Eg Expansion

The Eq value for a bulk compound varies with the extent of chemical reaction [69, 70]. For example, the Eq for the SiOx varies from 1.12 (Si) to 9.0 (Si02) eV. It is not realistic to fit the measured data perfectly without considering the effect of surface passivation. One should focus on the trends of change and their physical origins. 

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Despite the magnitude difference between the measurements [93] and the theoretical calculations [92, 94, 98], the energetic origin for the width-dependent Eg expansion is under debate. The Eg expansion corresponds to carrier... 

Fig. 34.5 a Bandgap expansion of ice-Vin under compression. Compression induced (a) valence DOS entrapment, and conduction DOS polarization results in b Eg expansion (reprinted with permission from [31])... 

With disk diameters above 5.25 in., all parameters, eg, water absorption and thermal expansion, become more critical which aggravates the expansion or warp of disks. If in the future disk rotation speeds have to be increased significantly to boost data transfer rates, higher demands will be placed on warp (tilt angle) and modulus to avoid creeping (ie, irreversible elongation in radial direction). A survey of the requirement profile for the substrate material of optical disks is given in Table 5 (182,186,187,189). 

Electronic-Grade MMCs. Metal-matrix composites can be tailored to have optimal thermal and physical properties to meet requirements of electronic packaging systems, eg, cotes, substrates, carriers, and housings. A controUed thermal expansion space tmss, ie, one having a high precision dimensional tolerance in space environment, was developed from a carbon fiber (pitch-based)/Al composite. Continuous boron fiber-reinforced aluminum composites made by diffusion bonding have been used as heat sinks in chip carrier multilayer boards. 

Other properties, eg, strength, resistivity, heat capacity, and thermal expansion, are given in the reference (2,4) from which this table is compiled. 

Precise measurements of the dimensional stabiUty of low expansion materials indicate that vitreous siUcas, eg. Corning 7940 and Homosil, display a length change at 25°C of approximately 0.5 parts per biUion (ppb) per day (145). 

Vitreous silica is used for gas-heated or electrically heated devices ia various shapes, eg, as a tube or muffle because of its electrical resistivity, impermeabihty, and low expansion. In its simplest form, an electric-resistance furnace consists of a vitreous siUca tube or pipe on which the resistance element is wound (see Furnaces, ELECTRIC). Because of its iadifference to temperature gradients, a tubular furnace of vitreous siUca maybe made to operate at different temperatures at various portions of the tube, either by arrangement of the heating elements or by cooling sections of the tube with water. Vitreous siUca pipes may be employed ia vacuum-iaduction and gas-fired furnaces (see Vacuum technology) (221). 

Coefficient of Thermal Expansion (GTE). The volumetric thermal expansion (VTE) of manufactured graphite expressed ia equation 1 is anomalously low when compared to that of the graphite single crystal, where wg designates with-grain and eg, cross-grain. 

Impression plasters are manufactured from the finest finishing plasters, selected for color and purity. Setting time accelerators, setting expansion control agents, fillers, flavors, colors, or other special modifying agents may be added, eg, starch, to cause disintegration of the plaster impression when it is boiled. 

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