Recently, the spectacle of the civil engineering structure has come to be often requested. Especially, harmony on the spectacle with surroundings is requested about the civil engineering structure in the city. Therefore, Public Works Research Institute executed the development of the coating materials to improve the spectacle function of the elevated structure in the city and executed a joint research with Hanshin Express-Highway Corporation. “Spectacle function improvement manual of the elevated structure in the city by coating materials (idea)” was made as the result. Moreover, the dirt of the structure with the car automotive exhaust gas etc. has come to often damage the spectacle. It is said that the decrease of the visual check due to dirt is a cause of an accident increase in the tunnel. Therefore, the coating materials and the dirt which did not become dirty easily as a spectacle maintenance technology advertised for the drop dirt coating materials in the official gazette, and a joint research was executed with 17 private companies. “Antifouling material use guideline (idea) for the civil engineering structure” was made as the result.
A marine antifouling paint has been shifted from diffusional to hydrolytic one, because tributyltin copolymer as a binder for a hydrolytic paint has excellent qualities for an antifouling paint. It has higher antifouling potential and longer lifetime against the growth of marine organisms. Recently, an antifouling paint based on tributyltin copolymer was limited to a considerable extent due to heavy concern over marine pollution, in Japan. In this situation, various hydrolytic polymers were developed to replace tributyltin copolymer. Further, non-pollutive, heavy metal free, fouling release coatings have been widely investigated.
There are some coatings and coating systems for zero-low VOC (volatile organic compounds) in anti-corrosion coatings. High solid and non-solvent coatings are widely applied in heavy-duty coating systems. In other case, these coatings are taken into service to avoid solvent poisoning in a closing up environment. As old style water-borne coatings are too hard to show good rust preventive performance for steel structures, and the drying or the hardening of wet film is influenced by low temperature, high humidity, rains or other weather conditions, they are seldom applied for anti-corrosive use. In recent years, some new drying or hardening techniques of water-borne coatings have been developed. Now we are able to get some water-borne coatings which perform excellent corrosion and weathering resistance.
Concern of people on safety of chemical products and preservation of the environment has been increasing for past several years. Paint industry is also required to cope with the problems on VOCs and toxic substances and so on which are generated from paints. This report focuses trend of development of protective coatings which contain no toxic heavy metals, with special emphasis on anticorrosive pigments. Anticorrosive pigments were classified into several types according to their functions, and current studies were introduced for each type. Synergism of different types of pigments, ion exchanging pigments, and chelate type pigments will be some of the alternatives, further, coatings free of anticorrosive pigments may be attained by use of chelate-modified polymers.
Concentrating behavior of hydrogen and chloride ion in the anolyte during electrolysis for type 304 stainless steel was studied using the cell separated with a glass filter in various concentrations of NaCl/NaF mixed solution. In NaCl solutions, charge passed during electrolysis, Q was in the linear relationship with pH decreasing, while two-stages in concentrating process with slow and then fast rate were observed for Cl-. Decreasing pH of the anolyte was mainly dependent on the increasing of Cl- concentration. NaCl/NaF mixed solutions, the rate of decreasing pH and increasing Cl- concentration in the anolyte during electrolysis decreased with increasing NaF concentration in constant concentrations of NaCl solution. The results suggest that fluoride ions act as a inhibitor to chloride ions-induced crevice corrosion for stainless steel.
