06-21 Afyonkarahisar Turkey

[Image above] In a village near the Turkish city of Afyonkarahisar, a clay deposit has the potential to serve as an alternative for Ukrainian clay in the manufacturing of white tiles. Credit: Ingeborg Simon, Wikimedia (CC BY-SA 3.0)

From earthy tones to bolder colors, avoiding neutral, polished white seems to be the tile trend for 2024. While there are many societal factors driving the popularity of this style choice, there is likely an economic component as well—the ongoing war in Ukraine.

Since the 1990s, Ukrainian clay gained a reputation around the world for its purity and good consistency. But when Russia invaded Ukraine and the country could no longer export its clay, tile manufacturers struggled to find alternative clay sources with the same special qualities, leading to shortages of very white and large-format tiles.

Some manufacturers explored reformulating their tiles based on clay in local deposits, but in many cases, these local sources contain high levels of iron, resulting in darker and reddish tiles. As such, some tile industry insiders believe red may become the new “white” due to the supply chain constraints.

Regardless of these market restrictions, consumer desire for white tiles will not simply go away. So, whoever can identify a new source of high-quality clay with low iron content would have an enviable position in the tile industry.

In a recent open-access paper, researchers from Spain and Türkiye investigated the potential of clay sourced from the Afyon region of Türkiye as a possible alternative to Ukrainian clay.

Commercially known as “Afyon clay,” this material is located around the village of Alanyurt, near the city of Afyonkarahisar. The clay here comes in three forms: white colored (mostly illite clays), beige and creamy (kaolinite-dominated clays), and green-pale or green (contains smectitic clays). Supply companies usually operate all the clay groups together, marketing them as a single product of Afyon clay.

Studies exist on the origin and geological structure of these deposits (see here and here), but practically no works consider the physico-chemical characterization of this clay nor its possible application in tile manufacturing. The lack of availability of Ukrainian clay, though, provides the impetus to finally evaluate Afyon clay’s potential more closely.

In the recent study, the researchers used commercial samples of Afyon and Ukrainian clays supplied by Çanakkale Seramik, the company known for being the first Turkish ceramic tile manufacturer, to determine Afyon clay’s potential as a replacement.

First, they characterized the Afyon and Ukrainian clays using chemical (X-ray fluorescence spectrometry) and mineralogical (X-ray diffraction) methods, followed by laser diffraction to determine the particle size distribution. They also performed thermal analysis to obtain the thermogravimetric curves and the differential scanning calorimetry curve.

Then, they investigated the Afyon and Ukrainian clays’ rheological behaviors by determining the deflocculation curve at a given solids content using a twist wire viscometer. They also determined the Atterberg plastic index via indentation, as well as assessed the clays’ behaviors during pressing and firing.

The researchers found that although some properties of the Afyon clay differed from those of the Ukrainian clay, its behavior during the different stages of processing, milling/deflocculation, pressing, and firing were similar to that of the Ukrainian clay.

In addition, when they substituted Afyon clay into a tile composition traditionally based on Ukrainian clay, the fired body demonstrated only a slight decrease in whiteness. However, the researchers attributed this effect to the presence of Istanbul clay in the composition rather than the Afyon clay.

Firing diagrams showing the linear shrinkage and water absorption versus firing temperature for the Afyon and Ukrainian clays. Credit: Castellano et al., Boletín de la Sociedad Española de Cerámica y Vidrio (CC BY-NC-ND 4.0)

“Consequently, it can be concluded that a porcelain tile composition can be designed using Afyon clay as the major clayey component, adapting adequately to the requirements demanded in industrial practice,” the researchers conclude.

The open-access paper, published in Boletín de la Sociedad Española de Cerámica y Vidrio, is “On the use of Afyon clay in Ukrainian clay-free compositions for porcelain tile manufacture” (DOI: 10.1016/j.bsecv.2024.05.002).