Early Stage Of Immersion Research Articles

Thermal and mechanical properties of biodegradable hydrophilic-hydrophobic hydrogels based on dextran and poly (lactic acid).

The thermal and mechanical properties of a new family of biodegradable hydrogels made of photocrosslinked dextran derivative of allyl isocyanate (dex-AI) and poly (D,L) lactide diacrylate macromer (PDLLAM) were studied. The changes of thermal and mechanical properties of the dex-AI/PDLLAM hydrogels as functions of dex-AI to PDLLAM composition ratio and immersion time in phosphate buffer solution at 37 degrees C were also investigated. Thermal property data showed that the chemical modification, crosslinking, swelling and hydrolytic degradation affected the glass transition and melting temperatures. Based on thermal data, no phase separation was observed in the bicomponent dex-AI/PDLLAM hydrogels. Mechanical property data showed that, by changing the composition ratio, dex-AI/PDLLAM hydrogels having a wide range of dry and swollen compression moduli could be obtained. The moduli of the dex-AI/DPLLAM hydrogels in dry state decreased with an increase in the PDLLAM composition due to the reduction in glass transition temperature of the hydrogels. The loss of mechanical strength in buffer solutions was attributed to the swelling-induced formation of 3D porous network structure in the early stage of immersion and the hydrolytic degradation of the PDLLAM in the late stage via the chain scission of ester linkages located in the PDLLAM backbone. Because swelling and degradation were composition dependent, the magnitude of the loss of mechanical strength was also composition-dependent.

Interactions between calcium, phosphate, and albumin on the surface of titanium.

The deposition of calcium phosphate on chemically polished commercially pure titanium immersed in Hank's balanced salt solution (HBSS) with bovine serum albumin (BSA) (concentrations 0 and 4 mg/mL) has been investigated. Electrochemical techniques, 125I labeling of albumin, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were used. A tricalcium phosphate layer with a thickness of ca. 1 microm was formed for periods of immersion in HBSS ranging between 1 and 2 weeks. A concentration of 4 mg/mL of BSA prevented its formation, even for periods as long as 1 month. In the absence of BSA, the electrochemical behavior of titanium specimens was significantly affected by the length of immersion time, reflecting the changes that slowly occur on their surface. In the presence of BSA, the surfaces maintained most of their original electrochemical activity. Surface studies have shown that calcium and phosphate become incorporated in the surface at very early stages of immersion. Albumin, which was rapidly adsorbed on titanium, was slowly desorbed when titanium was placed in HBSS. Protein and phosphate may coexist on the same surface, but initially adsorbed albumin molecules prevent the precipitation of a thick layer of tricalcium phosphate.

Incentives for Using LEIM in the Investigation of Corrosion Initiation on Organic Coated Alloys

AbstractLocal electrochemical impedance mapping and spectroscopy (LEIM/S) have become important tools for the investigation of local electrochemical breakdown events associated with the degradation of organically coated metals in aqueous environments. LEIM/S of organic coated metal substrates has revealed local degradation events that are distributed spatially and temporally. These observations provide support to a number of long-standing theories, as well as provide new insight into the damage process. The local changes in impedance observed at early stages of immersion support the presence of virtual pores, while the metastability of impedance peaks representing the local changes provide evidence of healing via corrosion product formation. Each of these are long-standing theories used to explain global electrochemical impedance measurements. This paper will provide an overview of some of the events observed using LEIM and examine these results in the context of recent analytical and numerical models. Models used to predict the electric field above an equipotential disk electrode support the interpretation of most experimental LEI data as being representative of chemical and physical phenomenon and not a result of measurement artifact. However, certain features may be an artifact of the finite nature of the experimental process. The interpretation of LEIM events in view of current experimental and modeling results will be discussed.

