An electrode impedance measurement system by time domain method has been set up, it is composed of an APPLE Ⅱ microcomputer and a self-made electrochemical interface. Pseudorandom white noise is adopted as the excitation signal. The signal average technique and FFT algorithm are employed in order to improve the ratio of signal to noise and the rate of transform calculation. The measurement system has been used to determine the impedances of equivalent circuits and real electrochemical systems. The results well agree with those obtained by SOLARTRON 1250 FRA and the data from literature. The problems about the selection of excitation signal, limits of measurement frequency and noise influence have been discussed.

Smooth specimens of 70/30 brass exposed to 1N NaNO_2 aqueous solution were used to investigate the retardation of incipient stress corrosion crack growth under low frequency cyclic loading (LFCL), a phenomenon previously observed in smooth specimens of mild steel when tested in carbonate/bicarbonate solutions. It is shown that retardation was more pronounced in fine grained brass than in coarse grained brass. Additionally, a greater number of cracks formed at grain boundaries or twin boundaries in the fine grained than in the coarse grained material. The retardation effect on crack growth could be eliminated by the introduction of a pre-crack prior to testing. The results have been interpreted in terms of multiple crack initiations at smooth surfaces which effectively dispersed the strain concentration at crack tips in the incipient growth stage.

Seven phosphonium salt compounds were synthesized as model substances in order to study the effect of molecular structure on inhibition efficiency. The inhibition of these compounds on corrosion of carbon steel in 1N HCl solution has been investigated by using the weight loss, potentiodynamic and double layer capacitance determination techniques. The experimental results show that the seven phosphonium salts all inhibit both the anodic and the cathodic processes of carbon steel in 1N HCl solution. The inhibition effect of bis-phosphonium salts was stronger than that of monophosphonium salts. The adsorption of benzyltriphenyl phosphonium bromide and 1, 4-di (triphenyl phosphonium bromide) butylane on carbon steel surface in 1N HCl at 25℃ followed Bockris-Swinkels isotherm. The adsorption free energies of phosphonium salts on carbon steel decreased with increasing temperature at 15～35℃ and increased with increasing temperature at 35～50℃. Therefore, two different entropy changes of adsorption and heats of adsorption were obtained. In addition, two apparent activation energies were calculated at different temperature ranges.

Effect of trace Cl~- on corrosion behavior of 316L SS in boiling 84％ acetic acid-10% formic acid-6％ water mixture is investigated by weight loss, polarization measurement and AES tests. Trace Cl~-(50ppm) has a slight inhibition effect on the anodic dissolution of the material because of its adsorption on the surface, but corrosion rate increases when the concentration of Cl~- increases to 200 ppm. Anodic passivation region is found on the anodic polarization curve and the passive film formed on the surface is enriched in Cr and O but depleted in Fe and Ni. The addition of Cl~- decreases the content of Cr and the Cr/Fe ratio in the film, and thus increases the O/(Cr+Fe) ratio. Then the protective effect of the passive film decreases and pitting incurs.

The crack growth behavior is investigated for low-carbon martensitic steels quenched and tempered at low temperature, under static loading and cyclic loading with three frequencies in 3.5% NaCl solution at 25℃. The fractorgraphs are examined with SEM. It is shown that there is a considerable influence of loading frequency on crack propagation dynamic characteristics of the steels, particularly in region of K_(max) References | Related Articles | Metrics

The synergistic effect between oxidizing inhibitor and other inhibitor of various kinds is studied in the passivation step of metals. A new parametersynergistic efficiency is proposed to evaluate the degree of the synergistic effect. It is proved theoretically that the synergistic efficiency is just equal to the degree of coverage of the adsorption inhibitor or precipitation inhiitor on the surface of the metal. Results show that the synergistic effect bmight occur between the oxidizing inhibitor and any kind of corrosion inhibitors in the passivation step of metals,

An experimental technique of pure sulphidation in reducing H_2S-H_2 environment has been investigated. Equilibrium of two reactions H_2+1/2O_2=H_2O and H_2S=H_2+1/12S_2 can be reached by the apparatus employed through ceful control of the flow rate, i. e. the total flow rate of H_2S plus H_2 is kept lower than 60Oral/min. Under such a condition, oxygen partial pressure at the sample is very low. While the sulphur partial pressure can be accurately controlled within the range of 10~(-2) atm-10~(-10) atm by carefully regulating and controlling the flow rates of H_2S and H_2 respectively. Experiments demostrate that corrosion products are pure sulphides without oxides. It is feasible and reliable to study sulphidation by this technique.

The authors have developed and practised a technique for cathodic protection of metallic structures on sea by using shared anode, individual reference electrodes and multichannel potentiostat.Results evidenced that the technique worked well. Application of this technique not only made conventional complex equipment of protection simple but also controlled potentials of coupons exactly at preseted values. Systems based on this technique will be economlc,effective, and easy to operate.

Ni-P amorphous alloy (a.a.)with four different phosphorous contents (8, 10, 12, 14 wr%P)were electro-deposited.The corrosion rates of these electrodeposits in H_2SO_4, HCl, HNO_2, NaOH and FeCl_3·6H_2O solutions were measured and the corrosion products were examined by means of SEM, X-ray diffraction and XPS.The electrochemical parameters of thc electrodeposits in 1M H_2SO_4, 1M HCl and 1M HNO_3 were also determined.The test results showed that: 1) The corrosion resistance of the electrodeposited Ni-P (a.a.) was better than that of Ni. The corrosion rates of Ni-P (a.a.) decreased with the increase of P content. 2) X-ray diffraction and XPS revealed that after being immersed in H_2SO_4, HCl, and FeCl_3·6H_2O solutions, a compound-Ni_2P or Ni Py would form on the'surface of Ni-P (a.a.). 3) Free corrosion potential and anodic polarization curves of these amorphous alloys in 1M H_2SO_4, HNO_3 or HCl solutions shifted remarkably to more noble potential with increase of P content,

The high temperature oxidation behaviour of two types of Fe-Cr-Ni alloys has been investigated. The results show that with titanium alloyed, the high temperature oxidation resistance of the alloy wilt decrease,and this tend will be more obvious with increase of titanium content and the oxidation temperature. The addition of titanium to the alloys results in a change of oxide scale structure with increasing quantities of holes in the scale. Meanwhile the internal oxidation along grain boundaries is accelerated,

The corrosion protective property of high polymer coat under certain temperature gradient was studied by using electric capacity method. The temperature of the coat which contacts the liquid medium is 40℃ and the temperature of the metal substrate is 21, 30, 40 and 60℃ respectively. The results indicate that if the surface of the coat in contact with the liquid medium is at higher temperature and the temperature of metal substrate is kept lower, the liquid will penetrate into the coat more quickly, theelectric capacity will become larger, and the life of the coat will be shortened. On the contrary, if the coat in contact with the liquid medium is at lower temperature and the temperature of the metal substrate is kept higher, the life of the coat will last longer.The penetration caused by temperature gradient plays more negative effect to the life of a coat than the penetration caused by concentration gradient does.

Heat coils made of austenitic stainless steels were installed in fluidized bed of an actifier of catalytic cracker installation in an oil refinery unit. Steam—water mixture circulated within the coils with high pressure. Corrosion fatigue failure occurred in the coils in about 40 days after commissioning of the unit. In the present paper, corrosion fatigue phenomenon of austenitic stainless steels in high temperature,high pressure water was discussed in the real engineering condition. It was indicated that the lifetime of the coils could be largely increased by improving the steamwater flow condition.