Apparently invisible. Chemistry in ceramics.

Suspending agents belong to a broad category of additives whose primary purpose is to provide ceramic suspensions (slips, glazes, engobes, or frits) with good internal stability, counteracting potential sedimentation phenomena.Available in both liquid and solid forms, these products act within the suspension to ensure the right balance.There are various mechanisms that can be employed to properly maintain the solid phase of the mixture in suspension.Among these, the most significant are about viscosity, electrostatic repulsion, and concentration (solid/liquid ratio).This episode, after reviewing the properties of suspending agents, focuses on these three main tools, delving into the reasons and mechanisms behind each, also considering the application systems through which suspensions are deposited onto the ceramic substrate—a detail that can significantly influence the type of suspending agent to be used.

Complexing agents are capable of catching multivalent cations present in suspension to prevent them from negatively affecting the ceramic process. They are responsible for one of the main mechanisms underlying the deflocculation process: complexation.Complexing agents (or chelating agents) are chemicals that bind to specific ions (such as calcium, magnesium, iron, etc.), forming stable complexes.This property allows them to "sequester" metals, making them less reactive or preventing their precipitation in solutions.These are simplified and very short descriptions of this particular category of additives. The episode takes a closer look at the mechanisms enacted by these substances within the ceramic production process, highlighting their functions, benefits, and sometimes, risks.

The topic of non-planar surfaces, which develop on multiple micro-levels and are sometimes improperly identified as 3D surfaces, plays a crucial role in giving ceramic surfaces not only a more natural appearance but also a broader and more extensive expressive potential.This is not a new requirement: it took its first steps with the help of traditional technologies, but it has found new momentum with the arrival of the latest digital techniques.The episode offers an overview of the main methodologies currently used to achieve textured surfaces, delving into the chemical mechanisms that occur on the surface and contribute to producing the desired effects.

In the previous episode (#45) we discussed the technical aspects of digital printing systems in relation to ceramic bricks.This second part looks at the necessary preparatory work for the printing phase, going through the various steps involved in preparing a print file.Regardless of the media on which you will work.Some key words: standardized lighting, colorimeter, spectrophotometer, linearization, chart...

At present, in the heavy clay industry, products are decorated mainly by applying engobe with the aid of scattered granules or by means of reduction effects created by the firing process.These techniques are suitable to produce traditional products for the existing market. What added value does digital printing offer in this field?

The operating temperature is an important parameter that ceramic producers must take into account in order to avoid application problems that can also negatively affect the quality of the finished product.However, this parameter is not always easy to manage, especially if we consider the fluctuations promoted by seasonability.The episode addresses the topic with the help of specific examples, highlighting the main scenarios and the different levers on which one can act to better manage the anomalies that may occur along the production lines.

Most ceramic production processes involve the dispersion of ceramic powders in a liquid medium - mostly water - to obtain a suspension or, more generally, a dispersed system.To provde the suspensions with the desired stability and workability, depending on the different applications, we use the addition of small quantities of suitable chemicals that, interacting with the solid particles, change the rheological behaviour of the whole system.The episode offers a picture of two categories of chemical - deflocculants and binders - almost always involved in order to achieve the right result and therefore the correct application performance. 

All analysis of ceramic suspensions carried out by those companies that supply chemicals for ceramic production are fundamental to properly develop the processes that take place along the production line.The episode provides an overview about the role of these important investigations, with a focus on the data and on the operations of the involved tools.We will talk about jars, pycnometers, laser granulometers, sieves, rheometers, pointing out how all these tools are important in providing ceramic producers with the correct information to proceed without problems or unexpected critical issues.

After addresing the impact that seasonality can have on the the fluidization of ceramic mixtures and on bacterial proliferation within semi-finished products, this second part of the episode 41 tries to show and explain the consequences that temperature changes may produce on the drying time of ceramic suspension, leading to alterations that often force producers to revise the parameters of the glazing line.After offering the usual suggestions to handle the problem, the episode ends with a focus on the solubility of surfactants that can be also susceptible to seasonal and temperature changes.

