S. Zhao

The influence of hydrogen sulfide on corrosion of iron under different conditions

Abstract Hydrogen sulfide (H 2 S) can either accelerate or inhibit corrosion of iron under different experimental conditions. What H 2 S has done to both the anodic iron dissolution and cathodic hydrogen evolution, in most cases, is to have a strong acceleration effect, causing iron to be seriously corroded in acidic medium, but H 2 S can also have a strong inhibition on the iron corrosion under certain special conditions where H 2 S concentration is below 0.04 mmol dm −3 , pH value of electrolyte solution is within 3–5 and the immersion time of the clectrode is over 2 h. The inhibition effect of H 2 S on the iron corrosion is attributed to formation of ferrous sulfide (FeS) protective film on the electrode surface. Moreover, the structure and composition of the protective film is closely related to H 2 S concentration, pH of solutions and the immersion time of iron. Accordingly, the influence of the three factors on the inhibition effect is investigated in this paper by means of AC impedance technology together with the potentiostatic steady-state polarization. A probable reaction mechanism is proposed to interpret theoretically how H 2 S inhibits the corrosion of iron.

Impedance spectroscopic study of corrosion inhibition of copper by surfactants in the acidic solutions

The inhibitive action of the four surfactants, cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate, sodium oleate and polyoxyethylene sorbitan monooleate (TWEEN-80), on the corrosion behavior of copper was investigated in aerated 0.5 mol dm(-3) H2SO4 solutions, by means of electrochemical impedance spectroscopy. These surfactants acted as the mixed-type inhibitors and lowered the corrosion reactions by blocking the copper surface through electrostatic adsorption or chemisorption. The inhibitor effectiveness increased with the exposure time to aggressive solutions, reached a maximum and then decreased, which implies the orientation change of adsorbed surfactant molecules on the surface. CTAB inhibited most effectively the copper corrosion among the four surfactants. The copper surface was determined to be positively charged in sulfuric acid solutions at the corrosion potential, which is unfavourable for electrostatic adsorption of cationic surfactant, CTAB. The reason why CTAB gave the highest inhibition efficiency was attributed to the synergistic effect between bromide anions and positive quaternary ammonium ions. C16H33N(CH3)(4)(+) ions may electrostatically adsorbed on the copper surface covered with primarily adsorbed bromide ions. On the basis of the variation of impedance behaviors of copper in the surfactant-containing solutions with the immersion time, the adsorption model of the surfactants on the copper surface was proposed

Inhibition of copper corrosion by several Schiff bases in aerated halide solutions

The inhibitive action of three Schiff bases, N,N′-o-phenylen-bis(3-methoxysalicylidenimine) (V–o-Ph–V), N,N′-p-phenylen-bis (3-methoxysalicylidenimine) (V–p-Ph–V) and N-[(2-hydroxy-3-methoxyphenyl)methylene]-histidine (V-His), on copper corrosion in aerated 0.5 mol dm−3 NaCl and NaBr solutions was investigated using EIS and steady-state polarization techniques. The inhibitor effectiveness depended strongly on the geometric structure of the Schiff bases. Among the three kinds of Schiff base used, the inhibition efficiency of V–o-Ph–V on copper corrosion was the highest, V–p-Ph–V the next and V-His the lowest. The Schiff bases inhibited the cathodic current more significantly than the anodic current. The different influences of V–o-Ph–V or V–p-Ph–V on the anodic and cathodic reactions led to the appearance of a low frequency capacitive loop in the impedance spectra. The inhibition action of the Schiff bases was due to their adsorption on the copper surface followed by complexation with Cu(I) or Cu(II) ions, forming a blocking barrier to copper corrosion.

Inhibition Effect of AC-Treated, Mixed Self-Assembled Film of Phenylthiourea and 1-Dodecanethiol on Copper Corrosion

A new method for preparing effective inhibition film on copper has been developed. Phenylthiourea was first adsorbed to a copper surface to form a self-assembled film. 1-Dodecanethiol was then self-assembled on the surface for subsequent modification. Finally, ac voltage was loaded on copper covered with the mixed film to further modify the film. After these procedures, an effective inhibition film was obtained as indicated by the low corrosion current density in polarization curves. High charge-transfer resistance in electrochemical impedance spectra reveals that the film hinders corrosion electrochemical reaction between the copper surface and NaCl solution. Film coverage on the copper surface is more than 99.0%, and inhibition efficiency is more than 97.2% in 0.5 mol dm(-3) NaCl solutions. The mixed films before and after ac treatment are stable in a wide region of potentials. X-ray photoelectron spectroscopy analysis reveals that the effect of ac treatment may associate with the formation of a new complex compound

A study of corrosion behavior of copper in acidic solutions containing cetyltrimethylammonium bromide

