Thermal shock

About: Thermal shock is a research topic. Over the lifetime, 5012 publications have been published within this topic receiving 58954 citations.

Utilização de testes de recebimento e acompanhamento como ferramentas de controle de qualidade do revestimento refratário aplicado em calcinadores: um estudo de caso

Abstract: Refractories are ceramic materials, made from clay minerals that have high melting point inorganic oxides, generally used as internal lining of alumina calciners because they can withstand many types of wear mechanisms when subjected to high temperatures, such as mechanical and thermal stresses. However, several aspects can compromise the integrity of this material, which in turn can lead to unexpected and emergency equipment shutdowns, affecting the production and maintenance costs of refineries. Therefore, this work proposes the implementation of a new testing methodology that seeks to compare the properties specified by the manufacturers in the technical data sheets (FDT) with the properties of the material received, and consequently improve the quality control. Thus, characterization tests were carried out for four dense refractory castable installed in an alumina calciner. The samples were subjected to two types of tests in order to evaluate the properties and performance of the material received and applied. In the receiving test, the tests performed were as follows: liquid absorption, porosity and apparent density (110°C); erosion resistance (after firing at 1000 °C for 5 hours, as well as the others tests followed by their respective temperatures); and permanent linear change (1000°C). As for the installation test, the tests considered were: erosion resistance (1250°C); permanent linear change (1250°C); thermal shock resistance (1250°C); hot modulus of rupture (1250°C); and refractoriness under load (1600 °C). After analyzing the results, a deviation was found in relation to the analyzed properties - such as mechanical strength and refractoriness -, as they presented values below those specified by the suppliers in their technical data sheets. Thus, the importance of receiving and monitoring tests as efficient tools in the quality control of the refractory used is evident, based on the need to specify materials that meet operational conditions and/or project requirements, with a focus on performance, safety and operational availability (production).

Thermal stress analysis of optimized functionally graded coatings during crack propagation based on finite element simulation

Abstract: Thermal barrier coatings (TBCs) are widely used in aircraft engines to protect their superalloy turbine blades in high inlet-temperature environments. However, the mismatch of the thermal expansion between the ceramic top layer and the bonding layer causes thermal stresses during thermal cycling, which can lead to cracks and failure of the TBCs system. In this paper, three different structures of TBCs were analyzed, which were single ceramic layer coatings (SCLC), double ceramic layer coatings (DCLC), and optimized functionally graded coatings (OFGC). In this paper, the propagation of horizontal and longitudinal cracks in TBCs of different structures during thermal cycling was analyzed by finite element simulations. The axial and radial maximum stress values and minimum stress values at the crack tip during thermal cycling of TBCs were analyzed. The results indicated that the OFGC structure could effectively reduce the thermal stress at the crack tip of the coating system during thermal cycling. The introduction of a gradient structure could improve the lifetime and thermal shock resistance of the coating.

Synthesis of Low-Thermal-Expansion Cordierite Ceramics Using Kaolin-Group Minerals

Abstract: Cordierite (2MgO·2Al2O3·5SiO2) in the MgO·Al2O3·SiO2 system exhibits a low thermal expansion coefficient, high thermal shock resistance, low dielectric constant, and excellent electrical insulation properties. However, the material has a narrow sintering-temperature range. If the sintering temperature is too low, the crystal structure of cordierite does not form sufficiently; conversely, if it is slightly higher than ideal, the material decomposes into postelite, spinel, and mullite, leading to a significant increase in its thermal expansion coefficient. To overcome this problem, we adjusted the composition of cordierite by mixing it with predetermined amounts of kaolin minerals. After sintering at 1340℃, the resulting ceramic showed satisfactory physical properties, such as bulk density, absorption rate, and porosity. The optimal mixing conditions included a MgO/Al2O3 molar ratio of 1.006 and SiO2/Al2O3 molar ratio of 2.4277. Given its low thermal expansion coefficient(2.20 × 10−6/℃ at 800℃ and 2.57 × 10−6/℃ at 1000℃) and favorable physical and shrinkage properties, the cordierite prepared in this work may have potential applications in the development of kiln furniture materials for sintering next-generation secondary battery cathode materials.