Corrosion Resistance Of Films Research Articles

Chemical vapour deposition of corrosion-resistant TiN film to the inner walls of long steel tubes

A uniform TiN film was coated on to the inner walls of long steel tubes by moving a chemical vapour deposition furnace along the tubes. The moving direction of the furnace from outlet side to inlet side gave a more homogeneous coating than the reverse moving direction. The TiN-coated steel tube (inside diameter 10 mm) was obtained under the following conditions; peak deposition temperature 1050° C, total flow rate of reactant gas (TiCl4 + N2 + H2) ∼ 6.0 ml sec−1, moving velocity of the furnace 2.8 mm min−1. The inner wall of the coated tube showed high corrosion resistance for dipping in 6N HCI aqueous solution for 17 h.

無電解ニッケルめっきの屋外暴露試験と促進試験

The corrosion resistance of films deposited from electroless nickel plating baths was evaluated by outdoor-exposure tests, salt spray tests and an accelerated atmospheric corrosion (complex cycle) test under cycle conditions of 35°C in the test tank, 42min in 20-25ppm sulfurous acid gas ambient (<80% RH)→18min in 1% NaCl solution spray→102min in moisture (>85% RH)→78min in dry condition, for a total of 4 hours/cycle.Deposited films that contained above 10% P content obtained from pH4.3 malic acid baths were superior under both outdoor-exposure tests and the accelerated corrosion test. A correlation was recognized between air temperature, humidity, and wetness time as weather factors in the outdoor-exposure test on the one hand and corrosion loss on the other. Absolute humidity was found to have a cleared effect than relative humidity on corrosion resistance. Since the salt spray test for electroless nickel plating showed a poor correlation to the corrosion pattern in the atmosphere and required a long period for corrosion to begin, this method was not suitable for corrosion test of the deposited films. On the other hand, specimens corroded in 4 cycles of the accerelated atmospheric corrosion test were found to have surface appearance similar to that of specimens in the outdoor-exposure test and the pits produced were uniform in size and distribution over the surface.

Résistance à la corrosion des fontes alliées

Owing to their relatively high alloy content, alloy cast irons often exhibit a high degree of corrosion resistance in many mediums. Nevertheless, it is necessary to know which kind of iron can be used in a definite medium. It seemed, therefore, interesting to collect information on this subject. It is the purpose of our paper.A large addition of nickel to cast iron produces materials with stable austenitic matrix which, being more noble than the matrix of unalloyed grey irons, gives very good corrosion resistance in most applications.High-chromium irons also have good corrosion-resistant properties due to the superficial formation of an impervious chromium oxide film. So, these irons are most useful in mediums containing a large supply of oxygen or oxidizing agents.The corrosion resistance developed by high-silicon alloys is due to the formation of a corrosion-resistant film containing a large amount of silica. These irons can withstand attacks from a very wide range of mediums, indeed few ions can penetrate this silica film.

The influence of boron and titanium in amorphous magnetic films

Saturation magnetization and magnetostriction, coercivity, thermal stability, and resistivity of amorphous magnetic films of FeTiB and CoTiB have been investigated as a function of boron and titanium content. Films with Fe have large positive magnetostriction; films with Co have small magnetostriction, positive or negative. Their thermal stability is slightly better than that of the transition metal-boron films; corrosion resistant films have, however, lower magnetization. The magnetic properties of polycrystalline FeTi films as a function of titanium content are also reported. In some cases, the addition of boron increases the magnetic moment of the Fe atom.

Mössbauer investigations of some chemical treatments of iron surfaces

The nature of corrosion- and abrasion-resistant surface phases formed by the chemical treatment of iron-containing solids has been investigated by conversion electron and conventional transmission mode Mossbauer spectroscopy. Corrosion-resistant films produced by oxidising alkaline solutions contain iron(III) oxyhydroxides and their formation appears to resemble the actual process of corrosion. Nitriding processes which harden the surface by reaction of the metal with cyanide ions give superficial phases which include the iron nitrides Fe2N and Fe4N. Sulphiding processes produce abrasion resistant surfaces by reaction of the metal with thiocyanate ions and give a surface phase containing the iron sulphide ‘Greigite.’ No evidence was found for the presence of iron carbides in materials treated by cyanate or thiocyanate.

