Polishing, electrochemical

The enormous scope of the subject of corrosion follows from the definition which has been adopted in the present work. Corrosion will include all reactions at a metal/environment interface irrespective of whether the reaction is beneficial or detrimental to the metal concerned —no distinction is made between chemical or electropolishing of a metal in an acid and the adventitious deterioration of metal plant by acid attack. It follows, therefore, that a comprehensive work on the subject of corrosion should include an account of batteries, electrorefining, chemical machining, chemical and electrochemical polishing, etc. 

The CPE model has been used152,154,270-274 and it has been found that for electrochemically polished surfaces, the surface roughness is very small compared with mechanically polished surfaces. 

The electrical double-layer structure and fractal geometry of a pc-Ag electrode have been tested by Se vasty an ov et al.272 They found that the geometrical roughness of electrochemically polished pc-Ag electrodes is not very high (/pz 1.5 to 1.25), but the dependence of Chtr curves on cej, as well as on/pz, is remarkable (C, =30 to 80 fi cm-2 if/pz =1.5 to 1.0). 

Khmelevaya and Damaskin621 have studied the electrical doublelayer structure at electrochemically polished pc-Sn. Effs0 = -0.63 V (SCE) (corrected by the asymmetrical type of electrolyte) the applicability of the GCSG theory has been tested and the values of /pz and C 0 have been reported. 

Electrochemically polished and chemically treated Cd(0001), Cd(10T0)t Cd(l 120), Cd(lOTl), and Cd(ll2l) electrodes have been studied by impedance and cychc voltammetry by Lust et al.152 153 249 664 665 a slight variation of capacitance (3 to 6%) has been observed with v. In the case of chemically treated electrodes, a somewhat higher (5 to 10%) dependence of C on v has been explained by the geometric roughness of the electrode surface. 

The value of E for pc-Cd10,637,643 as well as for pc-Zn lies between the Ea= i values of these two groups of planes. <7=0 for a cut Cd(0001)c electrode is in good agreement with that for electrochemically polished Cd(0001). For chemically treated Cd electrodes, a remarkable dependence of min on Cnbf has been observed.249 These results are confirmed by data for other electrodes with a polycrystalline surface structure,10,74 and can... 

D and fractional exponent a (Table 15) show that the surface of electrochemically polished Cd electrodes is flat and free from components of pseudo-capacitance. The somewhat higher values of D for electrochemically polished high-index planes and for chemically treated electrodes indicate that the surface of these electrodes is to some extent geometrically and energetically inhomogeneous. However, the surface of chemically treated Cd electrodes, in comparison with the surface of mechanically polished or mechanically cut electrodes, is relatively... 

Mishuk et a/.675,676 have applied the modified amplitude demodulation method to electrochemically polished pc-Bi in aqueous NaF solution. The curves of the real component of the nonlinear impedance Z" as a function of the electrode potential, unlike pc-Cd and pc-Pb, intersect for various cNaF at E - -0.62 V (SCE),674 i.e., at Ea=0 for pc-Bi, as obtained by impedance.666-672 The different behavior of pc-Bi from pc-Cd and pc-Pb at a > 0 has been explained by the semimetallic nature of pc-Bi electrodes. A comparison of inner-layer nonlinear parameter values for Hg, Cd, and Bi electrodes at a < 0 shows that the electrical double-layer structure at negative charges is independent of the metal.675,676... 

Later, Bi(OlT), Bi(2TT), Bi(001), and Bi(101) faces were stud-ied.28,152 253 254,705 The accuracy of the experimental results has been established by statistical analysis. A very slight variation in capacitance (3-6%) with v (from 60 to 21,000 Hz) was observed for electrochemically polished single-crystal Bi. Therefore, to a first approximation, the measured admittance was identified with the differential capacitance C. 

Adsorption of aliphatic alcohols and tetra-alkylammonium cations from Na2S04 + HjO solutions on Sb electrodes has been investi-gated.721 724 Splitting of the adsorption-desorption peak into two independent maxima has been found725,726 for cyclohexanol adsorption at an electrochemically polished pc-Sb electrode accordingly, the difference between the [Pg.120]

Fe electrodes with electrochemically polished (cathodically pretreated for 1 hr) and renewed surfaces have been investigated in H20 + KF and H20 + Na2S04 by Rybalka et al.721,m by impedance. A diffuse-layer minimum was observed at E = -0.94 V (SCE) in a dilute solution of Na2S04 (Table 19). In dilute KC1 solutions E,njn was shifted 40 to 60 mV toward more negative potentials. The adsorbability of organic compounds (1-pentanol, 1-hexanol, cyclohexanol, diphenylamine) at the Fe electrode was very small, which has been explained in terms of the higher hydro-philicity of Fe compared with Hg and Hg-like metals. 

Formation of a continuous passivating layer is difficult at raised points the degree of passivation is lower, and dissolution will be faster. The overall phenomenon of electrochemical polishing is highly complex, and a variety of factors contribute to the effect of surface leveling. 

Muller (1951, 1956) developed this instrument, which for the first time enabled extensive details of the atomic structure of a solid surface to be seen directly. Figure 1.1 illustrates schematically the basic construction of a FIM. The specimen is prepared in the form of a fine wire or needle, which has been chemically or electrochemically polished to a sharp point with an end radius typically 50-100 nm. It is mounted along the axis of a vacuum chamber, about 50 mm from a phosphor screen (perhaps 75 mm in diameter). The specimen is mounted on an electrical insulator within a cryostat, and it can be raised to a high positive potential (3-30 kV) by means of the leads attached. 

Nitric acid evaporation from liquors of the electrochemical polishing circuit. 

Before introduction into the spectrometer, a mechanical and/or electrochemical polishing of the sample surface has to be performed. While a good empirical knowledge has been gained for most current materials the right procedure to follow in the case of actinide compounds is still not well established. 

The main properties of the double layer of solid lead electrodes have been already described in the Encyclopedia [1]. New achievements in this field have been the subject of reviews [for example [2-6]. Some of the new results relate to impedance of polycrystalline Pb electrodes in aqueous [7-9] and nonaqueous solvents (references in [3, 6[). Special attention has been paid to chemically and electrochemically polished polycrystalline electrodes, mainly in aqueous [10-12] and methanolic [13] fluoride solutions. 

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