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Effects of electrolytic bubbles on the IR drop of caustic soda solution in a vertical cell of one meter height were studied under both free and forced convection. Three pairs of Luggin-Haber probes were positioned near the anode and the cathode to determine the solution IR drop during electrolysis. A sectioned electrode having 10 segments was employed to obtain the current distribution from the bottom to the top of cell. The superficial resistivity of the solution containing gas bubbles agreed well with the Bruggemann equation.The solution IR drop decreased significantly when adequate conditions or cell geometry for solution circulation were provided. The anode-to-cathode gap was found to be the most important parameter for reduction of the solution IR drop in a vertical cell.

No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, microfilming, recording, or otherwise, without written permission from the Publisher FOREWORD This book has been planned and written by Dr. Hine with his knowledge and experience in electrochemical science and engineering for over thirty years since he joined with me at Kyoto University in 1948.This book is unique and is useful for engineers as well as scientists who are going to work in any interdisciplinary field connected with electrochemistry.Science is sure to clarify the truth of nature as well as bring prosperity and an improvement to the welfare of human beings. The origin of the word "science" is the same as of "conscience," which means the truth of our heart.When we consider a scientific and technological subject, first we classify it into the components and/or factors involved, and then we clarify them individually. Second, we combine them to grasp the whole meaning and feature of the subject under discussion. Computers may help us greatly, but how to establish the software that will be most desirable for our purposes is of great importance. We need to make these efforts ourselves, and not decorate with borrowed plumes.With this concept in mind, this book is attractive because the author describes the basic science in electrochemistry and practice, and discusses the electrochemical engineering applications as a combination of science and technology.Furthermore, Dr. Hine discusses the present situation and future trends in the industry with a number of drawings and photographs. He also tries to compare the electrochemical process to other competitive processes. He does this well because he has experience both in the field of science and in chemical process industries. Also, he is very happy that he has many friends worldwide who give him useful information and ideas.Dr. Hine attended classes in electrical engineering at the technical college in Osaka, then he came to my laboratory at the Department of Industrial Chemistry, Kyoto University, where he received his doctorate degree. He has studied hard and specialized in electrochemical engineering. This book is the fruit of his efforts. v vi FOREWORD It is a pleasure to provide these introductory remarks for Fumio Hine, who is so willing to work actively with an international sense. SHINZO OKADA

Polarization measurement and an accelerated life test of the oxide-coated titanium anodes in relatively dilute solutions of NaCl and in HClO4 solution were conducted. The OCTA failed at potentials higher than 1.3V vs. SCE, probably due to anodic oxidation of RuO2 and passivation of Ti substrate. An accelerated life test based on those results has been investigated to estimate the OCTA. The polarizing current decreases quickly when the OCTA becomes inactive, and the service life of material is evaluated by the time-to-failure from the start-up.A n u m b e r of the oxide-coated titanium anodes (OCTA) consisting of RuO2 and TiO~ are being used because of durability and low chlorine overvoltage in chlor-alkali cells. But eventually the OCTA becomes inactive and a part of the oxide drops out (arrow in Fig. 1). Low oxygen overvoltage is another problem for this oxide anode in chlorine cells.The OCTA is stable and its chlorine overvoltage is p r e f e r a b l y low in concentrated NaC1 solutions even a t high current densities, whereas it is attacked g r a d u a l l y and the anode potential becomes high in dilute N a C 1 solutions.Since the OCTA has come into the m a r k e t in early 1970's, m a n y articles on its preparation, modification, physico-chemical properties, electrochemical characteristics, and applications have been published. Degradation and deactivation of its unique material have also been discussed. With those articles and patents, degradation of the OCTA in chlor-alkali cells can be classified into three types: (i) coating dissolution, (ii) substrate a t t a c k , and (iii) substrate oxidation leading to electrical insulation, as stated by W a r r e n et al., who have studied the P t -I r alloy coated anodes for chlorate cells (1, 2).Extensive studies on the OCTA as well as the solid Ru metal anodes in sulfuric acid solution and solid p o l y m e r electrolyte have been conducted as a part of new developments in high-performance water electrolysis. Low oxygen overvoltage of those materials is a reason. However, dissolution a n d / o r degradation of the anode material at high potential ranges, and hence at high current densities, is a problem (3).Experiment of the OCTA under the operating conditions of chlorine cells are time-consuming, about one y e a r or more for only one run. Consequently, this paper deals mainly~with an accelerated life test and its procedure for the OCTA. The procedure is simple and requires minimum labor even for a prolonged period. The test specimen of the OCTA is electrolyzed in a mixed solution of HC104 and NaCI or in HC104 single solution under a constant terminal voltage, and the current is recorded until the test specimen breaks down. The concept is based on gradual degradation of the active material due to oxygen evolution. ExperimentsTest specimen.--Titanium sheet of 5 m m wide, about 150 m m long, and 0.5 m m thick was pickled with 10% oxalic acid at about 80~ for about 3 hr, rinsed Fig. I. SEM photograph ot degraded surface of OCTA 1439 ) unless CC License in place (s...

The bubble effects on the resistivity of solution under various conditions of electrolysis was examined with a rectangular cell, in which hydrogen evolution took place from a stainless steel cathode in dilute caustic soda solution. The resistivity of electrolyte containing hydrogen bubbles was a function of the current density, the operating temperature, the flow rate of solution, and the geometry of channel. An experimental equation was obtained.

Formation of the mixed oxide consisting of RuO2 and TiO2 was studied by the DTA/TGA technique and x‐ray diffraction. The coating agent containing RuCl3 and tetra‐n‐butyl titanate converted into the mixed oxide of RuO2 and TiO2 at about 400°C on the Ti substrate, and the reaction was exothermic. The electric resistance through the oxide film depends much on the fire temperature, and an optimum condition arises between 450° and 500°C. The solution composition and the time of preparation are also important factors. The anodic polarization behavior in the normalNaCl solution was also affected by the material or the condition of preparation of the oxide‐coated Ti electrode.

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Correlation of mass transfer with current distribution, for deposition and dissolution of metals, on vertical electrodes, under free convection conditions, is discussed. The equation of mass transfer and the Laplace equation, determining the concentration and potential distributions, respectively, are solved simultaneously. The results explain most features of observed current distributions.