Showing papers in "Journal of The Electrochemical Society in 1957"

Electrochemical Polarization I . A Theoretical Analysis of the Shape of Polarization Curves

Abstract: At low overvoltage values, deviations from Tafel behavior for a noncorroding electrode are due primarily to the reverse reaction of the oxidation‐reduction system, and at high overvoltages to concentration and/or resistance polarization. It is shown further that the practice of placing straight lines through a few experimental points is extremely hazardous, while the indiscriminate introduction of "breaks" is contrary to the electrode kinetics described.Further complexities arising from a corroding electrode are described. In this instance, the forward and reverse reactions of both of the oxidation‐reduction systems forming the corrosion couple must be considered. This representation of the local polarization diagram of a corroding metal is more fundamental than that used previously in the literature, and thus provides a clearer picture of the various factors which affect the corrosion rate and the shape of polarization curves.A region of linear dependence of potential on applied current is described for a corroding electrode by treating it in a manner analogous to that for a noncorroding electrode. An equation is derived relating the slope of this linear region to the corrosion rate and Tafel slopes. This relation provides an important new experimental approach to the study of the electrochemistry of corroding metals since, in some instances, interfering reactions prevent determination of Tafel slopes at higher current densities.

Vacuum Deposition of Thin Films

Abstract: Vacuum deposition of thin films , Vacuum deposition of thin films , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Measurements on Galvanic Cells Involving Solid Electrolytes

Abstract: Electromotive force measurements on galvanic cells involving solid electrolytes have been made in order to obtain the standard molar free energy of formation of , , , , , , and several phases of the system Ag‐Te at elevated temperatures.

Hydrogen Evolution Reaction on Copper, Gold, Molybdenum, Palladium, Rhodium, and Iron Mechanism and Measurement Technique under High Purity Conditions

Abstract: Various aspects of technique in measurements of electrode kinetics under conditions where competing reactions due to the presence of trace impurities in the solution are important are examined.The kinetics of the hydrogen evolution reaction in acid and alkaline solutions on several transition metals has been examined with special reference to the low current density region. Inferences concerning the rate ‐determining step in the reactive are thus drawn. In general, there is a tendency for the metals examined in acid solution to have a rate‐controlling electrochemical desorption reaction and for those in alkaline solution to have a rate ‐determining discharge step.

Surface Protection and Selective Masking during Diffusion in Silicon

Abstract: An apparatus is described for the vapor‐solid diffusion of donors and acceptors into silicon at atmospheric pressure. It consists essentially of a fused silica tube extending through one or more controlled temperature zones. A gas such as nitrogen carries the vapors from the heated impurity element or one of its compounds past the heated silicon.At temperatures above about 1000 °C, gases such as helium or nitrogen are shown to cause serious pitting or erosion of the silicon surfaces. A thin vitreous silicon dioxide envelope enclosing the silicon during the high temperature heating operation is shown to provide complete protection of the underlying surface against damage. Methods of obtaining surface passivation are described.In addition to surface protection, a silicon dioxide surface layer also is shown to provide a selective mask against the diffusion into silicon of some donors and acceptors at elevated temperatures. Data are presented showing the masking effectiveness of the silicon dioxide layer against the diffusion of several donors and acceptors into silicon.The application of the masking technique to produce precise surface patterns of both n‐ and p‐type is described. An example of its feasibility in device considerations is illustrated by the construction of a transistor by double diffusion. This transistor is unique in that both the emitter and base contacts are made at the surface in adjacent areas.Finally a new predeposition technique is described for controlling the impurity levels in diffused layers over wide ranges. Data are presented to illustrate this technique.

Galvanic Cells for the Determination of the Standard Molar Free Energy of Formation of Metal Halides, Oxides, and Sulfides at Elevated Temperatures

Abstract: The use of electromotive force measurements on galvanic cells for the determination of standard molar free energies of formation of halides, oxides, sulfides, and other compounds at elevated temperatures is surveyed. New potentialities and inherent limitations are shown. Formulas for the estimate of errors resulting from electronic conduction and from transference of the components of electrolytes between different activity levels are derived.

