Fabrication, Properties and Nonlinear Thermal Conductivity Model of Highly Porous Mullite Ceramics

doi:10.15541/jim20140048

Abstract

Abstract:

Highly porous mullite ceramics were prepared by bauxite and silica fume as raw materials and corn starch as the pore-forming agent. The phase and morphology were characterized by XRD and SEM, respectively. The influence of corn starch content on apparent porosity, bulk density and flexural strength were studied. Thermal conductivity of porous mullite was measured at 473-1273 K. A new nonlinear thermal conductivity model and several models between bulk density, flexural strength and apparent porosity were established. The results indicate that, bulk density and flexural strength of porous mullite decrease with porosity increase and conform to the exponential function relationship. Thermal conductivity of porous mullite increases with the rise of temperature and the measured values are in good agreement with values calculated by nonlinear thermal conductivity model. The new model can accurately reflect the thermal conductivity correlations for temperature, porosity, radiation and mean pore size.

Key words: highly porous mullite, fabrication, thermal conductivity model, nonlinear

CLC Number:

TQ175

LUO Xue-Wei, LI Hai-Feng, XIANG Wu-Guo, YUAN Hui, CHENG Cheng, SHEN Xu-Gen, YAN Chun-Jie. Fabrication, Properties and Nonlinear Thermal Conductivity Model of Highly Porous Mullite Ceramics[J]. Journal of Inorganic Materials, 2014, 29(11): 1179-1185.

Figures/Tables 10

Fig. 1 XRD patterns of the samples calcined at different temperatures for 1 h

Fig. 2 SEM images of starch (a) and porous mullite (b, c) and MIP pore size distribution curve (d)

Fig. 3 Influence of starch content on the apparent porosity, bulk density and flexural strength

Fig. 4 Influence porosity (P) on bulk density (D) and flexural strength (F) and exponential fitting curves of F-P and D-P

Fig. 5 Calculated values of the relationships between thermal conductivity and porosity by five basic models and the experimental values at 298 K

Fig. 6 Contrast of the calculated values according to Shimizu model and experimental values of this work

Table 1 Typical values of the thermal conductivity for bulk mullite and air at different temperature

T / K	λ_air×10² / (W·m^-1·K^-1)	λ_m / (W·m^-1·K^-1)
273	2.05	-
473	3.35	-
673	4.47	1.45
873	5.34	1.52
1073	6.02	1.58
1273	6.55	1.63
1473	-	1.67

Table 2 Parameter values of α1- α5

Parameters	Mathematical formula
Parameters	ξ₁/×10^-5	ξ₂/×10^-8
α₁	-1.69	-1.59
α₂	7.04	6.63
α₃	-6.24	-5.87
α₄	-0.13	-0.12
α₅	-0.14	-0.13

Fig. 7 The contrast of the calculated values according to the new thermal conductivity model Eq.10 and experimental values

Fig. 8 Thermal conductivity correlations for temperature and porosity as predicted by Eq.10 for porous mullite

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