Apparently invisible. Chemistry in ceramics‪.‬ Zschimmer & Schwarz Ceramco

Among the several issues that may arise along the glazing line, the excessive foaming within glaze suspensions is one of the most frequent and problematic.

The phenomenon is already visible on the surface of the glaze inside the stirring systems but consequences can persist even after the end of the production, that is after the firing cycle.

Chemistry speaking, what is foam? What are the causes of its presence and what do we need to know to prevent its formation or to remove it in case of unexpected phenomena?

Speaking of ceramic glaze applications and technical defects, one of the strangest and most interesting is the "TV effect".

It consists of a preferential migration of the glaze towards the perimeters of the tile that produces in those areas a thickening of the glaze.

The unaesthetic result is a quite regular surface swelling along the edge of the ceramic material. 

A result that recalls the old cathode-ray television sets and that may be visible even after the firing cycle.

What is exactly the TV effect? 

How does it manifest itself and what are the causes?

What can we finally do to prevent the problem?

Viscosity (or viscous friction coefficient) measures a substance attitude on generating friction between its layers. In other words, it defines the resistance of the fluid to its proper flow.

The barbottina's viscosity values - that is the suspension of inorganic raw materials, water and dispersants that after the atomization process will form under the weight of the presses the raw ceramic body - can sometimes rapidly and suddenly change, and grow.

In the event of an excessive or out of standard increase, many critical issues may occur, compromising the use of the watery system or even forcing producers to repeatedly stop the production line.

What are the main causes that can significantly affect the viscosity values of the slip and what do we need to know the proptly act, avoiding the worst-case scenarios?

All process water involved in ceramic production, both tap and well waters, usually contains bacteria.

And the same applies to inorganic raw materials used in the grinding process to produce the semi-finished products that will later be applied along the glazing line: frits, clays, feldspar, nepheline, etc. 

Because of the huge amount of water use, glazes and engobes grinding departments can sometimes be under the attack of significant bacterial proliferations.

Microorganisms' activity (especially that of bacteria) is able to decrease or even nullify the action of chemicals that should provide suspensions with the right features to develop a proper application, also ensuring outstanding technical and aestethic results.

In this perspective, what are the main consequences of bacterial degradations?

Thanks to the digitalization of some of its processes, the ceramic industry has evolved pretty significantly over the last few years, and in this perspective the digital printing system plays one of the most important roles.

In fact, the use of digital inks has made it possible to almost totally replace the old decoration systems.

Their formulation and therefore their production is very delicate and complex, since it must strictly comply with specific parameters.

What are digital inks?

What are their components and their most important properties?

The episode tries to give simple answers to those questions, offering a short identikit of this important category of products.