Structure of Chemically Deposited Nickel

Abstract: An analysis was made of the structure of the Ni deposit produced by the catalytic Ni reduction process. X‐ray and electron diffraction revealed that the Ni deposit was an amorphous solid. The structure appeared to be unrelated to and independent of the nature of the substrate and thickness of the deposit.Metallographic examination revealed a dense material, free of voids, and perfect conformity to the substrate surface profile. Etching produced a lamellar structure, the variation in etching intensity being interpreted as variations in dissolved P. In platings, the lamellae lay parallel to the plane of the substrate. Growth faults were observed traversing the thickness dimension from substrate surface irregularities. The amorphous structure reverted to a crystalline phase mixture of Ni and at low temperatures with a large heat evolution.

Preparation of Pure Fused Lithium Chloride‐Potassium Chloride Eutectic Solvent

Abstract: Hydro ly t i c decomposi t ion occurs dur ing the fusion of a eutectic mix tu re of l i th ium chlor ide-potass ium chlor ide conta in ing t races of mois ture if the fusion condit ions are not controlled. The resu l tan t contaminat ion by h y d r o x y l ion g rea t ly lowers the u t i l i ty of this mix tu re as a fused salt solvent. The effectiveness of var ious procedures used for p repa ra t ion of the fused sal t solvent was fol lowed by observat ion of the character is t ic po larographic res idual cur ren t using a p l a t inum microelectrode. A p repa ra t ive method is descr ibed which involves d ry ing the mix tu re under modera te vacuum, fusion under anhydrous hydrogen chloride, and remova l of the hydrogen chloride f rom the melt . F o r the in i t i a l w o r k of a l o n g t e r m g e n e r a l i n v e s t i g a t i o n in fused sa l t e l e c t r o c h e m i s t r y , a eu tec t i c m i x t u r e of LiC1-KC1 w a s se l ec t ed as t h e fused sa l t so lvent . A d v a n t a g e o u s c h a r a c t e r i s t i c s of th is solven t a r e good t h e r m a l s t ab i l i t y , w ide span of e l e c t ro ly t i c decompos i t i on po ten t i a l , absence of s t r o n g l y ac id ic or bas ic p rope r t i e s , h igh c o n d u c t i v i t y and f luidi ty , and c o m m e r c i a l a v a i l a b i l i t y of i ts componen t s as t he r e a g e n t g r a d e sal ts . F u r t h e r , the m e l t i n g po in t is low enough and i ts c h e m i c a l r e a c t i v i t y is such t h a t P y r e x glass can be u t i l i zed as a m a t e r i a l of cons t ruc t ion . The p r o p e r t i e s of t h e so lven t t hus pe rmi t , in theory , a s t u d y of t he e l ec t r o c h e m i s t r y of a w ide v a r i e t y of so lu tes w i t h a m i n i m u m of i n t e r f e r e n c e f r o m so lven t effects a n d w i t h on ly m o d e r a t e e x p e r i m e n t a l d i f f icul ty as h igh t e m p e r a t u r e w o r k goes. In p rac t ice , t h e p o t e n t i a l i t y of these d e s i r a b l e so l ven t p r o p e r t i e s , p a r t i c u l a r l y the w ide d e c o m p o s i t ion p o t e n t i a l span, is l i m i t e d b y the p u r i t y of t he fused so lven t w h i c h can be p r e p a r e d . The mos t t r o u b l e s o m e aspec t of p r e p a r i n g a p u r e LiC1-KC1 eu tec t ic fus ion ar i ses f r o m the h i g h l y de l i quescen t p r o p e r t y of the LiC1. Unless spec ia l p r e c a u t i o n s a r e t aken , h y d r o l y t i c decompos i t i on occurs as the t e m p e r a t u r e is r a i s e d and HC1 is