Electrode classification

On recharging the battery these half-reactions are inverted, and electrical energy has to be supplied. 

There are many electrode materials, with a great diversity of behaviour. The historical classification5,6 is a first approach, and as it is still referred to it will be described here. Electrode materials, together with the solutions with which they contact, are divided into four categories  

An electrode in contact with a solution of its ions. This can be subdivided into two cases  

In this type of electrode the potential arises from electron transfer between the neutral species and the ion. 

A metallic electrode in contact with a solution containing anions 

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There is vast literature detailing the use of different electrochemical reactors used for metal removal [2, 6]. The main types of electrochemical reactors can be classified first according to the kind of electrode as two or three-dimensional. The second classification considers the movement of the electroactive material with relation to a fixed referential. Thus the electrodes can be classified as static or mobile. Figure 1 shows the major electrode classifications according to geometry and fluid dynamics [1]. 

NOTE Intentional additions of doping oxides other than indicated for a particular electrode classification is prohibited. RGB color values and color samples can be found at the following website http //msdn2.microsoft.com/en-us/library/ms531197.aspx N.A. = Not applicable. 

Bl.l The purpose of this guide is to correlate the electrode classifications with their intended applications so the specification can be used effectively. 

B2.1 The system for identifying the electrode classifications in this specification follows the standard pattern used in other AWS filler metal specifications. The letter E at the beginning of the classification designation stands for electrode. The W indicates that the electrode is primarily tungsten. The F indicates that the electrode is essentially pure tungsten and contains no intentionally added emission enhancing elements. The Ce, La, Th, and Zr indicate that the electrode is doped with oxides of cerium, lanthanum, thorium, or zirconium, respectively. The numeral at the end of some of the classifications indicates a different chemical composition level or product within a specific group. 

A request to establish a new electrode classification must be a written request, and it needs to provide sufficient detail to permit the A5 Committee on Filler Metals and Allied Materials or the Subcommittee to determine whether the new classification or the modification of an existing classification is more appropriate, and whether either is necessary to satisfy the need. In particular, the request needs to include ... 

B6.4 Many electrode classifications contain emissive oxide additions. These additions lower the temperature at which the electrode emits electrons, to a temperature below the melting point of tungsten. Such an electrode operates cooler, or it can operate at higher currents, as can be noted from Table A.2. Benefits of these additions include easier starting, particularly when using superimposed high frequency, more stable operation, and reduced contamination. These benefits are noted in the description listed for the various classifications containing oxide additives. 

B6.5 All tungsten electrodes may be used in a similar manner. However, electrodes of each classification have distinct advantages with respect to other classifications. The following section discusses the specific electrode classifications with regard to their operating characteristics and usability. 

B7.3 EWLa-X Electrode Classifications. The EWLa-X electrodes are tungsten electrodes containing lanthanum oxide, referred to as lanthana. The advantages and operating characteristics of these electrodes are similar to that of the EWCe-2 electrodes. Unlike thoria, lanthana is not a radioactive material. 

B7.4.1 EWTh-1 (WTh 10) Electrode Classification (Yellow). These electrodes were designed for direct current... 

B7.4.2 EWTh-2 (WTh 20) Electrode Classification (Red). The higher thoria content (1.7-2.2 percent) in the EWTh-2 electrode causes the operating characteristic improvements to be more pronounced than in the lower thoria content EWTh-1. 

B7.4.3 (WTh 30) Electrode Classification (Violet). This 3% thoriated electrode has no commercial significance in... 

B7.5.1 EWZr-1 (WZr 3) Electrode Classification (Brown). The EWZr-1 electrode is a tungsten electrode containing about 0.3% zirconium oxide, referred to as zirconia. This electrode is preferred for applications where tungsten contamination of the weld must be minimized. This electrode performs well when used with alternating current, as it retains a balled end during welding and has a high resistance to contamination. 

B7.5.2 EWZr-8 (WZr 8) Electrode Classification (White). This 0.8% zirconiated electrode has no commercial significance in the United States. 

B7.6 EWG Electrode Classification (manufacturer may select any color not already in use). The EWG electrode is a tungsten electrode containing an additive not specified by an existing classification. The purpose of the addition is to affect the nature or characteristics of the arc, as defined by the manufacturer. Although no additive is specified, the manufacturer must identify any specific additions and the nominal quantities added. 

I. Intentional additions of doping oxides other than indicated for a particular electrode classification is prohibited in Table 1. 

The suffixes Al, B3, C2, etc. designate the chemical composition ofthe electrode classification. For determining the chemical composition, DECN (electrode negative) may be used where DC, both polarities, is specified. 

Filler Metals. For welding titanium thicker than about 2.5 mm (0.10 in.) by the GTAW process, a filler metal must be used. Fourteen titanixim and titanium alloy fiUer-metal (or electrode) classifications are given in AWS A5.16 (see Table 2). Five of these are essentially imalloyed ti-tanixim and the remainder are titanium alloy filler metals. Maximums are set on carbon, oxygen, hydrogen, and nitrogen contents. 

Kutner W, Wang J, L Her M, Buck RP (1998) Analytical aspects of chemically modified electrodes classification, critical evaluation and recommendations. Pine Appl Chem 70 1301-1318... 

The identity of the cathode materials is essential for the outcome of CO2 electroreduction. While an earlier electrode classification was based on whether the cathode metal belonged to the sp- or the d-metal group [50], Hori considered that the performance of various metals is loosely related to the periodic table. For aqueous electrolytes, Hori [82,83] suggested regrouping the electrode metals into two categories (1) CO formation metals (Cu, Au, Ag, Zn, Pd, Ga, Ni and Ft) and (2) metals that yield formate (Hg, Pb, Zn, In, Sn, Cd and Tl). As discussed in the previous section, copper represents a very special electrode material, enabling the formation of various hydrocarbons, such as methane and ethylene [82]. 

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