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Hits: 7108
Raman scattering (RS) studies of graphite-like phases BC
x N (g-BC
x N) obtained by various methods were carried out using an excitation laser operating in the near infrared range. The most typical for g-BC
x N under this excitation are two peaks at 1300 cm-1 (D-peak) and 1595 cm-1 (G-peak). It is shown that the origin of the D and G peaks is associated with disordered graphite: the D peak is observed due to a change in the selection rules, and its intensity correlates with the size of the sp
2 graphite cluster in polycrystalline graphite; the G band is associated with the graphite mode active in the RR in the E
2g plane. Displacement of the D-peak in g-BC
x N (1300 cm
? 1 ) compared to the position of this peak in graphite (1355 cm
? 1 ) can be explained by the dispersion of the position of the D-peak with the excitation wavelength. The Raman line with a center at 1260 cm
? 1 , which can be associated with the mode active in Raman, is observed only for samples with a high degree of crystallinity and for Raman spectra obtained at high pressures and high temperatures.
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Hits: 7084
For sitalls based on the lithium aluminosilicate system, the possibility of precision regulation of the temperature coefficient of linear expansion (TCLE) near values ??approaching zero in the temperature range from -80 to +500 & # 176; C is shown. It has been established that heat treatments lasting several hours in the temperature range corresponding to the stage of nucleation of the crystalline phase, after a long incubation period, make it possible to change the sign of the TCLE of the sitall from positive to negative, keeping its sign constancy in the entire temperature range near zero TCLE values.
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Hits: 7066
Materials based on Si
3 N
4 -BN were obtained by liquid-phase sintering using 20 & # 37; (by volume) YAG as a sintering aid. To obtain composite materials, we used boron nitride powders of hexagonal (h-BN) and turbostratic (t-BN) structures. Highly amorphous t-BN contributes to the compaction of the material of the composition (& # 37; by volume): 60 Si
3 N
4 + 20 t-BN + 20 YAG and the achievement of the highest physical mechanical properties: & # 961; = 2.78 g / cm
3 ; P = 14.5 & # 37 ;; E
control = 92.3 GPa; & # 963;
outgrowth = 161.4 MPa. The chemical resistance of the obtained materials reaches 97.0 & # 37; and increases in the series H
2 SO
4 - HCl - HNO
3 , which indicates intergranular corrosion without propagation into the bulk of the material. However, resistance to exposure to 48 & # 37; HF is lowest due to small cracks in surface intergranular layers and
deeper corrosion