Potential variation of a temporarily protective oil coating before its degradation

A wire-beam electrode using mild steel wires was developed and used to study the potential variation of temporarily preventive oil coating before its degradation. It was found that the distribution of corrosion potential on the surface of oil-coated wire-beam electrode was heterogeneous before the degradation of temporarily protective oil coating. At the early stage of immersion, the distribution of corrosion potential gradually shifted to a higher potential range with increasing of immersion time. When the distribution of corrosion potential reached to a highest potential range, it began to shift negatively to a lower potential range. It is suggested that this situation may be due to metal corrosion taking place at the metal/coating interface. The distribution of corrosion potential on oil-painted wire-beam electrode followed a normal probability distribution before the degradation of oil coating. With increasing of immersion time, the distribution of corrosion potential on oil-painted wire-beam electrode may change from normal probability distribution before the degradation of oil coating to discontinuous binomial distribution after the degradation of oil coating.

Conducting Polymers and Corrosion: Part 2 — Polyaniline on Aluminum Alloys

Abstract The electrochemical behavior of conducting polyaniline coatings on various aluminum alloys subjected to immersion in dilute Harrison solution (0.35% ammonium sulfate [(NH4)2SO4], 0.05% sodium chloride [NaCl]) was studied. Electrochemical impedance spectroscopy revealed that the charge-transfer resistance (Rct) of polyaniline-coated alloys increased as a function of immersion time. Polyaniline-coated platinum did not exhibit a significant increase in impedance under similar conditions, indicating that an active metal in contact with the polyaniline is required for the observed increase in Rct. A similar pattern of increasing Rct was observed for Alodine (Product A)-treated Al 7075T-6 (UNS A97075) alloys. Mean current and mean potential values obtained from electrochemical noise measurements also suggest a substantial electrochemical interaction between the polyaniline and the aluminum alloy during the early stages of immersion. Polarization experiments and opencircuit potential measurements reveal...

Adsorption of proteins on an AISI 316 stainless-steel surface in natural seawater

The surface of a metal immersed in solutions containing organic and inorganic molecules is modified by an adsorbed layer that influences the subsequent biofilm formation. Little is known about the first steps of surface modifications in the complex medium of seawater. The ‘BASIS’ group has characterized the conditioning film formed on a stainless-steel surface immersed in natural seawater. The chemical composition, morphology and growth mode of this film have been determined using complementary surface analytical techniques: x-ray photoelectron spectroscopy (XPS), infrared reflection absorption spectroscopy (IRAS), atomic force microscopy (AFM), surface free energy measurements and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The XPS and ToF-SIMS data show that the primary film is mainly composed of proteins in the early stages of immersion. The SIMS, XPS, surface free energy and AFM data indicate that the adsorbed protein layer is discontinuous, leaving bare oxide areas. Our results and interpretations are supported by similar experiments in artificial seawater containing controlled amounts of proteins. Copyright © 2000 John Wiley & Sons, Ltd.

Conducting Polymers and Corrosion: Polyaniline on Steel

Abstract Polyaniline-coated steel panels were studied by electrochemical impedance spectroscopy (EIS) and electrochemical noise methods (ENM). EIS data for the polyaniline sample was obtained for increasing time of immersion. An increase in charge-transfer resistance (Rct) with immersion time was observed. ENM data showed that active electrochemical changes occurred during the early stages of immersion. The mean current from ENM exhibited a rather large oscillatory behavior during early stages of immersion, and the mean potential from ENM displayed a tendency toward positive values. Noise resistance (Rn) values also showed initial oscillatory fluctuations, with values that reflected a poor barrier property for polyaniline coating. Tafel plots showed a lower corrosion rate and a more noble corrosion potential for the polyaniline-coated sample as compared to a bare steel sample. Electrochemical data confirmed that significant interactions between the polyaniline and steel occurred during the first 5 days of...

Alkali-silica reaction and pore solution composition in mortars in sea water

The promotion of expansion of mortars containing a reactive aggregate in 1N NaCl solution at 38 °C was attributed to a rise of OH − ion concentration in the pore solution in the mortars. However, it is ambiguous whether the promotion of expansion of mortars in sea water at a room temperature can be explained in the same way as in NaCl solution at an elevated temperature. This study aims at pursuing the expansion behavior of mortars containing a reactive aggregate relating it to their pore solution composition and the extent of alkalisilica reaction occurring within reactive grains. The alkali-silica reaction in mortars in sea water and 0.51N NaCl solution at 20 °C appears to progress differently from that in mortars in 1N NaCl solution at an elevated temperature of 38 °C. The promotion of expansion of mortars in sea water at 20 °C was found to be responsible for an effect of Cl − ions on the alkali-silica reaction at early stages of immersion. Only when OH − ion concentration in the pore solution was relatively high, NaCl and sea water could accelerate the alkali-silica reaction in mortars at 20 °C.

