Oxide field strength

Two of the many products of ethylene radiolysis—methane and propane—show no or only negligible variation with field strength. Methane is produced by a molecular elimination process, as evidenced by the inability of oxygen or nitric oxide to quench its formation even when these additives are present in 65 mole % concentration (34). Propane is completely eliminated by trace amounts of the above scavengers, suggesting methyl and ethyl radicals as precursors ... 

In summary, a key aspect to the utility of U-series isotopes in the study of arc lavas is that whereas Th and Pa are observed and predicted to behave as relatively immobile high field strength elements (HFSE), Ra and (under oxidizing conditions) U behave like large ion lithophile elements (LILE) and are significantly mobilized in aqueous fluids. Fluid-wedge interaction will only serve to increase these fractionations. Just how robust the experimental partition coefficients are remains to be established by future experiments. 

Inasmuch as the protonation of the oxide can be favored by the direction of the field at the O/S interface (cf. Fig. 1) at equilibrium, the proton current in this direction should decrease exponentially with increasing anodic polarization, as the field strength is decreasing and can even change sign. Conversly, the deprotonation should be favored, becoming the main mechanism of formation of the anhydrous oxide. 

Ionic conduction studies in solids date back to the work of Gunterschultze and Betz,50 who derived the empirical relationship between the electric field strength, E = [(o) " (4>o)jV (cf. Fig. lb), in an oxide and the nonohmic ionic current density, j9... 

The fact is that, on the one hand, a significant field strength, E9 is needed to provide significant current. On the other hand, once in the practical current density range between 0.1 and 10 mA/cm2, a relative insensitivity of the field to the current density is found. In fact, an inverse field of 1.3 to 1.8 nm/V is accepted in the literature as characteristic of the oxide growth, without mention of the current density used. 

However, there are indications that these values depend on the conditions of ionization. Vermilyea88 has interpreted the change from compressive to tensile stress, recorded in the oxide, to be due to the dependence of the transport number of aluminum on the electric field strength. Brown89 has found this transport number to depend on the electrolyte used in anodization. 

Metal Current density (mA/ cm2) Oxide thickness (nm) Electric field strength (V/nm) t+... 

Grain boundary defects are primarily responsible for the operation of zinc oxide (ZnO) varistors, a shortened form of variable resistor. The varistor behaves like an insulator or poor semiconductor at lower electrical field strengths, but at a critical breakdown voltage the resistance decreases enormously and the material behaves like an electrical conductor (Fig. 3.36). When a varistor is connected in parallel with electrical equipment, negligible power flows through it under normal low... 

For galvanostatic anodization a first potential maximum is again observed at about 19 V, and the thickness of the anodic oxide at this maxima has been determined to be about 11 nm, as shown in Fig. 5.4. Note that these values correspond to an electric field strength of about 17 MV cm4. The first maximum may be followed by several more, as shown in Fig. 5.1c and d. Note that these pronounced maxima become smeared out or even disappear for an increase in anodization current density (Fig. 5.Id), a reduction in temperature (Fig. 5.1c), or an increase in electrolyte resistivity. The latter value is usually too large for organic electrolytes to observe any current maxima. A dependence of these maxima on crystal orientation [Le4] or doping kind and density [Pa9] is not observed. The rich structure of the anodization curves is interpreted as transition of the oxide morphology and is discussed in detail in the next section. 

An anodic oxide grown in pure water at 10 pA cm-2 to thicknesses between 4 and 10 nm and subsequently annealed at 700 °C in N2 for 1 hour, showed an interface charge density (1011 eV 1 cnT2) and a dielectric breakdown field strength (11-14 MV cm-1) that are comparable with known values for thermal oxides [Ga2]. While the breakdown field strength of anodic oxides is comparable to thermal... 

Other models are based on electric breakdown of the oxide [Fo2, Chl2]. It is not clear whether this breakdown should be thought of in terms of an electronic or an ionic effect. However, in both cases breakdown may cause a degradation in the oxide morphology, which leads to an enhanced etch rate. An electric field strength in the order of 10 MV cm4, the observation of an electroluminescent burst associated with the current peak of the oscillation, and the presence of an electronic component in the interface current are in favor of this model [CalO, Chl2]. 

It is obvious that the acid-base property of a dissolved oxide may markedly affect the structure of a silicate melt. A dissolved acidic oxide associates the free oxygen, thus displacing reaction 6.4 toward the right, resulting in a marked correlation between the field strength of the dissolved cation and the polymerization constant of the melt. This correlation is shown in the values listed in table 6.2. 

As described in chapter 6, the main factors determining the solubility of a given element in a silicate melt are the Lux-Flood acidity of its oxide and the relative proportions of the cations of different field strengths (cation charge over squared sum of cation plus ligand radii ZIA ) or charge densities (cation charge over ionic radius Z/r). 

---