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  • Author or Editor: S. Mrowec x
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Abstract  

Kinetic methods for studying the transport properties of non-stoichiometric transition metal oxides and sulphides have been described. It has been shown that modern microthermogravimetric techniques enable, in rather simple way, the determination of the concentration and the mobility of point defects in these materials as a function of temperature and oxidant activity, with an accuracy difficult to attain with other, much more complicated and time consuming methods. The advantages of the kinetic methods described in this paper have been illustrated by the results obtained on Mn-MnS-S2 system which has been extensively studied in detail by different authors using various conventional techniques.

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A thermobalance for studies of the high-temperature sulfidation of metals and alloys is described. This apparatus permits the determination of mass changes in the sulfidized sample as functions of temperature and sulfur vapour pressure with an accuracy of 10−6 g. Besides heterogeneous kinetics measurements, it has been shown that the chemical diffusion coefficients and deviations from stoichiometry of metal sulfides can also be studied as functions of temperature and sulfur pressure by means of equilibration measurements.

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Abstract  

A thermobalance for studies of the high-temperature sulfidation of metals and alloys is described. This apparatus permits the determination of mass changes in a sulfidized sample as a function of temperature and sulfur vapour pressure. The main parts of this apparatus are the container with liquid sulfur and the reaction chamber with the quartz space and quartz spiral. All parts of the apparatus are equipped with thermostating furnaces. The temperature within the apparatus is controlled with an accuracy of 0.5 K. The quartz spiral (diameter 0.2 mm), consisting of 50 coils (diameter 30 mm), permits the recording of mass changes in the sample (about 200 mg) with an accuracy of 10-5 g. Besides heterogeneous kinetics measurements, it has been shown that the self- and chemical diffusion coefficients or the deviation from stoichiometry of the metal sulfides can also be studied as functions of temperature and sulfur pressure by means of equilibration measurements.

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Abstract  

A novel microthermogravimetric apparatus to study the kinetics of metal sulphur reactions and transport properties of transition metal sulphides has been described. The main feature of this arrangement includes the application of the carrier gas for sulphur vapour transportation and the protection of the balance chamber from sulphur attack. As a consequence, the helix balance could have been replaced by an automatic electronic microbalance and the accuracy of the mass change measurements increased more than two orders of magnitude, up to 10–7 g. The application of two liquid sulphur reservoirs created very stable, strictly defined reaction conditions, and enabled to make rapid changes of sulphur partial pressure in the reaction chamber. It has been demonstrated that all these innovations make it possible to study not only the kinetics of very slow sulphidation processes but also to determine deviations from stoichiometry and defect mobility in transition metal sulphides.

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