Hot corrosion behavior of Na)2SO_4 coated B-1900 alloy was studied in air at 827 and 750℃.Corrosion kinetics of the coated alloy was gravimetrically measured,and contents of water soluble ions in the reaction products were chemically analyzed.X-ray diffraction and EMP techniques were employed to determine the components and morphology of the corrosion product scale.The experimental results indicate that B-1900 alloy is subject to catastrophic oxidation when covered with Na)2SO_4,and that the hot corrosion is related to the formation of molten Na_2SO_4-Na_2MoO_4-MoO_3 salt on the alloy surface.On the basis of experimental results a corrosion mechanism is proposed for the Na_2SO_4 induced hot corrosion of B-1900 alloy at intermediate temperat- ures.MoO_3(probably as Mo_2O~(2-)_7or Mo_3O~(2-)_(10))is believed to take part in the reduction reaction.The countertransport of MoO_3 and MoO~(2-)_3in the meit carries the reduction reaction of oxygen to the scale (melt)/air interface,which is responsible for the rapid corrosion.The high acidity of the melt and internal sulfidation of the alloy caused by SO_3 resulting from the reaction of Na_2SO_4 with MoO_3 enhance rapid hot corrosion.

Passive films formed on nickel in boric acld-borax solution at first passive potential(-0.5,vs.SCE),steady passive potential(0.4V,vs. SCE)and passive-transpassive potential(0.8V,vs.SCE)have been stu- died by ellipsometry.The results show that the thickness,kinetics, composition and mechanism of passive films are dependent upon applied potential;at above mentioned potentials,the passive films have a two- layer structure,in which the inner layer of the film grows subsequently from the outer layer of the film inwards;the growth of all inner layers follows a linear dependence on time whilst the kinetics of outer layers at-0.5,0.4 and 0,8 V is linear,parabolic and logarithmic respectively. At constant potential-0.5V,the thickness and composition of inner and outer layers are 223 ,β-Ni(OH)_2and 69,NiO·xH_2O;at 0.4 V,88 ,α-Ni(OH)_2and 33 ,NiO·xH_2O;and at 0,8V,254 ,γ_2-NiOOH and 304 ,β-NiOOH,respectively.

In this paper an on-line measurement system of potentiostatic-galvanos- tatic(P-G)transient response of passive metals was established.A mathematical model for P-G response curves in the case of pitting was set up.By Monte Carlo method the electrochemical parameters which characterized the stability of passive films were calculated from the sampling data of the response curves Using the P-G transient technique one can(i) detect the breakdown of passive films,(ii)determine the electrochemical parameters which characterize the performance of pass- ire films and evaluate their stability,and(iii)analyze the cause of localized breakdown of passive films. The results for some steels in sodium chloride solution measured by this technique were presented.For 18-8 SS in 3% NaCl,the autocataly- tic effect of pitting is the cause of localized breakdown of passive film.The passive films of 25Cr5Mn2Mo steel in 3% NaCl are instable at a wide potential region.This instability comes from the dissolution of passive films themselves but doesn't relate to the auto-catalytic effect of pitting.

The effects of pH,C1-ions,temperature,Ti(Ⅲ)and Ti(Ⅳ)ions, as well as dissolved oxygen on anodic behavior of Ti in hot acid NaCl solution were investigated by electrochemical method and surface ana- lysis techniques.Three experimental equations relating critical passiva- tion current density(in)to pH,Cl~- and temperature(T)respectively were obtained as follows: log im/pH=-1.5 log im/log[Cl~-]=1.0 log im=A-4.29×10~3/T According to the experimental results,a mechanism for active dissolution-passivation of Ti in this solution has been suggested.

Under coulostatic perturbation,the transition process may be described by a group of linear differential equations,The key of deriving the equations is to determine the value of start condition. At the moment of coulostatic perturbation,the mechanism of tran- sition process for existing solution resistance is different from that of neglecting solution resistance,hence the polarization potenial change with time varies correspondingly.With the existance of solution resis- tance,the transport of charge can not complete instantaneously and the polarization potential can not change abruptly. On neglecting the influence of solution resistance,based on the law of Killkoff,the polarization potential must abruptly change at the moment of coulostatic perturbation.At the same time the circuit must be controlled by coulostat. Regardlessly at the moment of abrupt change or during all process of transport charge the constant theorem of charge must be obeyed. Thus we can set up the start condition of the transition process and derive the equations of polarization potential decay curve under cou- lostatic perturbation.

