Monosulfate phase

Alkali aluminate (5-calcium disilicate monosulfate), phase in Portland cement clinker, 5 472t Alkali aluminate (8-calcium disodium trialuminate), phase in Portland cement clinker, 5 472t Alkali belite, phase in Portland cement clinker, 5 472t Alkali blue toners, 14 318 Alkali borate glasses, 12 572, 573, 584 Alkali catalysed pad-dry-bake procedure, 9 485... 

Calcium cyanamid process, for ammonia synthesis, 11 114, 115 Calcium cyanide, 8 194-197 Calcium cyanide diammoniate, 8 195 Calcium dichromate, molecular formula, properties, and uses, 6 561t 5-Calcium disilicate monosulfate, phase in Portland cement clinker, 5 472t 5-Calcium disilicate monocarbonate, phase in Portland cement clinker, 5 472t Calcium disilicide, 4 530 8-Calcium disodium trialuminate, phase in Portland cement clinker, 5 472t Calcium doping, 23 842-844 Calcium P-alumina, 2 406t Calcium ethylenediaminetetraacetate, 7 596t... 

In the conduction calorimetric curves of the aluminate-gypsum system,the first stage is characterized by a peak at 30 minutes for the formation of ettringite. In the second stage, the peak occurs at 24-48 hours when the monosulfate phase forms by the reaction between ettringite and aluminate. 

The reactions in the regulated-set cements containing Cjj A3CF2 (note mixed notation) as a principal phase resemble those in ordinary Portiand cements. Initial reaction rates are controlled by ettringite formation. Setting occurs with formation of the monosulfate, along with some transitory lower-limed calcium aluminate hydrates that convert to the monosulfate within a few hours. 

In this final peak, the remaining tricalcium aluminate reacts with both gypsum and water to form ettringite and subsequently the tricalcium aluminate monosulfate. C3A hydrates formed are of varying composition but eventually form the stable cubic phase C3AH6 in solid solution with the tricalcium aluminate monosulfate. 

The most widely used single component, calcium sulfoaluminate admixture, is composed of 30% CAS, 50% CaSO and 20% CaO with small amounts of glassy phase. Particle s3ize is coarser than that of Portland cement. Larger particle size ensures that the potential expansion due to hydration is extended over a period of time. Chemical and physical properties of the most widely used proprietary product, Denka CSA, are given in Table 6.10 [74], Other CSAs include mixtures of C ASH and 2 CS (monosulfate and gypsum) and mixtures of Type I cement, liigh-aiumina cement, CaSO, 2H O, Ca(OH) and CaO [75], 4 2... 

Final phase in the solidification ettringite reacts with tricalcium aluminate forming monosulfate"... 

From the results the tendency of ettringite formation can be observed in those samples that do not have latex. In fact, this phase showed a significant reduction in peak intensity, possibly indicating that the latex inhibits its formation due to reduction of sulfate/aluminate ratio (Figures 6 and 7). Ettringite is a phase that does not remain in the concrete at ages over 28 days with time it gradually incorporates hydrated monosulfate [18]. 

If calcium sulfate is interground with alinite clinker, an AFt phase may be also formed. It converts to monosulfate in the latter course of hydration. 

In the presence of calcium sulfate, ettringite—in addition to the C-S-H phase—is the main hydration product formed. At lower CaSO additions the primary formed ettringite may partially or completely convert to monosulfate in the later course of hydration. 

If mixed with water, the existing calcium hydroxide, or that formed in the hydration of added lime, dissolves in the liquid phase and reacts with the glass phase of the ash. An amorphous C-S-(A)-H phase is formed as the product of reaction, which—at appropriate water/solid ratios of the starting mix—causes setting and hardening of the system. Limited amounts of ettringite (AFt) and monosulfate (AFm) may also be formed in the reaction, if sulfate ions are present in the ash. 

The setting and hardening of lime-fly ash pastes may be accelerated by adding appropriate activators to the system (Shi, 19%) an addition of Na SO raises the alkalinity of the liquid phase, which accelerates the formation of the C-SKA)-H phase. In addition, ettringite may also be formed. As a result of both effects the strength development is accelerated and the nltimate strength is increased. In the preserKe of CaCl2 a solid solntion of calcium aluminate monosulfate hydrate... 

At lower SO3 contents in the blend, monosulfate may also be formed, or the primary formed ettringite may convert to this phase ... 

