Ceramic slabs and tiles: same mineralogical composition

On the occasion of the 4th edition of the Master's Degree Course in Ceramic Enterprise and Technology, a specialised training programme created thanks to the collaboration between the two universities and the Confindustria Ceramica and Federchimica Ceramicolor industrial associations, a thesis on crystalline silica in the Italian ceramic industry was produced. The thesis (academic year 2023/24) sought to highlight the results of prevention activities implemented in ceramic production contexts to reduce the risk of exposure to respirable crystalline silica from the production stages to product installation. The paper closely examined and discussed the results of the study conducted to determine the percentage of crystalline silica in ceramic products for floors, walls and kitchen and bathroom countertops.
 
Crystalline silica in ceramic products
In the past, several studies have been conducted by national and international research institutions on ceramic products, and on porcelain stoneware in particular, showing an average crystalline silica content of 21% (with a range of 10÷32%).
In recent years, however, there have been changes to ceramic production. The increase in the production of formats and slabs and the need to reduce environmental impacts by optimising the use of resources, together with the consequences of the war between Russia and Ukraine, which caused a significant reduction in imports from Ukraine of raw materials for ceramic production, led to the search for new formulations for ceramic mixes to maintain the already high quality standards achieved by porcelain stoneware.
In collaboration with Unimore and Unibo, Confindustria Ceramica therefore promoted the thesis with a view to obtaining an up-to-date picture of the composition of ceramic products, also in the light of recent European and international regulations that highlighting the growing attention paid by lawmakers to respirable crystalline silica.
The thesis, promoted within the framework of the Technical Standardisation Commission of Confindustria Ceramica, saw the contribution of 11 companies, which provided information on the composition of the ceramic tiles produced (a total of 23, with which a total of 257 different types of products are manufactured). Mineralogical analyses were conducted mainly by certified external laboratories, using XRD analysis.

The study shows that the main component is the amorphous (glassy) component, with an average percentage of 63% (with values varying between 54% and 70%), which incorporates all the constituents of the ceramic material and plays a key role in the development of the technical properties of the end product. The crystalline silica content is confirmed as averaging 23% (with values of between 8% and 30%), regardless of product size or thickness. The study shows that in slabs and traditional tiles, the amount of quartz remains more or less the same.

Graph: the quartz content in ceramic tiles remains constant, with values of between 8% and 30% (average 23%), regardless of the size or thickness of the product. In both slabs and traditional tiles, the average amount of quartz is roughly the same.

The results highlight the versatility of the ceramic product, which lends itself to the use of a wide range of raw materials without entailing significant changes to the composition of the finished product; during the firing process (above 1200° C), the main minerals used (feldspars, kaolins, clays) melt, allowing for the consolidation of the material and the formation of the amorphous phase.
The role of crystalline silica in the ceramic industry was also discussed at the event organised on 16 April by Società Ceramica Italiana (I.Cer.S) in the auditorium of Confindustria Ceramica.

Following speeches by representatives of the university world and research institutions, who effectively highlighted the form and role of silica both in nature and in ceramic bodies and glazes, the two speeches by Confindustria Ceramica illustrated the results of the research carried out by the Association and provided an overview of the recent regulatory changes adopted in Australia and California, where, due to the significant increase in cases of silica-related diseases in operators working with artificial stone, regulatory measures have been introduced to contain the phenomenon.
The meeting also recalled the activities shared in the ceramic district with the Emilia-Romagna Region and the trade unions. In light of the established practice of sharing Agreements, 2021 saw the signing of a "Memorandum of Understanding" to ensure a practical, shared application of Directive 2017/2398 (transposed in Italy by Legislative Decree 44/2020). 

The work, which is nearing completion, has attracted interest at European level. Activities are now under way for the morphological characterisation of the respirable crystalline silica dust generated in dry cutting and grinding processes; the activity, with the favourable opinion of the Emilia-Romagna Region, has been entrusted to Prof. Francesco Saverio Violante – professor of Occupational Medicine at the University of Bologna – who, once the activities have been completed, will draw up an overall risk assessment for the ceramic sector.

(Article by Simone Mosconi  pubblished in the magazine "CER il giornale della ceramica" n. 411)