Boundary regions

In order to obtain appreciable conductivities, semiconductors must be doped witli small amounts of selected impurities. It is possible to switch tire doping type from n to p type, or vice versa, eitlier during tire growtli of a crystal or by tire selective introduction of impurities after tire growtli. The boundary region between tire p type and n type regions is... 

In polycrystalline materials, ion transport within the grain boundary must also be considered. For oxides with close-packed oxygens, the O-ion almost always diffuses much faster in the boundary region than in the bulk. In general, second phases at grain boundaries are less close packed and provide a pathway for more rapid diffusion of ionic species. Thus the simplified picture of bulk ionic conduction is made more complex by these additional effects. 

The obvious application of microfocus Raman spectroscopy is the measurement of individual grains, inclusions, and grain boundary regions in polycrystalline materials. No special surface preparation is needed. Data can be obtained from fresh fracture surfeces, cut and polished surfaces, or natural surfeces. It is also possible to investigate growth zones and phase separated regions if these occur at a scale larger than the 1-2 pm optical focus limitation. 

The carbide precipitation that leads to sensitised grain boundary regions can be minimised by reducing the carbon to 0.03% or less but this increases the cost and reduces the strength. The alternative is to add stabilising elements such as titanium or niobium, which are stronger carbide formers than chromium. There are numerous texts that describe the metallurgy of... 

Electrochemical processes (e.g., electrolysis, electroplating, electromachirring, crrnetrt generation, and corrosion [Plate 8]) are distinguished by their occturence in a boundary region between an electrolyte (liqtrid or solid) and an electrode. The corrrse of these processes is strongly dependent on the potential at the electrode surface, the composition and stmcture of the electrode, the composition of the electrolyte, and the microstmcture of the electrolyte in the boundary layer near the electrode surface. In certain applications, the pore size and coimectivity of the electrode can also be important. 

Submarine hydrothermal fluid end-member data observed at various plate boundary regions (end-member values are those obtained by extrapolation to an assumed value of zero magnesium, except for the values at site 2). BAB back-arc basin (Game, 1995)... 

To evaluate the contribution of the SHG active oriented cation complexes to the ISE potential, the SHG responses were analyzed on the basis of a space-charge model [30,31]. This model, which was proposed to explain the permselectivity behavior of electrically neutral ionophore-based liquid membranes, assumes that a space charge region exists at the membrane boundary the primary function of lipophilic ionophores is to solubilize cations in the boundary region of the membrane, whereas hydrophilic counteranions are excluded from the membrane phase. Theoretical treatments of this model reported so far were essentially based on the assumption of a double-diffuse layer at the organic-aqueous solution interface and used a description of the diffuse double layer based on the classical Gouy-Chapman theory [31,34]. 

This constraint is not exact because the boundary regions can also exchange energy with the interior of the subsystem. However, it may be assumed that the rate of this exchange is much slower than that with the reservoir. This point is addressed further below. 

Within the inverse model catalyst approach, the y/7-V309-Rh(l 11) nanostructures have been used to visualize surface processes in the STM with atomic-level precision [104]. The promoting effect of the V-oxide boundary regions on the oxidation of CO on Rh(l 1 1) has been established by STM and XPS by comparing the reaction on two differently prepared y/7-V309-Rh(l 11) inverse catalyst surfaces, which consist of large and small two-dimensional oxide islands and bare Rh areas in between [105]. A reduction of the V-oxide islands at their perimeter by CO has been observed, which has been suggested to be the reason for the promotion of the CO oxidation near the metal-oxide phase boundary. 

Boundary Region Determination on Tricoordinate Contour Plots... 

The oxidation of the crystalline phase occurs 15 times more slowly than the oxidation of the amorphous phase and is likely localized in the boundary regions. The autoxidation of PE and PP occurs at the rate, which is slower at higher crystallinity of polymers and vice versa, as indicated by the amount of the oxygen consumed. Based on the evidence accumulated, it is safe to say that PE and PP are oxidized in their amorphous regions [12,33,34,42,67],... 

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