings and conventional WC-17Co coating were prepared by High Velocity Oxygen Flame (HVOF) spray technique. The elastic modulus, fracture toughness and crack spread path were studied. The residual stress, different phases, microstructure from surface to the depth of coatings were also analyzed. While the nanostructured WC-12Co coating showed the highest elastic modulus, the nanostructured WC-17Co coating has the highest fracture toughness. The compressive residual stress of the nanostructured coatings was higher than the conventional coating. Both WC and W2C phases showed compressive residual stress, but Co6W6C phase showed tensile stress. The distribution of residual stress showed that the stress is the lowest at the surface and the highest close to the interface.

Comparison of the thermal stability of magnesium phosphate (newberyite) coating with conventional zinc phosphate (hopeite) coating

This article presents a detail comparison of the thermal stability of the new magnesium phosphate (newberyite – MgHPO4·3H2O) coating with a conventional coating of zinc phosphate (hopeite – Zn3(PO4)2·4H2O). It was confirmed that dehydration of zinc phosphate (hopeite) occurs gradually (dehydration start temperature: 115 °C). The start of magnesium phosphate (newberyite) dehydration is indeed shifted to somewhat higher temperatures (about 125 °C) but the dehydration has an intense jump character. When using magnesium phosphate (newberyite) coating for further surface treatment at higher temperatures, dehydration of the coating can result in reduction of the adhesion between the phosphate/primer coatings. Under these conditions, it is recommended to use a coating of conventional zinc phosphate (hopeite) or manganese phosphate (hurealite).