Quality anodes

Quality control tests are intended to detect produced materials which deviate from manufacturing specifications, and thus may result in questionable performance. The materials are usually subjected to spectrographic analysis which is the primary quality control check. The exposure tests are necessarily of short duration (hours or days), in which the test conditions attempt to reflect the environment of operation, for example using artificial seawater for a marine application. Since a property that is reproducible and indicative of a consistent quality anode is all that is required, there is no attempt to mirror, except in the crudest fashion, current density profiles. 

Coke is produced when organic matter is heated to 400-600°C, essentially in the absence of air. The organic matter used for anode binder coke has come primarily from coal tar, with minor amounts from petroleum residues. In contrast, filler coke is produced almost entirely from petroleum, with minor amounts from coal-tar pitch. Also in recent years, solvent-refined coal (SRC) filler coke has been found to produce high quality anode carbon. 

Coke for the aluminum industry must be calcined before use to produce quality anode carbon. This calcined coke should be relatively hard, strong, dense, with low electrical resistivity and oxidation sensitivity, high purity, and available in aggregate sizing from -1 inch particles to cover standard anode filler sizing requirements. The desired range of property values is as as given in Table I. 

The coefficient of thermal expansion of calcined shot coke is too high, making it unsuitable for high-quality anode production. 

Alloy 5005 contains about 0.6% Mg and replaces 1050A or 1200 whenever a slight improvement in mechanical properties is required. Anodised (OAB quality, anodic oxidation quality for building) or coil-coated 5005 is very widely used for building applications (external cladding panels, etc.). 

The quality control of galvanic anodes is reduced mainly to the analytical control of the chemical composition of the alloy, to the quality and coating of the support, to an adequate joint between support and anode material, as well as to restricting the weight and size of the anode. The standards in Refs. 6, 7, 22, 27, 31 refer to magnesium and zinc anodes. Corresponding specifications for aluminum anodes do not exist. In addition, the lowest values of the rest potentials are also given [16]. The analytical data represent the minimum requirements, which are usually exceeded. 

Anodes for boilers can be tested by such methods. Good-quality magnesium anodes have a mass loss rate per unit area < 30 g m d", corresponding to a current yield of >18% under galvanostatic anode loading of 50 /xA cm" in 10 M NaCl at 60°C. In 10 M NaCl at 60°C, the potential should not be more positive than t/jj = -0.9 V for the same polarization conditions [27],... 

The safety, availability and capacity of production plants are predetermined by the quality of the materials and the corrosion protection measures in the essential areas both are major considerations in the initial planning. Even today, damage to equipment and tanks is often assumed to be unavoidable and the damaged components are routinely replaced. By carrying out damage analysis, which points the way to knowledge of prevention of damage, the availability and life of plants can be increased considerably. This particularly applies to the use of anodic protection. 

Compared with XPS and AES, the higher surface specificity of SSIMS (1-2 mono-layers compared with 2-8 monolayers) can be useful for more precise determination of the chemistry of an outer surface. Although from details of the 01s spectrum, XPS could give the information that OH and oxide were present on a surface, and from the Cls spectrum that hydrocarbons and carbides were present, only SSIMS could be used to identify the particular hydroxide or hydrocarbons. In the growth of oxide films for different purposes (e.g. passivation or anodization), such information is valuable, because it provides a guide to the quality of the film and the nature of the growth process. 

EPA, 1993. U.S. EPA, Office of Air Quality Planning and Standards, "Chromium Emissions from Chromium Electroplating and Chromic Acid Anodizing Operations Background Information for Proposed Standards," EPA-453[R-93-030a, Research Triangle Park, NC, July 1993. 

Only ihe highest quality MnOs ore can be ti.sed directly for this purpose, and "syniheiic dioxide", usually produced eleetrolytieally by anodic oxidation of rnangane.scdl) sulfaie, is increasingly employed. 

For these reasons alloying elements appear in all the commercial anodes, and very careful quality control is required to keep disadvantageous tramp elements (notably iron and copper) below defined threshold levels. Many anode failures can be attributed to poor production quality control. A guide to minimum quality standards has been produced ... 

Alloying additions are made to improve the performance of an anode material. Of equal importance is the control of the levels of impurity in the final anode, since impurities (notably iron and copper) can adversely affect anode performance. Thus careful quality control of the raw materials used and the manufacturing process adopted is essential to sound anode production. This too is discussed below. 

