μ-CT Based Structure Analysis and Performance Simulation of Mullite Fibrous Porous Ceramics

Author:Hu Xiao Xia

Supervisor:liu jia chen

Database:Doctor

Degree Year:2017

Download:26

Pages:124

Size:8467K

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The complexity of the structure of fibrous porous ceramics makes it difficult to characterize its internal structure.The length and orientations of the fiber segments in the fiber network structure have a significant impact on the structure and properties of the fiber porous ceramics.The quantitative characterization and analysis of the structure characteristics of materials to study of the relationship between structure and properties,is an effective way to guide experiments and expand the application area of materials.The mullite fibrous porous ceramics were prepared by freeze casting innovatively.The structure and properties of fibrous porous ceramics prepared by vacuum filtration and freeze casting method were compared.The results showed that the mullite fibrous porous ceramics prepared by freeze casting had excellent properties of light weight(0.339 g/cm~3),high compressive strength(2.12 MPa)and small thermal conductivity(0.053 W/(m.K)).In addition,the influences of binder content and fiber aspect ratio on the structure and properties of mullite fibrous porous ceramics prepared by freeze casting were investigated.The results showed that when the binder content was 5 wt%and the fiber aspect ratio was 33.1,the mullite fibrous porous ceramics have low density(0.378g/cm3),high strength(2.01MPa)and low thermal conductivity(0.058W/m.K).The three-dimensional structural characteristics of mullite fibrous porous ceramics fabricated by the mullite fibers with different aspect ratios were quantitatively extracted and analyzed by X ray tomography and 3D image analysis software.The results showed that when the fiber aspect ratios were 43.1,33.1 and22.3,the fiber segment aspect ratios were 9.65,7.26 and 6.47,respectively,and the anisotropy parameters were 1.45,0.98 and 0.87 respectively.Based on the model of Markaki et.al and the deformation mechanism of a single fiber under the combined action of bending moment and axial force,the elastic properties of materials were predicted coupled extracted structural feature parameters.The predicted elastic modlus was smaller than that of Maikaki et.al model due to the introduction of axial force.The predicted Poisson’s ratio was a function related to the fiber segments aspect ratio,which was different from the Poisson’s ratio deduced from Markaki et.al model which considered it to be a constant(1/π).In addition,the predicted value of elastic modulus was in good agreement with the experimental data,which validates the reliability of the model in the application of random homogeneous three-dimensional fiber network structure.A structural controllable fiber network model was established by coupling the structural characteristic parameters.The influences of the bonding point size(R=0,a,1.3a,1.5a),the fiber volume fraction(2~4 vol%)and the anisotropic parameter(1~10)on the thermal conductivity of the fiber network were investigated.In the process of establishing the fiber network model,the relative position of fibers was judged,and according to this,the bonding points were introduced to the network structure innovatively and the size of the bonding points was controlled.The results showed that the anisotropy parameter(fiber orientation)has a significant effect on the thermal conductivity of the material compared with the size of the bonding point and the volume fraction of the fiber.