Page 99 - QRedition5.0 062021

Quality Requirements Edition 5.0 European Enamel Association

0.01m Complexion-III-solution 8.3 Examination of enamels and additives for enamelling

Complexion-III is the disodium salt of ethylene diamine tetraacetic acid
®
®
(mol.wt. 372.1 and available as Titriplex (Merck) and Idranal (Riedel de Haen)). 8.3.1 Surface tension of enamels

Explanation
Surface tension or interfacial tension is, the surface of a liquid effecting, inwards directed
force. Because of these molecular forces liquids attempt to reduce their surface. Quite
small amounts of liquids endeavour to form a spherical shape. The higher the surface
tension the sooner the ideal spherical shape is attained (Mercury has a high, water a low
surface tension in relation to it). There are substances by which the surface tension of
liquids can be altered.

In the field of enamels and enamelling the surface tension is an object, when the material
changes over from the solid to the liquid state and vice versa. This takes place while melting
as well as while firing the enamel. Porcelain and vitreous enamels with a high surface
tension are aligned during firing towards the metal substrate; those with a low surface
tension towards the surface against air. In fact, the frit manufacturer greatly attends to this
and chooses an oxide composition of the enamel accordingly. Quincke (1868),
Winkelmann and Schott (1884) and others had found relations between surface tension
and the oxide composition of glasses. Dietzel picked up the tasks and obtained similar
correlations to the oxide composition of enamels. In 1942, he published a list of surface
tension factors comprehending a lot of enamel raw materials. The factors have been
established for mN/m percentage by weight. They permit a quite exact predetermination of
the surface tension of enamels. Later on, the list has been enlarged several times. In the
rank described below a small excerpt out of the table of these factors is given to calculate
the surface tension of enamels. The factors relate to 1 percent by weight at times.

-10 - 5.9 0.1 0.8 1.5 3.0 3.4 4.1 4.5 6.2 6.6

MoO Cr O K O B O Na O TiO SiO ZrO CoO/ NiO Al2O MgO
3 3 3 2 2 3 2 2 2 2 3

© EEA2020 page 99
EEA2020