Impedance spectra for aluminum 7075 during the early stages of immersion in sodium chloride

The impedance spectra obtained at short exposure times for Al 7075-T6 immersed in 0.5 N NaCl do not agree with the pitting model proposed by Mansfeld and co-workers. Instead of a transmission line impedance, an inductive loop is observed at low frequencies. This result is due to the non-linearity of the system at short exposure times, when E corr is close to E pit. The application of the anodic portion of the ac signal causes this non-linear behavior. The observed impedance is therefore a system response and not a true impedance. For longer exposure times agreement with the pitting model is observed.

Corrosion Behavior of Tantalum and Niobium in Hydrobromic Acid Solutions (II) on Passive Films and Hydrogen Absorption

Abstract The corrosion behavior of tantalum (Ta) and niobium (Nb) in hydrobromic acid solutions has been studied with respect to their surface states and hydrizing by scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS), a hydrogen determinator, and x-ray diffraction (XRD). The test specimens were immersed in a 47 wt% HBr solution bubbled with hydrogen and in another that contained 0.05 mol/dm3 of bromine at 25 and 100°C for 15, 30, and 45 days. On Ta under every condition and Nb at 25°C, the surface films consisting of their pentoxides thickened with increasing immersion time and exhibited no significant changes in appearance or hydrogen content. However, fine pits less than 5 µm in diameter were formed on Nb specimens in both the solutions at 100°C at the early stage of immersion. In the solution with hydrogen, the pitting extended over the specimen surfaces with increasing immersion time, and developed into general corrosion after 45 days, while the progress of the pitting was ter...

Structural changes induced in tussah silk (Antheraea pernyi) fibroin films by immersion in methanol

AbstractThe crystalline transition induced by immersion in a methanol/water mixture of tussah silk fibroin (from Antheraea pernyi) film obtained by casting from a 1% solution was studied by x‐ray diffraction, differential scanning calorimetry, and infrared spectroscopy. The molecular conformation of the fibroin, consisting mostly of the α‐helix and random‐coil forms, was transformed into a random‐coil and β‐rich conformation containing only a small amount of α‐helix after immersion for no more than 5 min. The intersheet packing of the β‐crystal of the original tussah silk fibroin film was imperfect in the early stage of immersion. However, crystallization proceeded further when the immersion time exceeded 10 min. As a result the sheets in the β‐form crystal became closely packed because of the decrease in the content of the random‐coil form. The exothermic peak, which appeared at 226°C in the original fibroin and was attributed to the random‐coil → β‐structure transition, disappeared completely after immersion for 5 min.

ChemInform Abstract: STUDY OF THE CORROSION AND INHIBITION PROCESSES OF A CARBON STEEL IN A LOW CONDUCTIVITY MEDIUM BY ELECTROCHEMICAL METHODS

AbstractEs werden potentiostatische Strom‐Spannungs‐ Kurven und Impedanzdiagramme von rotierenden Scheibenelektroden aus gekohltem "Stahl in NaCl‐Lösungen mit und ohne Zugabe von Oleylaminopropylen und Amino‐trümethylphosphonlsäure (FA + TM PA) aufgenommen.

Study of the corrosion and inhibition processes of a carbon steel in a low conductivity medium by electrochemical methods

Ohmic drop corrected steady-state current—voltage curves and electrochemical impedance diagrams have been obtained for carbon steel rotating disc electrodes in 200 mg l −1 NaCl solutions with and without addition of 1 g l −1 of the association of oleylamino propylene and amino-tri[methyl-phosphonic] acid (FA + TMPA). Corrosion rates determined from both steady state and impedance data are in fairly good agreement with those determined from gravimetric measurements carried out on a semi-pilot scale circuit. Because impedance measurements are non-destructive and not affected by low electrolyte conductivity, they allow us to follow the evolution of the corrosion rate as a function of time: in the absence of inhibitor the corrosion rate increases during the early stages of immersion whereas it decreases in the presence of 1 g l −1 (FA + TMPA). Impedance diagrams obtained in inhibited solutions reveal a high frequency loop unobserved in the absence of the inhibitor; the very low value (1–2 μF cm −2) of the capacity associated to this loop suggests that the inhibitor (FA + TMPA) acts in forming a relatively thick and compact protective film on the metal surface.

