StatusThe thesis was presented on the 27 May, 2022
Approved by NCAA on the 30 September, 2022
Abstract– 1.54 Mb / in romanian
– 0.98 Mb / in english
7.64 Mb /
The elimination of stick effect between metallic and non-metallic surfaces using graphite pellicles”, PhD thesis in engineering sciences, Chisinau, 2022
The work consists of an introduction, four chapters, general conclusions and recommandations, a bibliography of 169 titles, 1 appendices, 126 pages (before the bibliography), 168 figures, 24 tables. The results are published in 24 scientific papers.
Keywords: graphite electrode, pulsed electric discharge machining, sub-exciting regime, graphite pellicle, polyurethane glue, 3D carbon structures, fullerene nanotubes.
Field of studies engineering sciences and technologies.
The purpose of the work: Development of technology for the formation of graphite coatings used to eliminate the stick and adhesion effect of metal surfaces with other metal or non-metal surfaces.
Objectives of work:
- identification of technological conditions for the formation of graphite pellicles on metal surfaces by applying pulsed electric discharge machining;
- development of physical model for obtaining graphite coatings under optimal conditions;
- determination of the chemical, structural and phase composition of coatings formed on the piece surfaces;
- determination of functional properties (solubility, absorption, anti-stick, anti-adhesive, anti-corrosion properties) of applied pellicles;
- development of recommendations for the practical application of graphite peliclles.
Scientific novelty: The main scientific novelty resulting from the title of the thesis reflecting the fact that a technology has been developed for the application of graphite films on a metal surface using an innovative process by plsed electric discharge machining (PEDM). The graphite film thus obtained has the ability to reduce the adhesion between two metallic or non-metallic surfaces in contact. The way of technical verification of this attribute of graphite film is another scientific novelty and was made using a structural polyurethane adhesive - a scientific concept of PhD student. A scientific novelty subsidiary to the thesis is the identification by specific analysis of 3D formations composed of carbon atoms such as fullerenes or carbon nanotubes in graphite film obtained by PEDM.
Results that contribute to solving a scientific problem. Following the PEDM treatment, graphite films were deposited on the metallic surfaces, the properties of which were studied during the elaboration of the thesis.
The important scientific problem: It consisted of a significant decrease the effect of stick and adhesion between metallic surfaces and other metallic and/or non-metallic surfaces at normal or high temperatures, by the formation of carbon films obtained through PEDM. They contain structures such as fullerenes and single-walled carbon nanotubes. In this context, the connection mode of components (the anode (workpiece) and the cathode (tool-electrode)) in the discharge circuit of the impulse generator was determined, because in this technological scheme both the efficiency of tool erosion and the transfer of material on the machined surface are ensured and also obtaining the carbon film deposition.
Theoretical significance: Based on theoretical and experimental research, a new hypothesis was advanced and substantiated of the erosion phenomenon which comes to prove that this is a complicated one being of physical, chemical nature accomplished by bombardment with energy particles and based on these findings in the paper physico-chemical and technological model of graphite erosion and the formation of carbon deposits with fullerenes and nanotubes under the action of PEDM under normal conditions is developed.
Applied value of the work: the scientific works that took place within the doctoral thesis are important because the technological parameters of the process of applying graphite pellicles on metallic and non-metallic surfaces through the PEDM process were established. Also, following the research works, a new method of obtaining fullerene and carbon nanotubes type 3D formations was identified. The non-stick properties of graphite film have a special technological value in technological processes that involve sliding one surface over another in order to reduce mutual friction, for anti-lock purposes in screw-nut joints, to decrease the adhesion between the fluid material and the surface of the mold at the flow through a mold of a fluid material. Carbon pellicles formed on the surface of parts used in glass-molding processes allowed to increase their functionality by about 3 times, eliminating the effect of adhesion and giving them refractory properties, and the pellicles applied on the surface of the screw-nut joints eliminate the stick-effect even at a temperature of 800 °C.
The implementation of scientific results: After the implementation of scientific results based on industrial tests in the State Enterprise “Chisinau Glass Factory”, an act of technology implementation was obtained. The scientific results are also used in the teaching of the master's course “Modern Technologies and Innovations în Engineering” at the Alecu Russo Balti State University.