rok 2007 - Fakulta chemickej a potravinárskej technológie

IV. CURRENT RESEARCH PROJECTS
VEGA Project No 1/2109/05 The Use of the Pulse Technique on the Preparation of the
Composite and Alloy Layers on the Metal Substrates (Marta Chovancová)
Ni-W alloy coatings were prepared on the steel substrate. The content of tungsten in coatings was
increased with the growing current density and the corrosion resistance raised with the tungsten content as well.
Annealed coatings showed better anticorrosion properties than the non-annealed ones.
The preparation of electrochemical composite coatings with nickel matrix and PTFE dispersion particles has been
studied and their mechanical properties has been evaluated.
The participation of solid Fe powder particles in the transfer of charge through the heterogeneous system
consisting of an electrolyte and conducting powder particles was studied by means of electrochemical impedance
spectroscopy.
The quality of coloured anodic oxidation layer of aluminium was analysed in dependence on alternative and pulse
reverse current and used pigmentation electrolyte. The quality of the pigmentation is determined not only by the
nickel content but the morphology of the deposited nickel as well.
Project duration: from January 2005 to December 2007
VEGA Project No 1/2108/05 The Chemical and Electrochemical Reactions of Sulphur Species
at Aluminium Electrolysis (Pavel Fellner)
The effect on the cathode and anode reactions when adding sodium sulphate to molten chlorides and fluorides
was investigated by chronopotentiometry and cyclic voltammetry in the temperature range 820 °C – 1000 °C. The
cathode process was explained under the assumption that Na 2 SO 4 thermally dissociates into Na 2 O and SO 3 ,
which is the electroactive species. The formation of sulphide was observed. The influence of sulphide on
aluminium electrolysis will be discussed. The anode reaction of sulphate depends on the electrode material. On
gold electrodes, no electrochemical activity of sulphate was observed. However, when a platinum anode was
used, sulphate was oxidized to oxygen and SO 3 that decomposed thermally. When a normal carbon anode was
used, the presence of COS and SO 2 in the anode gas leaving the laboratory aluminium cell was observed.
Adsorption of SO 2 on alumina used in the aluminium industry (so-called smelter-grade alumina) was studied in the
temperature range 15 °C – 120 °C. The specific surface area of the smelter grade alumina was 88 m 2 /g. It was
found that at temperatures lower than 40 °C, sulphur dioxide is bonded to alumina reversibly by physical forces,
and the adsorption can be described satisfactorily by the Langmuir adsorption isotherm. The heat of adsorption
was estimated to be –33 kJ.mol -1 .
At temperatures in the range 80 °C – 120 °C, which prevail in dry scrubbers in the aluminium industry, the heat of
adsorption was determined to be –56 kJ.mol -1 . When SO 2 was adsorbed at temperatures higher than 80 °C, about
30 % of the SO 2 could not be desorbed when the samples were heated up to 250 °C. In the presence of SO 2 and
oxygen, the formation of sulphate was determined at temperatures higher than 90 °C.
Project duration: from January 2005 to December 2007
VEGA Project No 1/2476/05 Ferrates– Thermodynamics and Kinetics of Chemical and
Electrochemical Reactions in Molten Electrolyte and on the Phase Boundary Electrode -
Electrolyte (Ján Híveš)
The main aim of this project was to examine the possibility of the preparation and provide first information on the
behaviour of the iron in a transpassive region of potentials in molten hydroxides environment.
Electrochemical measurements (cyclic voltammetry and chronopotentiometry) were performed in eutectic mixture
of NaOH-KOH. A maximum value of polarization potential in anodic way plays very important role in the ferrate
(VI) formation. Increasing of potential does not result in production of higher amount of ferrate (VI) but competitive
reaction (evolution of oxygen) is getting more intensive. In the beginning of the DC electrolysis process the high
current efficiency (91%) is reached but quickly decreases in time of electrolysis down to 14% at the lower
temperatures. Regarding the higher temperatures at the beginning of electrolysis is reached the current efficiency
equal to 72%. Then with increasing time of electrolysis the current efficiency drops slowly down to the value of
47% (3 h).
Project duration: from January 2005 to December 2007
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