Magnetic influence on ferronanofluid flow is gaining increasing interest from not only the scientific community but also industry. The aim of this study is the examination of the potentials of magnetic forces to control heat transfer. Experiments are conducted to investigate the interaction between four different configurations of permanent magnets and laminar pipe flow with mixed convection. For that purpose a pipe flow test rig is operated with a water-magnetite ferronanofluid. The Reynolds number is varied over one order of magnitude (120–1200). To characterise this suspension, density, solid content, viscosity, thermal conductivity, and specific heat capacity are measured. It is found that, depending on the positioning of the magnet(s) and the Reynolds number, heat transfer is either increased or decreased. The experiments indicate that this is a local effect. After relaxation lengths ranging between 2 and 3.5 lengths of a magnet, all changes disappeared. The conclusion from these findings is that magnetic forces are rather a tool to control heat transfer locally than to enhance the overall heat transfer of heat exchangers or the like. Magnetically caused disturbances decay due to viscous dissipation and the flow approaches the basic state again.

By adjusting the thermal spraying suspension technology, coatings with excellent microstructure, surface morphology, and phase composition can be obtained to meet the application needs in mechanical, electrical or friction fields. The use of suspensions as feedstock material allows a high degree of flexibility with regard to the chemical composition of the sprayed coatings. Moreover, suspension thermal spraying (STS) is a promising technique for the production of coatings, the use of which was previously limited by expensive starting materials. A mixture of less expensive starting materials in the suspension and an "in situ" reaction to the desired product during the spraying process make this possible. Zn2TiO4 coatings are one example where the high costs of blended oxide powders as feedstock material hinder the market introduction, whereas their outstanding electrical properties and photocatalytic activity are of great interest for various industrial applications. In this work, single oxides ZnO and TiO2, Zn acetate salt as ZnO precursor, as well as a Zn2TiO4 powder were used to develop tailored aqueous suspension feedstocks suitable for thermal spraying. To follow the formation of the compositions in the system ZnO-TiO2, differential thermal analysis (DTA) measurements were performed. Preparation routes of stable suspensions and suspension-solution mixtures with low sedimentation rates, low viscosities and good flowabilities are discussed. Microstructures and phase compositions of sprayed coatings are shown, and the “in situ” formation of Zn2TiO4 phase during Suspension High Velocity Oxygen Fuel Spraying (S-HVOF) is demonstrated. This work shows the high potential of suspension feedstocks from single oxide raw materials to obtain Zn2TiO4 sprayed coatings.

Electrosteric stabilization of a commercially available boehmite powder in water was investigated to perform milling experiments and reduce the particle size to the nanoscale range. The effect of three sodium polyacrylate dispersants (Na-PA) with different molar masses (2,100, 8,000, 15,000 g/mol) on the suspension properties before and after milling experiments was assessed by electroacoustic measurements in comparison with rheological tests. A significant loss of the stabilizing effect of the sodium polyacrylates due to the application of mechanical energy was detectable. Measurements of the adsorbed amount of the dispersants after milling via detection of the COD in the background solution show a considerable desorption from the particle surface. Accessorily performed analyses of the molar mass of the polymers yielded a destruction of the polymer chains due to the mechanical energy.

Thermally sprayed WC-based hardmetal coatings offer high hardness, good sliding wear and abrasion performance and find large applications in mechanical engineering, valve construction, or offshore applications. WC-Co coatings are mainly produced by high-velocity oxy-fuel spraying (HVOF) from conventional spray feedstock powders. In this work, suspension-HVOF spraying (S-HVOF) was used to produce dense-structured WC-12Co coatings and their microstructural, mechanical and tribological properties were investigated. Significant work was devoted to the development of appropriate aqueous suspensions starting from commercially available fine WC and Co raw powders feedstock. Suspension spraying was carried out using gas-fuelled HVOF TopGun system; for comparison purposes, liquid-fuelled HVOF K2 was employed to spray WC-12Co coatings starting from commercially available spray powder. Microstructural characterization, x-ray diffraction and microhardness of the coatings were evaluated. Oscillating sliding wear tests were conducted against sintered alumina and WC-6Co balls. The sliding wear performances of the WC-Co sprayed coatings were discussed in term of their microstructure, phase composition and coating-ball test couples.

Thermally sprayed WC-based hardmetal coatings offer high hardness, good sliding wear and abrasion performance and find large applications in mechanical engineering, valve construction, or offshore applications. WC-Co coatings are mainly produced by high-velocity oxy-fuel spraying (HVOF) from conventional spray feedstock powders. In our previous work, the potential of the suspension-HVOF spraying (S-HVOF) to produce dense-structured WC-12Co coatings has been shown. Significant work was devoted to the development of appropriate aqueous hardmetal suspensions starting from commercially available fine WC and Co raw powders feedstock. This contribution proposes a step forward in the development of the S-HVOF WC-12Co coatings and evaluation of their microstructural and tribological properties. Suspension spraying trials were carried out using gas-fuelled HVOF TopGun system. For comparison purposes, liquid-fuelled HVOF K2 was employed to spray WC-12Co coatings starting from commercial available spray powder. Microstructural characterization, X-Ray diffraction and microhardness of the coatings were evaluated. Oscillating sliding wear tests were conducted against sintered Al2O3 and WC-6Co balls. The sliding wear performances of the WC-Co sprayed coatings were discussed in term of the microstructure, phase composition and coating-ball test couples.