Comentario sobre "Abrasión Superficial de Azulejos"

Abstract

Esposito and Tucci have published recently an interesting paper on the assessment of surface abrasion of glazed ceramic tiles [1]. They studied the dependence of the wear behaviour of the glaze layer on several parameters such as porosity, hardness and fracture toughness of the glaze. Six single-fired glazed ceramic tiles were chosen for the experiments. The wear behaviour was assessed by measuring the material removal resulting from the standard PEI abrasion test, determined after two stages of 6000 and 12000 revolutions. A summary of the materials investigated, including hardness (H) and fracture toughness (K Ic ) measured on the glazes and data on wear behaviour, given both as PEI classification and normalised weight loss, is given in Table 1.The work confirmed that the standard PEI classification is insufficient to differentiate the wear behaviour of ceramic glazes. While the materials investigated fall into only two PEI classes, they exhibited markedly different wear resistance, with sample 2 clearly showing the lowest material loss.The results of Esposito and Tucci also showed that the wear behaviour of the glazes could be correlated with their fracture toughness values. This behaviour is shown in Figure 1, indicating that wear resistance increased with increasing fracture toughness (in other words, normalised weight loss decreased with increasing fracture toughness). Due to the fact that the hardness of all samples was nearly identical (Table 1), the authors concluded that this property would not affect the material removal during abrasion test [1]. The present comment has been prompted by this last conclusion of Esposito and Tucci [1], which seems to suggest that fracture toughness is the only property affecting wear response of glazed tiles.In fact, in studies of the wear behaviour of engineering ceramics, the comparison of wear resistance parameters (e.g. wear rate or volume of loss material) with hardness or toughness values taken separately has not always resulted in clear, unambiguous correlations [2][3][4]. On the basis of fracture mechanics analysis, the product K Icn H m has been suggested to be related to the wear resistance, with the exponents n and m depending on the mechanisms of material removal: n=3/4 and m=1/2 being applicable for abrasion and n=4/3 and m= 1/4 for erosion [5,6]. Comparison of experimental data on engineering ceramics and ceramic composites with the prediction of these models has not been always successful and discrepancies have remained [7][8][9]. Independently of the material removal process involved, when the exponents in the fracture mechanics expression take the values n= -1 m= 1, the aforementioned product yields the so-called "brittleness index" (B) of the material [10]. We have suggested in a recently article the use of the brittleness index (B) for a qualitative estimation of the wear and 309