Porosity typical values

Whereas a maximum number of contact points between PVC grains is desired to achieve mechanical stability, this prevents higher porosities. Typical values for porosity are 30 - 35 percent therefore the electrical resistance is rather high, i.e., 170 mQcm2, despite thin 0.3 mm backwebs for top qualities. As mentioned, the range is very wide — even considerably higher electrical resistances are sometimes acceptable, e.g., in areas where cold crank performance is of no significant importance. 

Typical results (Fig. 8.7) show that the distribution moves to smaller values as hydration proceeds. The observed porosity is mainly in the 3 nm to 1 pm range for young pastes, and in the 3-100 nm range for mature pastes. For mature pastes of low w/c ratio, which according to the Powers-Brownyard theory consist entirely of hydration product, nearly all the porosity is below 50 nm (S77). We shall refer to the porosities obtained using mercury at the maximum pressures employed as mercury porosities. Typical values for mature pastes (Fig. 8.5) are somewhat lower than the calculated free water porosities. 

The reduction procedure entails an increase in porosity of the Ni-based anode material, which is well predicted by simple relations [102, 106]. Data on the temperature dependence of the Young s modulus of the common compositions of Ni-YSZ anodes remain scarce, but reported trends are fairly similar [11, 73, 100]. The Young s modulus in oxidised state exhibits a peak related to the antiferromagnetic to paramagnetic transition of NiO, already reflected in the CTE, followed by a decline, though a shift in temperature appears when comparing data between [100] and [11]. Because of the possible differences in porosity, typical values lie in the range of 80-170 GPa (oxidised state) and 30-100 GPa (reduced state). 

The typical value of porosity for a clean, consolidated, and reasonably uniform sand is 20%. The carbonate rocks (limestone and dolomite) normally exhibit lower values, e.g., 6-8%. These are approximate values and do not fit all situations. The principal factors that complicate intergranular porosity magnitudes are uniformity of grain size, degree of cementation, packing of the grains, and particle shape. 

The effective diffusivity is obtained from D, but must also take into account the two features that (1) only a portion of the catalyst particle is permeable, and (2) the diffusion path through the particle is random and tortuous. These are allowed for by the particle voidage or porosity, p, and the tortuosity, rp, respectively. The former must also be measured, and is usually provided by the manufacturer for a commercial catalyst. For a straight cylinder, rp = 1, but for most catalysts, the value lies between 3 and 7 typical values are given by Satterfield. 

It varies with the tightness of the packing and has a typical value of 0.40 to 0.45. Nonporous, or solid-core, solids have only one porosity, of course. 

Some typical values of permeability and porosity for a few materials are shown in Table 10.1. 

The intracrystalline porosity is often taken as the fraction of volume occupied by liquid water evolved on heating and evacuating the zeolite. Typical values are ... 

Total water porosities are obtained experimentally from the loss in weight when a saturated paste is D-dried or subjected to some procedure regarded as equivalent, such as heating to constant weight at 105 "C. Reabsorption of water by materials thus dried gives identical results (D32). The procedures should be carried out under COj-free conditions. A value for the specific volume of the evaporable water must be assumed this has usually been 1.00 X lO m kg . Fig. 8.5 includes typical values thus obtained. 

Subsequent studies have shown that K is not related to the total water porosity but depends on the volume and connectivity of the larger pores. Mehta and Manmohan (M75) and Nyame and Illston (N16) found linear relations between log and estimates of the maximum continuous pore radius, obtained from MIP, and other quantities derived from the pore size distribution and degree of reaction. A high proportion of the flow appears to be through pores wider than about 100 nm. Typical values of log K for mature pastes cured at ordinary temperatures range from around - 13.4 at w c 0.3 to around — 11.8 at w/c 0.7 (M75,N16,G67,M76,H47). K increases with temperature (G67,M76). 

One of the oldest membrane materials used for dialysis is porous cellophane, a thin, transparent sheet made of regenerated cellulose. Typical values of parameters for commercial cellophane membranes are as follows thickness = 80 p.m, porosity = 0.45, tortuosity = 5.0, and pore diameter = 40 A (Seader and Henley, 2006). 

Porous silica gel is used to adsorb propane from helium at 373 K and 1 atm. Typical values of parameters for porous silica gel are as follows porosity = 0.486, tortuosity = 3.35, and pore diameter = 22 A. 

The basic properties of the rock matrix were determined from laboratory tests on intact samples and were provided by JNC (2000). Typical values are effective porosity 0.379 % Young s modulus 61 GPa Poisson s ratio 0.303 coefficient of linear thermal expansion 8.21x 10 °C thermal... 

---