los t f r om the sys tem. C o n c u r r e n t l y , the m e l t becomes c o n t a m i n a t e d w i t h a l k a l i n e p roduc t s . Va r ious m e t h o d s h a v e been p r o p o s e d and used to p r e v e n t h y d r o l y t i c decompos i t i on d u r i n g the p r e p a r a t i o n of a n h y d r o u s ch lor ides . The h e a t i n g of h y d r a t e d r a r e e a r t h ch lo r ides w i t h gross a m o u n t s of NH,C1 is one c lass ic me thod . F o r the p r e p a r a t i o n of fused LiC1-KC1 m i x t u r e s con ta in ing p o t a s s i u m h e x a c h l o r o m o l y b d a t e , t he m e t h o d of h e a t i n g the sa l t m i x t u r e to fus ion in a s t r e a m of d ry , i n e r t gas fo l l owed by an e l ec t ro lys i s of t he m e l t for r e m o v a l of o x y g e n as m o l y b d e n u m ox ides a t t he c a thode and b y v o l a t i l i z a t i o n of m o l y b d e n u m o x y c h l o r i d e s has been used (1) . A n o t h e r p r o c e d u r e invo lves d r y i n g the LiC1 and the KC1 s e p a r a t e l y b y f irst s l o w l y h e a t i n g the sa l t s to b e t w e e n 480 ~ and 500~ u n d e r h igh v a c u u m (10 -~ to less t h a n 104 m m H g ) , t hen m i x i n g the d r i e d sa l t s t o g e t h e r u n d e r a c on t ro l l ed a t m o s p h e r e in a d r y box, and f ina l ly fus ing the d r y m i x t u r e u n d e r h igh v a c u u m (2, 3) . The m e t h o d to be d e s c r i b e d h e r e invo lves d r y i n g the eu tec t ic m i x t u r e u n d e r m o d e r a t e va c uum, fus ing the m i x t u r e u n d e r a n h y d r o u s HC1 at a t m o s p h e r i c p re s su re , and t hen r e m o v i n g the excess HC1 f r o m the fused solvent . Experimental Procedure The a p p a r a t u s used in th i s w o r k inc ludes t h e fo l l owing : F u r n a c e : C e n c o C o o l e y No. 13627, 115 V, 700 W, C e n t r a l Scient i f ic C o m p a n y , Chicago. A s e p a r a t e h e a t i n g c i rcu i t e q u i v a l e n t to 25% of the o r i g i n a l f u r n a c e h e a t i n g c a p a c i t y was i n s t a l l e d in t he bo t t om of t he f u r n a c e cav i ty . O n l y th is a u x i l i a r y c i r cu i t was o p e r a t e d b y t h e f u r n a c e con t ro l l e r . Con t ro l l e r : Whee lco I n d i c a t i n g C o n t r o l l e r Mode l 241-P, B a r b e r C o l e m a n C o m p a n y , Rockford , I l l inois . V a c u u m P u m p : Cenco " P re s sova c , " C e n t r a l Sc ien tific C o m p a n y , Chicago. Chemica l s : T a n k gases of t he M a t h e s o n C o m p a n y ,

Anodic Formation of Oxide Films on Silicon

Abstract: Dense oxide films have been formed anodically on p‐ and n‐type single‐crystal Si in connection with the electrical properties of Si surfaces. Concentrated or permit forming, but the highest voltage obtainable is less than 200 v. A solution of in N‐methylacetamide permits forming to 560 v, and is also preferable in other respects.The field during forming is of the order corresponding to a thickness increment of about 3.8Aa/v. The ratio has been found as well from interference colors and direct weighing, as by capacitance measurements. Above an oxide thickness of 400Aa the rate‐limiting step for film growth is inside the oxide.The ionic current efficiency of film growth is very low. In methylacetamide it can be increased by addition, for example, of chloride ions or more so by fluoride ions. The oxide is an electrolytic rectifier and behaves similar to an oxide on Al or Ta. The direction of easy flow for electrons is from the Si to the electrolyte.