Protection of carbon steel (C-steel) from atmospheric corrosion by TiO2 coating was demonstrated. TiO2 coating, as a non-sacrificial anode, absorbed solar energy and transformed it to electricity so as to provide cathodic protection to the substrate steel. A TiO2-Fe galvanic couple was developed as an ACM (atmospheric corrosion monitor) sensor to evaluate the photoeffect and corrosion behavior of TiO2/C-steel in atmosphere. For the TiO2-Fe couple, type 1 sensor, an anodic output related to the anodic dissolution of the coupled Fe electrode was detected in the dark (night time), whereas in the bright (day time) the output changed from anodic to cathodic. Moreover, the cathodic output remained for a long time after stopping illumination for the multi-layer coating, TiO2 (amorphous)/TiO2 (anatase)/Ti-Fe oxide/α-Fe2O3/C-steel, type 2 sensor. Enviromental conditions in terms of relative humidity, RH, and amount of deposited sea salt, Ws, where 1mm wide Fe coupled to 5mm wide TiO2 could be protected were determined based on the following examinations: a) visual observation for degree of rust developed on the Fe electrodes, for the type 2 sensor b) comparison of corrosion potential of carbon steel with photo potential of TiO2 electrode measured by Kelvin probe, c) polarity of output current for the type 1 sensor. It is concluded that the carbon steel could be protected from atmospheric corrosion by TiO2 coating under conditions of lower amount of deposited sea salt and lower relative humidities.
High temperature intergranular corrosion of a SCH 13 heat resistant steel in the waste incinerator, where plastics and used tires were burned under thermal cycling condition as at 1423K after 6.2ks and at 1150K for 17ks then cooled down to room temperature, was investigated by means of scanning electron microscope, electron probe micro-analysis and X-ray diffraction analysis. The network of intergranular corrosion within the alloy beneath the outer scale were identified. Si and Cr oxides as well as Cr and Mn sulfides were observed in the center of corroded area that was surrounded by Fe and Ni concentrated zone where Cr, Si, Mn were depleted. The sulfur partial pressure calculated from composition of combustion gases was smaller than the dissolution pressure of sulfides of alloy element in SCH 13, it was supposed that Cr and Mn oxides that were near the surface and Cr, Mn sulfides that were at the inside of alloy were produced by a reaction between Cr, Mn and SO2, O2 gases. At the initial stage of intergranular corrosion, Cr-Fe carbide channel that developed on grain boundary by repeated thermal cycle in waste incineration furnace was changed to oxide and then SiO2 and voids were formed. Cr, Mn oxide and sulfide were formed by a reaction between Cr, Mn and SO2, O2 gases that were introduced by means of voids from gas side. It is concluded that the Si, Cr, Mn depletion zone is caused by the formation of Si, Cr, Mn oxides and Cr, Mn sulfides, then Fe and Ni are relatively enriched on this depletion zone.
It has been known that CrN has high hardness and high resistance against wear, oxidation and corrosion. Although many studies have been done on its mechanical and high temperature oxidation properties, studies on its electrochemical and corrosion properties in aqueous solutions are still limited. The aim of this study is to produce CrN thin films by ion-beam-enhanced deposition (IBED) and to make clear the corrosion behavior of CrN by electrochemical measurements. CrN thin films were prepared by IBED under various conditions and their polarization curves were measured in 1kmol·m-3 H2SO4 and 12kmol·m-3 HCl. Changes in the surface of the thin films by polarization were examined by XPS and in-situ ellipsometry. The thin films prepared by IBED were composed of the large amount of CrN and small amounts of Cr2N and Cr. The fraction of CrN in the films increased with increasing flow rate of nitrogen. Potentiodynamic polarization curves exhibited that the active dissolution rate of the films decreased with increasing CrN content of the films. The films with high CrN content showed excellent corrosion resistance up to the start potential of transpassive dissolution without formation of passive films. That is, the excellent corrosion resistance of CrN results from the intrinsic inactive nature of CrN surface.
In order to study the corrosion performance of a hot-dipped aluminized steel pipe in the seawater, the measurements of the corrosion current for 2 weeks were performed by using the scanning vibrating electrode technique. It was found that the hot-dipped aluminized steel pipe which has no defect corrodes in the order of aluminum, Fe-Al alloy and carbon steel. But if the Fe-Al alloy layer has a defect of a penetration which gets at the base steel, the corrosion of base steel is prior to the corrosion of Fe-Al alloy. Especially when the defect exists near weld (Type 309 stainless steel), the corrosion rate of the exposed base steel is accelerated more.