RESUMEN
Ultrasonic Liquid Phase Exfoliation (LPE) has gathered attention from both scientific and industrial communities for its accessibility and cost-effectiveness in producing graphene. However, this technique has faced challenges such as low yield and long production time. In this study, we developed a cyclic ultrasonication system to exfoliate expanded graphite (EG) by applying static pressure to a flow chamber to address these challenges. Using deionized water (DIW) as solvent and polyvinylpyrrolidone (PVP) as dispersion, we obtained graphene slurries with an average lateral size of 7 µm and averaged number of layers of 3.5 layers, after 40 min of ultrasonication. After centrifugation, the yield of single and bilayer graphene was approximately 16 %. The findings showed that regulating hydrostatic pressure can effectively affect the lateral size and number of layers of few-layer graphene. The proposed method is of good potential for scaled-up production of few-layer graphene.
RESUMEN
Ultrasonic shot peening(USP) is an advanced surface treatment technology for obtaining excellent surface properties or manufacturing a three-dimensional curved surface of the metal sheets. The impact of the medium driven by ultrasonic vibration is significant to parameter optimization and excellent performance of the USP technology. However, the impact characteristics of the medium lack careful study, which is a complex dynamic analysis involving many factors, such as collision, plastic deformation, air pressure, etc. In this paper, a detection system is successfully developed to investigate the needle impact force and frequency against the material surface, consisting of a piezoelectric load sensor, oscilloscope, and a single needle USP device. Moreover, the FE model of the needle impact is developed simultaneously to study the characteristics of residual stress implantation induced by needle impact. Based on the experiment and FE simulation results, it is discovered that the impacts with high speed primarily determine the thickness of the modified layer implanted with residual stress during multiple impacts at different rates. According to residual stress implantation characteristics, the low-speed impact whose speed does not reach 50% of the maximum impact speed was defined as the ineffective impact. Besides, increasing the amplitude of ultrasonic vibration results in a significant increase in the maximum impact force and the effective impact frequency. The travel distance of needle impact has a considerable effect on the effective impact frequency, but it has little effect on the maximum impact force. Finally, it was concluded that the low air pressure plays a positive role in the needle impact. Furthermore, excessive air pressure hinders the needle impact and results in a decline in the effective impact frequency and the maximum impact force.
