An estimate of size of copper nanoparticles levitating over the melt surface using the measurements of spectral reflectance

A strong decrease in normal reflectance of a probe laser beam of 660 nm wavelength reflected from the surface of copper sample just after the beginning of the sample melting in a rarefied argon atmosphere has been observed recently by the authors. A similar time dependence of the reflectance is obtained in the laboratory experiments of the present paper at the wavelengths of 532 nm. The additional spectral measurements enable the authors to estimate the size of condensed nanoparticles levitating over the copper melt.

The Oxidation of Copper in Air at Temperatures up to 100 °C

The aim of this study was to investigate the oxidation kinetics of copper at low temperatures (60 °C to 100 °C) in air by isothermal thermogravimetric analysis (TGA) and quartz crystal microbalance (QCM). The weight change in thermogravimetric tests showed periodic weight increase and decrease. In thermogravimetric tests the mass of the copper sample increased until the oxidation gradually slowed down and finally started to decrease due to cracking and spalling of the oxide formed on the surface. In QCM tests using electrodeposited copper film, the weight change was rapid at the beginning but slowed to a linear relationship after few minutes. Temperature and exposure time appeared to have a large effect on oxide film thickness and composition. With QCM, oxidation at 60–80 °C produced less than 40 nm films in 10 days. Oxidation at 90–100 °C produced 40 nm thick films in a day and over 100 nm films in a week. Although SEM-EDS analyses in TGA tests indicated that oxygen was adsorbed on the copper surface, neither XRD patterns nor Raman spectroscopy measurements showed any trace of Cu2O or CuO formation on the copper surface. Electrochemical reduction analysis of oxidized massive copper samples indicated that the oxide film is mostly Cu2O, and CuO develops only after several days at 90–100 °C.

Viscoplastic flow of functional cellular materials with use of peridynamics

The subject of the study is the deformation of the oxygen-free high conductivity copper. The copper sample is given in the form of a foam. The sample undergoes an impact into an elastic wall. The strain rate hardening effect is investigated. The numerical model of the open-cell foam skeleton is prepared in the framework of the peridynamics method. The dynamic process of compression with different impact velocities is simulated. It has been found that the strain rate hardening effect is essential for the load-carrying capacity of the material under study. Taylor impact test of solid cylinder analysis precedes the analysis of the metallic foam.

Эффекты амплитудно-зависимого внутреннего трения в низкочастотном стержневом резонаторе из отожженной поликристаллической меди

Experimental and theoretical studies of the effects of amplitude-dependent internal friction in a low-frequency rod resonator made of annealed polycrystalline copper are carried out. The results of measurements of nonlinear losses and the shift of resonant frequencies at the first three longitudinal modes of the resonator in the kilohertz frequency range from 2 to 11 kHz are presented. The analytical description of the observed effects is carried out in the framework of the rheological model and the equation of state of a microhomogeneous medium with saturation of hysteresis losses and relaxation of its visco-elastic defects. From the comparison of experimental and analytical results, the values of the effective parameters of the hysteresis nonlinearity of the annealed copper sample and their dependence on the frequency are determined.

Interaction of a Low-Power Laser Radiation with Nanoparticles Formed over the Copper Melt in Rarefied Argon Atmosphere

Two effects have been recently observed by the authors for the copper sample melted in a rarefied argon atmosphere. The first of these effects is a strong decrease in the normal reflectance of a copper sample with time just after the beginning of melting. A partially regular crystal structure was also formed on the surface of the solid sample after the experiment. Both effects were explained by generation of a cloud of levitating nanoparticles. Additional experiments reported in the present paper show that the rate of decrease in reflectance increases with pressure of argon atmosphere and the surface pattern on the solid sample after the experiment depends on the probe laser radiation. It is theoretically shown for the first time that the dependent scattering effects in the cloud of copper nanoparticles are responsible for the abnormal decrease in normal reflectance and also for the observed significant role of light pressure in deposition of nanoparticles on the sample surface. The predicted minimum of normal reflectance is in good agreement with the experimental value.

ТЕОРЕТИЧНА МОДЕЛЬ ФОРМУВАННЯ ОДНОВИМІРНИХ НАНОСТРУКТУР ОКСИДУ МІДІ В УМОВАХ ПЛАЗМОВОГО СЕРЕДОВИЩА

The work is devoted to the development of a theoretical model of the formation of 1D nanostructures of copper oxide under conditions of action on a copper sample of elevated temperatures and fluxes of charged particles. One of the promising methods for obtaining copper oxide nanowires is the use of plasma to activate the sample surface and heat it. Although the thermal growth is the most applied, plasma methods have a number of advantages, such as process rate (tens of minutes compared to several hours – for thermal methods), better process control (the ability to use ions with specified energy), low cost on electricity, environmental safety, etc. However, plasma methods have some disadvantages, like relatively small aspect ratio (the characteristic value ranges from 20 to 40, while for thermal methods – 60 to 100), as well as rapid achieving of the saturation mode in length. To synthesize a new technology that combines the advantages of both methods and eliminates their disadvantages, a developed theoretical basis is necessary, which, unfortunately, is absent today. The proposed model of formation of oxide nanostructures considers the dynamics of growth of oxide layers (Cu2O and CuO) on the surface of the copper sample, as well as the formation of nanowires on the surface of the oxide exposed to the gas phase. The model takes into account the temperature of the sample, the gas pressure in the chamber, and the energy of the plasma ions. It was found that although the diffusion rate increases significantly with increasing the sample temperature, the main factors limiting the growth process are: the rate of CuO formation and the intensity of surface sputtering due to the ion bombardment; limited supply of copper atoms to the top of the nanowire, as well as their unlimited supply to the base of the nanowire. Uneven spraying of the nanowire material along its surface is also an important factor: the ion current density on the side surface of the nanowire is much lower compared to the density on its top, because ions bombard the side surface at a very small angle. Thus, the increased energy of the ions can prevent the formation of nanowires at a significant electric potential of the sample.

Multiscale Assessment of Nanoscale Manufacturing Process on the Freeform Copper Surface

The nanocutting has been paid great attention in ultra-precision machining and high sealing mechanical devices due to its nanometer level machining accuracy and surface quality. However, the conventional methods applicable to reproduce the cutting process numerically such as finite element (FE) and molecular dynamics (MD) are challenging to unveil the cutting machining mechanism of the nanocutting due to the limitation of the simulation scale and computational cost. Here a modified quasi-continuous method (QC) is employed to analyze the dynamic nanocutting behavior (below 10 nm) of the copper sample. After preliminary validation of the effectiveness via the wave propagation on the copper ribbon, we have assessed the effects of cutting tool parameters and back-engagement on the cutting force, stress distribution and surface metamorphic layer depth during the nanocutting process of the copper sample. The cutting force and depth of the surface metamorphic layer is susceptible to the back-engagement, and well tolerant to the cutting tool parameters such as the tool rank angle and tool rounded edge diameter. The results obtained by the QC method are comparable to those from the MD method, which indicate the effectiveness and applicability of the modified QC method in the nanocutting process. Overall, our work provides an applicable and efficient strategy to investigate the nanocutting machining mechanism of the large-scale workpiece and shed light on its applications in the super-precision and high surface quality devices.