Synchrotron radiation is useful and powerful tool for research and development on materials science, life science, environmental science and so on. The SPring-8 (Super Photon ring 8GeV) has been operated more than 5 years since October 1997. At the moment, 44 beamlines are operating for the users and another 3 beamlines are under construction. The present status and some research frontiers on the materials science at the SPring-8 are summarized.
Medium scale synchrotron radiation facility, NewSUBARU (1.5GeV), whose energy levels are much less than SPring-8 (8GeV), is introduced including storage ring (circumference is 119m) and several beamlines. Synchrotron radiation light between soft X-ray and ultraviolet light is NewSUBARU's favorite one. Examples for industry applications performed by beamlines of NewSUBARU, lithography, new materials production and so on, are also shown
Correlation between local structure around Cr in the protective rust layer on weathering steel and protective performance of the rust layer is presented as an example of corrosion research using synchrotron radiation which has recently been applied in various research fields as a useful tool. In addition, in situ observation of initial process of rust formation on steel is also mentioned. It was pointed out by considering the X-ray absorption fine structure spectra that the nanostructure of the protective rust layer on weathering steel primarily comprises of small Cr-goethite crystals containing surface adsorbed and/or intergranular CrOx3-2X complex anions. This CrOx3-2X explains the protective performance of the rust layer originated by dense aggregation of fine crystals with cation selectivity of the Cr-goethite. It is very advantageous to employ white X-rays for in situ observation of rusting process of a carbon steel covered with electrolyte thin films because rust structure might change very quickly. This in situ observation revealed the effect of ion species on the change in rust phase during wet/dry repeating. It can be said that application of synchrotron radiation on corrosion research is so useful to understand the nanostructure of surface oxides which closely relate to corrosion behavior of metals and alloys.
Synchrotron-radiation has been applied to investigation of corrosion at surface/interfaces of steel. Three topics are shown: (1) In situ observation of reactions at the interface has been carried out for localized corrosion of stainless steel. It is shown that change in states of Cr3+ and Br- ions near the interface is deeply related with a breakout of the passivation film. (2) Phase transformation of Zn-coated steel at high temperature was investigated by a new system of in situ observation. It has been found that an addition of small amount of phosphorus changes an incubation time before the alloying reaction starts. (3) Nano structures of rusts formed on steel after atmospheric corrosion. Evolution of “Fe(O, OH)6 network” is the key to understand how the durable rusts of weathering steel prevent from formation of more rusts.
The recent progress of use of ultra-bright synchrotron radiation (SR) for environmental degradation studies of structural materials was reviewed. Refraction contrast X-ray imaging experiments were conducted in BL24XU of SPring-8 to aluminum alloys, mild steel, forged steel, etc. with cracks and voids. As a result, much more distinct images of cracks and voids in these materials were successfully observed by this new method, as compared with conventional X-ray absorption method. In-situ observations of crack initiation and propagation were also successfully done. SR-XAFS measurements were also conducted in SPring-8 to investigate the influence of hydrogen on the structure and electron state of titanium, and the influence of alloying elements on the formation and structure of iron rust to elucidate the corrosion mechanism of steel. In-situ XRD experiments were also performed in Spring-8 towards pure iron under wet and dry corrosion cycle so as to make sure so-called Evans model.
The influence of corrosion on cavitation erosion of metallic materials, with emphasis on the behavior of the material surface during the incubation period in a corrosive environment was investigated. As expected, in the case of brass, the duration of the incubation period was reduced in the corrosive environment, but that for pure copper was prolonged. This can be explained by the tensile force caused by the adsorption of ions in the corrosive solution. The relationship between the increment of surface area and testing time during the incubation period, a key to predieting the duration of the incubation period as well as of damage rate thereafter, was moved parallel to the time axis, but maintained the same shape for each material tested independent of the environment. Polarization curves of each material under cavitation were measured and the corrosion rate was found to be accelerated by the solution agitating effect of cavitation. Thus it is confirmed that the duration of the incubation period of cavitation erosion-corrosion for a material can be determined by measurement of the increment of the surface area of the material, and the corrosion rate can be predicted from polarization curves, which can be measured under the condition of cavitation.
Anhydrous alcohol is known to react with aluminum at high temperatures, resulting in aluminum alkoxide formation. However the reaction when a mixture of two or more alcohols are used has not been reported. Moreover the addition of minute quantities of water has been shown to prevent this alkoxide reaction. This paper describes (1) the reaction of aluminum with a number of mixed alcohol solutions near the azeotropy point, and (2) the minimum water concentration, in mixed alcohol solutions, at which the alkoxide reaction was prevented. Pieces of pure aluminum (JIS-A1085) were reacted with 50ml each of a range of mixed alcohol solutions in a vessel made from SUS304. The solutions were prepared from five kinds of 2-4 carbon alcohol, namely ethanol, n-propanol, iso-propanol, n-butanol and iso-butanol, in different combinations. The reactions were carried out for 72 hours each at 353K, 373K and 393K respectively. Results showed that reactions using mixed alcohol solutions tended to have lower reaction temperatures than those using single-alcohol solutions. The minimum water concentration at which the alkoxide reaction was prevented also tended to be higher for mixed alcohol solutions than for single-alcohol solutions. Considering these results from the point of view of the dissolution phenomenon of alcohol, I postulated that the size, structure and stability of alcoholic clusters in mixed alcohol solutions may be important factors contributing to the reaction.