Formation Of Silicon Oxide Layer Research Articles

Self lubrication of pressureless sintered SiC ceramics

The self lubrication of SiC ceramics prepared by pressureless sintering was investigated by annealing at different temperatures in air. It was found that low coefficient of friction can be obtained for SiC ceramics by annealing, and the coefficient of friction of SiC ceramics decreased with the increase of annealing temperature. The SiC ceramics with annealing at 1500 °C revealed the best self lubricating property, with the coefficient of friction of 0.4, while the coefficient of friction of SiC ceramics without annealing was as high as 0.7. The SiC ceramics with annealing at 1000 °C can show self lubrication over a long sliding distance without increasing wear. The formation of α-cristobalite on the annealed SiC ceramics can further lubricate SiC ceramics and shorten run in period. Self lubrication mechanism of SiC ceramics with annealing is considered that on the one hand, the formation of silicon oxide layers after annealing can reduce the number of SiC grains directly exposed to the sliding interface in the early stage of the sliding, decreasing the number of hard SiC wear particles formed on the sliding interface; and on the other hand, silicon oxide wear particles generated by the wear of the silicon oxide layers formed by annealing can be used as solid lubricant.

Synthesis of Chromium Silicides in Ionic Melts

We study the currentless diffusion saturation, metal-thermal reduction, and the electrochemical behaviors of chromium- and silicon-containing melts and establish the conditions of synthesis of chromium silicides in the form of superfine powders and coatings. It is shown that the role of limiting stage of the process of diffusion saturation of chromium, molybdenum, and tungsten with silicon in chloride-fluoride melts is played by the diffusion of silicon atoms in the solid phase. In the course of currentless transfer of silicon to metals of group VIB, silicide coatings are formed on their surfaces. The combined reduction of chromium (III) chloride and sodium fluorine-silicate by metallic sodium or magnesium makes it possible to obtain silicide powders. We formulate the conditions required for getting powders of chromium silicides by electrolysis of chloride-fluoride melts containing fluorine-silicate and potassium chromate. The oxidation resistance of the obtained silicide powders is explained by the formation of silicon-oxide layers on their surfaces.

Chemical and phase compositions of silicon oxide films with nanocrystals prepared by carbon ion implantation

The chemical and phase compositions of silicon oxide films with self-assembled nanoclusters prepared by ion implantation of carbon into SiO x (x < 2) suboxide films with subsequent annealing in a nitrogen atmosphere have been investigated using X-ray photoelectron spectroscopy in combination with depth profiling by ion sputtering. It has been found that the relative concentration of oxygen in the maximum of the distribution of implanted carbon atoms is decreased, whereas the relative concentration of silicon remains almost identical over the depth in the layer containing the implanted carbon. The in-depth distributions of carbon and silicon in different chemical states have been determined. In the regions adjacent to the layer with a maximum carbon content, the annealing results in the formation of silicon oxide layers, which are close in composition to SiO2 and contain silicon nanocrystals, whereas the implanted layer, in addition to the SiO2 phase, contains silicon oxide species Si2+ and Si3+ with stoichiometric formulas SiO and Si2O3, respectively. The film contains carbon in the form of SiC and elemental carbon phases. The lower limit of the average size of silicon nanoclusters has been estimated as ∼2 nm. The photoluminescence spectra of the films have been interpreted using the obtained results.

Electrical Properties of Polysilicon Electrodes for Conductometric Measurement

The miniaturized polysilicon electrodes for conductometric sensors have been fabricated by standard CMOS process. The interface impedance of polysilicon and saline solution (0.9 % NaCl) are measured in the frequency range of 100 Hz–1 MHz. At this frequency range, the impedance can be described as K/((iω)β, where K is around 33 MΩ Hz0.93 and β is about 0.93 for the electrode area of 2 mm2. Compared to Pt black and Pt electrode, the impedance of polysilicon electrodes is quite large. This is supposedly due to the formation of silicon oxide layer at the surface of polysilicon electrodes in saline solution. The response of a pair of polysilicon electrodes to 0–75 mM KCl in saline solution at 20 KHz has good linearity. With the deposition of urease on the top of the pair of polysilicon electrodes, it is also possible to detect urea concentration with this conductometric setup.