A corrosion rate meter for coulostatic perturbation method has been made and a on-line measuring system combined with microcomputer is set up.It can be used to evaluate the corrosion resistance of coated metals by coulostatic perturbation method. Important parameters such as R_p,R_f,C_u,C_f and R_s can be obtained in experiment with only for once weak polarization.For uncoated metal systems,TAFEL slopes b_a and b_c can be obtained with twice strong polarization,and the corrosion current I_(corr)can be calculated with the aid of STERN-GEARY equation.

The surface composition of Al-Zn-In sacrificial anode which had been galvanostaticly discharged in 3%-NaCl aqueous solution,was studied by quantitative XPS method,combined with Ar~+ ion etching. The results showed that: 1.During galvanostatic discharging in 3%-NaCl solution,alloy elements Zn and In enriched in the surface oxidized film in accordance with dissolution-redeposition mechanism,then formed Zn and In enric- hed phases. 2.The quantity of Zn and In enrichment on anode surface was controlled by discharge conditions. 3.Zn and In can affect the active dissolution to different degrees due to their different enrichment depthes. According to these resales,an enrichment model of Al-Zn-In anode surface was proposed.

The heat of adsorption for corrosion inhibitors obeying Langmuir isotherm,and the energy of lateral interaction between the adsorbed molecules for corrosion inhibitors obeying Temkin isotherm were ten- tatively treated with the ensemble theory in statistical mechanics.Based on Langmuir's theory,the expression of adsorption heat(q)for inhibitor was derived,which,revealed the relationship between adsorption heat and the microscopic properties of the adsorbed inhibitor molecules,as well as temperature.Based on the model set up for adsorption system,the expres- sion of moar at rr craction energ between the adsorbed inhibitor molecules was derived,from wich the constant of interaction was defined for the quantitative description of the lateral interaction between the adsorbed inhibitor molecules.The methods of evaluating the values of q andfrom the experimental data of inhibition efficiency were also presented respectively.By treating the experimental data of inhibition efficiency from literature with these methods,the values of q andwere evaluated for some corrosion inhibitors.The evaluated results revealed that for some corrosion iahibitors with simllar nature or structure,the larger the value of q is.the better the perfermance of inhibitor becomes; the smaller the value ofis,the better the performance of inhibitor becomes,which are in agreement with the conclusion drawn from the viewpoint of energy.

High temperature corrosion behavior of Fe-A1 ,Fe-Cr alloys was studied in SO_2 gaseous environment at 800,900 and 950℃.The corrosion kinetics of the alloys was determined by monitoring weight changes of alloy specimens with a quartz spring .The corrosion product was exa- mined by means of SEM,EMP and X-ray diffraction. For Fe-Al and Fe-Cr alloys tested in this study the materials were subjected to simultaneous sulfidation/oxidation at the early stage of corrosion with a rapid diffusion path for metal ions along sulfides formed.At.the later stage the inerease in corrosion product scale thick- nces was sololy due to growth of iron oxides on the scale surface .At the some time,SO_2 molecules transport inward through the corrosion product scale,thus inducing internal sulfidation/oxidation of the ma- terials.

Many techniques,such as the Q-t curves,IR,XPS ,SEM etc.,are used to examine the corrosion resistance of brominated bisphenol-A type unsaturated polyester resin (code name FZ) and to deduce its corrosion mechanism in a series of chemical media ,involving boiling de-ionized water,20% and 5% NaOH aqueous solution at 60℃ ,and 20%o and 5% HCl aqueous solution at 60℃.The results show that FZ resin displays outstanding corrosion resistance.There are evidances that the bromine element does not drop out during immersion process. When immersed in boiling deionized water for a long time(70 days), part of ester groups of the resin are hydrolyzed and small molecules, such as alcohol and carboxy acid etc.,run into media .There are not only small molecules produced during hydrolysis process but also end carboxyl negative ions when the resin is immersed in 20% NaOH aque- ous solution at 60℃ for the same time.

