Sintering of alumina powder compacts and their compressive mechanical properties

The Effect of Particle Shape on Sintering Behavior and Compressive Strength of Porous Alumina

“…The controlled cell size and porosity are key factors to fabricate a strong porous structure [ 14 ]. In our previous papers [ 15 , 16 , 17 , 18 ], we proposed Equation (2) for the compressive strength ( σ p ) of partially sintered porous alumina, where y is the radius of a circular grain boundary and N is the number of spherical grains in the bulk volume ( V ) of a sintered porous compact. The σ 0 value corresponds to the strength needed to fracture the several grain boundaries ( n ) surrounding three-dimensionally one grain at 0% porosity, and is expressed by Equation (3), where n is the coordination number of grains and σ (dense) is the compressive strength at 0% porosity.…”

“…Equation (2) indicates that the increase in the grain boundary radius and the grain number leads to the increase in the compressive strength. The development of grain boundaries with sintering is related to the decrease in the specific surface area of the porous ceramic compact [ 15 , 16 ]. The area ( A gs ) of the gas–solid interface and the grain boundary area ( A pp ) of the particle–particle interface per particle of radius r are expressed by Equations (5) and (6), respectively, where S 1 is the disappeared surface area due to sintering, r 0 is the radius of the starting particles and p is the ratio of the shortened distance ( h ) between two particles to the particle size ( r ) ( p = h / r ) during sintering.…”

“…The area ( A gs ) of the gas–solid interface and the grain boundary area ( A pp ) of the particle–particle interface per particle of radius r are expressed by Equations (5) and (6), respectively, where S 1 is the disappeared surface area due to sintering, r 0 is the radius of the starting particles and p is the ratio of the shortened distance ( h ) between two particles to the particle size ( r ) ( p = h / r ) during sintering. The p value can be determined from a specific surface area by assuming no change in the particle number in one sintered powder compact using Equation (7) [ 16 ]. …”

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“…Therefore, the compressive strength increases with an increase in grain boundary area during sintering and an increase in packing density. Young's moduli of sintered alumina compacts are also closely related to the grain boundary development [14,16]. The scattering of the stressstrain curves in Fig.…”

“…8. The compressive strength (σ) of a sintered porous alumina compact is discussed in our recent papers [14,16], and is expressed by Eq. (3)…”