Complex permittivity of polycrystalline AlN was measured over the frequency range 100 MHz to 13 GHz using reflection coefficient and cavity resonator methods. Dielectric relaxation peaks of loss tangent were observed in the frequency range 200 MHz to 3 GHz. The maximum value of loss tangent was ∼200 × 10−4. Relative permittivities decreased by ∼4% with increased frequency at the region of relaxation peaks. It was shown that these dispersion frequencies were inversely proportional to the grain sizes of AlN and independent of purities and processes. Model calculations for elastic vibration of a single‐crystal grain of AlN were performed to investigate the origin of the dielectric dispersion due to piezoelectric effect. The calculated results of elastic sphere and 14‐faced‐polyhedron models showed a good quantitative agreement with the observed dispersion frequencies, which suggested that the dispersion was due to a piezoelectric vibration of a single grain of AlN ceramics at microwave frequencies.

3D printing methods are developing and they have become popular recently. 3D printing can easily make complex and seamless parts, however, there are questions about their strength. In particular, the strength of the places where the lamination layer joins is important. We performed rolling contact fatigue (RCF) tests in dry conditions using 3D-printed bearing race and observed the fracture behavior and cracks. We found that the main crack is related to the stress moving direction.

7-Membered lactam thioether and lactam sulfone which contain amide and thioether or sulfone grmps within the ring have been synthesized and polymerized in the presence of various catalysts. Phosphoric acid was the most effective catalyst for the polymerization of the lactam thioether but the lactam sulfone did not polymerize owing to thermal decomposition. The resulting polyamide thioether had a mp of 180 to 185'C which was much higher than that of the polymer from the lactam ether of the same 7-membered ring. The polymerizability of the lactam thioether was higher than that of E-caprolactam and it was found that the reactivity of the amide group is influenced by the thioether group within the ring. ZUSAMMENFASSUNG:ES wurden der 7-gliedrige Lactamthioather und das entsprechende Lactamsulfon, die Amid-und Thioather-bnv. Sulfongruppen im Ring enthalten, synthetisiert und in Gegenwart von verschiedenen Katalysatoren polymerisiert. Der wirksamste Katalysator fur die Polymerisation des Lactamthioathers war Phosphorsaure, w a r e n d das Lactamsulfon infolge thermischer Zersetzuag nicht polymerisierte. Der Polyamidthioather schmilzt zwischen 180 und 185 ' C, also erheblich hoher als das Polymere aus dem analogen 7-gliedrigen Lactamather. Der Lactamthioather polymerisiert leichter als E-Caprolactam, d. h., die Reaktivitat der Amidgruppe wird durch die Thioathergruppe im Ring beeinfluat.

No abstract

Abstract. Polymer bearing was widely used in the corrosive conditions because of its high corrosion durability. The polymer bearing had been formed using molding and machining until the new 3-D printing method was developed. In this study, we performed the rolling contact fatigue tests of the 3-D printed specimens in water and observed the fracture behaviour of the specimens. We found that the surface cracks are related to both the rolling direction and the lamination directions.