Nenad Tadić

Real-time imaging, spectroscopy, and structural investigation of cathodic plasma electrolytic oxidation of molybdenum

In this paper, the results of the investigation of cathodic plasma electrolytic oxidation (CPEO) of molybdenum at 160 V in a mixed solution of borax, water, and ethylene glycol are presented. Real-time imaging and optical emission spectroscopy were used for the characterization of the CPEO. During the process, vapor envelope is formed around the cathode and strong electric field within the envelope caused the generation of plasma discharges. The spectral line shape analysis of hydrogen Balmer line Hβ (486.13 nm) shows that plasma discharges are characterized by the electron number density of about 1.4 × 1021 m−3. The electron temperature of 15 000 K was estimated by measuring molybdenum atomic lines intensity. Surface morphology, chemical, and phase composition of coatings formed by CPEO were characterized by scanning electron microscopy with energy dispersive x-ray spectroscopy and x-ray diffraction. The elemental components of CPEO coatings are Mo and O and the predominant crystalline form is MoO3.

Variation of electric properties across the grain boundaries in BiFeO3 film

Stark differences in charge transport properties between the interior and the boundary regions of grains in an undoped BiFeO3 thin film have been found. The material is ferroelectric and each grain is a single domain. A spatial resolution that distinguishes between the grain interior and the boundary between the grains has been achieved by using piezoelectric force microscopy and conductive atomic force microscopy measurements. The local electric properties, as well as the local band gap show hysteresis only when probed in the grain interior, but do not show hysteresis when probed in the region around the boundary between two grains. The leakage current is more pronounced at the grain boundaries, and the region that carries significant current increases with the applied voltage.

The characterization of cathodic plasma electrolysis of tungsten by means of optical emission spectroscopy techniques

Cathodic plasma electrolysis (CPE) of tungsten is investigated by means of optical emission spectroscopy in order to measure the electron temperature T e and the electron number density N e from CPE micro-arc discharges. The relative intensity of W I lines recorded from seven spectral ranges are used in conjunction with the Boltzmann plot (BP) technique to measure . For N e diagnostics, the complex line shape of the and the lines are analyzed in the frame of the spectral line broadening theory. The results showed two N e values, and , corresponding to different regions of CPE micro-arc discharges. The self-absorption effect on both studied H I lines was revealed and discussed as well. The SEM and XRD analysis showed a weak formation of rough oxide coating featured by the number of grains, channels, and holes.

The determination of micro-arc plasma composition and properties of nanoparticles formed during cathodic plasma electrolysis of 304 stainless steel

This paper presents the research focused on the determination of micro-arc plasma composition during cathodic plasma electrolysis of AISI304 stainless steel in water solution of sodium hydroxide. The complex line shape of several Fe I spectral lines was observed and, by means of a dedicated fitting procedure based on the spectral line broadening theory and H2 O thermal decomposition data, the mole fraction of micro-arc plasma constituents (H2 , Fe, O, H, H2 O, and OH) was determined. Subsequent characterization of the cathodic plasma electrolysis product formed during the process revealed that it consists of Fe-nanoparticles with median diameter of approximately 60 nm.

The study of micro-arc discharges during cathodic plasma electrolysis of refractory metals using the spectral line shape of Na I lines

The micro-arc discharges during cathodic plasma electrolysis of refractory metals (Zr, Ti, Ta) are studied by means of optical emission spectroscopy. The fitting procedure based on three mutually shifted profiles is developed to analyze the complex line shape of Na I 568.64 nm and 615.86 nm doublets. Each profile includes effects of instrumental, Doppler, Stark, van der Waals and resonance broadening. The results show the existence of three discharge zones with electron number density values , and while those of sodium ground-state atoms are , and .