5:15 PM - 6:45 PM
[PPS07-P17] Experimental study on changes in the mechanical properties of porous primitive bodies due to sintering
Keywords:sintering, planetesimals, dust, filling factor
Sintering likely played an important role in the accumulation of dust aggregates in the protoplanetary disk (Sirono, 1999; Sirono & Ueno, 2017; Okuzumi et al., 2016). Planetesimals are thought to have undergone sintering during the thermal evolution (e.g., Henke et al., 2012; Neumann et al., 2014, 2021). Therefore, understanding the mechanical properties of sintered porous materials is essential for understanding physical phenomena in the early stages of the planet formation process. In this study, we prepared sintered samples with a filling factor of 0.4-0.8. We investigated changes in the mechanical properties of the sintered samples, in particular longitudinal wave velocity and bending strength, with the filling factor. In addition, we sintered a granular sample consisting of polydisperse and irregularly shaped dust particles as a realistic granular material and observed its sintering behavior.
In our experiments, we used four types of soda-lime glass particles; GB-94 (monodisperse and spherical glass beads with a median diameter of 94 μm and an average diameter of 92±7 μm), GB-55 (monodisperse and spherical glass beads with a median diameter of 55 μm and an average diameter of 53±7 μm), GB-22 (polydisperse and spherical glass beads with a median diameter of 22 μm and an average diameter of 11±6 μm), and GP-53 (polydisperse and irregularly shaped glass powder with a medial diameter of 53 μm and an average diameter of 12±15 μm). Soda-lime glass has a softening point at about 730℃.
We performed the experiments as follows. (1) Almina containers were filled with glass particles, when random loosely packed samples were prepared by sieving, and random densely packed samples were prepared by tapping. (2) The samples were heated in an oven at 620℃. The temperature rise time was fixed at 30 minutes, and the heating time at the peak temperature was varied to change the degree of sintering. The peak temperature was set for some samples at 630℃ or 640℃. (3) We observed the surface of the sintered samples using scanning electron microscopy. (4) We calculated the filling factor from the mass and volume of the sintered samples. (5) We measured the longitudinal wave velocity of the sintered samples by the pulse transmission method and the bending strength by the three-point bending test.
From the scanning electron microscopic observations for the irregularly shaped dust particles, we found that heating at a temperature near the melting point causes not only the formation of inter-particle necks but also changes in particle morphology. The corners became rounded, and the surface became smooth. The densification curves of the samples showed that a sample consisting of polydisperse and irregularly shaped dust particles sinters relatively quickly, even if it contains dust particles with a large radius. We consider that this is due to the large number of particles with a small radius in the sample and to the fact that the actual surface curvature radius of the irregularly shaped particles is much smaller than the apparent radius.
The longitudinal wave velocity of the sintered samples increased in proportion to the filling factor, regardless of the particle size, particle size distribution, filling method, and particle shape. Such an increase is also observed in the measurement of sintered ice aggregates (Shimaki and Arakawa, 2021) and Greenland snow (Smith, 1965). We found that the increase in the bending strength of sintered samples with the filling factor follows the power-law trend and the linear trend. The power-law trend is consistent with the measured tensile strength of sintered ice aggregates (Shimaki and Arakawa, 2021). However, the linear trend is not observed for sintered ice aggregates. The linear trend appears to asymptotically approach the power-law trend with increasing filling factor.
In our experiments, we used four types of soda-lime glass particles; GB-94 (monodisperse and spherical glass beads with a median diameter of 94 μm and an average diameter of 92±7 μm), GB-55 (monodisperse and spherical glass beads with a median diameter of 55 μm and an average diameter of 53±7 μm), GB-22 (polydisperse and spherical glass beads with a median diameter of 22 μm and an average diameter of 11±6 μm), and GP-53 (polydisperse and irregularly shaped glass powder with a medial diameter of 53 μm and an average diameter of 12±15 μm). Soda-lime glass has a softening point at about 730℃.
We performed the experiments as follows. (1) Almina containers were filled with glass particles, when random loosely packed samples were prepared by sieving, and random densely packed samples were prepared by tapping. (2) The samples were heated in an oven at 620℃. The temperature rise time was fixed at 30 minutes, and the heating time at the peak temperature was varied to change the degree of sintering. The peak temperature was set for some samples at 630℃ or 640℃. (3) We observed the surface of the sintered samples using scanning electron microscopy. (4) We calculated the filling factor from the mass and volume of the sintered samples. (5) We measured the longitudinal wave velocity of the sintered samples by the pulse transmission method and the bending strength by the three-point bending test.
From the scanning electron microscopic observations for the irregularly shaped dust particles, we found that heating at a temperature near the melting point causes not only the formation of inter-particle necks but also changes in particle morphology. The corners became rounded, and the surface became smooth. The densification curves of the samples showed that a sample consisting of polydisperse and irregularly shaped dust particles sinters relatively quickly, even if it contains dust particles with a large radius. We consider that this is due to the large number of particles with a small radius in the sample and to the fact that the actual surface curvature radius of the irregularly shaped particles is much smaller than the apparent radius.
The longitudinal wave velocity of the sintered samples increased in proportion to the filling factor, regardless of the particle size, particle size distribution, filling method, and particle shape. Such an increase is also observed in the measurement of sintered ice aggregates (Shimaki and Arakawa, 2021) and Greenland snow (Smith, 1965). We found that the increase in the bending strength of sintered samples with the filling factor follows the power-law trend and the linear trend. The power-law trend is consistent with the measured tensile strength of sintered ice aggregates (Shimaki and Arakawa, 2021). However, the linear trend is not observed for sintered ice aggregates. The linear trend appears to asymptotically approach the power-law trend with increasing filling factor.