Nanocrystalline TiO₂ coatings were successfully deposited on metallic substrate surfaces through low-pressure cold spray. Sol–gel amorphous TiO₂ dry gel was for the first time used as a feedstock powder. Agglomerated morphology of the amorphous powder with high-density packing of particles and reduced pores number was an important factor for successful low-pressure cold spraying. However, in the present study one more factor contributing to anchoring of TiO₂ particles by cold gas spraying onto a substrate was indicated. This factor enabling effective powder deposition and coating production is based on an exotic for conventional ceramic materials’ plastic deformation of amorphous powder. Furthermore, the detailed analysis of SEM, Raman and XRD measurements clearly demonstrated that amorphous titanium dioxide is transformed into crystalline anatase form during the process of low-pressure cold spraying.

A major challenge in materials engineering is the development of new materials and methods and/or novel combination of existing ones, all fostering innovation. For that reason, this study aims at the synergy between low-pressure cold spray (LPCS) as a tool for coating deposition and sol-gel technique for fabrication of the feedstock powder. The complementarity of both methods is important for the examined topic. On one side, the LPCS being automized and quick mean provides the solid-state of feedstock material in nondestructive conditions and hence the hydrophobicity imparted on the sol-gel route is preserved. On the other side, the sol-gel synthesis enables the production of oxide materials with enhanced deformability due to amorphous form which supports the anchoring while LPCS spraying. In the paper, several aspects including optimal fluoroalkylsilane (FOTS) concentration or substrate roughness are examined initially for altering the superhydrophobicity of produced coatings. Further, it is shown that the appropriate optimization of feedstock powder, being submicron silica matrices covered with two-layer FOTS sheath, may facilitate the anchoring process, support roughening the substrate or cause enhancement the coating hydrophobicity. All the discussion is supported by the characteristics including surface morphology, wettability and thermal behaviour examined by electron microscopy, water contact angle measurements and thermal analysis (TGA/DSC), respectively. The coatings presented in the paper are characterized by an uneven thickness of up to a few silica particles, but final hydrophobicity is provided uniformly on the surface by the formation of multi-level roughness by a detachment of outer layer from the SiO₂ particles. Thus, the presented approach constitutes a simple and fast solution for the fabrication of functionalized coatings using LPCS including industrial potential and fundamental research character.

Composite materials containing zero valent copper (ZVC) dispersed in the matrix of two commercially available strongly basic anion exchangers with a macroreticular (Amberlite IRA 900Cl) and gel-like (Amberlite IRA 402OH) structure were obtained. Cu⁰ particles appeared in the resin phase as the product of the reduction of the precursor, i.e., copper oxide(I) particles previously deposited in the two supporting materials. As a result of a one-step transformation of preformed Cu₂O particles as templates conducted using green reductant ascorbic acid and under mild conditions, macroporous and gel-type hybrid products containing ZVC were obtained with a total copper content of 7.7 and 5.3 wt%, respectively. X-ray diffraction and FTIR spectroscopy confirmed the successful transformation of the starting oxide particles into a metallic deposit. A scanning electron microscopy study showed that the morphology of the deposit is mainly influenced by the type of matrix exchanger. In turn, the drying steps were crucial to its porosity and mechanical resistance. Because both the shape and size of copper particles and the internal structure of the supporting solid materials can have a decisive impact on the potential applications of the obtained materials, the results presented here reveal a great possibility for the design and synthesis of functional nanocrystalline solids.

Intermetallic compounds, especially aluminides, show good high-temperature strength, oxidation resistance, high melting points, and thus have received considerable attention as potential substitutes for superalloys in high-temperature applications. Aluminides are especially interesting because they are stable up to the critical temperature of ordering, which is close to the melting temperature. In the Al-Ni system, the most studied intermetallics are Ni₃Al, NiAl and NiAl₃. In the presented study, Al and Ni powders were mixed together with Al₂O₃ in various proportions to produce dense coatings by low-temperature cold spraying. Two types of post-deposition treatments were applied to produce aluminides, namely furnace heating and resistance spot welding. The former caused a long time diffusion while the latter a self-propagating high temperature synthesis. Both heating methods enabled formations of intermetallic phases. However, the furnace heating provides high porosity. The microstructure of the samples was analyzed by SEM (scanning electron microscope), EDS (energy dispersive X-ray spectroscopy) and XRD (X-ray diffraction) together with microhardness measurements.

Visible-light active photocatalysts in the form of coatings that can be produced using large-scale methods have attracted considerable attention. Here we show a facile approach to deposit coatings using the low pressure cold spray (LPCS) from oxygen-rich amorphous titanium dioxide, which is a structurally-unconventional feedstock powder for LPCS. We synthesized amorphous TiO₂, in which we introduced numerous defects, such as oxide groups (peroxy and superoxy) in volume and hydroxyl groups on the surface. Then we deposited as-prepared powder preserving the presence of active groups, which we demonstrated using Raman spectroscopy. To show the activity of the prepared coatings, we perform methylene blue degradation under visible light. Our research shows that it is worth considering the internal atomic structure and surface chemistry of the powders to be preserved after low pressure cold spraying.