Effects of temperature on formation and corrosion resistance of boehmite films

Studies were made on the effects of temperature on the formation and corrosion resistance of boehmite films on aluminum by treatments in aqueous sulution and water vapor. The experiments were conducted by measurements of the film thickness, electron microscopy, electron diffractiometry, X-ray diffractiometry, and corrosion resistance.The following results were obtained.(1) The thickness of the film formed on aluminum in deionized water at 70°C or higher was different from that formed at 60°C. The former film had the same thickness, independent of temperature, except for at the initial stage of formation.The X-ray diffractiometry revealed that the film consisted of bayerite at 70°C or lower, amorphous substances at 80°C or higher, and boehmite and bayerite at 100°C.(2) In triethanolamine solution, the temperature gave a remarkable effect on the film thickness and the film was thicker with the rise of temperature. As the results of X-ray diffractiometry, it was found that the film in amorphous state when formed at 6090°C, but consisted of boehmite at 100°C.(3) In ammonia solution, the film was thicker with the rise of temperature at the initial stage of film formation. After 1hr., however, the film formed at 80 and 90°C showed the maximum in thickness and high corrosion resistance. The X-ray diffractiometry revealed that bayerite was detected in the film formed at 90°C or lower, and bayerite and hoehmite in the film formed at 100°C.(4) In water vapor treatment, temperature rise had a little effcet on the increase in the film thickness on alloys, but the film on the high purity aluminum was made thicker with the temperature rise, which increased the content of γs-phase in the film.However, there were no significant effects of treating temperature on the corrosion resistance of the film.

Film and pH Effects in the Stress Corrosion Cracking of Type 304 Stainless Steel

Abstract Rapid stress corrosion cracking of 304 stainless steel in MgCl2-FeCl3 solutions at 125 C has been shown to occur only when the pH of the corrodent liquid within the crack lay between 1.2 and 2.5. A film of more acidic corrodent solution is raised to pH = 1.2 by reaction with the metal within a few seconds after isolation in a pit, crack, or crevice. MgCl2 solutions of pH higher than 2 became more acidic when in contact with stainless steel as a result of corrosion processes. The pH of small amounts of such solution isolated in pits or crevices eventually fell to near 1.5, where stress corrosion cracking could occur. This pH range is considered to be critical for stress corrosion cracking of 304 stainless steel because it is the range in which a corrosion resistant protective film is formed in the presence of the corrodent solution. This film is essential to crack propagation. If there is added to a corrodent , solution in this pH range an organic complexing agent such as glycerine or glycol which prevents-formation of the protective oxide film, the general corrosion process continues unchecked but no stress corrosion cracking occurs. The data support a model in which stress corrosion cracking is driven by a highly localized galvanic cell within the crack. The cell operates in such a way that there is no large change in pH of the solution in the crack. These results emphasize the importance of the corrosion resistant film in the chemical aspect of the stress corrosion mechanism.

A Fresh Look at the Mechanism of Corrosion in Boilers

Block specimen, hydrogen effusion, and model boiler experiments have shown that mild steel, after a brief period of “flash” oxidation immediately following immersion in aqueous solution, either corrodes relatively slowly with the formation of a thin, corrosion-resistant magnetite film, or corrosion proceeds rapidly with the development of a non-protective accumulation of iron oxide. In the latter case, film-destructive mechanisms induced experimentally by combinations of high temperature, stress, and quite high concentrations of hydroxide alkalinity or ferrous chloride have produced examples of generalized severe metal loss, pitting, heavy oxide accumulation, and hydrogen damage remarkably similar to corrosion manifestations responsible for metal failure in real boilers.

Parkerizing sintered parts with preliminary heat treatment

1. The use of a zinc monophosphate solution for parkerizing sintered parts gives corrosion-resistant phosphate films which protect the outer surface against atmospheric corrosion. 2. Protection of the inner surface against corrosion requires pretreatment with steam or GKZh-94 (a 10% solution in gasoline), without subsequent sandblasting.

On the protective film of aluminium prodby boiling in a weak alkaline aqueous solution

We can produce a milk-white, transparent and very excellent corrosion-resistant film by putting an aluminium sheet in the steam of 4kg/cm2 for 30-60 minutes after boiling in a 0.2-0.4% NH4OH aqueous solution (with soft or distilled water) for several minutes.This report is concerned with the experimental procedure and the research of production conditions of this film in the industrial scale, i. e. in this report, it is clarified that both of the films obtained in the laboratory and factory are equally of high corrosion-resistivity.

The Corrosion of Metals-I. Mechanism of Corrosion Processes

This paper outlines the application of electrochemical methods to corrosion investigations. It discusses the position of the potential of a metal against its environment and the trend of this potential with time, pointing out that it is thereby possible to determine whether the corrosion process is controlled by reactions occurring at the anodic areas, the cathodic areas, or both; that is, whether there is a tendency toward passivity, inhibition or progressive attack. Measurements of film stability whether in terms of the leakage current which may be passed through the film or in terms of the amount of film forming material required to produce passivity or the amount of film destroying material required to render a metal active, furnish information as to the quality of corrosion resistant films. Measurements of the rate at which a film forms on a metal when placed in a film-forming environment throws light on its relative surface reactivity, and such information is of assistance in determining the rate of corrosion in homogeneous corrosive environments or the rate of passivation in the film-forming environments. On the basis of such measurements and with a chemical knowledge of the environments in which metals are used as well as the composition and physical state or structure of the metals, it is possible to predict corrosion behavior and to obtain an understanding of corrosion problems usually not possible by ordinary empirical corrosion tests.