reaction of a platinum electrode for the measurement of ...to improve the problem, we used the...

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腈腋腍腇腂 Eh 腉腊腁腐腀腃腎腆腌腅腂腏腄 臇膷臊臹*臦臼臌膵** Reaction of a Platinum Electrode for the Measurement of Redox Potential of Paddy Soil Daisuke MURAKAMI* and Tatsuaki KASUBUCHI** * The United Graduate School of Agricultural Science, Iwate University ** Faculty of Agriculture, Yamagata University, +,- Wakaba-machi, Tsuruoka, Yamagata, 3312///, Japan Abstract Redox potential (Eh) of soil has been measured to know the redox state in paddy soil. How- ever, it was di$cult to get reliable data because the Eh values in the field fluctuated largely. Although the measurement method had been examined to improve the problem since the +3/*’s, it still remained to be analyzed. To improve the problem, we used the cyclic voltammetry (CV) to examine the reaction of the platinum electrode. The results obtained were as follows. The causes that fluctuated the data consisted of two factors. One was the chemical reactions of plati- num electrode with the surrounding materials. The other was associated with the property of the soil. The platinum electrode induced reaction with oxygen in the oxygenated medium and made oxide layer in the surface of the electrode. This layer disturbed to make the Eh stable. Polishing the sensor could remove the layer. In the reductive state, the sensor adsorbed some materials in the reductive state around its surface. This also decreased the stabilizing time. In addition, the di#usivity of ions in the soil was too small because of the large surface area and electro double-layer of soil solid. These factors decreased the moving speed of electron or ion transport and non-equilibrium condition was formed in the soil. Key words : redox potential, measurement method, cyclic voltammetry, paddy soil, di#use dou- ble layer +腇腅腈腆 臞膺腝膨膅膋膛臝腻 Eh腝臆臙腞腏腩腡腘膼臜臞 膺腜腈腎腨臍臔膝膶腙腝膍臻腤膼膀腝膿腽膻臑腛腚自 膟腇臱臛腜臷臵腐腩腗腋腔 膃臣+3., ; 膥膡+32, ; 臎臩臧臇+32, 腛腚腄腀 腑腉腑腾臭腘腞膣膝膾腝腆 腨臆臙臒腊臡腦腩腜腌腇臠腒臬膹腘腣膹膳腜腥腧臒腊 腼腛腨腛腚腝臲臋腊膪臚腐腩腗腇腨 臀膈腦+30* ; +32,腄腀 腏腝腔腢臬膹腝膜腻臓腘腞腛腌膤臞腑腔膫臺 腜腖腇腗臆臙腓腨臭臮腊臈腌臵腇腦腩腗腋腔 膐腹+31*腄腀 膤臞腑腔膫臺腝 Eh 臆臙腜膍腑腗腏腩腡腘腜臰腦腉 腜腐腩腗腋腔膝膶腙腑腗臏膼臂腝 Eh 腞臥膕臝膔腪 臃臣膞腓腍腜腾臙臒腪膭腓腝腜臉腑腗臞膺腝膹膠腜腞 臃臣膞膽膬膌膬腜腞腾臕至腺膷腙腇腕腔臗膬膌腪膘 膇腑腛腇腙腸臙腑腔腱腂腯腊臡腦腩腛腇腏腙 膖臜+3.2腄腁 臥膕臝膔腊臗腌腛腨腙腸臙膅腓腨腡腘腝膬膌 腊臐腌腛腨腏腙 臀膈腦+30* ; 膥膡膢臟+302腄腁 臥膕臝膔腪膙臯腑腗膫臺腜臃臣腓腨腙膙臯腑腛腇膹膠 腜臨腠腗臄腌腾臙臒腜腛腨腏腙 膥膡膢臟+302* 膎膯臊膊臊膊膂臻膠臤膊膙膒膆 * 膝膰膳 : 膧膓膑膲臅膠膙膒膳 -*/**.1 膁膸膚腖腌腟膩膴致臁 +0+ 腖腌腟腮腷腯腂臀 ** 膥膗臊膊臤膊臩 3312/// 膥膗膚臘膄膩膮臶臖 +,- 腉腁腋腁腊 : 膨膅膋膛臝腻臆臙臭臮腭腫腬腵腰腬腳腶腯腷腴腲腵腂膼臜臞膺膉膦臝膏臢膱臂 J. Jpn. Soc. Soil Phys. 臞膺腝臫臸膾 No. +*0, p. -+* ,**1

