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Application of low-temperature low-pressure hydrogen plasma: treatment of artificially prepared corrosion layers

100%

Fojtíková P., Řádková L., Janová D., Krčma F.

Open Chemistry

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2015

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vol. 13

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issue 1

EN

The aim of this work is the application of low-temperature low-pressure hydrogen plasma on artificially prepared corrosion layers, so called plasma chemical reduction. It is necessary to use samples with artificially prepared corrosion layers because it is impossible to use the real artifacts for fundamental research. The bronze was chosen as a sample material. Formation of corrosion layers on the bronze samples was carried out in concentrated hydrochloric acid vapors with the addition of sand. The radio-frequency hydrogen plasma was generated in the flowing regime at a pressure of 160 Pa. Different values of supplied power were chosen as well as different discharge modes: continuous or pulsed mode with varied duty cycles. By the combination of supplied power and mode factors, we selected two values of effective power. The process of plasma chemical reduction was monitored by optical emission spectroscopy (OES) and simultaneously, the sample temperature was measured. Rotational temperatures were calculated from OH radicals spectra. Changes in the structure and elemental composition were determined using scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX).

2

Influence of electrode material on hydrogen peroxide generation by DC pinhole discharge

100%

Vyhnánková E., Kozáková Z., Krčma F., Hrdlička A.

Open Chemistry

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2015

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vol. 13

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issue 1

EN

In this work, several materials were studied as electrodes in a pinhole configuration of a DC plasma discharge to estimate their effect on the efficiency of the discharge, indicated by hydrogen peroxide production. Detection was carried out using a specific titanium reagent. This was combined with ICP-OES analysis of the final solutions to determine the difference between the amount of electrode material released during the discharge operation and electrolysis experiment carried out under the same conditions. It was found that from seven studied electrode materials, graphite gives the best results, while lower cost aluminum and titanium-zinc still work well. The most unsuitable materials were copper and brass; in these cases, no hydrogen peroxide was detected in the cathode part of the reactor. Results obtained by ICP analysis indicate that even in the case of brass, the absence of hydrogen peroxide is due to the presence of copper in the material. It probably affects both directly the phase of discharge creation and propagation and the decomposition reactions.

3

Generation of High Frequency Pin-hole Discharge in Water Solutions

100%

Krčma F., Kozáková Z., Vašíček M.

Open Chemistry

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2015

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vol. 13

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issue 1

EN

This paper presents results on electric discharge generation by high frequency high voltage (15–100 kHz) in NaCl solutions with different initial conductivity (100–1300 mS cm-1), and compares them with DC discharge in the same electrode configuration. A batch plasma reactor in the pin-hole configuration contained a ceramic dielectric barrier separating two planar stainless steel electrodes; barrier thickness of 0.6 mm and pin-hole diameter of 0.6 mm was used. Lissajous charts were evaluated from electric measurements for different discharge phases (electrolysis, bubble formation and discharge regular operation). Breakdown moments for different solution conductivities were determined from discharge power evaluation as a function of applied frequency. Breakdown voltage amplitude was decreased by the increasing conductivity in both regimes while frequency and current decreased. Changes of physical parameters (temperature, solution conductivity and pH) as well as production of hydrogen peroxide at different solution conductivities were compared. Solution conductivity was increased in both discharge regimes and with the initial conductivity value. Solution temperature was increased by the discharge in both regimes and with the increasing initial conductivity, too. Solution pH dropped to acidic conditions when HF or DC positive regime was applied while it was enhanced by DC negative regime.

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3 Open Chemistry

3 2014

3 Krčma F.

2 Kozáková Z.

1 Fojtíková P.

1 Hrdlička A.

1 Janová D.

1 Vašíček M.

1 Vyhnánková E.

1 Řádková L.

Application of low-temperature low-pressure hydrogen plasma: treatment of artificially prepared corrosion layers

Influence of electrode material on hydrogen peroxide generation by DC pinhole discharge

Generation of High Frequency Pin-hole Discharge in Water Solutions