Estudo das propriedades mecânicas de porcelanato através da avaliação de tensões residuais microscópicas originadas durante a etapa de resfriamento do ciclo de queima
The porcelain tile is composed by clay minerals, quartz and feldspars. It is the best ceramic tile considering the technical properties. Basically it is constituted by 50-60% glassy phase, 10-25% quartz, <10% mullite, 0-10% non-fused feldspar and 3-7% of close porosity. Manufacturing is normally done by dry pressing from fine wet grid raw materials which are spray-dried. Sintering is carried out by fast firing, i.e., 40-60 min, and maximum temperature between 1180 and 1220ºC. Cooling stage is done as fast as possible, with a lack of specific control. Only a little decrease is done on the cooling rate during the quartz allotropic transition. The mechanism of developing mechanical properties of porcelain tile is normally associated with that of technical porcelain, but it is not so evident what the most relevant mechanism is. In the present work, the mechanical properties of porcelain tile was evaluated based on the developing of macroscopic and microscopic residual stress. Different levels of macroscopic residual stress were produced by changing the cooling rate and the initial composition (kaolinite, quartz, albite).The effect of microscopic residual stress was evaluated by changing the initial composition and the particle size of quartz. The macroscopic residual stress was measured by deformation-relaxation method with incremental cuts and the microscopic residual stress by x-ray diffraction. The mechanical strength and fracture toughness, SENB method, was measured by three points bending using a universal test machine. The results show that porcelain tile develops tempering when submitted to fast cooling rate. This process is controlled by the same factors of those in float glass, them it can be considered a kind of reinforcing mechanism. As the tempering occurs, a microstructural deterioration also occurs, which was quantified by a proposed model based on an increasing of the Griffith flaw size. This deterioration is the most important mechanism that differs the mechanical properties all the studied composition. The high strength was obtained for those compositions with macroscopic residual stress, matrix reinforced byquartz particles, but with no deterioration during fast cooling. The deterioration was least for those microstructures where interconnected mullite crystal was observed. The observed changing in microscopic residual stress on the quartz particles was related with changes in the interface nature (amorphous silica, mullite/ kaolinite glass or albite glass) and can not be directly associated with matrix reinforced by increasing the fracture energies without considering the deleterious effect of those low thermal expansion phases. The proposed methodology for determination of microscopic residual stress under quartz particle together with dilatometric experiments, could confirm that the quartz particles in porcelain tile are partially disconnected. This phenomenon is controlled by anisotropic behavior of the quartz unit cell. In this way, the quartz presents two critical diameters and the particles can be completely or partially disconnected.
Advisor:Antônio Pedro Novaes de Oliveira; Hazim Ali Al-Qureshi; Dachamir Hotza
School:Universidade Federal de Santa Catarina
Source Type:Master's Thesis
Keywords:ciencia dos materiais engenharia de porcelanatos propriedades mecânicas tensões residuais engenharias
Date of Publication:07/16/2007