Vapor pressure measurements, thermodynamic parameters, and phase diagram for the system potassium oxide--silicon oxide at high temperatures

Journal Article · Thu May 04 00:00:00 EDT 1978 · J. Phys. Chem.; (United States)

DOI:https://doi.org/10.1021/j100498a012· OSTI ID:6795236

Eliezer, N; Howald, R A; Marinkovic, M; Eliezer, I

Potassium oxide vaporizes from solutions in SiO/sub 2/ primarily according to the equation: KO/sub 0/./sub 5/(1) ..-->.. K(g) + /sup 1///sub 4/O/sub 2/(g) (1). We have studied this equilibrium using atomic absorption in a constant temperature graphite furnace to measure the absorbance of the steady-state distribution of potassium atoms. The potassium atoms were introduced at the center of the furnace by diffusion through an orifice in sample cells which we developed for vapor pressure measurement. We have shown both experimentally and theoretically that, at a particular temperature, the absorbance we measure is proportional to the rate of diffusion of potassium atoms from the vapor pressure sample cells. For a particular cell with a particular orifice, there is a temperature-dependent conversion factor between absorbance and pressure which we evaluated from measurements with potassium aluminate standards in the cells. The pressure of potassium atoms was measured over a sufficient range of temperature to obtain the heat of vaporization. The Redlich-Kister coefficients for the enthalpy of mixing of liquid KO/sub 0/./sub 5/ and SiO/sub 2/ (A = -86, B = -53 kcal mol/sup -1/) were obtained from this data and estimates for the thermodynamic properties of KO/sub 0/./sub 5/ (liquid), literature data on the enthalpy of glasses, the temperature dependence of rate of vaporization, and the variation of the activity of SiO/sub 2/ with temperature. Redlich-Kister coefficients for log ..gamma../sub KO/sub 0.5// were obtained from the concentration dependence of the vapor pressure of potassium over the KO/sub 0/./sub 5/-SiO/sub 2/ samples: A = -10.9923, B = -6.7801, and C = -1.0101 at 1500 K. From these values, together with the enthalpy coefficients above, activities of both KO/sub 0/./sub 5/ and SiO/sub 2/ can be calculated over a wide range of temperatures and compositions. The KO/sub 0/./sub 5/-SiO/sub 2/ phase diagram was calculated from these values. Thermodynamic quantities are given for tridymite and for two potassium silicates, K/sub 2/Si/sub 4/O/sub 9/ and K/sub 2/Si/sub 2/O/sub 5/.

• Research Organization: Montana State Univ., Bozeman
• OSTI ID: 6795236
• Journal Information: J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 82:9; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

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ABSORPTION SPECTROSCOPY
ALKALI METAL COMPOUNDS
CHALCOGENIDES
CHEMICAL REACTIONS
DECOMPOSITION
DIAGRAMS
DISPERSIONS
ENTHALPY
EQUILIBRIUM
EVAPORATION
KINETICS
MINERALS
MIXTURES
OXIDES
OXYGEN COMPOUNDS
PHASE DIAGRAMS
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
POTASSIUM COMPOUNDS
POTASSIUM OXIDES
REACTION KINETICS
SAMPLE PREPARATION
SILICA
SILICON COMPOUNDS
SILICON OXIDES
SOLUTIONS
SPECTROSCOPY
TEMPERATURE DEPENDENCE
THERMODYNAMIC ACTIVITY
THERMODYNAMIC PROPERTIES
TRANSITION HEAT
VAPOR PRESSURE
VAPORIZATION HEAT
VERY HIGH TEMPERATURE