Mechanism and Experiment Study of Non-Contact Ultrasonic Assisted Grinding

Ultrasonic-assisted grinding processing can effectively reduce the surface roughness and enhance the processing efficiency in the processing of hard and brittle materials. However, the most common ultrasonic assisted grinding is a type of contact ultrasonic grinding where the grinding tool directly contacts the workpiece, which means that it is necessary to accurately control the pre-pressure of the grinding tool on the workpiece. The control of pre-pressure will inevitably increase the complexity of the grinding device, and it is easy to wear the workpiece because of improper pre-pressure control. In this paper, a non-contact ultrasonic grinding method is proposed and the machining mechanism of non-contact ultrasonic grinding is revealed. The resonant frequency of the ultrasonic vibration system and vibration amplitude of the grinding tool working face were simulated and experimentally tested, respectively. Then, the experiment of non-contact ultrasonic grinding of a sapphire wafer was carried out. The result showed that non-contact ultrasonic grinding of the sapphire wafer could reduce the surface roughness by 48.6%. Compared with traditional contact grinding of sapphire wafer under certain pre-pressure conditions, the experimental results show that non-contact ultrasonic grinding has better effects in reducing surface roughness, improving processing efficiency, and improving the quality uniformity of the workpiece machining surface.

Temperature Increase Research of Particles Formed by Ultrasonic Grinding of Spinach Leaves

The researchers chose spinach leaves as the research object for obtaining a natural dye based on chlorophyll because the vegetable is a food raw material rich in this pigment, and biologically active substances source with variety of its functional properties. To solve the problem of more complete chlorophyll extraction from crushed spinach leaves, they are to subject to a preliminary short-term soaking in a water/organic reagent emulsion under ultrasonic influence. Given that the water-based spinach suspension is thermolabile, a man must observe temperature restrictions, since when a certain critical temperature value is exceeded, the chlorophyll decomposition probability with its consumer properties loss is high. As it is practically impossible to determine the temperature inside a fine particle suspended in an aqueous emulsion experimentally, the authors considered to model internal and external heat transfer by solving the differential equation of heat energy transfer under appropriate boundary conditions using the numerical method of finite differences. The research determined structural-mechanical and thermophysical characteristics of crushed spinach leaves experimentally using the complex calculation method of thermophysical parameters based on the thermal inertia properties of a thermocouple. A man verified the solution adequacy by empirically determined suspension temperature after completion of the technological procedure. According to the developed algorithm, the authors compiled a program for the temperature fields evolution in the object of study considering the incident ultrasonic flow and an internal heat source with the new surface formation when grinding spinach particles in order to comply with thermal restrictions and maximize the quality parameters preservation. The article considers the rational duration of the ultrasonic grinding process without exceeding the recommended threshold temperatures.

Semiconductor Quantum Dots as Materials for Lasers Based on Them

Quantum dots (QDs) today belong to the central research objects of many scientific groups. The study of theproperties of structures of small size is important both for the further development of electronics, and for theimprovement of existing semiconductor devices. At present, there are many methods of obtaining QDsobtainingunder the laboratory conditions: the method of ultrasonic grinding, molecular beam epitaxy, pulsed laser ablation,as well as using such methods of chemical synthesis as organometall synthesis, synthesis in reverse micelles,electrothermal synthesis, sol-gel synthesis, synthesis using thiol stabilizers, synthesis in a non-aqueous medium.Nowadays, the most promising methods are based on the use of the phenomenon of self-organization. These aremolecular-beam epitaxy and colloidal chemistry methods, and the latter are used for synthesisof nanosizedcrystals.The band gap width and the energy of luminescence peak are determined by the size of the particles.