In ceramics, the use of chemicals plays a fundamental role in providing the final product with high technical and aesthetic results and in promoting a proper application process.However, their actions can be sometimes less effective or compromised. There are several reasons for this performance change and seasonality is surely one of the most interesting.Through a series of examples, the episode addresses the actions that should be taken to prevent the temperature to negatively affecting both processes and products.

Glaze and grit suspensions are made up of a liquid part (usually made-up of water and one or more rheological chemicals) and a dispersed solid part.However, these two different suspensions show a lot of differences that may lead to very contrasting results, also implying a different approach about chemicals, both during the grinding phase and along the glazing line.From this point of view, all chemicals involved must be marked by specific features according their intened use. What do we need to know about the subject?

Cratering phenomena are defects that appear as microscopic craters on the surface of ceramic bodies on which an aqueous (and still drying) suspension has been discharged.It is an application problem that leads to a misalignment of the suspension due to the presence of one or more dips.The problem, that is already visible along the glazing line and not only after the firing process, may arise for several reasons: for example due to the presence of impurity within the ceramic raw materials or because of an improper use of defoamers.The episode try to offer a list of the most important causes, pointing out the mechanisms behind the problem, also providing some suggestions to prevent and/or eliminate it.

CMC are organic compounds, water-soluble polymers derived from cellulose, widely used in several fields of industrial production. In ceramics, sodium CMCs perform multiple functions within suspensions and solutions and can be marked by very different properties depending on the situation.What is the main role of this substance in the ceramic production process, and what needs to be done to properly manage it?

The plasticity values of ceramic mixtures is a very important issue, since it affects the values and features of the mix and therefore the proper development of the ceramic production process.In general, the use of clays marked by high plasticity values is usually synonymous with easier process management.However, high-performing clays are not always available and it is therefore important to keep in mind other production parameters, finding a balance or even good compromises.After a short definition of this amazing physical property, the episode offers a general overview on the issue.Not only in relation to tiles production.

In ceramics, digital technology (use of digital glues and digital inks) has definitely riform the sector, making the production process much more flexible and expanding creative and aesthetic possibilities.The extraordinary precision with which the ink is discharged on the ceramic support, in fact, has opend to new extraordinary results.However, the topic "printing definition" must be addressed with great attention, being subjected to several variables that can affect the final product.What are these variables? What mechanisms are behind them and what can be done to not compromise a good resolution?

Scanning Electron Microscope is a sophisticated tool used in many fields of scientific research, even in ceramics.The use of an electron beam instead of light allows to get not only outstanding high resolution images but also detailed information on the composition of the sample.Insights are so accurate and exhaustive that offer manufacturers clear solutions or, at least, suggestions about the actions that should be taken to properly solve production critical issues.How does the tool work and what are its most important functions to support ceramic industry?

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?

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:Electrostatic repulsion by cationic exchange2. Steric repulsion3. 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.

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?

The ceramic mixture usually used in ceramic production, largely consists of inorganic raw materials (clay, feldspar, sand, etc.), grinding water and chemical.These mixtures, since they must be properly managed in the various stages of the production process - from grinding to pressing (or forming) - must be marked by specific and particular features.In addition to this, the raw ceramic material, once it has been pressed, must have the right properties to prevent and avoid the problems that may occur along the lines (before entering the kilns) and to develop ceramic surfaces without aesthetic or technical defects.To do this, the use of specific chemicals is a must.What are the main chemical categories involved and added to ceramic mixtures? What role do they play and what kind of actions do they promote?

In ceramic, the drying process takes place inside dryers where raw tiles are placed on metal supports (roller stands) for a preset time, until the residual humidity's percentage is close to 0%.The heating to which the ceramic body is subjected leads to a migration of the water molecules and so to their evaporation.Sometimes this process can be not completely homogeneous over the entire surface of the tile. More precisely: the parts of the ceramic body that rest on the basket rollers may have different evaporation times compared to those areas of the tile that are not in contact with the metal parts of the dryer.This different evaporation process can sometimes produce striped halos on the surface that may remain visible even after the drying cycle. What are the reasons and the mechanisms of the problem and what kind of actions must be previously take to avoid it?

