Vol 59, No 3 (2023)

We have demonstrated general kinetic aspects of the formation of nitrides of Zr–Nb alloys (containing 0.1, 2.5, and 5 wt % Nb) at a temperature of 1900°C. The nitridation process has been shown to have a two-stage character, with both stages having an exponential rate law. The reaction rate in the second stage is considerably lower than in the first stage. We have determined the composition of the resulting heterostructures of the form Zr1–хNbхN–ZrN1–n /β-solid solution of zirconium in niobium (Zr1–хNbхN) and identified the nitridation sequence of the components of the starting alloy. The first stage of the process is the formation of an α-solid solution of nitrogen in Zr and its conversion into a nonstoichiometric nitride. The kinetic curve of the second stage describes nitridation of the β-Nb phase resulting from the decomposition of the Zr〈Nb〉 solid solution. The duration of the second stage of the process has been shown to be determined by the amount of niobium in the starting solid solution. Experimental evidence is presented that single-stage nitridation of Zr–M alloys can be used for producing single-phase ceramics containing active additions and having the shape of the starting metallic workpiece.

This paper presents corrosion and electrochemical characterization data illustrating the effect of 0.05–1.0 wt % lithium as a structure modifier on the anodic behavior of lead–antimony alloy SSu3 (Pb + 3 wt % Sb) in NaCl electrolyte. The alloy was studied potentiostatically in potentiodynamic mode at a potential sweep rate of 2 mV/s. The results demonstrate that increasing the concentration of the aqueous NaCl solution shifts the corrosion, pitting, and repassivation potentials of the alloys to negative values. The free corrosion potential of the alloys shifts over time to positive values. The same occurs with increasing lithium concentration in SSu3. Moreover, increasing the NaCl concentration in the electrolyte increases the corrosion rate of the alloys, independent of their composition. Lithium additions to SSu3 improve its corrosion resistance. The alloys have been shown to corrode by the pitting mechanism. Acting as a structure modifier, lithium increases their pitting and repassivation potentials, improving the pitting corrosion resistance of the alloys and helping to eliminate emerging pitting corrosion spots.

We have studied photoelectrochemical and photocatalytic properties of porous materials based on hollow α-Fe2O3 microspheres, characterized by the presence of dangling magnetic Fe–O–Fe bonds due to an increased oxygen vacancy concentration on the wall/closed pore interface. Using such powder and firing slips at an isothermal holding temperature of 400°C, we obtained two series of thin-film samples on glass with a conductive layer from suspensions of two compositions: aqueous Fe(NO3)3 solution + hollow α-Fe2O3 microspheres (series 1) and aqueous Fe(NO3)3 solution + polyethylene glycol + hollow α-Fe2O3 microspheres (series 2). The films of series 2 were shown to have a structure with spatially separated particles differing in size: α-Fe2O3 nanoparticles and hollow α-Fe2O3 microspheres. The films of series 1 consisted predominantly of hollow microspheres connected by “necks” formed during heat treatment. The thickness of the films of series 2 was of order 2 μm and that of the films of series 1 was of order 4 μm. The structural distinctions between the films of the two series had a significant effect on the optical properties of the material. In the wavelength range 350–1500 nm, the absorption coefficient of the films of series 2 (3.50 × 105 m–1) was about twice that of the films of series 1 (1.75 × 105 m–1). Photoelectrochemical characterization in an aqueous 0.1 M KOH solution showed that the onset potential for the anodic reaction was 0.87 V vs. Ag/AgCl in the case of the films of series 2 and 0.97 V vs. Ag/AgCl in the case of series 1. The films of both series showed an unusual increase in current density during prolonged illumination at a potential of 1 V vs. Ag/AgCl, due to Fe(IV) formation on the photoanode surface. Photocatalytic properties of the materials were assessed from the rate of methylene blue degradation. The reaction rate constant (k) was determined to be 0.015 and 0.018 min–1 for the films of series 1 and 2, respectively, whereas the k of the photocatalyst-free reaction was 2.8 × 10–4 min–1.

The Tb2O3–Li6Tb(BO3)3 system, promising for the growth of cubic terbium oxide crystals, has been characterized by physicochemical techniques. We have studied terbium oxide solubility in Li6Tb(BO3)3 and the vaporization of a saturated solution in the temperature range 1055–1285°C. The solubility results have been compared to data in the literature and represented graphically. The high-temperature solution has been shown to vaporize incongruently. The major components of the vapor phase are lithium and boron oxides, in the ratio near Li2O : B2O3 = 4 : 1. As the vaporization temperature is raised, the percentage of terbium oxide in the composition of the vapor phase increases. At 1250°C, the ratio of the constituent oxides in the vapor phase is Li2O : B2O3 : Tb2O3 = 62 : 15 : 1.

This paper presents our results on ultrasound-induced changes in the surface topography of quartz glass studied using the Allan variance method. The use of this method has made it possible to quantitatively assess roughness components corresponding to surface defects of particular size. Prolonged ultrasonic treatment of quartz glass plates at a power density of 10 W/cm2 has been shown to cause significant changes in surface roughness: the profile height due to small surface defects, 0.125 μm in size, increased by about 40% and the one due to large defects (12 μm) decreased by about 30%. The observed changes in surface topography seem to be related to cavitation destruction of large surface defects by local cumulative jets.

Fe/TaON/β-Si3N4/β-Si3Al3O3N5 metal–ceramic composites have been prepared via autowave combustion of ferrosilicoaluminum and metallic tantalum additions (0, 5, 10, and 15 wt %) in nitrogen. We have determined the phase composition of the composites and studied their morphological features and optical properties. Acid–base properties of the surface of the composites have been investigated and their adsorptive and photocatalytic activity for chloramphenicol degradation has been assessed under UV and visible light illumination. The composites have been shown to be highly effective in oxidative degradation of chloramphenicol (98%) under illumination with visible light.

Colloidal solutions of silver nanoparticles have been prepared by the electric discharge method using three distinct modifiers: carbonate and citrate ions and polyethylenimine. According to optical absorption spectroscopy data and their zeta potential, the solutions were highly stable. The geometric parameters of the nanoparticles have been determined by transmission electron microscopy. The nanoparticles have been immobilized on the surface of polyethylene terephthalate track-etched membranes. The resultant surface nanostructures have been examined by scanning electron microscopy and Raman spectroscopy. The materials thus obtained have been shown to exhibit surface-enhanced Raman scattering using 4-aminothiophenol as test molecule. Relative Raman gain coefficients have been calculated