Nailya S. Akhmadullina

Interaction of β-sialons Si₅AlON₇ and Si₄Al₂O₂N₆ with a boron oxide was studied. Boron oxide was introduced in the form of boric acid, the acid content was set up at 0.5 and 5.0 wt %. Samples were sintered at 1650°C in the stream of N₂ for 2 h. It was found that all the samples showed higher densities against those for samples sintered with no aids, however, the densities were still lower as compared to theoretical levels. In most cases disproportionation of the basic phase into phases enriched with aluminum (Si₃Al₆O₁₂N₂) and silicon (Si₂N₂O) occurred. Moreover, when Si₄Al₂O₂N₆ was sintered with an addition of 0.5 wt % of boric acid, a noticeable amount of SiO₂ was also formed. Sintering of Si₅AlON₇ with an addition of boric acid did not lead to sufficient changes in microhardness and bending strength. In contrast, sintering of Si₄Al₂O₂N₆ sintered with an addition of 0.5 wt % of boric acid resulted in an increase in bending strength by ~14%, however, an addition of 5.0 wt % of boric acid caused a decrease in hardness by ~9% and a drop in bending strength by ~36%.

Objectives. The work set out to summarize the results of the studies of aluminum oxynitrides (AlONs) doped with rare earth (REM) and transition metals (TM) and to highlight the main effects of REM and TM dopants on the formation, phase composition, and optical properties of the AlON.Results. The presented analysis of the literature data includes the results of our own studies of the AlON doped with REM and TM ions. The influence of REM and TM additives on the formation of AlON and its phase com position, as well as optical properties, was considered.Conclusions. It is clearly shown that the doping with REM and TM ions enhances the formation of pure AlON phase via high-temperature synthesis from oxide and nitride. The oxynitride matrix exhibits reducing properties with respect to both REM and TM. Doping with the REM ions leads to the emergence of luminescent properties in the visible range, while doping with TM ions affects the band gap in AlON as a semiconductor. The solubility limits of all metals in the AlON matrix do not exceed 1–2 at. % vs Al. Concentration quenching of luminescence is observed at REM contents from 0.1 to 0.5 at. %.

A plasma-chemical process resulting from a microwave discharge initiated in metal–dielectric powder mixtures was used to produce luminescent materials based on Al₅O₆N doped with Ce³⁺ ions. The self-non-selfsustained discharge was initiated by microwave radiation pulses with a frequency of 75 GHz, power of 400 kW, and duration of 8 ms in Al/γ-Al₂O₃/melamine powder mixtures, cerium was introduced in the form of CeO₂ and Ce(acac)₃·H₂O, and by preliminary doping of γ-Al₂O₃ with Ce³⁺ ions. Kinetic parameters of the plasma-chemical process were determined, microscopic and X-ray diffraction analyses of the products were conducted, and pulsed cathodoluminescence spectra were recorded. It was shown that the rate of the plasma-chemical process and the efficiency of Ce³⁺ ions introduction into the produced Al₅O₆N aluminum oxynitride phase are determined to a large extent by the form of cerium present in the reaction mixture.

The phase composition of Si_{6 – z}Al_zO_zNg_{8 – z} β-sialon samples Si₅AlON₇ (z = 1) and Si₄Al₂O₂N₆ (z = 2) before and after two-stage firing at 900°C in air and at 1650°C in a nitrogen flow without sintering additives and with addition of 0.5 and 2.0 wt % NaF has been thoroughly investigated by the Rietveld method. It is shown that the initial β-sialon samples (1 and 2) are two-phase and contain Si_4.8Al_1.2O_1.2N_6.8 and Si_4.4Al_1.6O_1.6N_6.4 in a weight ratio of 70 : 30. Firing without sintering additives barely changes the composition of sample 1, while sample 2 is enriched in the Si_4.4Al_1.6O_1.6N_6.4 phase. Firing with NaF leads to the occurrence of the third phase in the composition of the samples: Si_2.8Al_3.2O_3.2N_4.8. At a NaF content of 0.5 wt %, the phase compositions of samples 1 and 2 after firing are almost identical, while when firing sample 2 with 2.0 wt % NaF, the dominant phase changes from Si_4.8Al_1.2O_1.2N_6.8 to Si_3.8SAl_2.2O_2.2N_6.8.

An original plasma chemical process initiated by microwave discharge in a mixture of metal and dielectric powders was applied to prepare specific materials, which consisted of microsized spherical particles of aluminum oxide covered with silver nanoparticles. The prepared materials are highly uniform in shape, size distribution, and composition. Their cytotoxicity was investigated using the human cell lines MCF7, HEK293T, A549, and VA-13 and the bacterial strains E. coli JW5503 (ΔtolC) and E. coli K12. Their cytotoxicity was found not to exceed the cytotoxicity of the starting materials. Thus, the prepared materials can be considered highly promising for catalysis and biotechnology applications.