Etching behavior acidic solution

While the microscopic etch mechanism of ZnO single crystals in alkaline and acid solutions is well understood [109,117], a detailed understanding of the etching behavior of compact polycrystalline films is still not available. In the following we will discuss the relation between etching behavior of... 

The surface segregation of Sr is of particular interest as SrO affects the surface reactivity and the activation behavior of the LSM electrode. Jiang and Love [36] studied the activation behavior of Lao72Sr018Mn03 cathode after treatment of the LSM coating with diluted hydrochloric acid (HC1) solution. The etched solution... 

In contrast to acidic electrolytes, chemical dissolution of a silicon electrode proceeds already at OCP in alkaline electrolytes. For cathodic potentials chemical dissolution competes with cathodic reactions, this commonly leads to a reduced dissolution rate and the formation of a slush layer under certain conditions [Pa2]. For potentials slightly anodic of OCP, electrochemical dissolution accompanies the chemical one and the dissolution rate is thereby enhanced [Pa6]. For anodic potentials above the passivation potential (PP), the formation of an anodic oxide, as in the case of acidic electrolytes, is observed. Such oxides show a much lower dissolution rate in alkaline solutions than the silicon substrate. As a result the electrode surface becomes passivated and the current density decreases to small values that correspond to the oxide etch rate. That the current density peaks at PP in Fig. 3.4 are in fact connected with the growth of a passivating oxide is proved using in situ ellipsometry [Pa2]. Passivation is independent of the type of cation. Organic compounds like hydrazin [Sul], for example, show a behavior similar to inorganic ones, like KOH [Pa8]. Because of the presence of a passivating oxide the current peak at PP is not observed for a reverse potential scan. 

As stated in Sec. 3.1, valuable information on the mechanism of chemical etching processes can similarly be obtained by studying the electrochemical behavior of the interface. In the particular case of GaP, the conclusion that open-circuit etching of GaP single crystals in acidic Br2 solutions proceeds via a chemical mechanism arises from two experimental observations. Firstly, current-potential measurements at p-GaP show that Br2 cannot inject holes into the valence band of GaP, so that elec-... 

The examination of the voltanunetric response at carbon fiber UMEs as a function of miCTOvial volume was undertaken by Clark et al. (89). The experimental volume was varied from about 4 nL to as little as 1 pL. For a 5 pm diameter electrode, the volammograms of ferrocenecarboxylic acid did not vary as a function of sample volume. The shape of the voltammograms was sigmoidal which is expected for disk microelectrodes scanned at slow rates (1-1000 mV/sec) under steady-state conditions (102). The half wave potential measured in the microvials was identical to that of ferrocenecarboxylic acid in bulk solution and the current value also matched the expected value. In addition, Clark et al. performed voltammetry with a 1 pm diameter flame etched carbon fiber electrode in a 1 pL vial however, no deviation from bulk solution behavior was apparent. 

Wedekind f has demonstrated that zirconium sol may be made by etching the metal with hydrochloric acid. A powder is thus obtained that goes into colloidal solution on washing with water. This hydrosol gives very peculiar reactions with electrolytes. Most acids precipitate it, but tartaric and picric acids will not. The hydroxides of the alkali metals precipitate it immediately, but ammonia water does so very slowly. Most neutral electrolytes have little or no effect. It is probable that the treatment with HCl forms a protective colloid which causes the unusual behavior. 

In general, polymers are much more resistant to attack by acidic and alkaline solutions than are metals. For example, hydrofluoric acid (HF) corrodes many metals as well as etch and dissolve glass, so it is stored in plastic bottles. A qualitative comparison of the behavior of various polymers in these solutions is also presented in Tables 17.4 and 17.5. Materials that exhibit outstanding resistance to attack by both solution types include polytetrafluoroethylene (and other fluorocarbons) and polyetheretherketone. 

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