The influence of the chemical composition of silicon nitride films on their thermal oxidation parameters

The thermal dry-oxygen oxidation of Si₃N₄ films prepared by the ammonolysis of monosilane was investigated. Multiple internal reflection and simple transmission spectroscopy at IR wavelengths were used to determine the chemical composition of the films. The decrease in the thickness of the Si₃N₄ films after each oxidation run was measured by an ellipsometric technique using a hollow quartz prism. The parameters of the parabolic equation for oxidation at 1100°C were calculated for films deposited in the temperature range 750–1100°C. It was found that the oxidation rate depended on the concentration of N—H bonds in the film material. The diffusion of oxygen through the overlying SiO₂ film was found to be the limiting step of the process. The activation energy of the process was 52 kcal mol^-1.     

Fusibility diagram of the BaAl2O4-Ba2SiO4-BaZrO3 system

Conclusions New types of cement were developed from the BaAl₂O₄-Ba₂SiO₄-BaZrO₃ system. The cements are characterized by high refractoriness (over 1800°C) and cold-crushing strength (up to 885 kgf/cm²) and a high content of BaO (up to 66%).A statistical method of extremum experiments was used to plot the fusibility diagram of this system. The analytically predicted data agree well with the measured quantities.Translated from Ogneupory, No. 3, pp. 48–50, March, 1978.     

The effect of different orientations in rigid rod polyimide films on the graphitized products

The effect of uniaxial and in-plane orientation of different rigid-rod homo- and co-polyimide films on the development of graphite structure after heat treatment up to 3070 K was investigated. The magnetoresistance and X-ray diffraction measurements were carried out to estimate the degree of graphitization and in-plane orientation of graphite crystallites. Both pristine and in-plane pre-oriented polyimide films show high degrees of graphitization. In-plane cold-drawing leads to the increase of in-plane orientation of polyimide films, but it produces the different actions on the graphitization parameters of homo- and co-polyimide films. While the cold pre-drawing of homo-polyimide films increases their graphitizability, this pre-treatment of the co-polyimide films does not lead to the improvement of graphitized material’s characteristics. The uniaxial orientation results in the hindrance of graphitization. The role of the supramolecular structure of ordered regions of polyimide films in the development of graphite structure under graphitization process has been discussed.     

Generalized diagrams and creep limits of dinas refractories for coke furnaces

Conclusions Creep in dinas refractories may be described in the framework of an elastoplastic model, facilitating the construction of generalized creep diagrams. With their aid we can obtain predictions of the values of long-term strength (creep limits) for dinas for periods of upto 12 years. It is shown that the creep limit of dinas after 15–25 years' service in coke ovens is 1.5–2.5 times higher than in the original refractories of contemporary production.Translated from Ogneupory, No. 5, pp. 16–21, May, 1989.