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Porous skeleton

The red PL band of PS can not only be excited by above bandgap photons, but also by an intense IR (1064 nm) pulse [Di6]. Such a thermostimulated luminescence is known for the case of glasses. This observation was attributed to PS having about 100 times the third-order nonlinear optical susceptibility of bulk Si, as discussed in Section 7.3. Multiphoton excitation of the red PL band by resonant pumping of the vibrational modes of surface groups like Si-O [Di4] or Si-H [Ch8] provided evidence for excitation modes that involve the porous skeleton surface. [Pg.145]

An approximation of the lifetime in PS at RT using an electron-hole pair density equal to one pair per crystallite and the radiative recombination parameter of bulk silicon give values in the order of 10 ms [Ho3]. The estimated radiative lifetime of excitons is strongly size dependent [Sa4, Hi4, Hi8] and increases from fractions of microseconds to milliseconds, corresponding to an increase in diameter from 1 to 3 nm [Hy2, Ta3], as shown in Fig. 7.18. For larger crystallites a recombination via non-radiative channels is expected to dominate. The experimentally observed stretched exponential decay characteristic of the PL is interpreted as a consequence of the randomness of the porous skeleton structure [Sa5]. [Pg.155]

Under certain time and temperature conditions, the homogeneous glass separates into two phases. One of the phases consists substantially of silicon dioxide which is insoluble in mineral acid. The other phase represents a soluble coherent boric acid phase rich in alkali borate. If the boric acid phase is dissolved out of this heterogeneous glass structure with a mineral acid, a porous skeleton of substantially insoluble silicon dioxide is left. The phase separation region occurs between 500°C and 800 C. [Pg.40]

Hence, on the pore level, e can be seen as the ratio of two length scales the characteristic pore scale length rneasrneas(1V ) and the problem related scale L. The balance (10) is quite natural for a porous medium, where meas(Tc) denotes the total surface of the porous skeleton and meas(fl) the total void volume. Assuming the medium being periodic with periodicity e it... [Pg.346]

The scattering intensity is proportional to the square of difference of electron density between the scattering heterogeneities and their surrounding. In porous materials the pores may be assumed as heterogeneities for which electron density differs from that of materials constituting the porous skeleton. There are many porous materials for which power law, I(q)=Io-q (o Iq are constants), is fulfilled in a certain q region. [Pg.658]

Non-dimensional complex B characterizes the ratio of the heat absorbed by the cold fluid and the heat transferred through the porous skeleton due to its thermal conductivity. [Pg.472]

The porous skeleton of activated carbon can be used as a template on which to construct other porous materials, for example, Si02, Ti02 and AI2O3. The oxide is first dissolved in supercritical CO2 (see Section 8.13) and then the activated carbon template is coated in the supercritical fluid. The carbon template is removed by treatment with oxygen plasma or by calcination in air at 870 K, leaving a nano-porous ( nano refers to the scale of the pore size) metal oxide with a macroporous structure that mimics that of the activated carbon template. [Pg.340]

The hypothesis according to which the solid phase of the mixture, that is the porous skeleton, has an ellipsoidal microstructure is made esplicit by... [Pg.536]

In general, higher initial gas pressure (P) favors the properties of the CS ceramics. Indeed, high P allows (i) higher amount of initial nitrogen in porous skeleton (ii) increased infiltration rates and (iii) may lead to the self-compression of the material on the post-combustion stage (see below). [Pg.68]

We treat the problem of coupled diffusion and seepage of a multi-component solution in a saturated porous medium with a deformable porous skeleton. The porosity is assumed to be n as defined by (5.1). [Pg.159]

Using an equation of equilibrium or motion, which determines the deformation of the solid skeleton, and (5.58), a system of differential equations for specifying the mean velocity v (i.e., the conventional consolidation problem) is achieved. Note that in (5.58)

total head excluding the velocity potential), k is the hydraulic conductivity tensor, p is the pore pressure of the fluid, g is the gravity constant, and is the datum potential. Thus by starting with the mass conservation laws for both fluid and solid phases, we can simultaneously obtain the diffusion equation and the seepage equation which includes a term that accounts for the volumetric deformation of the porous skeleton. [Pg.167]

Figure 3.66 shows the scanning electron microscopic images of the surfaces of the reduced A301 catalysts. The porous skeleton structures and the morphology of the catalysts after reductions can be viewed vividly (see Fig. 3.66). The pore skeleton structures of the particles are commonly expressed by three kinds of parameters Porosity, pore volume and pore diameters. Both the pore volume and porosity of iron catalyst after reduction are calculated by the lattice constants measured by XRD before and after the reduction, as seen in Chapter 7. Figure 3.66 shows the scanning electron microscopic images of the surfaces of the reduced A301 catalysts. The porous skeleton structures and the morphology of the catalysts after reductions can be viewed vividly (see Fig. 3.66). The pore skeleton structures of the particles are commonly expressed by three kinds of parameters Porosity, pore volume and pore diameters. Both the pore volume and porosity of iron catalyst after reduction are calculated by the lattice constants measured by XRD before and after the reduction, as seen in Chapter 7.
Fig. 1 shows the small ang e X-ray scattering fisr the three samples investigated. The curves qualitatively tiiow tiiat the micropore characteristics are almost identical for all aerogels investigated while the scattering related to the envelope surface of the particle forming ftie open porous skeleton of the hard carbons clearly varies. [Pg.352]

The activated carbon acts as new porous-skeleton builder to increase the porosity and active surface of the negative active material, and thus facilitates the electrolyte diffusion from surface to inner plate and provides more sites for crys-tallization/dissolution of lead sulfate... [Pg.51]

Figure 8.3 shows transmission electron micrographs of selected regions of the anodic film located near the surface (Fig. 8.3a), within the film (Fig. 8.3b), and adjacent to the alloy/film interface (Fig. 8.3c). The anodic film reveals a porous morphology, with pores confined within alumina cells the barrier layer is evident beneath the pore base together with the scalloped alloy/film interface. The cell and pore diameters are about 30 and 10 nm, respectively, with a barrier layer thickness of 11 nm. Titania nanoparticles are distributed in a thin, outer layer of several tens of nanometres thickness the particles have diameters up to 10 nm. No particles are evident in the porous skeleton of the anodic film. Figure 8.3 shows transmission electron micrographs of selected regions of the anodic film located near the surface (Fig. 8.3a), within the film (Fig. 8.3b), and adjacent to the alloy/film interface (Fig. 8.3c). The anodic film reveals a porous morphology, with pores confined within alumina cells the barrier layer is evident beneath the pore base together with the scalloped alloy/film interface. The cell and pore diameters are about 30 and 10 nm, respectively, with a barrier layer thickness of 11 nm. Titania nanoparticles are distributed in a thin, outer layer of several tens of nanometres thickness the particles have diameters up to 10 nm. No particles are evident in the porous skeleton of the anodic film.

See other pages where Porous skeleton is mentioned: [Pg.29]    [Pg.121]    [Pg.127]    [Pg.128]    [Pg.135]    [Pg.140]    [Pg.995]    [Pg.506]    [Pg.3142]    [Pg.7]    [Pg.31]    [Pg.283]    [Pg.104]    [Pg.3141]    [Pg.445]    [Pg.254]    [Pg.70]    [Pg.290]    [Pg.218]    [Pg.78]    [Pg.3343]    [Pg.587]    [Pg.381]    [Pg.270]    [Pg.949]    [Pg.546]    [Pg.179]    [Pg.385]   
See also in sourсe #XX -- [ Pg.270 ]




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