クロム酸溶液中の純鉄およびFe<sub>3</sub>O<sub>4</sub>皮膜の電位

The electrode potentials of pure iron covered with Fe3O4 film in acidic chromate solutions were measured at 25°C in relation to the Pourbaix diagram of Fe-CrO3-H2O system.The potential at the early stage of immersion showed a stable value corresponding to the oxidizing reaction from Fe3O4 to γ-Fe2O3. The relation between the potential and pH value of the solution changed with the structural change of chromic ion species: Cr3+ag. (pH<2), CrO-2aq. (2<pH<4), and CrO3-3aq. (4<pH).The potential at about 30min. after immersion showed a stable value corresponding to the dissolution of iron. The relation between the potential and pH value changed with the structurall change of ferric and chromic ion species: Fe3+aq., Cr3+aq. (pH<2); FeOH2+aq., CrO-2aq. (2<pH<4); and. Fe(OH)+2aq., CrO3-3aq. (4<pH).The observed pH-potential relations were discussed in connection with the electrochemical equilibrium of cathodic and anodic reactions on the surfaces. The electrode potential of the reaction of pure iron with chromic acid solution through the Fe3O4 film was found to have a correlation with the anodic reaction of solid electrolyte, i.e., the dissolution of Fe2+ from iron crystal surface into the Fe3O4 film.

濃硫酸中における耐候性鋼の腐食特性

The atmospheric corrosion of steel is thought to proceed in a concentrated sulfuric acid environment, because ferrous sulfate probably formed by its reaction with SO2 in atmosphere exists under the rust layer and is not oxidized immediately by oxygen supplied through the rust layer. Thus the corrosion characteristics of low-alloy steel in 98% sulfuric acid was investigated in comparison with carbon steel. The conclusions obtained were as follows:(1) The results of the rotating immersion test in 98% sulfuric acid showed that the corrosion rate of low-alloy steel was remarkably lowered with the lapse of time after four weeks of immersion. This behavior is quite different from that of carbon steel.(2) The anodic polarization of low-alloy steel was nearly the same as that of carbon steel in the early stage of immersion. However, as the corrosion progressed, the anodic reaction of low-alloy steel was suppressed more remarkably than that of carbon steel.(3) Corrosion products of both low-alloy steel and carbon steel were FeSO4 n H2O. However, from the analytical results by the X-ray microanalyzer, it was found for low-alloy steel that there was a very thin oxide film containing chromium, copper and other alloying elements in high concentrations at the alloy/iron sulfate interface.(4) Addition of Cl− ion into 98% sulfuric acid lowered the anodic polarization of steel. The role of Cl− ion is thought to destruct the stability of the passive oxide films. The passive film formed on low-alloy steel is more stable than that of carbon steel.From the above experimental results, the corrosion characteristics of steel in concentrated sulfuric acid is quite similar to that of atmospheric corrosion. It is certain that the very thin oxide film existing between the iron sulfate layer and the substrate metal plays a predominant role in the corrosion of steels.

Electrical measurements of immersed paint coatings on metal. II. Effect of osmotic pressure and ionic concentration of solution on paint breakdown

AbstractElectrical capacitance and electrode potential measurements have been used to study the behaviour of painted steel panels immersed in solutions of sucrose, of sodium chloride and other electrolytes, and in sea water.The water uptake of the paint in the early stages of immersion depends only on the osmotic pressure of the solution. The time to reach breakdown of the paint in sodium chloride solutions depends primarily on water uptake and secondarily on ionic concentration. The time to reach breakdown in sea water is considerably greater than that in sodium chloride solutions of similar ionic concentration. Corrosion rate after breakdown is primarily a function of the anodic‐cathodic pore resistance, which is related to the electrolytic conductivity of the ambient solution; it is decreased in concentrated solutions by diminishing oxygen solubility. A mechanism of the course of paint breakdown is suggested.