CHEMISTRY GLOSSARY

supercritical carbon dioxide    →   superkritični ugljikov dioksid

Supercritical carbon dioxide (scCO₂) is a powerful, cheap, non-toxic and environmental friendly solvent. When used at a supercritical state (over 74 bar and 31 °C), it achieves similar solvating power as its organic competitors, such as hydrocarbons and chlorinated solvents. Supercritical carbon dioxide is one of few solvents that can be unrestrictedly used for food processing.

Tafel plot    →   Tafelov dijagram

Tafel plot is the graph of the logarithm of the current density j against the overpotential η in electrochemistry in the high overpotential limit. An electrode when polarised frequently yields a current potential relationship over a region which can be approximated by:

where η is change in open circuit potential, i is the current density, B and i₀ is constants. B is known as the Tafel Slope. If this behaviour is observed a plot of the semilogarithmic components is known as the Tafel line and the diagram is called the Tafel diagram.

Heyrovsky-Ilkovic equation    →   Heyrovsky-Ilkovičeva jednadžba

The Heyrovsky-Ilkovic equation describes the entire current-potential curve (polarographic wave) of a reversible redox system in polarography

where R is the gas constant, T is the absolute temperature, F is the Faraday constant, n denotes the number of electrons taking part in the electrode reaction. E_1/2 is a unique potential (for a given reaction and supporting electrolyte) termed the half-wave potential.

In order to obtain E_1/2 from the above equation, we plot a graph of ln[(i_d-i)/i] against E. The intercept on the x-axis gives then an accurate value of E_1/2. The slope of the obtained straight line is equal to nF/RT from which n is determined.