Layer types

Fig. 5. Bipolar transistor (a) schematic and (b) doping profiles of A, arsenic ion implanted into the silicon of the emitter ( -type) B, boron ion implanted into the silicon of the base (p-type) C, antimony ion implanted into the buried layer ( -type) and D, the epi layer...

Man-Made Leathers. These materials contain a nonwoven fabric which is impregnated with a polyurethane to improve fiexibiHty, processibiHty, and conformabiHty (Fig. 9). Advanced man-made leathers contain microfibers as fine as 0.03 tex (0.3 den) or less to imitate coUagen fiber bundles, thereby attaining the soft feel and appearance essential for soft leather use. Polyurethane in the substrate is usually provided with porous stmcture by poromeric technology. The coating layer is also porous in the two-layer type man-made leathers (5—10). 

Clays are composed of extremely fine particles of clay minerals which are layer-type aluminum siUcates containing stmctural hydroxyl groups. In some clays, iron or magnesium substitutes for aluminum in the lattice, and alkahes and alkaline earths may be essential constituents in others. Clays may also contain varying amounts of nonclay minerals such as quart2 [14808-60-7] calcite [13397-26-7] feldspar [68476-25-5] and pyrite [1309-36-0]. Clay particles generally give well-defined x-ray diffraction patterns from which the mineral composition can readily be deterrnined. 

Figure 13.1 Layer-type dezincification on a brass casting. The red layers are uniformly corroded regions. The original yellow of the brass is visible in between.

Layer-type dezincification is easy to recognize visually. The original component shape and dimensions are usually preserved, but the metal color changes from the golden yellow of zinc brass to the red of ele-... 

Flgure 13.2 Layer-type dezincification of a thin brass plate. The 0.019-in. (0.048-cm) plate is shown in cross section. The dezincified layers converge toward the plate edge. Note the porosity of the dezincified metal. 

Figure 13.3 Layer-type dezindfication on the internal surface of a cast brass pipe 90° elbow.

Because wastage is usually slight, identification by visual observation alone is difficult microscopic examination is usually required. Layer-type dealloying commonly occurs. Plug-type denickelification attack has never been observed at this laboratory. Surfaces have a reddish color due to the accumulation of denickelified metal. 

A pump impeller and a shaft bushing from a small cooling water pump assembly were generally corroded. Reddish surface discoloration revealed layer-type dezincification (Figs. 13.14 and 13.15). 

Low-temperature eorrosion eharaeteristieally shows no denuded zone, no intergranular attaek, and a layered type of eorrosion seale. 

Fig. 4.11. Characteristic intensity profiles for three different kinds of concentration (a) bulk type (b) particulate type and (c) thin-layer type. The critical angle d>c is determined by total reflection at the substrate ([4.21], after Ref [4.44]).

Layer tyf)e Company and Catalogue No. pH Layer type Company and Catalogue No. pH... 

In certain alloys and under certain environmental conditions selective removal of one metal (the most electrochemically active) can occur resulting in either localised attack, with the consequent possibility of perforation (plug type), or in a more uniform attack (layer type) that results in a weakening of the strength of the component. Although the selective removal of metals such as Al, Fe, Co, Ni and Cr from their alloys is known, the most prevalent form of de-alloying is the selective removal of zinc from the brasses —a phenomenon that is known as dezincification. 

Dezincification is readily apparent, since the yellow colour of the brass is replaced by the characteristic red of copper, which may take the form of small plugs or of layers that in some cases can extend over the whole of the surface (Fig. 1.60). In plug-type dezincification a mechanically weak, porous residue of copper is produced, which may remain in situ or become removed by the pressure of water, leading to a perforation. In the layer type the transformation of the alloy into a mechanically weak layer of copper results in loss of strength, and failure may occur by splitting when the metal is subjected to water pressure or to external stress. 

With a single-phase brass the whole of the metal in the corroded areas is affected. Dezincification may proceed fairly uniformly over the surface, and this layer type takes much longer to cause perforation than the localised plug type that more often occurs . With a two-phase brass the zinc-rich 8 phase is preferentially attacked as shown in Fig. 4.12. Eventually the a phase may be attacked as well. The zinc corrosion products that accompany dezincification may be swept away, or in some conditions may form voluminous deposits on the surface which may lead to blockages, e.g. in fittings. 

Crystal chemistry ofTa and Nb fluorides - Compounds with layered-type structures... 

A further decrease in the X Me ratio, to 4, leads to linkage of the octahedral units by sharing more than one ligand so as to achieve coordination saturation. Sharing of two vertexes (two comers of the each octahedron) leads to the formation of compounds with layered-type structures. 

Layered-type structure, 92-100 Lewis acidity, 15 Liquid - liquid extraction collective, 276-277 counter-current scheme, 272 equipment, 273 extractants, 279-281 mechanism, 274-276 multistage counter-current, 271 multistage cross-current, 270 one-stage process, 270 principals, 267-269 process performance, 282-283 process schemes, 277,278, selective, 277-278 with 2-octanol, 284-291... 

Figure 10. Projection of of the crystal of lithiophorite, (Li,Al)Mn02(0H)2. along the LUO] direction of the hexagonal cell [58], The connections within the Mn06 and (Li,Al)(OH)6 octahedra layers are emphasized. For a better understanding the O - H bridging bounds between the two layer types are not shown.

Adjustable iris diaphragm 11. Barrier-layer type photocell... 

Many studies have been made of the rates of water evolution from layer-type silicate minerals which contain structural hydroxyl groups (clays and micas). Variations in composition of mineral specimens from different sources hinders comparison of the results of different workers. Furthermore, the small crystallite sizes and poor crystallinity that are features of clays limit and sometimes prevent the collection of ancillary observations (e.g. microscopic examination and diffraction measurements). 

Fig. 14. Compensation plot for dehydroxylation of kaolinite ( ) and other layer-type silicates (X = montmorillonite, illite and muscovite) data and sources given in Table 11. (Redrawn, with permission, from Advances in Catalysis, ref. 36).

AlSCl has an orthorhombic structure, with the lattice constants a - 8.09, b = 10.52, c = 3.86 A, andZ = 4. It is probably isotypic with SbSCl and BiSCl, crystallizing in a layer type of lattice (157) (see Section XII,C,5). The selenide halides are monoclinic, with the probable space-group P2,/m. The lattice constants are given in Table XVII. The constancy of the b parameters for all three compounds suggests the general presence of an Al-Se chain extending in that direction (266). 

The telluride halides crystallize in monoclinic lattices, but only In-TeBr and InTel are isotypic 162). InTeCl forms a layer type of structure, as do InSCl and its analogs, but, owing to the size of the Te atom and the enhanced covalency of the In-Te bond, only a coordination number of 4 for indium is realized. The structure is built up of strongly distorted, InTesraCli/j tetrahedra that share the corners and edges occupied by Te atoms. The Cl atoms are coordinated to one tetrahedron each, and do not take part in the layer formation 324, 325). 

Table 2.1 Summary of some examples of detection after merely heating aluminium oxide layers (Types 150/T or 60/E) after chromatography.

Ca3(BN2)2 is readily formed when (distilled) calcium metal is melted in the presence of (layer-type) boron nitride. This reaction provides some insight on how alkaline-earth metals like calcium may act as a catalyst in the phase transformation of layered a-BN into its cubic modification. Instead of metals, nowadays alkaline-earth (Ca, Sr, Ba) nitridoborates can be used as a flux catalyst in high-pressure and high-temperature transformation reactions to produce cubic boron nitride [15]. 

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