The inhibitive effect of cetyltrimethylammonium bromide (CTAB) on copper corrosion in aerated H2SO4 solutions was investigated by means of electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. CTAB inhibited copper corrosion more strongly than tetramethylammonium bromide (TMAB) under the same conditions due to the chemisorption of the n-cetyl group on the copper surface. The surface of the copper electrode was positively charged in sulfuric acid solution at the corrosion potential. The copper corrosion inhibition of CTAB and TMAB was attributed to the synergistic effect between bromide anions and positive quaternary ammonium ions. The C16H33N(CH3)(3)(+) and N(CH3)(4)(+) ions may electrostatically adsorb on the copper surface, which is primarily covered with adsorbed bromide ions. The inhibition efficiency of CTAB depended on the CTAB concentration and the immersion time for the copper electrode in corrosive solutions. Based upon the variation of impedance display of copper with the CTAB concentration and the immersion time, an adsorption model of CTAB on the copper surface was proposed. The C16H33N(CH3)(3)(+) ions adsorbed on the copper surface by horizontal binding to hydrophobic hydrocarbon chains at the low CTAB concentrations, whereas a perpendicular adsorption dominated as a result of an interhydrophobic chain interaction when the CTAB concentration increased

A study of phase transfer processes of Ag nanoparticles

With the protection of sodium oleate, Ag nanoparticles are produced through the reduction of AgNO3 with NaBH4 in an aqueous solution. The possible mechanism of phase transfer of the Ag nanoparticles was discussed. At a suitable concentration of sodium oleate, after adding NaH2PO4, the oleic acid molecule can change its position on the surface of Ag nanoparticles under the effects of water and toluene and become amphipathic. So most of the nanoparticles form a film between water/toluene. For the case of a higher concentration of sodium oleate, excess sodium oleate will form a closed monolayer film on the surface of the Ag nanoparticles. After adding NaH2PO4, the oleic acid molecule cannot move on the Ag nanoparticles surface, thus the colloid particles are hydrophobic but not amphipathic. So most of the particles transfer to the organic phase. UV-Vis spectra, TEM and conventional metallographic microscopy are used to characterize the Ag nanoparticles and nanoparticles films

Diode-pumped passively Q-switched mode-locked Nd:LuVO4 laser with a semiconductor saturable absorber mirror

We present a compact passively Q-switched mode-locked Nd:LuVO4 laser run in a Z-type folded cavity with semiconductor saturable absorber mirror (SESAM). The repetition rates of the passively Q-switched pulse envelope ranges from 22.99 to 141.18 kHz as the pump power increased from 2.372 to 8.960 W. The repetition rates of mode-locked laser pulses in the Q-switched pulse envelope has 111 MHz determined by the cavity length and the mode-locked pulse duration is evaluated to be 257 ps. An average output power of 823.5 mW is achieved at the pump power of 8.96 W, corresponding to an optical conversion efficiency of 9.2%.

Diode-pumped passively Q-switched mode-locking Nd:Y0.5Gd0.5VO4 laser at 1.34 μm with Co2+:LaMgAl11O19 saturable absorber

We reporte a passively Q-switched and mode-locked Nd:Y0.5Gd0.5VO4 laser at 1.34 μm with Co2+:LaMgAl11O19(Co:LMA) crystal as the saturable absorber. With the incident pump power of 6.56 W, a maximum output power of 242 mW was obtained. Q-switched mode-locking pulses with modulation depth nearly 100% were obtained. The width of the mode-locked pulse was estimated to be less than 600 ps.

Analysis of a laser-diode end-pumped intracavity frequency-doubled passively Q-switched and mode-locked Nd:GdVO4/KTP laser with a semiconductor saturable absorber

A diode-pumped passively Q-switched mode-locked (QML) intracavity frequency-doubled Nd:GdVO4/KTP green laser with a semiconductor saturable absorber is presented. Nearly 100% modulation depth for the mode-locked green pulses can be achieved at any pump power over 1.92 W. The width of the mode-locked green pulse was estimated to be about 150 ps. The mode-locked pulse interval within the Q-switched envelope of 320 ns and the repetition rate of 97.5 kHz were obtained, at an incident pump power of 4.4 W. The repetition rate of the mode-locked green pulses inside the Q-switched envelope was 140 MHz.

Control of the pulse duration in a diode-pumped passively Q-switched intracavity frequency-doubling laser

Different techniques to control the pulse duration of a diode-pumped passively Q-switched intracavity frequency-doubled laser are studied, which shows that varying the pump beam radius in the gain medium and mode-spot sizes on a saturable absorber are two efficient ways to control the pulse duration. The output pulse durations obtained from a diode-pumped passively Q-switched Nd:GdVO4/KTP laser with a GaAs wafer can be controlled in a wide range over 100 ns, which indicates a simple way of controlling the pulse duration of the intracavity frequency-doubled passively Q-switched laser.