Effects of ferrous ions on the shape and activity of sulfate-reducing bacteria (SRB) have been investigated using a phase-difference microscope, hydrogen sulfide gas detector, and measuring the amount of ferrous sulfide in the medium. SRB changed its shape at an interval of several hours as the culturing time increased. At the time of maximum activity of SRB, SRB evolved a significant amount of hydrogen sulfide and changed from rod like shape to comma like shape. After this period, pH of the medium increased above 9.0 and the size of SRB became less with reduced evolution of hydrogen sulfide. Even if some amount of HCl was added to keep pH of the medium at 7.0, the hydrogen sulfide evolution was not recovered. In the medium with high concentration (0.01mol kg-1) of ferrous ions, colloidal substance were present and seemed to provide a comfortable place for SRB to grow, ripen, and split easily. In the medium with low concentration (0.00036mol kg-1) of ferrous ions, the colloidal materials were few and the number of SRB was less than that in the high concentration (0.01mol kg-1) medium. It is concluded that ferrous ions do not only affect directly the metabolism of SRB, but also form the colloidal substance on which SRB can keep alive easily.
Carbon steel was exposed for long time to an inoculation medium of sulfate-reducing bacteria (SRB). The corrosion behavior was investigated by measuring weight loss of the specimens and by using surface-analytical methods such as EPMA. In the medium containing ferrous ions of high concentration (0.01mol kg-1), the corrosion rate of carbon steel took a maximum value. The weight loss increased linearly with time after exposure above four weeks, although the weight loss was insignificant during the exposure up to four weeks. The corrosion rate in the medium containing ferrous ions of 3.6×10-4mol kg-1 and 0.3mol kg-1 was not so large as that in the medium containing ferrous ions of 0.01mol kg-1. The activity of SRB as well as the corrosion rate depended strongly on the concentration of ferrous ions. The EPMA results suggested that the some area of steel surface covered with the scale would act as a cathode and the other area would act as an anode. The formation of effective cathode area was closely related to the formation of FeS and dependent on the exposed time. Even if an antibiotic was added into the medium after exposure of two weeks, the corrosion did not cease and increased linearly with time after exposure above four weeks. Thus it is found that the contribution of SRB to the corrosion is associated with the creation of corrosive environment in the initial stage of culture (up to two weeks).
The oxidation behaviour of Ti5Si3 was assessed by thermogravimetry in a temperature range 1400 to 1600K in ambient air for 100ks. Detailed metallographic examinations were performed using conventional methods for the specimens oxidised under specified conditions. The kinetics follows nearly cubic laws at 1400 and 1500K, and at 1550K for up to 50ks when a breakaway starts. During the cubic oxidation two-layer scales are formed; the outer layer is rutile while the inner layer is amorphous silica with the activation energy of 262kJ·mol-1 At 1600K the scale consists of an outer rutile layer and a porous inner layer which is a mixture of rutile and silica grains. Thus, the scale is not protective.
The oxide film on Al-Mg alloy that grew in pure water at low temperatures was investigated with respect to the rate of growth and structure, motivated by development of processes to cleans electronic parts with water-based solutions. The film was composed of amorphous Al (OH)3. Growth of the film was influenced by solubility of the hydroxide of the metal dissolved in pure water. The rate of growth the film in pure water was 70 times faster than moist air. The apparent activation energy of the growing rate pronouncedly changed at about 60°C being 80kJ/mol at temperatures below about 60°C and 10kJ/mol at temperatures above about 60°C.
Effective electrodes for electrolysis of seawater for production of hydrogen (H2) without releasing chlorine into atmosphere and catalysts for production of methane (CH4) by the reaction of carbon dioxide (CO2) with H2 have been tailored. Using these novel materials a CO2 recycling plant for substantiation of our proposal has been built on the roof of Institute for Materials Research, Tohoku University. The CO2 recycling plant consists of a desert, a coast close to the desert and an energy consuming district. At the desert electricity is generated by solar cell operation and transmitted to the coast close to the desert. At the coast H2 is produced by electrolysis of seawater using the electricity, and then CH4 is formed by the reaction of H2 and CO2. CH4 is transported to the energy consuming district. At the energy consuming district combustion of CH4 is carried out not by air but by O2 and CO2 is recovered after removing H2O from the exhaust gas composed only of CO2 and H2O. The recovered CO2 is sent again to the coast close to the desert for reproduction of CH4. The CO2 recycling plant has substantiated that the solar energy at the desert can be used by energy consumers in the form of CH4 without emitting CO2 into atmosphere.