Optimal design on the high-temperature mechanical properties of porous alumina ceramics based on fractal dimension analysis

Abstract

Abstract:Fractal theory and regression analysis were employed for the first time to investigate the effect of pore size and pore distribution on high-temperature mechanical properties of porous alumina ceramics (PAC). In the present work, PAC with the comparable porosity, different pore sizes and pore distributions were prepared using carbon black as the pore-forming agent. Particular emphasis in this study was placed on the establishment of correlation between the thermal shock resistance and pore properties. The relationship between fractal dimension ( f D ) and thermal shock resistance parameter ( ) in specimens presented the negative power function, indicating that low st R f D could benefit the improvement of thermal shock resistance in specimens. The results showed that the increase of pore size and pore sphericity leads to a reduced f D , the enhanced hot modulus of rupture (HMOR) and . The decrease of proportion of micro-pores below 2 µm, the increase of mean pore size and pore sphericity could result in the decrease of st R f D , and then improve and HMOR of specimens. Based on the correlation between and pore characteristics, PAC with improved thermal shock st R st R resistance could be achieved when their pore structure meets the above features.

The use of bagasse in the preparation of fireclay insulating bricks

“…Finally, the variation of bulk density with increasing both pore creating materials is illustrated in Figure 8 showing steady decrease with either addition, although as evidenced from the correlation Table , the effect of adding PS exceeds that of bagasse. This figure also indicates combinations of PS and bagasse levels which can be used to obtain a density <1.03 g/cm 3 , the allowable value for the commonly used class C‐30 insulating refractories …”

“…As stated earlier, thermal conductivity was measured at three different temperatures (400, 600, and 800°C), each time for three specimens and the mean value recorded. For C‐30 insulating bricks category, the maximum allowable values at these temperatures are 0.41, 0.43, and 0.44 W/m/K, respectively . At all temperatures, all samples exhibited thermal conductivity values lower than standard values.…”

“…Table summarizes the properties of the chosen combination comprising 3% bagasse and 1% PS as well as a brick containing 1% PS with no bagasse added compared to standard values . It is clear that addition of 1% PS without bagasse fails to comply with density standard requirement.…”

“…Recently, the optimization of porosity and pore size in PS containing firebricks was conducted by Ramezani et al who found out that, for the same amount of porosity, samples with low sized pores tend to display higher mechanical strength then those with higher size. A fractal analysis of pore structure and its effect on conductivity was also recently reported by Liu et al They elaborated a relation indicating the effect of pore size and sphericity on thermal shock resistance of porous alumina refractories, depending on the fractal dimension of pores. Finally, Miyazaki et al recently studied the effect of pore size and its distribution on the strength of porous alumina.…”

Effect of Holding Time During Sintering on Microstructure and Properties of 3D Printed Alumina Ceramics

“…The holding time during sintering involves a process of mass transfer, grain boundary migration, and particle growth (Gao et al, 2000). Appropriate holding time can eliminate pores and promote densification, but a very long holding time would decrease the density, due to abnormal growth of particles and deformation of green bodies, and reduce the mechanical properties of materials (Cha and Hong, 2003;Liu et al, 2018;Cheng et al, 2019;Tangcharoen et al, 2019). Therefore, the holding time should not be blindly extended.…”