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Page 1: Reaction of a Platinum Electrode for the Measurement of ...To improve the problem, we used the cyclic voltammetry (CV) to examine the reaction of the platinum electrode. The results

����� Eh����� �����

����*�����**

Reaction of a Platinum Electrode for the Measurement of

Redox Potential of Paddy Soil

Daisuke MURAKAMI* and Tatsuaki KASUBUCHI**

* The United Graduate School of Agricultural Science, Iwate University

** Faculty of Agriculture, Yamagata University, +�,- Wakaba-machi,

Tsuruoka, Yamagata, 331�2///, Japan

Abstract

Redox potential (Eh) of soil has been measured to know the redox state in paddy soil. How-

ever, it was di$cult to get reliable data because the Eh values in the field fluctuated largely.

Although the measurement method had been examined to improve the problem since the +3/*’s,

it still remained to be analyzed. To improve the problem, we used the cyclic voltammetry (CV)

to examine the reaction of the platinum electrode. The results obtained were as follows. The

causes that fluctuated the data consisted of two factors. One was the chemical reactions of plati-

num electrode with the surrounding materials. The other was associated with the property of

the soil. The platinum electrode induced reaction with oxygen in the oxygenated medium and

made oxide layer in the surface of the electrode. This layer disturbed to make the Eh stable.

Polishing the sensor could remove the layer. In the reductive state, the sensor adsorbed some

materials in the reductive state around its surface. This also decreased the stabilizing time. In

addition, the di#usivity of ions in the soil was too small because of the large surface area and

electro double-layer of soil solid. These factors decreased the moving speed of electron or ion

transport and non-equilibrium condition was formed in the soil.

Key words : redox potential, measurement method, cyclic voltammetry, paddy soil, di#use dou-

ble layer

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J. Jpn. Soc. Soil Phys.

�»¼JNo. +*0, p. -+* �,**1�

Page 2: Reaction of a Platinum Electrode for the Measurement of ...To improve the problem, we used the cyclic voltammetry (CV) to examine the reaction of the platinum electrode. The results

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��+ ,�:��� Eh��3 [A\ � -�:��� CV��3 [B\

Fig. + Two electrodes method of Eh (A) and

three electrodes method of CV (B)

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Page 3: Reaction of a Platinum Electrode for the Measurement of ...To improve the problem, we used the cyclic voltammetry (CV) to examine the reaction of the platinum electrode. The results

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sensors (soil , ponded water)

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Page 4: Reaction of a Platinum Electrode for the Measurement of ...To improve the problem, we used the cyclic voltammetry (CV) to examine the reaction of the platinum electrode. The results

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��- ·�1¸�¹º/Z[1�! �XY Eh�@Fig. - Change in Soil Eh by repetitive insertion

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Page 5: Reaction of a Platinum Electrode for the Measurement of ...To improve the problem, we used the cyclic voltammetry (CV) to examine the reaction of the platinum electrode. The results

,**,�� CV���� ���� ������������������� � ���� ��� !�����"#$�%&�'�()���()���*+)"#��,-./01�2()3456�7)"#8�$)�

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Page 6: Reaction of a Platinum Electrode for the Measurement of ...To improve the problem, we used the cyclic voltammetry (CV) to examine the reaction of the platinum electrode. The results

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��3 >�2 � MNOPI?9���!"3��#$�%&'�Q*�RSTU*I>Fig. 3 The relation between the oxidative peak of current and square root of

sweeping speed from figure 2.

JK�VWX Y +*0 Z 1,**128

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