The solubility of oxygen in iron-silicon melts in equilibrium with silica was measured within the range from 0.1 up to 70 mass% Si at 1 873 K. The experimental procedure involved alloys melting in silica crucibles under argon atmosphere. The sampling was made by melt sucking into quartz tubes, equipped with copper chillers. The oxygen content of analytical samples was determined with inert gas fusion analysis after careful sample preparation. The results obtained were treated by thermodynamic model, which allowed to calculated the activity and solubility of oxygen in Fe-Si melts up to 100 mass% Si.The isotherm of oxygen solubility exhibits both intermediate minimum and maximum at 20 and 85 mass% Si, respectively. The corresponding values of oxygen saturated contents are as follows: 1.4 and 94 mg/g. The activity coefficient of oxygen shows alternating deviations from the additive behaviour. These are positive in the iron rich melts, containing up to 45 mass% Si. In the melts with higher silicon content the deviations from additivity are negative. The following values of interaction parameters were calculated: e

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Thermodynamic analysis of oxygen solutions in iron-nickel melts with chromium has been carried out. Since the bond strength of oxygen with such a melt becomes weaker with an increase in the nickel concentration (g°O (Fe) ϭ0.0105; g°O (Ni) ϭ0.357), the deoxidation power of the chromium in liquid nickel is higher than that in iron melt.The deoxidation power of chromium remains almost constant when the nickel concentration in melt increases to 20 % but it rises sharply with a further increase in its content. Oxygen solubility curves pass through a minimum, which shifts to lower chromium contents in a range of from Ϫ7% Cr (pure iron) to Ϫ1.7 % Cr (pure nickel) when the nickel concentration rises. Minimum oxygen concentrations in nickel are lower almost by an order of magnitude as compared to iron. Subsequent chromium additions cause an increase in the oxygen concentration in melt; in this case, the higher the nickel content, the sharper the rise in the oxygen concentration after the minimum when chromium is added. Deoxidation of iron-nickel melts with chromium was experimentally studied for the Fe-20%Ni, Fe-40%Ni and Fe-60%Ni alloys. Experimental and calculated results are in good agreement.

The paper presents the application of an improved procedure for oxide speciation in steels by temperature ramped inert gas fusion technique on commercially available instruments. Main steps of analysis, data processing and interpretation of the results are described. The effects of instrumentation and auxiliary materials on the evolution kinetics of oxygen during an analysis are emphasised. The procedure is applied to determine the content of alumina and spinel species in high-carbon steels, attested as reference materials. The results of the gas fusion technique are correlated to those of the chemical analysis and scanning electron microscopy equipped with energy dispersive X-ray detector.

The conditions of surface layer properties formation for 40X steel samples at technological impact interactions of gas-metal plasma flows are considered. The special features of interaction of plasma flow elemental composition interaction with elemental composition of the substrate during the ion-plasma treatment as a function of reference voltage was studied. The influence of this interaction on formation of physic-chemical, mechanical and energy properties was investigated.