Conditions required for the formation of carbooxide phase in the course of treatment of titanium from carbon-and-oxygen-
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CONDITIONS REQUIRED FOR THE FORMATION OF CARBOOXIDE PHASE IN THE COURSE OF TREATMENT OF TITANIUM FROM CARBON-AND-OXYGEN-CONTAINING MEDIA S. V. Huryn, I. M. Pohrelyuk, and V. M. Fedirko
UDC 669.295:620.196
The thermodynamic aspects of the interaction of titanium with carbon-and-oxygen-containing media are investigated. On the basis of thermodynamic calculations and experimental results, we propose a hypothesis of the formation of carbooxide phase in the surface layer of titanium in the course of thermodiffusion saturation including the diffusion of carbon atoms over the vacancies through the oxide film toward the metal.
The thermodynamic analysis enables one to predict the probability of chemical interactions and transformations and explain the possibility of their realization. It is especially useful for the investigation of thermochemical treatment of metals and alloys in multicomponent media [1–4]. In what follows, we analyze the thermodynamic aspects of the formation of carbooxide compounds as a result of interaction of titanium with carbon-andoxygen-containing media and, in particular, with powder graphite at a partial pressure of oxygen of 10 – 2– 103 Pa. Procedure of Investigation The probability of the formation of chemical compounds as a result of interaction of the components of the Ti–O–C systems is evaluated by analyzing the behavior of the standard isobaric–isothermal potential ΔGT0 under normal conditions and the isobaric–isothermal potential Δ GT for low partial pressures of oxygen (10– 2 Pa) within the range 25–1000°C (from the beginning of heating up to the attainment of stationary conditions of saturation). Our numerical calculations are based on the use of standard formulas and reference values of the thermodynamic parameters of the reagents and products of the reactions [5]. The literature data on the thermodynamic properties of ternary interstitial compounds are quite poor. This is why titanium carbooxide is regarded as a Ti O–Ti C quasibinary system. This enables us to represent the thermodynamic properties of this ternary compound as an additive sum of two simple compounds by using the condition of equality of the mean energies of bonding in related compounds [6]. In the investigated temperature range, the influence of the energy of mixing is neglected. The results of thermodynamic analysis are compared with the data of X-ray phase diffraction analysis of the surface layers of titanium after interaction with carbon-and-oxygen-containing media. The X-ray phase diffraction analysis was performed by using a DRON-3.0 diffractometer in the Cu Kα-radiation at a voltage U = 30 kV and a current I = 20 μA. The tube was focused according to the Bragg–Brettano scheme. The procedure of scanning was carried out with steps of 0.05°C. At each point, the exposure was equal to 4 sec. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, Lviv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 41, No. 6, pp. 33–36, November–December, 2005. Original article submitted May 25, 2005. 1068
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