Apparently invisible. Chemistry in ceramics.

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.

In general, wet grinding systems offer best performances and best production results only when the chemical and physical features of slips are constant over the duration of the entire process. More precisely, this happens when the main parameters of the atomized product (such as grain size, density, viscosity, and thixotropy) remain within a very short range. However, slurries may suddenly change their rheological features during production. Sometimes drastically. What are the main elements that may affect, positively or negatively, the proper rheology of the barbottina and what do we need to know to prevent and avoid fluctuations, therefore preserving the proper features of suspensions?

Formaldehyde, despite its wide use in many fields of the industrial production, in high percentage may be a serious problem. In Ceramics, it must be carefully checked since it can seriously and negatively affect the environment. What do we need to know about this topic?

Rheology is the science that deals with the flow and the strain rate of matter. It’s a branch of Physics that studies the origin, the nature and the deformation’s characteristics of a matter under the influence of external forces, with particular regard to non-Newtonian liquids. Its main goal is to define the correlations between causes (forces) and effects (deformations and flows), identifying all mechanisms that are the basis of the different rheological behavior on a microscopic and molecular scale. The episode offers an overview about the most important rheological behaviors of ceramic suspensions: barbottine, glaze and grit suspensions, engobes and inks. All these mixtures, in fact, in order to develop a good application and avoid serious problems along the production lines, must be marked by proper rheological features. Which ones?

The episode focuses on the flocculation phenomena of ceramic mixtures. The problem is marked by a progressive aggregation of solid particles and it often takes place due to phenomena of electrostatic attraction between the clay micelles in suspension. This process leads to a significant increase in viscosity within the system, negatively affecting the proper development of the production process. The episode offers a general overview about ceramic mixtures, focusing on the corrective action of some specific chemicals, able to develop and trigger an opposite process that provides the ceramic mixture with the proper features, restoring the parameters required for a good development of the process. With particular reference to the three major mechanisms underlying the deflocculation process:

The lack of cohesion that occurs not only between the glaze’s particles but also between the glaze and the raw ceramic support can lead to a problem commonly called "dusting phenomenon". This kind of glaze, that we could define as fragile, is easily removable from the ceramic surface, especially when it undergoes to the mechanical solicitations that take place along the production line. What happens inside the glaze and what can we do to prevent and to properly manage the problem?

The episode focuses on a subject that may seem unimportant but that, instead, is quite relevant if we consider the recent and new intended use of ceramic surfaces (tables, countertops, etc). Since tiles now are used not only for floors and walls (but also for furniture: tables, top, countertops, ect) the contact with the food we eat is frequent and it must be considered. Given that ceramics are, by their very nature, one of the most hygienic and antiseptic material in the world, it is also true that surface protective treatments that are applied after the firing cycle may represent in this perspective a serious issue: the products involved in the process, unlike ceramics, do not undergo to any modification after treatment, being not transformed by the very high temperatures of the kilns. Even if toxic emissions provided by ceramic glass and protective products are extremely rare, it's nevertheless important to take stock and dissect the issue, looking more closely at all mechanisms (not only related to chemistry) that take place behind the scenes.

This episode is the second part of a general overview about the most important categories of chemicals for ceramic prodution and their positive role in terms of environmental impact. The perspective wants to scratch - with a deliberately provocatory approach - the idea that chemistry cannot provide, by nature, any environmental benefit. Actually, if we addressed the subject by using a "magnifiying glass", we would notice that the use of chemicals often allows you to avoid making choices that could be much more impactful. The challenge is to change perspective, trying to look at the scenario with a different approach, without taking anything for granted.

The episode aims to refocus, from a special and provocative perspective, the role of chemicals used in ceramics: from the beginning to the end of the process, that is from the grinding of the clays that form the basis of the ceramic mixture up to the firing cycle. The reading filter is "chemicals and environmental impact" and the goal is to break the preconception about the word "chemistry", often related to the pollution, contamination, infections. We do not want to belittle or deny the wrong use of potentially dangerous products by some industrial producers but, for sure, we also want to fight against the word "chemofobia" that is the irrational fear or idea that all chemicals are dangerous and harmful. In each steps of the production process, the wise use of chemicals can promote some environmental improvements that should not be underestimated or even disclaimed.

Ceramic glazes can be applied by means of several technologies but the most common and popular is the airless spray system. However, sometimes glazes can still be discharged on the raw tile by means of bell or vela systems. Each application system required different evaluations about the glaze's rheology. The glaze must be marked by specific properties according to the system with which is applied along the production line. The episode focuses on these differences and on the chemicals that can - or must - be used to get the proper features. At the end, a brief focus on synthetic chemicals, very useful to prevent the proliferation of bacterial attacks before and during application.

In ceramics, the water-based digital system represents a topic of great interest. The R&D departments of all the players have been doing research for some time, trying to improve the sector with a technology that is already widely used in many other fields of industrial production. The #technical #problems of both the application machines and the products (such as inks and glues) seem to have been overcome, and the time is ripe for a definitive diffusion of this technology which certainly offers many #advantages at a technical, aesthetic and environmental level. After a brief introduction to the chemical nature and main characteristics of water-based glues, the episode focuses on the most significant advantages promoted by this important type of product, also highlighting its underlying mechanisms.

In ceramic production, the use of digital glues for glaze and grit applications has almost completely replaced the spray/airless application system. Even if each glue differently acts on glass powders and grits, there are two main categories that must be considered: solvent-based digital glues (based on non polar solvents) and water-based digital glues (based polar solvents and water). This episode opens with a general introduction on the chemical nature of these products, then offering two important focuses on the operation and mechanisms of action that they develop on the raw tile support. Both with similarities and differences.

The black core is a localized area marked by a brown/black (or even white) color, clearly visible in the thickness of the ceramic tile. Its presence is usually sign of inadequate oxidation and it has not to be considered as a defect that compromises the product functionality. However it's a very serious aesthetic problem, especially if we consider the increasingly different intended use of ceramics. The origins of this particular defect are many and, according to the specific production conditions, even the actions and solutions to reduce or prevent it can be different. The episode focuses exactly on this topic, offering a journey that starts at the origins of the problem,and then ending with a range of possible interventions.

After introducing the topic in the previous episode and getting into the details of the problems that may arise before the inkjet application, this new episode focuses on the repellency phenomena that occur after the digital printing process at the interface between the solvent-based inks and the subsequent watery applications of glaze or grit suspensions. The different chemical nature of the inks (non polar polymers) and all the water-based suspensions (polar), is the basis of the critical issue and it basically results in a incompatibility between the two applications due to a lack of interaction. Just like between water and oil. The episode looks closer at the mechanisms behind the phenomenon, offering some effective actions to avoid or reduce it.

The ink-jet decoration - that has replaced traditional decoration systems - has removed several problems bringing out, however, new and more complex critical issues. The new scenario has forced a different attention to all those applications that occur along the glazing line both before and after the digital printing process. In particular, the different nature of the solvent-based inks, with respect to all the water-based applications of the glazing line (engobes, glazes, grits, etc.), often leads to repellency phenomena that can compromise the proper printing process. In addition, the glaze applied as a final protection (on the ink), when not accurately mixed with proper chemicals, may lead to excessive or low drainage, or even to phenomena of inhomogeneous ink's absorption. What kind of action must be taken in all these cases? What are the PRIMERS usually involved and how do they work?