Riitta Mahlberg

Photocatalytic Activity of Atomic Layer Deposited TiO2 Coatings on Austenitic Stainless Steels and Copper Alloys

Photocatalytic activity of TiO 2 -coated austenitic stainless steel (AISI 304) and copper alloys [deoxidized high phosphorus (DHP) copper and Nordic Gold] was studied by means of decomposition of methylene blue model waste water and open-circuit electrochemical potential measurements, and the photoinduced hydrophilicity was studied by means of contact angle measurements of water under ultraviolet irradiation. The TiO 2 coatings were prepared by an atomic layer deposition technique from TiCl 4 and H 2 O. The thicknesses of the prepared coatings were 5, 10, 50, 100, 150, and 200 nm. Morphology and crystal structure of the TiO 2 coatings were studied using scanning electron microscope and X-ray diffraction techniques. Photocatalytic activity of the studied coatings was low with a coating thickness of 5 and 10 nm. When the coating thickness was 50 nm or higher for AISI 304 stainless steel, and 100 nm or higher for DHP and Nordic Gold copper alloys, the photoactivity was good, but no saturation or systematic effect of coating thickness or surface finish was observed. The photoinduced hydrophilicity was good with all studied coating thicknesses (50, 100, 150, and 200 nm), with some exceptions.

Adhesion and tribological properties of hydrophobin proteins in aqueous lubrication on stainless steel surfaces

Macroscale tribological properties of hydrophobin layers bound on stainless steel surfaces were investigated in an aqueous environment. Emphasis was on boundary lubrication because water easily fails in hydrodynamic lubrication due to its low viscosity. We studied the affinities of two different proteins, HFBI and FpHYD5, on stainless steel and their ability to bind water at the surface by combining quartz crystal microbalance (QCM-D) and ellipsometry. Both proteins contained an adhesive hydrophobic domain, but FpHYD5 also had a very strongly hydrating carbohydrate structure attached to it. The lubrication properties of the proteins were studied with two different methods, pin-on-disc (POD) (stainless steel vs. stainless steel) and circular translation pin-on-disc (CTPOD) (UHMWPE vs. stainless steel). It was observed that both hydrophobins could adhere to the stainless steel surface and form highly hydrated layers. Both proteins reduced friction and wear of the sliding contact between two stainless steel surfaces. With UHMWPE against stainless steel, the hydrophobins prevented the polyethylene transfer to the counterface. The lowest coefficient of friction (COF) 0.13 was observed when FpHYD5 hydrophobins were employed in pure water. On the other hand, the lowest wear was observed when FpHYD5 proteins were added in a 50 mM sodium acetate buffer. Increasing the water content and loosening the hydrophobin film structure on the stainless steel surface led to a reduction in friction and wear.

Biomimetic approach to water lubrication with biomolecular additives

The aim of this study is to find a connection between mechanical engineering and biotechnology by utilizing biomimetics in lubrication. The objective is to improve boundary lubrication by biomolecules in water-based systems. Proteins were used because they can form films and multilayers on the surfaces and thus prevent direct contact between them. In this study, hydrophobin and albumin proteins are studied as additives to enable water lubrication.

Scalable synthesis and functionalization of cobalt nanoparticles for versatile magnetic separation and metal adsorption

Magnetic cobalt nanoparticles coated with a thin carbon shell were produced by means of a scalable method based on hydrogen reduction synthesis. The presence of oxidized groups on the surface of the carbon shell enabled the reaction with alkoxysilanes bearing amino and thiol reactive functions under mild conditions, and therefore the formation of a thin functional silane layer which holds the potential for further modification in consideration of specific applications, e.g., in the separation and catalysis fields. The magnetic nanoparticles bearing surface thiol groups were also used in metal adsorption tests. These nanoparticles could efficiently adsorb not only gold from a chloride salt aqueous solution, but also several other metals when incubated in a thiocyanate-leached solution obtained from crushed printed circuit boards. The combination of a scalable production method with a simple and versatile surface modification strategy opens up a wide array of potential industrial applications in the fields of separation, sensing, and biomedical devices.

Screening of the effect of biocidal agents released from poly (acrylic acid) matrices on mould growth

Abstract Recently, surface treatment concepts with slow release encapsulated activates have shown to provide a potential approach for the control of biological surface contamination. These new protection concepts respond to the current regulations and demands set for the sustainable development. In this study, screening of the efficacy of biocidal agents – benzoic acid and sodium benzoate – embedded in poly(acrylic acid) matrices was carried out. The efficacy of the polymer systems on mould growth was tested with the blue stain fungus Aureobasidium pullulans and with the mould fungi Trichoderma harzianum and Aspergillus niger. In addition, release of the active agents at different pH was determined in aqueous media. The release tests in aqueous media showed that the release of the active agents is more pronounced at pH higher than 4. The efficacy of the polymer systems according to the present arrangements was dependent on the fungi and the release rate of the active agents from the matrix.

Surface Characteristics and Water Absorption of Sol-Gel Coated Impregnated Paper Pressed onto Plywood

Two silane-based hybrid coatings were developed to modify the surface energy of phenolic resin impregnated paper. The coated paper samples were further pressed onto surfaces of plywood. The surface properties and water repellence of coated paper were investigated by AFM, XPS and water contact angle measurements. The water absorption of plywood with pressed paper was studied by water uptake tests. It was found that the sol-gel coatings had slightly improved the water repellence of the impregnated paper. The water absorption of plywood was also slightly decreased.

Evaluation of different floor materials in cattle barns.

Floor surfaces in livestock barns are of special interest, since they should withstand strong mechanical and chemical stress and they should also be as comfortable as possible to stand and lie on. Furthermore, the floors should be easy to clean. The aim of this project was to develop well-functioning floor surface materials for use in animal houses. Both laboratory and field tests were performed. Changes in repellence and surface properties, cleanability, colour and gloss of materials were measured. Materials for the field test were chosen according to the results of laboratory studies with the exception of silane-impregnated concrete. The other materials selected were epoxy-, polyurethane- and acrylic coatings for floorings and feeding tables, and polyester coating for feeding tables. Two materials not tested in the laboratory were also included in the field tests. Traditional concrete was used as reference. The surface materials had more effect on changes in cleanability and repellence of tested materials than the chemical stresses introduced. SEM pictures showed that during wear the surfaces became rougher or scratches appeared on them. According to profilometer measurements no significant differences between the changes in the surface roughness of test materials were observed. The results of colour and gloss measurements varied considerably, but in general, coating decreased the changes of colour and gloss of the surface materials. The field study provides practical information about the behaviour of the surface materials examined.