Simulations on current fluctuations observed during anodic polarization below the pitting potential have been made assuming several different shapes of current spikes. The power spectra calculated by FFT method were characterized by the power at the lowest frequency G⁰(f), the break-point frequency on the spectrum f₀, and the slope m. It was revealed that the power G⁰(f) corresponded to the energy of the spikes, so it depended upon the number of spikes (rate of pit embryo formation), their maximum amplitude and the life times. The slope m was determined by the shape of each spike, such as m=1 for rectangular and saw tooth shape spikes and m=2 for triangles. The break-point frequency f₀ which depended slightly upon the life time and the number of spikes was considered as an index of the duration in which relatively many spikes were observed.

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The effects of Ni increase and then Al or Al and Y addition to this type of stainless steel on corrosion have been investigated in molten carbonate at 750°C under oxidant gas atmosphere. Ni increase in order to stabilize the microstructure had no influence on the corrosion resistance of this type of stainless steel. Al addition improved the corrosion resistance of this type of stainless steel and more improvement of corrosion resistance was observed at the stainless steel added with Y and Al. In this type of stainless steel, the corrosion rate on the test coupons coated with carbonate deposit obeyed parabolic rule, and then corrosion dipped in carbonate melt obeyed linear rule at this type of stainless steel. But the corrosion rate of the stainless steel added with Al or Al and Y nearly obeyed parabolic rule at both test cases. The mean diameter of corrosion products (mainly consisted of Fe) on the surface at the corrosion test coated with carbonate deposit grew proportionately to the t^1/3. (t is test time.)

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In order to endow the sprayed 80wt%Ni-20%Cr coat with a high anti-corrosion performance, infrared laser remelting was done utilizing a beam scanning and rotating disk method. Both the improvement of anti-corrosion performance of laser treated Ni-Cr coat, and the problems in laser surface modification are introduced. The results obtained are summarized as follows: (1) As-sprayed Ni-Cr coat contains a number of Cr-oxide and pores in it, and allows the corrosive environment quickly impregnate into the substrate metal as long as the sealing of pores is not successfully completed. (2) The Ni-Cr coat fully remelted and strongly bonded to the substrate by beam scanning method was inevitably diluted by the iron diffused from the substrate. Defect-free Ni-Cr coat with iron concentration less than 20wt% could be obtained by very limited laser irradiation condition, and showed anti-corrosion performance against relatively mild environment. (3) Rotating disk method made it possible to refuse the surface thin layer of sprayed Ni-Cr coat, and prevented the iron from diffusing into refused layer. The specimen treated by this method showed an excellent anti-corrosion performance against severe molton salt oxidation. Laser irradiation under highly controlled condition is necessary for remelting the surface thin layer of sprayed coat.

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A new surface treatment has been examined to improve the corrosion resistance of aluminum alloys. In the treatment the alloys were immersed in aqueous solution composed of 0.01M LiNO₃ and 0.005M NaHCO₃ at 95°C for 30min. Preferable resistance of those alloys pretreated to pitting corrosion was elucidated by the polarization measurements in 0.01M NaCl solution and the measurements of the maximum depth of pits formed in aerated NaCl solution containing cupric ions. The SEM photographs showed uniform but porous film of 2-4μm thick formed on the alloy surface treated. The film was identified by the X-ray diffraction analysis to be a mixture of Al₂(OH)₆·H₂O and LiOH·2Al(OH)₃·nH₂O. It raised the pitting potential and depress reduction of oxygen dissolved in solution, resulting in the improvement of corrosion resistance. The surface treatment of pure aluminum, A 3003, A 5052, and A 7072 was useful to prevent pitting corrosion in chloride solution, but was ineffective to BA 4045 because of difficult formation of uniform protective film on the eutectic silicon segregation.

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Recently, scientific interest to plastic materials has been grown as the important materials in the various fields of biology. However, these materials are not always utilized efficiently. There are various levels of utilization among various fields of biology. In this paper, present situation and problems of the utilization of plastic materials was discussed concentratedly focusing in the fields of neural cell culture and fish farming.

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