Composition of Ceramic Colors

As mentioned above, Ceran glass ceramic cooktops are decorated with ceramic colors of varying chemical composition to achieve an extensive color selection. 

Here e is the expansion (A///), a is the tensile stress, —a is the compressive stress, a is the average linear coefficient of thermal expansion, E is the modulus of elasticity, d is the thickness, p is Poisson s ratio, and T — To is the temperature difference hot/cold. The indices are for glass ceramic (GK) and for color (F) respectively. 

The calculations show that only a very thin color layer ( 5-7 pm) can be applied so as to adhere, since otherwise the tension threshold is exceeded, leading to chipping-off of the composite. This makes it necessary to produce colors that are opaque at such minimum layer thicknesses, which can lead to difficulties in view of pigment particle sizes often exceeding 10 pm. Another difficulty is that the upper cooktop surface of the colors deemed generally suitable for decoration of Ceran cooktop panels must also withstand other - sometimes extreme - thermal, mechanical, and chemical loads (see also Sect. 3.2). 

The precise chemical formulas for individual colors the result of exhaustive developmental work involving statistical trials and constant optimization - are of course commercial secrets. Table 3.6 lists some of the physical properties of the colors. 

The manufacturing process for Ceran cooktop panels can be divided into two fundamentally different partial processes. The first process, the production of the parent glass, is basically not different from the production process 

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