A new brass condenser tube containing trace boron ,which has been used in heat power station for more than four years,shows higher cor- rosion resistance than that of normal brass tubes.Therefore the anti- corrosion properties of 70/30 brass containing different amounts of boron with or without arsenic were investigated systematically.The measur- ements of corrosion weight loss and dezincification coefficient showed that the boron improved the corrosion resistance especially to dezinc- ification ,whether the brass contained arsenic or not.The optimum amount of boron in brass is 0.03～0.05wt.% in the absence of arsenic and 0.02～0.03wt.% in the presence of arsenic. An improved material with better corrosion resistance could possibly be developed by adding trace boron to brass with a certain amount of arsenic content.The improvement of corrosion resistance of this new kind of brass can be explained by the obstruction of boron to the diff- usion path of zinc for dezincification.

A research technique was developed to investigate the variation of anodic current density in aqueous environment,The theoretical analysis testified that the anodic current depended on the strain and strain rate for a regular material-environment,Testing results revealed that the anodic current density of 15Mn steel wire increased with increasing strain and strain rate.Moreover fihe increment of corrosion fatigue crack growth rate induced by anodic dissolution was computed to deter- mine the corrosion fatigue mechanism of mild steels in aqueous environ- ments,The calculation proved that in the early stage of crack growth the anodic dissolution had notable influence on crack growth and the corrosion fatigue mechanism was dissolution-assisted-fatigue,In the second stage of crack growth,the corrosion fatigue mechanism transf- ered to hydrogen-assisted-cracking.

The inhibition efficiency of imidazoline derivatives containing N,Sor O for steel in hydrofluoric acid,hydrochloric acid and citric acid was studied.The electron density of various atoms and the energy of HOMO, LUMO in the molecules are computed by CNDO/2 method. The experimental results shown that the inhibition efficiency decreases in the following order:2-undecyl-1-(trithioureido)-ethyl-imidazoline (SM-3)>2-undecyl-1-(dithioureido)-ethyl-imidazoline(SM 2)>2- undeeyl-1-(monothioureido)-ethyl-imidazoline(SM-1)>2-undecyl-1- (carboxyethylthioureido)-ethyl-imidazoline(PSM-1)>2-undecyl-1- (carboxyethyl-amino)-ethyl-imidazolne(pAI)>2 undecyl-1-(mul eylamido)-ethyl-imidazo line(MAI)>2-unecyl-1-(aminoethyl)- imidazoline(UAEI). The inhibition efficiency of SM-2 at diffierent concentrations and temperates in 0.166 mol/L citric acid for 20A steel agrees well with Arrhenius formula,i.e.P=A exp(-E/RT),where P is the efficiency of corrosion inhibition and T,the temperature(K).This indicates that the mechanism of corrosion inhibition of SM-type inhibitors is chemical adsorption on the metal surface. The chemical adsorption of SM-type inhibitors on metal surface is explained with computational results by CNDO/2 method.In the mol- ecules of SM-type inhibitors,there are two unsaturated centres:the π-bond on the imidazoline-ring and on the thiourea group.These two centres form feed-back bonds on metal surface with a result of chief donative effect of electron.

The inhibition effect of polycondensates of thiourea and imidazoline derivativatives(i.e.SM)to carbon steel in hydrofluoric acid solution has been studied by means of chemical and electrochemical methods and the adsorption rule of SM has been discussed. It is shown that,in acidic solution,SM can be adsorbed on the metal surface through rather strong multiple centres adsorption.The ethylene radical in the molecule plays a role of segregation,which makes SM possess both the inhibiting characters of imidazoline and thiourea,and the fatty radical forms a hydrophobic film towards the solution,all these make SM present strong inhibiting action.At lower concentration, the adsorption rule of SM obeys Langmiur isothermal equation,but at higher concentration(1.8×10~(-5)mol/L),it will be in accordance with Frumkin isothermal equation. The mechanism of multiple centers adsorption can be proved indirect ly by the adsorbing model and by the calculated electron density. It would be meaningful for designing new molecules of organic inhibitors.