The potential and current density distribution in micro areas on metal surface is significant for studying localized corrosion.A measurement system, the scanning micro-reference electrode techuiques(SRET),is established by the authors and described in this paper.The method of preparing micro- reference electrode,the autodeviee for scanning electrode and the electronic circuit for automatic recording potential distribution are described in detail. Its etectrochemical principle is stated briefly. This apparatus is of higher accuracy with simple and efficient device and meets the requirements of practical experimental systems well.

The established scanning micro-reference electrode technique(SRET) is used to study the electrochemical behaviour of various type of localized corrosion in electrolytes and the mutual influence of active corrosion sites bY measuring potential and current density distribution.The active and the inactive sites revealed by the potential contour measured are examined with scanning elee- tronic microscope (SEM).Some preliminary and interesting experimental results are obtained.The initiation and propagation of localized corrosion are discussed.

The inhibiting effect of benzothiazole(BT)and 2-mereaptobenzothiazole (MBT)and the effect of -SH group in this respect on the corrosion of a car- bon steel in HCl solutions at various concentrations and temperatures were investigated.It is shown that the inhibiting effect of MBT is much more pro- nounced than that of BT due to increased surface activity of BT raised by -SH group.Langmiur isotherm equation is observed by both compounds ad- sorbed on steel surface when their concentrations in HCl solutions are not very high.The values of the equilibrium constant B of the adsorption process were determined at θ=0.5.It was found the value of B for MBT (10~5 is of one order of magnitude higher than that for BT(10~4).Impedance measure- ments showed that for both compounds the data of electrode boundary capa- citance which vary with the value of θ fall on the same straight line,and the same value of boundary capacitance (14μF/cm~2)was obtained by extra- polating the experimental data to θ=1.These facts imply that there are no changes in the characteristics of adsorption and the mode of arrangements of the molecules adsorbed on the electrode surface when the -SH group is intro- duced onto the BT.Polarization measurements indicated that both inhibitors belong to the mixed type with predominant anodic control.However,the inhibitive action to the cathodic reaction of the corrosion process is some- what strengthened by introducing the -SH group onto BT molecules.

Natural immersion of barrier-type anodic films on aluminium in chromate /dichromate solutions of varying pH leads to a progressive increase in the film capacitance which is normally attributed to simple uniform thinning of the anodie films.However,transmission electron microscopy of ultramicro- tomed sections of the immersed films shows an overall film thickness decrease which is much less than anticipated from the measured capacitance data. This significant discrepancy between thickness data is associated with a more complex penetration of chromate species within the anodic film,with the outer layer eventually becoming disaggregated and dissolved.This conclusion is supported by Auger electron spectroscopy data,which show a chromium uptake in the outer layers of the immersed films.

The pH value of the crack tip solution of both Ti-5Al-2.5Sn and Ti-5Al- 4V under stress corrosion was measured by micro-electrode methol and indi- cator paper method to be 1.7 to 2.0,while the bulk solution of 3.5%wt NaCl- was nearly neutral.The results so obtained are in good agreement with those obtained from the simulation experiment.The propagation of the SCC was observed dynamically by optical microscope and was proved as follows:some mierocraeks first formed in the plastic region in front of the crack tip, then both the main crack and microcracks extended to each other and con joined finally.The fractography of the SCC was examined by SEM.Based on these experimental results,a model for the SCC of titanium alloys is proposed and discussed.

In this paper,the effect of copper on the corrosion resistance of the Ni- 18Cr-16Mo alloy was evaluated by corrosion tests,electrochemical measure- ments,AES(Auger) and XPS analysis technique.The corrosion tests were carried out in boiling 40%HF,10%HCl and 50% H_2SO_4+42g/1Fe_2 (SO_4)_3 so- lutions.It was found that suitable amount of copper added into the Ni-18Cr 16Mo alloy remarkably increased the corrosion resistance in boiling 40%HF acid.The corrosion rate decreased from 30—50g/m~2·hr for the alloy without copper to 0.3-0.6g/m~2·hr for the copper-containing alloy.In addition,the characteristics of corrosion resistance of parental ahoy without copper can be maintain ed.The data of the electrochemical measurements and surface film analysis show that the unusual effect of copper is due to the formation of copper-rich film on the surfaee of the alloy rather than changes in micro- structure of the alloy.

A new corrosion inhibitor for N80 steel in concentrated hydrochloric acid at high temperature,denoted by “7801”,was synthesised from acetophenone, aniline,hexamine and propiolic alcohol.The evaluation of its inhibitive characteristics was carried out by means of corrosion experiments both under ordinary temperature and pressure and under high temperature and pres- sure ( 150℃,150atm ),tests of resistance against H_2S corrosion and hydro- gen embrittlement and long term immersion tests at room temperature.The experimental results indicate that“7801” possesses satisfactory inhibition efficiency.It is proposed as the inhibitor in 28% HCl,which is injected in- to deep oil-and gas-wells (up to 5 kilometers) to remove calcareous pro- ducts by acidification,even without addition of iodide.The condensation re- action and the inhibition mechanism are also discussed.

The anodic polarization curves of PbO_2/Ti electrode in 10% diluted sea water,natural sea water,0.5N Na_2SO_4 and 5M NaCl solutions at 25℃ have been measured.The chloride and oxygen overvoltages of PbO_2/Ti electrode are lower than those of Pt/Ti electrode at high current density region. Corrosion rates at given current density are determined by the weight loss method during electrolysis in the above mentioned solutions.The results have shown that corrosion rates of PbO_2/Ti anode are greater than those of Pt/Ti anode,but they are far smaller than those of Pb-2%Ag anode. PbO_2/Ti electrode has been used successfully in cathodic protection sys- tem and in the reacting vessel for the production of sodium hypochlorite.