Electrochemical Polarization II . Ferrous‐Ferric Electrode Kinetics on Stainless Steel

Abstract: The oxidation‐reduction kinetics of the ferrous‐ferric sulfate system have been measured on a stainless steel surface. The data completely support theoretical equations which describe the potential‐current relationships for such a system. The analysis applies to reversible electrodes and to corroding electrodes where the potential is determined by two intersecting activation over‐ voltage functions. Also, the analysis permits calculation of a number of electrochemical constants with a minimum number of experimental observations. The possibility of determining anode‐to‐cathode area ratios for corroding metals is discussed.

Corrosion Inhibition by Organic Amines

Abstract: The corrosion of pure iron in 1N HC1 is discussed in terms of the theory of mxed potentials and the theory is applied to inhibition by organic compounds Corrosion rates with and without inhibition by aniline, several aniline derivatives, and alkylamines were determned by cathodic polarization measurements as well as by colorimetric analysis of the solution It is shown that all compounds show a maximum inhibitor efficiency at a concentration of approxdmately 01 mole/1, that with one exception all are cathodic as well as anodic inhibitors, and that in most cases they are predominantly anodic inhibitors An interpretation of the data on cathodic inhibition is suggested on the basis of the assumption of a uniform metal surface and uniform adsorption The interpretation of anodic inhibition is found to be difficult due to a lack of satisfactory experimental data (auth)

The Kinetics and Mechanism of Formation of Anode Films on Single‐Crystal InSb

Abstract: Studies of the kinetics-of-form ation and composition of anode films on several crystal faces of indium antimonide are reported. A marked dependence of oxidation rate on crystal face is observed at low fields, the (111) and (332) faces oxidizing at more than ten times the rate of the (110) and (hl) and (332) faces. At high fields all faces oxidize at the same rate. Data are interpreted in terms of the detailed structure of InSb and the theories of Cabrera and Mort and of Dewald. With one major exception, the composition effects, the data may be qualitatively understood in terms of these theories.

Electrodeposition of Metals from Organic Solutions V . Electrodeposition of Magnesium and Magnesium Alloys

Abstract: The electrodeposition of Mg from ether solutions of such Mg compounds as (a) halides, (b) aluminohydrides, (c) borohydrides, and (d) Grignard reagents was investigated. White, metallic deposits containing 90% Mg and 10% B were obtained from an ether solution of and . However, thick deposits could not be built up. An alloy (7% Mg, 93% Al) was obtained from a bath containing , , and . Electrodeposited alloys of Zr, Ti, or Be with Mg, obtained from hydride or borohydride baths, were stressed, treed, or powdery. The preparation and solubilities of some of the solutes are given.

Potential‐pH Diagram of the Antimony‐Water System Its Applications to Properties of the Metal, Its Compounds, Its Corrosion, and Antimony Electrodes

Abstract: Using methods and conventions described previously together with the available thermodynamic and electrochemical data, equations have been formulated and represented as a potential-pH equilibrium diagram of the antimony-water system for 25 °C. Other diagrams are presented for the domains of solubility, predominance of ions, and for corrosion. The reason for the observed resistance of antimony coatings to hydrochloric and hydrofluoric acids is made clear. Applications are made to the antimony electrodes. The free energies of formation of the antimonate, Sb(OH)6-,, and the Sb02+ ion have been calculated and are given. © 1957, The Electrochemical Society, Inc. All rights reserved.

Some Unusual Effects of Hydrogen in Corrosion Reactions

Abstract: Consideration of corrosion in the presence of water has led to the postulation of damage by hydrogen produced in the reaction. For cases where the metal surface is covered with a protective layer, it is considered that some hydrogen ions diffuse through the layer and form hydrogen atoms beneath it. The consequence of the production of hydrogen in this location is to decrease corrosion resistance. Three types of harmful effects are illustrated.