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Silicon based nanoparticulates of various composition and morphology have been produced by smelting reduction method which includes a carbothermic reduction of SiO 2 -Al 2 O 3 -CaO starting materials to SiO vapor at 2073 K and transfer of the vapor with a carrier-gas to cooler surfaces inside the experimental reactor where the nanoparticulates were deposited. The chemical composition of the starting materials was matched to the basic composition of silica-rich coal ash which is considered as a potential source of Si in this study. Special emphasis was placed upon examining the degree of SiO 2 reduction from starting materials, purity and morphology of the as-obtained nanomaterials. It is shown that up to 20% of Si can be converted from the silica-based melt into rounded nanoparticles, nanoparticle chains and nanowires containing Si,O and C in variable proportions depending on deposition temperature and gas flow conditions. The diameter of nanoparticulates was estimated to be in the range of 20$100 nm. The nanoparticles and chains were found to be deposited at lower temperature locations (293$1320 K) while the nanowires were obtained at higher temperatures (1320$1570 K). There was a tendency for an increase in Si concentration in order of nanowires, nanoparticles chains and nanoparticles. The carbon concentration, on the contrary, was much higher in nanowires as compared to that in nanoparticles. Although the degree of SiO 2 reduction from silica-containing melt to SiO vapor is limited because a part of SiO 2 reacts with C producing SiC, its good controllability, high productivity and possibility for processing cheap starting materials make the smelting reduction a very attractive technique for production of silicon based nanostructured materials.

Spark plasma sintering (SPS) investigations were carried out on three sets of Co specimens: untreated, high energy mechanically (HEMT) pre-treated, and nanomodified powders. The microstructure, density, and mechanical properties of sintered pellets were investigated as a function of various pre-treatments and sintering temperatures (700–1000 °C). Fine-grained sinters were obtained for pre-treated Co powders; nano-additives tended to inhibit grain growth by reinforcing particles at grain boundaries and limiting grain-boundary movement. High degree of compaction was also achieved with relative densities of sintered Co pellets ranging between 95.2% and 99.6%. A direct co-relation was observed between the mechanical properties and densities of sintered Co pellets. For a comparable sinter quality, sintering temperatures for pre-treated powders were lower by 100 °C as compared to untreated powders. Highest values of bending strength (1997 MPa), microhardness (305 MPa), and relative density (99.6%) were observed for nanomodified HEMT and SPS processed Co pellets, sintered at 700 °C.

Nanostructured zero-valent iron (NSZVI) particles were synthesized by the method of ferric ion reduction with sodium borohydride with subsequent drying and passivation at room temperature in technical grade nitrogen. The obtained sample was characterized by means of X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy and dynamic light scattering studies. The prepared NSZVI particles represent 100–200[Formula: see text]nm aggregates, which consist of 20–30[Formula: see text]nm iron nanoparticles in zero-valent oxidation state covered by thin oxide shell. The reactivity of the NSZVI sample, as the removal efficiency of refractory azo dyes, was investigated in this study. Two azo dye compounds, namely, orange G and methyl orange, are commonly detected in waste water of textile production. Experimental variables such as NSZVI dosage, initial dye concentration and solution pH were investigated. The kinetic rates of degradation of both dyes by NSZVI increased with the decrease of solution pH from 10 to 3 and with the increase of NSZVI dosage, but decreased with the increase of initial dye concentration. The removal efficiencies achieved for both orange G and methyl orange were higher than 90% after 80[Formula: see text]min of treatment.

The effect of Ni and Co metal microparticles (MPs) and nanoparticles (NPs) on the structural and mechanical properties of Fe + 0.5 % C steel powder alloy was analyzed. The results revealed that the modification of the alloy by (Ni, Co) NPs can lead to the formation of a fine-grained compact and less porous structure, hence, significantly improve the mechanical properties of the sintered material. MPs modified samples were found to be highly porous when compared to the control. The introduction of 0.5 wt.% Co NPs increased the hardness value of the alloy to 58 HRB, whereas 0.5 wt.% Co MPs reduced the hardness to 47 HRB. The most beneficial effect is observed with 0.5 wt.% Ni NPs addition, wherein the hardness value increased to 63 HRB when compared to 52 HRB of the control sample. The highest flexural strength of 313 MPa was observed for Ni NPs incorporated alloy, whereas the least flexural strength of 156 MPa was noticed for the alloy containing 0.5 wt.% Co MPs. The fracture study confirmed that (Ni, Co) NPs increased the degree of densification, whereas Co MPs additives lead to the formation of large pits and cracks, consequently, to the destruction of material by a brittle inter-granular mechanism. Thus, this study introduces the use of Ni and Co NPs as modifiers in Fe + 0.5 % C alloy via powder metallurgy.