The effectiveness of different fly ashes as additives preventing sulfate-induced expansion can vary greatly. When the mineral composition of the fly ash is such that the formation of ettringite occurs before exposure to sulfate solution, the blended cement performs well. However, if at the time of exposure to sulfates phases vulnerable to sulfate attack (such as monosulfate) are present, the sulfate resistance of the binder is poor (Mehta 1986, 1992). It has also been reported that at lower replacement levels (10% and 20%) class F fly ashes perform better than class C ashes (Soroushian and Alhozaimi, 1992). 

The response of blended cements to sulfate attack may be distinctly improved by a caibonation of the surface of the material prior to exposure to sulfates (Sersale et al 1997). Improved resistance may also be achieved by adding finely dispersed calcium carbonate to the original mix. In its presence monocalcium caiboaluminate (C3A.CC.Hj2) is formed instead of monosulfate, and this phase does not convert to ettringite in the course of sulfate attack (Piasta et al, 1997). 

The mechanism of the sulfate attack on Portland-slag cement is broadly similar to that observed in pure Portland cement pastes. In an attack by alkali sulfates the dominant reactions are the partial decalcification of the C-S-H phase and the conversion of the existing monosulfate to ettringite. The amount of ettringite formed is lower than in the case of Portland cement, as monosulfate is the only phase that can serve as a direct source for ettringite formation, whereas neither Al incorporated in the C-S-H phase nor that present in hydrotalcite are available for such a reaction, jnst like Al in ettringite already formed independently of snUate attack (Gollop and Taylor, 1992-1996). 

Anionic alkylglucoside chiral surfactants, such as dodecyl (3-D-glucopyranoside monophosphate and monosulfate, and sodium hexadecyl D-glucopyranoside 6-hydrogen sulfate, were used as chiral pseudostationary phases in MEKC, where several enantiomers (e.g., PTH-dl-AAs and binaphthol) were resolved. 

In an excellent study, White and Catterick [1033] characterized and analyzed 40 acidic dyes according to their composition, shape, and retention on a PLRP-S column (photodiode array detector, A = 190-600 nm). A 50/50 acetonitrile/water (0.7 g/L citric acid with 3.4 g/L tetrabutylammonium hydrogen sulfate adjusted to pH 9.0 with ammonia) mobile phase was used. Five classes of dyes were included in the study phenyl-N=N-monosulfonated naphthols, naphthyl-N=N-naphthols, phenyl-N=N-p-hydroxyIated nt hthyls, monosulfated phenyl-N=N-naphthols, and phenyl-N=N-disulfonated naphthols. Tables were generated in which the relative retention times, relative ahsoihances (vs. 500nm) for 250-450 nm (50 nm intervals), and UV maximum absorbances were listed. Fran positional/spatial arguments and data presented in the study, information about the chemical structure of an analyte could be determined with as little as 100 ng of sample. Structures were presented for all compounds. 

If the sulfate concentration in the soluhon decreases, ettringite will become unstable and transform to monosulfate, a member of the AFm phases (AI2O3-Fe203 monosulfate) according to ... 

For example. Union Carbide claimed the addition of water to the final reaction mixture in Af-methylpyrrolidone (NMP) [28]. Under these conditions, phase separation took place and the Rh(TPPMS) (TPPMS = triphenylphosphine monosulfate) catalyst was completely transferred into the aqueous phase. 

In a mature hydrated portland cement, the products formed are C-S-H gel, Ca(OH)2, ettringite (AFt phase), monosulfate (AFm phase), hydrogamet phases, and possible amorphous phases high in Al" and SO4 ions. A small amount of cryptocrystalline CH may be intimately mixed with C-S-H phase. 

The monosulfate group, also known as the AFm phase, is represented by the formula C4ASH12 or C3A CS Hj2. AFm stands for Al-Fe-mono, in which one mole of CS is present. In portland cement this phase forms after the AFt phase disappears. This phase may constitute about 10% of the solid phase in a mature cement paste. In SEM, this phase has a hexagonal morphology resembling that of Ca(OH)2 and the crystals are of sub-micrometer thickness. The principle ionic substitutions in the AFm phase are Fe for AP+, and OH", C03 , Cl", etc. for S04. The density of this phase is 2.02 g/ml. The amount of crystalline hydrogamet present in cement paste is less than 3 %. It is of the type Ca3 Al2(OH)j2 in which part... 

It reappeared when alkalis were leached out into the aqueous phase. More than one type of C-S-H appears to have been detected. Small amounts of MgO were present at three days of hydration and beyond. At one year, phases identified included C-S-H, monosulfate/C4AHi3, syngenite (only in the low alkali cement), brucite, and Ca(OH)2. 

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