Apparently invisible. Chemistry in ceramics. – Détails, épisodes et analyse

Sodium silicate is an inorganic substance that at room temperature it is in solid state.

It is a chemical compound used in several areas of industrial production. In ceramics, sodium silicate is very effective within ceramic mixtures.

Among the several effects it produces, it plays a very important role in terms of fluidization.

The episode is about the function that this substance performs, highlighting its several properties and the benefits it promotes.

With a focus on deflocculation of ceramic mixtures.

Polluting and odor emissions are two important critical issues that producers have been looking for some time with considerable attention.

This is a problem that appears in the final stage of the ceramic production cycle, inside the kilns, but whose origin can be found in the previous application processes that mostly take place along the glazing line.

Scenarios can be different but emissions are mostly produces by the use of digital glues and digital inks that, due to their particular chemism, can be considered the core of the problem.

What do we need to know about it?

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:

1. Electrostatic repulsion by cationic exchange
2. 2. Steric repulsion
3. 3. Complexation

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.