Dezhong Meng

As an important basic course for students majoring in materials discipline, college physics plays a crucial role in the whole undergraduate training program. At present, there are few reports on the research about the construction of college physics courses for materials majors through the combination of online and offline methods. This paper summarizes the content system, teaching mode and assessment method for the reform of university physics courses in materials related majors through years of teaching practice. Furthermore, the teaching effect has been unanimously satisfied by students. It is hoped that this teaching method can adapt to the teaching of college physics courses for more students majoring in materials in universities, and promote the display of college physics courses in in the training of science and engineering students.

It is known that a crystal structure and symmetry determine the physical properties of materials. Lattice distortion can strongly affect the symmetry of the crystal structure. Polar materials show changes in polarization with temporal fluctuations of temperature due to the asymmetry. As a polar crystal, hemimorphite shows excellent pyroelectric properties. However, to date, there are a few studies on its intrinsic physical properties, and the mechanism of its pyroelectricity remains unclear. In this paper, single-crystal x-ray diffraction measurement was carried out to obtain the atomic positions at 100–400 K. Furthermore, the electric dipole moments of [ZnO4] and [SiO4] polyhedrons along a, b, and c axes have been calculated. The calculated pyroelectric coefficient derived from the intrinsic electric dipole moment was compared with the experimental measurement. The results indicate that the pyroelectric coefficients of hemimorphite at different temperatures mainly come from the variation of the electric dipole moment of [ZnO4] and [SiO4] polyhedrons along the c axis. The electric dipole moment changes as a function of temperature from 100 to 400 K, which is induced by the random lattice distortion. It is found that pyroelectricity is strongly correlated with the random lattice distortion. The establishment of the relationship between lattice distortion and pyroelectricity helps us to regulate the specific electrical parameters of the material, which may lead to future work in energy harvesting and further properties.

Since the millennium, incremental breakthroughs in aerospace have attracted widespread attention from countries around the world on deep space exploration. Technological innovations in ceramic and superhard materials have also played a key role in deep space exploration. Inspired by this, a tribological ball-disk experiment of polycrystalline cubic boron nitride (PcBN) sliding against aluminum oxide (Al2O3) was implemented in air and vacuum conditions, in order to evaluate the friction and wear properties of PcBN based on drilling in the deep space environment. The results prove that the coefficient of friction (CoF) is interrelated with load and wear conditions, where CoFs gradually decrease with load growth in both air and vacuum. When the loads keep increasing, however, the wear mechanisms finally change under the high Hertz contact stress and lead to the CoF lift. Detailed characterizations were made to verify the tribological behaviors of the microscopic surface and chemical composition. Finally, by analyzing the surface topographies and chemical residues, it is certain that the wear mechanisms change due to the high Hertz contact stress. As a result, abrasive wear and adhesive wear turn to furrow wear in air and three-body wear in vacuum. These results can influence actual work in deep space by reducing large stress loads to avoid the impact of severe vibrations on precision instruments during work and improving cutting removal efficiency by selecting the appropriate loading.