The constituent elements of anode materials, other than the basis metal, are present whether as a result of being impurities in the raw materials or deliberate alloying additions. The impurity elements can be deleterious to anode performance, thus it is necessary to control the quality of the input materials in order to achieve the required anode performance. Since this will usually have an adverse impact on costs it is often desirable to tolerate a level of impurities and to overcome their action by making alloying additions. Alloying elements may also be added for other reasons which are important to anode production and performance. These matters are discussed in this section. 

Table 10.8 outlines the quality requirements of the basis, or primary, metal for the three generic types of anode. These are the qualities required even when sequestering is also adopted. It will be seen that two grades are listed in the case of aluminium. This is because certain patented formulations permit the lower (99- 8%) grade material providing that the iron and silicon are within the limit given. 

Tests of sacrificial anode materials are generally conducted for three reasons for screening (or ranking), performance information and quality control. 

In electrolytes containing both sulphate and chloride ions, the sulphate ion favours the formation of lead sulphate which is rapidly transformed to lead dioxide. The continuing satisfactory operation of the anode depends upon the initial conditions of polarisation. The lead dioxide is of better quality and more adherent when formed below 108 Am in solutions containing higher sulphate concentrations or when the water is agitated" . 

Since the corrosion resistance of anodic films on aluminium is markedly dependent on the efficacy of sealing (provided the film thickness is adequate for the service conditions), tests for sealing quality are frequently employed as an index of potential resistance to corrosion. While it is admitted that an unequivocal evaluation of corrosion behaviour can only be obtained by protracted field tests in service, accelerated corrosion tests under closely controlled conditions can also provide useful information in a shorter time within the limitations of the particular test environment employed. 

Tests for quality of sealing of anodic coatings have become internationally standardised. They include dye spot tests with prior acid treatment of the surface (ISO 2143 1981 and BS 6161 Part 5 1982), measurement of admittance or impedance (ISO 2931 1983 and BS 6161 Part 6 1984), or measurement of weight loss after acid immersion (ISO 3210 1983 and BS 6161 Part 3 1984, and ISO 2932 1981 and BS 6161 Part 4 1981). Of these the chromic-phosphoric acid immersion test (ISO 3210) has become the generally accepted reference test. 

Qualanod, Specifications for the Quality Sign for Anodic Oxidation Coatings on Wrought Aluminium for Architectural Purposes, Zurich (1983)... 

Architectural Anodising Sulphuric Acid Anodic Film Quality, British Anodising Association (1981)... 

It is now well established that in lithium batteries (including lithium-ion batteries) containing either liquid or polymer electrolytes, the anode is always covered by a passivating layer called the SEI. However, the chemical and electrochemical formation reactions and properties of this layer are as yet not well understood. In this section we discuss the electrode surface and SEI characterizations, film formation reactions (chemical and electrochemical), and other phenomena taking place at the lithium or lithium-alloy anode, and at the Li. C6 anode/electrolyte interface in both liquid and polymer-electrolyte batteries. We focus on the lithium anode but the theoretical considerations are common to all alkali-metal anodes. We address also the initial electrochemical formation steps of the SEI, the role of the solvated-electron rate constant in the selection of SEI-building materials (precursors), and the correlation between SEI properties and battery quality and performance. 

As MTHW and HTHW system temperatures and pressures rise, so the need to provide softened or deionized FW becomes increasingly necessary, although there is not always a clear cut-off point. Where these systems are supplied with higher quality water, traditional, inorganic anodic inhibitor chemistries tend to be replaced by all-polymer, all-organic, or all-volatile chemistries to keep measurable TDS to a... 

In the study by Hetsroni et al. (2006b) the test module was made from a squareshaped silicon substrate 15 x 15 mm, 530 pm thick, and utilized a Pyrex cover, 500 pm thick, which served as both an insulator and a transparent cover through which flow in the micro-channels could be observed. The Pyrex cover was anod-ically bonded to the silicon chip, in order to seal the channels. In the silicon substrate parallel micro-channels were etched, the cross-section of each channel was an isosceles triangle. The main parameters that affect the explosive boiling oscillations (EBO) in an individual channel of the heat sink such as hydraulic diameter, mass flux, and heat flux were studied. During EBO the pressure drop oscillations were always accompanied by wall temperature oscillations. The period of these oscillations was very short and the oscillation amplitude increased with an increase in heat input. This type of oscillation was found to occur at low vapor quality. 

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