Pore alkali content

Compared with cathodic blisters, which can be recognized by their alkali content, anodic blisters can be easily overlooked. Intact blisters can be recognized by the slightly lower pH value of the hydrolyzed corrosion product. The pitted surface at a damaged blister cannot be distinguished from that formed at pores. 

This type of flood can be successful only if, as the fluid moves through the reservoir, a sufficient amount of the alkali remains in solution to react with the oil. Reaction of the flood with minerals and fluid in the reservoir, however, can consume the flood s alkali content. Worse, the reactions may precipitate minerals in the formation s pore space, decreasing permeability near the wellbore where free flow is most critical. A special problem for this type of flood is the reaction of clay minerals to form zeolites (Sydansk, 1982). 

Zone two can be defined by the absence of montmorillonite and by the tie-line mica-opal (Figure 37). Zone one, which contains montmorillonite shows the coexistence of feldspar and montmorillonite (Figure 37a). Trona and halite found in the sediments are considered to indicate higher alkalinity and alkali content of the pore fluids that effected the crystallization of the feldspar "facies" in zone two at the lake center. Here the evaporated fluids became more concentrated. 

The specific surface area and pore volume of the catalyst support was determined by nitrogen adsorption using a Sorptomatic 1900 (Carlo Erba Instruments). Increase in the calcination temperature fi-om 973 to 1173 K resulted in a decreased surface area fi-om 184 to 81 m /g (Figure 2). The pore volume was also decreased fi-om 0.41 to 0.18 mVg. The support sintering was studied by subjecting the support prepared at 1173 K to steam (12 vol% water in nitrogen) at 1073 K for 8 h. The N2-physisorption data indicated that the water vapor treatment resulted in a decrease of the BET specific surface area of ca. 9% as well as in closure of the pores smaller than 5 nm in diameter. The alkali content of the silica is probably the main contributor to the loss of surface during the hydrothermal treatment [6]. 

Alkali content in the pore liquid of concrete. Use of concrete with a low effective alkali content wiU prevent deleterious ASR. Figure 3.5 shows how the expansive effect induced by the reaction between alkaHs and aggregate with chalcedony will be neghgible if the equivalent content of Na20 in concrete is less than 3 kg/m Theoretically the alkali content in concrete may derive also from external sources, as in marine structures or in bridges where de-icing salts are employed. However, the penetration of alkalis into concrete is relatively slow (slower than diffusion of chloride ions) and in most practical cases, external alkahs do not contri-... 

Since the pH of the concrete pore solution may vary in the interval where remarkable changes in the behaviour of zinc occur (Section 2.1.1), the behaviour of galvanized steel may be influenced by the composition of the concrete and, especially by the cement type and its alkali content. In practice, however, the pH of the pore solution in concrete usually is below 13.3 during the first hours after mixing, due to the presence of sulfate ions from the gypsum added to the Portland cement as a set regulator. A protective layer thus can be formed on galvanized bars. 

Concerning the SRA influence, the higher surface area of cement Se may have the opposite effect on hydration, once higher amount of SRA is potentially adsorbed onto cement particles. The higher delay in initial setting time of paste with cement Se suggests that this characteristic is important. However the interaction between cement fineness and SRA behavior should be better evaluated. The alkali content on pore solution may also have a role in the initial reactions of the cement [8], but, based in the initial setting times of reference pastes, their influence does not seem to be mandatory. 

The alkali limiting criterion, for example 0.6% Na O in cement, is linked with the aim to reduce the concentration of sodium and potassium ions in the concrete pore solutiou Simultaneously, these ions cause a substantial decrease of Ca(OH)2 concentration in the capillary solution. Some doubts arouse as the calculation of alkali content in the form of sodium equivalent is concerned hence it is known that the potassimn silicate gel reveals lower expansion that the sodium silicate. 

There are generally more alkalis in fly ash than in Portland cement. Most of these alkalis occur in the vitreous phase and hence only a part is water soluble, usually about 0.1% Na20g [60]. On the other side one should remember that the glass is the most reactive component of fly ash in cement paste. It is not clear what part participate in the pozzolanic reaction and what is released to the pore solution. However, there is a dominant opinion that the release of alkalis to the solution from fly ash occurs slowly and hence they cannot participate in the reaction with aggregates [60]. Therefore Hobbs [110] proposes to take only 0.2% Na20 as an income of alkalis from fly ash, when the total alkalis content in concrete is calculated. However, better effect are showing fly ash with low alkalis and CaO content [60, 121]. 

As it has been shown by Roy [80] the alkahs content in the pore solution of cement paste was significantly lower at 50% slag addition (Fig. 6.35). It should be tmderlined that this phenomenon is observed irrespectively of the alkali content in mineral additions, which can be higher than in cement. Similarly, the sodium and potassirrm content decrease in pore solution occirrs in case of fly ash cement paste [115]. The effect of fly ash is, however, not clear, because in some cases Diamond [129], as well as Glasser and Marr [130], observed the increase of these ions concentration in the liquid phase of cement paste. However, these authors are of the opinion that silica firme arrd, after longer period of time, fly ash, reduce the sodium and potassium soluble corttpotmd content [129, 130]. 

Fig. 6.35 Alkali content in the pore solution of cement paste, 50% of slag addition, (according to [80]) 1—cement with 65 % of slag addition 0.97 % Na O in clinker, 3 eement without slag, 0.97 % NajO, in clinker 1,4 cement with 5 % of slag addition, 0.97 % Na O. in clinker 7 slag as in 1, 5—cement without slag, 1.47 % Na O. in cUnker, 6 cement with 50 % of slag, slag as in 1, clinker as in 5, 7—cement with 50 % of two slags (35 % as in 7,15 % of the seeond), elinker as in 7...

Mordenite in the H-form displays a product mixture similar to the equilibrium level. Great increase in selectivity for dimethylamine can be achieved by careful adjustment of the alkali content of the mordenite, i.e. by narrowing the pore diameter [48]. Bob Shannon from Dupont [49, 50] could show us that on narrow pore zeolites such as HRHO and HZK-5 only 13 % and 11 % TMA are formed. The selectivity for dimethyl.amine rises to over 60 %. K. Segawa and co-workers have recently found [51] that, surprisingly, on a Na-mordenite treated with SiCl, the TMA content can be lowered below 0,5 %. The selectivity for DMA is 73 %. However this catalyst in the H-form does not show this drastic effect. 

Nixon, P. J. et al. (1986) The effect of pfa with a high total alkali content on pore solution composition and alkali silica reaction. Magazine of Concrete Research 38,30-35. 

The surface area, pore volume, and pore size distributions of supports and catalysts were determined using a Micromeritics ASAP 2000 unit. Scanning electron microscopy (Zeiss DSM 940) was used for characterization of the whiskers-covered surface and washcoated samples. The thicknesses of the washcoats on flat samples were determined by an electro-magnetic method (Fischer Deltascope MP 3). The alkali content of the prepared supports was... 

Washcoats with varying pore size distributions were prepared from the different colloidal sols. Sols with larger particles (See Table 1) yield silica with large pores and lower surface area, as is shown in Figure 3 and Table 3. The surface areas of the washcoats varied between 60 and 143 m /g. On the other hand, the pore volume did not vary more than 15 % between the different samples. This allowed us to study the influence of the surface on the catalytic performance, without much disturbance from variations in porosity. It was calculated from the alkali contents of the samples that the washing procedure removed approximately 70 % of the sodium and 70 - 80 % of the potassium from the washcoat. 

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