Abstract
ABSTRACTTextured porous Si3N4-ZrB2 composites were prepared by the gel-casting method assisted by magnetic field alignment technology and subsequent pressureless sintering. These results showed that when a 6 T magnetic field was applied, the ZrB2 grains also formed a c-axis orientation in the textured green bodies, except for β-Si3N4 grains, which formed an a- or b-axis orientation. The increasing ZrB2 content inhibited the degree of texture of the Si3N4 and ZrB2 grains in the green bodies, respectively. After sintering at 1800 °C, new ZrN and BN phases without grain orientation characteristics formed by the reaction between Si3N4, ZrB2 and N2 and the ZrB2 phase disappeared completely. The sintering process promoted the degree of texture of Si3N4 as the matrix increases. Meanwhile, the variations in the degree of texture of Si3N4 with changes in the ZrB2 content were consistent with that in the green body. Additionally, when 10 wt% ZrB2 content was introduced, the apparent porosity reached its highest value and the bulk-density reached its lowest value, leading to the appearance of least strength. In textured porous composites, the strength was mainly affected by the densification process instead of the grain orientation. Also, no evident difference in strength existed between the two directions owing to the function of high porosity.
Highlights
Porous Si3N4 ceramics have been widely researched owing to their excellent properties, such as high strength, low density, high thermal shock resistance and low coefficient of thermal expansion
In this study, textured porous Si3N4-ZrB2 composites were prepared by gel-casting assisted by magnetic field alignment technology
For ZrB2 grains, the peak intensities of the (00l) crystal face perpendicular to the c-axis of ZrB2 grains are highest on the top surface, while the intensities are lowest on the side surfaces such as the (001) and (002) crystal faces
Summary
Porous Si3N4 ceramics have been widely researched owing to their excellent properties, such as high strength, low density, high thermal shock resistance and low coefficient of thermal expansion These properties enable them to be used successfully in many fields, including separation membranes, catalyst supports, gas filters and heat exchangers [1,2,3,4]. Many technologies have been developed to prepare porous ceramics by tailoring the microstructure These include emerging technologies for controlling the microstructures of porous ceramics by magnetic field alignment, which can give them special microstructures that include grain orientation and special pore channels [5,6]. Grains with anisotropic magnetic susceptibility will form an orientation along one direction with minimal system energy when acted upon by a magnetic force [6,8,9] At present, these technologies are mainly used to prepare textured dense ceramics.
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