Koichi Katoh

The electrochemical behavior and impedance characteristics of the passive film on carbon steel in nitric acid solutions

Abstract The impedances of passivated carbon steel in 1.0 M HNO 3 were measured at various polarization potentials. Complex impedance diagrams having two capacitive loops in the high frequency range and a Warburg response at low frequencies were obtained. The charge transfer at the metal|oxide interface was a reversible reaction, and the resistance was independent of the potential. The impedance of the charge transport in passive films can be described by a nonlinear transport equation. The diffusion coefficient in the passive film formed on carbon steel in 1.0 M HNO 3 was about 9.8×10 −17 cm 2 s −1 , and the charge transport in the film followed a diffusion mechanism. The surface layer of the film was a stable n-type semiconductor phase in the low potential range (0.4 to 1.3 V), but it can be converted to a metal-like layer due to degeneration of the surface layer at high potentials (>1.3 V).

The behaviour of passive films on carbon steel in sulfuric acid solutions

Abstract A kinetic study of the passive state of carbon steel in H 2 SO 4 solutions was performed based on impedance measurements. Complex impedance diagrams with only two capacitive components were obtained in the potential range 0.6–1.4 V/SCE. The parameters of the passive electrode ( R HF , C HF , α and R m ) were obtained as a function of potential. The product IR m of the passive current I and the transport resistance R m in the passive film was found to be proportional to the film thickness. The thickness of the passive film increased with increasing polarization potential at relatively low potentials, but decreased with increasing degeneration of the outer layer of the film at high potentials. The polarization potential is lower than both trans-passive potential and the oxygen evolution potential.

Distribution of selenium and molybdenum and cancer mortality in Niigata, Japan

Selenium and molybdenum have inhibitory effects on gastrointestinal carcinogenesis. We investigated the levels of selenium and molybdenum in sediments and mortality from cancers at specific sites in 19 areas of Niigata Prefecture, Japan, and compared these factors. The average concentrations of selenium and molybdenum were 0.44 +/- 0.19 ppm (micrograms/g dry weight; mean +/- standard deviation) and 3.82 +/- 1.03 ppm, respectively. Selenium was not associated significantly with cancer mortality. There were inverse correlations between molybdenum levels and female mortality from cancers of the esophagus (r = -.446, .05 < p < .1) and rectum (r = -.529, p < .05). Molybdenum was correlated positively with female mortality from cancer of the pancreas (r = .603, p < .01). Further investigations are needed for causal interpretation of these results.

Application of voltammetric sensors to the determination of chloride in sea sand and cement pastes.

微小銀電極ボルタンメトリックセンサーを用いて,海砂及びセメントペースト中の塩化物の分析方法を検討した.電極の前処理として,粒径8μmのアルミナで研磨し,2%塩化ナトリウム水溶液中で活性化処理を行うと良い結果が得られた.海砂中の塩化物の分析は,海砂30gに水50mlを加え10分間かき混ぜて得た溶液を,0.1mol dm-3硝酸ナトリウムを支持電解質として,電流を測定することによって求められた.モール法による塩分分析との相関は極めて良く,相関係数は0.994であった.セメントペースト中の塩化物については,その濾過液を0.1mol dm-3リン酸塩(pH7.0)又は酢酸塩緩衝溶液に加え,酸化電流を測定すると定量できることが分かった.モール法で求めた塩分濃度との間には良い相関(ともに相関係数0.994)がみられた.これらのことから,本研究のボルタンメトリックセンサーは,フレッシュコンクリート中の塩化物の分析に利用できると期待される.