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

Jingjing Liu,Wenlong Huo,Xiaoyan Zhang,Yuanbing Li,Zaijuan Zhang,Jinlong Yang,Bo Ren

doi:10.1007/s40145-018-0260-x

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 (Df) andthermal shock resistance parameter (Rst) in specimens presented the negative power function, indicating that low Df 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 Df, 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 Df, and then improve Rst and HMOR of specimens. Based on the correlation between Rst and pore characteristics, PAC with improved thermal shock resistance could be achieved when their pore structure meets the above features.

Highlights

Porous alumina ceramics (PAC) have attracted considerable attention as thermal insulators, gas/liquid filters, catalytic supports, and high-temperature structural material, due to their high-temperature refractoriness, high surface area, and low thermal conductivity [1,2,3].In the majority of applications, PAC often encounter strong heat flow and/or abrupt temperature shock, leading to instantaneous thermal stresses
As for the porosity, Shyam et al [8] found high porosity shows great benefits on enhancement of thermal shock resistance of porous ceramics since both crack propagation and thermal stress in ceramics are generally absorbed by porosity
In order to develop an accurate quantitative parameter for the pore size and its distribution, fractal dimension is employed to give a deeper understanding between pore size and its distribution and thermal shock resistance parameters ( Rst ) as well as mechanical strength

Summary

Introduction

Porous alumina ceramics (PAC) have attracted considerable attention as thermal insulators, gas/liquid filters, catalytic supports, and high-temperature structural material, due to their high-temperature refractoriness, high surface area, and low thermal conductivity [1,2,3]. As for the porosity, Shyam et al [8] found high porosity shows great benefits on enhancement of thermal shock resistance of porous ceramics since both crack propagation and thermal stress in ceramics are generally absorbed by porosity It was reported by Jin et al [9] that the increase of porosity and decrease of pore size result in superior thermal shock resistance. Jin et al [14] found the critical difference temperature ( Tc ) of porous Al2O3–ZrO2 ceramics shows a deceasing trend with increasing the pore size from 2.21 to 4.23 μm All these interesting results were failed to describe the relationship between pore-related characteristics and their thermal shock resistance quantitatively, which was attributed to the difficulty in characterization of such pore-related parameters. This work makes a contribution to the effect of pore characteristics on performance of PAC

Experiment

Results and discussion

Conclusions