In the previous episode, we offered a general overview on the most important chemicals normally used for ceramic glaze applications.We went deeper by addressing all those categories that are used during the preparatory step, that is the grinding stage, moving later towards the glazing line where we focused on the so-called binders for glazes.This episode closes the subject with a panorama about actions and benefits provided by surfactants, wetting and suspending agents, defoamers and binders usually added along the glazing line, when the production is already ongoing.

The ceramic glaze application that takes place along the glazing line is one of the most delicate steps of the ceramic production process.If you want to get high performances in terms of process and product, the glaze must be marked by proper rheological features that always change according to the application conditions of the production line.The right formulation of glaze suspensions, therefore is a precondition for a proper application and a result without technical and aesthetic defects.What are the most important categories of chemicals used for glaze suspensions?How do they act, and what kind of problems do they solve?

In ceramic production, grit applications are mainly "wet applications" made by means of airless spraying systems.A kind of application that involves a huge amount of water within which the grit is suspended. Nevertheless, in recent time a different application method is spreading.We could define it as a dry method that, however, has nothing to do with digital systems (that involve, instead, the use of digital glues together with a dry application of grit).Without forcing the words, in this case we could talk about "analogue dry application of grits".How does this application work and what sort of features must the grit have to properly develop the process and to produce high-performing ceramic tiles?

In the field of ceramics, glazes are usually applied on the raw tile by means of spray “analogical” systems (airless application system). Nevertheless, recently some new application machines have appeared on the market.They cannot be defined as completely digital but they cannot even be comparable to traditional analogue techniques. How do they work?What kind of features should the glaze have to be properly applied?

Along the ceramic production line that from the pressing stage leads to the kilns, raw tiles (still delicate and fragile) often undergo to stresses on the conveyor roller that can compromise them.Chipping or breakage may occur if no preventive action is taken to increase the material's mechanical resistance.What does the mechanical resistance value mean?How do chemicals used to increase it work?What measures can be taken to achieve better results?Temporary binders surely have the most important role but what should be taken into account to emphasize their action?

The ceramic production process - after the early stages that from the formation of the tile under the press lead to the applications of the glazing line - usually involves a final application of grit or glaze. Sometimes in huge amount.If you do not meet the proper parameters of the process, this application can lead to several problems able to compromise the ceramic surface, both technically and aesthetically.The formation of pinholes is one of the most frequent. What are the roots of the problem and what can we do to prevent it?

In the ceramic tiles prodcution, engobes, grits, and glazes are still applied - to a large extent - by means of airless spray systems.chine is equipped with spraying guns that end with special nozzles that properly discharge the suspension on the raw ceramic surface. Sometimes these nozzles can be clogged during application stage, forcing producers to slow down or even stop the production cycle.The problem, that has a significant and negative impact on the industrial productivity, can arise because of several scenarios such as a wrong set-up of the application machine, an improper grit grain size or the presence of localized sedimentation phenomena.In detail, what are the mechanisms that can lead to the problem and what do you need to know to take the right actions to prevent it?

The lapping and polishing processes that provide ceramic tiles with the proper aesthetic features, both involve the removal of a very thin layer of glaze that is on the very external part of the tile.Even if the amount of removed material is very small, these processes may bring out to the surface all that micro-porosity that are inside the glaze.Since they are no more protected and sealed, the pores remain exposed chemical and dirt attack.How do the protective treatments work? What are the chemical mechanisms and what kind of benefit do they promote?

Process water play a very important role within ceramic activities, being involved in a wide range of production's steps. If on the one hand they are strictly necessary to the course of the work, they can lead on the other hand to problems when they do not fits the required production parameters.The fourth episode of the podcast APPARENTLY INVISIBLE. CHEMISTRY IN CERAMIC, now available on the leading audio platform, is exactly focused on this topic. We talk about electrical conductivity, net and groundwater, waters clarification, sanitization, pH, depuration, tank storage...Which are the most impotant issues?What do we should know to prevent or minimize them?

During their storage in the tanks, semi-finished products can be affected by bacterial degradations that, if they are not properly managed, may lead to application critical issues as well as to serious defects in the finished tile product, such as pinholes Just to give an example.What kind of action must be taken to face the problem?Is it possible to restore the right features of a bacterially compromised suspension?

The gelling phenomena of slurries inside the storage tanks is not so unusual as one might suppose.Let's find out the causes and identify possible solutions.